Self-Catalyzed Growth of Axial GaAs/GaAsSb Nanowires by Molecular Beam Epitaxy for Photodetectors

DTIC Science & Technology

2015-06-01

blende structure with mixture of stacking faults and twins and the presence of these faults were significantly reduced in the NWs grown on chemically...a) TEM image of the core NW (b) HR-TEM image displaying the stacking faults and twinning defects. (c)SAED pattern showing the ZB crystal structure...of stacking faults and twins and the presence of these faults were significantly reduced in the NWs grown on chemically etched substrates. For

Cathodoluminescence of stacking fault bound excitons for local probing of the exciton diffusion length in single GaN nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nogues, Gilles, E-mail: gilles.nogues@neel.cnrs.fr; Den Hertog, Martien; Inst. NEEL, CNRS, F-38042 Grenoble

We perform correlated studies of individual GaN nanowires in scanning electron microscopy combined to low temperature cathodoluminescence, microphotoluminescence, and scanning transmission electron microscopy. We show that some nanowires exhibit well localized regions emitting light at the energy of a stacking fault bound exciton (3.42 eV) and are able to observe the presence of a single stacking fault in these regions. Precise measurements of the cathodoluminescence signal in the vicinity of the stacking fault give access to the exciton diffusion length near this location.

Driving force of stacking-fault formation in SiC p-i-n diodes.

PubMed

Ha, S; Skowronski, M; Sumakeris, J J; Paisley, M J; Das, M K

2004-04-30

The driving force of stacking-fault expansion in SiC p-i-n diodes was investigated using optical emission microscopy and transmission electron microscopy. The stacking-fault expansion and properties of the partial dislocations were inconsistent with any stress as the driving force. A thermodynamic free energy difference between the perfect and a faulted structure is suggested as a plausible driving force in the tested diodes, indicating that hexagonal polytypes of silicon carbide are metastable at room temperature.

Ab initio study of point defects near stacking faults in 3C-SiC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xi, Jianqi; Liu, Bin; Zhang, Yanwen

Interactions between point defects and stacking faults in 3C-SiC are studied using an ab initio method based on density functional theory. The results show that the discontinuity of the stacking sequence considerably affects the configurations and behavior of intrinsic defects, especially in the case of silicon interstitials. The existence of an intrinsic stacking fault (missing a C-Si bilayer) shortens the distance between the tetrahedral-center site and its second-nearest-neighboring silicon layer, making the tetrahedral silicon interstitial unstable. Instead of a tetrahedral configuration with four C neighbors, a pyramid-like interstitial structure with a defect state within the band gap becomes a stablemore » configuration. In addition, orientation rotation occurs in the split interstitials that has diverse effects on the energy landscape of silicon and carbon split interstitials in the stacking fault region. Moreover, our analyses of ionic relaxation and electronic structure of vacancies show that the built-in strain field, owing to the existence of the stacking fault, makes the local environment around vacancies more complex than that in the bulk.« less

Ab initio study of point defects near stacking faults in 3C-SiC

DOE PAGES

Xi, Jianqi; Liu, Bin; Zhang, Yanwen; ...

2016-07-02

Interactions between point defects and stacking faults in 3C-SiC are studied using an ab initio method based on density functional theory. The results show that the discontinuity of the stacking sequence considerably affects the configurations and behavior of intrinsic defects, especially in the case of silicon interstitials. The existence of an intrinsic stacking fault (missing a C-Si bilayer) shortens the distance between the tetrahedral-center site and its second-nearest-neighboring silicon layer, making the tetrahedral silicon interstitial unstable. Instead of a tetrahedral configuration with four C neighbors, a pyramid-like interstitial structure with a defect state within the band gap becomes a stablemore » configuration. In addition, orientation rotation occurs in the split interstitials that has diverse effects on the energy landscape of silicon and carbon split interstitials in the stacking fault region. Moreover, our analyses of ionic relaxation and electronic structure of vacancies show that the built-in strain field, owing to the existence of the stacking fault, makes the local environment around vacancies more complex than that in the bulk.« less

X-ray diffuse scattering study of the kinetics of stacking fault growth and annihilation in boron-implanted silicon

NASA Astrophysics Data System (ADS)

Luebbert, D.; Arthur, J.; Sztucki, M.; Metzger, T. H.; Griffin, P. B.; Patel, J. R.

2002-10-01

Stacking faults in boron-implanted silicon give rise to streaks or rods of scattered x-ray intensity normal to the stacking fault plane. We have used the diffuse scattering rods to follow the growth of faults as a function of time when boron-implanted silicon is annealed in the range of 925 to 1025 degC. From the growth kinetics we obtain an activation energy for interstitial migration in silicon: EI=1.98plus-or-minus0.06 eV. Fault intensity and size versus time results indicate that faults do not shrink and disappear, but rather are annihilated by a dislocation reaction mechanism.

Domain wall pinning on strain relaxation defects (stacking faults) in nanoscale FePd (001)/MgO thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsiao, C. H.; Ouyang, Chuenhou, E-mail: wei0208@gmail.com, E-mail: houyang@mx.nthu.edu.tw; Yao, Y. D.

FePd (001) films, prepared by an electron beam deposition system on MgO(100), exhibit a perpendicular magnetic anisotropy (1.7 × 10{sup 7 }erg/cc) with a high order parameter (0.92). The relation between stacking faults induced by the strain relaxation, which act as strong domain wall pinning sites, and the perpendicular coercivity of (001) oriented L1{sub 0} FePd films prepared at different temperatures have been investigated. Perpendicular coercivity can be apparently enhanced by raising the stacking fault densities, which can be elevated by climbing dissociation of total dislocation. The increased stacking fault densities (1.22 nm{sup −2}) with large perpendicular coercivity (6000 Oe) are obtained for samples preparedmore » at 650 °C. This present work shows through controlling stacking fault density in FePd film, the coercivity can be manipulated, which can be applied in future magnetic devices.« less

Temperature dependence of stacking faults in catalyst-free GaAs nanopillars.

PubMed

Shapiro, Joshua N; Lin, Andrew; Ratsch, Christian; Huffaker, D L

2013-11-29

Impressive opto-electronic devices and transistors have recently been fabricated from GaAs nanopillars grown by catalyst-free selective-area epitaxy, but this growth technique has always resulted in high densities of stacking faults. A stacking fault occurs when atoms on the growing (111) surface occupy the sites of a hexagonal-close-pack (hcp) lattice instead of the normal face-centered-cubic (fcc) lattice sites. When stacking faults occur consecutively, the crystal structure is locally wurtzite instead of zinc-blende, and the resulting band offsets are known to negatively impact device performance. Here we present experimental and theoretical evidence that indicate stacking fault formation is related to the size of the critical nucleus, which is temperature dependent. The difference in energy between the hcp and fcc orientation of small nuclei is computed using density-function theory. The minimum energy difference of 0.22 eV is calculated for a nucleus with 21 atoms, so the population of nuclei in the hcp orientation is expected to decrease as the nucleus grows larger. The experiment shows that stacking fault occurrence is dramatically reduced from 22% to 3% by raising the growth temperature from 730 to 790 ° C. These data are interpreted using classical nucleation theory which dictates a larger critical nucleus at higher growth temperature.

Stacking Fault Enriching the Electronic and Transport Properties of Few-Layer Phosphorenes and Black Phosphorus.

PubMed

Lei, Shuangying; Wang, Han; Huang, Lan; Sun, Yi-Yang; Zhang, Shengbai

2016-02-10

Interface engineering is critical for enriching the electronic and transport properties of two-dimensional materials. Here, we identify a new stacking, named Aδ, in few-layer phosphorenes (FLPs) and black phosphorus (BP) based on first-principles calculation. With its low formation energy, the Aδ stacking could exist in FLPs and BP as a stacking fault. The presence of the Aδ stacking fault induces a direct to indirect transition of the band gap in FLPs. It also affects the carrier mobilities by significantly increasing the carrier effective masses. More importantly, the Aδ stacking enables the fabrication of a whole spectrum of lateral junctions with all the type-I, II, and III alignments simply through the manipulation of the van der Waals stacking without resorting to any chemical modification. This is achieved by the widely tunable electron affinity and ionization potential of FLPs and BP with the Aδ stacking.

Suzuki segregation in a binary Cu-Si alloy.

PubMed

Mendis, Budhika G; Jones, Ian P; Smallman, Raymond E

2004-01-01

Suzuki segregation to stacking faults and coherent twin boundaries has been investigated in a Cu-7.15 at.% Si alloy, heat-treated at temperatures of 275, 400 and 550 degrees C, using field-emission gun transmission electron microscopy. Silicon enrichment was observed at the stacking fault plane and decreased monotonically with increasing annealing temperature. This increase in the concentration of solute at the fault is due to the stacking fault energy being lowered at higher values of the electron-to-atom ratio of the alloy. From a McLean isotherm, the binding energy for segregation was calculated to be -0.021 +/- 0.019 eV atom(-1). Hardly any segregation was observed to coherent twin boundaries in the same alloy. This is because a twin has a lower interfacial energy than a stacking fault, so that the driving force for segregation is diminished.

Stacking Faults and Mechanical Behavior beyond the Elastic Limit of an Imidazole-Based Metal Organic Framework: ZIF-8.

PubMed

Hegde, Vinay I; Tan, Jin-Chong; Waghmare, Umesh V; Cheetham, Anthony K

2013-10-17

We determine the nonlinear mechanical behavior of a prototypical zeolitic imidazolate framework (ZIF-8) along two modes of mechanical failure in response to tensile and shear forces using first-principles simulations. Our generalized stacking fault energy surface reveals an intrinsic stacking fault of surprisingly low energy comparable to that in copper, though the energy barrier associated with its formation is much higher. The lack of vibrational spectroscopic evidence for such faults in experiments can be explained with the structural instability of the barrier state to form a denser and disordered state of ZIF-8 seen in our analysis, that is, large shear leads to its amorphization rather than formation of faults.

High spatial resolution correlated investigation of Zn segregation to stacking faults in ZnTe/CdSe nanostructures

NASA Astrophysics Data System (ADS)

Bonef, Bastien; Grenier, Adeline; Gerard, Lionel; Jouneau, Pierre-Henri; André, Regis; Blavette, Didier; Bougerol, Catherine

2018-02-01

The correlative use of atom probe tomography (APT) and energy dispersive x-ray spectroscopy in scanning transmission electron microscopy (STEM) allows us to characterize the structure of ZnTe/CdSe superlattices at the nanometre scale. Both techniques reveal the segregation of zinc along [111] stacking faults in CdSe layers, which is interpreted as a manifestation of the Suzuki effect. Quantitative measurements reveal a zinc enrichment around 9 at. % correlated with a depletion of cadmium in the stacking faults. Raw concentration data were corrected so as to account for the limited spatial resolution of both STEM and APT techniques. A simple calculation reveals that the stacking faults are almost saturated in Zn atoms (˜66 at. % of Zn) at the expense of Cd that is depleted.

Temperature-dependent stability of stacking faults in Al, Cu and Ni: first-principles analysis.

PubMed

Bhogra, Meha; Ramamurty, U; Waghmare, Umesh V

2014-09-24

We present comparative analysis of microscopic mechanisms relevant to plastic deformation of the face-centered cubic (FCC) metals Al, Cu, and Ni, through determination of the temperature-dependent free energies of intrinsic and unstable stacking faults along [1 1̄ 0] and [1 2̄ 1] on the (1 1 1) plane using first-principles density-functional-theory-based calculations. We show that vibrational contribution results in significant decrease in the free energy of barriers and intrinsic stacking faults (ISFs) of Al, Cu, and Ni with temperature, confirming an important role of thermal fluctuations in the stability of stacking faults (SFs) and deformation at elevated temperatures. In contrast to Al and Ni, the vibrational spectrum of the unstable stacking fault (USF[1 2̄ 1]) in Cu reveals structural instabilities, indicating that the energy barrier (γusf) along the (1 1 1)[1 2̄ 1] slip system in Cu, determined by typical first-principles calculations, is an overestimate, and its commonly used interpretation as the energy release rate needed for dislocation nucleation, as proposed by Rice (1992 J. Mech. Phys. Solids 40 239), should be taken with caution.

Experimental and computational studies on stacking faults in zinc titanate

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, W.; Ageh, V.; Mohseni, H.

Zinc titanate (ZnTiO{sub 3}) thin films grown by atomic layer deposition with ilmenite structure have recently been identified as an excellent solid lubricant, where low interfacial shear and friction are achieved due to intrafilm shear velocity accommodation in sliding contacts. In this Letter, high resolution transmission electron microscopy with electron diffraction revealed that extensive stacking faults are present on ZnTiO{sub 3} textured (104) planes. These growth stacking faults serve as a pathway for dislocations to glide parallel to the sliding direction and hence achieve low interfacial shear/friction. Generalized stacking fault energy plots also known as γ-surfaces were computed for themore » (104) surface of ZnTiO{sub 3} using energy minimization method with classical effective partial charge potential and verified by using density functional theory first principles calculations for stacking fault energies along certain directions. These two are in qualitative agreement but classical simulations generally overestimate the energies. In addition, the lowest energy path was determined to be along the [451{sup ¯}] direction and the most favorable glide system is (104) 〈451{sup ¯}〉 that is responsible for the experimentally observed sliding-induced ductility.« less

Effect of stacking faults on the photoluminescence spectrum of zincblende GaN

NASA Astrophysics Data System (ADS)

Church, S. A.; Hammersley, S.; Mitchell, P. W.; Kappers, M. J.; Lee, L. Y.; Massabuau, F.; Sahonta, S. L.; Frentrup, M.; Shaw, L. J.; Wallis, D. J.; Humphreys, C. J.; Oliver, R. A.; Binks, D. J.; Dawson, P.

2018-05-01

The photoluminescence spectra of a zincblende GaN epilayer grown via metal-organic chemical vapour deposition upon 3C-SiC/Si (001) substrates were investigated. Of particular interest was a broad emission band centered at 3.4 eV, with a FWHM of 200 meV, which extends above the bandgap of both zincblende and wurtzite GaN. Photoluminescence excitation measurements show that this band is associated with an absorption edge centered at 3.6 eV. Photoluminescence time decays for the band are monoexponential, with lifetimes that reduce from 0.67 ns to 0.15 ns as the recombination energy increases. TEM measurements show no evidence of wurtzite GaN inclusions which are typically used to explain emission in this energy range. However, dense stacking fault bunches are present in the epilayers. A model for the band alignment at the stacking faults was developed to explain this emission band, showing how both electrons and holes can be confined adjacent to stacking faults. Different stacking fault separations can change the carrier confinement energies sufficiently to explain the width of the emission band, and change the carrier wavefunction overlap to account for the variation in decay time.

Characterization of individual straight and kinked boron carbide nanowires

NASA Astrophysics Data System (ADS)

Cui, Zhiguang

Boron carbides represent a class of ceramic materials with p-type semiconductor natures, complex structures and a wide homogeneous range of carbon compositions. Bulk boron carbides have long been projected as promising high temperature thermoelectric materials, but with limited performance. Bringing the bulk boron carbides to low dimensions (e.g., nanowires) is believed to be an option to enhance their thermoelectric performance because of the quantum size effects. However, the fundamental studies on the microstructure-thermal property relation of boron carbide nanowires are elusive. In this dissertation work, systematic structural characterization and thermal conductivity measurement of individual straight and kinked boron carbide nanowires were carried out to establish the true structure-thermal transport relation. In addition, a preliminary Raman spectroscopy study on identifying the defects in individual boron carbide nanowires was conducted. After the synthesis of single crystalline boron carbide nanowires, straight nanowires accompanied by the kinked ones were observed. Detailed structures of straight boron carbide nanowires have been reported, but not the kinked ones. After carefully examining tens of kinked nanowires utilizing Transmission Electron Microscopy (TEM), it was found that they could be categorized into five cases depending on the stacking faults orientations in the two arms of the kink: TF-TF, AF-TF, AF-AF, TF-IF and AF-IF kinks, in which TF, AF and IF denotes transverse faults (preferred growth direction perpendicular to the stacking fault planes), axial faults (preferred growth direction in parallel with the stacking fault planes) and inclined faults (preferred growth direction neither perpendicular to nor in parallel with the stacking fault planes). Simple structure models describing the characteristics of TF-TF, AF-TF, AF-AF kinked nanowires are constructed in SolidWorks, which help to differentiate the kinked nanowires viewed from the zone axes where stacking faults are invisible. In collaboration with the experts in the field of thermal property characterization of one dimensional nanostructures, thermal conductivities of over 60 nanowires including both straight and kinked ones have been measured in the temperature range of 20 - 420 K and the parameters (i.e., carbon contents, diameters, stacking faults densities/orientations and kinks) affecting the phonon transport were explored. The results disclose strong carbon content and diameter dependence of thermal conductivities of boron carbide nanowires, which decreases as lowering the carbon content and diameter. Stacking fault orientations do modulate the phonon transport (kappaTF < kappa AF), while stacking fault densities seems to only have obvious effects on phonon transport when meeting certain threshold ( 39%). The most interesting discovery is significant reduction of thermal conductivity (15% - 40%) in kinked boron carbide nanowires due to phonon mode conversions and scattering at the kink site. Last but not least, micro-Raman spectroscopy study on individual boron carbide nanowires has been performed for the first time, to the best of our knowledge. Based on the preliminary data, it is found that the stacking fault orientations have no apparent effect on the Raman scattering, but the stacking fault densities do. In addition, up as the size going down to nanoscale, some Raman modes are inactive while some new ones show up, which is largely ascribed to the quantum confinement effects. One more important finding is that the carbon content also plays important role in the Raman scattering of boron carbide nanowires in the low frequency region (< 600 cm-1), which mainly comes from the 3-atom chains (C-B-C or C-B-B).

In situ nanoindentation study on plasticity and work hardening in aluminium with incoherent twin boundaries.

PubMed

Bufford, D; Liu, Y; Wang, J; Wang, H; Zhang, X

2014-09-10

Nanotwinned metals have been the focus of intense research recently, as twin boundaries may greatly enhance mechanical strength, while maintaining good ductility, electrical conductivity and thermal stability. Most prior studies have focused on low stacking-fault energy nanotwinned metals with coherent twin boundaries. In contrast, the plasticity of twinned high stacking-fault energy metals, such as aluminium with incoherent twin boundaries, has not been investigated. Here we report high work hardening capacity and plasticity in highly twinned aluminium containing abundant Σ3{112} incoherent twin boundaries based on in situ nanoindentation studies in a transmission electron microscope and corresponding molecular dynamics simulations. The simulations also reveal drastic differences in deformation mechanisms between nanotwinned copper and twinned aluminium ascribed to stacking-fault energy controlled dislocation-incoherent twin boundary interactions. This study provides new insight into incoherent twin boundary-dominated plasticity in high stacking-fault energy twinned metals.

Stacking fault energies and slip in nanocrystalline metals.

PubMed

Van Swygenhoven, H; Derlet, P M; Frøseth, A G

2004-06-01

The search for deformation mechanisms in nanocrystalline metals has profited from the use of molecular dynamics calculations. These simulations have revealed two possible mechanisms; grain boundary accommodation, and intragranular slip involving dislocation emission and absorption at grain boundaries. But the precise nature of the slip mechanism is the subject of considerable debate, and the limitations of the simulation technique need to be taken into consideration. Here we show, using molecular dynamics simulations, that the nature of slip in nanocrystalline metals cannot be described in terms of the absolute value of the stacking fault energy-a correct interpretation requires the generalized stacking fault energy curve, involving both stable and unstable stacking fault energies. The molecular dynamics technique does not at present allow for the determination of rate-limiting processes, so the use of our calculations in the interpretation of experiments has to be undertaken with care.

Strong carrier localization in stacking faults in semipolar (11-22) GaN

NASA Astrophysics Data System (ADS)

Okur, Serdal; Monavarian, Morteza; Das, Saikat; Izyumskaya, Natalia; Zhang, Fan; Avrutin, Vitaliy; Morkoç, Hadis; Özgür, Ümit

2015-03-01

The effects of stacking faults (SFs) on optical processes in epitaxially grown semipolar (1122) GaN on m-sapphire substrate have been investigated in detail using steady-state photoluminescence (PL) and time- and polarization-resolved PL. We demonstrate that the carrier recombination dynamics are substantially influenced due to strong carrier localization in the stacking faults. In addition to nonradiative recombination, carrier trapping/detrapping and carrier transfer between the stacking faults and donors are also found to be among the mechanisms affecting the recombination dynamics at different temperatures. PL decay times of both I1-type BSF and 3.31 eV SF (E-type BSF or prismatic stacking fault) do not show temperature dependence up to 80 K while 3.31 eV SF exhibits longer PL decay times (~3 ns) at low temperatures as compared to I1-type BSF (~1 ns), indicative of lower efficiency for radiative recombination. After 80 K, PL decay times decreased by power of ~-1 and ~-2 for 3.31 eV SF and I1-type BSF, respectively. It is obtained from radiative decay times with respect to temperature that the carrier localization becomes higher in I1-type BSF compared to 3.31 eV SF increasing the temperature. I1-type BSF also shows higher PL intensity, which is attributed to larger density, and therefore, larger contribution to recombination dynamics as compared to other type of stacking faults. Polarization-resolved PL measurements also revealed that the degree of polarization for the I1-type BSF (0.30) was twice that for the 3.31 eV SF.

Conjugated π electron engineering of generalized stacking fault in graphene and h-BN.

PubMed

Ouyang, Bin; Chen, Cheng; Song, J

2018-03-02

Generalized-stacking-fault energy (GSFE) serves as an important metric that prescribes dislocation behaviors in materials. In this paper, utilizing first-principle calculations and chemical bonding analysis, we studied the behaviors of generalized stacking fault in graphene and h-BN. It has been shown that the π bond formation plays a critical role in the existence of metastable stacking fault (MSF) in graphene and h-BN lattice along certain slip directions. Chemical functionalization was then proposed as an effective means to engineer the π bond, and subsequently MSF along dislocation slips within graphene and h-BN. Taking hydrogenation as a representative functionalization method, we demonstrated that, with the preferential adsorption of hydrogen along the slip line, π electrons along the slip would be saturated by adsorbed hydrogen atoms, leading to the moderation or elimination of MSF. Our study elucidates the atomic mechanism of MSF formation in graphene-like materials, and more generally, provides important insights towards predictive tuning of mechanic properties in two-dimensional nanomaterials.

Effect of vacancy defects on generalized stacking fault energy of fcc metals.

PubMed

Asadi, Ebrahim; Zaeem, Mohsen Asle; Moitra, Amitava; Tschopp, Mark A

2014-03-19

Molecular dynamics (MD) and density functional theory (DFT) studies were performed to investigate the influence of vacancy defects on generalized stacking fault (GSF) energy of fcc metals. MEAM and EAM potentials were used for MD simulations, and DFT calculations were performed to test the accuracy of different common parameter sets for MEAM and EAM potentials in predicting GSF with different fractions of vacancy defects. Vacancy defects were placed at the stacking fault plane or at nearby atomic layers. The effect of vacancy defects at the stacking fault plane and the plane directly underneath of it was dominant compared to the effect of vacancies at other adjacent planes. The effects of vacancy fraction, the distance between vacancies, and lateral relaxation of atoms on the GSF curves with vacancy defects were investigated. A very similar variation of normalized SFEs with respect to vacancy fractions were observed for Ni and Cu. MEAM potentials qualitatively captured the effect of vacancies on GSF.

Evolution of stacking fault tetrahedral and work hardening effect in copper single crystals

NASA Astrophysics Data System (ADS)

Liu, Hai Tao; Zhu, Xiu Fu; Sun, Ya Zhou; Xie, Wen Kun

2017-11-01

Stacking fault tetrahedral (SFT), generated in machining of copper single crystal as one type of subsurface defects, has significant influence on the performance of workpiece. In this study, molecular dynamics (MD) simulation is used to investigate the evolution of stacking fault tetrahedral in nano-cutting of copper single crystal. The result shows that SFT is nucleated at the intersection of differently oriented stacking fault (SF) planes and SFT evolves from the preform only containing incomplete surfaces into a solid defect. The evolution of SFT contains several stress fluctuations until the complete formation. Nano-indentation simulation is then employed on the machined workpiece from nano-cutting, through which the interaction between SFT and later-formed dislocations in subsurface is studied. In the meanwhile, force-depth curves obtained from nano-indentation on pristine and machined workpieces are compared to analyze the mechanical properties. By simulation of nano-cutting and nano-indentation, it is verified that SFT is a reason of the work hardening effect.

Strain-Driven Stacking Faults in CdSe/CdS Core/Shell Nanorods.

PubMed

Demortière, Arnaud; Leonard, Donovan N; Petkov, Valeri; Chapman, Karena; Chattopadhyay, Soma; She, Chunxing; Cullen, David A; Shibata, Tomohiro; Pelton, Matthew; Shevchenko, Elena V

2018-04-19

Colloidal semiconductor nanocrystals are commonly grown with a shell of a second semiconductor material to obtain desired physical properties, such as increased photoluminescence quantum yield. However, the growth of a lattice-mismatched shell results in strain within the nanocrystal, and this strain has the potential to produce crystalline defects. Here, we study CdSe/CdS core/shell nanorods as a model system to investigate the influence of core size and shape on the formation of stacking faults in the nanocrystal. Using a combination of high-angle annular dark-field scanning transmission electron microscopy and pair-distribution-function analysis of synchrotron X-ray scattering, we show that growth of the CdS shell on smaller, spherical CdSe cores results in relatively small strain and few stacking faults. By contrast, growth of the shell on larger, prolate spheroidal cores leads to significant strain in the CdS lattice, resulting in a high density of stacking faults.

Conjugated π electron engineering of generalized stacking fault in graphene and h-BN

NASA Astrophysics Data System (ADS)

Ouyang, Bin; Chen, Cheng; Song, J.

2018-03-01

Generalized-stacking-fault energy (GSFE) serves as an important metric that prescribes dislocation behaviors in materials. In this paper, utilizing first-principle calculations and chemical bonding analysis, we studied the behaviors of generalized stacking fault in graphene and h-BN. It has been shown that the π bond formation plays a critical role in the existence of metastable stacking fault (MSF) in graphene and h-BN lattice along certain slip directions. Chemical functionalization was then proposed as an effective means to engineer the π bond, and subsequently MSF along dislocation slips within graphene and h-BN. Taking hydrogenation as a representative functionalization method, we demonstrated that, with the preferential adsorption of hydrogen along the slip line, π electrons along the slip would be saturated by adsorbed hydrogen atoms, leading to the moderation or elimination of MSF. Our study elucidates the atomic mechanism of MSF formation in graphene-like materials, and more generally, provides important insights towards predictive tuning of mechanic properties in two-dimensional nanomaterials.

Zn-dopant dependent defect evolution in GaN nanowires

NASA Astrophysics Data System (ADS)

Yang, Bing; Liu, Baodan; Wang, Yujia; Zhuang, Hao; Liu, Qingyun; Yuan, Fang; Jiang, Xin

2015-10-01

Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3-5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (101&cmb.macr;3), (101&cmb.macr;1) and (202&cmb.macr;1), as well as Type I stacking faults (...ABABC&cmb.b.line;BCB...), are observed in the nanowires. The increasing Zn doping level (<1 at%) induces the formation of screw dislocations featuring a predominant screw component along the radial direction of the GaN nanowires. At high Zn doping level (3-5 at%), meta-stable cubic zinc blende (ZB) domains are generated in the WZ GaN nanowires. The WZ/ZB phase boundary (...ABABAC&cmb.b.line;BA...) can be identified as Type II stacking faults. The density of stacking faults (both Type I and Type II) increases with increasing the Zn doping levels, which in turn leads to a rough-surface morphology in the GaN nanowires. First-principles calculations reveal that Zn doping will reduce the formation energy of both Type I and Type II stacking faults, favoring their nucleation in GaN nanowires. An understanding of the effect of Zn doping on the defect evolution provides an important method to control the microstructure and the electrical properties of p-type GaN nanowires.Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3-5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (101&cmb.macr;3), (101&cmb.macr;1) and (202&cmb.macr;1), as well as Type I stacking faults (...ABABC&cmb.b.line;BCB...), are observed in the nanowires. The increasing Zn doping level (<1 at%) induces the formation of screw dislocations featuring a predominant screw component along the radial direction of the GaN nanowires. At high Zn doping level (3-5 at%), meta-stable cubic zinc blende (ZB) domains are generated in the WZ GaN nanowires. The WZ/ZB phase boundary (...ABABAC&cmb.b.line;BA...) can be identified as Type II stacking faults. The density of stacking faults (both Type I and Type II) increases with increasing the Zn doping levels, which in turn leads to a rough-surface morphology in the GaN nanowires. First-principles calculations reveal that Zn doping will reduce the formation energy of both Type I and Type II stacking faults, favoring their nucleation in GaN nanowires. An understanding of the effect of Zn doping on the defect evolution provides an important method to control the microstructure and the electrical properties of p-type GaN nanowires. Electronic supplementary information (ESI) available: HRTEM image of undoped GaN nanowires and first-principles calculations of Zn doped WZ-GaN. See DOI: 10.1039/c5nr04771d

Floating stacking faults on the (111) surface of FCC metals: a finite-temperature first-principles study

NASA Astrophysics Data System (ADS)

Rechtsman, Mikael; de Gironcoli, Stefano; Ceder, Gerbrand; Marzari, Nicola

2003-03-01

The (111) surfaces of FCC metals can develop anomalous thermal expansion properties at high temperatures (e.g. for the case of Ag(111)), and display floating stacking faults during homoepitaxial growth in the presence of surfactants. Inspired by the results of high-temperature ensemble-DFT molecular dynamics simulations, we investigate here the relative stability of FCC and HCP stacking in simple and transition metals (Al, Ag, Zn), searching for a structural phase transition taking place at the surface layer in the high-temperature regime. We use a combination of total-energy structural relaxations and linear-response perturbation theory to determine the surface phonon dispersions, and then the relative free energies in the quasi-harmonic approximation. Our results in Al show that the vibrational entropy strongly favors HCP stacking, substantially offsetting the energetic cost of the stacking fault that becomes favored close to the melting temperature. Besides its fundamental interest, HCP phonon softening is relevant in determining the relative stability of small islands during homoeptiaxial growth.

Determination of the gaseous hydrogen ductile-brittle transition in copper-nickel alloys

NASA Technical Reports Server (NTRS)

Parr, R. A.; Johnston, M. H.; Davis, J. H.; Oh, T. K.

1985-01-01

A series of copper-nickel alloys were fabricated, notched tensile specimens machined for each alloy, and the specimens tested in 34.5 MPa hydrogen and in air. A notched tensile ratio was determined for each alloy and the hydrogen environment embrittlement (HEE) determined for the alloys of 47.7 weight percent nickel to 73.5 weight percent nickel. Stacking fault probability and stacking fault energies were determined for each alloy using the x ray diffraction line shift and line profiles technique. Hydrogen environment embrittlement was determined to be influenced by stacking fault energies; however, the correlation is believed to be indirect and only partially responsible for the HEE behavior of these alloys.

Model-based diagnosis through Structural Analysis and Causal Computation for automotive Polymer Electrolyte Membrane Fuel Cell systems

NASA Astrophysics Data System (ADS)

Polverino, Pierpaolo; Frisk, Erik; Jung, Daniel; Krysander, Mattias; Pianese, Cesare

2017-07-01

The present paper proposes an advanced approach for Polymer Electrolyte Membrane Fuel Cell (PEMFC) systems fault detection and isolation through a model-based diagnostic algorithm. The considered algorithm is developed upon a lumped parameter model simulating a whole PEMFC system oriented towards automotive applications. This model is inspired by other models available in the literature, with further attention to stack thermal dynamics and water management. The developed model is analysed by means of Structural Analysis, to identify the correlations among involved physical variables, defined equations and a set of faults which may occur in the system (related to both auxiliary components malfunctions and stack degradation phenomena). Residual generators are designed by means of Causal Computation analysis and the maximum theoretical fault isolability, achievable with a minimal number of installed sensors, is investigated. The achieved results proved the capability of the algorithm to theoretically detect and isolate almost all faults with the only use of stack voltage and temperature sensors, with significant advantages from an industrial point of view. The effective fault isolability is proved through fault simulations at a specific fault magnitude with an advanced residual evaluation technique, to consider quantitative residual deviations from normal conditions and achieve univocal fault isolation.

Shear response of Σ3{112} twin boundaries in face-centered-cubic metals

NASA Astrophysics Data System (ADS)

Wang, J.; Misra, A.; Hirth, J. P.

2011-02-01

Molecular statics and dynamics simulations were used to study the mechanisms of sliding and migration of Σ3{112} incoherent twin boundaries (ITBs) under applied shear acting in the boundary in the face-centered-cubic (fcc) metals, Ag, Cu, Pd, and Al, of varying stacking fault energies. These studies revealed that (i) ITBs can dissociate into two phase boundaries (PBs), bounding the hexagonal 9R phase, that contain different arrays of partial dislocations; (ii) the separation distance between the two PBs scales inversely with increasing stacking fault energy; (iii) for fcc metals with low stacking fault energy, one of the two PBs migrates through the collective glide of partials, referred to as the phase-boundary-migration (PBM) mechanism; (iv) for metals with high stacking energy, ITBs experience a coupled motion (migration and sliding) through the glide of interface disconnections, referred to as the interface-disconnection-glide (IDG) mechanism.

Zn-dopant dependent defect evolution in GaN nanowires.

PubMed

Yang, Bing; Liu, Baodan; Wang, Yujia; Zhuang, Hao; Liu, Qingyun; Yuan, Fang; Jiang, Xin

2015-10-21

Zn doped GaN nanowires with different doping levels (0, <1 at%, and 3-5 at%) have been synthesized through a chemical vapor deposition (CVD) process. The effect of Zn doping on the defect evolution, including stacking fault, dislocation, twin boundary and phase boundary, has been systematically investigated by transmission electron microscopy and first-principles calculations. Undoped GaN nanowires show a hexagonal wurtzite (WZ) structure with good crystallinity. Several kinds of twin boundaries, including (101¯3), (101¯1) and (202¯1), as well as Type I stacking faults (…ABABCBCB…), are observed in the nanowires. The increasing Zn doping level (<1 at%) induces the formation of screw dislocations featuring a predominant screw component along the radial direction of the GaN nanowires. At high Zn doping level (3-5 at%), meta-stable cubic zinc blende (ZB) domains are generated in the WZ GaN nanowires. The WZ/ZB phase boundary (…ABABACBA…) can be identified as Type II stacking faults. The density of stacking faults (both Type I and Type II) increases with increasing the Zn doping levels, which in turn leads to a rough-surface morphology in the GaN nanowires. First-principles calculations reveal that Zn doping will reduce the formation energy of both Type I and Type II stacking faults, favoring their nucleation in GaN nanowires. An understanding of the effect of Zn doping on the defect evolution provides an important method to control the microstructure and the electrical properties of p-type GaN nanowires.

Segregation and Phase Transformations Along Superlattice Intrinsic Stacking Faults in Ni-Based Superalloys

NASA Astrophysics Data System (ADS)

Smith, T. M.; Esser, B. D.; Good, B.; Hooshmand, M. S.; Viswanathan, G. B.; Rae, C. M. F.; Ghazisaeidi, M.; McComb, D. W.; Mills, M. J.

2018-06-01

In this study, local chemical and structural changes along superlattice intrinsic stacking faults combine to represent an atomic-scale phase transformation. In order to elicit stacking fault shear, creep tests of two different single crystal Ni-based superalloys, ME501 and CMSX-4, were performed near 750 °C using stresses of 552 and 750 MPa, respectively. Through high-resolution scanning transmission electron microscopy (STEM) and state-of-the-art energy dispersive X-ray spectroscopy, ordered compositional changes were measured along SISFs in both alloys. For both instances, the elemental segregation and local crystal structure present along the SISFs are consistent with a nanoscale γ' to D019 phase transformation. Other notable observations are prominent γ-rich Cottrell atmospheres and new evidence of more complex reordering processes responsible for the formation of these faults. These findings are further supported using density functional theory calculations and high-angle annular dark-field (HAADF)-STEM image simulations.

X-ray analysis of temperature induced defect structures in boron implanted silicon

NASA Astrophysics Data System (ADS)

Sztucki, M.; Metzger, T. H.; Kegel, I.; Tilke, A.; Rouvière, J. L.; Lübbert, D.; Arthur, J.; Patel, J. R.

2002-10-01

We demonstrate the application of surface sensitive diffuse x-ray scattering under the condition of grazing incidence and exit angles to investigate growth and dissolution of near-surface defects after boron implantation in silicon(001) and annealing. Silicon wafers were implanted with a boron dose of 6×1015 ions/cm2 at 32 keV and went through different annealing treatments. From the diffuse intensity close to the (220) surface Bragg peak we reveal the nature and kinetic behavior of the implantation induced defects. Analyzing the q dependence of the diffuse scattering, we are able to distinguish between point defect clusters and extrinsic stacking faults on {111} planes. Characteristic for stacking faults are diffuse x-ray intensity streaks along <111> directions, which allow for the determination of their growth and dissolution kinetics. For the annealing conditions of our crystals, we conclude that the kinetics of growth can be described by an Ostwald ripening model in which smaller faults shrink at the expense of the larger stacking faults. The growth is found to be limited by the self-diffusion of silicon interstitials. After longer rapid thermal annealing the stacking faults disappear almost completely without shrinking, most likely by transformation into perfect loops via a dislocation reaction. This model is confirmed by complementary cross-sectional transmission electron microscopy.

Crystal structure of stacking faults in InGaAs/InAlAs/InAs heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Trunkin, I. N.; Presniakov, M. Yu.; Vasiliev, A. L., E-mail: a.vasiliev56@gmail.com

Stacking faults and dislocations in InGaAs/InAlAs/InAs heterostructures have been studied by electron microscopy. The use of different techniques of transmission electron microscopy (primarily, highresolution dark-field scanning transmission electron microscopy) has made it possible to determine the defect structure at the atomic level.

In-situ observation of stacking fault evolution in vacuum-deposited C60

NASA Astrophysics Data System (ADS)

Hardigree, J. F. M.; Ramirez, I. R.; Mazzotta, G.; Nicklin, C.; Riede, M.

2017-12-01

We report an in-situ study of stacking fault evolution in C60 thin films using grazing-incidence x-ray scattering. A Williamson-Hall analysis of the main scattering features during growth of a 15 nm film on glass indicates lattice strain as high as 6% in the first 5 nm of the film, with a decrease to 2% beyond 8 nm thickness. Deformation stacking faults along the {220} plane are found to occur with 68% probability and closely linked to the formation of a nanocrystalline powder-like film. Our findings, which capture monolayer-resolution growth, are consistent with previous work on crystalline and powder C60 films, and provide a crystallographic context for the real-time study of organic semiconductor thin films.

Generalized-stacking-fault energy and twin-boundary energy of hexagonal close-packed Au: A first-principles calculation.

PubMed

Wang, Cheng; Wang, Huiyuan; Huang, Tianlong; Xue, Xuena; Qiu, Feng; Jiang, Qichuan

2015-05-22

Although solid Au is usually most stable as a face-centered cubic (fcc) structure, pure hexagonal close-packed (hcp) Au has been successfully fabricated recently. However, the phase stability and mechanical property of this new material are unclear, which may restrict its further applications. Here we present the evidence that hcp → fcc phase transformation can proceed easily in Au by first-principles calculations. The extremely low generalized-stacking-fault (GSF) energy in the basal slip system implies a great tendency to form basal stacking faults, which opens the door to phase transformation from hcp to fcc. Moreover, the Au lattice extends slightly within the superficial layers due to the self-assembly of alkanethiolate species on hcp Au (0001) surface, which may also contribute to the hcp → fcc phase transformation. Compared with hcp Mg, the GSF energies for non-basal slip systems and the twin-boundary (TB) energies for and twins are larger in hcp Au, which indicates the more difficulty in generating non-basal stacking faults and twins. The findings provide new insights for understanding the nature of the hcp → fcc phase transformation and guide the experiments of fabricating and developing materials with new structures.

Inverse scattering pre-stack depth imaging and it's comparison to some depth migration methods for imaging rich fault complex structure

NASA Astrophysics Data System (ADS)

Nurhandoko, Bagus Endar B.; Sukmana, Indriani; Mubarok, Syahrul; Deny, Agus; Widowati, Sri; Kurniadi, Rizal

2012-06-01

Migration is important issue for seismic imaging in complex structure. In this decade, depth imaging becomes important tools for producing accurate image in depth imaging instead of time domain imaging. The challenge of depth migration method, however, is in revealing the complex structure of subsurface. There are many methods of depth migration with their advantages and weaknesses. In this paper, we show our propose method of pre-stack depth migration based on time domain inverse scattering wave equation. Hopefully this method can be as solution for imaging complex structure in Indonesia, especially in rich thrusting fault zones. In this research, we develop a recent advance wave equation migration based on time domain inverse scattering wave which use more natural wave propagation using scattering wave. This wave equation pre-stack depth migration use time domain inverse scattering wave equation based on Helmholtz equation. To provide true amplitude recovery, an inverse of divergence procedure and recovering transmission loss are considered of pre-stack migration. Benchmarking the propose inverse scattering pre-stack depth migration with the other migration methods are also presented, i.e.: wave equation pre-stack depth migration, waveequation depth migration, and pre-stack time migration method. This inverse scattering pre-stack depth migration could image successfully the rich fault zone which consist extremely dip and resulting superior quality of seismic image. The image quality of inverse scattering migration is much better than the others migration methods.

Tight-binding study of stacking fault energies and the Rice criterion of ductility in the fcc metals

NASA Astrophysics Data System (ADS)

Mehl, Michael J.; Papaconstantopoulos, Dimitrios A.; Kioussis, Nicholas; Herbranson, M.

2000-02-01

We have used the Naval Research Laboratory (NRL) tight-binding (TB) method to calculate the generalized stacking fault energy and the Rice ductility criterion in the fcc metals Al, Cu, Rh, Pd, Ag, Ir, Pt, Au, and Pb. The method works well for all classes of metals, i.e., simple metals, noble metals, and transition metals. We compared our results with full potential linear-muffin-tin orbital and embedded atom method (EAM) calculations, as well as experiment, and found good agreement. This is impressive, since the NRL-TB approach only fits to first-principles full-potential linearized augmented plane-wave equations of state and band structures for cubic systems. Comparable accuracy with EAM potentials can be achieved only by fitting to the stacking fault energy.

Growth of non-polar and semi-polar gallium nitride with plasma assisted molecular beam epitaxy: Relatonships between film microstructure, reciprocal lattice and transport properties

NASA Astrophysics Data System (ADS)

McLaurin, Melvin Barker

2007-12-01

The group-III nitrides exhibit significant spontaneous and piezoelectric polarization parallel to the [0001] direction, which are manifested as sheet charges at heterointerfaces. While polarization can be used to engineer the band-structure of a device, internal electric fields generated by polarization discontinuities can also have a number of negative consequences for the performance and design of structures utilizing heterojunctions. The most direct route to polarization free group-III nitride devices is growth on either one of the "non-polar" prismatic faces of the crystal (m-plane (1010) or a-plane (1120)) where the [0001] direction lies in the plane of any heterointerfaces. This dissertation focuses on the growth of non-polar and semi-polar GaN by MBE and on how the dominant feature of the defect structure of non-polar and semi-polar films, basal plane stacking faults, determines the properties of the reciprocal lattice and electrical transport of the films. The first part is a survey of the MBE growth of the two non-polar planes (10 10) and (1120) and three semi-polar planes (1011), (1013) and {11 22} investigated in this work. The relationship between basal plane stacking faults and broadening of the reciprocal lattice is discussed and measured with X-ray diffraction using a lateral-variant of the Williamson-Hall analysis. The electrical properties of m-plane films are investigated using Hall-effect and TLM measurements. Anisotropic mobilities were observed for both electrons and holes along with record p-type conductivities and hole concentrations. By comparison to both inversion-domain free c-plane films and stacking-fault-free free-standing m-plane GaN wafers it was determined that basal plane stacking faults were the source of both the enhanced p-type conductivity and the anisotropic carrier mobilities. Finally, we propose a possible source of anisotropic mobilities and enhanced p-type conduction in faulted films is proposed. Basal plane stacking faults are treated as heterostructures of the wurtzite and zincblende polytypes of GaN. The band parameter and polarization differences between the polytypes result in large offsets in both the conduction and valence band edges at the stacking faults. Anisotropy results from scattering from the band-edge offsets and enhanced mobility from screening due to charge accumulation at these band edge offsets.

Stacking fault induced tunnel barrier in platelet graphite nanofiber

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lan, Yann-Wen, E-mail: chiidong@phys.sinica.edu.tw, E-mail: ywlan@phys.sinica.edu.tw; Chang, Yuan-Chih; Chang, Chia-Seng

A correlation study using image inspection and electrical characterization of platelet graphite nanofiber devices is conducted. Close transmission electron microscopy and diffraction pattern inspection reveal layers with inflection angles appearing in otherwise perfectly stacked graphene platelets, separating nanofibers into two domains. Electrical measurement gives a stability diagram consisting of alternating small-large Coulomb blockade diamonds, suggesting that there are two charging islands coupled together through a tunnel junction. Based on these two findings, we propose that a stacking fault can behave as a tunnel barrier for conducting electrons and is responsible for the observed double-island single electron transistor characteristics.

Energetics analysis of interstitial loops in single-phase concentrated solid-solution alloys

NASA Astrophysics Data System (ADS)

Wang, Xin-Xin; Niu, Liang-Liang; Wang, Shaoqing

2018-04-01

Systematic energetics analysis on the shape preference, relative stability and radiation-induced segregation of interstitial loops in nickel-containing single-phase concentrated solid-solution alloys have been conducted using atomistic simulations. It is shown that the perfect loops prefer rhombus shape for its low potential energy, while the Frank faulted loops favor ellipse for its low potential energy and the possible large configurational entropy. The decrease of stacking fault energy with increasing compositional complexity provides the energetic driving force for the formation of faulted loops, which, in conjunction with the kinetic factors, explains the experimental observation that the fraction of faulted loops rises with increasing compositional complexity. Notably, the kinetics is primarily responsible for the absence of faulted loops in nickel-cobalt with a very low stacking fault energy. We further demonstrate that the simultaneous nickel enrichment and iron/chromium depletion on interstitial loops can be fully accounted for by their energetics.

Effect of Na presence during CuInSe{sub 2} growth on stacking fault annihilation and electronic properties

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stange, H., E-mail: helena.stange@helmholtz-berlin.de; Brunken, S.; Hempel, H.

While presence of Na is essential for the performance of high-efficiency Cu(In,Ga)Se{sub 2} thin film solar cells, the reasons why addition of Na by post-deposition treatment is superior to pre-deposition Na supply—particularly at low growth temperatures—are not yet fully understood. Here, we show by X-ray diffraction and electron microscopy that Na impedes annihilation of stacking faults during the Cu-poor/Cu-rich transition of low temperature 3-stage co-evaporation and prevents Cu homogeneity on a microscopic level. Lower charge carrier mobilities are found by optical pump terahertz probe spectroscopy for samples with remaining high stacking fault density, indicating a detrimental effect on electronic propertiesmore » if Na is present during growth.« less

High-velocity projectile impact induced 9R phase in ultrafine-grained aluminium.

PubMed

Xue, Sichuang; Fan, Zhe; Lawal, Olawale B; Thevamaran, Ramathasan; Li, Qiang; Liu, Yue; Yu, K Y; Wang, Jian; Thomas, Edwin L; Wang, Haiyan; Zhang, Xinghang

2017-11-21

Aluminium typically deforms via full dislocations due to its high stacking fault energy. Twinning in aluminium, although difficult, may occur at low temperature and high strain rate. However, the 9R phase rarely occurs in aluminium simply because of its giant stacking fault energy. Here, by using a laser-induced projectile impact testing technique, we discover a deformation-induced 9R phase with tens of nm in width in ultrafine-grained aluminium with an average grain size of 140 nm, as confirmed by extensive post-impact microscopy analyses. The stability of the 9R phase is related to the existence of sessile Frank loops. Molecular dynamics simulations reveal the formation mechanisms of the 9R phase in aluminium. This study sheds lights on a deformation mechanism in metals with high stacking fault energies.

Generalized-stacking-fault energy and twin-boundary energy of hexagonal close-packed Au: A first-principles calculation

PubMed Central

Wang, Cheng; Wang, Huiyuan; Huang, Tianlong; Xue, Xuena; Qiu, Feng; Jiang, Qichuan

2015-01-01

Although solid Au is usually most stable as a face-centered cubic (fcc) structure, pure hexagonal close-packed (hcp) Au has been successfully fabricated recently. However, the phase stability and mechanical property of this new material are unclear, which may restrict its further applications. Here we present the evidence that hcp → fcc phase transformation can proceed easily in Au by first-principles calculations. The extremely low generalized-stacking-fault (GSF) energy in the basal slip system implies a great tendency to form basal stacking faults, which opens the door to phase transformation from hcp to fcc. Moreover, the Au lattice extends slightly within the superficial layers due to the self-assembly of alkanethiolate species on hcp Au (0001) surface, which may also contribute to the hcp → fcc phase transformation. Compared with hcp Mg, the GSF energies for non-basal slip systems and the twin-boundary (TB) energies for and twins are larger in hcp Au, which indicates the more difficulty in generating non-basal stacking faults and twins. The findings provide new insights for understanding the nature of the hcp → fcc phase transformation and guide the experiments of fabricating and developing materials with new structures. PMID:25998415

Influence of preliminary ultrasonic treatment upon the steady-state creep of metals of different stacking fault energies.

PubMed

Rusinko, A

2014-01-01

This paper addresses the issue of the ultrasound effects upon the creep deformation of metals with different levels of stacking fault energy. The influence of preliminary ultrasound irradiation time upon the steady state creep rate is considered. Synthetic theory of irrecoverable deformation is taken as a mathematical apparatus. The analytical results show good agreement with experimental data. Copyright © 2013 Elsevier B.V. All rights reserved.

Solute effect on basal and prismatic slip systems of Mg.

PubMed

Moitra, Amitava; Kim, Seong-Gon; Horstemeyer, M F

2014-11-05

In an effort to design novel magnesium (Mg) alloys with high ductility, we present a first principles data based on the Density Functional Theory (DFT). The DFT was employed to calculate the generalized stacking fault energy curves, which can be used in the generalized Peierls-Nabarro (PN) model to study the energetics of basal slip and prismatic slip in Mg with and without solutes to calculate continuum scale dislocation core widths, stacking fault widths and Peierls stresses. The generalized stacking fault energy curves for pure Mg agreed well with other DFT calculations. Solute effects on these curves were calculated for nine alloying elements, namely Al, Ca, Ce, Gd, Li, Si, Sn, Zn and Zr, which allowed the strength and ductility to be qualitatively estimated based on the basal dislocation properties. Based on our multiscale methodology, a suggestion has been made to improve Mg formability.

Electronically decoupled stacking fault tetrahedra embedded in Au(111) films

PubMed Central

Schouteden, Koen; Amin-Ahmadi, Behnam; Li, Zhe; Muzychenko, Dmitry; Schryvers, Dominique; Van Haesendonck, Chris

2016-01-01

Stacking faults are known as defective structures in crystalline materials that typically lower the structural quality of the material. Here, we show that a particular type of defect, that is, stacking fault tetrahedra (SFTs), exhibits pronounced quantized electronic behaviour, revealing a potential synthetic route to decoupled nanoparticles in metal films. We report on the electronic properties of SFTs that exist in Au(111) films, as evidenced by scanning tunnelling microscopy and confirmed by transmission electron microscopy. We find that the SFTs reveal a remarkable decoupling from their metal surroundings, leading to pronounced energy level quantization effects within the SFTs. The electronic behaviour of the SFTs can be described well by the particle-in-a-box model. Our findings demonstrate that controlled preparation of SFTs may offer an alternative way to achieve well-decoupled nanoparticles of high crystalline quality in metal thin films without the need of thin insulating layers. PMID:28008910

Electronically decoupled stacking fault tetrahedra embedded in Au(111) films.

PubMed

Schouteden, Koen; Amin-Ahmadi, Behnam; Li, Zhe; Muzychenko, Dmitry; Schryvers, Dominique; Van Haesendonck, Chris

2016-12-23

Stacking faults are known as defective structures in crystalline materials that typically lower the structural quality of the material. Here, we show that a particular type of defect, that is, stacking fault tetrahedra (SFTs), exhibits pronounced quantized electronic behaviour, revealing a potential synthetic route to decoupled nanoparticles in metal films. We report on the electronic properties of SFTs that exist in Au(111) films, as evidenced by scanning tunnelling microscopy and confirmed by transmission electron microscopy. We find that the SFTs reveal a remarkable decoupling from their metal surroundings, leading to pronounced energy level quantization effects within the SFTs. The electronic behaviour of the SFTs can be described well by the particle-in-a-box model. Our findings demonstrate that controlled preparation of SFTs may offer an alternative way to achieve well-decoupled nanoparticles of high crystalline quality in metal thin films without the need of thin insulating layers.

Dislocation Ledge Sources: Dispelling the Myth of Frank-Read Source Importance

NASA Astrophysics Data System (ADS)

Murr, L. E.

2016-12-01

In the early 1960s, J.C.M. Li questioned the formation of dislocation pileups at grain boundaries, especially in high-stacking-fault free-energy fcc metals and alloys, and proposed grain boundary ledge sources for dislocations in contrast to Frank -Read sources. This article reviews these proposals and the evolution of compelling evidence for grain boundary or related interfacial ledge sources of dislocations in metals and alloys, including unambiguous observations using transmission electron microscopy. Such observations have allowed grain boundary ledge source emission profiles of dislocations to be quantified in 304 stainless steel (with a stacking-fault free energy of 23 mJ/m2) and nickel (with a stacking-fault free energy of 128 mJ/m2) as a function of engineering strain. The evidence supports the conclusion that FR dislocation sources are virtually absent in metal and alloy deformation with ledges at interfaces dominating as dislocation sources.

Structural instabilities and wrinkles at the grain boundaries in 2-D h-BN: a first-principles analysis.

PubMed

Singh, Anjali; Waghmare, Umesh V

2014-10-21

The structure of grain boundaries (GBs) or interfaces between nano-forms of carbon determines their evolution into 3-D forms with nano-scale architecture. Here, we present a general framework for the construction of interfaces in 2-D h-BN and graphene in terms of (a) stacking faults and (b) growth faults, using first-principles density functional theoretical analysis. Such interfaces or GBs involve deviation from their ideal hexagonal lattice structure. We show that a stacking fault involves a linkage of rhombal and octagonal rings (4 : 8), and a growth fault involves a linkage of paired pentagonal and octagonal rings (5 : 5 : 8). While a growth fault is energetically more stable than a stacking fault in graphene, the polarity of B and N leads to the reversal of their relative stability in h-BN. We show that the planar structure of these interfacing grains exhibits instability with respect to buckling (out-of-plane deformation), which results in the formation of a wrinkle at the grain boundary (GB) and rippling of the structure. Our analysis leads to prediction of new types of low-energy GBs of 2-D h-BN and graphene. Our results for electronic and vibrational signatures of these interfaces and an STM image of the most stable interface will facilitate their experimental characterization, particularly of the wrinkles forming spontaneously at these interfaces.

Application of Phase-Weighted Stacking to Low-Frequency Earthquakes near the Alpine Fault, Central Southern Alps, New Zealand

NASA Astrophysics Data System (ADS)

Baratin, L. M.; Townend, J.; Chamberlain, C. J.; Savage, M. K.

2015-12-01

Characterising seismicity in the vicinity of the Alpine Fault, a major transform boundary late in its typical earthquake cycle, may provide constraints on the state of stress preceding a large earthquake. Here, we use recently detected tremor and low-frequency earthquakes (LFEs) to examine how slow tectonic deformation is loading the Alpine Fault toward an anticipated major rupture. We work with a continuous seismic dataset collected between 2009 and 2012 from a network of short-period seismometers, the Southern Alps Microearthquake Borehole Array (SAMBA). Fourteen primary LFE templates have been used to scan the dataset using a matched-filter technique based on an iterative cross-correlation routine. This method allows the detection of similar signals and establishes LFE families with common hypocenter locations. The detections are then combined for each LFE family using phase-weighted stacking (Thurber et al., 2014) to produce a signal with the highest possible signal to noise ratio. We find this method to be successful in increasing the number of LFE detections by roughly 10% in comparison with linear stacking. Our next step is to manually pick polarities on first arrivals of the phase-weighted stacked signals and compute preliminary locations. We are working to estimate LFE focal mechanism parameters and refine the focal mechanism solutions using an amplitude ratio technique applied to the linear stacks. LFE focal mechanisms should provide new insight into the geometry and rheology of the Alpine Fault and the stress field prevailing in the central Southern Alps.

Disentangling vortex pinning landscape in chemical solution deposited superconducting YBa2Cu3O7-x films and nanocomposites

NASA Astrophysics Data System (ADS)

Palau, A.; Vallès, F.; Rouco, V.; Coll, M.; Li, Z.; Pop, C.; Mundet, B.; Gàzquez, J.; Guzman, R.; Gutierrez, J.; Obradors, X.; Puig, T.

2018-07-01

In-field angular pinning performances at different temperatures have been analysed on chemical solution deposited (CSD) YBa2Cu3O7-x (YBCO) pristine films and nanocomposites. We show that with this analysis we are able to quantify the vortex pinning strength and energies, associated with different kinds of natural and artificial pinning defects, acting as efficient pinning centres at different regions of the H-T phase diagram. A good quantification of the variety of pinning defects active at different temperatures and magnetic fields provides a unique tool to design the best vortex pinning landscape under different operating conditions. We have found that by artificially introducing a unique defect in the YBCO matrix, the stacking faults, we are able to modify three different contributions to vortex pinning (isotropic-strong, anisotropic-strong, and isotropic-weak). The isotropic-strong contribution, widely studied in CSD YBCO nanocomposites, is associated with nanostrained regions induced at the partial dislocations surrounding the stacking faults. Moreover, the stacking fault itself acts as a planar defect which provides a very effective anisotropic-strong pinning at H//ab. Finally, the large presence of Cu-O cluster vacancies found in the stacking faults have been revealed as a source of isotropic-weak pinning sites, very active at low temperatures and high fields.

Low-Frequency Earthquakes Associated with the Late-Interseismic Central Alpine Fault, Southern Alps, New Zealand

NASA Astrophysics Data System (ADS)

Baratin, L. M.; Chamberlain, C. J.; Townend, J.; Savage, M. K.

2016-12-01

Characterising the seismicity associated with slow deformation in the vicinity of the Alpine Fault may provide constraints on the state of stress of this major transpressive margin prior to a large (≥M8) earthquake. Here, we use recently detected tremor and low-frequency earthquakes (LFEs) to examine how slow tectonic deformation is loading the Alpine Fault toward an anticipated large rupture. We initially work with a continous seismic dataset collected between 2009 and 2012 from an array of short-period seismometers, the Southern Alps Microearthquake Borehole Array. Fourteen primary LFE templates are used in an iterative matched-filter and stacking routine. This method allows the detection of similar signals and establishes LFE families with common locations. We thus generate a 36 month catalogue of 10718 LFEs. The detections are then combined for each LFE family using phase-weighted stacking to yield a signal with the highest possible signal to noise ratio. We found phase-weighted stacking to be successful in increasing the number of LFE detections by roughly 20%. Phase-weighted stacking also provides cleaner phase arrivals of apparently impulsive nature allowing more precise phase and polarity picks. We then compute improved non-linear earthquake locations using a 3D velocity model. We find LFEs to occur below the seismogenic zone at depths of 18-34 km, locating on or near the proposed deep extent of the Alpine Fault. Our next step is to estimate seismic source parameters by implementing a moment tensor inversion technique. Our focus is currently on generating a more extensive catalogue (spanning the years 2009 to 2016) using synthetic waveforms as primary templates, with which to detect LFEs. Initial testing shows that this technique paired up with phase-weighted stacking increases the number of LFE families and overall detected events roughly sevenfold. This catalogue should provide new insight into the geometry of the Alpine Fault and the prevailing stress field in the central Southern Alps.

The synchronous improvement of strength and plasticity (SISP) in new Ni-Co based disc superalloys by controling stacking fault energy.

PubMed

Xu, H; Zhang, Z J; Zhang, P; Cui, C Y; Jin, T; Zhang, Z F

2017-08-14

It is a great challenge to improve the strength of disc superalloys without great loss of plasticity together since the microstructures benefiting the strength always do not avail the plasticity. Interestingly, this study shows that the trade-off relationship between strength and plasticity can be broken through decreasing stacking fault energy (SFE) in newly developed Ni-Co based disc superalloys. Axial tensile tests in the temperature range of 25 to 725 °C were carried out in these alloys with Co content ranging from 5% to 23% (wt.%). It is found that the ultimate tensile strength (UTS) and uniform elongation (UE) are improved synchronously when microtwinning is activated by decreasing the SFE at 650 and 725 °C. In contrast, only UTS is improved when stacking fault (SF) dominates the plastic deformation at 25 and 400 °C. These results may be helpful for designing advanced disc superalloys with relatively excellent strength and plasticity simultaneously.

Mobility and coalescence of stacking fault tetrahedra in Cu

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martínez, Enrique; Uberuaga, Blas P.

Stacking fault tetrahedra (SFTs) are ubiquitous defects in face-centered cubic metals. They are produced during cold work plastic deformation, quenching experiments or under irradiation. From a dislocation point of view, the SFTs are comprised of a set of stair-rod dislocations at the (110) edges of a tetrahedron bounding triangular stacking faults. These defects are extremely stable, increasing their energetic stability as they grow in size. At the sizes visible within transmission electron microscope they appear nearly immobile. Contrary to common belief, we show in this report, using a combination of molecular dynamics and temperature accelerated dynamics, how small SFTs canmore » diffuse by temporarily disrupting their structure through activated thermal events. More over, we demonstrate that the diffusivity of defective SFTs is several orders of magnitude higher than perfect SFTs, and can be even higher than isolated vacancies. Finally, we show how SFTs can coalesce, forming a larger defect in what is a new mechanism for the growth of these omnipresent defects.« less

Mobility and coalescence of stacking fault tetrahedra in Cu

DOE PAGES

Martínez, Enrique; Uberuaga, Blas P.

2015-03-13

Stacking fault tetrahedra (SFTs) are ubiquitous defects in face-centered cubic metals. They are produced during cold work plastic deformation, quenching experiments or under irradiation. From a dislocation point of view, the SFTs are comprised of a set of stair-rod dislocations at the (110) edges of a tetrahedron bounding triangular stacking faults. These defects are extremely stable, increasing their energetic stability as they grow in size. At the sizes visible within transmission electron microscope they appear nearly immobile. Contrary to common belief, we show in this report, using a combination of molecular dynamics and temperature accelerated dynamics, how small SFTs canmore » diffuse by temporarily disrupting their structure through activated thermal events. More over, we demonstrate that the diffusivity of defective SFTs is several orders of magnitude higher than perfect SFTs, and can be even higher than isolated vacancies. Finally, we show how SFTs can coalesce, forming a larger defect in what is a new mechanism for the growth of these omnipresent defects.« less

Mobility and coalescence of stacking fault tetrahedra in Cu

PubMed Central

Martínez, Enrique; Uberuaga, Blas P.

2015-01-01

Stacking fault tetrahedra (SFTs) are ubiquitous defects in face-centered cubic metals. They are produced during cold work plastic deformation, quenching experiments or under irradiation. From a dislocation point of view, the SFTs are comprised of a set of stair-rod dislocations at the (110) edges of a tetrahedron bounding triangular stacking faults. These defects are extremely stable, increasing their energetic stability as they grow in size. At the sizes visible within transmission electron microscope they appear nearly immobile. Contrary to common belief, we show in this report, using a combination of molecular dynamics and temperature accelerated dynamics, how small SFTs can diffuse by temporarily disrupting their structure through activated thermal events. More over, we demonstrate that the diffusivity of defective SFTs is several orders of magnitude higher than perfect SFTs, and can be even higher than isolated vacancies. Finally, we show how SFTs can coalesce, forming a larger defect in what is a new mechanism for the growth of these omnipresent defects. PMID:25765711

Generalized stacking fault energies of alloys.

PubMed

Li, Wei; Lu, Song; Hu, Qing-Miao; Kwon, Se Kyun; Johansson, Börje; Vitos, Levente

2014-07-02

The generalized stacking fault energy (γ surface) provides fundamental physics for understanding the plastic deformation mechanisms. Using the ab initio exact muffin-tin orbitals method in combination with the coherent potential approximation, we calculate the γ surface for the disordered Cu-Al, Cu-Zn, Cu-Ga, Cu-Ni, Pd-Ag and Pd-Au alloys. Studying the effect of segregation of the solute to the stacking fault planes shows that only the local chemical composition affects the γ surface. The calculated alloying trends are discussed using the electronic band structure of the base and distorted alloys.Based on our γ surface results, we demonstrate that the previous revealed 'universal scaling law' between the intrinsic energy barriers (IEBs) is well obeyed in random solid solutions. This greatly simplifies the calculations of the twinning measure parameters or the critical twinning stress. Adopting two twinnability measure parameters derived from the IEBs, we find that in binary Cu alloys, Al, Zn and Ga increase the twinnability, while Ni decreases it. Aluminum and gallium yield similar effects on the twinnability.

Injected carrier concentration dependence of the expansion of single Shockley-type stacking faults in 4H-SiC PiN diodes

NASA Astrophysics Data System (ADS)

Tawara, T.; Matsunaga, S.; Fujimoto, T.; Ryo, M.; Miyazato, M.; Miyazawa, T.; Takenaka, K.; Miyajima, M.; Otsuki, A.; Yonezawa, Y.; Kato, T.; Okumura, H.; Kimoto, T.; Tsuchida, H.

2018-01-01

We investigated the relationship between the dislocation velocity and the injected carrier concentration on the expansion of single Shockley-type stacking faults by monitoring the electroluminescence from 4H-SiC PiN diodes with various anode Al concentrations. The injected carrier concentration was calculated using a device simulation that took into account the measured accumulated charge in the drift layer during diode turn-off. The dislocation velocity was strongly dependent on the injected hole concentration, which represents the excess carrier concentration. The activation energy of the dislocation velocity was quite small (below 0.001 eV between 310 and 386 K) over a fixed range of hole concentrations. The average threshold hole concentration required for the expansion of bar-shaped single Shockley-type stacking faults at the interface between the buffer layer and the substrate was determined to be 1.6-2.5 × 1016 cm-3 for diodes with a p-type epitaxial anode with various Al concentrations.

Breakdown of Shape Memory Effect in Bent Cu-Al-Ni Nanopillars: When Twin Boundaries Become Stacking Faults.

PubMed

Liu, Lifeng; Ding, Xiangdong; Sun, Jun; Li, Suzhi; Salje, Ekhard K H

2016-01-13

Bent Cu-Al-Ni nanopillars (diameters 90-750 nm) show a shape memory effect, SME, for diameters D > 300 nm. The SME and the associated twinning are located in a small deformed section of the nanopillar. Thick nanopillars (D > 300 nm) transform to austenite under heating, including the deformed region. Thin nanopillars (D < 130 nm) do not twin but generate highly disordered sequences of stacking faults in the deformed region. No SME occurs and heating converts only the undeformed regions into austenite. The defect-rich, deformed region remains in the martensite phase even after prolonged heating in the stability field of austenite. A complex mixture of twins and stacking faults was found for diameters 130 nm < D < 300 nm. The size effect of the SME in Cu-Al-Ni nanopillars consists of an approximately linear reduction of the SME between 300 and 130 nm when the SME completely vanishes for smaller diameters.

The effect of aluminium on mechanical properties and deformation mechanisms of hadfield steel single crystals

NASA Astrophysics Data System (ADS)

Zakharova, E. G.; Kireeva, I. V.; Chumlyakov, Y. I.; Shul'Mina, A. A.; Sehitoglu, H.; Karaman, I.

2004-06-01

On single crystals of Hadfield steel (Fe-13Mn-1.3C, Fe-13Mn-2.7Al-1.3C, wt.%) the systematical investigations of deformation mechanisms - slip and twinning, stages of plastic flow, strain hardening coefficient depending on orientation of tensile axis have been carried out by methods of optical and electron microscopy, x-ray analysis. Is has been shown that the combination of low stacking fault energy (γ{SF}=0.03J/m^2) with high concentration of carbon atoms in aluminium-free steel results in development of the mechanical twinning at room temperature in all crystal orientations. The new type of twinning with formation of extrinsic stacking fault has been found out in [001] single crystals. Experimentally it has been established that alloying with aluminium leads to increase of stacking fault energy of Hadfield steel and suppresses twinning in all orientations of crystals at preservation of high values of strain-hardening coefficients θ.

Direct observation of a stacking fault in Si(1 - x)Ge(x) semiconductors by spherical aberration-corrected TEM and conventional ADF-STEM.

PubMed

Yamasaki, Jun; Kawai, Tomoyuki; Tanaka, Nobuo

2004-01-01

Spherical aberration (C(S))-corrected transmission electron microscopy (TEM) and annular dark-field scanning TEM (ADF-STEM) are applied to high-resolution observation of stacking faults in Si(1 - x)Ge(x) alloy films prepared on a Si(100) buffer layer by the chemical vapor deposition method. Both of the images clarify the individual nature of stacking faults from their directly interpretable image contrast and also by using image simulation in the case of the C(S)-corrected TEM. Positions of the atomic columns obtained in the ADF-STEM images almost agree with a projection of the theoretical model studied by Chou et al. (Phys. Rev. B 32(1985): 7979). Comparison between the C(S)-corrected TEM and ADF-STEM images shows that their resolution is at a similar level, but directly interpretable image contrast is obtained in ultrathin samples for C(S)-corrected TEM and in slightly thicker samples for ADF-STEM.

Temperature-dependent ideal strength and stacking fault energy of fcc Ni: a first-principles study of shear deformation.

PubMed

Shang, S L; Wang, W Y; Wang, Y; Du, Y; Zhang, J X; Patel, A D; Liu, Z K

2012-04-18

Variations of energy, stress, and magnetic moment of fcc Ni as a response to shear deformation and the associated ideal shear strength (τ(IS)), intrinsic (γ(SF)) and unstable (γ(US)) stacking fault energies have been studied in terms of first-principles calculations under both the alias and affine shear regimes within the {111} slip plane along the <112> and <110> directions. It is found that (i) the intrinsic stacking fault energy γ(SF) is nearly independent of the shear deformation regimes used, albeit a slightly smaller value is predicted by pure shear (with relaxation) compared to the one from simple shear (without relaxation); (ii) the minimum ideal shear strength τ(IS) is obtained by pure alias shear of {111}<112>; and (iii) the dissociation of the 1/2[110] dislocation into two partial Shockley dislocations (1/6[211] + 1/6[121]) is observed under pure alias shear of {111}<110>. Based on the quasiharmonic approach from first-principles phonon calculations, the predicted γ(SF) has been extended to finite temperatures. In particular, using a proposed quasistatic approach on the basis of the predicted volume versus temperature relation, the temperature dependence of τ(IS) is also obtained. Both the γ(SF) and the τ(IS) of fcc Ni decrease with increasing temperature. The computed ideal shear strengths as well as the intrinsic and unstable stacking fault energies are in favorable accord with experiments and other predictions in the literature.

Surface dislocation nucleation controlled deformation of Au nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Roos, B.; Kapelle, B.; Volkert, C. A., E-mail: volkert@ump.gwdg.de

2014-11-17

We investigate deformation in high quality Au nanowires under both tension and bending using in-situ transmission electron microscopy. Defect evolution is investigated during: (1) tensile deformation of 〈110〉 oriented, initially defect-free, single crystal nanowires with cross-sectional widths between 30 and 300 nm, (2) bending deformation of the same wires, and (3) tensile deformation of wires containing coherent twin boundaries along their lengths. We observe the formation of twins and stacking faults in the single crystal wires under tension, and storage of full dislocations after bending of single crystal wires and after tension of twinned wires. The stress state dependence of themore » deformation morphology and the formation of stacking faults and twins are not features of bulk Au, where deformation is controlled by dislocation interactions. Instead, we attribute the deformation morphologies to the surface nucleation of either leading or trailing partial dislocations, depending on the Schmid factors, which move through and exit the wires producing stacking faults or full dislocation slip. The presence of obstacles such as neutral planes or twin boundaries hinder the egress of the freshly nucleated dislocations and allow trailing and leading partial dislocations to combine and to be stored as full dislocations in the wires. We infer that the twins and stacking faults often observed in nanoscale Au specimens are not a direct size effect but the result of a size and obstacle dependent transition from dislocation interaction controlled to dislocation nucleation controlled deformation.« less

Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

DOE PAGES

Zhang, Lihua; Su, Dong; Kisslinger, Kim; ...

2014-12-04

Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted regionmore » with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.« less

Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Lihua; Su, Dong; Kisslinger, Kim

Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted regionmore » with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.« less

Characterization of individual stacking faults in a wurtzite GaAs nanowire by nanobeam X-ray diffraction.

PubMed

Davtyan, Arman; Lehmann, Sebastian; Kriegner, Dominik; Zamani, Reza R; Dick, Kimberly A; Bahrami, Danial; Al-Hassan, Ali; Leake, Steven J; Pietsch, Ullrich; Holý, Václav

2017-09-01

Coherent X-ray diffraction was used to measure the type, quantity and the relative distances between stacking faults along the growth direction of two individual wurtzite GaAs nanowires grown by metalorganic vapour epitaxy. The presented approach is based on the general property of the Patterson function, which is the autocorrelation of the electron density as well as the Fourier transformation of the diffracted intensity distribution of an object. Partial Patterson functions were extracted from the diffracted intensity measured along the [000\\bar{1}] direction in the vicinity of the wurtzite 00\\bar{1}\\bar{5} Bragg peak. The maxima of the Patterson function encode both the distances between the fault planes and the type of the fault planes with the sensitivity of a single atomic bilayer. The positions of the fault planes are deduced from the positions and shapes of the maxima of the Patterson function and they are in excellent agreement with the positions found with transmission electron microscopy of the same nanowire.

Characterization of individual stacking faults in a wurtzite GaAs nanowire by nanobeam X-ray diffraction

PubMed Central

Davtyan, Arman; Lehmann, Sebastian; Zamani, Reza R.; Dick, Kimberly A.; Bahrami, Danial; Al-Hassan, Ali; Leake, Steven J.; Pietsch, Ullrich; Holý, Václav

2017-01-01

Coherent X-ray diffraction was used to measure the type, quantity and the relative distances between stacking faults along the growth direction of two individual wurtzite GaAs nanowires grown by metalorganic vapour epitaxy. The presented approach is based on the general property of the Patterson function, which is the autocorrelation of the electron density as well as the Fourier transformation of the diffracted intensity distribution of an object. Partial Patterson functions were extracted from the diffracted intensity measured along the direction in the vicinity of the wurtzite Bragg peak. The maxima of the Patterson function encode both the distances between the fault planes and the type of the fault planes with the sensitivity of a single atomic bilayer. The positions of the fault planes are deduced from the positions and shapes of the maxima of the Patterson function and they are in excellent agreement with the positions found with transmission electron microscopy of the same nanowire. PMID:28862620

Rapid and Nondestructive Identification of Polytypism and Stacking Sequences in Few-Layer Molybdenum Diselenide by Raman Spectroscopy

DOE PAGES

Lu, Xin; Utama, M. Iqbal Bakti; Lin, Junhao; ...

2015-07-02

Various combinations of interlayer shear modes emerge in few-layer molybdenum diselenide grown by chemical vapor deposition depending on the stacking configuration of the sample. Raman measurements may also reveal polytypism and stacking faults, as supported by first principles calculations and high-resolution transmission electron microscopy. Thus, Raman spectroscopy is an important tool in probing stacking-dependent properties in few-layer 2D materials.

New twinning route in face-centered cubic nanocrystalline metals.

PubMed

Wang, Lihua; Guan, Pengfei; Teng, Jiao; Liu, Pan; Chen, Dengke; Xie, Weiyu; Kong, Deli; Zhang, Shengbai; Zhu, Ting; Zhang, Ze; Ma, Evan; Chen, Mingwei; Han, Xiaodong

2017-12-15

Twin nucleation in a face-centered cubic crystal is believed to be accomplished through the formation of twinning partial dislocations on consecutive atomic planes. Twinning should thus be highly unfavorable in face-centered cubic metals with high twin-fault energy barriers, such as Al, Ni, and Pt, but instead is often observed. Here, we report an in situ atomic-scale observation of twin nucleation in nanocrystalline Pt. Unlike the classical twinning route, deformation twinning initiated through the formation of two stacking faults separated by a single atomic layer, and proceeded with the emission of a partial dislocation in between these two stacking faults. Through this route, a three-layer twin was nucleated without a mandatory layer-by-layer twinning process. This route is facilitated by grain boundaries, abundant in nanocrystalline metals, that promote the nucleation of separated but closely spaced partial dislocations, thus enabling an effective bypassing of the high twin-fault energy barrier.

Formation and Growth of Stacking Fault Tetrahedra in Ni via Vacancy Aggregation Mechanism

DOE PAGES

Aidhy, Dilpuneet S.; Lu, Chenyang; Jin, Ke; ...

2015-12-29

Using molecular dynamics simulations, the formation and growth of stacking fault tetrahedra (SFT) are captured by vacancy cluster diffusion and aggregation mechanisms in Ni. The vacancytetrahedron acts as a nucleation point for SFT formation. Simulations show that perfect SFT can grow to the next size perfect SFT via a vacancy aggregation mechanism. The stopping and range of ions in matter (SRIM) calculations and transmission electron microscopy (TEM) observations reveal that SFT can form farther away from the initial cascade-event locations, indicating the operation of diffusion-based vacancy-aggregation mechanism.

Formation and Growth of Stacking Fault Tetrahedra in Ni via Vacancy Aggregation Mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aidhy, Dilpuneet S.; Lu, Chenyang; Jin, Ke

Using molecular dynamics simulations, the formation and growth of stacking fault tetrahedra (SFT) are captured by vacancy cluster diffusion and aggregation mechanisms in Ni. The vacancytetrahedron acts as a nucleation point for SFT formation. Simulations show that perfect SFT can grow to the next size perfect SFT via a vacancy aggregation mechanism. The stopping and range of ions in matter (SRIM) calculations and transmission electron microscopy (TEM) observations reveal that SFT can form farther away from the initial cascade-event locations, indicating the operation of diffusion-based vacancy-aggregation mechanism.

Ductilizing bulk metallic glass composite by tailoring stacking fault energy.

PubMed

Wu, Y; Zhou, D Q; Song, W L; Wang, H; Zhang, Z Y; Ma, D; Wang, X L; Lu, Z P

2012-12-14

Martensitic transformation was successfully introduced to bulk metallic glasses as the reinforcement micromechanism. In this Letter, it was found that the twinning property of the reinforcing crystals can be dramatically improved by reducing the stacking fault energy through microalloying, which effectively alters the electron charge density redistribution on the slipping plane. The enhanced twinning propensity promotes the martensitic transformation of the reinforcing austenite and, consequently, improves plastic stability and the macroscopic tensile ductility. In addition, a general rule to identify effective microalloying elements based on their electronegativity and atomic size was proposed.

Dislocation Dissociation Strongly Influences on Frank—Read Source Nucleation and Microplasticy of Materials with Low Stacking Fault Energy

NASA Astrophysics Data System (ADS)

Huang, Min-Sheng; Zhu, Ya-Xin; Li, Zhen-Huan

2014-04-01

The influence of dislocation dissociation on the evolution of Frank—Read (F-R) sources is studied using a three-dimensional discrete dislocation dynamics simulation (3D-DDD). The classical Orowan nucleation stress and recently proposed Benzerga nucleation time models for F-R sources are improved. This work shows that it is necessary to introduce the dislocation dissociation scheme into 3D-DDD simulation, especially for simulations on micro-plasticity of small sized materials with low stacking fault energy.

New Growth Mode through Decorated Twin Boundaries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bleikamp, Sebastian; Thoma, Arne; Polop, Celia

2006-03-24

Scanning tunneling microscopy and low energy electron diffraction were used to investigate the growth of partly twinned Ir thin films on Ir(111). A transition from the expected layer-by-layer to a defect dominated growth mode with a fixed lateral length scale and increasing roughness is observed. During growth, the majority of the film is stably transformed to twinned stacking. This transition is initiated by the energetic avoidance of the formation of intrinsic stacking faults compared to two independent twin faults. The atomistic details of the defect kinetics are outlined.

New growth mode through decorated twin boundaries.

PubMed

Bleikamp, Sebastian; Thoma, Arne; Polop, Celia; Pirug, Gerhard; Linke, Udo; Michely, Thomas

2006-03-24

Scanning tunneling microscopy and low energy electron diffraction were used to investigate the growth of partly twinned Ir thin films on Ir(111). A transition from the expected layer-by-layer to a defect dominated growth mode with a fixed lateral length scale and increasing roughness is observed. During growth, the majority of the film is stably transformed to twinned stacking. This transition is initiated by the energetic avoidance of the formation of intrinsic stacking faults compared to two independent twin faults. The atomistic details of the defect kinetics are outlined.

Mesoscale models for stacking faults, deformation twins and martensitic transformations: Linking atomistics to continuum

NASA Astrophysics Data System (ADS)

Kibey, Sandeep A.

We present a hierarchical approach that spans multiple length scales to describe defect formation---in particular, formation of stacking faults (SFs) and deformation twins---in fcc crystals. We link the energy pathways (calculated here via ab initio density functional theory, DFT) associated with formation of stacking faults and twins to corresponding heterogeneous defect nucleation models (described through mesoscale dislocation mechanics). Through the generalized Peieirls-Nabarro model, we first correlate the width of intrinsic SFs in fcc alloy systems to their nucleation pathways called generalized stacking fault energies (GSFE). We then establish a qualitative dependence of twinning tendency in fee metals and alloys---specifically, in pure Cu and dilute Cu-xAl (x= 5.0 and 8.3 at.%)---on their twin-energy pathways called the generalized planar fault energies (GPFE). We also link the twinning behavior of Cu-Al alloys to their electronic structure by determining the effect of solute Al on the valence charge density redistribution at the SF through ab initio DFT. Further, while several efforts have been undertaken to incorporate twinning for predicting stress-strain response of fcc materials, a fundamental law for critical twinning stress has not yet emerged. We resolve this long-standing issue by linking quantitatively the twin-energy pathways (GPFE) obtained via ab initio DFT to heterogeneous, dislocation-based twin nucleation models. We establish an analytical expression that quantitatively predicts the critical twinning stress in fcc metals in agreement with experiments without requiring any empiricism at any length scale. Our theory connects twinning stress to twin-energy pathways and predicts a monotonic relation between stress and unstable twin stacking fault energy revealing the physics of twinning. We further demonstrate that the theory holds for fcc alloys as well. Our theory inherently accounts for directional nature of twinning which available qualitative models do not necessarily account for. Finally, we extend the present work to martensitic transformations and determine the energy pathway for B2→B19 transformation in NiTi. Based on our ab initio DFT calculations, we propose a combined distortion-shuffle pathway for B2→B19 transformation in NiTi. Our results indicate that in NiTi, a barrier of 0.48 mRyd/atom (relative to B2 phase) must be overcome to transform the parent B2 into orthorhombic B19 phase.

Solid-State Fault Current Limiter Development : Design and Testing Update of a 15kV SSCL Power Stack

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dr. Ram Adapa; Mr. Dante Piccone

2012-04-30

ABSTRACT The Solid-State Fault Current Limiter (SSCL) is a promising technology that can be applied to utility power delivery systems to address the problem of increasing fault currents associated with load growth. As demand continues to grow, more power is added to utility system either by increasing generator capacity or by adding distributed generators, resulting in higher available fault currents, often beyond the capabilities of the present infrastructure. The SSCL is power-electronics based equipment designed to work with the present utility system to address this problem. The SSCL monitors the line current and dynamically inserts additional impedance into the linemore » in the event of a fault being detected. The SSCL is based on a modular design and can be configured for 5kV through 69kV systems at nominal current ratings of 1000A to 4000A. Results and Findings This report provides the final test results on the development of 15kV class SSCL single phase power stack. The scope of work included the design of the modular standard building block sub-assemblies, the design and manufacture of the power stack and the testing of the power stack for the key functional tests of continuous current capability and fault current limiting action. Challenges and Objectives Solid-State Current Limiter technology impacts a wide spectrum of utility engineering and operating personnel. It addresses the problems associated with load growth both at Transmission and Distribution class networks. The design concept is pioneering in terms of developing the most efficient and compact power electronics equipment for utility use. The initial test results of the standard building blocks are promising. The independent laboratory tests of the power stack are promising. However the complete 3 phase system needs rigorous testing for performance and reliability. Applications, Values, and Use The SSCL is an intelligent power-electronics device which is modular in design and can provide current limiting or current interrupting capabilities. It can be applied to variety of applications from distribution class to transmission class power delivery grids and networks. It can also be applied to single major commercial and industrial loads and distributed generator supplies. The active switching of devices can be further utilized for protection of substation transformers. The stress on the system can be reduced substantially improving the life of the power system. It minimizes the voltage sag by speedy elimination of heavy fault currents and promises to be an important element of the utility power system. DOE Perspective This development effort is now focused on a 15kV system. This project will help mitigate the challenges of increasing available fault current. DOE has made a major contribution in providing a cost effective SSCL designed to integrate seamlessly into the Transmission and Distribution networks of today and the future. Approach SSCL development program for a 69kV SSCL was initiated which included the use of the Super GTO advanced semiconductor device which won the 2007 R&D100 Award. In the beginning, steps were identified to accomplish the economically viable design of a 69kV class Solid State Current Limiter that is extremely reliable, cost effective, and compact enough to be applied in urban transmission. The prime thrust in design and development was to encompass the 1000A and the 3000A ratings and provide a modular design to cover the wide range of applications. The focus of the project was then shifted to a 15kV class SSCL. The specifications for the 15kV power stack are reviewed. The design changes integrated into the 15kV power stack are discussed. In this Technical Update the complete project is summarized followed by a detailed test report. The power stack independent high voltage laboratory test requirements and results are presented. Keywords Solid State Current Limiter, SSCL, Fault Current Limiter, Fault Current Controller, Power electronics controller, Intelligent power-electronics Device, IED« less

Near band gap luminescence in hybrid organic-inorganic structures based on sputtered GaN nanorods.

PubMed

Forsberg, Mathias; Serban, Elena Alexandra; Hsiao, Ching-Lien; Junaid, Muhammad; Birch, Jens; Pozina, Galia

2017-04-26

Novel hybrid organic-inorganic nanostructures fabricated to utilize non-radiative resonant energy transfer mechanism are considered to be extremely attractive for a variety of light emitters for down converting of ultaviolet light and for photovoltaic applications since they can be much more efficient compared to devices grown with common design. Organic-inorganic hybrid structures based on green polyfluorene (F8BT) and GaN (0001) nanorods grown by magnetron sputtering on Si (111) substrates are studied. In such nanorods, stacking faults can form periodic polymorphic quantum wells characterized by bright luminescence. In difference to GaN exciton emission, the recombination rate for the stacking fault related emission increases in the presence of polyfluorene film, which can be understood in terms of Förster interaction mechanism. From comparison of dynamic properties of the stacking fault related luminescence in the hybrid structures and in the bare GaN nanorods, the pumping efficiency of non-radiative resonant energy transfer in hybrids was estimated to be as high as 35% at low temperatures.

The role of surface diffusion and wing tilt in the formation of localized stacking faults in high In-content InGaN MQW nanostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakajima, Yoshitake; Dapkus, P. Daniel

Yellow and green emitting multiple quantum well structures are grown on nanostripe templates with {10-11} facets. SEM and cathodoluminescence measurements show a correlation between rough surface morphology near the bottom of the stripes and non-radiative recombination centers. Transmission electron microscopy (TEM) analysis shows that these surface instabilities are a result of stacking faults generated from the quantum well (QW) regions near the bottom of the pyramid that propagate to the surface. HRTEM images show that the stacking faults are I{sub 1} type which is formed by removal of one half basal plane to relieve the compressive strain in the InGaNmore » QW. Thicker QWs near the bottom as a result of growth rate enhancement due to the surface diffusion of the precursors from the mask regions cause increased strain. Additionally, the compressive strain induced by the bending of the nanostructure towards the growth mask further increases the strain experienced by the QW thereby causing the localized defect generation.« less

Deformation-mechanism map for nanocrystalline metals by molecular-dynamics simulation.

PubMed

Yamakov, V; Wolf, D; Phillpot, S R; Mukherjee, A K; Gleiter, H

2004-01-01

Molecular-dynamics simulations have recently been used to elucidate the transition with decreasing grain size from a dislocation-based to a grain-boundary-based deformation mechanism in nanocrystalline f.c.c. metals. This transition in the deformation mechanism results in a maximum yield strength at a grain size (the 'strongest size') that depends strongly on the stacking-fault energy, the elastic properties of the metal, and the magnitude of the applied stress. Here, by exploring the role of the stacking-fault energy in this crossover, we elucidate how the size of the extended dislocations nucleated from the grain boundaries affects the mechanical behaviour. Building on the fundamental physics of deformation as exposed by these simulations, we propose a two-dimensional stress-grain size deformation-mechanism map for the mechanical behaviour of nanocrystalline f.c.c. metals at low temperature. The map captures this transition in both the deformation mechanism and the related mechanical behaviour with decreasing grain size, as well as its dependence on the stacking-fault energy, the elastic properties of the material, and the applied stress level.

Anisotropy of Earth's D'' layer and stacking faults in the MgSiO3 post-perovskite phase.

PubMed

Oganov, Artem R; Martonák, Roman; Laio, Alessandro; Raiteri, Paolo; Parrinello, Michele

2005-12-22

The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral phase of the Earth's lowermost mantle (the D'' layer). Its properties explain numerous geophysical observations associated with this layer-for example, the D'' discontinuity, its topography and seismic anisotropy within the layer. Here we use a novel simulation technique, first-principles metadynamics, to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskite phases. Metadynamics trajectories identify plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition, and as a likely mechanism for plastic deformation of perovskite and post-perovskite. In particular, the predicted slip planes are {010} for perovskite (consistent with experiment) and {110} for post-perovskite (in contrast to the previously expected {010} slip planes). Dominant slip planes define the lattice preferred orientation and elastic anisotropy of the texture. The {110} slip planes in post-perovskite require a much smaller degree of lattice preferred orientation to explain geophysical observations of shear-wave anisotropy in the D'' layer.

Significant contribution of stacking faults to the strain hardening behavior of Cu-15%Al alloy with different grain sizes.

PubMed

Tian, Y Z; Zhao, L J; Chen, S; Shibata, A; Zhang, Z F; Tsuji, N

2015-11-19

It is commonly accepted that twinning can induce an increase of strain-hardening rate during the tensile process of face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE). In this study, we explored the grain size effect on the strain-hardening behavior of a Cu-15 at.%Al alloy with low SFE. Instead of twinning, we detected a significant contribution of stacking faults (SFs) irrespective of the grain size even in the initial stage of tensile process. In contrast, twinning was more sensitive to the grain size, and the onset of deformation twins might be postponed to a higher strain with increasing the grain size. In the Cu-15 at.%Al alloy with a mean grain size of 47 μm, there was a stage where the strain-hardening rate increases with strain, and this was mainly induced by the SFs instead of twinning. Thus in parallel with the TWIP effect, we proposed that SFs also contribute significantly to the plasticity of FCC alloys with low SFE.

Significant contribution of stacking faults to the strain hardening behavior of Cu-15%Al alloy with different grain sizes

PubMed Central

Tian, Y. Z.; Zhao, L. J.; Chen, S.; Shibata, A.; Zhang, Z. F.; Tsuji, N.

2015-01-01

It is commonly accepted that twinning can induce an increase of strain-hardening rate during the tensile process of face-centered cubic (FCC) metals and alloys with low stacking fault energy (SFE). In this study, we explored the grain size effect on the strain-hardening behavior of a Cu-15 at.%Al alloy with low SFE. Instead of twinning, we detected a significant contribution of stacking faults (SFs) irrespective of the grain size even in the initial stage of tensile process. In contrast, twinning was more sensitive to the grain size, and the onset of deformation twins might be postponed to a higher strain with increasing the grain size. In the Cu-15 at.%Al alloy with a mean grain size of 47 μm, there was a stage where the strain-hardening rate increases with strain, and this was mainly induced by the SFs instead of twinning. Thus in parallel with the TWIP effect, we proposed that SFs also contribute significantly to the plasticity of FCC alloys with low SFE. PMID:26582568

The role of surface diffusion and wing tilt in the formation of localized stacking faults in high In-content InGaN MQW nanostructures

NASA Astrophysics Data System (ADS)

Nakajima, Yoshitake; Dapkus, P. Daniel

2016-08-01

Yellow and green emitting multiple quantum well structures are grown on nanostripe templates with {10-11} facets. SEM and cathodoluminescence measurements show a correlation between rough surface morphology near the bottom of the stripes and non-radiative recombination centers. Transmission electron microscopy (TEM) analysis shows that these surface instabilities are a result of stacking faults generated from the quantum well (QW) regions near the bottom of the pyramid that propagate to the surface. HRTEM images show that the stacking faults are I1 type which is formed by removal of one half basal plane to relieve the compressive strain in the InGaN QW. Thicker QWs near the bottom as a result of growth rate enhancement due to the surface diffusion of the precursors from the mask regions cause increased strain. Additionally, the compressive strain induced by the bending of the nanostructure towards the growth mask further increases the strain experienced by the QW thereby causing the localized defect generation.

Stacking faults and mechanisms strain-induced transformations of hcp metals (Ti, Mg) during mechanical activation in liquid hydrocarbons

NASA Astrophysics Data System (ADS)

Lubnin, A. N.; Dorofeev, G. A.; Nikonova, R. M.; Mukhgalin, V. V.; Lad'yanov, V. I.

2017-11-01

The evolution of the structure and substructure of metals Ti and Mg with hexagonal close-packed (hcp) lattice is studied during their mechanical activation in a planetary ball mill in liquid hydrocarbons (toluene, n-heptane) and with additions of carbon materials (graphite, fullerite, nanotubes) by X-ray diffraction, scanning electron microscopy, and chemical analysis. The temperature behavior and hydrogen-accumulating properties of mechanocomposites are studied. During mechanical activation of Ti and Mg, liquid hydrocarbons decay, metastable nanocrystalline titanium carbohydride Ti(C,H) x and magnesium hydride β-MgH2 are formed, respectively. The Ti(C,H) x and MgH2 formation mechanisms during mechanical activation are deformation ones and are associated with stacking faults accumulation, and the formation of face-centered cubic (fcc) packing of atoms. Metastable Ti(C,H)x decays at a temperature of 550°C, the partial reverse transformation fcc → hcp occurs. The crystalline defect accumulation (nanograin boundaries, stacking faults), hydrocarbon destruction, and mechanocomposite formation leads to the enhancement of subsequent magnesium hydrogenation in the Sieverts reactor.

Molecular Dynamics Study of High Symmetry Planar Defect Evolution during Growth of CdTe/CdS Films

DOE PAGES

Chavez, Jose Juan; Zhou, Xiao W.; Almeida, Sergio F.; ...

2017-12-15

The growth dynamics and evolution of intrinsic stacking faults, lamellar, and double positioning twin grain boundaries were explored using molecular dynamics simulations during the growth of CdTe homoepitaxy and CdTe/CdS heteroepitaxy. Initial substrate structures were created containing either stacking fault or one type of twin grain boundary, and films were subsequently deposited to study the evolution of the underlying defect. Results show that during homoepitaxy the film growth was epitaxial and the substrate’s defects propagated into the epilayer, except for the stacking fault case where the defect disappeared after the film thickness increased. In contrast, films grown on heteroepitaxy conditionsmore » formed misfit dislocations and grew with a small angle tilt (within ~5°) of the underlying substrate’s orientation to alleviate the lattice mismatch. Grain boundary proliferation was observed in the lamellar and double positioning twin cases. Finally, our study indicates that it is possible to influence the propagation of high symmetry planar defects by selecting a suitable substrate defect configuration, thereby controlling the film defect morphology.« less

Molecular Dynamics Study of High Symmetry Planar Defect Evolution during Growth of CdTe/CdS Films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chavez, Jose Juan; Zhou, Xiao W.; Almeida, Sergio F.

The growth dynamics and evolution of intrinsic stacking faults, lamellar, and double positioning twin grain boundaries were explored using molecular dynamics simulations during the growth of CdTe homoepitaxy and CdTe/CdS heteroepitaxy. Initial substrate structures were created containing either stacking fault or one type of twin grain boundary, and films were subsequently deposited to study the evolution of the underlying defect. Results show that during homoepitaxy the film growth was epitaxial and the substrate’s defects propagated into the epilayer, except for the stacking fault case where the defect disappeared after the film thickness increased. In contrast, films grown on heteroepitaxy conditionsmore » formed misfit dislocations and grew with a small angle tilt (within ~5°) of the underlying substrate’s orientation to alleviate the lattice mismatch. Grain boundary proliferation was observed in the lamellar and double positioning twin cases. Finally, our study indicates that it is possible to influence the propagation of high symmetry planar defects by selecting a suitable substrate defect configuration, thereby controlling the film defect morphology.« less

A first principles study of commonly observed planar defects in Ti/TiB system

DOE PAGES

Nandwana, Peeyush; Gupta, Niraj; Srinivasan, Srivilliputhur G.; ...

2018-04-20

Here, TiB exhibits a hexagonal cross-section with growth faults on (1 0 0) planes and contains B27-B f bicrystals. The hexagonal cross-section is presently explained by surface free energy minimization principle. We show that interfacial energy calculations explain the longer (1 0 0) facet compared to (1 0 1) type facets whereas free surface energy arguments do not provide the true picture. No quantitative explanation of stacking faults and B27-B f interfaces in TiB exists. We show that the low formation energy of stacking faults and B27-B f interfaces explain their abundance. The low energy barrier for B f formationmore » is shown to be responsible for their presence in TiB.« less

A first principles study of commonly observed planar defects in Ti/TiB system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nandwana, Peeyush; Gupta, Niraj; Srinivasan, Srivilliputhur G.

Here, TiB exhibits a hexagonal cross-section with growth faults on (1 0 0) planes and contains B27-B f bicrystals. The hexagonal cross-section is presently explained by surface free energy minimization principle. We show that interfacial energy calculations explain the longer (1 0 0) facet compared to (1 0 1) type facets whereas free surface energy arguments do not provide the true picture. No quantitative explanation of stacking faults and B27-B f interfaces in TiB exists. We show that the low formation energy of stacking faults and B27-B f interfaces explain their abundance. The low energy barrier for B f formationmore » is shown to be responsible for their presence in TiB.« less

Order-disorder twinning model and stacking faults in alpha-NTO.

PubMed

Schwarzenbach, Dieter; Kirschbaum, Kristin; Pinkerton, A Alan

2006-10-01

Crystals of the recently published [Bolotina, Kirschbaum & Pinkerton (2005). Acta Cryst. B61, 577-584] triclinic (P\\overline1) structure of 5-nitro-2,4-dihydro-1,2,4-triazol-3-one (alpha-NTO) occur as fourfold twins. There are Z' = 4 independent molecules per asymmetric unit. We show that the structure contains layers with 2-periodic layer-group symmetry p2(1)/b 1 (1). This symmetry is lost through the stacking of the layers, which is a possible explanation for Z' = 4. A layer can assume four different but equivalent positions with respect to its nearest neighbor. Twinning arises through stacking faults and is an instructive example of the application of order-disorder theory using local symmetry operations. The near-neighbor relations between molecules remain unchanged through all twin boundaries. The four structures with maximum degree of order, one of which is the observed one, and the family reflections common to all domains are identified. Rods of weak diffuse scattering confirm the stacking model.

The role of the cubic structure in freezing of a supercooled water droplet on an ice substrate

NASA Astrophysics Data System (ADS)

Takahashi, T.; Kobayashi, T.

1983-12-01

The possibility of the formation of a metastable cubic (diamond) structure and its role in freezing of a supercooled water droplet on an ice substrate are discussed in terms of two-dimensional nucleation. The mode of stacking sequence of new layers formed by two-dimensional nucleation is divided into single and multi-nucleation according to the degree of supercooling and to the size of the supercooled droplet. In the case of single nucleation a frozen droplet develops into a complete hexagonal single crystal or an optically single crystal (containing discontinuous stacking faults). In the case of multi-nucleation attention is paid to the size effect and the stacking direction of the nucleus to calculate the waiting time in the nucleation. Then the frozen droplets are crystallographically divided into three categories: completely single crystals, optically single crystals (containing a small cubic structure, i.e. stacking faults) and polycrystals with a misorientation of 70.53° between the c-axes.

Stacking fault-mediated ultrastrong nanocrystalline Ti thin films

NASA Astrophysics Data System (ADS)

Wu, K.; Zhang, J. Y.; Li, G.; Wang, Y. Q.; Cui, J. C.; Liu, G.; Sun, J.

2017-11-01

In this work, we prepared nanocrystalline (NC) Ti thin films with abundant stacking faults (SFs), which were created via partial dislocations emitted from grain boundaries and which were insensitive to grain sizes. By employing the nanoindentation test, we investigated the effects of SFs and grain sizes on the strength of NC Ti films at room temperature. The high density of SFs significantly strengthens NC Ti films, via dislocation-SF interactions associated with the reported highest Hall-Petch slope of ˜20 GPa nm1/2, to an ultrahigh strength of ˜4.4 GPa, approaching ˜50% of its ideal strength.

Interaction potential for indium phosphide: a molecular dynamics and first-principles study of the elastic constants, generalized stacking fault and surface energies.

PubMed

Branicio, Paulo Sergio; Rino, José Pedro; Gan, Chee Kwan; Tsuzuki, Hélio

2009-03-04

Indium phosphide is investigated using molecular dynamics (MD) simulations and density-functional theory calculations. MD simulations use a proposed effective interaction potential for InP fitted to a selected experimental dataset of properties. The potential consists of two- and three-body terms that represent atomic-size effects, charge-charge, charge-dipole and dipole-dipole interactions as well as covalent bond bending and stretching. Predictions are made for the elastic constants as a function of density and temperature, the generalized stacking fault energy and the low-index surface energies.

Teaching earth science

USGS Publications Warehouse

Alpha, Tau Rho; Diggles, Michael F.

1998-01-01

This CD-ROM contains 17 teaching tools: 16 interactive HyperCard 'stacks' and a printable model. They are separated into the following categories: Geologic Processes, Earthquakes and Faulting, and Map Projections and Globes. A 'navigation' stack, Earth Science, is provided as a 'launching' place from which to access all of the other stacks. You can also open the HyperCard Stacks folder and launch any of the 16 stacks yourself. In addition, a 17th tool, Earth and Tectonic Globes, is provided as a printable document. Each of the tools can be copied onto a 1.4-MB floppy disk and distributed freely.

An improved low-frequency earthquakes catalogue in the vicinity of the late-interseismic central Alpine Fault, Southern Alps, New Zealand

NASA Astrophysics Data System (ADS)

Baratin, Laura-May; Chamberlain, Calum J.; Townend, John; Savage, Martha K.

2017-04-01

Characterising the seismicity associated with slow deformation in the vicinity of the Alpine Fault may provide constraints on the state of stress of this major transpressive margin prior to a large (≥M8) earthquake. Here, we use recently detected tectonic tremor and low-frequency earthquakes (LFEs) to examine how slow tectonic deformation is loading the Alpine Fault toward an anticipated large rupture. We initially work with a continous seismic dataset collected between 2009 and 2012 from an array of short-period seismometers, the Southern Alps Microearthquake Borehole Array. Fourteen primary LFE templates, found through visual inspection within previously identified tectonic tremor, are used in an iterative matched-filter and stacking routine. This method allows the detection of similar signals and establishes LFE families with common locations. We thus generate a 36 month catalogue of 10718 LFEs. The detections are then combined for each LFE family using phase-weighted stacking to yield a signal with the highest possible signal to noise ratio. We found phase-weighted stacking to be successful in increasing the number of LFE detections by roughly 20%. Phase-weighted stacking also provides cleaner phase arrivals of apparently impulsive nature allowing more precise phase picks. We then compute non-linear earthquake locations using a 3D velocity model and find LFEs to occur below the seismogenic zone at depths of 18-34 km, locating on or near the proposed deep extent of the Alpine Fault. To gain insight into deep fault slip behaviour, a detailed study of the spatial-temporal evolution of LFEs is required. We thus generate a more extensive catalogue of LFEs spanning the years 2009 to 2016 using a different technique to detect LFEs more efficiently. This time 638 synthetic waveforms are used as primary templates in the match-filter routine. Of those, 38 templates yield no detections over our 7-yr study period. The remaining 600 templates end up detecting between 370 and 730 events each totalling ˜310 000 detections. We then focus on only keeping the detections that robustly stack (i.e. representing real LFEs) for each synthetic template hence creating new LFE templates. From there, we rerun the match-filter routine with our new LFE templates. Finally, each LFE template and its subsequent detections form a LFE family, itself associated with a single source. Initial testing shows that this technique paired up with phase-weighted stacking increases the number of LFE families and overall detected events roughly thirtyfold. Our next step is to study in detail the spatial and temporal activity of our LFEs. This new catalogue should provide new insight into the deep central Alpine Fault structure and its slip behaviour.

Fault Creep along the Southern San Andreas from Interferometric Synthetic Aperture Radar, Permanent Scatterers, and Stacking

NASA Technical Reports Server (NTRS)

Lyons, Suzanne; Sandwell, David

2003-01-01

Interferometric synthetic aperture radar (InSAR) provides a practical means of mapping creep along major strike-slip faults. The small amplitude of the creep signal (less than 10 mm/yr), combined with its short wavelength, makes it difficult to extract from long time span interferograms, especially in agricultural or heavily vegetated areas. We utilize two approaches to extract the fault creep signal from 37 ERS SAR images along the southem San Andreas Fault. First, amplitude stacking is utilized to identify permanent scatterers, which are then used to weight the interferogram prior to spatial filtering. This weighting improves correlation and also provides a mask for poorly correlated areas. Second, the unwrapped phase is stacked to reduce tropospheric and other short-wavelength noise. This combined processing enables us to recover the near-field (approximately 200 m) slip signal across the fault due to shallow creep. Displacement maps fiom 60 interferograms reveal a diffuse secular strain buildup, punctuated by localized interseismic creep of 4-6 mm/yr line of sight (LOS, 12-18 mm/yr horizontal). With the exception of Durmid Hill, this entire segment of the southern San Andreas experienced right-lateral triggered slip of up to 10 cm during the 3.5-year period spanning the 1992 Landers earthquake. The deformation change following the 1999 Hector Mine earthquake was much smaller (4 cm) and broader than for the Landers event. Profiles across the fault during the interseismic phase show peak-to-trough amplitude ranging from 15 to 25 mm/yr (horizontal component) and the minimum misfit models show a range of creeping/locking depth values that fit the data.

Synthesis and crystal structure of a new aluminum-silicon-nitride phosphor containing boron, Ba5B2Al4Si32N52:Eu

NASA Astrophysics Data System (ADS)

Yoshimura, Fumitaka; Yamane, Hisanori; Nagasako, Makoto

2017-07-01

Single crystals of Ba5B2Al4Si32N52:Eu were grown on the wall of a boron nitride crucible by heating a starting mixture of binary nitrides at 2050 °C and a N2 pressure of 0.85 MPa. The fundamental reflections of X-ray diffraction (XRD) for the crystals were indexed with triclinic cell parameters, a=9.7879(11) Å, b=9.7920(11) Å, c=12.7226(15) Å, α=96.074(4)°, β=112.330(3)°, and γ=94.080(4)°. Streak lines were observed between the fundamental reflections in the direction of the c* axis in the oscillation XRD images and selected area electron diffraction (SAED) patterns, indicating stacking faults in the structure. The atomic images of stacking faults with a slip system of (0 0 1)[-1 1 0]/3, and displacement of a Ba atom layer with (0 0 1)[-1 -1 0]/6 were observed with a scanning transmission electron microscope (STEM). The models of the basic (normal-stacking) structure with space group P1 and local structures of the stacking faults are herein presented. The single crystals emitted blue light with a peak wavelength of 472 nm and a full width at half maximum of 78 nm under 365 nm excitation.

Reliability analysis and initial requirements for FC systems and stacks

NASA Astrophysics Data System (ADS)

Åström, K.; Fontell, E.; Virtanen, S.

In the year 2000 Wärtsilä Corporation started an R&D program to develop SOFC systems for CHP applications. The program aims to bring to the market highly efficient, clean and cost competitive fuel cell systems with rated power output in the range of 50-250 kW for distributed generation and marine applications. In the program Wärtsilä focuses on system integration and development. System reliability and availability are key issues determining the competitiveness of the SOFC technology. In Wärtsilä, methods have been implemented for analysing the system in respect to reliability and safety as well as for defining reliability requirements for system components. A fault tree representation is used as the basis for reliability prediction analysis. A dynamic simulation technique has been developed to allow for non-static properties in the fault tree logic modelling. Special emphasis has been placed on reliability analysis of the fuel cell stacks in the system. A method for assessing reliability and critical failure predictability requirements for fuel cell stacks in a system consisting of several stacks has been developed. The method is based on a qualitative model of the stack configuration where each stack can be in a functional, partially failed or critically failed state, each of the states having different failure rates and effects on the system behaviour. The main purpose of the method is to understand the effect of stack reliability, critical failure predictability and operating strategy on the system reliability and availability. An example configuration, consisting of 5 × 5 stacks (series of 5 sets of 5 parallel stacks) is analysed in respect to stack reliability requirements as a function of predictability of critical failures and Weibull shape factor of failure rate distributions.

Investigations of stacking fault density in perpendicular recording media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piramanayagam, S. N., E-mail: prem-SN@dsi.a-star.edu.sg; Varghese, Binni; Yang, Yi

In magnetic recording media, the grains or clusters reverse their magnetization over a range of reversal field, resulting in a switching field distribution. In order to achieve high areal densities, it is desirable to understand and minimize such a distribution. Clusters of grains which contain stacking faults (SF) or fcc phase have lower anisotropy, an order lower than those without them. It is believed that such low anisotropy regions reverse their magnetization at a much lower reversal field than the rest of the material with a larger anisotropy. Such clusters/grains cause recording performance deterioration, such as adjacent track erasure andmore » dc noise. Therefore, the observation of clusters that reverse at very low reversal fields (nucleation sites, NS) could give information on the noise and the adjacent track erasure. Potentially, the observed clusters could also provide information on the SF. In this paper, we study the reversal of nucleation sites in granular perpendicular media based on a magnetic force microscope (MFM) methodology and validate the observations with high resolution cross-section transmission electron microscopy (HRTEM) measurements. Samples, wherein a high anisotropy CoPt layer was introduced to control the NS or SF in a systematic way, were evaluated by MFM, TEM, and magnetometry. The magnetic properties indicated that the thickness of the CoPt layer results in an increase of nucleation sites. TEM measurements indicated a correlation between the thickness of CoPt layer and the stacking fault density. A clear correlation was also observed between the MFM results, TEM observations, and the coercivity and nucleation field of the samples, validating the effectiveness of the proposed method in evaluating the nucleation sites which potentially arise from stacking faults.« less

ICME for Crashworthiness of TWIP Steels: From Ab Initio to the Crash Performance

NASA Astrophysics Data System (ADS)

Güvenç, O.; Roters, F.; Hickel, T.; Bambach, M.

2015-01-01

During the last decade, integrated computational materials engineering (ICME) emerged as a field which aims to promote synergetic usage of formerly isolated simulation models, data and knowledge in materials science and engineering, in order to solve complex engineering problems. In our work, we applied the ICME approach to a crash box, a common automobile component crucial to passenger safety. A newly developed high manganese steel was selected as the material of the component and its crashworthiness was assessed by simulated and real drop tower tests. The crashworthiness of twinning-induced plasticity (TWIP) steel is intrinsically related to the strain hardening behavior caused by the combination of dislocation glide and deformation twinning. The relative contributions of those to the overall hardening behavior depend on the stacking fault energy (SFE) of the selected material. Both the deformation twinning mechanism and the stacking fault energy are individually well-researched topics, but especially for high-manganese steels, the determination of the stacking-fault energy and the occurrence of deformation twinning as a function of the SFE are crucial to understand the strain hardening behavior. We applied ab initio methods to calculate the stacking fault energy of the selected steel composition as an input to a recently developed strain hardening model which models deformation twinning based on the SFE-dependent dislocation mechanisms. This physically based material model is then applied to simulate a drop tower test in order to calculate the energy absorption capacity of the designed component. The results are in good agreement with experiments. The model chain links the crash performance to the SFE and hence to the chemical composition, which paves the way for computational materials design for crashworthiness.

Generalized stacking fault energies, cleavage energies, ionicity and brittleness of Cu(Al/Ga/In)Se2 and CuGa(S/Se/Te)2

NASA Astrophysics Data System (ADS)

Xue, H. T.; Tang, F. L.; Gruhn, T.; Lu, W. J.; Wan, F. C.; Rui, Z. Y.; Feng, Y. D.

2014-04-01

We calculate the generalized stacking fault (GSF) energies and cleavage energies γcl of the chalcopyrite compounds CuAlSe2, CuGaSe2, CuInSe2, CuGaS2 and CuGaTe2 using first principles. From the GSF energies, we obtain the unstable stacking fault energies γus and intrinsic stacking fault energies γisf. By analyzing γus and γisf, we find that the \\langle \\bar{{1}}\\,1\\,0\\rangle (1 1 2) direction is the easiest slip direction for these five compounds. Also, for CuInSe2, it is most possible to undergo a dislocation-nucleation-induced plastic deformation along the \\langle \\bar{{1}}\\,1\\,0\\rangle (1 1 2) slip direction. We show that the (1 1 2) plane is the preferable plane for fracture in the five compounds by comparing γcl of the (0 0 1) and (1 1 2) planes. It is also found that both γus and γcl decrease as the cationic or anionic radius increases in these chalcopyrites, i.e. along the sequences CuAlSe2 → CuGaSe2 → CuInSe2 and CuGaS2 → CuGaSe2 → CuGaTe2. Based on the values of the ratio γcl/γus, we discuss the brittle-ductile properties of these compounds. All of the compounds can be considered as brittle materials. In addition, a strong relationship between γcl/γus and the total proportion of ionic bonding in these compounds is found.

Effect of Alloying on the Strength Properties and the Hardening Mechanisms of Nitrogen-Bearing Austenitic Steels after Hot Deformation and Annealing

NASA Astrophysics Data System (ADS)

Bannykh, I. O.

2017-11-01

The main mechanisms of hardening nitrogen-bearing austenitic steels that operate under various thermomechanical treatment conditions at various steel compositions are considered. The strength properties of the steels are shown to depend on the content of interstitial elements, namely, carbon and nitrogen, and the influence of these elements on the stacking fault energy is estimated. The ratios of the main alloying elements that favor an increase or a decrease in the stacking fault energy are found to achieve the desirable level of strain hardening provided that an austenitic structure of steel is retained.

Composition-dependence of stacking fault energy in austenitic stainless steels through linear regression with random intercepts

NASA Astrophysics Data System (ADS)

Meric de Bellefon, G.; van Duysen, J. C.; Sridharan, K.

2017-08-01

The stacking fault energy (SFE) plays an important role in deformation behavior and radiation damage of FCC metals and alloys such as austenitic stainless steels. In the present communication, existing expressions to calculate SFE in those steels from chemical composition are reviewed and an improved multivariate linear regression with random intercepts is used to analyze a new database of 144 SFE measurements collected from 30 literature references. It is shown that the use of random intercepts can account for experimental biases in these literature references. A new expression to predict SFE from austenitic stainless steel compositions is proposed.

Interaction of sodium atoms with stacking faults in silicon with different Fermi levels

NASA Astrophysics Data System (ADS)

Ohno, Yutaka; Morito, Haruhiko; Kutsukake, Kentaro; Yonenaga, Ichiro; Yokoi, Tatsuya; Nakamura, Atsutomo; Matsunaga, Katsuyuki

2018-06-01

Variation in the formation energy of stacking faults (SFs) with the contamination of Na atoms was examined in Si crystals with different Fermi levels. Na atoms agglomerated at SFs under an electronic interaction, reducing the SF formation energy. The energy decreased with the decrease of the Fermi level: it was reduced by more than 10 mJ/m2 in p-type Si, whereas it was barely reduced in n-type Si. Owing to the energy reduction, Na atoms agglomerating at SFs in p-type Si are stable compared with those in n-type Si, and this hypothesis was supported by ab initio calculations.

Defects in paramagnetic Co-doped ZnO films studied by transmission electron microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kovacs, Andras; Ney, A.; Duchamp, Martial

2013-12-23

We have studied planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al2O3) and the Co:ZnO/Al2O3 interface structure at atomic resolution using aberration-corrected transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS). Comparing Co:ZnO samples deposited by pulsed laser deposition and reactive magnetron sputtering, both exhibit extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers at the interface.. In addition, we have measured the local strain which reveals the lattice distortion around the stacking faults.

Creep Mechanisms of a Ni-Co-Based-Wrought Superalloy with Low Stacking Fault Energy

NASA Astrophysics Data System (ADS)

Tian, Chenggang; Xu, Ling; Cui, Chuanyong; Sun, Xiaofeng

2015-10-01

In order to study the influences of stress and temperature on the creep deformation mechanisms of a newly developed Ni-Co-based superalloy with low stacking fault energy, creep experiments were carried out under a stress range of 345 to 840 MPa and a temperature range of 923 K to 1088 K (650 °C to 815 °C). The mechanisms operated under the various creep conditions were identified and the reasons for their transformation were well discussed. A deformation mechanism map under different creep conditions was summarized, which provides a qualitative representation of the operative creep mechanisms as a function of stress and temperature.

Validation of the Concurrent Atomistic-Continuum Method on Screw Dislocation/Stacking Fault Interactions

DOE PAGES

Xu, Shuozhi; Xiong, Liming; Chen, Youping; ...

2017-04-26

Dislocation/stacking fault interactions play an important role in the plastic deformation of metallic nanocrystals and polycrystals. These interactions have been explored in atomistic models, which are limited in scale length by high computational cost. In contrast, multiscale material modeling approaches have the potential to simulate the same systems at a fraction of the computational cost. In this paper, we validate the concurrent atomistic-continuum (CAC) method on the interactions between a lattice screw dislocation and a stacking fault (SF) in three face-centered cubic metallic materials—Ni, Al, and Ag. Two types of SFs are considered: intrinsic SF (ISF) and extrinsic SF (ESF).more » For the three materials at different strain levels, two screw dislocation/ISF interaction modes (annihilation of the ISF and transmission of the dislocation across the ISF) and three screw dislocation/ESF interaction modes (transformation of the ESF into a three-layer twin, transformation of the ESF into an ISF, and transmission of the dislocation across the ESF) are identified. Here, our results show that CAC is capable of accurately predicting the dislocation/SF interaction modes with greatly reduced DOFs compared to fully-resolved atomistic simulations.« less

Validation of the Concurrent Atomistic-Continuum Method on Screw Dislocation/Stacking Fault Interactions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Shuozhi; Xiong, Liming; Chen, Youping

Dislocation/stacking fault interactions play an important role in the plastic deformation of metallic nanocrystals and polycrystals. These interactions have been explored in atomistic models, which are limited in scale length by high computational cost. In contrast, multiscale material modeling approaches have the potential to simulate the same systems at a fraction of the computational cost. In this paper, we validate the concurrent atomistic-continuum (CAC) method on the interactions between a lattice screw dislocation and a stacking fault (SF) in three face-centered cubic metallic materials—Ni, Al, and Ag. Two types of SFs are considered: intrinsic SF (ISF) and extrinsic SF (ESF).more » For the three materials at different strain levels, two screw dislocation/ISF interaction modes (annihilation of the ISF and transmission of the dislocation across the ISF) and three screw dislocation/ESF interaction modes (transformation of the ESF into a three-layer twin, transformation of the ESF into an ISF, and transmission of the dislocation across the ESF) are identified. Here, our results show that CAC is capable of accurately predicting the dislocation/SF interaction modes with greatly reduced DOFs compared to fully-resolved atomistic simulations.« less

Strain-induced structure transformations on Si(111) and Ge(111) surfaces: a combined density-functional and scanning tunneling microscopy study.

PubMed

Zhachuk, R; Teys, S; Coutinho, J

2013-06-14

Si(111) and Ge(111) surface formation energies were calculated using density functional theory for various biaxial strain states ranging from -0.04 to 0.04, and for a wide set of experimentally observed surface reconstructions: 3 × 3, 5 × 5, 7 × 7 dimer-adatom-stacking fault reconstructions and c(2 × 8), 2 × 2, and √3×√3 adatoms based surfaces. The calculations are compared with scanning tunneling microscopy data obtained on stepped Si(111) surfaces and on Ge islands grown on a Si(111) substrate. It is shown that the surface structure transformations observed in these strained systems are accounted for by a phase diagram that relates the equilibrium surface structure to the applied strain. The calculated formation energy of the unstrained Si(111)-9 × 9 dimer-adatom-stacking fault surface is reported for the first time and it is higher than corresponding energies of Si(111)-5 × 5 and Si(111)-7 × 7 dimer-adatom-stacking fault surfaces as expected. We predict that the Si(111) surface should adopt a c(2 × 8) reconstruction when tensile strain is above 0.03.

First principle study on generalized-stacking-fault energy surfaces of B2-AlRE intermetallic compounds

NASA Astrophysics Data System (ADS)

Li, Shaorong; Wang, Shaofeng; Wang, Rui

2011-12-01

First-principles calculations are used to predict the generalized-stacking-fault energy (GSFE) surfaces of AlRE intermetallics. The calculations employ the projector augmented-wave (PAW) method within the generalized gradient approximation (GGA) using the density functional theory (DFT). GSFE curves along <1 1 1> {1 1 0} direction, <1 1 0> {1 1 0} direction and <1 0 0> {1 1 0} direction have been calculated. The fitted GSFE surfaces have been obtained from the Fourier series based on the translational symmetry. In order to illuminate the reasonable of our computational accuracy, we have compared our theoretical results of B2 intermetallics YCu with the previous calculated results. The unstable-stacking-fault energy (γus) on the {1 1 0} plane has the laws of AlPr, <1 1 0> and <1 1 1> directions. For the antiphase boundary (APB) energy, that of AlSc is the lowest in the calculated AlRE intermetallics. So the superdislocation with the Burgers vector along <1 1 1> direction of AlSc will easily split into two superpartials.

Dislocation imaging for orthopyroxene using an atom-resolved scanning transmission electron microscopy.

PubMed

Kumamoto, Akihito; Kogure, Toshihiro; Raimbourg, Hugues; Ikuhara, Yuichi

2014-11-01

Dislocations, one-dimensional lattice defects, appear as a microscopic phenomenon while they are formed in silicate minerals by macroscopic dynamics of the earth crust such as shear stress. To understand ductile deformation mechanisms of silicates, atomic structures of the dislocations have been examined using transmission electron microscopy (TEM). Among them, it has been proposed that {100}<001> primary slip system of orthopyroxene (Opx) is dissociated into partial dislocations, and a stacking fault with the clinopyroxene (Cpx) structure is formed between the dislocations. This model, however, has not been determined completely due to the complex structures of silicates. Scanning transmission electron microscopy (STEM) has a potential to determine the structure of dislocations with single-atomic column sensitivity, particularly by using high-angle annular dark field (HAADF) and annular bright field (ABF) imaging with a probing aberration corrector.[1] Furthermore, successive analyses from light microscopy to atom-resolved STEM have been achieved by focused ion beam (FIB) sampling techniques.[2] In this study, we examined dislocation arrays at a low-angle grain boundary of ∼1° rotation about the b-axis in natural deformed Opx using a simultaneous acquisition of HAADF/ABF (JEM-ARM200F, JEOL) equipped with 100 mm2 silicon drift detector (SDD) for energy dispersive X-ray spectroscopy (EDS). Figure 1 shows averaged STEM images viewed along the b- axis of Opx extracted from repeating units. HAADF provides the cation-site arrangement, and ABF distinguishes the difference of slightly rotated SiO4 tetrahedron around the a- axis. This is useful to distinguish the change of stacking sequence between the partial dislocations. Two types of stacking faults with Cpx and protopyroxene (Ppx) structures were identified between three partial dislocations. Furthermore, Ca accumulation in M2 (Fe) site around the stacking faults was detected by STEM-EDS. Interestingly, Ca is distributed not only in these stacking faults but also Opx matrix around the faults. jmicro;63/suppl_1/i17/DFU063F1F1DFU063F1Fig. 1. (a) HAADF and (b) ABF of Opx view of [010] direction with inset simulation images and models of its unit cell (a = 0.52, c = 1.83 nm). © The Author 2014. Published by Oxford University Press on behalf of The Japanese Society of Microscopy. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

AIC-based diffraction stacking for local earthquake locations at the Sumatran Fault (Indonesia)

NASA Astrophysics Data System (ADS)

Hendriyana, Andri; Bauer, Klaus; Muksin, Umar; Weber, Michael

2018-05-01

We present a new workflow for the localization of seismic events which is based on a diffraction stacking approach. In order to address the effects from complex source radiation patterns, we suggest to compute diffraction stacking from a characteristic function (CF) instead of stacking the original waveform data. A new CF, which is called in the following mAIC (modified from Akaike Information Criterion) is proposed. We demonstrate that both P- and S-wave onsets can be detected accurately. To avoid cross-talk between P and S waves due to inaccurate velocity models, we separate the P and S waves from the mAIC function by making use of polarization attributes. Then, the final image function is represented by the largest eigenvalue as a result of the covariance analysis between P- and S-image functions. Results from synthetic experiments show that the proposed diffraction stacking provides reliable results. The workflow of the diffraction stacking method was finally applied to local earthquake data from Sumatra, Indonesia. Recordings from a temporary network of 42 stations deployed for nine months around the Tarutung pull-apart basin were analysed. The seismic event locations resulting from the diffraction stacking method align along a segment of the Sumatran Fault. A more complex distribution of seismicity is imaged within and around the Tarutung basin. Two lineaments striking N-S were found in the centre of the Tarutung basin which support independent results from structural geology.

A Reference Stack for PHM Architectures

DTIC Science & Technology

2014-10-02

components, fault modes and prognostics such as that described by MIMOSA (2009) and ISO 13374-3:2012 (2012). Section 2.6 described a semantic...architecture, and the use of a SOA is further discussed in Section 3.3.2. MIMOSA is a stack-oriented data architecture. Figure 11 shows its stack of...format (US Army PEWG, 2011). The tagging in ABCD format respects the data layers that are found in the MIMOSA standard ( MIMOSA , 2009) and in ISO

Stacking faults density driven collapse of magnetic energy in hcp-cobalt nano-magnets

NASA Astrophysics Data System (ADS)

Nong, H. T. T.; Mrad, K.; Schoenstein, F.; Piquemal, J.-Y.; Jouini, N.; Leridon, B.; Mercone, S.

2017-06-01

Cobalt nanowires with different shape parameters were synthesized via the polyol process. By calculating the magnetic energy product (BH max) both for dried nano-powder and for nanowires in their synthesis solution, we observed unexpected independent BH max values from the nanowires shape. A good alignment of the nanowires leads to a higher BH max value. Our results show that the key parameter driving the magnetic energy product of the cobalt nanowires is the stacking fault density. An exponential collapse of the magnetic energy is observed at very low percentage of structural faults. Cobalt nanowires with almost perfect hcp crystalline structures should present high magnetic energy, which is promising for application in rare earth-free permanent magnets. Oral talk at 8th International Workshop on Advanced Materials Science and Nanotechnology (IWAMSN2016), 8-12 November 2016, Ha Long City, Vietnam.

Lacustrine Paleoseismology Reveals Earthquake Segmentation of the Alpine Fault, New Zealand

NASA Astrophysics Data System (ADS)

Howarth, J. D.; Fitzsimons, S.; Norris, R.; Langridge, R. M.

2013-12-01

Transform plate boundary faults accommodate high rates of strain and are capable of producing large (Mw>7.0) to great (Mw>8.0) earthquakes that pose significant seismic hazard. The Alpine Fault in New Zealand is one of the longest, straightest and fastest slipping plate boundary transform faults on Earth and produces earthquakes at quasi-periodic intervals. Theoretically, the fault's linearity, isolation from other faults and quasi-periodicity should promote the generation of earthquakes that have similar magnitudes over multiple seismic cycles. We test the hypothesis that the Alpine Fault produces quasi-regular earthquakes that contiguously rupture the southern and central fault segments, using a novel lacustrine paleoseismic proxy to reconstruct spatial and temporal patterns of fault rupture over the last 2000 years. In three lakes located close to the Alpine Fault the last nine earthquakes are recorded as megaturbidites formed by co-seismic subaqueous slope failures, which occur when shaking exceeds Modified Mercalli (MM) VII. When the fault ruptures adjacent to a lake the co-seismic megaturbidites are overlain by stacks of turbidites produced by enhanced fluvial sediment fluxes from earthquake-induced landslides. The turbidite stacks record shaking intensities of MM>IX in the lake catchments and can be used to map the spatial location of fault rupture. The lake records can be dated precisely, facilitating meaningful along strike correlations, and the continuous records allow earthquakes closely spaced in time on adjacent fault segments to be distinguished. The results show that while multi-segment ruptures of the Alpine Fault occurred during most seismic cycles, sequential earthquakes on adjacent segments and single segment ruptures have also occurred. The complexity of the fault rupture pattern suggests that the subtle variations in fault geometry, sense of motion and slip rate that have been used to distinguish the central and southern segments of the Alpine Fault can inhibit rupture propagation, producing a soft earthquake segment boundary. The study demonstrates the utility of lakes as paleoseismometers that can be used to reconstruct the spatial and temporal patterns of earthquakes on a fault.

Deformation mechanisms of nanotwinned Al

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xinghang

The objective of this project is to investigate the role of different types of layer interfaces on the formation of high density stacking fault (SF) in Al in Al/fcc multilayers, and understand the corresponding deformation mechanisms of the films. Stacking faults or twins can be intentionally introduced (via growth) into certain fcc metals with low stacking fault energy (such as Cu, Ag and 330 stainless steels) to achieve high strength, high ductility, superior thermal stability and good electrical conductivity. However it is still a major challenge to synthesize these types of defects into metals with high stacking fault energy, suchmore » as Al. Although deformation twins have been observed in some nanocrystalline Al powders by low temperature, high strain rate cryomilling or in Al at the edge of crack tip or indentation (with the assistance of high stress intensity factor), these deformation techniques typically introduce twins sporadically and the control of deformation twin density in Al is still not feasible. This project is designed to test the following hypotheses: (1) Certain type of layer interfaces may assist the formation of SF in Al, (2) Al with high density SF may have deformation mechanisms drastically different from those of coarse-grained Al and nanotwinned Cu. To test these hypotheses, we have performed the following tasks: (i) Investigate the influence of layer interfaces, stresses and deposition parameters on the formation and density of SF in Al. (ii) Understand the role of SF on the deformation behavior of Al. In situ nanoindentation experiments will be performed to probe deformation mechanisms in Al. The major findings related to the formation mechanism of twins and mechanical behavior of nanotwinned metals include the followings: 1) Our studies show that nanotwins can be introduced into metals with high stacking fault energy, in drastic contrast to the general anticipation. 2) We show two strategies that can effectively introduce growth twins in high-stacking-energy metals: use Ag as a template to introduce high density growth twins in epitaxial Al; and the film thickness is important in determination of volume fraction of growth twins. 3) We prove that high density twin boundaries can lead to significant work hardening capability in nanotwinned Al. We have published 13 articles, including Nature Communications, Nano Letters, and two review articles, one in Annual Review of Materials Research; and one in MRS Bulletin. Two postdocs and three graduate students have worked on the project. Two of them have become postdoc at Sandia National Laboratory and Los Alamos National Laboratory. One of the postdoc has become a faculty at a University. One patent has been filed.« less

Characterization of double Shockley-type stacking faults formed in lightly doped 4H-SiC epitaxial films

NASA Astrophysics Data System (ADS)

Yamashita, T.; Hayashi, S.; Naijo, T.; Momose, K.; Osawa, H.; Senzaki, J.; Kojima, K.; Kato, T.; Okumura, H.

2018-05-01

Double Shockley-type stacking faults (2SSFs) formed in 4H-SiC epitaxial films with a dopant concentration of 1.0 × 1016 cm-3 were characterized using grazing incident X-ray topography and high-resolution scanning transmission electron microscopy. The origins of 2SSFs were investigated, and it was found that 2SSFs in the epitaxial layer originated from narrow SFs with a double Shockley structure in the substrate. Partial dislocations formed between 4H-type and 2SSF were also characterized. The shapes of 2SSFs are related with Burgers vectors and core types of the two Shockley partial dislocations.

Effect of dislocation pile-up on size-dependent yield strength in finite single-crystal micro-samples

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Bo; Shibutani, Yoji, E-mail: sibutani@mech.eng.osaka-u.ac.jp; Zhang, Xu

2015-07-07

Recent research has explained that the steeply increasing yield strength in metals depends on decreasing sample size. In this work, we derive a statistical physical model of the yield strength of finite single-crystal micro-pillars that depends on single-ended dislocation pile-up inside the micro-pillars. We show that this size effect can be explained almost completely by considering the stochastic lengths of the dislocation source and the dislocation pile-up length in the single-crystal micro-pillars. The Hall–Petch-type relation holds even in a microscale single-crystal, which is characterized by its dislocation source lengths. Our quantitative conclusions suggest that the number of dislocation sources andmore » pile-ups are significant factors for the size effect. They also indicate that starvation of dislocation sources is another reason for the size effect. Moreover, we investigated the explicit relationship between the stacking fault energy and the dislocation “pile-up” effect inside the sample: materials with low stacking fault energy exhibit an obvious dislocation pile-up effect. Our proposed physical model predicts a sample strength that agrees well with experimental data, and our model can give a more precise prediction than the current single arm source model, especially for materials with low stacking fault energy.« less

Dose dependence of helium bubble formation in nano-engineered SiC at 700 °C

DOE PAGES

Chen, Chien -Hung; Zhang, Yanwen; Wang, Yongqiang; ...

2016-02-03

Knowledge of radiation-induced helium bubble nucleation and growth in SiC is essential for applications in fusion and fission environments. Here we report the evolution of microstructure in nano-engineered (NE) 3C SiC, pre-implanted with helium, under heavy ion irradiation at 700 °C up to doses of 30 displacements per atom (dpa). Elastic recoil detection analysis confirms that the as-implanted helium depth profile does not change under irradiation to 30 dpa at 700 °C. While the helium bubble size distribution becomes narrower with increasing dose, the average size of bubbles remains unchanged and the density of bubbles increases somewhat with dose. Thesemore » results are consistent with a long helium bubble incubation process under continued irradiation at 700 °C up to 30 dpa, similar to that reported under dual and triple beam irradiation at much higher temperatures. The formation of bubbles at this low temperature is enhanced by the nano-layered stacking fault structure in the NE SiC, which enhances point defect mobility parallel to the stacking faults. Here, this stacking fault structure is stable at 700 °C up to 30 dpa and suppresses the formation of dislocation loops normally observed under these irradiation conditions.« less

Structure and energetics of extended defects in ice Ih

NASA Astrophysics Data System (ADS)

Silva Junior, Domingos L.; de Koning, Maurice

2012-01-01

We consider the molecular structure and energetics of extended defects in proton-disordered hexagonal ice Ih. Using plane-wave density functional theory (DFT) calculations, we compute the energetics of stacking faults and determine the structure of the 30∘ and 90∘ partial dislocations on the basal plane. Consistent with experimental data, the formation energies of all fully reconstructed stacking faults are found to be very low. This is consistent with the idea that basal-plane glide dislocations in ice Ih are dissociated into partial dislocations separated by an area of stacking fault. For both types of partial dislocation we find a strong tendency toward core reconstruction through pairwise hydrogen-bond reformation. In the case of the 30∘ dislocation, the pairwise hydrogen-bond formation leads to a period-doubling core structure equivalent to that seen in zinc-blende semiconductor crystals. For the 90∘ partial we consider two possible core reconstructions, one in which the periodicity of the structure along the core remains unaltered and another in which it is doubled. The latter is preferred, although the energy difference between both is rather small, so that a coexistence of both reconstructions appears plausible. Our results imply that a mobility theory for dislocations on the basal plane in ice Ih should be based on the idea of reconstructed partial dislocations.

Structural and dynamic characteristics in monolayer square ice.

PubMed

Zhu, YinBo; Wang, FengChao; Wu, HengAn

2017-07-28

When water is constrained between two sheets of graphene, it becomes an intriguing monolayer solid with a square pattern due to the ultrahigh van der Waals pressure. However, the square ice phase has become a matter of debate due to the insufficient experimental interpretation and the slightly rhomboidal feature in simulated monolayer square-like structures. Here, we performed classical molecular dynamics simulations to reveal monolayer square ice in graphene nanocapillaries from the perspective of structure and dynamic characteristics. Monolayer square-like ice (instantaneous snapshot), assembled square-rhombic units with stacking faults, is a long-range ordered structure, in which the square and rhombic units are assembled in an order of alternative distribution, and the other rhombic unit forms stacking faults (polarized water chains). Spontaneous flipping of water molecules in monolayer square-like ice is intrinsic and induces transformations among different elementary units, resulting in the structural evolution of monolayer square ice in dynamics. The existence of stacking faults should be attributed to the spontaneous flipping behavior of water molecules under ambient temperature. Statistical averaging results (thermal average positions) demonstrate the inherent square characteristic of monolayer square ice. The simulated data and insight obtained here might be significant for understanding the topological structure and dynamic behavior of monolayer square ice.

Atomistically determined phase-field modeling of dislocation dissociation, stacking fault formation, dislocation slip, and reactions in fcc systems

NASA Astrophysics Data System (ADS)

Rezaei Mianroodi, Jaber; Svendsen, Bob

2015-04-01

The purpose of the current work is the development of a phase field model for dislocation dissociation, slip and stacking fault formation in single crystals amenable to determination via atomistic or ab initio methods in the spirit of computational material design. The current approach is based in particular on periodic microelasticity (Wang and Jin, 2001; Bulatov and Cai, 2006; Wang and Li, 2010) to model the strongly non-local elastic interaction of dislocation lines via their (residual) strain fields. These strain fields depend in turn on phase fields which are used to parameterize the energy stored in dislocation lines and stacking faults. This energy storage is modeled here with the help of the "interface" energy concept and model of Cahn and Hilliard (1958) (see also Allen and Cahn, 1979; Wang and Li, 2010). In particular, the "homogeneous" part of this energy is related to the "rigid" (i.e., purely translational) part of the displacement of atoms across the slip plane, while the "gradient" part accounts for energy storage in those regions near the slip plane where atomic displacements deviate from being rigid, e.g., in the dislocation core. Via the attendant global energy scaling, the interface energy model facilitates an atomistic determination of the entire phase field energy as an optimal approximation of the (exact) atomistic energy; no adjustable parameters remain. For simplicity, an interatomic potential and molecular statics are employed for this purpose here; alternatively, ab initio (i.e., DFT-based) methods can be used. To illustrate the current approach, it is applied to determine the phase field free energy for fcc aluminum and copper. The identified models are then applied to modeling of dislocation dissociation, stacking fault formation, glide and dislocation reactions in these materials. As well, the tensile loading of a dislocation loop is considered. In the process, the current thermodynamic picture is compared with the classical mechanical one as based on the Peach-Köhler force.

Effects of alloying element and temperature on the stacking fault energies of dilute Ni-base superalloys.

PubMed

Shang, S L; Zacherl, C L; Fang, H Z; Wang, Y; Du, Y; Liu, Z K

2012-12-19

A systematic study of stacking fault energy (γ(SF)) resulting from induced alias shear deformation has been performed by means of first-principles calculations for dilute Ni-base superalloys (Ni(23)X and Ni(71)X) for various alloying elements (X) as a function of temperature. Twenty-six alloying elements are considered, i.e., Al, Co, Cr, Cu, Fe, Hf, Ir, Mn, Mo, Nb, Os, Pd, Pt, Re, Rh, Ru, Sc, Si, Ta, Tc, Ti, V, W, Y, Zn, and Zr. The temperature dependence of γ(SF) is computed using the proposed quasistatic approach based on a predicted γ(SF)-volume-temperature relationship. Besides γ(SF), equilibrium volume and the normalized stacking fault energy (Γ(SF) = γ(SF)/Gb, with G the shear modulus and b the Burgers vector) are also studied as a function of temperature for the 26 alloying elements. The following conclusions are obtained: all alloying elements X studied herein decrease the γ(SF) of fcc Ni, approximately the further the alloying element X is from Ni on the periodic table, the larger the decrease of γ(SF) for the dilute Ni-X alloy, and roughly the γ(SF) of Ni-X decreases with increasing equilibrium volume. In addition, the values of γ(SF) for all Ni-X systems decrease with increasing temperature (except for Ni-Cr at higher Cr content), and the largest decrease is observed for pure Ni. Similar to the case of the shear modulus, the variation of γ(SF) for Ni-X systems due to various alloying elements is traceable from the distribution of (magnetization) charge density: the spherical distribution of charge density around a Ni atom, especially a smaller sphere, results in a lower value of γ(SF) due to the facility of redistribution of charges. Computed stacking fault energies and the related properties are in favorable accord with available experimental and theoretical data.

A novel micro-Raman technique to detect and characterize 4H-SiC stacking faults

DOE Office of Scientific and Technical Information (OSTI.GOV)

Piluso, N., E-mail: nicolo.piluso@imm.cnr.it; Camarda, M.; La Via, F.

A novel Micro-Raman technique was designed and used to detect extended defects in 4H-SiC homoepitaxy. The technique uses above band-gap high-power laser densities to induce a local increase of free carriers in undoped epitaxies (n < 10{sup 16} at/cm{sup −3}), creating an electronic plasma that couples with the longitudinal optical (LO) Raman mode. The Raman shift of the LO phonon-plasmon-coupled mode (LOPC) increases as the free carrier density increases. Crystallographic defects lead to scattering or recombination of the free carriers which results in a loss of coupling with the LOPC, and in a reduction of the Raman shift. Given that the LOmore » phonon-plasmon coupling is obtained thanks to the free carriers generated by the high injection level induced by the laser, we named this technique induced-LOPC (i-LOPC). This technique allows the simultaneous determination of both the carrier lifetime and carrier mobility. Taking advantage of the modifications on the carrier lifetime induced by extended defects, we were able to determine the spatial morphology of stacking faults; the obtained morphologies were found to be in excellent agreement with those provided by standard photoluminescence techniques. The results show that the detection of defects via i-LOPC spectroscopy is totally independent from the stacking fault photoluminescence signals that cover a large energy range up to 0.7 eV, thus allowing for a single-scan simultaneous determination of any kind of stacking fault. Combining the i-LOPC method with the analysis of the transverse optical mode, the micro-Raman characterization can determine the most important properties of unintentionally doped film, including the stress status of the wafer, lattice impurities (point defects, polytype inclusions) and a detailed analysis of crystallographic defects, with a high spectral and spatial resolution.« less

Clustering on Magnesium Surfaces - Formation and Diffusion Energies.

PubMed

Chu, Haijian; Huang, Hanchen; Wang, Jian

2017-07-12

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and [Formula: see text]. In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a [Formula: see text], clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface [Formula: see text] is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich-Schwoebel barriers converge as the step height is three atomic layers or thicker. Adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.

Seismic Reflectivity of the Crust in the Northern Salton Trough

NASA Astrophysics Data System (ADS)

Bauer, K.; Fuis, G. S.; Goldman, M.; Persaud, P.; Ryberg, T.; Langenheim, V. E.; Scheirer, D. S.; Rymer, M. J.; Hole, J. A.; Stock, J. M.; Catchings, R.

2015-12-01

The Salton Trough in southern California is a tectonically active pull-apart basin that was formed by migrating step-overs between strike-slip faults, of which the San Andreas Fault (SAF) and the Imperial Fault are the current, northernmost examples. The Salton Seismic Imaging Project (SSIP) was undertaken to improve our knowledge of fault geometry and seismic velocities within the sedimentary basins and underlying crystalline crust around the SAF. Such data are useful as input for modeling scenarios of strong ground shaking in the surrounding high-population areas. We used pre-stack depth migration of line segments from shot gathers in several seismic profiles that were acquired in the northern part of the SSIP study area (Lines 4 - 7). Our migration approach can be considered as an infinite-frequency approximation of the Fresnel volume pre-stack depth migration method. We use line segments instead of the original waveform data. We demonstrate the method using synthetic data and analyze real data from Lines 4 - 7 to illustrate the relationship between distinct phases in the time domain and their resulting image at depth. We show both normal-moveout reflections from sub-horizontal interfaces and reverse-moveout reflections from steep interfaces, such as faults. Migrated images of dipping faults, such as the SAF and the Pinto Mountain Fault, are presented in this way. The SAF is imaged along Line 4, through the Mecca Hills, as a number of steeply dipping fault segments that collectively form a flower structure, above 5 km depth, that sole into a moderately NE-dipping fault below that depth. The individual migrated reflection packages correlate with mapped surface fault traces in the Mecca Hills. A similar geometry is seen on Line 6, from Palm Springs through Yucca Valley, where fault splays sole or project into a moderately dipping SAF below 10-km depth. We also show and discuss the reflectivity pattern of the middle and lower crust for Lines 4 - 7.

Atomistic structures of nano-engineered SiC and radiation-induced amorphization resistance

NASA Astrophysics Data System (ADS)

Imada, Kenta; Ishimaru, Manabu; Sato, Kazuhisa; Xue, Haizhou; Zhang, Yanwen; Shannon, Steven; Weber, William J.

2015-10-01

Nano-engineered 3C-SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. The resultant strain field probably contributes to the enhancement of radiation tolerance of this material.

Stacking fault related luminescence in GaN nanorods.

PubMed

Forsberg, M; Serban, A; Poenaru, I; Hsiao, C-L; Junaid, M; Birch, J; Pozina, G

2015-09-04

Optical and structural properties are presented for GaN nanorods (NRs) grown in the [0001] direction on Si(111) substrates by direct-current reactive magnetron sputter epitaxy. Transmission electron microscopy (TEM) reveals clusters of dense stacking faults (SFs) regularly distributed along the c-axis. A strong emission line at ∼3.42 eV associated with the basal-plane SFs has been observed in luminescence spectra. The optical signature of SFs is stable up to room temperatures with the activation energy of ∼20 meV. Temperature-dependent time-resolved photoluminescence properties suggest that the recombination mechanism of the 3.42 eV emission can be understood in terms of multiple quantum wells self-organized along the growth axis of NRs.

Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches

NASA Astrophysics Data System (ADS)

Li, Ruihuan; Lu, Song; Kim, Dongyoo; Schönecker, Stephan; Zhao, Jijun; Kwon, Se Kyun; Vitos, Levente

2016-10-01

The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the ‘pseudo-interfacial energy’ that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches.

Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches.

PubMed

Li, Ruihuan; Lu, Song; Kim, Dongyoo; Schönecker, Stephan; Zhao, Jijun; Kwon, Se Kyun; Vitos, Levente

2016-10-05

The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the 'pseudo-interfacial energy' that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches.

Ab initio molecular dynamics simulation of the effects of stacking faults on the radiation response of 3C-SiC

PubMed Central

Jiang, M.; Peng, S. M.; Zhang, H. B.; Xu, C. H.; Xiao, H. Y.; Zhao, F. A.; Liu, Z. J.; Zu, X. T.

2016-01-01

In this study, an ab initio molecular dynamics method is employed to investigate how the existence of stacking faults (SFs) influences the response of SiC to low energy irradiation. It reveals that the C and Si atoms around the SFs are generally more difficult to be displaced than those in unfaulted SiC, and the corresponding threshold displacement energies for them are generally larger, indicative of enhanced radiation tolerance caused by the introduction of SFs, which agrees well with the recent experiment. As compared with the unfaulted state, more localized point defects are generated in faulted SiC. Also, the efficiency of damage production for Si recoils is generally higher than that of C recoils. The calculated potential energy increases for defect generation in SiC with intrinsic and extrinsic SFs are found to be higher than those in unfaulted SiC, due to the stronger screen-Coulomb interaction between the PKA and its neighbors. The presented results provide a fundamental insight into the underlying mechanism of displacement events in faulted SiC and will help to advance the understanding of the radiation response of SiC with and without SFs. PMID:26880027

Improvement of optical quality of semipolar (11 2 ¯ 2 ) GaN on m-plane sapphire by in-situ epitaxial lateral overgrowth

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Izyumskaya, Natalia; Müller, Marcus; Metzner, Sebastian; Veit, Peter; Can, Nuri; Das, Saikat; Özgür, Ümit; Bertram, Frank; Christen, Jürgen; Morkoç, Hadis; Avrutin, Vitaliy

2016-04-01

Among the major obstacles for development of non-polar and semipolar GaN structures on foreign substrates are stacking faults which deteriorate the structural and optical quality of the material. In this work, an in-situ SiNx nano-network has been employed to achieve high quality heteroepitaxial semipolar (11 2 ¯ 2 ) GaN on m-plane sapphire with reduced stacking fault density. This approach involves in-situ deposition of a porous SiNx interlayer on GaN that serves as a nano-mask for the subsequent growth, which starts in the nanometer-sized pores (window regions) and then progresses laterally as well, as in the case of conventional epitaxial lateral overgrowth (ELO). The inserted SiNx nano-mask effectively prevents the propagation of defects, such as dislocations and stacking faults, in the growth direction and thus reduces their density in the overgrown layers. The resulting semipolar (11 2 ¯ 2 ) GaN layers exhibit relatively smooth surface morphology and improved optical properties (PL intensity enhanced by a factor of 5 and carrier lifetimes by 35% to 85% compared to the reference semipolar (11 2 ¯ 2 ) GaN layer) which approach to those of the c-plane in-situ nano-ELO GaN reference and, therefore, holds promise for light emitting and detecting devices.

Atomic configurations at InAs partial dislocation cores associated with Z-shape faulted dipoles.

PubMed

Li, Luying; Gan, Zhaofeng; McCartney, Martha R; Liang, Hanshuang; Yu, Hongbin; Gao, Yihua; Wang, Jianbo; Smith, David J

2013-11-15

The atomic arrangements of two types of InAs dislocation cores associated by a Z-shape faulted dipole are observed directly by aberration-corrected high-angle annular-dark-field imaging. Single unpaired columns of different atoms in a matrix of dumbbells are clearly resolved, with observable variations of bonding lengths due to excess Coulomb force from bare ions at the dislocation core. The corresponding geometric phase analysis provides confirmation that the dislocation cores serve as origins of strain field inversion while stacking faults maintain the existing strain status.

Diffraction Seismic Imaging of the Chalk Group Reservoir Rocks

NASA Astrophysics Data System (ADS)

Montazeri, M.; Fomel, S.; Nielsen, L.

2016-12-01

In this study we investigate seismic diffracted waves instead of seismic reflected waves, which are usually much stronger and carry most of the information regarding subsurface structures. The goal of this study is to improve imaging of small subsurface features such as faults and fractures. Moreover, we focus on the Chalk Group, which contains important groundwater resources onshore and oil and gas reservoirs in the Danish sector of the North Sea. Finding optimum seismic velocity models for the Chalk Group and estimating high-quality stacked sections with conventional processing methods are challenging tasks. Here, we try to filter out as much as possible of undesired arrivals before stacking the seismic data. Further, a plane-wave destruction method is applied on the seismic stack in order to dampen the reflection events and thereby enhance the visibility of the diffraction events. After this initial processing, we estimate the optimum migration velocity using diffraction events in order to obtain a better resolution stack. The results from this study demonstrate how diffraction imaging can be used as an additional tool for improving the images of small-scale features in the Chalk Group reservoir, in particular faults and fractures. Moreover, we discuss the potential of applying this approach in future studies focused on such reservoirs.

Structural modifications due to interface chemistry at metal-nitride interfaces

DOE PAGES

Yadav, S. K.; Shao, S.; Wang, J.; ...

2015-11-27

Based on accurate first principles density functional theory (DFT) calculations, an unusual phenomenon of interfacial structural modifications, due to the interface chemistry influence is identified at two metal-nitride interfaces with strong metal-nitrogen affinity, Al/TiN {111} and Al/VN {111} interfaces. It is shown that at such interfaces, a faulted stacking structure is energetically preferred on the Al side of the interface. And both intrinsic and extrinsic stacking fault energies in the vicinity Al layers are negligibly small. However, such phenomenon does not occur in Pt/TiN and Pt/VN interfaces because of the weak Pt-N affinity. As a result, corresponding to structural energiesmore » of metal-nitride interfaces, the linear elasticity analysis predicts characteristics of interfacial misfit dislocations at metal-nitride interfaces.« less

Structural modifications due to interface chemistry at metal-nitride interfaces

PubMed Central

Yadav, S. K.; Shao, S.; Wang, J.; Liu, X.-Y.

2015-01-01

Based on accurate first principles density functional theory (DFT) calculations, an unusual phenomenon of interfacial structural modifications, due to the interface chemistry influence is identified at two metal-nitride interfaces with strong metal-nitrogen affinity, Al/TiN {111} and Al/VN {111} interfaces. It is shown that at such interfaces, a faulted stacking structure is energetically preferred on the Al side of the interface. And both intrinsic and extrinsic stacking fault energies in the vicinity Al layers are negligibly small. However, such phenomenon does not occur in Pt/TiN and Pt/VN interfaces because of the weak Pt-N affinity. Corresponding to structural energies of metal-nitride interfaces, the linear elasticity analysis predicts characteristics of interfacial misfit dislocations at metal-nitride interfaces. PMID:26611639

Atomistic structures of nano-engineered SiC and radiation-induced amorphization resistance

DOE PAGES

Imada, Kenta; Ishimaru, Manabu; Sato, Kazuhisa; ...

2015-06-18

In this paper, nano-engineered 3C–SiC thin films, which possess columnar structures with high-density stacking faults and twins, were irradiated with 2 MeV Si ions at cryogenic and room temperatures. From cross-sectional transmission electron microscopy observations in combination with Monte Carlo simulations based on the Stopping and Range of Ions in Matter code, it was found that their amorphization resistance is six times greater than bulk crystalline SiC at room temperature. High-angle bright-field images taken by spherical aberration corrected scanning transmission electron microscopy revealed that the distortion of atomic configurations is localized near the stacking faults. Finally, the resultant strain fieldmore » probably contributes to the enhancement of radiation tolerance of this material.« less

Wurtzite/zinc-blende electronic-band alignment in basal-plane stacking faults in semi-polar GaN

NASA Astrophysics Data System (ADS)

Monavarian, Morteza; Hafiz, Shopan; Izyumskaya, Natalia; Das, Saikat; Özgür, Ümit; Morkoç, Hadis; Avrutin, Vitaliy

2016-02-01

Heteroepitaxial semipolar and nonpolar GaN layers often suffer from high densities of extended defects including basal plane stacking faults (BSFs). BSFs which are considered as inclusions of cubic zinc-blende phase in wurtzite matrix act as quantum wells strongly affecting device performance. Band alignment in BSFs has been discussed as type of band alignment at the wurtzite/zinc blende interface governs the response in differential transmission; fast decay after the pulse followed by slow recovery due to spatial splitting of electrons and heavy holes for type- II band alignment in contrast to decay with no recovery in case of type I band alignment. Based on the results, band alignment is demonstrated to be of type II in zinc-blende segments in wurtzite matrix as in BSFs.

The Design of a Fault-Tolerant COTS-Based Bus Architecture for Space Applications

NASA Technical Reports Server (NTRS)

Chau, Savio N.; Alkalai, Leon; Tai, Ann T.

2000-01-01

The high-performance, scalability and miniaturization requirements together with the power, mass and cost constraints mandate the use of commercial-off-the-shelf (COTS) components and standards in the X2000 avionics system architecture for deep-space missions. In this paper, we report our experiences and findings on the design of an IEEE 1394 compliant fault-tolerant COTS-based bus architecture. While the COTS standard IEEE 1394 adequately supports power management, high performance and scalability, its topological criteria impose restrictions on fault tolerance realization. To circumvent the difficulties, we derive a "stack-tree" topology that not only complies with the IEEE 1394 standard but also facilitates fault tolerance realization in a spaceborne system with limited dedicated resource redundancies. Moreover, by exploiting pertinent standard features of the 1394 interface which are not purposely designed for fault tolerance, we devise a comprehensive set of fault detection mechanisms to support the fault-tolerant bus architecture.

Precise tremor source locations and amplitude variations along the lower-crustal central San Andreas Fault

USGS Publications Warehouse

Shelly, David R.; Hardebeck, Jeanne L.

2010-01-01

We precisely locate 88 tremor families along the central San Andreas Fault using a 3D velocity model and numerous P and S wave arrival times estimated from seismogram stacks of up to 400 events per tremor family. Maximum tremor amplitudes vary along the fault by at least a factor of 7, with by far the strongest sources along a 25 km section of the fault southeast of Parkfield. We also identify many weaker tremor families, which have largely escaped prior detection. Together, these sources extend 150 km along the fault, beneath creeping, transitional, and locked sections of the upper crustal fault. Depths are mostly between 18 and 28 km, in the lower crust. Epicenters are concentrated within 3 km of the surface trace, implying a nearly vertical fault. A prominent gap in detectible activity is located directly beneath the region of maximum slip in the 2004 magnitude 6.0 Parkfield earthquake.

Clustering on Magnesium Surfaces – Formation and Diffusion Energies

DOE PAGES

Chu, Haijian; Huang, Hanchen; Wang, Jian

2017-07-12

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and {more » $$\\bar{1}$$011} . In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a {$$\\bar{1}$$011} , clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface {$$\\bar{1}$$011} is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich–Schwoebel barriers converge as the step height is three atomic layers or thicker. FInally, adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.« less

Clustering on Magnesium Surfaces – Formation and Diffusion Energies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chu, Haijian; Huang, Hanchen; Wang, Jian

The formation and diffusion energies of atomic clusters on Mg surfaces determine the surface roughness and formation of faulted structure, which in turn affect the mechanical deformation of Mg. This paper reports first principles density function theory (DFT) based quantum mechanics calculation results of atomic clustering on the low energy surfaces {0001} and {more » $$\\bar{1}$$011} . In parallel, molecular statics calculations serve to test the validity of two interatomic potentials and to extend the scope of the DFT studies. On a {0001} surface, a compact cluster consisting of few than three atoms energetically prefers a face-centered-cubic stacking, to serve as a nucleus of stacking fault. On a {$$\\bar{1}$$011} , clusters of any size always prefer hexagonal-close-packed stacking. Adatom diffusion on surface {$$\\bar{1}$$011} is high anisotropic while isotropic on surface (0001). Three-dimensional Ehrlich–Schwoebel barriers converge as the step height is three atomic layers or thicker. FInally, adatom diffusion along steps is via hopping mechanism, and that down steps is via exchange mechanism.« less

Structure analysis of Si(111)-7 × 7 reconstructed surface by transmission electron diffraction

NASA Astrophysics Data System (ADS)

Takayanagi, Kunio; Tanishiro, Yasumasa; Takahashi, Shigeki; Takahashi, Masaetsu

1985-12-01

The atomic structure of the 7 × 7 reconstructed Si(111) surface has been analysed by ultra-high vacuum (UHV) transmission electron diffraction (TED). A possible projected structure of the surface is deduced from the intensity distribution in TED patterns of normal electron incidence and from Patterson and Fourier syntheses of the intensities. A new three-dimensional structure model, the DAS model, is proposed: The model consists of 12 adatoms arranged locally in the 2 × 2 structure, a stacking fault layer and a layer with a vacancy at the corner and 9 dimers on the sides of each of the two triangular subcells of the 7 × 7 unit cell. The silicon layers in one subcell are stacked with the normal sequence, CcAaB + adatoms, while those in the other subcell are stacked with a faulted sequence, CcAa/C + adatoms. The model has only 19 dangling bonds, the smallest number among models so far proposed. Previously proposed models are tested quantitatively by the TED intensity. Advantages and limits of the TED analysis are discussed.

On-line experimental validation of a model-based diagnostic algorithm dedicated to a solid oxide fuel cell system

NASA Astrophysics Data System (ADS)

Polverino, Pierpaolo; Esposito, Angelo; Pianese, Cesare; Ludwig, Bastian; Iwanschitz, Boris; Mai, Andreas

2016-02-01

In the current energetic scenario, Solid Oxide Fuel Cells (SOFCs) exhibit appealing features which make them suitable for environmental-friendly power production, especially for stationary applications. An example is represented by micro-combined heat and power (μ-CHP) generation units based on SOFC stacks, which are able to produce electric and thermal power with high efficiency and low pollutant and greenhouse gases emissions. However, the main limitations to their diffusion into the mass market consist in high maintenance and production costs and short lifetime. To improve these aspects, the current research activity focuses on the development of robust and generalizable diagnostic techniques, aimed at detecting and isolating faults within the entire system (i.e. SOFC stack and balance of plant). Coupled with appropriate recovery strategies, diagnosis can prevent undesired system shutdowns during faulty conditions, with consequent lifetime increase and maintenance costs reduction. This paper deals with the on-line experimental validation of a model-based diagnostic algorithm applied to a pre-commercial SOFC system. The proposed algorithm exploits a Fault Signature Matrix based on a Fault Tree Analysis and improved through fault simulations. The algorithm is characterized on the considered system and it is validated by means of experimental induction of faulty states in controlled conditions.

Reversible loss of Bernal stacking during the deformation of few-layer graphene in nanocomposites.

PubMed

Gong, Lei; Young, Robert J; Kinloch, Ian A; Haigh, Sarah J; Warner, Jamie H; Hinks, Jonathan A; Xu, Ziwei; Li, Li; Ding, Feng; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S

2013-08-27

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (~0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

PubMed Central

2013-01-01

The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed. PMID:23899378

Advancements in understanding the aeromagnetic expressions of basin-margin faults—An example from San Luis Basin, Colorado

USGS Publications Warehouse

Grauch, V. J.; Bedrosian, Paul A.; Drenth, Benjamin J.

2013-01-01

Herein, we summarize and expand on an investigation of the sources of aeromagnetic anomalies related to faults along the eastern margin of the San Luis Basin, northern Rio Grande Rift, Colorado (Grauch et al., 2010). Similar to the faults examined in the central Rio Grande Rift, magnetic sources can be completely explained by tectonic juxtaposition and produce multiple, vertically stacked magnetic contrasts at individual faults. However, the geologic sources are different. They arise from both the sedimentary cover and the underlying bedrock rather than from stratified sediments. In addition, geologic evidence for secondary growth or destruction of magnetic minerals at the fault zone is lacking.

Polarization of stacking fault related luminescence in GaN nanorods

NASA Astrophysics Data System (ADS)

Pozina, G.; Forsberg, M.; Serban, E. A.; Hsiao, C.-L.; Junaid, M.; Birch, J.; Kaliteevski, M. A.

2017-01-01

Linear polarization properties of light emission are presented for GaN nanorods (NRs) grown along [0001] direction on Si(111) substrates by direct-current magnetron sputter epitaxy. The near band gap photoluminescence (PL) measured at low temperature for a single NR demonstrated an excitonic line at ˜3.48 eV and the stacking faults (SFs) related transition at ˜3.43 eV. The SF related emission is linear polarized in direction perpendicular to the NR growth axis in contrast to a non-polarized excitonic PL. The results are explained in the frame of the model describing basal plane SFs as polymorphic heterostructure of type II, where anisotropy of chemical bonds at the interfaces between zinc blende and wurtzite GaN subjected to in-built electric field is responsible for linear polarization parallel to the interface planes.

Dependences of contraction/expansion of stacking faults on temperature and current density in 4H-SiC p–i–n diodes

NASA Astrophysics Data System (ADS)

Okada, Aoi; Nishio, Johji; Iijima, Ryosuke; Ota, Chiharu; Goryu, Akihiro; Miyazato, Masaki; Ryo, Mina; Shinohe, Takashi; Miyajima, Masaaki; Kato, Tomohisa; Yonezawa, Yoshiyuki; Okumura, Hajime

2018-06-01

To investigate the mechanism of contraction/expansion behavior of Shockley stacking faults (SSFs) in 4H-SiC p–i–n diodes, the dependences of the SSF behavior on temperature and injection current density were investigated by electroluminescence image observation. We investigated the dependences of both triangle- and bar-shaped SSFs on the injection current density at four temperature levels. All SSFs in this study show similar temperature and injection current density dependences. We found that the expansion of SSFs at a high current density was converted to contraction at a certain value as the current decreased and that the value is temperature-dependent. It has been confirmed that SSF behavior, which was considered complex or peculiar, might be explained mainly by the energy change caused by SSFs.

First-principles study of the atomic and electronic properties of (1 0 0) stacking faults in BaSnO3 crystal

NASA Astrophysics Data System (ADS)

Xue, Yuanbin; Wang, Wenyuan; Guo, Yao

2018-02-01

We investigated the atomic and electronic properties of (1 0 0) stacking fault (SF) in undoped and La-doped BaSnO3 by first-principles calculations. It was found that 1/2[1 1 1] (1 0 0) SF is energetically favorable when Ba atoms occupy the interface while 1/2 (1 0 0) [1 0 1] SF becomes the most stable when the SF interface is occupied by Sn atoms. SF influences the distribution of La dopant and the electric properties of the system. In the presence of SF, electronic states near the Fermi level decrease and the bandgap expands by about 0.6 eV. Our results suggest that SF is one of the possible origins for the performance degradation.

Basic criteria for formation of growth twins in high stacking fault energy metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, K. Y.; Zhang, X.; Department of Mechanical Engineering, Texas A and M University, College Station, Texas 77843

Nanotwinned metals received significant interest lately as twin boundaries may enable simultaneous enhancement of strength, ductility, thermal stability, and radiation tolerance. However, nanotwins have been the privilege of metals with low-to-intermediate stacking fault energy (SFE). Recent scattered studies show that nanotwins could be introduced into high SFE metals, such as Al. In this paper, we examine several sputter-deposited, (111) textured Ag/Al, Cu/Ni, and Cu/Fe multilayers, wherein growth twins were observed in Al, Ni, and face-centered cubic (fcc) Fe. The comparisons lead to two important design criteria that dictate the introduction of growth twins in high SFE metals. The validity ofmore » these criteria was then examined in Ag/Ni multilayers. Furthermore, another twin formation mechanism in high SFE metals was discovered in Ag/Ni system.« less

Morphology of single Shockley-type stacking faults generated by recombination enhanced dislocation glide in 4H-SiC

NASA Astrophysics Data System (ADS)

Matsuhata, Hirofumi; Sekiguchi, Takashi

2018-04-01

Morphology of single Shockley-type stacking faults (SFs) generated by recombination enhanced dislocation glide (REDG) in 4H-SiC are discussed and analysed. A complete set of the 12 different dissociated states of basal-plane dislocation loops is obtained using the crystallographic space group operations. From this set, six different double rhombic-shaped SFs are derived. These tables indicate the rules that connect shapes of SFs with the locations of partial dislocations having different core structures, the positions of slip planes in a unit cell, and the Burgers vectors of partial dislocations. We applied these tables for the analysis of SFs generated by the REDG effect reported in the past articles. Shapes, growing process of SFs and perfect dislocations for origins of SFs were well analysed systematically.

Microstructural defects in He-irradiated polycrystalline α-SiC at 1000 °C

NASA Astrophysics Data System (ADS)

Han, Wentuo; Li, Bingsheng

2018-06-01

In order to investigate the effect of the high-temperature irradiation on microstructural evolutions of the polycrystalline SiC, an ion irradiation at 1000 °C with the 500 keV He2+ was imposed to the α-SiC. The platelets, He bubbles, dislocation loops, and particularly, their interaction with the stacking fault and grain boundaries were focused on and characterized by the cross-sectional transmission electron microscopy (XTEM). The platelets expectably exhibit a dominant plane of (0001), while planes of (01-10) and (10-16) are also found. Inside the platelet, the over-pressurized bubbles exist and remarkably cause a strong-strain zone surrounding the platelet. The disparate roles between the grain boundaries and stacking faults in interacting with the bubbles and loops are found. The results are compared with the previous weighty findings and discussed.

I2 basal stacking fault as a degradation mechanism in reverse gate-biased AlGaN/GaN HEMTs

NASA Astrophysics Data System (ADS)

Lang, A. C.; Hart, J. L.; Wen, J. G.; Miller, D. J.; Meyer, D. J.; Taheri, M. L.

2016-09-01

Here, we present the observation of a bias-induced, degradation-enhancing defect process in plasma-assisted molecular beam epitaxy grown reverse gate-biased AlGaN/GaN high electron mobility transistors (HEMTs), which is compatible with the current theoretical framework of HEMT degradation. Specifically, we utilize both conventional transmission electron microscopy and aberration-corrected transmission electron microscopy to analyze microstructural changes in not only high strained regions in degraded AlGaN/GaN HEMTs but also the extended gate-drain access region. We find a complex defect structure containing an I2 basal stacking fault and offer a potential mechanism for device degradation based on this defect structure. This work supports the reality of multiple failure mechanisms during device operation and identifies a defect potentially involved with device degradation.

Novel Cross-Slip Mechanism of Pyramidal Screw Dislocations in Magnesium.

PubMed

Itakura, Mitsuhiro; Kaburaki, Hideo; Yamaguchi, Masatake; Tsuru, Tomohito

2016-06-03

Compared to cubic metals, whose primary slip mode includes twelve equivalent systems, the lower crystalline symmetry of hexagonal close-packed metals results in a reduced number of equivalent primary slips and anisotropy in plasticity, leading to brittleness at the ambient temperature. At higher temperatures, the ductility of hexagonal close-packed metals improves owing to the activation of secondary ⟨c+a⟩ pyramidal slip systems. Thus, understanding the fundamental properties of corresponding dislocations is essential for the improvement of ductility at the ambient temperature. Here, we present the results of large-scale ab initio calculations for ⟨c+a⟩ pyramidal screw dislocations in magnesium and show that their slip behavior is a stark counterexample to the conventional wisdom that a slip plane is determined by the stacking fault plane of dislocations. A stacking fault between dissociated partial dislocations can assume a nonplanar shape with a negligible energy cost and can migrate normal to its plane by a local shuffling of atoms. Partial dislocations dissociated on a {21[over ¯]1[over ¯]2} plane "slither" in the {011[over ¯]1} plane, dragging the stacking fault with them in response to an applied shear stress. This finding resolves the apparent discrepancy that both {21[over ¯]1[over ¯]2} and {011[over ¯]1} slip traces are observed in experiments while ab initio calculations indicate that dislocations preferably dissociate in the {21[over ¯]1[over ¯]2} planes.

Interlayer interactions in graphites.

PubMed

Chen, Xiaobin; Tian, Fuyang; Persson, Clas; Duan, Wenhui; Chen, Nan-xian

2013-11-06

Based on ab initio calculations of both the ABC- and AB-stacked graphites, interlayer potentials (i.e., graphene-graphene interaction) are obtained as a function of the interlayer spacing using a modified Möbius inversion method, and are used to calculate basic physical properties of graphite. Excellent consistency is observed between the calculated and experimental phonon dispersions of AB-stacked graphite, showing the validity of the interlayer potentials. More importantly, layer-related properties for nonideal structures (e.g., the exfoliation energy, cleave energy, stacking fault energy, surface energy, etc.) can be easily predicted from the interlayer potentials, which promise to be extremely efficient and helpful in studying van der Waals structures.

Focal mechanisms and inter-event times of low-frequency earthquakes reveal quasi-continuous deformation and triggered slow slip on the deep Alpine Fault

NASA Astrophysics Data System (ADS)

Baratin, Laura-May; Chamberlain, Calum J.; Townend, John; Savage, Martha K.

2018-02-01

Characterising the seismicity associated with slow deformation in the vicinity of the Alpine Fault may provide constraints on the stresses acting on a major transpressive margin prior to an anticipated great (≥M8) earthquake. Here, we use recently detected tremor and low-frequency earthquakes (LFEs) to examine how slow tectonic deformation is loading the Alpine Fault late in its typical ∼300-yr seismic cycle. We analyse a continuous seismic dataset recorded between 2009 and 2016 using a network of 10-13 short-period seismometers, the Southern Alps Microearthquake Borehole Array. Fourteen primary LFE templates are used in an iterative matched-filter and stacking routine, allowing the detection of similar signals corresponding to LFE families sharing common locations. This yields an 8-yr catalogue containing 10,000 LFEs that are combined for each of the 14 LFE families using phase-weighted stacking to produce signals with the highest possible signal-to-noise ratios. We show that LFEs occur almost continuously during the 8-yr study period and highlight two types of LFE distributions: (1) discrete behaviour with an inter-event time exceeding 2 min; (2) burst-like behaviour with an inter-event time below 2 min. We interpret the discrete events as small-scale frequent deformation on the deep extent of the Alpine Fault and LFE bursts (corresponding in most cases to known episodes of tremor or large regional earthquakes) as brief periods of increased slip activity indicative of slow slip. We compute improved non-linear earthquake locations using a 3-D velocity model. LFEs occur below the seismogenic zone at depths of 17-42 km, on or near the hypothesised deep extent of the Alpine Fault. The first estimates of LFE focal mechanisms associated with continental faulting, in conjunction with recurrence intervals, are consistent with quasi-continuous shear faulting on the deep extent of the Alpine Fault.

Wide-angle Marine Seismic Refraction Imaging of Vertical Faults: Pre-Stack Turning Wave Migrations of Synthetic Data and Implications for Survey Design

NASA Astrophysics Data System (ADS)

Miller, N. C.; Lizarralde, D.; McGuire, J.; Hole, J. A.

2006-12-01

We consider methodologies, including survey design and processing algorithms, which are best suited to imaging vertical reflectors in oceanic crust using marine seismic techniques. The ability to image the reflectivity structure of transform faults as a function of depth, for example, may provide new insights into what controls seismicity along these plate boundaries. Turning-wave migration has been used with success to image vertical faults on land. With synthetic datasets we find that this approach has unique difficulties in the deep ocean. The fault-reflected crustal refraction phase (Pg-r) typically used in pre-stack migrations is difficult to isolate in marine seismic data. An "imagable" Pg-r is only observed in a time window between the first arrivals and arrivals from the sediments and the thick, slow water layer at offsets beyond ~25 km. Ocean- bottom seismometers (OBSs), as opposed to a long surface streamer, must be used to acquire data suitable for crustal-scale vertical imaging. The critical distance for Moho reflections (PmP) in oceanic crust is also ~25 km, thus Pg-r and PmP-r are observed with very little separation, and the fault-reflected mantle refraction (Pn-r) arrives prior to Pg-r as the observation window opens with increased OBS-to-fault distance. This situation presents difficulties for "first-arrival" based Kirchoff migration approaches and suggests that wave- equation approaches, which in theory can image all three phases simultaneously, may be more suitable for vertical imaging in oceanic crust. We will present a comparison of these approaches as applied to a synthetic dataset generated from realistic, stochastic velocity models. We will assess their suitability, the migration artifacts unique to the deep ocean, and the ideal instrument layout for such an experiment.

Dislocation creation and void nucleation in FCC ductile metals under tensile loading: a general microscopic picture.

PubMed

Pang, Wei-Wei; Zhang, Ping; Zhang, Guang-Cai; Xu, Ai-Guo; Zhao, Xian-Geng

2014-11-10

Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies.

Interseismic secular deformation in Southern California from InSAR-derived maps over the time period between 1992 and 2006

NASA Astrophysics Data System (ADS)

Rivet, D. N.; Fialko, Y.

2007-12-01

We analyzed secular deformation in Southern California using an extensive catalog of InSAR data that spans 15 years between 1992 and 2006. We generated a map of the satellite line-of-sight displacements based on a stack of ~300 interferograms from 6 adjacent tracks of the ERS-1 and ERS-2 satellites covering Southern California. The main limitation to the accuracy of InSAR measurements of tectonic deformation is the atmospheric phase delay. We introduce a new method aimed to improve the signal-to-noise ratio in the InSAR- derived maps of secular deformation. The method involves identifying SAR acquisitions that are highly affected by atmospheric noise, and an optimal choice of interferometric pairs for stacking. We begin by generating a set of all possible interferometric pairs having baselines and time spans within prescribed limits. We then select interferograms with sufficiently high correlation. Subsequently, we identify noisy SAR acquisitions by means of calculating RMS of the phase signal. Finally, we generate a stack of interferograms by following a "connectivity tree" that minimizes contributions of noisy scenes. Using this method we obtained a continuous velocity field characterizing surface deformation in Southern California over the last 15 years. We identify interseismic deformation on a number of major faults, including those of the southern San Andreas system, and the Eastern California Shear Zone (ECSZ). We study the time dependency from 1992 to 2006 of those deformation patterns. Variations in the line-of- sight velocity across the Eastern California Shear Zone are non-monotonic, with the maximum along the strike of the Hector Mine fault of ~4 mm/yr, and total LOS velocity between the eastern and western boundaries of the shear zone of less than 2 mm/yr. We observe increases in the radar range to the east of ECSZ. This signal most likely results from subsidence east of the Death Valley-Mule Springs fault system, either due to hydrologic effects, or dip-slip tectonics. No resolvable interseismic deformation is detected across the Garlock fault. The Blackwater fault is associated with line-of-sight velocity of 2 mm/yr. By combining data from the ascending and descending satellite orbits, we infer that most of that strain is associated with the differential vertical motion across the fault (east side up), so that the accelerated strike-slip motion on the deep extension of the Blackwater fault is not required.

Molecular dynamics simulation of the plastic behavior anisotropy of shock-compressed monocrystal nickel

NASA Astrophysics Data System (ADS)

Chen, Ya-Zhou; Zhou, Liu-Cheng; He, Wei-Feng; Sun, Yu; Li, Ying-Hong; Jiao, Yang; Luo, Si-Hai

2017-01-01

Molecular dynamics simulations were used to study the plastic behavior of monocrystalline nickel under shock compression along the [100] and [110] orientations. The shock Hugoniot relation, local stress curve, and process of microstructure development were determined. Results showed the apparent anisotropic behavior of monocrystalline nickel under shock compression. The separation of elastic and plastic waves was also obvious. Plastic deformation was more severely altered along the [110] direction than the [100] direction. The main microstructure phase transformed from face-centered cubic to body-centered cubic and generated a large-scale and low-density stacking fault along the family of { 111 } crystal planes under shock compression along the [100] direction. By contrast, the main mechanism of plastic deformation in the [110] direction was the nucleation of the hexagonal, close-packed phase, which generated a high density of stacking faults along the [110] and [1̅10] directions.

Studies of molecular-beam epitaxy growth of GaAs on porous Si substrates

NASA Technical Reports Server (NTRS)

Mii, Y. J.; Kao, Y. C.; Wu, B. J.; Wang, K. L.; Lin, T. L.; Liu, J. K.

1988-01-01

GaAs has been grown on porous Si directly and on Si buffer layer-porous Si substrates by molecular-beam epitaxy. In the case of GaAs growth on porous Si, transmission electron microscopy (TEM) reveals that the dominant defects in GaAs layers grown on porous Si are microtwins and stacking faults, which originate from the GaAs/porous Si interface. GaAs is found to penetrate into the porous Si layers. By using a thin Si buffer layer (50 nm), GaAs penetration diminishes and the density of microtwins and stacking faults is largely reduced and localized at the GaAs/Si buffer interface. However, there is a high density of threading dislocations remaining. Both Si (100) aligned and four degree tilted substrates have been examined in this study. TEM results show no observable effect of the tilted substrates on the quality of the GaAs epitaxial layer.

High-resolution transmission electron microscopy of hexagonal and rhombohedral molybdenum disulfide crystals.

PubMed

Isshiki, T; Nishio, K; Saijo, H; Shiojiri, M; Yabuuchi, Y; Takahashi, N

1993-07-01

Natural (molybdenite) and synthesized molybdenum disulfide crystals have been studied by high-resolution transmission electron microscopy. The image simulation demonstrates that the [0001] and [0110] HRTEM images of hexagonal and rhombohedral MoS2 crystals hardly disclose their stacking sequences, and that the [2110] images can distinguish the Mo and S columns along the incident electron beam and enable one to determine not only the crystal structure but also the fault structure. Observed [0001] images of cleaved molybdenite and synthesized MoS2 crystals, however, reveal the strain field around partial dislocations limiting an extended dislocation. A cross-sectional image of a single molecular (S-Mo-S) layer cleaved from molybdenite has been observed. Synthesized MoS2 flakes which were prepared by grinding have been found to be rhombohedral crystals containing many stacking faults caused by glides between S/S layers.

Charge optimized many-body potential for aluminum.

PubMed

Choudhary, Kamal; Liang, Tao; Chernatynskiy, Aleksandr; Lu, Zizhe; Goyal, Anuj; Phillpot, Simon R; Sinnott, Susan B

2015-01-14

An interatomic potential for Al is developed within the third generation of the charge optimized many-body (COMB3) formalism. The database used for the parameterization of the potential consists of experimental data and the results of first-principles and quantum chemical calculations. The potential exhibits reasonable agreement with cohesive energy, lattice parameters, elastic constants, bulk and shear modulus, surface energies, stacking fault energies, point defect formation energies, and the phase order of metallic Al from experiments and density functional theory. In addition, the predicted phonon dispersion is in good agreement with the experimental data and first-principles calculations. Importantly for the prediction of the mechanical behavior, the unstable stacking fault energetics along the [Formula: see text] direction on the (1 1 1) plane are similar to those obtained from first-principles calculations. The polycrsytal when strained shows responses that are physical and the overall behavior is consistent with experimental observations.

First principles pseudopotential calculation of electron energy loss near edge structures of lattice imperfections.

PubMed

Mizoguchi, Teruyasu; Matsunaga, Katsuyuki; Tochigi, Eita; Ikuhara, Yuichi

2012-01-01

Theoretical calculations of electron energy loss near edge structures (ELNES) of lattice imperfections, particularly a Ni(111)/ZrO₂(111) heterointerface and an Al₂O₃ stacking fault on the {1100} plane, are performed using a first principles pseudopotential method. The present calculation can qualitatively reproduce spectral features as well as chemical shifts in experiment by employing a special pseudopotential designed for the excited atom with a core-hole. From the calculation, spectral changes observed in O-K ELNES from a Ni/ZrO₂ interface can be attributable to interfacial oxygen-Ni interactions. In the O-K ELNES of Al₂O₃ stacking faults, theoretical calculation suggests that the spectral feature reflects coordination environment and chemical bonding. Powerful combinations of ELNES with a pseudopotential method used to investigate the atomic and electronic structures of lattice imperfections are demonstrated. Copyright © 2011 Elsevier Ltd. All rights reserved.

Atomistic Origin of Deformation Twinning in Biomineral Aragonite.

PubMed

Liu, Jialin; Huang, Zaiwang; Pan, Zhiliang; Wei, Qiuming; Li, Xiaodong; Qi, Yue

2017-03-10

Deformation twinning rarely occurs in mineral materials which typically show brittle fracture. Surprisingly, it has recently been observed in the biomineral aragonite phase in nacre under high rate impact loading. In this Letter, the twinning tendency and the competition between fracture and deformation twinning were revealed by first principles calculations. The ratio of the unstable stacking fault energy and the stacking fault energy in orthorhombic aragonite is hitherto the highest in a broad range of metallic and oxide materials. The underlining physics for this high ratio is the multineighbor shared ionic bonds and the unique relaxation process during sliding in the aragonite structure. Overall, the unique deformation twining along with other highly coordinated deformation mechanisms synergistically work in the hierarchical structure of nacre, leading to the remarkable strengthening and toughening of nacre upon dynamic loading, and thus protecting the mother-of-pearl from predatory attacks.

In situ monitoring of stacking fault formation and its carrier lifetime mediation in p-type 4H-SiC

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Bin, E-mail: chenbinmse@gmail.com; Chen, Jun; Yao, Yuanzhao

Using the fine control of an electron beam (e-beam) in scanning electron microscopy with the capabilities of both electrical and optical imaging, the stacking fault (SF) formation together with its tuning of carrier lifetime was in situ monitored and investigated in p-type 4H-SiC homoepitaxial films. The SFs were formed through engineering basal plane dislocations with the energy supplied by the e-beam. The e-beam intensity required for the SF formation in the p-type films was ∼100 times higher than that in the n-type ones. The SFs reduced the minority-carrier lifetime in the p-type films, which was opposite to that observed inmore » the n-type case. The reason for the peculiar SF behavior in the p-type 4H-SiC is discussed with the cathodoluminescence results.« less

Synthesis and microstructure of electrodeposited and sputtered nanotwinned face-centered-cubic metals

DOE PAGES

Bufford, Daniel C.; Wang, Morris; Liu, Yue; ...

2016-04-01

The remarkable properties of nanotwinned (NT) face-centered-cubic (fcc) metals arise directly from twin boundaries, the structures of which can be initially determined by growth twinning during the deposition process. When we understand the synthesis process and its relation to the resulting microstructure, and ultimately to material properties, we realize how key it is to understanding and utilizing these materials. Furthermore, our article presents recent studies on electrodeposition and sputtering methods that produce a high density of nanoscale growth twins in fcc metals. Nanoscale growth twins tend to form spontaneously in monolithic and alloyed fcc metals with lower stacking-fault energies, whilemore » engineered approaches are necessary for fcc metals with higher stacking-fault energies. Finally, growth defects and other microstructural features that influence nanotwin behavior and stability are introduced here, and future challenges in fabricating NT materials are highlighted.« less

Stacking fault energies of face-centered cubic concentrated solid solution alloys

DOE PAGES

Zhao, Shijun; Stocks, G. Malcolm; Zhang, Yanwen

2017-06-22

We report the stacking fault energy (SFE) for a series of face-centered cubic (fcc) equiatomic concentrated solid solution alloys (CSAs) derived as subsystems from the NiCoFeCrMn and NiCoFeCrPd high entropy alloys based on ab initio calculations. At low temperatures, these CSAs display very low even negative SFEs, indicating that hexagonal close-pack ( hcp) is more energy favorable than fcc structure. The temperature dependence of SFE for some CSAs is studied. With increasing temperature, a hcp-to- fcc transition is revealed for those CSAs with negative SFEs, which can be attributed to the role of intrinsic vibrational entropy. The analysis of themore » vibrational modes suggests that the vibrational entropy arises from the high frequency states in the hcp structure that originate from local vibrational mode. Furthermore, our results underscore the importance of vibrational entropy in determining the temperature dependence of SFE for CSAs.« less

Replace with abstract title

NASA Astrophysics Data System (ADS)

Coho, Aleksander; Kioussis, Nicholas

2003-03-01

We use the semidiscrete variational generelized Peierls-Nabarro model to study the effect of Cu alloying on the dislocation properties of Al. First-principles density functional theory (DFT) is used to calculate the generalized-stacking-fault (GSF) energy surface when a <111> plane, on which one in four Al atoms has been replaced with a Cu atom, slips over a pure Al <111> plane. Various dislocation core properties (core width, energy, Peierls stress, dissociation tendency) are investigated and compared with the pure Al case. Cu alloying lowers the intrinsic stacking fault (ISF) energy, which makes dislocations more likely to dissociate into partials. We also try to understand the lowering of ISF energy in terms of Al-Cu and Al-Al bond formation and braking during shearing along the <112> direction. From the above we draw conclusions about the effects of Cu alloying on the mechanical properties of Al.

Stacking fault energies of face-centered cubic concentrated solid solution alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Shijun; Stocks, G. Malcolm; Zhang, Yanwen

We report the stacking fault energy (SFE) for a series of face-centered cubic (fcc) equiatomic concentrated solid solution alloys (CSAs) derived as subsystems from the NiCoFeCrMn and NiCoFeCrPd high entropy alloys based on ab initio calculations. At low temperatures, these CSAs display very low even negative SFEs, indicating that hexagonal close-pack ( hcp) is more energy favorable than fcc structure. The temperature dependence of SFE for some CSAs is studied. With increasing temperature, a hcp-to- fcc transition is revealed for those CSAs with negative SFEs, which can be attributed to the role of intrinsic vibrational entropy. The analysis of themore » vibrational modes suggests that the vibrational entropy arises from the high frequency states in the hcp structure that originate from local vibrational mode. Furthermore, our results underscore the importance of vibrational entropy in determining the temperature dependence of SFE for CSAs.« less

Synthesis and microstructure of electrodeposited and sputtered nanotwinned face-centered-cubic metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bufford, Daniel C.; Wang, Morris; Liu, Yue

The remarkable properties of nanotwinned (NT) face-centered-cubic (fcc) metals arise directly from twin boundaries, the structures of which can be initially determined by growth twinning during the deposition process. When we understand the synthesis process and its relation to the resulting microstructure, and ultimately to material properties, we realize how key it is to understanding and utilizing these materials. Furthermore, our article presents recent studies on electrodeposition and sputtering methods that produce a high density of nanoscale growth twins in fcc metals. Nanoscale growth twins tend to form spontaneously in monolithic and alloyed fcc metals with lower stacking-fault energies, whilemore » engineered approaches are necessary for fcc metals with higher stacking-fault energies. Finally, growth defects and other microstructural features that influence nanotwin behavior and stability are introduced here, and future challenges in fabricating NT materials are highlighted.« less

Cordilleran front range structural features in northwest Montana interpreted from vintage seismic reflection data

NASA Astrophysics Data System (ADS)

Porter, Mason C.; Rutherford, Bradley S.; Speece, Marvin A.; Mosolf, Jesse G.

2016-04-01

Industry seismic reflection data spanning the Rocky Mountain Cordillera front ranges of northwest Montana were reprocessed and interpreted in this study. Five seismic profiles represent 160 km of deep reflection data collected in 1983 that span the eastern Purcell anticlinorium, Rocky Mountain Trench (RMT), Rocky Mountain Basal Décollement (RMBD), and Lewis thrust. The data were reprocessed using modern techniques including refraction statics, pre-stack time migration (PSTM), and pre- and post-stack depth migration. Results indicate the RMBD is 8-13 km below the Earth's surface and dip 3-10° west. Evidence for the autochthonous Mesoproterozoic Belt and basal Cambrian rocks beneath the RMBD is present in all of the profiles and appears to extend east of the RMT. The Lewis thrust was identified in the seismic profiles and appears to sole into the RMBD east of the RMT. The RMT fault system has a dip displacement of 3-4 km and forms a half graben filled with 1 km of unconsolidated Tertiary sedimentary deposits. The RMT and adjacent Flathead fault systems are interpreted to be structurally linked and may represent a synthetic, en echelon fault system.

Magnetic fabric of fault breccia: Revealing the direction of the Cretaceous nappe-stacking in the Inner Western Carpathians by AMS analyses

NASA Astrophysics Data System (ADS)

Pomella, Hannah; Kövér, Szilvia; Fodor, László

2017-04-01

The anisotropy of magnetic susceptibility (AMS) has been recognized as a highly sensitive indicator of rock fabric and is widely employed in the field of structural geology. Brittle faults are often characterized by fault breccia, fault rocks with clast-in-matrix textures. A noteworthy feature of the breccia is the presence of a fabric defined by the preferred orientation of clasts and grains in the matrix. However, this fabric is often not visible in the field or in thin sections but can be detected by AMS analyses. The sample area of the present study is located within the Cretaceous thin-skinned nappe-system of the Inner Western Carpathians. This Alpine-type orogenic belt is built up by large-scale, few km thick nappes without connection to their root areas. These thin rock slices thrust over large distances without sign of mayor deformation within the nappe slice. All the deformation took place along highly strained, narrow shear zones lubricated by hot fluids. These hydrostatically pressurized zones develop on the bases of the nappes, where basal tectonic breccia was formed. Newly formed, syn-kinematic minerals are growing from the overpressured fluids. These polymict breccias have typical block-in-matrix texture with clast size vary between mm and few cm. The matrix is mainly submillimetre-scale rock fragments and cement. In spite of detailed studies about the physical conditions of nappe movements, there is no information about the tectonic transport direction. Analyses of brittle fault kinematics within the different tectonic slices suggest either NW-SE or N-S compressional stress field during the nappe-stacking. With this study we want to test if the magnetic fabric of tectonic breccia can help to determine the transport direction. The first results are very promising: Area 1 (basal tectonic breccia from Tisovec): the magnetic lineation is well defined and plunges gently towards N-NNW. The stretching lineation observable in the field within the uppermost part of the footwall dips towards ENE and is probably related to an ENE-WSW extensional event affecting the whole nappe-pile after the nappe-stacking. However, the detected magnetic foliation fits nicely into the supposed NW/N-SE/S oriented compressional stress field during the nappe-stacking, prior to the extensional event. Following this interpretation the breccia was formed during nappe stacking and its magnetic fabric was not overprinted by the following extensional event. Area 2 (basal tectonic breccia from Puste Pole): two magnetic fabrics can be measured in different sites: a well-defined magnetic lineation plunging towards NNW/SSE, and a weaker fabric with either WSW or E dipping magnetic lineation. The first fabric can be interpreted in the same way as in area 1. However, the WSW or E oriented magnetic lineation is parallel to the structural stretching lineation associated to the later extensional event. Area 3 (basal tectonic breccia from Telgárt): the magnetic lineation is well defined and dips gently to W, which is parallel to the post-stacking stretching direction. This preliminary results show, that AMS-study of the basal tectonic breccia of thin-skinned nappes can be a powerful method in the future for detecting the hidden anisotropic fabric related to the tectonic movements, even if there are several tectonic events with different directions of movement.

Improved 3D seismic attribute mapping by CRS stacking instead of NMO stacking: Application to a geothermal reservoir in the Polish Basin

NASA Astrophysics Data System (ADS)

Pussak, Marcin; Bauer, Klaus; Stiller, Manfred; Bujakowski, Wieslaw

2014-04-01

Within a seismic reflection processing work flow, the common-reflection-surface (CRS) stack can be applied as an alternative for the conventional normal moveout (NMO) or the dip moveout (DMO) stack. The advantages of the CRS stack include (1) data-driven automatic determination of stacking operator parameters, (2) imaging of arbitrarily curved geological boundaries, and (3) significant increase in signal-to-noise (S/N) ratio by stacking far more traces than used in a conventional stack. In this paper we applied both NMO and CRS stackings to process a sparse 3D seismic data set acquired within a geothermal exploration study in the Polish Basin. The stacked images show clear enhancements in quality achieved by the CRS stack in comparison with the conventional stack. While this was expected from previous studies, we also found remarkable improvements in the quality of seismic attributes when the CRS stack was applied instead of the conventional stack. For the major geothermal target reservoir (Lower Jurassic horizon Ja1), we present a comparison between both stacking methods for a number of common attributes, including root-mean-square (RMS) amplitudes, instantaneous frequencies, coherency, and spectral decomposition attributes derived from the continuous wavelet transform. The attribute maps appear noisy and highly fluctuating after the conventional stack, and are clearly structured after the CRS stack. A seismic facies analysis was finally carried out for the Ja1 horizon using the attributes derived from the CRS stack by using self-organizing map clustering techniques. A corridor parallel to a fault system was identified, which is characterized by decreased RMS amplitudes and decreased instantaneous frequencies. In our interpretation, this region represents a fractured, fluid-bearing compartment within the sandstone reservoir, which indicates favorable conditions for geothermal exploitation.

The Effect of Grain Size on the Radiation Response of Silicon Carbide and its Dependence on Irradiation Species and Temperature

NASA Astrophysics Data System (ADS)

Jamison, Laura

In recent years the push for green energy sources has intensified, and as part of that effort accident tolerant and more efficient nuclear reactors have been designed. These reactors demand exceptional material performance, as they call for higher temperatures and doses. Silicon carbide (SiC) is a strong candidate material for many of these designs due to its low neutron cross-section, chemical stability, and high temperature resistance. The possibility of improving the radiation resistance of SiC by reducing the grain size (thus increasing the sink density) is explored in this work. In-situ electron irradiation and Kr ion irradiation was utilized to explore the radiation resistance of nanocrystalline SiC (nc-SiC), SiC nanopowders, and microcrystalline SiC. Electron irradiation simplifies the experimental results, as only isolated Frenkel pairs are produced so any observed differences are simply due to point defect interactions with the original microstructure. Kr ion irradiation simulates neutron damage, as large radiation cascades with a high concentration of point defects are produced. Kr irradiation studies found that radiation resistance decreased with particle size reduction and grain refinement (comparing nc-SiC and microcrystalline SiC). This suggests that an interface-dependent amorphization mechanism is active in SiC, suggested to be interstitial starvation. However, under electron irradiation it was found that nc-SiC had improved radiation resistance compared to single crystal SiC. This was found to be due to several factors including increased sink density and strength and the presence of stacking faults. The stacking faults were found to improve radiation response by lowering critical energy barriers. The change in radiation response between the electron and Kr ion irradiations is hypothesized to be due to either the change in ion type (potential change in amorphization mechanism) or a change in temperature (at the higher temperatures of the Kr ion irradiation, critical energy barriers can be overcome without the assistance of stacking faults). The dependence of the radiation response of SiC on grain size is not as straight forward as initially presumed. The stacking faults present in many nc-SiC materials boost radiation resistance, but an increased number of interfaces may lead to a reduction in radiation response.

Computer Simulations to Study Diffraction Effects of Stacking Faults in Beta-SiC: II. Experimental Verification. 2; Experimental Verification

NASA Technical Reports Server (NTRS)

Pujar, Vijay V.; Cawley, James D.; Levine, S. (Technical Monitor)

2000-01-01

Earlier results from computer simulation studies suggest a correlation between the spatial distribution of stacking errors in the Beta-SiC structure and features observed in X-ray diffraction patterns of the material. Reported here are experimental results obtained from two types of nominally Beta-SiC specimens, which yield distinct XRD data. These samples were analyzed using high resolution transmission electron microscopy (HRTEM) and the stacking error distribution was directly determined. The HRTEM results compare well to those deduced by matching the XRD data with simulated spectra, confirming the hypothesis that the XRD data is indicative not only of the presence and density of stacking errors, but also that it can yield information regarding their distribution. In addition, the stacking error population in both specimens is related to their synthesis conditions and it appears that it is similar to the relation developed by others to explain the formation of the corresponding polytypes.

Structure of ice crystallized from supercooled water

PubMed Central

Malkin, Tamsin L.; Murray, Benjamin J.; Brukhno, Andrey V.; Anwar, Jamshed; Salzmann, Christoph G.

2012-01-01

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. At ambient conditions, ice is considered to exist in two crystalline forms: stable hexagonal ice and metastable cubic ice. Using X-ray diffraction data and Monte Carlo simulations, we show that ice that crystallizes homogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I. Stacking disorder and stacking faults have been reported earlier for metastable ice I, but only for ice crystallizing in mesopores and in samples recrystallized from high-pressure ice phases rather than in water droplets. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder. These findings highlight the need to reevaluate the physical and thermodynamic properties of this metastable ice as a function of the nature and extent of stacking disorder using well-characterized samples. PMID:22232652

Structure of ice crystallized from supercooled water.

PubMed

Malkin, Tamsin L; Murray, Benjamin J; Brukhno, Andrey V; Anwar, Jamshed; Salzmann, Christoph G

2012-01-24

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. At ambient conditions, ice is considered to exist in two crystalline forms: stable hexagonal ice and metastable cubic ice. Using X-ray diffraction data and Monte Carlo simulations, we show that ice that crystallizes homogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I. Stacking disorder and stacking faults have been reported earlier for metastable ice I, but only for ice crystallizing in mesopores and in samples recrystallized from high-pressure ice phases rather than in water droplets. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder. These findings highlight the need to reevaluate the physical and thermodynamic properties of this metastable ice as a function of the nature and extent of stacking disorder using well-characterized samples.

Seafloor Age-Stacking Reveals No Evidence for Milankovitch Cycle Influence on Abyssal Hills at Intermediate, Fast and Super-Fast Spreading Rates

NASA Astrophysics Data System (ADS)

Goff, J.; Zahirovic, S.; Müller, D.

2017-12-01

Recently published spectral analyses of seafloor bathymetry concluded that abyssal hills, highly linear ridges that are formed along seafloor spreading centers, exhibit periodicities that correspond to Milankovitch cycles - variations in Earth's orbit that affect climate on periods of 23, 41 and 100 thousand years. These studies argue that this correspondence could be explained by modulation of volcanic output at the mid-ocean ridge due to lithostatic pressure variations associated with rising and falling sea level. If true, then the implications are substantial: mapping the topography of the seafloor with sonar could be used as a way to investigate past climate change. This "Milankovitch cycle" hypothesis predicts that the rise and fall of abyssal hills will be correlated to crustal age, which can be tested by stacking, or averaging, bathymetry as a function of age; stacking will enhance any age-dependent signal while suppressing random components, such as fault-generated topography. We apply age-stacking to data flanking the Southeast Indian Ridge ( 3.6 cm/yr half rate), northern East Pacific Rise ( 5.4 cm/yr half rate) and southern East Pacific Rise ( 7.8 cm/yr half rate), where multibeam bathymetric coverage is extensive on the ridge flanks. At the greatest precision possible given magnetic anomaly data coverage, we have revised digital crustal age models in these regions with updated axis and magnetic anomaly traces. We also utilize known 2nd-order spatial statistical properties of abyssal hills to predict the variability of the age-stack under the null hypothesis that abyssal hills are entirely random with respect to crustal age; the age-stacked profile is significantly different from zero only if it exceeds this expected variability by a large margin. Our results indicate, however, that the null hypothesis satisfactorily explains the age-stacking results in all three regions of study, thus providing no support for the Milankovitch cycle hypothesis. The random nature of abyssal hills is consistent with a primarily faulted origin. .

A set-associative, fault-tolerant cache design

NASA Technical Reports Server (NTRS)

Lamet, Dan; Frenzel, James F.

1992-01-01

The design of a defect-tolerant control circuit for a set-associative cache memory is presented. The circuit maintains the stack ordering necessary for implementing the Least Recently Used (LRU) replacement algorithm. A discussion of programming techniques for bypassing defective blocks is included.

Dislocation creation and void nucleation in FCC ductile metals under tensile loading: A general microscopic picture

PubMed Central

Pang, Wei-Wei; Zhang, Ping; Zhang, Guang-Cai; Xu, Ai-Guo; Zhao, Xian-Geng

2014-01-01

Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies. PMID:25382029

Anatomy of anomalously thick sandstone units in the Brent Delta of the northern North Sea

NASA Astrophysics Data System (ADS)

Wei, Xiaojie; Steel, Ronald J.; Ravnås, Rodmar; Jiang, Zaixing; Olariu, Cornel; Ma, Yinsheng

2018-05-01

Some potentially attractive reservoirs, containing anomalously thick (10s to a few 100 m), cross-stratified sandstone, have been locally encountered within both the classic regressive (lower Brent) and the transgressive (upper Brent) segments of the Brent Delta. Three documented cases of these sandstone bodies are re-examined. They are internally dominated by simple or compound dunes, and typified by two types of deepening-upward succession, recording a retrogradational or transgressive shoreline history. Type I is expressed as a single estuarine succession changing upwards from erosive, coarse-grained channelized deposits into outer estuary tidal bar deposits. The estuary is underlain and overlain by deltaic deposits. Type II lacks significant basal river deposits but is composed by stacked mixed-energy and tide-dominated estuarine deposits. It is underlain by deltaic deposits and overlain by open marine sediments. Considering the structural evolution in the northern North Sea basin, we suggest (as did some earlier researchers) that these sandstone bodies were local, but sometimes broad transgressive estuaries, formed at any time during large-scale Brent Delta growth and decay. The estuary generation was likely triggered by fluvial incision coupled with active faulting, producing variable accommodation embayments, where tidal currents became focused and deposition became transgressive. The spatial variations of the interpreted estuary deposits were linked with variable, fault-generated accommodation. The relatively simple, lower Brent estuarine units were created by short-lived, fault activity in places, whereas the complex, stacked upper-Brent estuarine units were likely a result of more long-lived, punctuated fault-induced subsidence leading into the northern North Sea main rifting stage. The thick cross-stratified units potentially accumulated in the hangingwall of large bounding faults.

Effect of the fcc-hcp martensitic transition on the equation of state of solid krypton up to 140 GPa

NASA Astrophysics Data System (ADS)

Rosa, A. D.; Garbarino, G.; Briggs, R.; Svitlyk, V.; Morard, G.; Bouhifd, M. A.; Jacobs, J.; Irifune, T.; Mathon, O.; Pascarelli, S.

2018-03-01

Solid krypton (Kr) undergoes a pressure-induced martensitic phase transition from a face-centered cubic (fcc) to a hexagonal close-packed (hcp) structure. These two phases coexist in a very wide pressure domain inducing important modifications of the bulk properties of the resulting mixed phase system. Here, we report a detailed in situ x-ray diffraction and absorption study of the influence of the fcc-hcp phase transition on the compression behavior of solid krypton in an extended pressure domain up to 140 GPa. The onset of the hcp-fcc transformation was observed in this study at around 2.7 GPa and the coexistence of these two phases up to 140 GPa, the maximum investigated pressure. The appearance of the hcp phase is also evidenced by the pressure-induced broadening and splitting of the first peak in the XANES spectra. We demonstrate that the transition is driven by a continuous nucleation and intergrowth of nanometric hcp stacking faults that evolve in the fcc phase. These hcp stacking faults are unaffected by high-temperature annealing, suggesting that plastic deformation is not at their origin. The apparent small Gibbs free-energy differences between the two structures that decrease upon compression may explain the nucleation of hcp stacking faults and the large coexistence domain of fcc and hcp krypton. We observe a clear anomaly in the equation of state of the fcc solid at ˜20 GPa when the proportion of the hcp form reaches ˜20 % . We demonstrate that this anomaly is related to the difference in stiffness between the fcc and hcp phases and propose two distinct equation of states for the low and high-pressure regimes.

Seismic Modeling of the Alasehir Graben, Western Turkey

NASA Astrophysics Data System (ADS)

Gozde Okut, Nigar; Demirbag, Emin

2014-05-01

The purpose of this study is to develop a depth model to make synthetic seismic reflection sections, such as stacked and migrated sections with different velocity models. The study area is east-west trending Alasehir graben which is one of the most prominent structure in the western Anatolia, proved to have geothermal energy potential by researchers and exploration companies. Geological formations were taken from Alaşehir-1 borehole drilled by Turkish Petroleum Corporation (Çiftçi, 2007) and seismic interval velocities were taken from check-shots in the same borehole (Kolenoǧlu-Demircioǧlu, 2009). The most important structure is the master graben bounding fault (MGBF) in the southern margin of the Alasehir graben. Another main structure is the northern bounding fault called the antithetic fault of the MGBF with high angle normal fault characteristic. MGBF is a crucial contact between sedimentary cover and the metamorphic basement. From basement to the surface, five different stratigraphic units constitute graben fill . All the sedimentary units thicknesses get thinner from the southern margin to the northern margin of the Alasehir graben displaying roll-over geometry. A commercial seismic data software was used during modeling. In the first step, a 2D velocity/depth model was defined. Ray tracing was carried out with diffraction option to produce the reflection travel times. The reflection coefficients were calculated and wavelet shaping was carried out by means of band-pass filtering. Finally synthetic stacked section of the Alasehir graben was obtained. Then, migrated sections were generated with different velocity models. From interval velocities, average and RMS velocities were calculated for the formation entires to test how the general features of the geological model may change against different seismic models after the migration. Post-stack time migration method was used. Pseudo-velocity analysis was applied at selected CDP locations. In theory, seismic migration moves events to their correct spatial locations and collapse energy from diffractions back to their scattering points. This features of migration can be distinguished in the migrated sections. When interval velocities used, all the diffractions are removed and fault planes can be seen clearly. When average velocities used, MGBF plane extends to greater depths. Additionally, slope angles and locations of antithetic faults in the northern margin of the graben changes. When RMS velocities used, a migrated section was obtained for which to make an interpretation was quite hard, especially for the main structures along the northern margin and reflections related to formations.

Fault Diagnosis for Rotating Machinery Using Vibration Measurement Deep Statistical Feature Learning.

PubMed

Li, Chuan; Sánchez, René-Vinicio; Zurita, Grover; Cerrada, Mariela; Cabrera, Diego

2016-06-17

Fault diagnosis is important for the maintenance of rotating machinery. The detection of faults and fault patterns is a challenging part of machinery fault diagnosis. To tackle this problem, a model for deep statistical feature learning from vibration measurements of rotating machinery is presented in this paper. Vibration sensor signals collected from rotating mechanical systems are represented in the time, frequency, and time-frequency domains, each of which is then used to produce a statistical feature set. For learning statistical features, real-value Gaussian-Bernoulli restricted Boltzmann machines (GRBMs) are stacked to develop a Gaussian-Bernoulli deep Boltzmann machine (GDBM). The suggested approach is applied as a deep statistical feature learning tool for both gearbox and bearing systems. The fault classification performances in experiments using this approach are 95.17% for the gearbox, and 91.75% for the bearing system. The proposed approach is compared to such standard methods as a support vector machine, GRBM and a combination model. In experiments, the best fault classification rate was detected using the proposed model. The results show that deep learning with statistical feature extraction has an essential improvement potential for diagnosing rotating machinery faults.

Fault Diagnosis for Rotating Machinery Using Vibration Measurement Deep Statistical Feature Learning

PubMed Central

Li, Chuan; Sánchez, René-Vinicio; Zurita, Grover; Cerrada, Mariela; Cabrera, Diego

2016-01-01

Fault diagnosis is important for the maintenance of rotating machinery. The detection of faults and fault patterns is a challenging part of machinery fault diagnosis. To tackle this problem, a model for deep statistical feature learning from vibration measurements of rotating machinery is presented in this paper. Vibration sensor signals collected from rotating mechanical systems are represented in the time, frequency, and time-frequency domains, each of which is then used to produce a statistical feature set. For learning statistical features, real-value Gaussian-Bernoulli restricted Boltzmann machines (GRBMs) are stacked to develop a Gaussian-Bernoulli deep Boltzmann machine (GDBM). The suggested approach is applied as a deep statistical feature learning tool for both gearbox and bearing systems. The fault classification performances in experiments using this approach are 95.17% for the gearbox, and 91.75% for the bearing system. The proposed approach is compared to such standard methods as a support vector machine, GRBM and a combination model. In experiments, the best fault classification rate was detected using the proposed model. The results show that deep learning with statistical feature extraction has an essential improvement potential for diagnosing rotating machinery faults. PMID:27322273

The defective nature of ice Ic and its implications for atmospheric science

NASA Astrophysics Data System (ADS)

Kuhs, W. F.; Hansen, T. C.

2009-04-01

The possible atmospheric implication of ice Ic (cubic ice) has already been suggested some time ago in the context of snow crystal formation [1]. New findings from air-borne measurements in cirrus clouds and contrails have put ice Ic into the focus of interest to understand the so-called "supersaturation puzzle" [2,3,4,5]. Our recent microstructural work on ice Ic [6,7] appears to be highly relevant in this context. We have found that ice Ic is characterized by a complex stacking fault pattern, which changes as a function of temperature as well as time. Indeed, from our own [8] and other group's work [9] one knows that (in contrast to earlier believe) ice Ic can form up to temperatures at least as high as 240K - thus in the relevant range for cirrus clouds. We have good preliminary evidence that the "cubicity" (which can be related to stacking fault probabilities) as well as the particle size of ice Ic are the relevant parameters for this correlation. The "cubicity" of stacking faulty ice Ic (established by diffraction) correlates nicely with the increased supersaturation at decreasing temperatures observed in cirrus clouds and contrails, a fact, which may be considered as further evidence for the presence of ice Ic. Moreover, the stacking faults lead to kinks in the outer shapes of the minute ice Ic crystals as seen by cryo scanning electron microscopy (cryo-SEM); these defective sites are likely to play some role in heterogeneous reactions in the atmosphere. The cryo-SEM work suggests that stacking-faulty ice Ic has many more active centres for such reactions than the usually considered thermodynamically stable form, ice Ih. [1] T Kobayashi & T Kuroda (1987) Snow Crystals. In: Morphology of Crystals (ed. I Sunagawa), Terra Scientific Publishing, Tokyo, pp.649-743. [2] DM Murphy (2003) Dehydration in cold clouds is enhanced by a transition from from cubic to hexagonal ice. Geophys.Res.Lett.,30, 2230, doi:10.1029/2003GL018566. [3] RS Gao & 19 other authors (2004) Evidence that nitric acid increases relative humidity in low-temperature cirrus clouds. Science 303, 516-520. [4] T Peter, C Marcolli, P Spaichinger, T Corti, MC Baker & T Koop (2006) When dry air is too humid. Science 314, 1399-1402. [5] JE Shilling, MA Tolbert, OB Toon, EJ Jensen, BJ Murray & AK Bertram (2006) Measurements of the vapor pressure of cubic ice and their implications for atmospheric ice clouds. Geophys.Res.Lett. 33, 026671. [6] TC Hansen, MM Koza & WF Kuhs (2008) Formation and annealing of cubic ice: I Modelling of stacking faults. J.Phys.Cond.Matt. 20, 285104. [7] TC Hansen, MM Koza, P Lindner & WF Kuhs (2008) Formation and annealing of cubic ice: II. Kinetic study. J.Phys.Cond.Matt. 20, 285105. [8] WF Kuhs, G Genov, DK Staykova & AN Salamatin (2004) Ice perfection and the onset of anomalous preservation of gas hydrates. Phys.Chem.Chem.Phys. 6, 4917-4920. [9] BJ Murray, DA Knopf & AK Bertram (2005) The formation of cubic ice under conditions relevant to Earth's atmosphere. Nature 434, 292-205.

Creep deformation mechanism mapping in nickel base disk superalloys

DOE PAGES

Smith, Timothy M.; Unocic, Raymond R.; Deutchman, Hallee; ...

2016-05-10

We investigated the creep deformation mechanisms at intermediate temperature in ME3, a modern Ni-based disk superalloy, using diffraction contrast imaging. Both conventional transmission electron microscopy (TEM) and scanning TEM were utilised. Distinctly different deformation mechanisms become operative during creep at temperatures between 677-815 °C and at stresses ranging from 274 to 724 MPa. Both polycrystalline and single-crystal creep tests were conducted. The single-crystal tests provide new insight into grain orientation effects on creep response and deformation mechanisms. Creep at lower temperatures (≤760 °C) resulted in the thermally activated shearing modes such as microtwinning, stacking fault ribbons and isolated superlattice extrinsicmore » stacking faults. In contrast, these faulting modes occurred much less frequently during creep at 815 °C under lower applied stresses. Instead, the principal deformation mode was dislocation climb bypass. In addition to the difference in creep behaviour and creep deformation mechanisms as a function of stress and temperature, it was also observed that microstructural evolution occurs during creep at 760 °C and above, where the secondary coarsened and the tertiary precipitates dissolved. Based on this work, a creep deformation mechanism map is proposed, emphasising the influence of stress and temperature on the underlying creep mechanisms.« less

Type-II domains in ferroelectric gadolinium molybdate (in German)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bohm, J.; Kuersten, H.D.

Etching (001)-faces of gadolinium molybdate (GMO) reveals new kinds of domains. They are created by a translation, that leaves the spontaneous polarization and the transition parameter invariant. The translation vector is a part of a lattice vector, similar to stacking faults. (auth)

Design for Fe-high Mn alloy with an improved combination of strength and ductility.

PubMed

Lee, Seung-Joon; Han, Jeongho; Lee, Sukjin; Kang, Seok-Hyeon; Lee, Sang-Min; Lee, Young-Kook

2017-06-15

Recently, Fe-Mn twinning-induced plasticity steels with an austenite phase have been the course of great interest due to their excellent combination of tensile strength and ductility, which carbon steels have never been able to attain. Nevertheless, twinning-induced plasticity steels also exhibit a trade-off between strength and ductility, a longstanding dilemma for physical metallurgists, when fabricated based on the two alloy design parameters of stacking fault energy and grain size. Therefore, we investigated the tensile properties of three Fe-Mn austenitic steels with similar stacking fault energy and grain size, but different carbon concentrations. Surprisingly, when carbon concentration increased, both strength and ductility significantly improved. This indicates that the addition of carbon resulted in a proportionality between strength and ductility, instead of a trade-off between those characteristics. This new design parameter, C concentration, should be considered as a design parameter to endow Fe-Mn twinning-induced plasticity steel with a better combination of strength and ductility.

Two-Dimensional Ordering of Solute Nanoclusters at a Close-Packed Stacking Fault: Modeling and Experimental Analysis

PubMed Central

Kimizuka, Hajime; Kurokawa, Shu; Yamaguchi, Akihiro; Sakai, Akira; Ogata, Shigenobu

2014-01-01

Predicting the equilibrium ordered structures at internal interfaces, especially in the case of nanometer-scale chemical heterogeneities, is an ongoing challenge in materials science. In this study, we established an ab-initio coarse-grained modeling technique for describing the phase-like behavior of a close-packed stacking-fault-type interface containing solute nanoclusters, which undergo a two-dimensional disorder-order transition, depending on the temperature and composition. Notably, this approach can predict the two-dimensional medium-range ordering in the nanocluster arrays realized in Mg-based alloys, in a manner consistent with scanning tunneling microscopy-based measurements. We predicted that the repulsively interacting solute-cluster system undergoes a continuous evolution into a highly ordered densely packed morphology while maintaining a high degree of six-fold orientational order, which is attributable mainly to an entropic effect. The uncovered interaction-dependent ordering properties may be useful for the design of nanostructured materials utilizing the self-organization of two-dimensional nanocluster arrays in the close-packed interfaces. PMID:25471232

Influence of antisite defects and stacking faults on the magnetocrystalline anisotropy of FePt

NASA Astrophysics Data System (ADS)

Wolloch, M.; Suess, D.; Mohn, P.

2017-09-01

We present density functional theory (DFT) calculations of the magnetic anisotropy energy (MAE) of FePt, which is of great interest for magnetic recording applications. Our data, and the majority of previously calculated results for perfectly ordered crystals, predict a MAE of ˜3.0 meV per formula unit, which is significantly larger than experimentally measured values. Analyzing the effects of disorder by introducing stacking faults (SFs) and antisite defects (ASDs) in varying concentrations we are able to reconcile calculations with experimental data and show that even a low concentration of ASDs are able to reduce the MAE of FePt considerably. Investigating the effect of exact exchange and electron correlation within the adiabatic-connection dissipation fluctuation theorem in the random phase approximation (ACDFT-RPA) reveals a significantly smaller influence on the MAE. Thus the effect of disorder, and more specifically ASDs, is the crucial factor in explaining the deviation of common DFT calculations of FePt to experimental measurements.

Direct observation of multiple rotational stacking faults coexisting in freestanding bilayer MoS2.

PubMed

Li, Zuocheng; Yan, Xingxu; Tang, Zhenkun; Huo, Ziyang; Li, Guoliang; Jiao, Liying; Liu, Li-Min; Zhang, Miao; Luo, Jun; Zhu, Jing

2017-08-16

Electronic properties of two-dimensional (2D) MoS 2 semiconductors can be modulated by introducing specific defects. One important type of defect in 2D layered materials is known as rotational stacking fault (RSF), but the coexistence of multiple RSFs with different rotational angles was not directly observed in freestanding 2D MoS 2 before. In this report, we demonstrate the coexistence of three RSFs with three different rotational angles in a freestanding bilayer MoS 2 sheet as directly observed using an aberration-corrected transmission electron microscope (TEM). Our analyses show that these RSFs originate from cracks and dislocations within the bilayer MoS 2 . First-principles calculations indicate that RSFs with different rotational angles change the electronic structures of bilayer MoS 2 and produce two new symmetries in their bandgaps and offset crystal momentums. Therefore, employing RSFs and their coexistence is a promising route in defect engineering of MoS 2 to fabricate suitable devices for electronics, optoelectronics, and energy conversion.

Plasticity mechanisms in HfN at elevated and room temperature.

PubMed

Vinson, Katherine; Yu, Xiao-Xiang; De Leon, Nicholas; Weinberger, Christopher R; Thompson, Gregory B

2016-10-06

HfN specimens deformed via four-point bend tests at room temperature and at 2300 °C (~0.7 T m ) showed increased plasticity response with temperature. Dynamic diffraction via transmission electron microscopy (TEM) revealed ⟨110⟩{111} as the primary slip system in both temperature regimes and ⟨110⟩{110} to be a secondary slip system activated at elevated temperature. Dislocation line lengths changed from a primarily linear to a curved morphology with increasing temperature suggestive of increased dislocation mobility being responsible for the brittle to ductile temperature transition. First principle generalized stacking fault energy calculations revealed an intrinsic stacking fault (ISF) along ⟨112⟩{111}, which is the partial dislocation direction for slip on these close packed planes. Though B1 structures, such as NaCl and HfC predominately slip on ⟨110⟩{110}, the ISF here is believed to facilitate slip on the {111} planes for this B1 HfN phase.

The effects of intrinsic properties and defect structures on the indentation size effect in metals

NASA Astrophysics Data System (ADS)

Maughan, Michael R.; Leonard, Ariel A.; Stauffer, Douglas D.; Bahr, David F.

2017-08-01

The indentation size effect has been linked to the generation of geometrically necessary dislocations that may be impacted by intrinsic materials properties, such as stacking fault energy, and extrinsic defects, such as statistically stored dislocations. Nanoindentation was carried out at room temperature and elevated temperatures on four different metals in a variety of microstructural conditions. A size effect parameter was determined for each material set combining the effects of temperature and existing dislocation structure. Extrinsic defects, particularly dislocation density, dominate the size effect parameter over those due to intrinsic properties such as stacking fault energy. A multi-mechanism description using a series of mechanisms, rather than a single mechanism, is presented as a phenomenological explanation for the observed size effect in these materials. In this description, the size effect begins with a volume scale dominated by sparse sources, next is controlled by the ability of dislocations to cross-slip and multiply, and then finally at larger length scales work hardening and recovery dominate the effect.

Effect of interstitial and substitution alloying elements on the intrinsic stacking fault energy of nanocrystalline fcc-iron by atomistic simulation study

NASA Astrophysics Data System (ADS)

Mohammadzadeh, Mina; Mohammadzadeh, Roghayeh

2017-11-01

The stacking fault energy (SFE) is an important parameter in the deformation mechanism of face centered cubic (fcc) iron-based alloy. In this study, the effect of interstitial (C and N) and substitution (Nb and Ti) alloying elements on the intrinsic SFE (ISFE) of nanocrystalline iron were investigated via molecular dynamics (MD) simulation. The modified embedded atom method (MEAM) inter-atomic potential was used in the MD simulations. The results demonstrate a strong dependence of ISFE with addition of interstitial alloying elements but only a mild increase in ISFE with addition of substitution alloying elements in the composition range of 0 < {CNb, CTi} < 3 (at%). Moreover, it is shown that alloying of fcc iron with N decreases ISFE, whereas it increases significantly by addition of carbon element [0 < {CC, CN} < 3.5 (at%)]. The simulation method employed in this work shows reasonable agreement with some published experimental/calculated data.

Creep mechanisms of a new Ni-Co-base disc superalloy at an intermediate temperature.

PubMed

Yuan, Y; Gu, Y F; Zhong, Z H; Osada, T; Cui, C Y; Tetsui, T; Yokokawa, T; Harada, H

2012-10-01

The microstructures of a new Ni-Co-base disc superalloy, TMW-4M3, before and after the creep test at 725 °C/630 MPa have been systematically investigated by transmission electron microscopy (TEM). The crept microstructures were marked as three different deformation stages (I, II and III) corresponding to the gradually increased strain. At stage I, stacking fault (SF) shearing was the main deformation mechanism. The SF was extrinsic and lay on {111} plane. However, deformation microtwinning became the dominant mode at stage II and III. The average spacing of deformation twins decreased from 109 ± 15 nm at stage II to 76 ± 12 nm at stage III, whereas the twin thickness did not change significantly. The influence of stacking fault energy (SFE) of γ matrix on the deformation mechanism is discussed. It is suggested that lower SFE in TMW-4M3 is partly responsible for the enhanced creep resistance. © 2012 The Authors Journal of Microscopy © 2012 Royal Microscopical Society.

Phase transformation strengthening of high-temperature superalloys

PubMed Central

Smith, T. M.; Esser, B. D.; Antolin, N.; Carlsson, A.; Williams, R. E. A.; Wessman, A.; Hanlon, T.; Fraser, H. L.; Windl, W.; McComb, D. W.; Mills, M. J.

2016-01-01

Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing increased engine efficiency and reduced CO2 emissions. Here we introduce a new ‘phase-transformation strengthening' mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ′ to η phase along stacking faults in γ′ precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties. PMID:27874007

Characterization of high-quality kerfless epitaxial silicon for solar cells: Defect sources and impact on minority-carrier lifetime

NASA Astrophysics Data System (ADS)

Kivambe, Maulid M.; Powell, Douglas M.; Castellanos, Sergio; Jensen, Mallory Ann; Morishige, Ashley E.; Lai, Barry; Hao, Ruiying; Ravi, T. S.; Buonassisi, Tonio

2018-02-01

We investigate the types and origins of structural defects in thin (<100 μm) kerfless epitaxial single crystal silicon grown on top of reorganized porous silicon layers. Although the structural defect density is low (has average defect density < 104 cm-2), localized areas with a defect density > 105 cm-2 are observed. Cross-sectional and systematic plan-view defect etching and microscopy reveals that the majority of stacking faults and dislocations originate at the interface between the porous silicon layer and the epitaxial wafer. Localised dislocation clusters are observed in regions of collapsed/deformed porous silicon and at decorated stacking faults. In localized regions of high extended defect density, increased minority-carrier recombination activity is observed. Evidence for impurity segregation to the extended defects (internal gettering), which is known to exacerbate carrier recombination is demonstrated. The impact of the defects on material performance and substrate re-use is also discussed.

Fallon, Nevada FORGE Seismic Reflection Profiles

DOE Data Explorer

Blankenship, Doug; Faulds, James; Queen, John; Fortuna, Mark

2018-02-01

Newly reprocessed Naval Air Station Fallon (1994) seismic lines: pre-stack depth migrations, with interpretations to support the Fallon FORGE (Phase 2B) 3D Geologic model. Data along seven profiles (>100 km of total profile length) through and adjacent to the Fallon site were re-processed. The most up-to-date, industry-tested seismic processing techniques were utilized to improve the signal strength and coherency in the sedimentary, volcanic, and Mesozoic crystalline basement sections, in conjunction with fault diffractions in order to improve the identification and definition of faults within the study area.

Fault zone structure and inferences on past activities of the active Shanchiao Fault in the Taipei metropolis, northern Taiwan

NASA Astrophysics Data System (ADS)

Chen, C.; Lee, J.; Chan, Y.; Lu, C.

2010-12-01

The Taipei Metropolis, home to around 10 million people, is subject to seismic hazard originated from not only distant faults or sources scattered throughout the Taiwan region, but also active fault lain directly underneath. Northern Taiwan including the Taipei region is currently affected by post-orogenic (Penglai arc-continent collision) processes related to backarc extension of the Ryukyu subduction system. The Shanchiao Fault, an active normal fault outcropping along the western boundary of the Taipei Basin and dipping to the east, is investigated here for its subsurface structure and activities. Boreholes records in the central portion of the fault were analyzed to document the stacking of post- Last Glacial Maximum growth sediments, and a tulip flower structure is illuminated with averaged vertical slip rate of about 3 mm/yr. Similar fault zone architecture and post-LGM tectonic subsidence rate is also found in the northern portion of the fault. A correlation between geomorphology and structural geology in the Shanchiao Fault zone demonstrates an array of subtle geomorphic scarps corresponds to the branch fault while the surface trace of the main fault seems to be completely erased by erosion and sedimentation. Such constraints and knowledge are crucial in earthquake hazard evaluation and mitigation in the Taipei Metropolis, and in understanding the kinematics of transtensional tectonics in northern Taiwan. Schematic 3D diagram of the fault zone in the central portion of the Shanchiao Fault, displaying regional subsurface geology and its relation to topographic features.

Structural Characterization of Lateral-grown 6H-SiC am-plane Seed Crystals by Hot Wall CVD Epitaxy

NASA Technical Reports Server (NTRS)

Goue, Ouloide Yannick; Raghothamachar, Balaji; Dudley, Michael; Trunek, Andrew J.; Neudeck, Philip G.; Woodworth, Andrew A.; Spry, David J.

2014-01-01

The performance of commercially available silicon carbide (SiC) power devices is limited due to inherently high density of screw dislocations (SD), which are necessary for maintaining polytype during boule growth and commercially viable growth rates. The NASA Glenn Research Center (GRC) has recently proposed a new bulk growth process based on axial fiber growth (parallel to the c-axis) followed by lateral expansion (perpendicular to the c-axis) for producing multi-faceted m-plane SiC boules that can potentially produce wafers with as few as one SD per wafer. In order to implement this novel growth technique, the lateral homoepitaxial growth expansion of a SiC fiber without introducing a significant number of additional defects is critical. Lateral expansion is being investigated by hot wall chemical vapor deposition (HWCVD) growth of 6H-SiC am-plane seed crystals (0.8mm x 0.5mm x 15mm) designed to replicate axially grown SiC single crystal fibers. The post-growth crystals exhibit hexagonal morphology with approximately 1500 m (1.5 mm) of total lateral expansion. Preliminary analysis by synchrotron white beam x-ray topography (SWBXT) confirms that the growth was homoepitaxial, matching the polytype of the respective underlying region of the seed crystal. Axial and transverse sections from the as grown crystal samples were characterized in detail by a combination of SWBXT, transmission electron microscopy (TEM) and Raman spectroscopy to map defect types and distribution. X-ray diffraction analysis indicates the seed crystal contained stacking disorders and this appears to have been reproduced in the lateral growth sections. Analysis of the relative intensity for folded transverse acoustic (FTA) and optical (FTO) modes on the Raman spectra indicate the existence of stacking faults. Further, the density of stacking faults is higher in the seed than in the grown crystal. Bundles of dislocations are observed propagating from the seed in m-axis lateral directions. Contrast extinction analysis of these dislocation lines reveals they are edge type basal plane dislocations that track the growth direction. Polytype phase transition and stacking faults were observed by high-resolution TEM (HRTEM), in agreement with SWBXT and Raman scattering.

Imaging Subsurface Structure of Central Zagros Zone/Iran Using Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Vahidravesh, Shaghayegh; Pakzad, Mehrdad, ,, Dr.; Hatami, Mohammad Reza, ,, Dr.

2017-04-01

The Central Zagros zone, of west Iran & east Iraq, is surrounded by many active faults (including Main Zagros Reversed Fault, Main Recent Fault, High Zagros Fault, Zagros Fold, & Thrust Belt). Recent studies show that cross-correlation of a long-term ambient seismic noise data recorded in station-pair, includes important information regarding empirical Green's functions (EGFs) between stations. Hence, ambient seismic noise carries valuable information of the wave propagation path (which can be extracted). The 2D model of surface waves (Rayleigh & Love) velocities for the studied area is obtained by seismic ambient noise tomography (ANT) method. Throughout this research, we use continuous records of all three vertical, radial, and tangential components (obtained by rotation) recorded by IRSC (Iranian Seismological Center) and IIEES (International Institute of Earthquake Engineering) networks for this area of interest. The IRSC & IIEES networks are equipped by SS-1 kinematics and Guralp CMG-3T sensors respectively. Data of 20 stations were used for 12 months from 2014/Nov. to 2015/Nov. The performed data processing is similar to the one, put into words in detail by Bensen et al. (2007) including the processed daily base data. Mean, trend, and instrument response were removed and the data were decimated to 5 sps (sample per second) to reduce the amount of storage space and computational time required. We then applied merge to handle data gaps. One-bit time-domain normalization was also applied to suppress the influence of instrument irregularities and earthquake signals followed by spectral (frequency-domain) normalization between 0.05-0.2 Hz (period 5-20 sec). After cross-correlation (processing step), we perform rms stacking (new approach of stacking) to stack many cross-correlation functions based on the highest energy in a time interval which we accordingly anticipate to receive Rayleigh & Love waves fundamental modes. To evaluate quality of the stacking process stability quantitatively, we calculate signal-to-noise ratio (SNR), defined as a ratio of the peak amplitude within a time window to the root-mean-square of noise trailing the signal arrival window (Bensen et al., 2007), for each cross-correlation. The cross-correlated time-series is equivalent to the Green's functions between pairs of receivers. We then apply multiple phase-matched filter method of Herrmann (2005) to measure the correct group velocity dispersion of the interferometric surface waves. Eventually, we apply fast marching surface wave tomography (FMST), the iterative nonlinear inversion package developed by Rawlinson, 2005, to extract the velocity model of shallow structure in Central Zagros zone /Iran.

Growth of Fault-Cored Anticlines by Flexural Slip Folding: Analysis by Boundary Element Modeling

NASA Astrophysics Data System (ADS)

Johnson, Kaj M.

2018-03-01

Fault-related folds develop due to a combination of slip on the associated fault and distributed deformation off the fault. Under conditions that are sufficient for sedimentary layering to act as a stack of mechanical layers with contact slip, buckling can dramatically amplify the folding process. We develop boundary element models of fault-related folding of viscoelastic layers embedded with a reverse fault to examine the influence of such layering on fold growth. The strength of bedding contacts, the thickness and stiffness of layering, and fault geometry all contribute significantly to the resulting fold form. Frictional contact strength between layers controls the degree of localization of slip within fold limbs; high contact friction in relatively thin bedding tends to localize bedding slip within narrow kink bands on fold limbs, and low contact friction tends to produce widespread bedding slip and concentric fold form. Straight ramp faults tend to produce symmetric folds, whereas listric faults tend to produce asymmetric folds with short forelimbs and longer backlimbs. Fault-related buckle folds grow exponentially with time under steady loading rates. At early stages of folding, fold growth is largely attributed to slip on the fault, but as the fold increases amplitude, a larger portion of the fold growth is attributed to distributed slip across bedding contacts on the limbs of the fold. An important implication for geologic and earthquake studies is that not all surface deformation associated with blind reverse faults may be attributed to slip on the fault during earthquakes.

Intelligent fault diagnosis of rolling bearings using an improved deep recurrent neural network

NASA Astrophysics Data System (ADS)

Jiang, Hongkai; Li, Xingqiu; Shao, Haidong; Zhao, Ke

2018-06-01

Traditional intelligent fault diagnosis methods for rolling bearings heavily depend on manual feature extraction and feature selection. For this purpose, an intelligent deep learning method, named the improved deep recurrent neural network (DRNN), is proposed in this paper. Firstly, frequency spectrum sequences are used as inputs to reduce the input size and ensure good robustness. Secondly, DRNN is constructed by the stacks of the recurrent hidden layer to automatically extract the features from the input spectrum sequences. Thirdly, an adaptive learning rate is adopted to improve the training performance of the constructed DRNN. The proposed method is verified with experimental rolling bearing data, and the results confirm that the proposed method is more effective than traditional intelligent fault diagnosis methods.

Non-Mutually Exclusive Deep Neural Network Classifier for Combined Modes of Bearing Fault Diagnosis.

PubMed

Duong, Bach Phi; Kim, Jong-Myon

2018-04-07

The simultaneous occurrence of various types of defects in bearings makes their diagnosis more challenging owing to the resultant complexity of the constituent parts of the acoustic emission (AE) signals. To address this issue, a new approach is proposed in this paper for the detection of multiple combined faults in bearings. The proposed methodology uses a deep neural network (DNN) architecture to effectively diagnose the combined defects. The DNN structure is based on the stacked denoising autoencoder non-mutually exclusive classifier (NMEC) method for combined modes. The NMEC-DNN is trained using data for a single fault and it classifies both single faults and multiple combined faults. The results of experiments conducted on AE data collected through an experimental test-bed demonstrate that the DNN achieves good classification performance with a maximum accuracy of 95%. The proposed method is compared with a multi-class classifier based on support vector machines (SVMs). The NMEC-DNN yields better diagnostic performance in comparison to the multi-class classifier based on SVM. The NMEC-DNN reduces the number of necessary data collections and improves the bearing fault diagnosis performance.

Quantification of Honeycomb Number-Type Stacking Faults: Application to Na 3Ni 2BiO 6 Cathodes for Na-Ion Batteries

DOE PAGES

Liu, Jue; Yin, Liang; Wu, Lijun; ...

2016-08-17

Here, ordered and disordered samples of honeycomb-lattice Na 3Ni 2BiO 6 were investigated as cathodes for Na-ion batteries, and it was determined that the ordered sample exhibits better electrochemical performance, with a specific capacity of 104 mA h/g delivered at plateaus of 3.5 and 3.2 V (vs Na +/Na) with minimal capacity fade during extended cycling. Advanced imaging and diffraction investigations showed that the primary difference between the ordered and disordered samples is the amount of number-type stacking faults associated with the three possible centering choices for each honeycomb layer. A labeling scheme for assigning the number position of honeycombmore » layers is described, and it is shown that the translational shift vectors between layers provide the simplest method for classifying different repeat patterns. We demonstrate that the number position of honeycomb layers can be directly determined in high-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) imaging studies. By the use of fault models derived from STEM studies, it is shown that both the sharp, symmetric subcell peaks and the broad, asymmetric superstructure peaks in powder diffraction patterns can be quantitatively modeled. About 20% of the layers in the ordered monoclinic sample are faulted in a nonrandom manner, while the disordered sample stacking is not fully random but instead contains about 4% monoclinic order. Furthermore, it is shown that the ordered sample has a series of higher-order superstructure peaks associated with 6-, 9-, 12-, and 15-layer periods whose existence is transiently driven by the presence of long-range strain that is an inherent consequence of the synthesis mechanism revealed through the present diffraction and imaging studies. This strain is closely associated with a monoclinic shear that can be directly calculated from cell lattice parameters and is strongly correlated with the degree of ordering in the samples. The present results are broadly applicable to other honeycomb-lattice systems, including Li 2MnO 3 and related Li-excess cathode compositions.« less

Quantification of Honeycomb Number-Type Stacking Faults: Application to Na 3Ni 2BiO 6 Cathodes for Na-Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jue; Yin, Liang; Wu, Lijun

Here, ordered and disordered samples of honeycomb-lattice Na 3Ni 2BiO 6 were investigated as cathodes for Na-ion batteries, and it was determined that the ordered sample exhibits better electrochemical performance, with a specific capacity of 104 mA h/g delivered at plateaus of 3.5 and 3.2 V (vs Na +/Na) with minimal capacity fade during extended cycling. Advanced imaging and diffraction investigations showed that the primary difference between the ordered and disordered samples is the amount of number-type stacking faults associated with the three possible centering choices for each honeycomb layer. A labeling scheme for assigning the number position of honeycombmore » layers is described, and it is shown that the translational shift vectors between layers provide the simplest method for classifying different repeat patterns. We demonstrate that the number position of honeycomb layers can be directly determined in high-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) imaging studies. By the use of fault models derived from STEM studies, it is shown that both the sharp, symmetric subcell peaks and the broad, asymmetric superstructure peaks in powder diffraction patterns can be quantitatively modeled. About 20% of the layers in the ordered monoclinic sample are faulted in a nonrandom manner, while the disordered sample stacking is not fully random but instead contains about 4% monoclinic order. Furthermore, it is shown that the ordered sample has a series of higher-order superstructure peaks associated with 6-, 9-, 12-, and 15-layer periods whose existence is transiently driven by the presence of long-range strain that is an inherent consequence of the synthesis mechanism revealed through the present diffraction and imaging studies. This strain is closely associated with a monoclinic shear that can be directly calculated from cell lattice parameters and is strongly correlated with the degree of ordering in the samples. The present results are broadly applicable to other honeycomb-lattice systems, including Li 2MnO 3 and related Li-excess cathode compositions.« less

Multimillion-Year Evolution of a Sublacustrine Fan System: Source-to-Sink History of the South Rukuru and Ruhuhu River Drainages, Lake Malawi (Nyasa) Rift, East Africa

NASA Astrophysics Data System (ADS)

Scholz, C. A.; Shillington, D. J.; McCartney, T.

2017-12-01

The development of long-lived continental rifts can be markedly influenced by surface processes, including sediment input and footwall erosion. This occurs through modifying crustal thickness and loading, as well as by influencing behaviors of individual faults. Here we report on the evolution of a long-lived system of sublacustrine fans in the Central Basin of the Lake Malawi (Nyasa) rift, East Africa. An extensive suite of crustal-scale seismic reflection data was acquired in 2015 as part of the SEGMeNT project, which resulted superb images of the syn-rift section. These data are augmented by legacy single-channel high resolution reflection data that provide detailed information on facies geometries and stacking architecture of the deep-water fan systems. The ages and lithologic character of the stratal surfaces observed in the reflection seismic data are constrained by ties to the 2005 scientific drill cores acquired during the Lake Malawi Scientific Drilling Project. The South Rukuru River is an eastward flowing regional drainage (11,900 km2) that enters Lake Malawi through an incision in the western border fault of the rift's Central Basin. The Rukuru River drainage (17,230 km2) enters the eastern side of the lake at an accommodation zone margin between the North and Central Basins. Both are antecedent drainages that prior to rifting may have delivered sediments to the Indian Ocean continental margin. Both systems now deliver sediment to a highly confined and focused depocenter in the Central Basin. The complex interplay of extension, mainly on the border fault systems, and high-frequency and high-amplitude lake levels shifts, has led to unique coarse sediment facies stacking architectures, with vertical stacking controlled by hydroclimate, and lateral positioning localized by fault behavior. Focused deep-water (700 m) deposition has resulted in overpressure within the sedimentary section in the localized depocenter, producing dramatic mud diapirs. Long-lived channel-levee systems observed in the seismic data demonstrate that both drainages systems have been operative for the past several million years.

A Multi-Scale Simulation Approach to Deformation Mechanism Prediction in Superalloys

NASA Astrophysics Data System (ADS)

Lv, Duchao

High-temperature alloys in general and superalloys in particular are crucial for manufacturing gas turbines for aircraft and power generators. Among the superalloy family, the Ni-based superalloys are the most frequently used due to their excellent strength-to-weight ratio. Their strength results from their ordered intermetallic phases (precipitates), which are relatively stable at elevated temperatures. The major deformation processes of Ni-based and Co-based superalloys are precipitate shearing and Orowan looping. The key to developing physics-based models of creep and yield strength of aircraft engine components is to understand the two deformation mechanisms mentioned above. Recent discoveries of novel dislocation structures and stacking-fault configurations in deformed superalloys implied that the traditional anti-phase boundary (APB)-type, yield-strength model is unable to explain the shearing mechanisms of the gamma" phase in 718-type (Ni-based) superalloys. While the onset of plastic deformation is still related to the formation of highly-energetic stacking faults, the physics-based yield strength prediction requires that the novel dislocation structure and the correct intermediate stacking-fault be considered in the mathematical expressions. In order to obtain the dependence of deformation mechanisms on a materials chemical composition, the relationship between the generalized-stacking-fault (GSF) surface and its chemical composition must be understood. For some deformation scenarios in which one precipitate phase and one mechanism are dominant (e.g., Orowan looping), their use in industry requires a fast-acting model that can capture the features of the deformation (e.g., the volume fraction of the sheared matrix) and reduces lost time by not repeating fine-scale simulations. The objective of this thesis was to develop a multi-scale, physics-based simulation approach that can be used to optimize existing superalloys and to accelerate the design of new alloys. In particular, density functional theory (DFT) was used to calculate the GSF surface of the gamma" phase in the 718-type superalloy. In addition, the deformation pathways inside the gamma" particles were identified, and the dislocation emissions were predicted. Many novel dislocation sources inside the gamma" particles were simulated by using the phase-field method, which predicts and explains the dislocation configurations that appear during the deformation process or that are left as debris. Moreover, based on the stacking-fault energies in the available literature, we calculated the dependence of the chemical composition of the GSF surface of the gamma' phase in Co-based, CoNi-based, and Ni-based superalloys. The phase-field simulation, which used the GSF surfaces as inputs, explained the relationship between the shearing mechanism and chemical composition. Thus, two fast-acting models were developed by using the modified analytic expressions of particle shearing and Orowan looping. These expressions were calibrated by using the GSF surface and the simulation of the phase-field, and they were used to predict the yield strength of 718-type superalloy and the localized creep features of the gamma/gamma' microstructure. The fast-acting yield models were trained by the available experimental results. Since the chemical re-ordering and the segregation effects are not considered in this work, the fast-acting models are designed to the predict mechanical behaviors at the room temperature and the intermediate temperature.

Microstructural study of Mg-doped p-type GaN: Correlation between high-resolution electron microscopy and Raman spectroscopy

NASA Astrophysics Data System (ADS)

Tsen, S.-C. Y.; Smith, David J.; Tsen, K. T.; Kim, W.; Morkoç, H.

1997-12-01

A series of Mg-doped GaN films (˜1-1.3 μm) grown by reactive molecular beam epitaxy at substrate temperatures of 750 and 800 °C has been studied by high-resolution electron microscopy (HREM) and Raman spectroscopy. Stacking defects parallel to the substrate surface were observed in samples grown on sapphire substrates at 750 °C with AlN buffer layers (60-70 nm) at low Mg concentration. A transition region with mixed zinc-blende cubic (c) and wurtzite hexagonal (h) phases having the relative orientations of (111)c//(00.1)h and (11¯0)c//(10.0)h was observed for increased Mg concentration. The top surfaces of highly doped samples were rough and assumed a completely zinc-blende phase with some inclined stacking faults. Samples grown with a Mg cell temperature of 350 °C and high doping levels were highly disordered with many small crystals having inclined stacking faults, microtwins, and defective wurtzite and zinc-blende phases. Correlation between HREM and Raman scattering results points towards the presence of compressive lattice distortion along the growth direction which might be attributable to structural defects. The films grown at 800 °C had better quality with less observable defects and less yellow luminescence than samples grown at 750 °C.

Thermoelectric Properties and Microstructure of Ca3 Co 4 O 9 thin films on SrTiO3 and Al2 O 3 Substrates

NASA Astrophysics Data System (ADS)

Paulauskas, T.; Qiao, Q.; Gulec, A.; Klie, R. F.; Ozdemir, M.; Boyraz, C.; Mazumdar, D.; Gupta, A.

2011-03-01

Ca 3 Co 4 O9 (CCO), a misfit layered structure exhibiting large Seebeck coefficient at temperatures up to 1000K has attracted increasing attention as a novel high-temperature thermoelectric material. In this work, we investigate CCO thin films grown on SrTi O3 (001) and Al 2 O3 (0001) using pulsed laser deposition. Quality of the thin films was examined using high-resolution transmission electron microscopy and thermoelectric transport measurements. HRTEM images show incommensurate stacks of Cd I2 -type Co O2 layer alternating with rock-salt-type Ca 2 Co O3 layer along the c-axis. Perovskite buffer layer about 10nm thick was found present between CCO and SrTi O3 accompanied by higher density of stacking faults. The CCO grown on Al 2 O3 exhibited numerous misoriented grains and presence of Ca x Co O2 phase. Seebeck coefficient measurements yield an improvement for both samples compared to the bulk value. We suggest that thermoelectric properties of CCO increase due to additional phonon scattering at the stacking faults as well as at the film surfaces/interfaces. This research was supported by the US Army Research Office (W911NF-10-1-0147) and the Sivananthan Undergraduate Research Fellowship.

Model-based development of a fault signature matrix to improve solid oxide fuel cell systems on-site diagnosis

NASA Astrophysics Data System (ADS)

Polverino, Pierpaolo; Pianese, Cesare; Sorrentino, Marco; Marra, Dario

2015-04-01

The paper focuses on the design of a procedure for the development of an on-field diagnostic algorithm for solid oxide fuel cell (SOFC) systems. The diagnosis design phase relies on an in-deep analysis of the mutual interactions among all system components by exploiting the physical knowledge of the SOFC system as a whole. This phase consists of the Fault Tree Analysis (FTA), which identifies the correlations among possible faults and their corresponding symptoms at system components level. The main outcome of the FTA is an inferential isolation tool (Fault Signature Matrix - FSM), which univocally links the faults to the symptoms detected during the system monitoring. In this work the FTA is considered as a starting point to develop an improved FSM. Making use of a model-based investigation, a fault-to-symptoms dependency study is performed. To this purpose a dynamic model, previously developed by the authors, is exploited to simulate the system under faulty conditions. Five faults are simulated, one for the stack and four occurring at BOP level. Moreover, the robustness of the FSM design is increased by exploiting symptom thresholds defined for the investigation of the quantitative effects of the simulated faults on the affected variables.

A Hybrid Feature Model and Deep-Learning-Based Bearing Fault Diagnosis

PubMed Central

Sohaib, Muhammad; Kim, Cheol-Hong; Kim, Jong-Myon

2017-01-01

Bearing fault diagnosis is imperative for the maintenance, reliability, and durability of rotary machines. It can reduce economical losses by eliminating unexpected downtime in industry due to failure of rotary machines. Though widely investigated in the past couple of decades, continued advancement is still desirable to improve upon existing fault diagnosis techniques. Vibration acceleration signals collected from machine bearings exhibit nonstationary behavior due to variable working conditions and multiple fault severities. In the current work, a two-layered bearing fault diagnosis scheme is proposed for the identification of fault pattern and crack size for a given fault type. A hybrid feature pool is used in combination with sparse stacked autoencoder (SAE)-based deep neural networks (DNNs) to perform effective diagnosis of bearing faults of multiple severities. The hybrid feature pool can extract more discriminating information from the raw vibration signals, to overcome the nonstationary behavior of the signals caused by multiple crack sizes. More discriminating information helps the subsequent classifier to effectively classify data into the respective classes. The results indicate that the proposed scheme provides satisfactory performance in diagnosing bearing defects of multiple severities. Moreover, the results also demonstrate that the proposed model outperforms other state-of-the-art algorithms, i.e., support vector machines (SVMs) and backpropagation neural networks (BPNNs). PMID:29232908

Investigation of the Microstructure Evolution in a Fe-17Mn-1.5Al-0.3C Steel via In Situ Synchrotron X-ray Diffraction during a Tensile Test

PubMed Central

Song, Wenwen; Bleck, Wolfgang

2017-01-01

The quantitative characterization of the microstructure evolution in high-Mn steel during deformation is of great importance to understanding its strain-hardening behavior. In the current study, in situ high-energy synchrotron X-ray diffraction was employed to characterize the microstructure evolution in a Fe-17Mn-1.5Al-0.3C steel during a tensile test. The microstructure at different engineering strain levels—in terms of ε-martensite and α’-martensite volume fractions, the stacking fault probability, and the twin fault probability—was analyzed by the Rietveld refinement method. The Fe-17Mn-1.5Al-0.3C steel exhibits a high ultimate tensile strength with a superior uniform elongation and a high strain-hardening rate. The remaining high strain-hardening rate at the strain level about 0.025 to 0.35 results from ε-martensite dominant transformation-induced-plasticity (TRIP) effect. The increase in the strain-hardening rate at the strain level around 0.35 to 0.43 is attributed to the synergetic α’-martensite dominant TRIP and twinning-induced-plasticity (TWIP) effects. An evaluation of the stacking fault energy (SFE) of the Fe-17Mn-1.5Al-0.3C steel by the synchrotron measurements shows good agreement with the thermodynamic calculation of the SFE. PMID:28946692

Investigation of the Microstructure Evolution in a Fe-17Mn-1.5Al-0.3C Steel via In Situ Synchrotron X-ray Diffraction during a Tensile Test.

PubMed

Ma, Yan; Song, Wenwen; Bleck, Wolfgang

2017-09-25

The quantitative characterization of the microstructure evolution in high-Mn steel during deformation is of great importance to understanding its strain-hardening behavior. In the current study, in situ high-energy synchrotron X-ray diffraction was employed to characterize the microstructure evolution in a Fe-17Mn-1.5Al-0.3C steel during a tensile test. The microstructure at different engineering strain levels-in terms of ε-martensite and α'-martensite volume fractions, the stacking fault probability, and the twin fault probability-was analyzed by the Rietveld refinement method. The Fe-17Mn-1.5Al-0.3C steel exhibits a high ultimate tensile strength with a superior uniform elongation and a high strain-hardening rate. The remaining high strain-hardening rate at the strain level about 0.025 to 0.35 results from ε-martensite dominant transformation-induced-plasticity (TRIP) effect. The increase in the strain-hardening rate at the strain level around 0.35 to 0.43 is attributed to the synergetic α'-martensite dominant TRIP and twinning-induced-plasticity (TWIP) effects. An evaluation of the stacking fault energy (SFE) of the Fe-17Mn-1.5Al-0.3C steel by the synchrotron measurements shows good agreement with the thermodynamic calculation of the SFE.

The core structure and recombination energy of a copper screw dislocation: a Peierls study

NASA Astrophysics Data System (ADS)

Szajewski, B. A.; Hunter, A.; Beyerlein, I. J.

2017-09-01

The recombination process of dislocations is central to cross-slip, and transmission through ?3 grain boundaries among other fundamental plastic deformation processes. Despite its importance, a detailed mechanistic understanding remains lacking. We apply a continuous dislocation model, inspired by Peierls and Nabarro, complete with an ab-initio computed ?-surface and continuous units of infinitesimal dislocation slip, towards computing the stress-dependent recombination path of both an isotropic and anisotropic Cu screw dislocation. Under no applied stress, our model reproduces the stacking fault width between Shockley partial dislocations as predicted by discrete linear elasticity. Upon application of a compressive Escaig stress, the two partial dislocations coalesce to a separation of ??. Upon increased loading the edge components of each partial dislocation recede, leaving behind a spread Peierls screw dislocation, indicating the recombined state. We demonstrate that the critical stress required to achieve the recombined state is independent of the shear modulus. Rather the critical recombination stress depends on an energy difference between an unstable fault energy (?) and the intrinsic stacking fault energy (?-?). We report recombination energies of ?W = 0.168 eV/Å and ?W = 0.084 eV/Å, respectively, for the Cu screw dislocation within isotropic and anisotropic media. We develop an analytic model which provides insight into our simulation results which compare favourably with other (similar) models.

Development of an automatic subsea blowout preventer stack control system using PLC based SCADA.

PubMed

Cai, Baoping; Liu, Yonghong; Liu, Zengkai; Wang, Fei; Tian, Xiaojie; Zhang, Yanzhen

2012-01-01

An extremely reliable remote control system for subsea blowout preventer stack is developed based on the off-the-shelf triple modular redundancy system. To meet a high reliability requirement, various redundancy techniques such as controller redundancy, bus redundancy and network redundancy are used to design the system hardware architecture. The control logic, human-machine interface graphical design and redundant databases are developed by using the off-the-shelf software. A series of experiments were performed in laboratory to test the subsea blowout preventer stack control system. The results showed that the tested subsea blowout preventer functions could be executed successfully. For the faults of programmable logic controllers, discrete input groups and analog input groups, the control system could give correct alarms in the human-machine interface. Copyright © 2011 ISA. Published by Elsevier Ltd. All rights reserved.

Automatic Fault Characterization via Abnormality-Enhanced Classification

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bronevetsky, G; Laguna, I; de Supinski, B R

Enterprise and high-performance computing systems are growing extremely large and complex, employing hundreds to hundreds of thousands of processors and software/hardware stacks built by many people across many organizations. As the growing scale of these machines increases the frequency of faults, system complexity makes these faults difficult to detect and to diagnose. Current system management techniques, which focus primarily on efficient data access and query mechanisms, require system administrators to examine the behavior of various system services manually. Growing system complexity is making this manual process unmanageable: administrators require more effective management tools that can detect faults and help tomore » identify their root causes. System administrators need timely notification when a fault is manifested that includes the type of fault, the time period in which it occurred and the processor on which it originated. Statistical modeling approaches can accurately characterize system behavior. However, the complex effects of system faults make these tools difficult to apply effectively. This paper investigates the application of classification and clustering algorithms to fault detection and characterization. We show experimentally that naively applying these methods achieves poor accuracy. Further, we design novel techniques that combine classification algorithms with information on the abnormality of application behavior to improve detection and characterization accuracy. Our experiments demonstrate that these techniques can detect and characterize faults with 65% accuracy, compared to just 5% accuracy for naive approaches.« less

Reliable High Performance Peta- and Exa-Scale Computing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bronevetsky, G

2012-04-02

As supercomputers become larger and more powerful, they are growing increasingly complex. This is reflected both in the exponentially increasing numbers of components in HPC systems (LLNL is currently installing the 1.6 million core Sequoia system) as well as the wide variety of software and hardware components that a typical system includes. At this scale it becomes infeasible to make each component sufficiently reliable to prevent regular faults somewhere in the system or to account for all possible cross-component interactions. The resulting faults and instability cause HPC applications to crash, perform sub-optimally or even produce erroneous results. As supercomputers continuemore » to approach Exascale performance and full system reliability becomes prohibitively expensive, we will require novel techniques to bridge the gap between the lower reliability provided by hardware systems and users unchanging need for consistent performance and reliable results. Previous research on HPC system reliability has developed various techniques for tolerating and detecting various types of faults. However, these techniques have seen very limited real applicability because of our poor understanding of how real systems are affected by complex faults such as soft fault-induced bit flips or performance degradations. Prior work on such techniques has had very limited practical utility because it has generally focused on analyzing the behavior of entire software/hardware systems both during normal operation and in the face of faults. Because such behaviors are extremely complex, such studies have only produced coarse behavioral models of limited sets of software/hardware system stacks. Since this provides little insight into the many different system stacks and applications used in practice, this work has had little real-world impact. My project addresses this problem by developing a modular methodology to analyze the behavior of applications and systems during both normal and faulty operation. By synthesizing models of individual components into a whole-system behavior models my work is making it possible to automatically understand the behavior of arbitrary real-world systems to enable them to tolerate a wide range of system faults. My project is following a multi-pronged research strategy. Section II discusses my work on modeling the behavior of existing applications and systems. Section II.A discusses resilience in the face of soft faults and Section II.B looks at techniques to tolerate performance faults. Finally Section III presents an alternative approach that studies how a system should be designed from the ground up to make resilience natural and easy.« less

Enhanced low-temperature critical current by reduction of stacking faults in REBCO coated conductors

NASA Astrophysics Data System (ADS)

Puichaud, A.-H.; Wimbush, S. C.; Knibbe, R.

2017-07-01

The effect of stacking faults (SF) on flux pinning and critical current (I c) in rare earth based coated conductors was investigated. The SF density in YBa2Cu3O7-δ (YBCO) films with and without Dy addition, produced by metal organic deposition, was modified by altering the oxygenation temperature. A detailed microstructural analysis of the coated conductors was performed by x-ray diffraction, scanning and transmission electron microscopy and energy dispersive spectroscopy, and the observed defect population was correlated with both the self-field and in-field I c. We report that the best self-field I c was obtained for samples having a low SF density, in spite of the SF being effective flux pinning defects at 77 K for magnetic fields applied within the ab plane. We also show that the SF have no observable flux pinning effect at low temperatures. This study demonstrates that for devices operated at low temperatures, the elimination of SF in the conductor wires is essential to attain higher I c.

Revisiting the Al/Al₂O₃ interface: coherent interfaces and misfit accommodation.

PubMed

Pilania, Ghanshyam; Thijsse, Barend J; Hoagland, Richard G; Lazić, Ivan; Valone, Steven M; Liu, Xiang-Yang

2014-03-27

We study the coherent and semi-coherent Al/α-Al2O3 interfaces using molecular dynamics simulations with a mixed, metallic-ionic atomistic model. For the coherent interfaces, both Al-terminated and O-terminated nonstoichiometric interfaces have been studied and their relative stability has been established. To understand the misfit accommodation at the semi-coherent interface, a 1-dimensional (1D) misfit dislocation model and a 2-dimensional (2D) dislocation network model have been studied. For the latter case, our analysis reveals an interface dislocation structure with a network of three sets of parallel dislocations, each with pure-edge character, giving rise to a pattern of coherent and stacking-fault-like regions at the interface. Structural relaxation at elevated temperatures leads to a further change of the dislocation pattern, which can be understood in terms of a competition between the stacking fault energy and the dislocation interaction energy at the interface. Our results are expected to serve as an input for the subsequent dislocation dynamics models to understand and predict the macroscopic mechanical behavior of Al/α-Al2O3 composite heterostructures.

Effect of rolling on phase composition and microhardness of austenitic steels with different stacking-fault energies

NASA Astrophysics Data System (ADS)

Melnikov, Eugene; Astafurova, Elena; Maier, Galina; Moskvina, Valentina

2017-12-01

The influence of multi-pass cold rolling on the phase composition and microhardness of austenitic Fe-18Cr-9Ni-0.21C, Fe-18Cr-9Ni-0.5Ti-0.08C, Fe-17Cr-13Ni-3Mo-0.01C (in wt %) steels with different stacking fault energies was studied. The metastable Fe-18Cr-9Ni-0.5Ti-0.08C steel undergoes γ → α' phase transformations during rolling, the volume fraction of strain-induced α'-martensite in steel structure is increased with increasing strain. Metastable austenite Fe-18Cr-9Ni-0.21C steel does not undergo the formation of an appreciable amount of strain-induced α'-martensite under rolling, but the magnetophase analysis reveals a small amount of ferrite phase in the structure of steel after rolling. The structure of stable Fe-17Cr-13Ni-3Mo-0.01C steel remains austenitic independently under strain. Investigations of microhardness of the steels show that their values are increased with strain and are dependent on propensity of steels to strain-induced martensitic transformation.

Atomic-scale study of stacking faults in Zr hydrides and implications on hydride formation.

PubMed

Besson, Remy; Thuinet, L; Louchez, Marc-Antoine

2018-06-25

We performed atomic-scale ab initio calculations to investigate the stacking fault (SF) properties of the metastable zeta-Zr2H zirconium hydride. The effect of H near the SF was found to entail the existence of negative SF energies, showing that the zeta compound is probably unstable with respect to shearing in the basal plane. The effect of temperature on SFs was investigated by means of free energy calculations in the quasiharmonic approximation. This evidenced unexpectedly large temperature effects, confirming the main conclusions drawn at 0 K, in particular the zeta mechanical instability. The complex behaviour of H atoms during the shear process suggested zeta-hcp --> Zr2H[111]-fcc as a plausible shear path leading to an fcc compound with same composition as zeta. Finally, as shown by an analysis based on microelasticity, this Zr2H[111]-fcc intermediate compound may be relevant for better interpreting the currently intricate issue of hydride habit planes in zirconium. © 2018 IOP Publishing Ltd.

Mechanism of Na accumulation at extended defects in Si from first-principles

NASA Astrophysics Data System (ADS)

Park, Ji-Sang; Chan, Maria K. Y.

2018-04-01

Sodium (Na) impurities in silicon solar cells are considered to play an important role in potential-induced degradation (PID), a significant cause of solar cell degradation and failure. Shorting due to Na accumulation at extended defects has been suggested as a culprit for PID. However, it is not clear how the extended defects are decorated by Na impurities. Using first-principles density functional theory calculations, we find that Na impurities segregate from the bulk into extended defects such as intrinsic stacking faults and Σ3 (111) grain boundaries. The energy barrier required for Na to escape from the extended defects is substantial and similar to the sum of the barrier energy in bulk Si (1.1-1.2 eV) and the segregation energy to the stacking fault (˜0.7 eV). Surprisingly, the migration barrier for Na diffusion within the extended defects is even higher than the energy barrier for escaping. The results suggest that the extended defects likely accumulate Na as the impurities segregate to the defects from the bulk, rather than because of migration through the extended defects.

Long exciton lifetimes in stacking-fault-free wurtzite GaAs nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Furthmeier, Stephan, E-mail: stephan.furthmeier@ur.de; Dirnberger, Florian; Hubmann, Joachim

We present a combined photoluminescence and transmission electron microscopy study of single GaAs nanowires. Each wire was characterized both in microscopy and spectroscopy, allowing a direct correlation of the optical and the structural properties. By tuning the growth parameters, the nanowire crystal structure is optimized from a highly mixed zincblende–wurtzite structure to pure wurtzite. We find the latter one to be stacking-fault-free over nanowire lengths up to 4.1 μm. We observe the emission of purely wurtzite nanowires to occur only with polarization directions perpendicular to the wurtzite c{sup ^}-axis, as expected from the hexagonal unit cell symmetry. The free exciton recombinationmore » energy in the wurtzite structure is 1.518 eV at 5 K with a narrow linewidth of 4 meV. Most notably, these pure wurtzite nanowires display long carrier recombination lifetimes of up to 11.2 ns, exceeding reported lifetimes in bulk GaAs and state-of-the-art 2D GaAs/AlGaAs heterostructures.« less

Signature of dislocations and stacking faults of face-centred cubic nanocrystals in coherent X-ray diffraction patterns: a numerical study.

PubMed

Dupraz, Maxime; Beutier, Guillaume; Rodney, David; Mordehai, Dan; Verdier, Marc

2015-06-01

Crystal defects induce strong distortions in diffraction patterns. A single defect alone can yield strong and fine features that are observed in high-resolution diffraction experiments such as coherent X-ray diffraction. The case of face-centred cubic nanocrystals is studied numerically and the signatures of typical defects close to Bragg positions are identified. Crystals of a few tens of nanometres are modelled with realistic atomic potentials and 'relaxed' after introduction of well defined defects such as pure screw or edge dislocations, or Frank or prismatic loops. Diffraction patterns calculated in the kinematic approximation reveal various signatures of the defects depending on the Miller indices. They are strongly modified by the dissociation of the dislocations. Selection rules on the Miller indices are provided, to observe the maximum effect of given crystal defects in the initial and relaxed configurations. The effect of several physical and geometrical parameters such as stacking fault energy, crystal shape and defect position are discussed. The method is illustrated on a complex structure resulting from the simulated nanoindentation of a gold nanocrystal.

Signature of dislocations and stacking faults of face-centred cubic nanocrystals in coherent X-ray diffraction patterns: a numerical study1

PubMed Central

Dupraz, Maxime; Beutier, Guillaume; Rodney, David; Mordehai, Dan; Verdier, Marc

2015-01-01

Crystal defects induce strong distortions in diffraction patterns. A single defect alone can yield strong and fine features that are observed in high-resolution diffraction experiments such as coherent X-ray diffraction. The case of face-centred cubic nanocrystals is studied numerically and the signatures of typical defects close to Bragg positions are identified. Crystals of a few tens of nanometres are modelled with realistic atomic potentials and ‘relaxed’ after introduction of well defined defects such as pure screw or edge dislocations, or Frank or prismatic loops. Diffraction patterns calculated in the kinematic approximation reveal various signatures of the defects depending on the Miller indices. They are strongly modified by the dissociation of the dislocations. Selection rules on the Miller indices are provided, to observe the maximum effect of given crystal defects in the initial and relaxed configurations. The effect of several physical and geometrical parameters such as stacking fault energy, crystal shape and defect position are discussed. The method is illustrated on a complex structure resulting from the simulated nanoindentation of a gold nanocrystal. PMID:26089755

Formation mechanism of fivefold deformation twins in a face-centered cubic alloy.

PubMed

Zhang, Zhenyu; Huang, Siling; Chen, Leilei; Zhu, Zhanwei; Guo, Dongming

2017-03-28

The formation mechanism considers fivefold deformation twins originating from the grain boundaries in a nanocrystalline material, resulting in that fivefold deformation twins derived from a single crystal have not been reported by molecular dynamics simulations. In this study, fivefold deformation twins are observed in a single crystal of face-centered cubic (fcc) alloy. A new formation mechanism is proposed for fivefold deformation twins in a single crystal. A partial dislocation is emitted from the incoherent twin boundaries (ITBs) with high energy, generating a stacking fault along {111} plane, and resulting in the nucleating and growing of a twin by the successive emission of partials. A node is fixed at the intersecting center of the four different slip {111} planes. With increasing stress under the indentation, ITBs come into being close to the node, leading to the emission of a partial from the node. This generates a stacking fault along a {111} plane, nucleating and growing a twin by the continuous emission of the partials. This process repeats until the formation of fivefold deformation twins.

Effect of Gas Tungsten Arc Welding Parameters on Hydrogen-Assisted Cracking of Type 321 Stainless Steel

NASA Astrophysics Data System (ADS)

Rozenak, Paul; Unigovski, Yaakov; Shneck, Roni

2016-05-01

The susceptibility of AISI type 321 stainless steel welded by the gas tungsten arc welding (GTAW) process to hydrogen-assisted cracking (HAC) was studied in a tensile test combined with in situ cathodic charging. Specimen charging causes a decrease in ductility of both the as-received and welded specimens. The mechanical properties of welds depend on welding parameters. For example, the ultimate tensile strength and ductility increase with growing shielding gas (argon) rate. More severe decrease in the ductility was obtained after post-weld heat treatment (PWHT). In welded steels, in addition to discontinuous grain boundary carbides (M23C6) and dense distribution of metal carbides MC ((Ti, Nb)C) precipitated in the matrix, the appearance of delta-ferrite phase was observed. The fracture of sensitized specimens was predominantly intergranular, whereas the as-welded specimens exhibited mainly transgranular regions. High-dislocation density regions and stacking faults were found in delta-ferrite formed after welding. Besides, thin stacking fault plates and epsilon-martensite were found in the austenitic matrix after the cathodic charging.

Twinning and martensite in a 304 austenitic stainless steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shen, Yongfeng; Li, Xi; Sun, Xin

2012-08-30

The microstructure characteristics and deformation behavior of 304L stainless steel during tensile deformation at two different strain rates have been investigated by means of interrupted tensile tests, electron-backscatter-diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The volume fractions of transformed martensite and deformation twins at different stages of the deformation process were measured using X-ray diffraction method and TEM observations. It is found that the volume fraction of martensite monotonically increases with increasing strain but decreases with increasing strain rate. On the other hand, the volume fraction of twins increases with increasing strain for strain level less than 57%. Beyondmore » that, the volume fraction of twins decreases with increasing strain. Careful TEM observations show that stacking faults (SFs) and twins preferentially occur before the nucleation of martensite. Meanwhile, both {var_epsilon}-martensite and {alpha}{prime}-martensite are observed in the deformation microstructures, indicating the co-existence of stress induced- transformation and strain-induced-transformation. We also discussed the effects of twinning and martensite transformation on work-hardening as well as the relationship between stacking faults, twinning and martensite transformation.« less

Stacking-fault strengthening of biomedical Co-Cr-Mo alloy via multipass thermomechanical processing.

PubMed

Yamanaka, Kenta; Mori, Manami; Sato, Shigeo; Chiba, Akihiko

2017-09-07

The strengthening of metallic biomaterials, such as Co-Cr-Mo and titanium alloys, is of crucial importance to the improvement of the durability of orthopedic implants. In the present study, we successfully developed a face-centered cubic (fcc) Co-Cr-Mo alloy with an extremely high yield strength (1400 MPa) and good ductility (12%) by multipass hot-rolling, which is suitable for industrial production, and examined the relevant strengthening mechanisms. Using an X-ray diffraction line-profile analysis, we revealed that a substantial increase in the number of stacking faults (SFs) in the fcc γ-matrix occurred at a greater height reduction (r), while physical modeling demonstrated that the contribution of the accumulated SFs (i.e., the reduction in SF spacing) with an increase in r successfully explains the entire strengthening behavior of the hot-rolled alloy. The present study sheds light on the importance of the SF strengthening mechanism, and will help to guide the design and manufacturing strategy for the high-strength Co-Cr-Mo alloys used in highly durable medical devices.

Formation mechanism of fivefold deformation twins in a face-centered cubic alloy

NASA Astrophysics Data System (ADS)

Zhang, Zhenyu; Huang, Siling; Chen, Leilei; Zhu, Zhanwei; Guo, Dongming

2017-03-01

The formation mechanism considers fivefold deformation twins originating from the grain boundaries in a nanocrystalline material, resulting in that fivefold deformation twins derived from a single crystal have not been reported by molecular dynamics simulations. In this study, fivefold deformation twins are observed in a single crystal of face-centered cubic (fcc) alloy. A new formation mechanism is proposed for fivefold deformation twins in a single crystal. A partial dislocation is emitted from the incoherent twin boundaries (ITBs) with high energy, generating a stacking fault along {111} plane, and resulting in the nucleating and growing of a twin by the successive emission of partials. A node is fixed at the intersecting center of the four different slip {111} planes. With increasing stress under the indentation, ITBs come into being close to the node, leading to the emission of a partial from the node. This generates a stacking fault along a {111} plane, nucleating and growing a twin by the continuous emission of the partials. This process repeats until the formation of fivefold deformation twins.

Influence of Austenite Stability on Steel Low Cycle Fatigue Response

NASA Astrophysics Data System (ADS)

Lehnhoff, G. R.; Findley, K. O.

Austenitic steels were subjected to tensile and total strain controlled, fully reversed axial low cycle fatigue (LCF) testing to determine the influence of stacking fault energy on austenite stability, or resistance to strain induced martensitic transformation during tensile and fatigue deformation. Expected differences in stacking fault energy were achieved by modifying alloys with different amounts of silicon and aluminum. Al alloying was found to promote martensite formation during both tensile and LCF loading, while Si was found to stabilize austenite. Martensite formation increases tensile work hardening rates, though Si additions also increase the work hardening rate without martensite transformation. Similarly, secondary cyclic strain hardening during LCF is attributed to strain induced martensite formation, but Si alloying resulted in less secondary cyclic strain hardening. The amount of secondary cyclic hardening scales linearly with martensite fraction and depends only on the martensite fraction achieved and not on the martensite (i.e. parent austenite) chemistry. Martensite formation was detrimental to LCF lives at all strain amplitudes tested, although the total amount of martensitic transformation during LCF did not always monotonically increase with strain amplitude nor correlate to the amount of tensile transformation.

New horizon for high performance Mg-based biomaterial with uniform degradation behavior: Formation of stacking faults

PubMed Central

Zhang, Jinghuai; Xu, Chi; Jing, Yongbin; Lv, Shuhui; Liu, Shujuan; Fang, Daqing; Zhuang, Jinpeng; Zhang, Milin; Wu, Ruizhi

2015-01-01

Designing the new microstructure is an effective way to accelerate the biomedical application of magnesium (Mg) alloys. In this study, a novel Mg–8Er–1Zn alloy with profuse nano-spaced basal plane stacking faults (SFs) was prepared by combined processes of direct-chill semi-continuous casting, heat-treatment and hot-extrusion. The formation of SFs made the alloy possess outstanding comprehensive performance as the biodegradable implant material. The ultimate tensile strength (UTS: 318 MPa), tensile yield strength (TYS: 207 MPa) and elongation (21%) of the alloy with SFs were superior to those of most reported degradable Mg-based alloys. This new alloy showed acceptable biotoxicity and degradation rate (0.34 mm/year), and the latter could be further slowed down through optimizing the microstructure. Most amazing of all, the uniquely uniform in vitro/vivo corrosion behavior was obtained due to the formation of SFs. Accordingly we proposed an original corrosion mechanism for the novel Mg alloy with SFs. The present study opens a new horizon for developing new Mg-based biomaterials with highly desirable performances. PMID:26349676

Using Ambient Seismic Noise to Monitor Post-Seismic Relaxation After the 2010 Mw 7.1 Darfield Earthquake, New Zealand

NASA Astrophysics Data System (ADS)

Savage, M. K.; Heckels, R.; Townend, J.

2015-12-01

Quantifying seismic velocity changes following large earthquakes can provide insights into the crustal response of the earth. The use of ambient seismic noise to monitor these changes is becoming increasingly widespread. Cross-correlations of long-duration ambient noise records can be used to give stable impulse response functions without the need for repeated seismic events. Temporal velocity changes were detected in the four months following the September 2010 Mw 7.1 Darfield event in South Island, New Zealand, using temporary seismic networks originally deployed to record aftershocks in the region. The arrays consisted of stations lying on and surrounding the fault, with a maximum inter-station distance of 156km. The 2010-2011 Canterbury earthquake sequence occurred largely on previously unknown and buried faults. The Darfield earthquake was the first and largest in a sequence of events that hit the region, rupturing the Greendale Fault. A surface rupture of nearly 30km was observed. The sequence also included the Mw 6.3 February 2011 Christchurch event, which caused widespread damage throughout the city and resulted in almost 200 deaths. Nine-component, day-long Green's functions were computed for frequencies between 0.1 - 1.0 Hz for full waveform seismic data from immediately after the 4th September 2010 earthquake until mid-January 2011. Using the moving window cross-spectral method, stacks of daily functions covering the study period (reference functions), were compared to consecutive 10 day stacks of cross-correlations to measure time delays between them. These were then inverted for seismic velocity changes with respect to the reference functions. Over the study period an increase in seismic velocity of 0.25% ± 0.02% was determined proximal to the Greendale fault. These results are similar to studies in other regions, and we attribute the changes to post-seismic relaxation through crack-healing of the Greendale Fault and throughout the region.

Non-Mutually Exclusive Deep Neural Network Classifier for Combined Modes of Bearing Fault Diagnosis

PubMed Central

Kim, Jong-Myon

2018-01-01

The simultaneous occurrence of various types of defects in bearings makes their diagnosis more challenging owing to the resultant complexity of the constituent parts of the acoustic emission (AE) signals. To address this issue, a new approach is proposed in this paper for the detection of multiple combined faults in bearings. The proposed methodology uses a deep neural network (DNN) architecture to effectively diagnose the combined defects. The DNN structure is based on the stacked denoising autoencoder non-mutually exclusive classifier (NMEC) method for combined modes. The NMEC-DNN is trained using data for a single fault and it classifies both single faults and multiple combined faults. The results of experiments conducted on AE data collected through an experimental test-bed demonstrate that the DNN achieves good classification performance with a maximum accuracy of 95%. The proposed method is compared with a multi-class classifier based on support vector machines (SVMs). The NMEC-DNN yields better diagnostic performance in comparison to the multi-class classifier based on SVM. The NMEC-DNN reduces the number of necessary data collections and improves the bearing fault diagnosis performance. PMID:29642466

Fault detection and isolation of high temperature proton exchange membrane fuel cell stack under the influence of degradation

NASA Astrophysics Data System (ADS)

Jeppesen, Christian; Araya, Samuel Simon; Sahlin, Simon Lennart; Thomas, Sobi; Andreasen, Søren Juhl; Kær, Søren Knudsen

2017-08-01

This study proposes a data-drive impedance-based methodology for fault detection and isolation of low and high cathode stoichiometry, high CO concentration in the anode gas, high methanol vapour concentrations in the anode gas and low anode stoichiometry, for high temperature PEM fuel cells. The fault detection and isolation algorithm is based on an artificial neural network classifier, which uses three extracted features as input. Two of the proposed features are based on angles in the impedance spectrum, and are therefore relative to specific points, and shown to be independent of degradation, contrary to other available feature extraction methods in the literature. The experimental data is based on a 35 day experiment, where 2010 unique electrochemical impedance spectroscopy measurements were recorded. The test of the algorithm resulted in a good detectability of the faults, except for high methanol vapour concentration in the anode gas fault, which was found to be difficult to distinguish from a normal operational data. The achieved accuracy for faults related to CO pollution, anode- and cathode stoichiometry is 100% success rate. Overall global accuracy on the test data is 94.6%.

High-Resolution Source Parameter and Site Characteristics Using Near-Field Recordings - Decoding the Trade-off Problems Between Site and Source

NASA Astrophysics Data System (ADS)

Chen, X.; Abercrombie, R. E.; Pennington, C.

2017-12-01

Recorded seismic waveforms include contributions from earthquake source properties and propagation effects, leading to long-standing trade-off problems between site/path effects and source effects. With near-field recordings, the path effect is relatively small, so the trade-off problem can be simplified to between source and site effects (commonly referred as "kappa value"). This problem is especially significant for small earthquakes where the corner frequencies are within similar ranges of kappa values, so direct spectrum fitting often leads to systematic biases due to corner frequency and magnitude. In response to the significantly increased seismicity rate in Oklahoma, several local networks have been deployed following major earthquakes: the Prague, Pawnee and Fairview earthquakes. Each network provides dense observations within 20 km surrounding the fault zone, recording tens of thousands of aftershocks between M1 to M3. Using near-field recordings in the Prague area, we apply a stacking approach to separate path/site and source effects. The resulting source parameters are consistent with parameters derived from ground motion and spectral ratio methods from other studies; they exhibit spatial coherence within the fault zone for different fault patches. We apply these source parameter constraints in an analysis of kappa values for stations within 20 km of the fault zone. The resulting kappa values show significantly reduced variability compared to those from direct spectral fitting without constraints on the source spectrum; they are not biased by earthquake magnitudes. With these improvements, we plan to apply the stacking analysis to other local arrays to analyze source properties and site characteristics. For selected individual earthquakes, we will also use individual-pair empirical Green's function (EGF) analysis to validate the source parameter estimations.

Structural and Depositional Evolution of the Stevenson Basin, a Gulf of Alaska Forearc Basin: Insights from Legacy Seismic and Borehole Data

NASA Astrophysics Data System (ADS)

Bhattacharya, R.; Liberty, L. M.; Almeida, R. V.; Hubbard, J.

2016-12-01

We explore the structural and depositional evolution of the Stevenson Basin, Gulf of Alaska from a dense network of 2-D marine seismic profiles that span the Gulf of Alaska continental margin. The grid of 71 seismic profiles was acquired as part of a 1975 Mineral Management Services (MMS) exploration project to assess basin architecture along the Alaska continental shelf. We obtained unmigrated and stacked seismic profiles in TIFF format. We converted the data to SEGY format and migrated each profile. Within the Stevenson Basin, we identify key seismic horizons, including the regional Eocene-Miocene unconformity, that provide insights into its depositional and structural history. Using these observations combined with stacking velocities, sonic logs from wells, and refraction velocities from the Edge profile of Ye et al. (1997), we develop a local 3D velocity model that we use to depth-convert the seismic reflection profiles. By using ties to >2.5 km deep exploration wells, we note the Stevenson Basin is one of many Eocene and younger depocenters that span the forearc between Kodiak and Prince William Sound. Well logs and seismic data suggest basal strata consist of Eocene sediments than are unconformably overlain by Neogene and younger strata. Faults that breach the sea floor suggest active deformation within and at the bounds of this basin, including on new faults that do not follow any pre-existing structural trends. This assessment is consistent with slip models that place tsunamigenic faults that ruptured during the 1964 Great Alaska earthquake in the vicinity of the basin. The catalog of faults, their slip history and the depositional evolution of the Stevenson Basin, all suggest that the basin evolution may be controlled by heterogeneities along the incoming plate.

Nanoscale heterogeneity as remnant hexagonal-type local structures in shocked Cu-Pb and Zr

NASA Astrophysics Data System (ADS)

Tayal, Akhil; Conradson, Steven D.; Batuk, Olga N.; Fensin, Saryu; Cerreta, Ellen; Gray, George T.; Saxena, Avadh

2017-09-01

Extended X-ray absorption fine structure spectroscopy was used to determine the local structure in: (1) Zr that had undergone quasistatic elongation; (2) Zr that had undergone plastic deformation by shock at pressures above and below the ω-phase transformation; and (3) shocked Cu that contained a few percent of insoluble Pb. Below the transition pressure, Zr samples showed only general disorder as increases in the widths of the Zr-Zr pair distributions. Above this pressure, Zr that was a mixture of the original hcp and the high pressure ω-phase when measured by diffraction showed two sets of peaks in its distribution corresponding to these two phases. Some of the ones from the ω-phase were at distances substantially different from those calculated from the diffraction pattern, although they are still consistent with small domains exhibiting stacking faults associated with hexagonal-type structural components exhibiting variability in the [0001] basal plane spacing. A similar result, new pairs at just over 3 and 4 Å consistent with hexagonal-type stacking faults in addition to the original fcc structure, is found in shocked Cu despite the absence of a second diffraction pattern and peak pressures being far below those expected to induce an fcc to hcp transition. This result, therefore, demonstrates that the correlation between high strain rates and reduced stacking fault energy continues down to the length scale of atom pairs. These findings are significant as: (1) a microscopic description of the behavior of systems far from equilibrium; (2) a demonstration of the importance of strain rate at short length scales; and (3) a bridge between the abruptness of macroscopic pressure-induced phase transitions and the continuity of martensitic ones over their fluctuation region in terms of the inverse relationship between the length scale of the martensitic texture, manifested here as ordered lattice distortions and the lower pressure at which such texture first appears relative to the bulk transition pressure.

Discussion Starter: The Case for Duplexing without Channel Flow During the Development and Emplacement of the Himalayan Middle Crust

NASA Astrophysics Data System (ADS)

Webb, A. G.; He, D.; Yu, H.

2015-12-01

This presentation and another presentation led by Dawn Kellett will preface a ten-minute open discussion on how the Himalayan middle crust was developed and emplaced. Current hypotheses are transitioning from a set including wedge extrusion, channel flow with focused denudation, and tectonic wedging to a revised dichotomy: models with intense upper plate out-of-sequence activity (i.e., tunneling of channel flow, and critical taper wedge behavior) versus models in which the upper plate mainly records basal accretion of horses (i.e., duplexing). Critical taper and duplexing offer a simple contrast that can be illustrated via food analogies. If a wedge is critical, it churns internally like a pile of CheeriosTM cereal pushed up an inclined plane. Stacking of a duplex acts like a deli meat-slicing machine: slice after slice is cut from the intact block to a stack of slices, but neither the block (~down-going plate) nor the stack (~upper plate) features much internal deformation. Thus critical taper and channel tunneling models predict much processing via out-of-sequence deformation, whereas duplexing predicts in-sequence thrusting. The two concepts may be considered end-members. Recent work shows that the Himalayan middle crust has been assembled along a series of mainly southwards-younging thrust faults. The thrust faults separate 1-5 km thick panels that experienced similar metamorphic cycles during different time periods. Out-of-sequence deformation is rare, with its apparent significance enhanced because of the high throw-to-heave ratio of out-of-sequence thrusting. Flattening fabrics developed prior to thrusting have been interpreted to record either (1) southwards channel tunneling across the upper plate, or (2) fabric development during metamorphism of the down-going plate. We will argue that the thrust faults dominantly represent in-sequence duplexing, and therefore conclude that the Himalaya and analogous hot orogens behave like other accretionary orogens.

A Spatially and Temporally Continuous LFE Catalogue for the Southern Alps, New Zealand

NASA Astrophysics Data System (ADS)

Chamberlain, C. J.; Townend, J.; Baratin, L. M.

2015-12-01

Using a brightness-based beamforming approach coupled with a matched-filter correlation method, we have developed a 6.5 year record of low-frequency earthquakes (LFEs) occuring on and near the deep extent of New Zealand's Alpine Fault. Our brightness template detection method, based on that of Frank et al. (2014), scans a pre-determined grid of possible seismic sources to automatically find LFE templates based on the stack of bandpassed squared seismic data. Previous work (Wech et al., 2012, Chamberlain et al., 2014) has shown that the depths of standard seismicity are anti-correlated with those of tremor and LFEs in the central Southern Alps: hence, by careful grid selection, shallow seismic sources can effectively be discriminated against. This beamforming approach produces many (>900) possible events. Initial beamforming detections are grouped by moveout and stacked to produce a subset of higher-quality events for use as templates in a cross-correlation detector. Events detected by cross-correlation are stacked to increase their signal-to-noise charectaristics before being located using a 3D velocity model. This method produces a spatially and temporally continuous catalogue of LFEs throughout the 6.5 year study period. The catalogue highlights quasi-continuous slow deformation occuring beneath the seismogenic zone near the Alpine Fault, punctuated by periods of increased LFE generation associated with tremor, and following large regional earthquakes. To date we have found no evidence of LFE generation north-east of Mt. Cook, the highest point in the Southern Alps, despite systematic searching throughout the region. We suggest that the along-strike cessation of tremor is due to changes in the fault's dip and the hypothesised presence of partially subducted passive margin material. This remnant passive margin would lie benath the tremor-generating region and has been linked to along-strike changes in subcrustal earthquake distributions (Boese et al., 2013).

2-D traveltime and waveform inversion for improved seismic imaging: Naga Thrust and Fold Belt, India

NASA Astrophysics Data System (ADS)

Jaiswal, Priyank; Zelt, Colin A.; Bally, Albert W.; Dasgupta, Rahul

2008-05-01

Exploration along the Naga Thrust and Fold Belt in the Assam province of Northeast India encounters geological as well as logistic challenges. Drilling for hydrocarbons, traditionally guided by surface manifestations of the Naga thrust fault, faces additional challenges in the northeast where the thrust fault gradually deepens leaving subtle surface expressions. In such an area, multichannel 2-D seismic data were collected along a line perpendicular to the trend of the thrust belt. The data have a moderate signal-to-noise ratio and suffer from ground roll and other acquisition-related noise. In addition to data quality, the complex geology of the thrust belt limits the ability of conventional seismic processing to yield a reliable velocity model which in turn leads to poor subsurface image. In this paper, we demonstrate the application of traveltime and waveform inversion as supplements to conventional seismic imaging and interpretation processes. Both traveltime and waveform inversion utilize the first arrivals that are typically discarded during conventional seismic processing. As a first step, a smooth velocity model with long wavelength characteristics of the subsurface is estimated through inversion of the first-arrival traveltimes. This velocity model is then used to obtain a Kirchhoff pre-stack depth-migrated image which in turn is used for the interpretation of the fault. Waveform inversion is applied to the central part of the seismic line to a depth of ~1 km where the quality of the migrated image is poor. Waveform inversion is performed in the frequency domain over a series of iterations, proceeding from low to high frequency (11-19 Hz) using the velocity model from traveltime inversion as the starting model. In the end, the pre-stack depth-migrated image and the waveform inversion model are jointly interpreted. This study demonstrates that a combination of traveltime and waveform inversion with Kirchhoff pre-stack depth migration is a promising approach for the interpretation of geological structures in a thrust belt.

A Deep Learning Approach for Fault Diagnosis of Induction Motors in Manufacturing

NASA Astrophysics Data System (ADS)

Shao, Si-Yu; Sun, Wen-Jun; Yan, Ru-Qiang; Wang, Peng; Gao, Robert X.

2017-11-01

Extracting features from original signals is a key procedure for traditional fault diagnosis of induction motors, as it directly influences the performance of fault recognition. However, high quality features need expert knowledge and human intervention. In this paper, a deep learning approach based on deep belief networks (DBN) is developed to learn features from frequency distribution of vibration signals with the purpose of characterizing working status of induction motors. It combines feature extraction procedure with classification task together to achieve automated and intelligent fault diagnosis. The DBN model is built by stacking multiple-units of restricted Boltzmann machine (RBM), and is trained using layer-by-layer pre-training algorithm. Compared with traditional diagnostic approaches where feature extraction is needed, the presented approach has the ability of learning hierarchical representations, which are suitable for fault classification, directly from frequency distribution of the measurement data. The structure of the DBN model is investigated as the scale and depth of the DBN architecture directly affect its classification performance. Experimental study conducted on a machine fault simulator verifies the effectiveness of the deep learning approach for fault diagnosis of induction motors. This research proposes an intelligent diagnosis method for induction motor which utilizes deep learning model to automatically learn features from sensor data and realize working status recognition.

Geomorphology, kinematic history, and earthquake behavior of the active Kuwana wedge thrust anticline, central Japan

NASA Astrophysics Data System (ADS)

Ishiyama, Tatsuya; Mueller, Karl; Togo, Masami; Okada, Atsumasa; Takemura, Keiji

2004-12-01

We combine surface mapping of fault and fold scarps that deform late Quaternary alluvial strata with interpretation of a high-resolution seismic reflection profile to develop a kinematic model and determine fault slip rates for an active blind wedge thrust system that underlies Kuwana anticline in central Japan. Surface fold scarps on Kuwana anticline are closely correlated with narrow fold limbs and angular hinges on the seismic profile that suggest at least ˜1.3 km of fault slip completely consumed by folding in the upper 4 km of the crust. The close coincidence and kinematic link between folded terraces and the underlying thrust geometry indicate that Kuwana anticline has accommodated slip at an average rate of 2.2 ± 0.5 mm/yr on a 27°, west dipping thrust fault since early-middle Pleistocene time. In contrast to classical fault bend folds the fault slip budget in the stacked wedge thrusts also indicates that (1) the fault tip propagated upward at a low rate relative to the accrual of fault slip and (2) fault slip is partly absorbed by numerous bedding plane flexural-slip faults above the tips of wedge thrusts. An historic earthquake that occurred on the Kuwana blind thrust system possibly in A.D. 1586 is shown to have produced coseismic surface deformation above the doubly vergent wedge tip. Structural analyses of Kuwana anticline coupled with tectonic geomorphology at 103-105 years timescales illustrate the significance of active folds as indicators of slip on underlying blind thrust faults and thus their otherwise inaccessible seismic hazards.

Resolution Analysis of finite fault inversions: A back-projection approach.

NASA Astrophysics Data System (ADS)

Ji, C.; Shao, G.

2007-12-01

The resolution of inverted source models of large earthquakes is controlled by frequency contents of "coherent" (or "useful") seismic observations and their spatial distribution. But it is difficult to distinguish whether some features consistent during different inversions are really required by data or a consequence of "prior" information, such as velocity structures, fault geometry, model parameterizations. Here, we investigate the model spatial resolution by first back projecting and stacking the data at the source regions and then analyzing the spatial- temporal variations of the focusing regions, which arbitrarily defined as the regions with 90% of the peak focusing amplitude. Our preliminary results indicated 1) The spatial-temporal resolution at a particularly direction is controlled by the region of directivity parameter [pcos(θ)] within the seismic network, where p is the horizontal slowness from the hypocenter and θ is the difference between the station azimuth and this orientation. Therefore, the network aperture is more important than the number of stations. 2) Simple stacking method is a robust method to capture the asperities but the sizes of focusing regions are usually much larger than what data could resolve. By carefully weighting the data before the stacking could enhance the spatial resolution in a particular direction. 3) The results based on the teleseismic P waves of a local network usually surfers the trade-off between the source's spatial location and its rupture time. The resolution of the 2001 Kunlunshan earthquake and 2006 Kuril island earthquake will be investigated.

Introduction

NASA Astrophysics Data System (ADS)

de Laat, Cees; Develder, Chris; Jukan, Admela; Mambretti, Joe

This topic is devoted to communication issues in scalable compute and storage systems, such as parallel computers, networks of workstations, and clusters. All aspects of communication in modern systems were solicited, including advances in the design, implementation, and evaluation of interconnection networks, network interfaces, system and storage area networks, on-chip interconnects, communication protocols, routing and communication algorithms, and communication aspects of parallel and distributed algorithms. In total 15 papers were submitted to this topic of which we selected the 7 strongest papers. We grouped the papers in two sessions of 3 papers each and one paper was selected for the best paper session. We noted a number of papers dealing with changing topologies, stability and forwarding convergence in source routing based cluster interconnect network architectures. We grouped these for the first session. The authors of the paper titled: “Implementing a Change Assimilation Mechanism for Source Routing Interconnects” propose a mechanism that can obtain the new topology, and compute and distribute a new set of fabric paths to the source routed network end points to minimize the impact on the forwarding service. The article entitled “Dependability Analysis of a Fault-tolerant Network Reconfiguration Strateg” reports on a case study analyzing the effects of network size, mean time to node failure, mean time to node repair, mean time to network repair and coverage of the failure when using a 2D mesh network with a fault-tolerant mechanism (similar to the one used in the BlueGene/L system), that is able to remove rows and/or columns in the presence of failures. The last paper in this session: “RecTOR: A New and Efficient Method for Dynamic Network Reconfiguration” presents a new dynamic reconfiguration method, that ensures deadlock-freedom during the reconfiguration without causing performance degradation such as increased latency or decreased throughput. The second session groups 3 papers presenting methods, protocols and architectures that enhance capacities in the Networks. The paper titled: “NIC-assisted Cache-Efficient Receive Stack for Message Passing over Ethernet” presents the addition of multiqueue support in the Open-MX receive stack so that all incoming packets for the same process are treated on the same core. It then introduces the idea of binding the target end process near its dedicated receive queue. In general this multiqueue receive stack performs better than the original single queue stack, especially on large communication patterns where multiple processes are involved and manual binding is difficult. The authors of: “A Multipath Fault-Tolerant Routing Method for High-Speed Interconnection Networks” focus on the problem of fault tolerance for high-speed interconnection networks by designing a fault tolerant routing method. The goal was to solve a certain number of link and node failures, considering its impact, and occurrence probability. Their experiments show that their method allows applications to successfully finalize their execution in the presence of several faults, with an average performance value of 97% with respect to the fault-free scenarios. The paper: “Hardware implementation study of the Self-Clocked Fair Queuing Credit Aware (SCFQ-CA) and Deficit Round Robin Credit Aware (DRR-CA) scheduling algorithms” proposes specific implementations of the two schedulers taking into account the characteristics of current high-performance networks. A comparison is presented on the complexity of these two algorithms in terms of silicon area and computation delay. Finally we selected one paper for the special paper session: “A Case Study of Communication Optimizations on 3D Mesh Interconnects”. In this paper the authors present topology aware mapping as a technique to optimize communication on 3-dimensional mesh interconnects and hence improve performance. Results are presented for OpenAtom on up to 16,384 processors of Blue Gene/L, 8,192 processors of Blue Gene/P and 2,048 processors of Cray XT3.

The structure of ice crystallized from supercooled water

NASA Astrophysics Data System (ADS)

Murray, Benjamin

2013-03-01

The freezing of water to ice is fundamentally important to fields as diverse as cloud formation to cryopreservation. Traditionally ice was thought to exist in two well-crystalline forms: stable hexagonal ice and metastable cubic ice. It has recently been shown, using X-ray diffraction data, that ice which crystallizes homogeneously and heterogeneously from supercooled water is neither of these phases. The resulting ice is disordered in one dimension and therefore possesses neither cubic nor hexagonal symmetry and is instead composed of randomly stacked layers of cubic and hexagonal sequences. We refer to this ice as stacking-disordered ice I (ice Isd) . This result is consistent with a number of computational studies of the crystallization of water. Review of the literature reveals that almost all ice that has been identified as cubic ice in previous diffraction studies and generated in a variety of ways was most likely stacking-disordered ice I with varying degrees of stacking disorder, which raises the question of whether cubic ice exists. New data will be presented which shows significant stacking disorder (or stacking faults on the order of 1 in every 100 layers of ice Ih) in droplets which froze heterogeneously as warm as 257 K. The identification of stacking-disordered ice from heterogeneous ice nucleation supports the hypothesis that the structure of ice that initially crystallises from supercooled water is stacking-disordered ice I, independent of nucleation mechanism, but this ice can relax to the stable hexagonal phase subject to the kinetics of recrystallization. The formation and persistence of stacking disordered ice in the Earth's atmosphere will also be discussed. Funded by the European Research Council (FP7, 240449 ICE)

The core structure and recombination energy of a copper screw dislocation: a Peierls study

DOE PAGES

Szajewski, B. A.; Hunter, A.; Beyerlein, I. J.

2017-05-19

The recombination process of dislocations is central to cross-slip, and transmission through Σ3 grain boundaries among other fundamental plastic deformation processes. Despite its importance, a detailed mechanistic understanding remains lacking. In this paper, we apply a continuous dislocation model, inspired by Peierls and Nabarro, complete with an ab-initio computed -surface and continuous units of infinitesimal dislocation slip, towards computing the stress-dependent recombination path of both an isotropic and anisotropic Cu screw dislocation. Under no applied stress, our model reproduces the stacking fault width between Shockley partial dislocations as predicted by discrete linear elasticity. Upon application of a compressive Escaig stress,more » the two partial dislocations coalesce to a separation of ~|b|. Upon increased loading the edge components of each partial dislocation recede, leaving behind a spread Peierls screw dislocation, indicating the recombined state. We demonstrate that the critical stress required to achieve the recombined state is independent of the shear modulus. Rather the critical recombination stress depends on an energy difference between an unstable fault energy (γτ) and the intrinsic stacking fault energy (γτ-γisf). We report recombination energies of ΔW = 0.168 eV/Å and ΔW = 0.084 eV/Å, respectively, for the Cu screw dislocation within isotropic and anisotropic media. Finally, we develop an analytic model which provides insight into our simulation results which compare favourably with other (similar) models.« less

The core structure and recombination energy of a copper screw dislocation: a Peierls study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szajewski, B. A.; Hunter, A.; Beyerlein, I. J.

The recombination process of dislocations is central to cross-slip, and transmission through Σ3 grain boundaries among other fundamental plastic deformation processes. Despite its importance, a detailed mechanistic understanding remains lacking. In this paper, we apply a continuous dislocation model, inspired by Peierls and Nabarro, complete with an ab-initio computed -surface and continuous units of infinitesimal dislocation slip, towards computing the stress-dependent recombination path of both an isotropic and anisotropic Cu screw dislocation. Under no applied stress, our model reproduces the stacking fault width between Shockley partial dislocations as predicted by discrete linear elasticity. Upon application of a compressive Escaig stress,more » the two partial dislocations coalesce to a separation of ~|b|. Upon increased loading the edge components of each partial dislocation recede, leaving behind a spread Peierls screw dislocation, indicating the recombined state. We demonstrate that the critical stress required to achieve the recombined state is independent of the shear modulus. Rather the critical recombination stress depends on an energy difference between an unstable fault energy (γτ) and the intrinsic stacking fault energy (γτ-γisf). We report recombination energies of ΔW = 0.168 eV/Å and ΔW = 0.084 eV/Å, respectively, for the Cu screw dislocation within isotropic and anisotropic media. Finally, we develop an analytic model which provides insight into our simulation results which compare favourably with other (similar) models.« less

Long-range empirical potential model: extension to hexagonal close-packed metals.

PubMed

Dai, Y; Li, J H; Liu, B X

2009-09-23

An n-body potential is developed and satisfactorily applied to hcp metals, Co, Hf, Mg, Re, Ti, and Zr, in the form of long-range empirical potential. The potential can well reproduce the lattice constants, c/a ratios, cohesive energies, and the bulk modulus for their stable structures (hcp) and metastable structures (bcc or fcc). Meanwhile, the potential can correctly predict the order of structural stability and distinguish the energy differences between their stable hcp structure and other structures. The energies and forces derived by the potential can smoothly go to zero at cutoff radius, thus completely avoiding the unphysical behaviors in the simulations. The developed potential is applied to study the vacancy, surface fault, stacking fault and self-interstitial atom in the hcp metals. The calculated formation energies of vacancy and divacancy and activation energies of self-diffusion by vacancies are in good agreement with the values in experiments and in other works. The calculated surface energies and stacking fault energies are also consistent with the experimental data and those obtained in other theoretical works. The calculated formation energies generally agree with the results in other works, although the stable configurations of self-interstitial atoms predicted in this work somewhat contrast with those predicted by other methods. The proposed potential is shown to be relevant for describing the interaction of bcc, fcc and hcp metal systems, bringing great convenience for researchers in constructing potentials for metal systems constituted by any combination of bcc, fcc and hcp metals.

Rayleigh Wave Phase Velocities in Alaska from Ambient Noise Tomography

NASA Astrophysics Data System (ADS)

Pepin, K. S.; Li, A.; Yao, Y.

2016-12-01

We have analyzed ambient noise data recorded at 136 broadband stations from the USArray Transportable Array and other permanent seismic networks in Alaska and westernmost Canada. Daily cross-correlations are obtained using vertical component seismograms and are stacked to form a single trace for each station pair. Rayleigh wave signals are extracted from the stacked traces and are used to calculate phase velocities in the Alaska region. Preliminary phase velocity maps show similar trends to those from previous studies, but also yield new anomalies given the wider geographical range provided by the Transportable Array. At short periods (6-12s), a high velocity anomaly is observed directly northeast of the Fairweather-Queen Charlotte fault, and a high velocity trend appears in the eastern Yukon terrane between the Denali and Tintina fault, probably reflecting mafic igneous crustal rocks. Significantly slow anomalies are present at the Prince William Sound, Cook Inlet, and the basins in southwestern and central Alaska, indicating sediment effects. The slow anomalies gradually shift to southeastern and south-central Alaska with increasing period (up to 40s), corresponding to the Wrangell volcano belt and the volcano arc near Cook Inlet. A broad high-velocity zone is also observed in central Alaska to the north of the Denali fault at long periods (30-40s). The Yakutat terrane is characterized as a high-velocity anomaly from period 14s to 25s but not imaged at longer periods due to poor resolution.

Lacustrine fan delta deposition alongside intrabasinal structural highs in rift basins: an example from the Early Cretaceous Jiuquan Basin, Northwestern China

NASA Astrophysics Data System (ADS)

Zhang, Chengcheng; Muirhead, James D.; Wang, Hua; Chen, Si; Liao, Yuantao; Lu, Zongsheng; Wei, Jun

2018-01-01

Development of fan deltas alongside intrabasinal structural highs has been overlooked compared to those forming on basin margins. However, these fan deltas may provide important clues regarding the tectonic and climatic controls on deposition during rift development. This paper documents fan delta deposition alongside an intrabasinal structural high within the Early Cretaceous Xiagou Formation of the Jiuquan Basin, China, using subsurface geological and geophysical data. Deposits observed in drill core support fan delta deposition occurring almost exclusively through subaerial and subaqueous gravity flows. Subsurface mapping reveals a consistent decrease in the areal extent of fan deltas from lowstand to highstand system tracts, suggesting that deposition alongside the structural high is sensitive to lake-level changes. The temporal and spatial distribution of the fan deltas display retrogradational stacking patterns, where fan deltas exhibit a decreasing lateral extent up-sequence until fan delta deposition terminated and was replaced by deposition of fine-grained lacustrine deposits. The retrogradational stacking patterns observed alongside the intrabasinal structural high are not observed in fan deltas along the basin margin in the lower parts of the Xiagou Formation. Subsidence profiles also show differential subsidence across the basin during the earliest stages of this formation, likely resulting from border fault movements. These data suggest that non-uniform stacking patterns in the lower parts of the Xiagou Formation reflect basin-scale tectonic movements as the dominant control on synrift deposition patterns. However, later stages of Xiagou Formation deposition were characterized by uniform subsidence across the basin, and uniform retrogradational stacking patterns for fan deltas alongside the intrabasinal structural high and border fault. These observations suggest that basin-scale tectonic movements played a relatively limited role in controlling sediment deposition, and imply a potential change to regional-scale processes affecting fan delta deposition during later synrift stages. Climate change is favored here as the region-scale control on the uniform retrogradational fan delta stacking patterns. This assertion is supported by pollen assemblages, isotope signatures, and organic geochemical analyses, which collectively suggest a change from a humid to semi-arid environment during later synrift stages. We suggest that variations in stacking patterns between different fan delta systems can provide insights into the basin- and regional-scale processes that control rift basin deposition.

Seismic reflection images of shallow faulting, northernmost Mississippi embayment, north of the New Madrid seismic zone

USGS Publications Warehouse

McBride, J.H.; Nelson, W.J.

2001-01-01

High-resolution seismic reflection surveys document tectonic faults that displace Pleistocene and older strata just beyond the northeast termination of the New Madrid seismic zone, at the northernmost extent of the Mississippi embayment. These faults, which are part of the Fluorspar Area fault complex in southeastern Illinois, are directly in line with the northeast-trending seismic zone. The reflection data were acquired using an elastic weight-drop source recorded to 500 msec by a 48-geophone array (24-fold) with a 10-ft (??3.0m) station interval. Recognizable reflections were recorded to about 200 msec (100-150 m). The effects of multiple reflections, numerous diffractions, low apparent velocity (i.e., steeply dipping) noise, and the relatively low-frequency content of the recorded signal provided challenges for data processing and interpreting subtle fault offsets. Data processing steps that were critical to the detection of faults included residual statics, post-stack migration, deconvolution, and noise-reduction filtering. Seismic migration was crucial for detecting and mitigating complex fault-related diffraction patterns, which produced an apparent 'folding' of reflectors on unmigrated sections. Detected individual offsets of shallow reflectors range from 5 to 10 m for the top of Paleozoic bedrock and younger strata. The migrated sections generally indicate vertical to steeply dipping normal and reverse faults, which in places outline small horsts and/or grabens. Tilting or folding of stratal reflectors associated with faulting is also locally observed. At one site, the observed faulting is superimposed over a prominent antiformal structure, which may itself be a product of the Quaternary deformation that produced the steep normal and reverse faults. Our results suggest that faulting of the Paleozoic bedrock and younger sediments of the northern Mississippi embayment is more pervasive and less localized than previously thought.

The San Gabriel mountains bright reflective zone: Possible evidence of young mid-crustal thrust faulting in southern California

USGS Publications Warehouse

Ryberg, T.; Fuis, G.S.

1998-01-01

During the Los Angeles Region Seismic Experiment (LARSE), a reflection/retraction survey was conducted along a line extending northeastward from Seal Beach, California, to the Mojave Desert, crossing the Los Angeles basin and San Gabriel Mountains. Shots and receivers were spaced most densely through the San Gabriel Mountains for the purpose of obtaining a combined reflection and refraction image of the crust in that area. A stack of common-midpoint (CMP) data reveals a bright reflective zone, 1-s thick, that dominates the stack and extends throughout most of the mid-crust of the San Gabriel Mountains. The top of this zone ranges in depth from 6 s (???18-km depth) in the southern San Gabriel Mountains to 7.5 s (???23-km depth) in the northern San Gabriel Mountains. The zone bends downward beneath the surface traces of the San Gabriel and San Andreas faults. It is brightest between these two faults, where it is given the name San Gabriel Mountains 'bright spot' (SGMBS). and becomes more poorly defined south of the San Gabriel fault and north of the San Andreas fault. The polarity of the seismic signal at the top of this zone is clearly negative, and our analysis suggests it represents a negative velocity step. The magnitude of the velocity step is approximately 1.7 km/s. In at least one location, an event with positive polarity can be observed 0.2 s beneath the top of this zone, indicating a thickness of the order of 500 m for the low-velocity zone at this location. Several factors combine to make the preferred interpretation of this bright reflective zone a young fault zone, possibly a 'master' decollement. (1) It represents a significant velocity reduction. If the rocks in this zone contain fluids, such a reduction could be caused by a differential change in fluid pressure between the caprock and the rocks in the SGMBS; near-lithostatic fluid pressure is required in the SGMBS. Such differential changes are believed to occur in the neighborhood of active fault zones, where 'fault-valve' action has been postulated. Less likely alternative explanations for this velocity reduction include the presence of magma and a change in composition to serpentinite or metagraywacke. (2) It occurs at or near the brittle-ductile transition, at least in the southern San Gabriel Mountains, a possible zone of concentrated shear. (3) A thin reflection rising from its top in the southern San Gabriel Mountains projects to the hypocenter of the 1987 M 5.9 Whittier Narrows earthquake, a blind thrust-fault earthquake with one focal plane subparallel to the reflection. Alternatively, one could argue that the bends or disruptions in the reflective zone seen at the San Gabriel and San Andreas faults are actually offsets and that the reflective zone is therefore an older feature, possibly an older fault zone. ?? 1998 Elsevier Science B.V. All rights reserved.

Configuration of twins in glass-embedded silver nanoparticles of various origin

NASA Astrophysics Data System (ADS)

Hofmeister, H.; Dubiel, M.; Tan, G. L.; Schicke, K.-D.

2005-09-01

Structural characterization using high resolution electron microscopy and diffractogram analysis of silver nanoparticles embedded in glass by various routes of fabrication was aimed at revealing the characteristic features of twin faults occuring in such particles. Nearly spherical silver nanoparticles well below 10 nm size embedded in commercial soda-lime silicate float glass have been fabricated either by silver/sodium ion exchange or by Ag+ ion implantation. Twinned nanoparticles, besides single crystalline species, have frequently been observed for both fabrication routes, mainly at sizes above 5 nm, but also at smaller sizes, even around 1 nm. The variety of particle forms comprises single crystalline particles of nearly cuboctahedron shape, particles containing single twin faults, and multiply twinned particles containing parallel twin lamellae, or cyclic twinned segments arranged around axes of fivefold symmetry. Parallel twinning is distinctly favoured by ion implantation whereas cyclic twinning preferably occurs upon ion exchange processing. Regardless of single or repeated twinning, parallel or cyclic twin arrangement, one may classify simple twin faults of regular atomic configuration and compound twin faults whose irregular configuration consists of additional planar defects like associated stacking faults or secondary twin faults. Besides, a particular superstructure composed of parallel twin lamellae of only three atomic layers thickness is observed.

The use of Stress Tensor Discriminator Faults in separating heterogeneous fault-slip data with best-fit stress inversion methods. II. Compressional stress regimes

NASA Astrophysics Data System (ADS)

Tranos, Markos D.

2018-02-01

Synthetic heterogeneous fault-slip data as driven by Andersonian compressional stress tensors were used to examine the efficiency of best-fit stress inversion methods in separating them. Heterogeneous fault-slip data are separated only if (a) they have been driven by stress tensors defining 'hybrid' compression (R < 0.375), and their σ1 axes differ in trend more than 30° (R = 0) or 50° (R = 0.25). Separation is not feasible if they have been driven by (b) 'real' (R ≥ 0.375) and 'hybrid' compressional tensors having their σ1 axes in similar trend, or (c) 'real' compressional tensors. In case (a), the Stress Tensor Discriminator Faults (STDF) exist in more than 50% of the activated fault slip data while in cases (b) and (c), they exist in percentages of much less than 50% or not at all. They constitute a necessary discriminatory tool for the establishment and comparison of two compressional stress tensors determined by a best-fit stress inversion method. The best-fit stress inversion methods are not able to determine more than one 'real' compressional stress tensor, as far as the thrust stacking in an orogeny is concerned. They can only possibly discern stress differences in the late-orogenic faulting processes, but not between the main- and late-orogenic stages.

First-principles Calculations of Twin-boundary and Stacking-fault Energies in Magnesium

DTIC Science & Technology

2010-01-01

Vasu KI. Scripta Mater 1969;3:927. [7] Couret A, Caillard D. Acta Metall 1985;33:1455. [8] Fleischer RL . Scripta Mater 1986;20:223. [9] Liu ZK. J...Jackson KA, Pederson MR, Singh DJ, Fiolhais C. Phys Rev B 1992;46:6671. [17] Kresse G, Furthmuller J. Phys Rev B 1996;54:11169. [18] Kresse G, Joubert

Expansion of Shockley stacking fault observed by scanning electron microscope and partial dislocation motion in 4H-SiC

NASA Astrophysics Data System (ADS)

Yamashita, Yoshifumi; Nakata, Ryu; Nishikawa, Takeshi; Hada, Masaki; Hayashi, Yasuhiko

2018-04-01

We studied the dynamics of the expansion of a Shockley-type stacking fault (SSF) with 30° Si(g) partial dislocations (PDs) using a scanning electron microscope. We observed SSFs as dark lines (DLs), which formed the contrast at the intersection between the surface and the SSF on the (0001) face inclined by 8° from the surface. We performed experiments at different electron-beam scanning speeds, observing magnifications, and irradiation areas. The results indicated that the elongation of a DL during one-frame scanning depended on the time for which the electron beam irradiated the PD segment in the frame of view. From these results, we derived a formula to express the velocity of the PD using the elongation rate of the corresponding DL during one-frame scanning. We also obtained the result that the elongation velocity of the DL was not influenced by changing the direction in which the electron beam irradiates the PD. From this result, we deduced that the geometrical kink motion of the PD was enhanced by diffusing carriers that were generated by the electron-beam irradiation.

Revisiting the Al/Al 2O 3 Interface: Coherent Interfaces and Misfit Accommodation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pilania, Ghanshyam; Thijsse, Barend J.; Hoagland, Richard G.

We report the coherent and semi-coherent Al/α-Al 2O 3 interfaces using molecular dynamics simulations with a mixed, metallic-ionic atomistic model. For the coherent interfaces, both Al-terminated and O-terminated nonstoichiometric interfaces have been studied and their relative stability has been established. To understand the misfit accommodation at the semi-coherent interface, a 1-dimensional (1D) misfit dislocation model and a 2-dimensional (2D) dislocation network model have been studied. For the latter case, our analysis reveals an interface dislocation structure with a network of three sets of parallel dislocations, each with pure-edge character, giving rise to a pattern of coherent and stacking-fault-like regions atmore » the interface. Structural relaxation at elevated temperatures leads to a further change of the dislocation pattern, which can be understood in terms of a competition between the stacking fault energy and the dislocation interaction energy at the interface. In conclusion, our results are expected to serve as an input for the subsequent dislocation dynamics models to understand and predict the macroscopic mechanical behavior of Al/α-Al 2O 3 composite heterostructures.« less

The shear instability energy: a new parameter for materials design?

NASA Astrophysics Data System (ADS)

Kanani, M.; Hartmaier, A.; Janisch, R.

2017-10-01

Reliable and predictive relationships between fundamental microstructural material properties and observable macroscopic mechanical behaviour are needed for the successful design of new materials. In this study we establish a link between physical properties that are defined on the atomic level and the deformation mechanisms of slip planes and interfaces that govern the mechanical behaviour of a metallic material. To accomplish this, the shear instability energy Γ is introduced, which can be determined via quantum mechanical ab initio calculations or other atomistic methods. The concept is based on a multilayer generalised stacking fault energy calculation and can be applied to distinguish the different shear deformation mechanisms occurring at TiAl interfaces during finite-temperature molecular dynamics simulations. We use the new parameter Γ to construct a deformation mechanism map for different interfaces occurring in this intermetallic. Furthermore, Γ can be used to convert the results of ab initio density functional theory calculations into those obtained with an embedded atom method type potential for TiAl. We propose to include this new physical parameter into material databases to apply it for the design of materials and microstructures, which so far mainly relies on single-crystal values for the unstable and stable stacking fault energy.

Kinetic effects in InP nanowire growth and stacking fault formation: the role of interface roughening.

PubMed

Chiaramonte, Thalita; Tizei, Luiz H G; Ugarte, Daniel; Cotta, Mônica A

2011-05-11

InP nanowire polytypic growth was thoroughly studied using electron microscopy techniques as a function of the In precursor flow. The dominant InP crystal structure is wurtzite, and growth parameters determine the density of stacking faults (SF) and zinc blende segments along the nanowires (NWs). Our results show that SF formation in InP NWs cannot be univocally attributed to the droplet supersaturation, if we assume this variable to be proportional to the ex situ In atomic concentration at the catalyst particle. An imbalance between this concentration and the axial growth rate was detected for growth conditions associated with larger SF densities along the NWs, suggesting a different route of precursor incorporation at the triple phase line in that case. The formation of SFs can be further enhanced by varying the In supply during growth and is suppressed for small diameter NWs grown under the same conditions. We attribute the observed behaviors to kinetically driven roughening of the semiconductor/metal interface. The consequent deformation of the triple phase line increases the probability of a phase change at the growth interface in an effort to reach local minima of system interface and surface energy.

Nitrogen in chromium-manganese stainless steels: a review on the evaluation of stacking fault energy by computational thermodynamics.

PubMed

Mosecker, Linda; Saeed-Akbari, Alireza

2013-06-01

Nitrogen in austenitic stainless steels and its effect on the stacking fault energy (SFE) has been the subject of intense discussions in the literature. Until today, no generally accepted method for the SFE calculation exists that can be applied to a wide range of chemical compositions in these systems. Besides different types of models that are used from first-principle to thermodynamics-based approaches, one main reason is the general lack of experimentally measured SFE values for these steels. Moreover, in the respective studies, not only different alloying systems but also different domains of nitrogen contents were analyzed resulting in contrary conclusions on the effect of nitrogen on the SFE. This work gives a review on the current state of SFE calculation by computational thermodynamics for the Fe-Cr-Mn-N system. An assessment of the thermodynamic effective Gibbs free energy, [Formula: see text], model for the [Formula: see text] phase transformation considering existing data from different literature and commercial databases is given. Furthermore, we introduce the application of a non-constant composition-dependent interfacial energy, б γ / ε , required to consider the effect of nitrogen on SFE in these systems.

Nitrogen in chromium–manganese stainless steels: a review on the evaluation of stacking fault energy by computational thermodynamics

PubMed Central

Mosecker, Linda; Saeed-Akbari, Alireza

2013-01-01

Nitrogen in austenitic stainless steels and its effect on the stacking fault energy (SFE) has been the subject of intense discussions in the literature. Until today, no generally accepted method for the SFE calculation exists that can be applied to a wide range of chemical compositions in these systems. Besides different types of models that are used from first-principle to thermodynamics-based approaches, one main reason is the general lack of experimentally measured SFE values for these steels. Moreover, in the respective studies, not only different alloying systems but also different domains of nitrogen contents were analyzed resulting in contrary conclusions on the effect of nitrogen on the SFE. This work gives a review on the current state of SFE calculation by computational thermodynamics for the Fe–Cr–Mn–N system. An assessment of the thermodynamic effective Gibbs free energy, , model for the phase transformation considering existing data from different literature and commercial databases is given. Furthermore, we introduce the application of a non-constant composition-dependent interfacial energy, бγ/ε, required to consider the effect of nitrogen on SFE in these systems. PMID:27877573

Revisiting the Al/Al 2O 3 Interface: Coherent Interfaces and Misfit Accommodation

DOE PAGES

Pilania, Ghanshyam; Thijsse, Barend J.; Hoagland, Richard G.; ...

2014-03-27

We report the coherent and semi-coherent Al/α-Al 2O 3 interfaces using molecular dynamics simulations with a mixed, metallic-ionic atomistic model. For the coherent interfaces, both Al-terminated and O-terminated nonstoichiometric interfaces have been studied and their relative stability has been established. To understand the misfit accommodation at the semi-coherent interface, a 1-dimensional (1D) misfit dislocation model and a 2-dimensional (2D) dislocation network model have been studied. For the latter case, our analysis reveals an interface dislocation structure with a network of three sets of parallel dislocations, each with pure-edge character, giving rise to a pattern of coherent and stacking-fault-like regions atmore » the interface. Structural relaxation at elevated temperatures leads to a further change of the dislocation pattern, which can be understood in terms of a competition between the stacking fault energy and the dislocation interaction energy at the interface. In conclusion, our results are expected to serve as an input for the subsequent dislocation dynamics models to understand and predict the macroscopic mechanical behavior of Al/α-Al 2O 3 composite heterostructures.« less

Mechanical properties and phase stability of monoborides using density functional theory calculations

NASA Astrophysics Data System (ADS)

Kim, Hyojung; Trinkle, Dallas R.

2017-06-01

We compute the structural energies, elastic constants, and stacking fault energies, and investigate the phase stability of monoborides with different compositions (" close=")X1-x 1Xx2)">X1-x 1Xx2B (X =Ti/Fe/Mo/Nb/V ) using density functional theory in order to search for Ti monoborides with improved mechanical properties. Our computed Young's modulus and Pugh's modulus ratio, which correlate with stiffness and toughness, agree well with predictions from Vegard's law with the exceptions of mixed monoborides containing Mo and Fe. Among all the monoborides considered in this paper, TiB has the smallest Pugh's ratio, which suggests that the addition of solutes can improve the toughness of a Ti matrix. When X1B and X2B are respectively most stable in the B27 and Bf structures, the mixed monoborides (X0.51X0.52)B , mixed (Ti0.5Mo0.5 )B and mixed (Ti0.5V0.5 )B have a higher Young's modulus, a higher Pugh's ratio, and a smaller stacking fault energy than TiB. We also construct phase diagrams and find large solubility limits for solid solutions containing Ti compared to those containing Fe.

Influence of stacking fault energy on defect structures and microhardness of Cu and Cu alloys.

PubMed

Tao, Jing-Mei; Li, Dai; Li, Cai-Ju; Zhu, Xin-Kun

2011-12-01

Nano-structured Cu, Cu-10 wt%Zn and Cu-2 wt%Al with stacking fault energies (SFE) of 78, 35 and 37 mJ/m2, respectively, were preprared through high energy ball milling. X-ray diffraction and Vickers microharness test were used to investigate the microstructure and microhardness of all the samples after ball milling. X-ray diffraction measurements indicate that lower SFEs lead both to decrease in grain size and increase in microstrain, dislocation and twin densities for Cu-10 wt%Zn and Cu-2 wt%Al after 5 h of ball milling. The microhardnesses of Cu-10 wt%Zn and Cu-2 wt%Al reach to nearly the same values of 2.5 GPa after 5 h of ball milling, which is higher than that of Cu of 2.0 GPa. Two factors are considered to contribute to the finer grian size and higher microhardness of Cu-10 wt%Zn and Cu-2 wt%Al: (1) the effect of solid solution strengthening, which result in the interaction of solute atoms with screw dislocations; (2) the introduction of deformation twins during ball milling process by the decreasing of SFE, which results in the grain refinement.

Effect of carbon tetrabromide on the morphology of GaAs nanowires.

PubMed

Salehzadeh, O; Watkins, S P

2011-04-22

Carbon is a commonly used p-type dopant in planar III-V semiconductors, however its use in nanowire (NW) growth has been much less reported. In this work we show that the morphology of gold assisted GaAs NWs can be strongly modified by the presence of CBr(4) vapor during growth by metalorganic vapor phase epitaxy. GaAs NWs were grown under conditions which result in strong tapering and lateral growth at low growth temperatures by the use of triethylgallium (TEGa) instead of the more usual precursor, trimethylgallium (TMGa). Under these conditions, NWs grown in the presence of CBr(4) exhibit higher axial and lower radial growth rates, and negligible tapering compared with NWs grown in the absence of CBr(4) under the same conditions. We attribute this primarily to the suppression of the 2d growth rate by CBr(4), which enhances the axial growth rate of the nanowires. NWs grown with CBr(4) show stacking-fault-free zincblende structure, while the NWs grown without CBr(4) show a high density of stacking faults. This work underlines the striking effects which precursor chemistry can have on nanowire morphology.

Segregation-Assisted Plasticity in Ni-Based Superalloys

NASA Astrophysics Data System (ADS)

Barba, D.; Smith, T. M.; Miao, J.; Mills, M. J.; Reed, R. C.

2018-03-01

Correlative high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy are used to study deformation-induced planar faults in the single-crystal superalloy MD2 crept at 800 °C and 650 MPa. Segregation of Cr and Co at microtwins, anti-phase boundaries (APB), and complex/superlattice extrinsic and intrinsic stacking faults (CESF/SESF and CISF/SISF) is confirmed and quantified. The extent of this is found to depend upon the fault type, being most pronounced for the APB. The CESF/SESF is studied in detail due to its role as a precursor of the microtwins causing the majority of plasticity under these conditions. Quantitative modeling is carried out to rationalize the findings; the experimental results are consistent with a greater predicted velocity for the lengthening of the CESF/SESF—compared with the other types of fault—and hence confirm its role in the diffusion-assisted plasticity needed for the microtwinning mechanism to be operative.

Fault linkage and continental breakup

NASA Astrophysics Data System (ADS)

Cresswell, Derren; Lymer, Gaël; Reston, Tim; Stevenson, Carl; Bull, Jonathan; Sawyer, Dale; Morgan, Julia

2017-04-01

The magma-poor rifted margin off the west coast of Galicia (NW Spain) has provided some of the key observations in the development of models describing the final stages of rifting and continental breakup. In 2013, we collected a 68 x 20 km 3D seismic survey across the Galicia margin, NE Atlantic. Processing through to 3D Pre-stack Time Migration (12.5 m bin-size) and 3D depth conversion reveals the key structures, including an underlying detachment fault (the S detachment), and the intra-block and inter-block faults. These data reveal multiple phases of faulting, which overlap spatially and temporally, have thinned the crust to between zero and a few km thickness, producing 'basement windows' where crustal basement has been completely pulled apart and sediments lie directly on the mantle. Two approximately N-S trending fault systems are observed: 1) a margin proximal system of two linked faults that are the upward extension (breakaway faults) of the S; in the south they form one surface that splays northward to form two faults with an intervening fault block. These faults were thus demonstrably active at one time rather than sequentially. 2) An oceanward relay structure that shows clear along strike linkage. Faults within the relay trend NE-SW and heavily dissect the basement. The main block bounding faults can be traced from the S detachment through the basement into, and heavily deforming, the syn-rift sediments where they die out, suggesting that the faults propagated up from the S detachment surface. Analysis of the fault heaves and associated maps at different structural levels show complementary fault systems. The pattern of faulting suggests a variation in main tectonic transport direction moving oceanward. This might be interpreted as a temporal change during sequential faulting, however the transfer of extension between faults and the lateral variability of fault blocks suggests that many of the faults across the 3D volume were active at least in part simultaneously. Alternatively, extension may have varied in direction spatially if it were a rotation about a pole located to the north.

Imaging the Moon's Core with Seismology

NASA Technical Reports Server (NTRS)

Weber, Renee C.; Lin, Pei-Ying Patty; Garnero, Ed J.; Williams, Quetin C.; Lognonne, Philippe

2011-01-01

Constraining the structure of the lunar core is necessary to improve our understanding of the present-day thermal structure of the interior and the history of a lunar dynamo, as well as the origin and thermal and compositional evolution of the Moon. We analyze Apollo deep moonquake seismograms using terrestrial array processing methods to search for the presence of reflected and converted energy from the lunar core. Although moonquake fault parameters are not constrained, we first explore a suite of theoretical focal spheres to verify that fault planes exist that can produce favorable core reflection amplitudes relative to direct up-going energy at the Apollo stations. Beginning with stacks of event seismograms from the known distribution of deep moonquake clusters, we apply a polarization filter to account for the effects of seismic scattering that (a) partitions energy away from expected components of ground motion, and (b) obscures all but the main P- and S-wave arrivals. The filtered traces are then shifted to the predicted arrival time of a core phase (e.g. PcP) and stacked to enhance subtle arrivals associated with the Moon s core. This combination of filtering and array processing is well suited for detecting deep lunar seismic reflections, since we do not expect scattered wave energy from near surface (or deeper) structure recorded at varying epicentral distances and stations from varying moonquakes at varying depths to stack coherently. Our results indicate the presence of a solid inner and fluid outer core, overlain by a partial-melt-containing boundary layer (Table 1). These layers are consistently observed among stacks from four classes of reflections: P-to-P, S-to-P, P-to-S, and S-to-S, and are consistent with current indirect geophysical estimates of core and deep mantle properties, including mass, moment of inertia, lunar laser ranging, and electromagnetic induction. Future refinements are expected following the successful launch of the GRAIL lunar orbiter and SELENE 2 lunar lander missions.

Is there a "blind" strike-slip fault at the southern end of the San Jacinto Fault system?

NASA Astrophysics Data System (ADS)

Tymofyeyeva, E.; Fialko, Y. A.

2015-12-01

We have studied the interseismic deformation at the southern end of the San Jacinto fault system using Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data. To complement the continuous GPS measurements from the PBO network, we have conducted campaign-style GPS surveys of 19 benchmarks along Highway 78 in the years 2012, 2013, and 2014. We processed the campaign GPS data using GAMIT to obtain horizontal velocities. The data show high velocity gradients East of the surface trace of the Coyote Creek Fault. We also processed InSAR data from the ascending and descending tracks of the ENVISAT mission between the years 2003 and 2010. The InSAR data were corrected for atmospheric artifacts using an iterative common point stacking method. We combined average velocities from different look angles to isolate the fault-parallel velocity field, and used fault-parallel velocities to compute strain rate. We filtered the data over a range of wavelengths prior to numerical differentiation, to reduce the effects of noise and to investigate both shallow and deep sources of deformation. At spatial wavelengths less than 2km the strain rate data show prominent anomalies along the San Andreas and Superstition Hills faults, where shallow creep has been documented by previous studies. Similar anomalies are also observed along parts of the Coyote Creek Fault, San Felipe Fault, and an unmapped southern continuation of the Clark strand of the San Jacinto Fault. At wavelengths on the order of 20km, we observe elevated strain rates concentrated east of the Coyote Creek Fault. The long-wavelength strain anomaly east of the Coyote Creek Fault, and the localized shallow creep observed in the short-wavelength strain rate data over the same area suggest that there may be a "blind" segment of the Clark Fault that accommodates a significant portion of the deformation on the southern end of the San Jacinto Fault.

Seismic imaging of the Main Frontal Thrust in Nepal reveals a shallow décollement and blind thrusting

NASA Astrophysics Data System (ADS)

Almeida, Rafael V.; Hubbard, Judith; Liberty, Lee; Foster, Anna; Sapkota, Soma Nath

2018-07-01

Because great earthquakes in the Himalaya have an average recurrence interval exceeding 500 yr, most of what we know about past earthquakes comes from paleoseismology and tectonic geomorphology studies of the youngest fault system there, the Main Frontal Thrust (MFT). However, these data are sparse relative to fault segmentation and length, and interpretations are often hard to validate in the absence of information about fault geometry. Here, we image the upper two km of strata in the vicinity of the fault tip of the MFT in central Nepal (around the town of Bardibas) applying a pre-stack migration approach to two new seismic reflection profiles that we interpret using quantitative fault-bend folding theory. Our results provide direct evidence that a shallow décollement produces both emergent (Patu thrust) and blind (Bardibas thrust) fault strands. We show that the décollement lies about 2 km below the land surface near the fault tip, and steps down to a regional 5 km deep décollement level to the north. This implies that there is significant variation in the depth of the décollement. We demonstrate that some active faults do not reach the surface, and therefore paleoseismic trenching alone cannot characterize the earthquake history at these locations. Although blind, these faults have associated growth strata that allow us to infer their most recent displacement history. We present the first direct evidence of fault dip on two fault strands of the MFT at depth that can allow terrace uplift measurements to be more accurately converted to fault slip. We identify a beveled erosional surface buried beneath Quaternary sediments, indicating that strath surface formation is modulated by both climate-related base level changes and tectonics. Together, these results indicate that subsurface imaging, in conjunction with traditional paleoseismological tools, can best characterize the history of fault slip in the Himalaya and other similar thrust fault systems.

Passive seismic imaging based on seismic interferometry: method and its application to image the structure around the 2013 Mw6.6 Lushan earthquake

NASA Astrophysics Data System (ADS)

Gu, N.; Zhang, H.

2017-12-01

Seismic imaging of fault zones generally involves seismic velocity tomography using first arrival times or full waveforms from earthquakes occurring around the fault zones. However, in most cases seismic velocity tomography only gives smooth image of the fault zone structure. To get high-resolution structure of the fault zones, seismic migration using active seismic data needs to be used. But it is generally too expensive to conduct active seismic surveys, even for 2D. Here we propose to apply the passive seismic imaging method based on seismic interferometry to image fault zone detailed structures. Seismic interferometry generally refers to the construction of new seismic records for virtual sources and receivers by cross correlating and stacking the seismic records on physical receivers from physical sources. In this study, we utilize seismic waveforms recorded on surface seismic stations for each earthquake to construct zero-offset seismic record at each earthquake location as if there was a virtual receiver at each earthquake location. We have applied this method to image the fault zone structure around the 2013 Mw6.6 Lushan earthquake. After the occurrence of the mainshock, a 29-station temporary array is installed to monitor aftershocks. In this study, we first select aftershocks along several vertical cross sections approximately normal to the fault strike. Then we create several zero-offset seismic reflection sections by seismic interferometry with seismic waveforms from aftershocks around each section. Finally we migrate these zero-offset sections to create seismic structures around the fault zones. From these migration images, we can clearly identify strong reflectors, which correspond to major reverse fault where the mainshock occurs. This application shows that it is possible to image detailed fault zone structures with passive seismic sources.

Shallow deformation of the San Andreas fault 5 years following the 2004 Parkfield earthquake (Mw6) combining ERS2 and Envisat InSAR.

PubMed

Bacques, Guillaume; de Michele, Marcello; Raucoules, Daniel; Aochi, Hideo; Rolandone, Frédérique

2018-04-16

This study focuses on the shallow deformation that occurred during the 5 years following the Parkfield earthquake (28/09/2004, Mw 6, San Andreas Fault, California). We use Synthetic Aperture Radar interferometry (InSAR) to provide precise measurements of transient deformations after the Parkfield earthquake between 2005 and 2010. We propose a method to combine both ERS2 and ENVISAT interferograms to increase the temporal data sampling. Firstly, we combine 5 years of available Synthetic Aperture Radar (SAR) acquisitions including both ERS-2 and Envisat. Secondly, we stack selected interferograms (both from ERS2 and Envisat) for measuring the temporal evolution of the ground velocities at given time intervals. Thanks to its high spatial resolution, InSAR could provide new insights on the surface fault motion behavior over the 5 years following the Parkfield earthquake. As a complement to previous studies in this area, our results suggest that shallow transient deformations affected the Creeping-Parkfield-Cholame sections of the San Andreas Fault after the 2004 Mw6 Parkfield earthquake.

Resilience Design Patterns - A Structured Approach to Resilience at Extreme Scale (version 1.0)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hukerikar, Saurabh; Engelmann, Christian

Reliability is a serious concern for future extreme-scale high-performance computing (HPC) systems. Projections based on the current generation of HPC systems and technology roadmaps suggest that very high fault rates in future systems. The errors resulting from these faults will propagate and generate various kinds of failures, which may result in outcomes ranging from result corruptions to catastrophic application crashes. Practical limits on power consumption in HPC systems will require future systems to embrace innovative architectures, increasing the levels of hardware and software complexities. The resilience challenge for extreme-scale HPC systems requires management of various hardware and software technologies thatmore » are capable of handling a broad set of fault models at accelerated fault rates. These techniques must seek to improve resilience at reasonable overheads to power consumption and performance. While the HPC community has developed various solutions, application-level as well as system-based solutions, the solution space of HPC resilience techniques remains fragmented. There are no formal methods and metrics to investigate and evaluate resilience holistically in HPC systems that consider impact scope, handling coverage, and performance & power eciency across the system stack. Additionally, few of the current approaches are portable to newer architectures and software ecosystems, which are expected to be deployed on future systems. In this document, we develop a structured approach to the management of HPC resilience based on the concept of resilience-based design patterns. A design pattern is a general repeatable solution to a commonly occurring problem. We identify the commonly occurring problems and solutions used to deal with faults, errors and failures in HPC systems. The catalog of resilience design patterns provides designers with reusable design elements. We define a design framework that enhances our understanding of the important constraints and opportunities for solutions deployed at various layers of the system stack. The framework may be used to establish mechanisms and interfaces to coordinate flexible fault management across hardware and software components. The framework also enables optimization of the cost-benefit trade-os among performance, resilience, and power consumption. The overall goal of this work is to enable a systematic methodology for the design and evaluation of resilience technologies in extreme-scale HPC systems that keep scientific applications running to a correct solution in a timely and cost-ecient manner in spite of frequent faults, errors, and failures of various types.« less

Structure of the Sumatra wedge affected by the 26th December 2004 :Effects of the lower plate volcanic ridges.

NASA Astrophysics Data System (ADS)

Rangin, C.; Sibuet, J. C.; Lin, J. Y.; Le Pichon, X.

2009-04-01

Detailed swath-bathymetry, coupled with echo-sounder data were collected offshore the northern tip of Sumatra over the rupture area of the 26th December 2004 Mw=9.2 earthquake during the Sumatra aftershock cruise. 20 ocean bottom seismometers were also deployed in the northern Sumatra area., and more than 1000 events were identified during the 12 days recording period. We mapped recently active steeply dipping thrust fault zone within the western termination of the Sunda accreted wedge. Main N10°W trending out of sequence thrust fault zones with a discrete westward vergency and some component of dextral strike-slip motion were continuously mapped within the wedge, on the basis of bathymetry and low frequency sounder profiles. The interplate boundary does not appear to extend into the frontal part of the wedge but most probably merges in its central part along these major faults, the Lower and Upper Splay Faults. After relocation, the seismicity shows different pattern in each side of this Upper Splay Fault. East of this boundary, beneath the Aceh basin, the earthquake depths ranged from 30 to 60 km allow us to illustrate the subducted plate. In the western part, the aftershock distribution is strongly influenced by the N-S orientated oceanic fracture zones. Two clusters of earthquakes between 10 and 50 km in depth trending along N-S direction are observed in the lower wedge that we interpret to be reactive fracture zones. The lower wedge is interpreted as the northern prolongation below the wedge of the lower plate NS oceanic fracture zone ridges affected by NS trending left lateral strike-slip faults. This wedge outer ridge is in the process of being transferred to the upper plate. On the other hand the central ridge is interpreted as possible stacked volcanic ridge slivers already incorporated into the upper plate along the subduction buttress (the inner ridge of the wedge). We propose that the tectonic interaction of the volcanic Indian Ocean fracture ridges of the subducted plate with the leading edge of the upper Sunda plate subduction zone is an active tectonic transfer process of oceanic material to the upper plate. The proposed emergence of the interplate boundary into the middle part of the wedge along the Lower Splay Fault, could have favoured the formation of the giant Sumatra tsunami at moderate water depth. This docking and temporary stacking of these volcanic ridges before their subduction at depth, is favoured by the strong oblique convergence that prevails up to the Bengal basin into the north.

Imaging a Fault Boundary System Using Controlled-Source Data Recorded on a Large-N Seismic Array

NASA Astrophysics Data System (ADS)

Paschall, O. C.; Chen, T.; Snelson, C. M.; Ralston, M. D.; Rowe, C. A.

2016-12-01

The Source Physics Experiment (SPE) is a series of chemical explosions conducted in southern Nevada with an objective of improving nuclear explosion monitoring. Five chemical explosions have occurred thus far in granite, the most recent being SPE-5 on April 26, 2016. The SPE series will improve our understanding of seismic wave propagation (primarily S-waves) due to explosions, and allow better discrimination of background seismicity such as earthquakes and explosions. The Large-N portion of the project consists of 996 receiver stations. Half of the stations were vertical component and the other half were three-component geophones. All receivers were deployed for 30 days and recorded the SPE-5 shot, earthquakes, noise, and an additional controlled-source: a large weight-drop, which is a 13,000 kg modified industrial pile driver. In this study, we undertake reflection processing of waveforms from the weight-drop, as recorded by a line of sensors extracted from the Large-N array. The profile is 1.2 km in length with 25 m station spacing and 100 m shot point spacing. This profile crosses the Boundary Fault that separates granite body and an alluvium basin, a strong acoustic impedance boundary that scatters seismic energy into S-waves and coda. The data were processed with traditional seismic reflection processing methods that include filtering, deconvolution, and stacking. The stack will be used to extract the location of the splays of the Boundary Fault and provide geologic constraints to the modeling and simulation teams within the SPE project.

Manipulation of domain-wall solitons in bi- and trilayer graphene

NASA Astrophysics Data System (ADS)

Jiang, Lili; Wang, Sheng; Shi, Zhiwen; Jin, Chenhao; Utama, M. Iqbal Bakti; Zhao, Sihan; Shen, Yuen-Ron; Gao, Hong-Jun; Zhang, Guangyu; Wang, Feng

2018-01-01

Topological dislocations and stacking faults greatly affect the performance of functional crystalline materials1-3. Layer-stacking domain walls (DWs) in graphene alter its electronic properties and give rise to fascinating new physics such as quantum valley Hall edge states4-10. Extensive efforts have been dedicated to the engineering of dislocations to obtain materials with advanced properties. However, the manipulation of individual dislocations to precisely control the local structure and local properties of bulk material remains an outstanding challenge. Here we report the manipulation of individual layer-stacking DWs in bi- and trilayer graphene by means of a local mechanical force exerted by an atomic force microscope tip. We demonstrate experimentally the capability to move, erase and split individual DWs as well as annihilate or create closed-loop DWs. We further show that the DW motion is highly anisotropic, offering a simple approach to create solitons with designed atomic structures. Most artificially created DW structures are found to be stable at room temperature.

Disorder-controlled superconductivity at YBa2Cu3O7/SrTiO3 interfaces

NASA Astrophysics Data System (ADS)

Garcia-Barriocanal, J.; Perez-Muñoz, A. M.; Sefrioui, Z.; Arias, D.; Varela, M.; Leon, C.; Pennycook, S. J.; Santamaria, J.

2013-06-01

We examine the effect of interface disorder in suppressing superconductivity in coherently grown ultrathin YBa2Cu3O7 (YBCO) layers on SrTiO3 (STO) in YBCO/STO superlattices. The termination plane of the STO is TiO2 and the CuO chains are missing at the interface. Disorder (steps) at the STO interface cause alterations of the stacking sequence of the intracell YBCO atomic layers. Stacking faults give rise to antiphase boundaries which break the continuity of the CuO2 planes and depress superconductivity. We show that superconductivity is directly controlled by interface disorder outlining the importance of pair breaking and localization by disorder in ultrathin layers.

The Alpine nappe stack in western Austria: a crustal-scale cross section

NASA Astrophysics Data System (ADS)

Pomella, Hannah; Ortner, Hugo; Zerlauth, Michael; Fügenschuh, Bernhard

2015-04-01

Based on an N-S-oriented crustal-scale cross section running east of the Rhine Valley in Vorarlberg, western Austria, we address the Alpine nappe stack and discuss the boundary between Central and Eastern Alps. For our cross section, we used surface geology, drillings and reinterpreted seismic lines, together with published sections. The general architecture of the examined area can be described as a typical foreland fold-and-thrust belt, comprising the tectonic units of the Subalpine Molasse, (Ultra-)Helvetic, Penninic and Austroalpine nappes. These units overthrusted the autochthonous Molasse along the south-dipping listric Alpine basal thrust. The European Basement, together with its autochthonous cover, dips gently towards the south and is dissected by normal faults and trough structures. The seismic data clearly show an offset not only of the top of the European Basement, but also of the Mesozoic cover and the Lower Marine Molasse. This indicates an activity of the structures as normal faults after the sedimentation of the Lower Marine Molasse. The Subalpine Molasse is multiply stacked, forming a triangle zone at the boundary with the foreland Molasse. The shortening within the Subalpine Molasse amounts to approximately 45 km (~67 %), as deduced from our cross section with the Lower Marine Molasse as a reference. The hinterland-dipping duplex structure of the Helvetic nappes is deduced from surface and borehole data. There are at least two Helvetic nappes needed to fill the available space between the Molasse below and the Northpenninic above. This is in line with the westerly located NRP20-East transect (Schmid et al., Tectonics 15(5):1047-1048, 1996; Schmid et al., The TRANSMED Atlas: the Mediterranean Region from Crust to Mantle, 2004), where the two Helvetic nappes are separated by the Säntis thrust. Yet in contrast to the Helvetic nappes in the NRP20-East transect, both of our Helvetic nappes comprise Cretaceous and Jurassic strata. This change is explained by an eastward down-stepping of the Säntis thrust along a pre-existing, approximately N-S striking lateral ramp bounding an inverted Jurassic graben structure below the Rhine Valley. This causes the Säntis thrust to detach the base Cretaceous west of the Rhine Valley and the base Jurassic units east of it. This graben-controlled change in detachment level leads to the formation of quite different nappe stacks on either side of the Rhine Valley and a "fault-controlled" appearance of the boundary between the Central and Eastern Alps.

Impact of extended defects on optical properties of (1-101)GaN grown on patterned Si

NASA Astrophysics Data System (ADS)

Okur, S.; Izyumskaya, N.; Zhang, F.; Avrutin, V.; Metzner, S.; Karbaum, C.; Bertram, F.; Christen, J.; Morkoç, H.; Özgür, Ü.

2014-03-01

The optical quality of semipolar (1 101)GaN layers was explored by time- and polarization-resolved photoluminescence spectroscopy. High intensity bandedge emission was observed in +c-wing regions of the stripes as a result of better structural quality, while -c-wing regions were found to be of poorer optical quality due to basal plane and prismatic stacking faults (BSFs and PSFs) in addition to a high density of TDs. The high optical quality region formed on the +cwings was evidenced also from the much slower biexponential PL decays (0.22 ns and 1.70 ns) and an order of magnitude smaller amplitude ratio of the fast decay (nonradiative origin) to the slow decay component (radiative origin) compared to the -c-wing regions. In regard to defect-related emission, decay times for the BSF and PSF emission lines at 25 K (~ 0.80 ns and ~ 3.5 ns, respectively) were independent of the excitation density within the range employed (5 - 420 W/cm2), and much longer than that for the donor bound excitons (0.13 ns at 5 W/cm2 and 0.22 ns at 420 W/cm2). It was also found that the emission from BSFs had lower polarization degree (0.22) than that from donor bound excitons (0.35). The diminution of the polarization degree when photogenerated carriers recombine within the BSFs is another indication of the negative effects of stacking faults on the optical quality of the semipolar (1101)GaN. In addition, spatial distribution of defects in semipolar (1101)-oriented InGaN active region layers grown on stripe patterned Si substrates was investigated using near-field scanning optical microscopy. The optical quality of -c- wing regions was found to be worse compared to +c-wing regions due to the presence of higher density of stacking faults and threading dislocations. The emission from the +c-wings was very bright and relatively uniform across the sample, which is indicative of a homogeneous In distribution.

Defect-Induced Nucleation and Epitaxy: A New Strategy toward the Rational Synthesis of WZ-GaN/3C-SiC Core-Shell Heterostructures.

PubMed

Liu, Baodan; Yang, Bing; Yuan, Fang; Liu, Qingyun; Shi, Dan; Jiang, Chunhai; Zhang, Jinsong; Staedler, Thorsten; Jiang, Xin

2015-12-09

In this work, we demonstrate a new strategy to create WZ-GaN/3C-SiC heterostructure nanowires, which feature controllable morphologies. The latter is realized by exploiting the stacking faults in 3C-SiC as preferential nucleation sites for the growth of WZ-GaN. Initially, cubic SiC nanowires with an average diameter of ∼100 nm, which display periodic stacking fault sections, are synthesized in a chemical vapor deposition (CVD) process to serve as the core of the heterostructure. Subsequently, hexagonal wurtzite-type GaN shells with different shapes are grown on the surface of 3C-SiC wire core. In this context, it is possible to obtain two types of WZ-GaN/3C-SiC heterostructure nanowires by means of carefully controlling the corresponding CVD reactions. Here, the stacking faults, initially formed in 3C-SiC nanowires, play a key role in guiding the epitaxial growth of WZ-GaN as they represent surface areas of the 3C-SiC nanowires that feature a higher surface energy. A dedicated structural analysis of the interfacial region by means of high-resolution transmission electron microscopy (HRTEM) revealed that the disordering of the atom arrangements in the SiC defect area promotes a lattice-matching with respect to the WZ-GaN phase, which results in a preferential nucleation. All WZ-GaN crystal domains exhibit an epitaxial growth on 3C-SiC featuring a crystallographic relationship of [12̅10](WZ-GaN) //[011̅](3C-SiC), (0001)(WZ-GaN)//(111)(3C-SiC), and d(WZ-GaN(0001)) ≈ 2d(3C-SiC(111)). The approach to utilize structural defects of a nanowire core to induce a preferential nucleation of foreign shells generally opens up a number of opportunities for the epitaxial growth of a wide range of semiconductor nanostructures which are otherwise impossible to acquire. Consequently, this concept possesses tremendous potential for the applications of semiconductor heterostructures in various fields such as optics, electrics, electronics, and photocatalysis for energy harvesting and environment processing.

Physical Properties of NiFeCrCo-based High-Entropy Alloys

NASA Astrophysics Data System (ADS)

Zaddach, Alexander Joseph

Conventional alloy design has been based on improving the properties of a single base, or solvent, element through relatively small additions of other elements. More recently, research has been conducted on alloys that contain multiple principal elements, particularly multi-component equiatomic alloys. When such alloys form solid solution phases, they are termed "high-entropy alloys" (HEAs) due to their high configurational entropy. These alloys often have favorable properties compared to conventional dilute solution alloys, but their compositional complexity and relative novelty means that they remain difficult to design and their basic properties are often unknown. The motivation for this work is a detailed experimental exploration of some of the basic physical properties of NiFeCrCo-based alloys. NiFeCrCoMn was one of the first equiatomic HEAs developed. As the compositional space within this single system is extremely large, this work focuses primarily on equiatomic alloys and a limited subset of non-equiatomic alloys chosen for their specific properties. Several alloys are prepared using both conventional methods (arc melting) and nonequilibrium methods (mechanical alloying). Properties studied include stacking fault energy, bulk mechanical properties, single crystal elastic constants, and magnetic properties. The equiatomic NiFeCrCo and NiFeCrCoMn alloys were found to have a moderate to low stacking fault energy, 18 -- 30 mJ m-2. As they are single-phase, fcc alloys, they have high tensile ductility. Additionally, they also exhibit high work-hardening rates, resulting in high toughness. NiFeCrCo outperforms the 5-component equiatomic alloy in ductility and toughness. A 5-component alloy with higher Co content to reduce the stacking fault energy also performs well. The single crystal elastic constants were measured using nanoindentation modulus measurements of grains of known orientation. The measured elastic constants were consistent with those calculated using first-principles modeling. Adding Zn in addition to Mn resulted in an alloy that preferred to form multiple phases. After the optimal heat treatment, it forms nano-sized grains of FeCo, which results in permanent magnetic behavior at room temperature.

Lithospheric structure beneath Mainland China from ambient noise tomography

NASA Astrophysics Data System (ADS)

Huang, J.; Peng, J.; Liu, Z.

2017-12-01

The Chinese continent is composed of several Precambrian craton blocks and Phanerozoic orogenic belts. To better understand the complex geological structure and tectonic evolution, it is important to develop a high-resolution shear velocity model of the lithosphere. In this study, we try to use ambient noise tomography to image the lithospheric structure beneath mainland China. However, in contrast with most of the existing ambient noise tomography studies which focus on the surface wave at periods shorter than 60 s, we apply the technique of phase-weighted stack (PWS) (Schimmel et al., 2011) when stacking the cross-correlations of ambient noise. We could extract long-period ( 125 s) dispersions to image the high-resolution lithospheric structure. We collected continuous seismic records from the broadband stations of China Regional Seismic Networks and NECESSArray between Sept., 2009 and Aug., 2011. We constructed Rayleigh wave group and phase velocity maps on 0.25 ×0.25 degree grids, and then inverted a high-resolution lithospheric 3D shear velocity model up to 150 km depth. The results exhibited pronounced lateral heterogeneity of the lithospheric structure of the study area. It is obvious that the high velocities beneath the Ordos and Sichuan Basin exceeds 150 km, representing the strong and thick lithosphere. The lithospheric thickness gradually thins from west to east for the North China Craton (NCC) and the Yangtze Craton (YZC). The lithospheric thickness of the eastern NCC is about 80-90 km, and which beneath the Bohai Bay is thinnest, only 60-80 km. For the lower YZC and the Cathaysia block, the lithospheric thickness is about 70-80 km, slightly thinner than the eastern NCC. The observed thin lithosphere (about 60-80 km) beneath the eastern Northeast China is likely to be associated with the Tanlu fault and the Quaternary Changbaishan and Jingpohu volcano. The lithosphere thickness beneath the Tanlu fault is thin or absent, which possibly be related to the upwelling of the hot asthenosphere, and the fault provides channels. *This work was supported by National Key R&D Plan (Grant No. 2017YFC0601406). KEYWORDS: Ambient noise, Phase-weighted stack, Lithosphere, Shear velocity

Structure of the Red Dog District, western Brooks Range, Alaska

USGS Publications Warehouse

de Vera, Jean-Pierre P.; McClay, K. R.

2004-01-01

The Red Dog district of the western Brooks Range of northern Alaska, which includes the sediment-hosted Zn-Pb-Ag ± Ba deposits at Red Dog, Su-Lik, and Anarraaq, contains one of the world's largest reserves of zinc. This paper presents a new model for the structural development of the area and shows that understanding the structure is crucial for future exploration efforts and new mineral discoveries in the district. In the Red Dog district, a telescoped Late Devonian through Jurassic continental passive margin is exposed in a series of subhorizontally stacked, internally imbricated, and regionally folded thrust sheets. These sheets were emplaced during the Middle Jurassic to Late Cretaceous Brookian orogeny and subsequently were uplifted by late tectonic activity in the Tertiary. The thrust sheet stack comprises seven tectonostratigraphically distinct allochthonous sheets, three of which have been subject to regional and detailed structural analysis. The lowermost of these is the Endicott Mountains allochthon, which is overlain by the structurally higher Picnic Creek and Kelly River allochthons. Each individual allochthon is itself internally imbricated into a series of tectonostratigraphically coherent and distinct thrust plates and subplates. This structural style gives rise to duplex development and imbrication at a range of scales, from a few meters to tens of kilometers. The variable mechanical properties of the lithologic units of the ancient passive margin resulted in changes in structural styles and scales of structures across allochthon boundaries. Structural mapping and analysis of the district indicate a dominant northwest to west-northwest direction of regional tectonic transport. Local north to north-northeast transport of thrust sheets is interpreted to reflect the influence of underlying lateral and/or oblique ramps, which may have been controlled by inherited basin margin structures. Some thrust-sheet stacking patterns suggest out-of-sequence thrusting. The west-northwest-east-southeast-trending Wrench Creek and Sivukat Mountain faults were previously interpreted to be strike-slip faults, but this study shows that they are Tertiary (Eocene?) late extensional faults with little or no lateral displacement.

Effects of neutron irradiation of Ti 3SiC 2 and Ti 3AlC 2 in the 121–1085 °C temperature range

DOE PAGES

Tallman, Darin J.; He, Lingfeng; Gan, Jian; ...

2016-11-19

Herein we report on the formation of defects in response to neutron irradiation of polycrystalline Ti 3SiC 2 and Ti 3AlC 2 samples exposed to doses of 0.14±0.01, 1.6±0.1, and 3.4±0.1 displacements per atom (dpa) at irradiation temperatures of 121±12, 735±6 and 1085±68 °C. After irradiation to 0.14 dpa at 121 °C and 735 °C, black spots are observed in both Ti 3SiC 2 and Ti 3AlC 2. After irradiation to 1.6 and 3.4 dpa at 735 °C, basal dislocation loops, with a Burgers vector of b = ½ [0001] are observed in Ti 3SiC 2, with loop diameters ofmore » 21±6 and 30±8 nm for 1.6 dpa and 3.4 dpa, respectively. In Ti3AlC2, larger dislocation loops, 75±34 nm in diameter are observed after 3.4 dpa at 735 °C, in addition to stacking faults. Impurity particles of TiC, as well as stacking fault TiC platelets in the MAX phases, are seen to form extensive dislocation loops under all conditions. Voids are observed at grain boundaries and within stacking faults after 3.4 dpa irradiation, with extensive void formation in the TiC regions at 1085 °C. Remarkably, denuded zones on the order of 1 µm are observed in Ti 3SiC 2 after irradiation to 3.4 dpa at 735 °C. Small grains, 3-5 µm in diameter, are damage free after irradiation at 1085 °C at this dose. The presence of the A-layer in the MAX phases is seen to provide enhanced irradiation tolerance. Based on these results, and up to 3.41 dpa, Ti 3SiC 2 remains a promising candidate for high temperature nuclear applications.« less

Effects of neutron irradiation of Ti 3SiC 2 and Ti 3AlC 2 in the 121–1085 °C temperature range

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tallman, Darin J.; He, Lingfeng; Gan, Jian

Herein we report on the formation of defects in response to neutron irradiation of polycrystalline Ti 3SiC 2 and Ti 3AlC 2 samples exposed to doses of 0.14±0.01, 1.6±0.1, and 3.4±0.1 displacements per atom (dpa) at irradiation temperatures of 121±12, 735±6 and 1085±68 °C. After irradiation to 0.14 dpa at 121 °C and 735 °C, black spots are observed in both Ti 3SiC 2 and Ti 3AlC 2. After irradiation to 1.6 and 3.4 dpa at 735 °C, basal dislocation loops, with a Burgers vector of b = ½ [0001] are observed in Ti 3SiC 2, with loop diameters ofmore » 21±6 and 30±8 nm for 1.6 dpa and 3.4 dpa, respectively. In Ti3AlC2, larger dislocation loops, 75±34 nm in diameter are observed after 3.4 dpa at 735 °C, in addition to stacking faults. Impurity particles of TiC, as well as stacking fault TiC platelets in the MAX phases, are seen to form extensive dislocation loops under all conditions. Voids are observed at grain boundaries and within stacking faults after 3.4 dpa irradiation, with extensive void formation in the TiC regions at 1085 °C. Remarkably, denuded zones on the order of 1 µm are observed in Ti 3SiC 2 after irradiation to 3.4 dpa at 735 °C. Small grains, 3-5 µm in diameter, are damage free after irradiation at 1085 °C at this dose. The presence of the A-layer in the MAX phases is seen to provide enhanced irradiation tolerance. Based on these results, and up to 3.41 dpa, Ti 3SiC 2 remains a promising candidate for high temperature nuclear applications.« less

Seismic Imaging and Characterization of Bright Spots in the West Bohemia Seismic Zone (Germany and Czech Republic)

NASA Astrophysics Data System (ADS)

Alexandrakis, C.; Schreiter, L.; Hlousek, F.; Jusri, T.; Buske, S.

2017-12-01

In crystalline environments, imaging faults, layer boundaries and small scale structures is challenging due to the complex geometry of the structures themselves and the influence of the hardrock environment on the seismic wavefield. Optimally designed active seismic surveys and careful processing can produce a clear image of the subsurface structures. However, if little is known about the local geology and tectonic state of the area, the imaged reflections can be difficult to interpret. This is the case in the West Bohemia Seismic Zone, located along the border of Germany and Czech Republic. This geodynamically active area is spotted with springs and gas vents, and frequently experiences low magnitude seismic swarms. The most active region is located in the Cheb basin and coincides with the junction of a northwest trending fault with a north-south trending shear zone, making for a structurally complex hardrock setting. In the early 1990s, two long-offset reflection seismic profiles were collected along the boundary of the Cheb basin: MVE-90 along the northern edge, and 9HR-91 in the east. These profiles were recently reprocessed using Kirchhoff PreStack Depth Migration, revealing high amplitude reflections, or bright spots, that correlate to nearby seismicity. Several studies have hypothesized that the 9HR-91 bright spots image a fluid trap, where mantle-sourced fluids accumulate, thereby facilitating slip on the faults and triggering the swarms. However, the exact nature of the bright spots remains an open question. They may be a change in lithology and/or porosity, an infilled vein or an impermeable fault. We aim to answer this question by first using Coherency-Based PreStack Depth Migration to produce detailed images of the bright spots. We then forward model the waveforms guided by the reflection coefficients in order to derive rock-physical parameters. Finally, the best-fitting models are interpreted in terms of their possible relationship to the West Bohemia swarms.

Along-strike variations of geometry and kinematics on the border fault of Nanpu sag, Bohai Bay Basin

NASA Astrophysics Data System (ADS)

Zhang, C.; Ren, J.; Liu, X.; Sun, Z.; Su, M.

2010-12-01

Nanpu sag is located in the north-eastern portion of the Huanghua depression, covering an area of approximately 1900km2, and comprises one of the most important petroliferous basins of the Bohai Bay Basin. The Nanpu sag is bordered by two master faults with long-term activity: the Xi’nanzhuang (XNZ) and Bogezhuang (BGZ) fault. By analysis of horizontal slices, gravity anomaly map and seismic reflection sections, we found there is no cutting relationship, and thus considered the XNZ and BGZ fault as a same one. However it showed striking differences between the XNZ and BGZ segment in fault occurrence, fault throw and residual formation thickness and so on. The BGZ fault was NW trending fault with a steep inclination. Taken section across the northern region in Nanpu sag for example, its controlling depocenter is located in eastern subsag (Fig.1); the XNZ fault was a NE fault and displayed a Shovel-shaped to plate-like geometry, with its controlling depocenter located in western subsag. We qualitify the fault throw, showing that the XNZ fault strongly acted during the sedimentary period of Es3-Es2, while the BGZ fault presented weak activity, and especially during Es31 submember-Es2 member, the XNZ fault acted so strongly that the hanging wall of BGZ fault was tilt-lifted and suffered erosion (Fig.1), which created Es1 uncomformity; The BGZ fault acted strongly during the sedimentary period of Es1-Ed, which led the hanging wall of XNZ fault to be tilt-lifted. Controlled by such segmented activity of the whole border fault, which we suggested a "seesaw" model for its evolution, the northern part in the Nanpu sag experienced an alternative variation between a deposition center and an erosion region after tilt-lifting. Combination of the sediment stacking patterns, we further classified the history of "seesaw" activities into four stages: 1) Early double-break stage (Es35-Es31), both of the XNZ and BGZ fault acted; 2) Middle the XNZ segment throw and the BGZ tilting (Es2); 3) Late the XNZ segment tilting and BGZ throw (Es1-Ed3); 4) End weak double-break stage (Ed2-Present), the whole fault acted weakly and were superposed by neotectonic movement. Fig.1 Seesaw activity of the whole border fault

Award ER25750: Coordinated Infrastructure for Fault Tolerance Systems Indiana University Final Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lumsdaine, Andrew

2013-03-08

The main purpose of the Coordinated Infrastructure for Fault Tolerance in Systems initiative has been to conduct research with a goal of providing end-to-end fault tolerance on a systemwide basis for applications and other system software. While fault tolerance has been an integral part of most high-performance computing (HPC) system software developed over the past decade, it has been treated mostly as a collection of isolated stovepipes. Visibility and response to faults has typically been limited to the particular hardware and software subsystems in which they are initially observed. Little fault information is shared across subsystems, allowing little flexibility ormore » control on a system-wide basis, making it practically impossible to provide cohesive end-to-end fault tolerance in support of scientific applications. As an example, consider faults such as communication link failures that can be seen by a network library but are not directly visible to the job scheduler, or consider faults related to node failures that can be detected by system monitoring software but are not inherently visible to the resource manager. If information about such faults could be shared by the network libraries or monitoring software, then other system software, such as a resource manager or job scheduler, could ensure that failed nodes or failed network links were excluded from further job allocations and that further diagnosis could be performed. As a founding member and one of the lead developers of the Open MPI project, our efforts over the course of this project have been focused on making Open MPI more robust to failures by supporting various fault tolerance techniques, and using fault information exchange and coordination between MPI and the HPC system software stack from the application, numeric libraries, and programming language runtime to other common system components such as jobs schedulers, resource managers, and monitoring tools.« less

An L-band interferometric synthetic aperture radar study on the Ganos section of the north Anatolian fault zone between 2007 and 2011: Evidence for along strike segmentation and creep in a shallow fault patch.

PubMed

de Michele, Marcello; Ergintav, Semih; Aochi, Hideo; Raucoules, Daniel

2017-01-01

We utilize L-band interferometric synthetic aperture radar (InSAR) data in this study to retrieve a ground velocity map for the near field of the Ganos section of the north Anatolian fault (NAF) zone. The segmentation and creep distribution of this section, which last ruptured in 1912 to generate a moment magnitude (Mw)7.3 earthquake, remains incompletely understood. Because InSAR processing removes the mean orbital plane, we do not investigate large scale displacements due to regional tectonics in this study as these can be determined using global positioning system (GPS) data, instead concentrating on the close-to-the-fault displacement field. Our aim is to determine whether, or not, it is possible to retrieve robust near field velocity maps from stacking L-band interferograms, combining both single and dual polarization SAR data. In addition, we discuss whether a crustal velocity map can be used to complement GPS observations in an attempt to discriminate the present-day surface displacement of the Ganos fault (GF) across multiple segments. Finally, we characterize the spatial distribution of creep on shallow patches along multiple along-strike segments at shallow depths. Our results suggest the presence of fault segmentation along strike as well as creep on the shallow part of the fault (i.e. the existence of a shallow creeping patch) or the presence of a smoother section on the fault plane. Data imply a heterogeneous fault plane with more complex mechanics than previously thought. Because this study improves our knowledge of the mechanisms underlying the GF, our results have implications for local seismic hazard assessment.

An L-band interferometric synthetic aperture radar study on the Ganos section of the north Anatolian fault zone between 2007 and 2011: Evidence for along strike segmentation and creep in a shallow fault patch

PubMed Central

Ergintav, Semih; Aochi, Hideo; Raucoules, Daniel

2017-01-01

We utilize L-band interferometric synthetic aperture radar (InSAR) data in this study to retrieve a ground velocity map for the near field of the Ganos section of the north Anatolian fault (NAF) zone. The segmentation and creep distribution of this section, which last ruptured in 1912 to generate a moment magnitude (Mw)7.3 earthquake, remains incompletely understood. Because InSAR processing removes the mean orbital plane, we do not investigate large scale displacements due to regional tectonics in this study as these can be determined using global positioning system (GPS) data, instead concentrating on the close-to-the-fault displacement field. Our aim is to determine whether, or not, it is possible to retrieve robust near field velocity maps from stacking L-band interferograms, combining both single and dual polarization SAR data. In addition, we discuss whether a crustal velocity map can be used to complement GPS observations in an attempt to discriminate the present-day surface displacement of the Ganos fault (GF) across multiple segments. Finally, we characterize the spatial distribution of creep on shallow patches along multiple along-strike segments at shallow depths. Our results suggest the presence of fault segmentation along strike as well as creep on the shallow part of the fault (i.e. the existence of a shallow creeping patch) or the presence of a smoother section on the fault plane. Data imply a heterogeneous fault plane with more complex mechanics than previously thought. Because this study improves our knowledge of the mechanisms underlying the GF, our results have implications for local seismic hazard assessment. PMID:28961264

Distribution of aseismic slip rate on the Hayward fault inferred from seismic and geodetic data

USGS Publications Warehouse

Schmidt, D.A.; Burgmann, R.; Nadeau, R.M.; d'Alessio, M.

2005-01-01

We solve for the slip rate distribution on the Hayward fault by performing a least squares inversion,of geodetic and seismic data sets. Our analysis focuses on the northern 60 km of the fault. Interferometric synthetic aperture radar (InSAR) data from 13 independent ERS interferograms are stacked to obtain range change rates from 1992 to 2000. Horizontal surface displacement rates at 141 bench marks are measured using GPS from 1994 to 2003. Surface creep observations and estimates of deep slip rates determined from characteristic repeating earthquake sequences are also incorporated in the inversion. The fault is discretized into 283 triangular dislocation elements that approximate the nonplanar attributes of the fault surface. South of the city of Hayward, a steeply, east dipping fault geometry accommodates the divergence of the surface trace and the microseismicity at depth. The inferred slip rate distribution is consistent with a fault that creeps aseismically at a rate of ???5 mm/yr to a depth of 4-6 km. The interferometric synthetic aperture radar (InSAR) data require an aseismic slip rate that approaches the geologic slip rate on the northernmost fault segment beneath Point Pinole, although the InSAR data might be complicated by a small dip-slip component at this location. A low slip rate patch of <1 mm/yr is inferred beneath San Leandro consistent with the source location of the 1868 earthquake. We calculate that the entire fault is accumulating a slip rate deficit equivalent to a Mw = 6.77 ?? 0.05 per century. However, this estimate of potential coseismic moment represents an upper bound because we do not know how much of the accumulated strain will be released through aseismic processes such as afterslip. Copyright 2005 by the American Geophysical Union.

Structure and U-Pb zircon geochronology of an Alpine nappe stack telescoped by extensional detachment faulting (Kulidzhik area, Eastern Rhodopes, Bulgaria)

NASA Astrophysics Data System (ADS)

Georgiev, Neven; Froitzheim, Nikolaus; Cherneva, Zlatka; Frei, Dirk; Grozdev, Valentin; Jahn-Awe, Silke; Nagel, Thorsten J.

2016-10-01

The Rhodope Metamorphic Complex is a stack of allochthons assembled during obduction, subduction, and collision processes from Jurassic to Paleogene and overprinted by extensional detachment faults since Middle Eocene. In the study area, the following nappes occur in superposition (from base to top): an orthogneiss-dominated unit (Unit I), garnet-bearing schist with amphibolite and serpentinite lenses (Unit II), greenschist, phyllite, and calcschist with reported Jurassic microfossils (Unit III), and muscovite-rich orthogneiss (Unit IV). U-Pb dating of zircons from a K-feldspar augengneiss (Unit I) yielded a protolith age of ca. 300 Ma. Garnet-bearing metasediment from Unit II yielded an age spectrum with distinct populations between 310 and 250 Ma (detrital), ca. 150 Ma, and ca. 69 Ma (the last two of high-grade metamorphic origin). An orthogneiss from Unit IV yielded a wide spectrum of ages. The youngest population gives a concordia age of 581 ± 5 Ma, interpreted as the age of the granitic protolith. Unit I represents the Lower Allochthon (Byala Reka-Kechros Dome), Unit II the Upper Allochthon (Krumovitsa-Kimi Unit), Unit III the Uppermost Allochthon (Circum-Rhodope Belt), and Unit IV a still higher, far-travelled unit of unknown provenance. Telescoping of the entire Rhodope nappe stack to a thickness of only a few 100 m is due to Late Eocene north directed extensional shearing along the newly defined Kulidzhik Detachment which is part of a major detachment system along the northern border of the Rhodopes. Older top-to-the south mylonites in Unit I indicate that Tertiary extension evolved from asymmetric (top-to-the-south) to symmetric (top-to-the-south and top-to-the-north), bivergent unroofing.

IR-LTS a powerful non-invasive tool to observe crystal defects in as-grown silicon, after device processing, and in heteroepitaxial layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kissinger, G.; Richter, H.; Vanhellemont, J.

1996-12-01

One of the main advantages of infrared light scattering tomography (IR-LST) is the wide range of defect densities that can be studied using this technique. As-grown defects of low density and very small size as well as oxygen precipitation related defects that appear in densities up to some 1010 cm{sup -3} can be observed. As-grown wafers with a {open_quotes}stacking fault ring{close_quotes} were investigated in order to correlate the defects observed by IR-LST with the results of Secco etching and alcaline cleaning solution (SC1) treatment revealing flow pattern defects (FPDs) and crystal originated particles (COPs), respectively. These wafers were studied aftermore » a wet oxidation at 1100{degrees}C for 100 min. In processed CZ silicon wafers it was possible to identify stacking faults and prismatic punching systems directly from the IR-LST image. Brewster angle illumination is a special mode to reveal defects in epitaxial layers in a non-destructive way. Misfit dislocations in the interface between a Ge{sub 0.92}Si{sub 0.08} layer and a silicon substrate were studied using this mode that allows to observe very low dislocation densities.« less

Influence of the Starting Microstructure on the Hot Deformation Behavior of a Low Stacking Fault Energy Ni-based Superalloy

NASA Astrophysics Data System (ADS)

McCarley, Joshua; Alabbad, B.; Tin, S.

2018-03-01

The influence of varying fractions of primary gamma prime precipitates on the hot deformation and annealing behavior of an experimental Nickel-based superalloy containing 24 wt pct. Co was investigated. Billets heat treated at 1110 °C or 1135 °C were subjected to hot compression tests at temperatures ranging from 1020 °C to 1060 °C and strain rates ranging from 0.001 to 0.1/s. The microstructures were characterized using electron back scatter diffraction in the as-deformed condition as well as following a super-solvus anneal heat treatment at 1140 °C for 1 hour. This investigation sought to quantify and understand what effect the volume fraction of primary gamma prime precipitates has on the dynamic recrystallization behavior and resulting length fraction ∑3 twin boundaries in the low stacking fault superalloy following annealing. Although deformation at the lower temperatures and higher strain rates led to dynamic recrystallization for both starting microstructures, comparatively lower recrystallized fractions were observed in the 1135 °C billet microstructures deformed at strain rates of 0.1/s and 0.05/s. Subsequent annealing of the 1135 °C billet microstructures led to a higher proportion of annealing twins when compared to the annealed 1110 °C billet microstructures.

Continuum understanding of twin formation near grain boundaries of FCC metals with low stacking fault energy

NASA Astrophysics Data System (ADS)

Jung, Jaimyun; Yoon, Jae Ik; Kim, Jung Gi; Latypov, Marat I.; Kim, Jin You; Kim, Hyoung Seop

2017-12-01

Deformation twinning from grain boundaries is often observed in face-centered cubic metals with low stacking fault energy. One of the possible factors that contribute to twinning origination from grain boundaries is the intergranular interactions during deformation. Nonetheless, the influence of mechanical interaction among grains on twin evolution has not been fully understood. In spite of extensive experimental and modeling efforts on correlating microstructural features with their twinning behavior, a clear relation among the large aggregate of grains is still lacking. In this work, we characterize the micromechanics of grain-to-grain interactions that contribute to twin evolution by investigating the mechanical twins near grain boundaries using a full-field crystal plasticity simulation of a twinning-induced plasticity steel deformed in uniaxial tension at room temperature. Microstructures are first observed through electron backscatter diffraction technique to obtain data to reconstruct a statistically equivalent microstructure through synthetic microstructure building. Grain-to-grain micromechanical response is analyzed to assess the collective twinning behavior of the microstructural volume element under tensile deformation. Examination of the simulated results reveal that grain interactions are capable of changing the local mechanical behavior near grain boundaries by transferring strain across grain boundary or localizing strain near grain boundary.

Size effects of nano-spaced basal stacking faults on the strength and deformation mechanisms of nanocrystalline pure hcp metals

NASA Astrophysics Data System (ADS)

Wang, Wen; Jiang, Ping; Yuan, Fuping; Wu, Xiaolei

2018-05-01

The size effects of nano-spaced basal stacking faults (SFs) on the tensile strength and deformation mechanisms of nanocrystalline pure cobalt and magnesium have been investigated by a series of large-scale 2D columnar and 3D molecular dynamics simulations. Unlike the strengthening effect of basal SFs on Mg alloys, the nano-spaced basal SFs are observed to have no strengthening effect on the nanocrystalline pure cobalt and magnesium from MD simulations. These observations could be attributed to the following two reasons: (i) Lots of new basal SFs are formed before (for cobalt) or simultaneously with (for magnesium) the other deformation mechanisms (i.e. the formation of twins and the < c + a > edge dislocations) during the tensile deformation; (ii) In hcp alloys, the segregation of alloy elements and impurities at typical interfaces, such as SFs, can stablilise them for enhancing the interactions with dislocation and thus elevating the strength. Without such segregation in pure hcp metals, the < c + a > edge dislocations can cut through the basal SFs although the interactions between the < c + a > dislocations and the pre-existing SFs/newly formed SFs are observed. The nano-spaced basal SFs are also found to have no restriction effect on the formation of deformation twins.

Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bazioti, C.; Kehagias, Th.; Pavlidou, E.

2015-10-21

We investigate the structural properties of a series of high alloy content InGaN epilayers grown by plasma-assisted molecular beam epitaxy, employing the deposition temperature as variable under invariant element fluxes. Using transmission electron microscopy methods, distinct strain relaxation modes were observed, depending on the indium content attained through temperature adjustment. At lower indium contents, strain relaxation by V-pit formation dominated, with concurrent formation of an indium-rich interfacial zone. With increasing indium content, this mechanism was gradually substituted by the introduction of a self-formed strained interfacial InGaN layer of lower indium content, as well as multiple intrinsic basal stacking faults andmore » threading dislocations in the rest of the film. We show that this interfacial layer is not chemically abrupt and that major plastic strain relaxation through defect introduction commences upon reaching a critical indium concentration as a result of compositional pulling. Upon further increase of the indium content, this relaxation mode was again gradually succeeded by the increase in the density of misfit dislocations at the InGaN/GaN interface, leading eventually to the suppression of the strained InGaN layer and basal stacking faults.« less

Evaluation of stacking faults and associated partial dislocations in AlSb/GaAs (001) interface by aberration-corrected high-resolution transmission electron microscopy

NASA Astrophysics Data System (ADS)

Wen, C.; Ge, B. H.; Cui, Y. X.; Li, F. H.; Zhu, J.; Yu, R.; Cheng, Z. Y.

2014-11-01

The stacking faults (SFs) in an AlSb/GaAs (001) interface were investigated using a 300 kV spherical aberration-corrected high-resolution transmission electron microscope (HRTEM). The structure and strain distribution of the single and intersecting (V-shaped) SFs associated with partial dislocations (PDs) were characterized by the [110] HRTEM images and geometric phase analysis, respectively. In the biaxial strain maps ɛxx and ɛyy, a SF can be divided into several sections under different strain states (positive or negative strain values). Furthermore, the strain state for the same section of a SF is in contrast to each other in ɛxx and ɛyy strain maps. The modification in the strain states was attributed to the variation in the local atomic displacements for the SF in the AlSb film on the GaAs substrate recorded in the lattice image. Finally, the single SF was found to be bounded by two 30° PDs. A pair of 30° PDs near the heteroepitaxial interface reacted to form a Lomer-Cottrell sessile dislocation located at the vertices of V-shaped SFs with opposite screw components. The roles of misfit dislocations, such as the PDs, in strain relaxation were also discussed.

Analysis of twin defects in GaAs(111)B molecular beam epitaxy growth

DOE Office of Scientific and Technical Information (OSTI.GOV)

Park, Yeonjoon; Cich, Michael J.; Zhao, Rian

2000-05-01

The formation of twin is common during GaAs(111) and GaN(0001) molecular beam epitaxy (MBE) metalorganic chemical vapor deposition growth. A stacking fault in the zinc-blende (ZB)(111) direction can be described as an insertion of one monolayer of wurtzite structure, sandwiched between two ZB structures that have been rotated 60 degree sign along the growth direction. GaAs(111)A/B MBE growth within typical growth temperature regimes is complicated by the formation of pyramidal structures and 60 degree sign rotated twins, which are caused by faceting and stacking fault formation. Although previous studies have revealed much about the structure of these twins, a well-establishedmore » simple nondestructive characterization method which allows the measurement of total aerial density of the twins does not exist at present. In this article, the twin density of AlGaAs layers grown on 1 degree sign miscut GaAs(111)B substrates has been measured using high resolution x-ray diffraction, and characterized with a combination of Nomarski microscopy, atomic force microscopy, and transmission electron microscopy. These comparisons permit the relationship between the aerial twin density and the growth condition to be determined quantitatively. (c) 2000 American Vacuum Society.« less

Local spin structure of the α -RuCl3 honeycomb-lattice magnet observed via muon spin rotation/relaxation

NASA Astrophysics Data System (ADS)

Yamauchi, Ichihiro; Hiraishi, Masatoshi; Okabe, Hirotaka; Takeshita, Soshi; Koda, Akihiro; Kojima, Kenji M.; Kadono, Ryosuke; Tanaka, Hidekazu

2018-04-01

We report a muon spin rotation/relaxation (μ SR ) study of single-crystalline samples of the α -RuCl3 honeycomb magnet, which is presumed to be a model compound for the Kitaev-Heisenberg interaction. It is inferred from magnetic susceptibility and specific-heat measurements that the present samples exhibit successive magnetic transitions at different critical temperatures TN with decreasing temperature, eventually falling into the TN=7 K antiferromagnetic (7 K) phase that has been observed in only single-crystalline specimens with the least stacking fault. Via μ SR measurements conducted under a zero external field, we show that such behavior originates from a phase separation induced by the honeycomb plane stacking fault, yielding multiple domains with different TN's. We also perform μ SR measurements under a transverse field in the paramagnetic phase to identify the muon site from the muon-Ru hyperfine parameters. Based on a comparison of the experimental and calculated internal fields at the muon site for the two possible spin structures inferred from neutron diffraction data, we suggest a modulated zigzag spin structure for the 7 K phase, with the amplitude of the ordered magnetic moment being significantly reduced from that expected for the orbital quenched spin-1/2 state.

A molecular dynamics simulation study of irradiation induced defects in gold nanowire

NASA Astrophysics Data System (ADS)

Liu, Wenqiang; Chen, Piheng; Qiu, Ruizhi; Khan, Maaz; Liu, Jie; Hou, Mingdong; Duan, Jinglai

2017-08-01

Displacement cascade in gold nanowires was studied using molecular dynamics computer simulations. Primary knock-on atoms (PKAs) with different kinetic energies were initiated either at the surface or at the center of the nanowires. We found three kinds of defects that were induced by the cascade, including point defects, stacking faults and crater at the surface. The starting points of PKAs influence the number of residual point defects, and this consequently affect the boundary of anti-radiation window which was proposed by calculation of diffusion of point defects to the free surface of nanowires. Formation of stacking faults that expanded the whole cross-section of gold nanowires was observed when the PKA's kinetic energy was higher than 5 keV. Increasing the PKA's kinetic energy up to more than 10 keV may lead to the formation of crater at the surface of nanowires due to microexplosion of hot atoms. At this energy, PKAs started from the center of nanowires can also result in the creation of crater because length of cascade region is comparable to diameter of nanowires. Both the two factors, namely initial positions of PKAs as well as the craters induced by higher energy irradiation, would influence the ability of radiation resistance of metal nanowires.

Nitrate-cancrinite precipitation on quartz sand in simulated Hanford tank solutions.

PubMed

Bickmore, B R; Nagy, K L; Young, J S; Drexler, J W

2001-11-15

Caustic NaNO3 solutions containing dissolved Al were reacted with quartz sand at 89 degrees C to simulate possible reactions between leaked nuclear waste and primary subsurface minerals at the U.S. Department of Energy's Hanford site in Washington. Nitrate-cancrinite began to precipitate onto the quartz after 2-10 days, cementing the grains together. Estimates of the equilibrium constant for the precipitation reaction differ for solutions with 0.1 or 1.0 m OH- (log Keq = 30.4 +/- 0.8 and 36.2 +/- 0.6, respectively). The difference in solubility may be attributable to more perfect crystallinity (i.e., fewer stacking faults) in the higher-pH cancrinite structure. This is supported by electron micrographs of crystal morphology and measured rates of Na volatilization under an electron beam. Precipitate crystallinity may affect radionuclide mobility, because stacking faults in the cancrinite structure can diminish its zeolitic cation exchange properties. The precipitation rate near the onset of nucleation depends on the total Al and Si concentrations in solution. The evolution of experimental Si concentrations was modeled by considering the dependence of quartz dissolution rate on AI(OH)4- activity, cancrinite precipitation, and the reduction of reactive surface area of quartz due to coverage by cancrinite.

Hydrogen Cracking in Gas Tungsten Arc Welding of an AISI Type 321 Stainless Steel

NASA Astrophysics Data System (ADS)

Rozenak, P.; Unigovski, Ya.; Shneck, R.

The effects of in situ cathodic charging on the tensile properties and susceptibility to cracking of an AISI type 321 stainless steel, welded by the gas tungsten arc welding (GTAW) process, was studied by various treatments. Appearance of delta-ferrite phase in the as-welded steels in our tested conditions was observed with discontinuous grain boundaries (M23C6) and a dense distribution of metal carbides MC ((Ti, Nb)C), which precipitated in the matrix. Shielding gas rates changes the mechanical properties of the welds. Ultimate tensile strength and ductility are increases with the resistance to the environments related the increase of the supplied shielding inert gas rates. Charged specimens, caused mainly in decreases in the ductility of welded specimens. However, more severe decrease in ductility was obtained after post weld heat treatment (PWHT). The fracture of sensitized specimens was predominantly intergranular, whereas the as-welded specimens exhibited massive transgranular regions. Both types of specimen demonstrated narrow brittle zones at the sides of the fracture surface and ductile micro-void coalescences in the middle. Ferrite δ was form after welding with high density of dislocation structures and stacking faults formation and the thin stacking fault plates with e-martensite phase were typically found in the austenitic matrix after the cathodical charging process.

A seismic refraction and reflection study across the central San Jacinto Basin, Southern California

USGS Publications Warehouse

Lee, T.-C.; Biehler, S.; Park, S.K.; Stephenson, W.J.

1996-01-01

The San Jacinto Basin is a northwest-trending, pullapart basin in the San Jacinto fault zone of the San Andreas fault system in southern California. About 24 km long and 2 to 4 km wide, the basin sits on a graben bounded by two strands of the San Jacinto fault zone: the Claremont Fault on the northeast and the Casa Loma Fault on the southwest. We present a case study of shallow structure (less than 1 km) in the central basin. A 2.75-km refraction line running from the northeast to southwest across the regional structural trend reveals a groundwater barrier (Offset I). Another line, bent southward and continued for 1.65-km, shows a crystalline basement offset (Offset III) near an inferred trace of the Casa Loma Fault. Although a basement refractor was not observed along the 2.75-km line, a mismatch between the estimate of its minimum depth and the basement depth determined for the 1.65-km line suggests that an offset in the basement (greater than 260 m) exists around the junction of the two refraction lines (Offset II). By revealing more faults and subtle sedimentary structures, the reflection stack sections confirm the two refraction offsets as faults. Offsets I and III each separate sediments of contrasting structures and, in addition. Offset III disrupts an unconformity. However, the sense and amount of the offset across Offset III contradict what may be expected across the Casa Loma Fault, which has its basinward basement down-thrown to about 2.5 km in the better defined southeastern part of the graben. The Casa Loma Fault trace has been mislinked in the existing geological maps and the trace should be remapped to Offset II where the reflector disruptions spread over a 400-m wide zone. Our Offset III is an unnamed, concealed fault.

Structure of the Wagner Basin in the Northern Gulf of California From Interpretation of Seismic Reflexion Data

NASA Astrophysics Data System (ADS)

Gonzalez, M.; Aguilar, C.; Martin, A.

2007-05-01

The northern Gulf of California straddles the transition in the style of deformation along the Pacific-North America plate boundary, from distributed deformation in the Upper Delfin and Wagner basins to localized dextral shear along the Cerro Prieto transform fault. Processing and interpretation of industry seismic data adquired by Petroleos Mexicanos (PEMEX) allow us to map the main fault structures and depocenters in the Wagner basin and to unravel the way strain is transferred northward into the Cerro Prieto fault system. Seismic data records from 0.5 to 5 TWTT. Data stacking and time-migration were performed using semblance coefficient method. Subsidence in the Wagner basin is controlled by two large N-S trending sub-parallel faults that intersect the NNW-trending Cerro Prieto transform fault. The Wagner fault bounds the eastern margin of the basin for more than 75 km. This fault dips ~50° to the west (up to 2 seconds) with distinctive reflectors displaced more than 1 km across the fault zone. The strata define a fanning pattern towards the Wagner fault. Northward the Wagner fault intersects the Cerro Prieto fault at 130° on map view and one depocenter of the Wagner basin bends to the NW adjacent to the Cerro Prieto fault zone. The eastern boundary of the modern depocenter is the Consag fault, which extends over 100 km in a N-S direction with an average dip of ~50° (up to 2s) to the east. The northern segment of the Consag fault bends 25° and intersects the Cerro Prieto fault zone at an angle of 110° on map view. The acoustic basement was not imaged in the northwest, but the stratigraphic succession increases its thickness towards the depocenter of the Wagner basin. Another important structure is El Chinero fault, which runs parallel to the Consag fault along 60 km and possibly intersects the Cerro Prieto fault to the north beneath the delta of the Colorado River. El Chinero fault dips at low-angle (~30°) to the east and has a vertical offset of about 0.5 seconds (TWTT). Seismic imaging indicates that the Wagner and Consag faults transfer most of their slip to the Cerro Prieto fault. Moreover, the 130° intersection between the Wagner and Cerro Prieto faults suggests that the Wagner fault has a significant strike-slip component. Our results indicate that most of the strain in this plate boundary is transferred along two main sub-parallel oblique faults in a narrow zone 35 km-wide.

CIT-9: A Fault-Free Gmelinite Zeolite.

PubMed

Dusselier, Michiel; Kang, Jong Hun; Xie, Dan; Davis, Mark E

2017-10-16

A synthetic, fault-free gmelinite (GME) zeolite is prepared using a specific organic structure-directing agent (OSDA), cis-3,5-dimethylpiperidinium. The cis-isomers align in the main 12-membered ring (MR) channel of GME. Trans-isomer OSDA leads to the small-pore zeolite SSZ-39 with the OSDA in its cages. Data from N 2 -physisorption and rotation electron diffraction provide evidence for the openness of the 12 MR channel in the GME 12×8×8 pore architecture and the absence of stacking faults, respectively. CIT-9 is hydrothermally stable when K + -exchanged, while in the absence of exchange, the material transforms into an aluminous AFI-zeolite. The process of this phase-change was followed by in situ variable temperature powder X-ray diffraction. CIT-9 has the highest Si/Al ratio reported for GME, and along with its good porosity, opens the possibility of using GME in a variety of applications including catalysis. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Effect of LPSO and SFs on microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy

NASA Astrophysics Data System (ADS)

Xu, Chao; Nakata, Taiki; Qiao, Xiaoguang; Zheng, Mingyi; Wu, Kun; Kamado, Shigeharu

2017-01-01

High performance Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy with high strength and excellent ductility has been successfully developed by hot extrusion. The effect of plate-shaped long period stacking ordered (LPSO) phases and solute-segregated stacking faults (SFs) on the dynamically recrystallization (DRX) behavior was analyzed. The plate-shaped LPSO phases stimulate the DRX by particle stimulated nucleation mechanism, leading to higher DRX ratio and weaker basal texture. While for the alloy with dense fine SFs inside the original grains, discontinuous DRX initially occurs at the original grain boundaries, and the DRX is obviously restricted. Consequently, alloy containing dense SFs exhibits higher strength but lower ductility compared with alloy with plated-shaped LPSO phases.

Effect of LPSO and SFs on microstructure evolution and mechanical properties of Mg-Gd-Y-Zn-Zr alloy

PubMed Central

Xu, Chao; Nakata, Taiki; Qiao, Xiaoguang; Zheng, Mingyi; Wu, Kun; Kamado, Shigeharu

2017-01-01

High performance Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy with high strength and excellent ductility has been successfully developed by hot extrusion. The effect of plate-shaped long period stacking ordered (LPSO) phases and solute-segregated stacking faults (SFs) on the dynamically recrystallization (DRX) behavior was analyzed. The plate-shaped LPSO phases stimulate the DRX by particle stimulated nucleation mechanism, leading to higher DRX ratio and weaker basal texture. While for the alloy with dense fine SFs inside the original grains, discontinuous DRX initially occurs at the original grain boundaries, and the DRX is obviously restricted. Consequently, alloy containing dense SFs exhibits higher strength but lower ductility compared with alloy with plated-shaped LPSO phases. PMID:28134297

Mapping tectonic and anthropogenic processes in central California using satellite and airborne InSAR

NASA Astrophysics Data System (ADS)

Liu, Z.; Lundgren, P.; Liang, C.; Farr, T. G.; Fielding, E. J.

2017-12-01

The improved spatiotemporal resolution of surface deformation from recent satellite and airborne InSAR measurements provides a great opportunity to improve our understanding of both tectonic and non-tectonic processes. In central California the primary plate boundary fault system (San Andreas fault) lies adjacent to the San Joaquin Valley (SJV), a vast structural trough that accounts for about one-sixth of the United Sates' irrigated land and one-fifth of its extracted groundwater. The central San Andreas fault (CSAF) displays a range of fault slip behavior with creeping in its central segment that decreases towards its northwest and southeast ends, where it transitions to being fully locked. Despite much progress, many questions regarding fault and anthropogenic processes in the region still remain. In this study, we combine satellite InSAR and NASA airborne UAVSAR data to image fault and anthropogenic deformation. The UAVSAR data cover fault perpendicular swaths imaged from opposing look directions and fault parallel swaths since 2009. The much finer spatial resolution and optimized viewing geometry provide important constraints on near fault deformation and fault slip at very shallow depth. We performed a synoptic InSAR time series analysis using Sentinel-1, ALOS, and UAVSAR interferograms. We estimate azimuth mis-registration between single look complex (SLC) images of Sentinel-1 in a stack sense to achieve accurate azimuth co-registration between SLC images for low coherence and/or long interval interferometric pairs. We show that it is important to correct large-scale ionosphere features in ALOS-2 ScanSAR data for accurate deformation measurements. Joint analysis of UAVSAR and ALOS interferometry measurements show clear variability in deformation along the fault strike, suggesting variable fault creep and locking at depth and along strike. In addition to fault creep, the L-band ALOS, and especially ALOS-2 ScanSAR interferometry, show large-scale ground subsidence in the SJV due to over-exploitation of groundwater. InSAR time series are compared to GPS and well-water hydraulic head in-situ time series to understand water storage processes and mass loading changes. We present model results to assess the influence of anthropogenic processes on surface deformation and fault mechanics.

Robust real-time fault tracking for the 2011 Mw 9.0 Tohoku earthquake based on the phased-array-interference principle

NASA Astrophysics Data System (ADS)

Zhang, Yong; Wang, Rongjiang; Parolai, Stefano; Zschau, Jochen

2013-04-01

Based on the principle of the phased array interference, we have developed an Iterative Deconvolution Stacking (IDS) method for real-time kinematic source inversion using near-field strong-motion and GPS networks. In this method, the seismic and GPS stations work like an array radar. The whole potential fault area is scanned patch by patch by stacking the apparent source time functions, which are obtained through deconvolution between the recorded seismograms and synthetic Green's functions. Once some significant source signals are detected any when and where, their signatures are removed from the observed seismograms. The procedure is repeated until the accumulative seismic moment being found converges and the residual seismograms are reduced below the noise level. The new approach does not need any artificial constraint used in the source parameterization such as, for example, fixing the hypocentre, restricting the rupture velocity and rise time, etc. Thus, it can be used for automatic real-time source inversion. In the application to the 2011 Tohoku earthquake, the IDS method is proved to be robust and reliable on the fast estimation of moment magnitude, fault area, rupture direction, and maximum slip, etc. About at 100 s after the rupture initiation, we can get the information that the rupture mainly propagates along the up-dip direction and causes a maximum slip of 17 m, which is enough to release a tsunami early warning. About two minutes after the earthquake occurrence, the maximum slip is found to be 31 m, and the moment magnitude reaches Mw8.9 which is very close to the final moment magnitude (Mw9.0) of this earthquake.

Seismic Imaging of the West Napa Fault in Napa, California

NASA Astrophysics Data System (ADS)

Goldman, M.; Catchings, R.; Chan, J. H.; Sickler, R. R.; Nevitt, J. M.; Criley, C.

2017-12-01

In October 2016, we acquired high-resolution P- and S-wave seismic data along a 120-m-long, SW-NE-trending profile in Napa, California. Our seismic survey was designed to image a strand of the West Napa Fault Zone (WNFZ), which ruptured during the 24 August 2014 Mw 6.0 South Napa Earthquake. We separately acquired P- and S-wave data at every station using multiple hammer hits, which were edited and stacked into individual shot gathers in the lab. Each shot was co-located with and recorded by 118 P-wave (40-Hz) geophones, spaced at 1 m, and by 180 S-wave (4.5-Hz) geophones, spaced at 1 m. We developed both P- and S-wave tomographic velocity models, as well as Poisson's ratio and a Vp/Vs ratio models. We observed a well-defined zone of elevated Vp/Vs ratios below about 10 m depth, centered beneath the observed surface rupture. P-wave reflection images show that the fault forms a flower-structure in the upper few tens of meters. This method has been shown to delineate fault structures even in areas of rough terrain.

Multi-interferogram method for measuring interseismic deformation: Denali Fault, Alaska

USGS Publications Warehouse

Biggs, Juliet; Wright, Tim; Lu, Zhong; Parsons, Barry

2007-01-01

Studies of interseismic strain accumulation are crucial to our understanding of continental deformation, the earthquake cycle and seismic hazard. By mapping small amounts of ground deformation over large spatial areas, InSAR has the potential to produce continental-scale maps of strain accumulation on active faults. However, most InSAR studies to date have focused on areas where the coherence is relatively good (e.g. California, Tibet and Turkey) and most analysis techniques (stacking, small baseline subset algorithm, permanent scatterers, etc.) only include information from pixels which are coherent throughout the time-span of the study. In some areas, such as Alaska, where the deformation rate is small and coherence very variable, it is necessary to include information from pixels which are coherent in some but not all interferograms. We use a three-stage iterative algorithm based on distributed scatterer interferometry. We validate our method using synthetic data created using realistic parameters from a test site on the Denali Fault, Alaska, and present a preliminary result of 10.5 ?? 5.0 mm yr-1 for the slip rate on the Denali Fault based on a single track of radar data from ERS1/2. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Structure Deformation of the Minjiang and Huya Fault, the Eastern Margin of the Tibetan Plateau Revealed by Deep Seismic Reflection Profiles

NASA Astrophysics Data System (ADS)

Gao, R.; Wang, H.; Li, W.; Li, H.

2014-12-01

The Minshan region, located along the eastern margin of the Tibetan Plateau north of the Sichuan Basin, provides an important natural laboratory in which to study the patterns of deformation and their relationship to mountain building at the margin of the plateau. The Minshan range is bounded by the Minjiang fault to the west and Huya fault to the east. Evidence from the Neotectonics sediments suggests that deformation along the western Min Shan may reflect the surface response to thickening of a weak lower crust at the margin of the Tibetan Plateau (Kirby et al., 2000). In 2014, two deep seismic profiles was carried out across the Minjiang fault (55 km long) and Huya fault (45 km long) respectively, supported by China geological survey project (No.1212011220260) and Crust Probe Project of China (SinoProbe-02-01). The recording of seismic waves from 4 big shots (500kg), 100 middle shots (120 kg) and 400 small shots (36 kg) were employed. The geophones spacing is 50 m. The preliminary stack sections provide us a detailed deformation mechanism of the Minshan region for the first time. The result shows that: (1) The Huya fault section shows different reflection characteristics on the west and east flank. (2) The Moho reflection beneath the Huya fault, which appeared at 12-13 s two-way time, tilts from the east to the west. (3) The Minjiang fault shows as a series of thrust nappe in the upper crust. (4) A strong reflector appears in the middle crust of the Minjiang section at 8-9 s two-way times, and it dips down to the lower crust from west to east.

High-Resolution Seismic Reflection Profiling Across the Black Hills Fault, Clark County, Nevada: Preliminary Results

NASA Astrophysics Data System (ADS)

Zaragoza, S. A.; Snelson, C. M.; Jernsletten, J. A.; Saldana, S. C.; Hirsch, A.; McEwan, D.

2005-12-01

The Black Hills fault (BHF) is located in the central Basin and Range Province of western North America, a region that has undergone significant Cenozoic extension. The BHF is an east-dipping normal fault that forms the northwestern structural boundary of the Eldorado basin and lies ~20 km southeast of Las Vegas, Nevada. A recent trench study indicated that the fault offsets Holocene strata, and is capable of producing Mw 6.4-6.8 earthquakes. These estimates indicate a subsurface rupture length at least 10 km greater than the length of the scarp. This poses a significant hazard to structures such as the nearby Hoover Dam Bypass Bridge, which is being built to withstand a Mw 6.2-7.0 earthquake on local faults. If the BHF does continue in the subsurface, this structure, as well as nearby communities (Las Vegas, Boulder City, and Henderson), may not be as safe as previously expected. Previous attempts to image the fault with shallow seismics (hammer source) were inconclusive. However, gravity studies imply that the fault continues south of the scarp. Therefore, a new experiment utilizing high-resolution seismic reflection was performed to image subsurface geologic structures south of the scarp. At each shot point, a stack of four 30-160 Hz vibroseis sweeps of 15 s duration was recorded on a 60-channel system with 40 Hz geophones. This produced two 300 m reflection profiles, with a maximum depth of 500-600 m. A preliminary look at these data indicates the existence of two faults, potentially confirming that the BHF continues in the subsurface south of the scarp.

The lithosphere-asthenosphere boundary beneath the South Island of New Zealand

NASA Astrophysics Data System (ADS)

Hua, Junlin; Fischer, Karen M.; Savage, Martha K.

2018-02-01

Lithosphere-asthenosphere boundary (LAB) properties beneath the South Island of New Zealand have been imaged by Sp receiver function common-conversion point stacking. In this transpressional boundary between the Australian and Pacific plates, dextral offset on the Alpine fault and convergence have occurred for the past 20 My, with the Alpine fault now bounded by Australian plate subduction to the south and Pacific plate subduction to the north. Using data from onland seismometers, especially the 29 broadband stations of the New Zealand permanent seismic network (GeoNet), we obtained 24,971 individual receiver functions by extended-time multi-taper deconvolution, and mapped them to three-dimensional space using a Fresnel zone approximation. Pervasive strong positive Sp phases are observed in the LAB depth range indicated by surface wave tomography. These phases are interpreted as conversions from a velocity decrease across the LAB. In the central South Island, the LAB is observed to be deeper and broader to the northwest of the Alpine fault. The deeper LAB to the northwest of the Alpine fault is consistent with models in which oceanic lithosphere attached to the Australian plate was partially subducted, or models in which the Pacific lithosphere has been underthrust northwest past the Alpine fault. Further north, a zone of thin lithosphere with a strong and vertically localized LAB velocity gradient occurs to the northwest of the fault, juxtaposed against a region of anomalously weak LAB conversions to the southeast of the fault. This structure could be explained by lithospheric blocks with contrasting LAB properties that meet beneath the Alpine fault, or by the effects of Pacific plate subduction. The observed variations in LAB properties indicate strong modification of the LAB by the interplay of convergence and strike-slip deformation along and across this transpressional plate boundary.

Aftershocks of microearthquakes as probes of the mechanics of rupture

NASA Astrophysics Data System (ADS)

Rubin, Allan M.

2002-07-01

Using a waveform cross-correlation technique, Rubin and Gillard [2000] obtained precise relative locations for 4300 0.5 < M < 3.5 earthquakes occurring along 50 km of the San Andreas fault. This study adds to that another 5000 earthquakes distributed along 10 km of the San Andreas fault and 20 km of the Calaveras fault. Errors in relative location are typically tens of meters for earthquakes separated by hundreds of meters and, after correcting for time-dependent station delays, meters for earthquakes separated by tens of meters. Along both faults, the minimum separation between consecutive earthquakes scales with magnitude in a manner consistent with a magnitude-independent stress drop. By treating each earthquake on the San Andreas as if it were a main shock, scaling the distances to all subsequent earthquakes by main shock size, and stacking the results, a ``composite'' aftershock sequence is produced that has many of the characteristics predicted by rate-and-state friction models. Projected onto the fault surface, these aftershocks outline a quasi-elliptical, roughly 4-MPa stress drop main shock elongate in the slip-parallel direction by ~40%. At the ends of the major axes of this ellipse over twice as many aftershocks occur to the NW than to the SE, an asymmetry attributed to the contrast in material properties across the fault. Unlike the San Andreas, the Calaveras fault exhibits little P wave velocity contrast and no discernible aftershock asymmetry; however, the earliest part of the aftershock sequence on the Calaveras might be truncated by the ~30-s ``blind'' time of the network following a triggering event.

Spectral element modelling of fault-plane reflections arising from fluid pressure distributions

USGS Publications Warehouse

Haney, M.; Snieder, R.; Ampuero, J.-P.; Hofmann, R.

2007-01-01

The presence of fault-plane reflections in seismic images, besides indicating the locations of faults, offers a possible source of information on the properties of these poorly understood zones. To better understand the physical mechanism giving rise to fault-plane reflections in compacting sedimentary basins, we numerically model the full elastic wavefield via the spectral element method (SEM) for several different fault models. Using well log data from the South Eugene Island field, offshore Louisiana, we derive empirical relationships between the elastic parameters (e.g. P-wave velocity and density) and the effective-stress along both normal compaction and unloading paths. These empirical relationships guide the numerical modelling and allow the investigation of how differences in fluid pressure modify the elastic wavefield. We choose to simulate the elastic wave equation via SEM since irregular model geometries can be accommodated and slip boundary conditions at an interface, such as a fault or fracture, are implemented naturally. The method we employ for including a slip interface retains the desirable qualities of SEM in that it is explicit in time and, therefore, does not require the inversion of a large matrix. We performa complete numerical study by forward modelling seismic shot gathers over a faulted earth model using SEM followed by seismic processing of the simulated data. With this procedure, we construct post-stack time-migrated images of the kind that are routinely interpreted in the seismic exploration industry. We dip filter the seismic images to highlight the fault-plane reflections prior to making amplitude maps along the fault plane. With these amplitude maps, we compare the reflectivity from the different fault models to diagnose which physical mechanism contributes most to observed fault reflectivity. To lend physical meaning to the properties of a locally weak fault zone characterized as a slip interface, we propose an equivalent-layer model under the assumption of weak scattering. This allows us to use the empirical relationships between density, velocity and effective stress from the South Eugene Island field to relate a slip interface to an amount of excess pore-pressure in a fault zone. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

Resilience Design Patterns - A Structured Approach to Resilience at Extreme Scale (version 1.1)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hukerikar, Saurabh; Engelmann, Christian

Reliability is a serious concern for future extreme-scale high-performance computing (HPC) systems. Projections based on the current generation of HPC systems and technology roadmaps suggest the prevalence of very high fault rates in future systems. The errors resulting from these faults will propagate and generate various kinds of failures, which may result in outcomes ranging from result corruptions to catastrophic application crashes. Therefore the resilience challenge for extreme-scale HPC systems requires management of various hardware and software technologies that are capable of handling a broad set of fault models at accelerated fault rates. Also, due to practical limits on powermore » consumption in HPC systems future systems are likely to embrace innovative architectures, increasing the levels of hardware and software complexities. As a result the techniques that seek to improve resilience must navigate the complex trade-off space between resilience and the overheads to power consumption and performance. While the HPC community has developed various resilience solutions, application-level techniques as well as system-based solutions, the solution space of HPC resilience techniques remains fragmented. There are no formal methods and metrics to investigate and evaluate resilience holistically in HPC systems that consider impact scope, handling coverage, and performance & power efficiency across the system stack. Additionally, few of the current approaches are portable to newer architectures and software environments that will be deployed on future systems. In this document, we develop a structured approach to the management of HPC resilience using the concept of resilience-based design patterns. A design pattern is a general repeatable solution to a commonly occurring problem. We identify the commonly occurring problems and solutions used to deal with faults, errors and failures in HPC systems. Each established solution is described in the form of a pattern that addresses concrete problems in the design of resilient systems. The complete catalog of resilience design patterns provides designers with reusable design elements. We also define a framework that enhances a designer's understanding of the important constraints and opportunities for the design patterns to be implemented and deployed at various layers of the system stack. This design framework may be used to establish mechanisms and interfaces to coordinate flexible fault management across hardware and software components. The framework also supports optimization of the cost-benefit trade-offs among performance, resilience, and power consumption. The overall goal of this work is to enable a systematic methodology for the design and evaluation of resilience technologies in extreme-scale HPC systems that keep scientific applications running to a correct solution in a timely and cost-efficient manner in spite of frequent faults, errors, and failures of various types.« less

Flux Pinning in YBa2Cu3O7-delta Thin Film Samples Linked to Stacking Fault Density (Postprint)

DTIC Science & Technology

2008-10-01

Driscoll, S. R. Foltyn, Q. X. Jia, H. Wang, A. Serquis, B. Maiorov, L. Civale, Y. Lin, M. E. Hawley , M. P. Maley, and D. E. Peter- son, Appl. Phys. Lett. 84...Civale, B. Maiorov, A. Serquis, J. O. Willis , J. Y. Coulter, H. Wang, Q. X. Jia, P. N. Arendt, J. L. MacManus-Driscoll, M. P. Maley, and S. R. Foltyn, Appl

Imaging the Crust in the Northern Sector of the 2009 L'Aquila Seismic Sequence through Oil Exploration Data Interpretation

NASA Astrophysics Data System (ADS)

Grazia Ciaccio, Maria; Improta, Luigi; Patacca, Etta; Scandone, Paolo; Villani, Fabio

2010-05-01

The 2009 L'Aquila seismic sequence activated a complex, about 40 km long, NW-trending and SW-dipping normal fault system, consisting of three main faults arranged in right-lateral en-echelon geometry. While the northern sector of the epicentral area was extensively investigated by oil companies, only a few scattered, poor-quality commercial seismic profiles are available in the central and southern sector. In this study we interpret subsurface commercial data from the northern sector, which is the area where is located the source of the strong Mw5.4 aftershock occurred on the 9th April 2009. Our primary goals are: (1) to define a reliable framework of the upper crust structure, (2) to investigate how the intense aftershock activity, the bulk of which is clustered in the 5-10 km depth range, relates to the Quaternary extensional faults present in the area. The investigated area lies between the western termination of the W-E trending Gran Sasso thrust system to the south, the SW-NE trending Mt. Sibillini thrust front (Ancona-Anzio Line Auctt.) to the north and west, and by the NNW-SSE trending, SW-dipping Mt. Gorzano normal fault to the east. In this area only middle-upper Miocene deposits are exposed (Laga Flysch and underlying Cerrogna Marl), but commercial wells have revealed the presence of a Triassic-Miocene sedimentary succession identical to the well known Umbria-Marche stratigraphic sequence. We have analyzed several confidential seismic reflection profiles, mostly provided by ENI oil company. Seismic lines are tied to two public wells, 5766 m and 2541 m deep. Quality of the reflection imaging is highly variable. A few good quality stack sections contain interpretable signal down to 4.5-5.5 s TWT, corresponding to depths exceeding 10-12 km and thus allowing crustal imaging at seismogenic depths. Key-reflectors for the interpretation correspond to: (1) the top of the Miocene Cerrogna marls, (2) the top of the Upper Albian-Oligocene Scaglia Group, (3) the Aptian-Albian Fucoid Marl horizon, (4) the top of the upper Jurassic "Calcari ad Aptici" Formation, (5) the top of the upper Triassic dolomites plus evaporites of the Burano Formation. Strong but discontinuous deep reflectors can be reasonably attributed to the Paleozoic-Trassic clastic sequence underlying the evaporites. Neogene compression is responsible for a system of NNW-SSE trending fault-propagation folds which have often grown on top of popup-like structures. Extensional features include shallow-seated low-angle faults, likely related to gravitational readjustments on top of compressional features, and younger NNW-SSE trending high-angle faults. The major high-angle fault in the investigated area is represented by the Mt. Gorzano Fault, a regional structure the surface trace of which is at least 20 km long. The Mt. Gorzano Fault is a listric fault that dips around 60° in the first 2 s TWT and flattens at greater depths until it becomes sub-horizontal at about 5 s TWT, i.e. at a depth averaging 12 kilometers. Depth converted sections, calibrated by well data, indicate that the bulk of the aftershock activity is confined between the Triassic dolomites plus evaporites and the underlying Paleozoic-Triassic terrigenous deposits, without affecting the overlying carbonates. Events alignment revealed by accurate Double-Difference relative locations suggests that the Mw5.4 aftershock activated a 12 km-long segment of the Mt. Gorzano Fault at depths ranging from 5 to 10-12 kilometers. Aftershocks cluster in the hanging-wall of the deep portion of the fault recognized in the stack sections, whose geometry is consistent with the fault plane highlighted by earthquakes alignment.

Correlation of Coseismic Velocity and Static Volumetric Strain Changes Induced by the 2010 Mw6.3 Jiasian Earthquake under the Southern Taiwan Orogenic Belt

NASA Astrophysics Data System (ADS)

Wu, S. M.; Hung, S. H.

2015-12-01

Earthquake-induced temporal changes in seismic velocity of the earth's crust have been demonstrated to be monitored effectively by the time-lapse shifts of coda waves recently. Velocity drop during the coseismic rupture has been explicitly observed in proximity to the epicenters of large earthquakes with different styles of faulting. The origin of such sudden perturbation in crustal properties is closely related to the damage and/or volumetric strain change influenced by seismic slip distribution. In this study, we apply a coda wave interferometry method to investigate potential velocity change in both space and time related to the moderate-sized (Mw6.3) 2010 Jiasian earthquake, which nucleated deeply in the crust (~23 km), ruptured and terminated around the depth of 10 km along a previously unidentified blind thrust fault near the lithotectonic boundary of the southern Taiwan orogenic belt. To decipher the surface and crustal response to this relatively deep rupture, we first measure relative time-lapse changes of coda between different short-term time frames spanning one year covering the pre- and post-seismic stages by using the Moving Window Cross Spectral Method. Rather than determining temporal velocity variations based on a long-term reference stack, we conduct a Bayesian least-squares inversion to obtain the optimal estimates by minimizing the inconsistency between the relative time-lapse shifts of individual short-term stacks. The results show the statistically significant velocity reduction immediately after the mainshock, which is most pronounced at the pairs with the interstation paths traversing through the hanging-wall block of the ruptured fault. The sensitivity of surface wave coda arrivals mainly in the periods of 3-5 s to shear wave speed perturbation is confined within the depth of 10 km, where the crust mostly experienced extensional strain changes induced by the slip distribution from the finite-fault model. Compared with coseismic slip distribution from GPS data and finite-fault inversion, peak ground velocity, and static volumetric strain field following the earthquake, the velocity decrease observed in the hanging wall side of the shallow crust is most likely attributed to pervasive dilatational strain changes induced by the slip rupture on the underlying blind thrust.

Characterization of HgCdTe and Related Materials For Third Generation Infrared Detectors

NASA Astrophysics Data System (ADS)

Vaghayenegar, Majid

Hg1-xCdxTe (MCT) has historically been the primary material used for infrared detectors. Recently, alternative substrates for MCT growth such as Si, as well as alternative infrared materials such as Hg1-xCdxSe, have been explored. This dissertation involves characterization of Hg-based infrared materials for third generation infrared detectors using a wide range of transmission electron microscopy (TEM) techniques. A microstructural study on HgCdTe/CdTe heterostructures grown by MBE on Si (211) substrates showed a thin ZnTe layer grown between CdTe and Si to mediate the large lattice mismatch of 19.5%. Observations showed large dislocation densities at the CdTe/ZnTe/Si (211) interfaces, which dropped off rapidly away from the interface. Growth of a thin HgTe buffer layer between HgCdTe and CdTe layers seemed to improve the HgCdTe layer quality by blocking some defects. A second study investigated the correlation of etch pits and dislocations in as-grown and thermal-cycle-annealed (TCA) HgCdTe (211) films. For as-grown samples, pits with triangular and fish-eye shapes were associated with Frank partial and perfect dislocations, respectively. Skew pits were determined to have a more complex nature. TCA reduced the etch-pit density by 72%. Although TCA processing eliminated the fish-eye pits, dislocations reappeared in shorter segments in the TCA samples. Large pits were observed in both as-grown and TCA samples, but the nature of any defects associated with these pits in the as-grown samples is unclear. Microstructural studies of HgCdSe revealed large dislocation density at ZnTe/Si(211) interfaces, which dropped off markedly with ZnTe thickness. Atomic-resolution STEM images showed that the large lattice mismatch at the ZnTe/Si interface was accommodated through {111}-type stacking faults. A detailed analysis showed that the stacking faults were inclined at angles of 19.5 and 90 degrees at both ZnTe/Si and HgCdSe/ZnTe interfaces. These stacking faults were associated with Shockley and Frank partial dislocations, respectively. Initial attempts to delineate individual dislocations by chemical etching revealed that while the etchants successfully attacked defective areas, many defects in close proximity to the pits were unaffected.

Relative role of transfer zones in controlling sequence stacking patterns and facies distribution: insights from the Fushan Depression, South China Sea

NASA Astrophysics Data System (ADS)

Liu, Entao; Wang, Hua; Li, Yuan; Huang, Chuanyan

2015-04-01

In sedimentary basins, a transfer zone can be defined as a coordinated system of deformational features which has good prospects for hydrocarbon exploration. Although the term 'transfer zone' has been widely applied to the study of extensional basins, little attention has been paid to its controlling effect on sequence tracking pattern and depositional facies distribution. Fushan Depression is a half-graben rift sub-basin, located in the southeast of the Beibuwan Basin, South China Sea. In this study, comparative analysis of seismic reflection, palaeogeomorphology, fault activity and depositional facies distribution in the southern slope indicates that three different types of sequence stacking patterns (i.e. multi-level step-fault belt in the western area, flexure slope belt in the central area, gentle slope belt in the eastern area) were developed along the southern slope, together with a large-scale transfer zone in the central area, at the intersection of the western and eastern fault systems. Further analysis shows that the transfer zone played an important role in the diversity of sequence stacking patterns in the southern slope by dividing the Fushan Depression into two non-interfering tectonic systems forming different sequence patterns, and leading to the formation of the flexure slope belt in the central area. The transfer zone had an important controlling effect on not only the diversity of sequence tracking patterns, but also the facies distribution on the relay ramp. During the high-stand stage, under the controlling effect of the transfer zone, the sediments contain a significant proportion of coarser material accumulated and distributed along the ramp axis. By contrast, during the low-stand stage, the transfer zone did not seem to contribute significantly to the low-stand fan distribution which was mainly controlled by the slope gradient (palaeogeomorphology). Therefore, analysis of the transfer zone can provide a new perspective for basin analysis. In addition, the transfer zone area demonstrated unique hydrocarbon accumulation models different from the western and eastern areas. It was not only a structural high combined with sufficient coarse-grained reservoir quality sands, but was also associated with large-scale sublacustrine fan deposits with high quality reservoirs, indicating that the recognition of transfer zones can improve the prediction of hydrocarbon occurrences in similar settings.

Why self-catalyzed nanowires are most suitable for large-scale hierarchical integrated designs of nanowire nanoelectronics

NASA Astrophysics Data System (ADS)

Noor Mohammad, S.

2011-10-01

Nanowires are grown by a variety of mechanisms, including vapor-liquid-solid, vapor-quasiliquid-solid or vapor-quasisolid-solid, oxide-assisted growth, and self-catalytic growth (SCG) mechanisms. A critical analysis of the suitability of self-catalyzed nanowires, as compared to other nanowires, for next-generation technology development has been carried out. Basic causes of superiority of self-catalyzed (SCG) nanowires over other nanowires have been described. Polytypism in nanowires has been studied, and a model for polytypism has been proposed. The model predicts polytypism in good agreement with available experiments. This model, together with various evidences, demonstrates lower defects, dislocations, and stacking faults in SCG nanowires, as compared to those in other nanowires. Calculations of carrier mobility due to dislocation scattering, ionized impurity scattering, and acoustic phonon scattering explain the impact of defects, dislocations, and stacking faults on carrier transports in SCG and other nanowires. Analyses of growth mechanisms for nanowire growth directions indicate SCG nanowires to exhibit the most controlled growth directions. In-depth investigation uncovers the fundamental physics underlying the control of growth direction by the SCG mechanism. Self-organization of nanowires in large hierarchical arrays is crucial for ultra large-scale integration (ULSI). Unique features and advantages of self-organized SCG nanowires, unlike other nanowires, for this ULSI have been discussed. Investigations of nanowire dimension indicate self-catalyzed nanowires to have better control of dimension, higher stability, and higher probability, even for thinner structures. Theoretical calculations show that self-catalyzed nanowires, unlike catalyst-mediated nanowires, can have higher growth rate and lower growth temperature. Nanowire and nanotube characteristics have been found also to dictate the performance of nanoelectromechanical systems. Defects, such as stacking faults, dislocations, and nanopipes, which are common in catalyst-mediated nanowires and nanotubes, adversely affect the efficiency of nanowire (nanotube) nanoelectro-mechanical devices. The influence of seed-to-seed distance and collection area radius on the self-catalyzed, self-aligned nanowire growths in large arrays of seeds has been examined. A hypothesis has been presented for this. The present results are in good agreement with experiments. These results suggest that the SCG nanowires are perhaps the best vehicles for revolutionary advancement of tomorrow's nanotechnology.

Effects of neutron irradiation of Ti3SiC2 and Ti3AlC2 in the 121-1085 °C temperature range

NASA Astrophysics Data System (ADS)

Tallman, Darin J.; He, Lingfeng; Gan, Jian; Caspi, El'ad N.; Hoffman, Elizabeth N.; Barsoum, Michel W.

2017-02-01

Herein we report on the formation of defects in response to neutron irradiation of polycrystalline Ti3SiC2 and Ti3AlC2 samples exposed to total fluences of ≈6 × 1020 n/m2, 5 × 1021 n/m2 and 1.7 × 1022 n/m2 at irradiation temperatures of 121(12), 735(6) and 1085(68)°C. These fluences correspond to 0.14, 1.6 and 3.4 dpa, respectively. After irradiation to 0.14 dpa at 121 °C and 735 °C, black spots are observed via transmission electron microscopy in both Ti3SiC2 and Ti3AlC2. After irradiation to 1.6 and 3.4 dpa at 735 °C, basal dislocation loops, with a Burgers vector of b = ½ [0001] are observed in Ti3SiC2, with loop diameters of 21(6) and 30(8) nm after 1.6 dpa and 3.4 dpa, respectively. In Ti3AlC2, larger dislocation loops, 75(34) nm in diameter are observed after 3.4 dpa at 735 °C, in addition to stacking faults. Impurity particles of TiC, as well as stacking fault TiC platelets in the MAX phases, are seen to form extensive dislocation loops under all conditions. Cavities were observed at grain boundaries and within stacking faults after 3.4 dpa irradiation, with extensive cavity formation in the TiC regions at 1085 °C. Remarkably, denuded zones on the order of 1 μm are observed in Ti3SiC2 after irradiation to 3.4 dpa at 735 °C. Small grains, 3-5 μm in diameter, are damage free after irradiation at 1085 °C at this dose. The results shown herein confirm once again that the presence of the A-layers in the MAX phases considerably enhance their irradiation tolerance. Based on these results, and up to 3.4 dpa, Ti3SiC2 remains a promising candidate for high temperature nuclear applications as long as the temperature remains >700 °C.

Prediction of weak topological insulators in layered semiconductors.

PubMed

Yan, Binghai; Müchler, Lukas; Felser, Claudia

2012-09-14

We report the discovery of weak topological insulators by ab initio calculations in a honeycomb lattice. We propose a structure with an odd number of layers in the primitive unit cell as a prerequisite for forming weak topological insulators. Here, the single-layered KHgSb is the most suitable candidate for its large bulk energy gap of 0.24 eV. Its side surface hosts metallic surface states, forming two anisotropic Dirac cones. Although the stacking of even-layered structures leads to trivial insulators, the structures can host a quantum spin Hall layer with a large bulk gap, if an additional single layer exists as a stacking fault in the crystal. The reported honeycomb compounds can serve as prototypes to aid in the finding of new weak topological insulators in layered small-gap semiconductors.

Phase stability tuning in the NbxZr1-xN thin-film system for large stacking fault density and enhanced mechanical strength

NASA Astrophysics Data System (ADS)

Joelsson, T.; Hultman, L.; Hugosson, H. W.; Molina-Aldareguia, J. M.

2005-03-01

The phase stability of hexagonal WC-structure and cubic NaCl-structure 4d transition metal nitrides was calculated using first-principles density functional theory. It is predicted that there is a multiphase or polytypic region for the 4d transition metal nitrides with a valence electron concentration around 9.5 to 9.7 per formula unit. For verification, epitaxial NbxZr1-xN (0⩽x⩽1) was grown by reactive magnetron sputter deposition on MgO(001) substrates and analyzed with transmission electron microscopy (TEM) and x-ray diffraction. The defects observed in the films were threading dislocations due to nucleation and growth on the lattice-mismatched substrate and planar defects (stacking faults) parallel to the substrate surface. The highest defect density was found at the x =0.5 composition. The nanoindentation hardness of the films varied between 21GPa for the binary nitrides, and 26GPa for Nb0.5Zr0.5N. Unlike the cubic binary nitrides, no slip on the preferred ⟨11¯0⟩{110} slip system was observed. The increase in hardness is attributed to the increase in defect density at x =0.5, as the defects act as obstacles for dislocation glide during deformation. The findings present routes for the design of wear-resistant nitride coatings by phase stability tuning.

Nanocrystal growth and morphology of PbTeSe-ZnSe composite thin films prepared by one-step synthesis method

NASA Astrophysics Data System (ADS)

Sato, Kazuhisa; Abe, Seishi

2016-10-01

The microstructure of polycrystalline PbTe1-xSex-ZnSe composite thin films has been studied by scanning transmission electron microscopy and electron diffraction. The films were prepared by the one-step synthesis method using simultaneous evaporation of PbTe and ZnSe. The nanocrystals of PbTe1-xSex are formed in a ZnSe matrix. Tellurium concentration can be tuned by controlling the PbTe evaporation source temperatures between 753 K and 793 K. Binary PbSe nanocrystals were formed at 753 K, while ternary PbTe1-xSex nanocrystals were formed at 793 K. The nanocrystals grow in a granular shape at the initial stage of film growth, and the morphology changes to nanowire-shape as the film grows, irrespective of the Te concentration. The ternary PbTe1-xSex nanocrystals were composed of two phases with different Te concentration; Te-rich (Se-poor) granular crystals were formed near the bottom half parts of the film and Te-poor (Se-rich) nanowires were formed at the upper half parts of the film. Columnar ZnSe crystals contain high-density {111} stacking faults due to the low stacking fault energy of ZnSe. A balance of deposition and re-evaporation on the substrate during the film growth will be responsible for the resultant nanocrystal morphology.

Dependence of Internal Crystal Structures of InAs Nanowires on Electrical Characteristics of Field Effect Transistors

NASA Astrophysics Data System (ADS)

Han, Sangmoon; Choi, Ilgyu; Lee, Kwanjae; Lee, Cheul-Ro; Lee, Seoung-Ki; Hwang, Jeongwoo; Chung, Dong Chul; Kim, Jin Soo

2018-02-01

We report on the dependence of internal crystal structures on the electrical properties of a catalyst-free and undoped InAs nanowire (NW) formed on a Si(111) substrate by metal-organic chemical vapor deposition. Cross-sectional transmission electron microscopy images, obtained from four different positions of a single InAs NW, indicated that the wurtzite (WZ) structure with stacking faults was observed mostly in the bottom region of the NW. Vertically along the InAs NW, the amount of stacking faults decreased and a zinc-blende (ZB) structure was observed. At the top of the NW, the ZB structure was prominently observed. The resistance and resistivity of the top region of the undoped InAs NW with the ZB structure were measured to be 121.5 kΩ and 0.19 Ω cm, respectively, which are smaller than those of the bottom region with the WZ structure, i.e., 251.8 kΩ and 0.39 Ω cm, respectively. The reduction in the resistance of the top region of the NW is attributed to the improvement in the crystal quality and the change in the ZB crystal structure. For a field effect transistor with an undoped InAs NW channel, the drain current versus drain-source voltage characteristic curves under various negative gate-source voltages were successfully observed at room temperature.

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS.

PubMed

Suturin, S M; Fedorov, V V; Korovin, A M; Valkovskiy, G A; Konnikov, S G; Tabuchi, M; Sokolov, N S

2013-08-01

In this work epitaxial growth of cobalt on CaF 2 (111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF 2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.

Multi-scale simulation of lithium diffusion in the presence of a 30° partial dislocation and stacking fault in Si

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Chao-Ying; Li, Chen-liang; Wu, Guo-Xun

The multi-scale simulation method is employed to investigate how defects affect the performances of Li-ion batteries (LIBs). The stable positions, binding energies and dynamics properties of Li impurity in Si with a 30° partial dislocation and stacking fault (SF) have been studied in comparison with the ideal crystal. It is found that the most table position is the tetrahedral (T{sub d}) site and the diffusion barrier is 0.63 eV in bulk Si. In the 30° partial dislocation core and SF region, the most stable positions are at the centers of the octagons (Oct-A and Oct-B) and pentahedron (site S), respectively. Inmore » addition, Li dopant may tend to congregate in these defects. The motion of Li along the dislocation core are carried out by the transport among the Oct-A (Oct-B) sites with the barrier of 1.93 eV (1.12 eV). In the SF region, the diffusion barrier of Li is 0.91 eV. These two types of defects may retard the fast migration of Li dopant that is finally trapped by them. Thus, the presence of the 30° partial dislocation and SF may deactivate the Li impurity and lead to low rate capability of LIB.« less

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS

PubMed Central

Suturin, S. M.; Fedorov, V. V.; Korovin, A. M.; Valkovskiy, G. A.; Konnikov, S. G.; Tabuchi, M.; Sokolov, N. S.

2013-01-01

In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles. PMID:24046491

Strain-induced structural defects and their effects on the electrochemical performances of silicon core/germanium shell nanowire heterostructures

DOE PAGES

Lin, Yung-Chen; Kim, Dongheun; Li, Zhen; ...

2016-12-14

Here we report on strain-induced structural defect formation in core Si nanowire of Si/Ge core/shell nanowire heterostructure and influences of the structural defects on the electrochemical performances in lithium-ion battery anodes based on Si/Ge core/shell nanowire heterostructures. The induced structural defects consisting of stacking faults and dislocations in the core Si nanowire were observed for the first time. The generation of stacking faults in Si/Ge core/shell nanowire heterostructure is observed to prefer settling in either only Ge shell region or in both Ge shell and Si core regions and is associated with the increase of the shell volume fraction. Themore » relax of misfit strain in [112] oriented core/shell nanowire heterostructure leads to subsequent gliding of Shockley partial dislocations, preferentially forming the twins. The observation of cross-over defect formation is of great importance for the understanding of heteroepitaxy in radial heterostructures at nanoscale and building the three dimensional heterostructures for the various applications. In addition, the effect of the defect formation on nanomaterial’s functionality is investigated by electrochemical performance test. The Si/Ge core/shell nanowire heterostructures enhance the gravimetric capacity of lithium ion battery anodes under fast charging/discharging rates compared to Si nanowires. However, the induced structural defects hamper lithiation of the Si/Ge core/shell nanowire heterostructure.« less

Self-assembled Multilayers of Silica Nanospheres for Defect Reduction in Non- and Semipolar Gallium Nitride Epitaxial Layers

PubMed Central

2015-01-01

Non- and semipolar GaN have great potential to improve the efficiency of light emitting devices due to much reduced internal electric fields. However, heteroepitaxial GaN growth in these crystal orientations suffers from very high dislocation and stacking faults densities. Here, we report a facile method to obtain low defect density non- and semipolar heteroepitaxial GaN via selective area epitaxy using self-assembled multilayers of silica nanospheres (MSN). Nonpolar (11–20) and semipolar (11–22) GaN layers with high crystal quality have been achieved by epitaxial integration of the MSN and a simple one-step overgrowth process, by which both dislocation and basal plane stacking fault densities can be significantly reduced. The underlying defect reduction mechanisms include epitaxial growth through the MSN covered template, island nucleation via nanogaps in the MSN, and lateral overgrowth and coalescence above the MSN. InGaN/GaN multiple quantum wells structures grown on a nonpolar GaN/MSN template show more than 30-fold increase in the luminescence intensity compared to a control sample without the MSN. This self-assembled MSN technique provides a new platform for epitaxial growth of nitride semiconductors and offers unique opportunities for improving the material quality of GaN grown on other orientations and foreign substrates or heteroepitaxial growth of other lattice-mismatched materials. PMID:27065755

Important role of the non-uniform Fe distribution for the ferromagnetism in group-IV-based ferromagnetic semiconductor GeFe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wakabayashi, Yuki K.; Ohya, Shinobu; Ban, Yoshisuke

2014-11-07

We investigate the growth-temperature dependence of the properties of the group-IV-based ferromagnetic semiconductor Ge{sub 1−x}Fe{sub x} films (x = 6.5% and 10.5%), and reveal the correlation of the magnetic properties with the lattice constant, Curie temperature (T{sub C}), non-uniformity of Fe atoms, stacking-fault defects, and Fe-atom locations. While T{sub C} strongly depends on the growth temperature, we find a universal relationship between T{sub C} and the lattice constant, which does not depend on the Fe content x. By using the spatially resolved transmission-electron diffractions combined with the energy-dispersive X-ray spectroscopy, we find that the density of the stacking-fault defects and the non-uniformitymore » of the Fe concentration are correlated with T{sub C}. Meanwhile, by using the channeling Rutherford backscattering and particle-induced X-ray emission measurements, we clarify that about 15% of the Fe atoms exist on the tetrahedral interstitial sites in the Ge{sub 0.935}Fe{sub 0.065} lattice and that the substitutional Fe concentration is not correlated with T{sub C}. Considering these results, we conclude that the non-uniformity of the Fe concentration plays an important role in determining the ferromagnetic properties of GeFe.« less

Strain-induced structural defects and their effects on the electrochemical performances of silicon core/germanium shell nanowire heterostructures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Yung-Chen; Kim, Dongheun; Li, Zhen

Here we report on strain-induced structural defect formation in core Si nanowire of Si/Ge core/shell nanowire heterostructure and influences of the structural defects on the electrochemical performances in lithium-ion battery anodes based on Si/Ge core/shell nanowire heterostructures. The induced structural defects consisting of stacking faults and dislocations in the core Si nanowire were observed for the first time. The generation of stacking faults in Si/Ge core/shell nanowire heterostructure is observed to prefer settling in either only Ge shell region or in both Ge shell and Si core regions and is associated with the increase of the shell volume fraction. Themore » relax of misfit strain in [112] oriented core/shell nanowire heterostructure leads to subsequent gliding of Shockley partial dislocations, preferentially forming the twins. The observation of cross-over defect formation is of great importance for the understanding of heteroepitaxy in radial heterostructures at nanoscale and building the three dimensional heterostructures for the various applications. In addition, the effect of the defect formation on nanomaterial’s functionality is investigated by electrochemical performance test. The Si/Ge core/shell nanowire heterostructures enhance the gravimetric capacity of lithium ion battery anodes under fast charging/discharging rates compared to Si nanowires. However, the induced structural defects hamper lithiation of the Si/Ge core/shell nanowire heterostructure.« less

Effect of substrate on the atomic structure and physical properties of thermoelectric Ca3Co4O9 thin films

NASA Astrophysics Data System (ADS)

Qiao, Q.; Gulec, A.; Paulauskas, T.; Kolesnik, S.; Dabrowski, B.; Ozdemir, M.; Boyraz, C.; Mazumdar, D.; Gupta, A.; Klie, R. F.

2011-08-01

The incommensurately layered cobalt oxide Ca3Co4O9 exhibits an unusually high Seebeck coefficient as a polycrystalline bulk material, making it ideally suited for many high temperature thermoelectric applications. In this paper, we investigate properties of Ca3Co4O9 thin films grown on cubic perovskite SrTiO3, LaAlO3, and (La0.3Sr0.7)(Al0.65Ta0.35)O3 substrates and on hexagonal Al2O3 (sapphire) substrates using the pulsed laser deposition technique. X-ray diffraction and transmission electron microscopy analysis indicate strain-free growth of films, irrespective of the substrate. However, depending on the lattice and symmetry mismatch, defect-free growth of the hexagonal CoO2 layer is stabilized only after a critical thickness and, in general, we observe the formation of a stable Ca2CoO3 buffer layer near the substrate-film interface. Beyond this critical thickness, a large concentration of CoO2 stacking faults is observed, possibly due to weak interlayer interaction in this layered material. We propose that these stacking faults have a significant impact on the Seebeck coefficient and we report higher values in thinner Ca3Co4O9 films due to additional phonon scattering sites, necessary for improved thermoelectric properties.

Effect of substrate on the atomic structure and physical properties of thermoelectric Ca₃Co₄O₉ thin films.

PubMed

Qiao, Q; Gulec, A; Paulauskas, T; Kolesnik, S; Dabrowski, B; Ozdemir, M; Boyraz, C; Mazumdar, D; Gupta, A; Klie, R F

2011-08-03

The incommensurately layered cobalt oxide Ca(3)Co(4)O(9) exhibits an unusually high Seebeck coefficient as a polycrystalline bulk material, making it ideally suited for many high temperature thermoelectric applications. In this paper, we investigate properties of Ca(3)Co(4)O(9) thin films grown on cubic perovskite SrTiO(3), LaAlO(3), and (La(0.3)Sr(0.7))(Al(0.65)Ta(0.35))O(3) substrates and on hexagonal Al(2)O(3) (sapphire) substrates using the pulsed laser deposition technique. X-ray diffraction and transmission electron microscopy analysis indicate strain-free growth of films, irrespective of the substrate. However, depending on the lattice and symmetry mismatch, defect-free growth of the hexagonal CoO(2) layer is stabilized only after a critical thickness and, in general, we observe the formation of a stable Ca(2)CoO(3) buffer layer near the substrate-film interface. Beyond this critical thickness, a large concentration of CoO(2) stacking faults is observed, possibly due to weak interlayer interaction in this layered material. We propose that these stacking faults have a significant impact on the Seebeck coefficient and we report higher values in thinner Ca(3)Co(4)O(9) films due to additional phonon scattering sites, necessary for improved thermoelectric properties.

Effect of hydrogenation conditions on the microstructure and mechanical properties of zirconium hydride

NASA Astrophysics Data System (ADS)

Muta, Hiroaki; Nishikane, Ryoji; Ando, Yusuke; Matsunaga, Junji; Sakamoto, Kan; Harjo, Stefanus; Kawasaki, Takuro; Ohishi, Yuji; Kurosaki, Ken; Yamanaka, Shinsuke

2018-03-01

Precipitation of brittle zirconium hydrides deteriorate the fracture toughness of the fuel cladding tubes of light water reactor. Although the hydride embrittlement has been studied extensively, little is known about physical properties of the hydride due to the experimental difficulties. In the present study, to elucidate relationship between mechanical properties and microstructure, two δ-phase zirconium hydrides and one ε-phase zirconium hydride were carefully fabricated considering volume changes at the metal-to-hydride transformation. The δ-hydride that was fabricated from α-zirconium exhibits numerous inner cracks due to the large volume change. Analyses of the neutron diffraction pattern and electron backscatter diffraction (EBSD) data show that the sample displays significant stacking faults in the {111} plane and in the pseudo-layered microstructure. On the other hand, the δ-hydride sample fabricated from β-zirconium at a higher temperature displays equiaxed grains and no cracks. The strong crystal orientation dependence of mechanical properties were confirmed by indentation test and EBSD observation. The δ-hydride hydrogenated from α-zirconium displays a lower Young's modulus than that prepared from β-zirconium. The difference is attributed to stacking faults within the {111} plane, for which the Young's modulus exhibits the highest value in the perpendicular direction. The strong influence of the crystal orientation and dislocation density on the mechanical properties should be considered when evaluating hydride precipitates in nuclear fuel cladding.

Ground-Penatrating Radar Investigations Across the Sawmill Branch Fault Near Charleston, South Carolina

NASA Astrophysics Data System (ADS)

Dura-Gomez, I.; Addison, A.; Knapp, C. C.; Talwani, P.; Chapman, A.

2005-12-01

During the 1886 Charleston earthquake, two parallel tabby walls of Fort Dorchester broke left-laterally, and a strike of ~N25°W was inferred for the causative Sawmill Branch fault. To better define this fault, which does not have any surface expression, we planned to cut trenches across it. However, as Fort Dorchester is a protected archeological site, we were required to locate the fault accurately away from the fort, before permission could be obtained to cut short trenches. The present GPR investigations were planned as a preliminary step to determine locations for trenching. A pulseEKKO 100 GPR was used to collect data along eight profiles (varying in length from 10 m to 30 m) that were run across the projected strike of the fault, and one 50 m long profile that was run parallel to it. The locations of the profiles were obtained using a total station. To capture the signature of the fault, sixteen common-offset (COS) lines were acquired by using different antennas (50, 100 and 200 MHz) and stacking 64 times to increase the signal-to-noise ratio. The location of trees and stumps were recorded. In addition, two common-midpoint (CMP) tests were carried out, and gave an average velocity of about 0.097 m/ns. Processing included the subtraction of the low frequency "wow" on the trace (dewow), automatic gain control (AGC) and the application of bandpass filters. The signals using the 50 MHz, 100 MHz and 200 MHz antennas were found to penetrate up to about 30 meters, 20 meters and 12 meters respectively. Vertically offset reflectors and disruptions of the electrical signal were used to infer the location of the fault(s). Comparisons of the locations of these disruptions on various lines were used to infer the presence of a N30°W fault zone We plan to confirm these locations by cutting shallow trenches.

Earthquake stress drops and inferred fault strength on the Hayward Fault, east San Francisco Bay, California

USGS Publications Warehouse

Hardebeck, J.L.; Aron, A.

2009-01-01

We study variations in earthquake stress drop with respect to depth, faulting regime, creeping versus locked fault behavior, and wall-rock geology. We use the P-wave displacement spectra from borehole seismic recordings of M 1.0-4.2 earthquakes in the east San Francisco Bay to estimate stress drop using a stack-and-invert empirical Green's function method. The median stress drop is 8.7 MPa, and most stress drops are in the range between 0.4 and 130 MPa. An apparent correlation between stress drop and magnitude is entirely an artifact of the limited frequency band of 4-55 Hz. There is a trend of increasing stress drop with depth, with a median stress drop of ~5 MPa for 1-7 km depth, ~10 MPa for 7-13 km depth, and ~50 MPa deeper than 13 km. We use S=P amplitude ratios measured from the borehole records to better constrain the first-motion focal mechanisms. High stress drops are observed for a deep cluster of thrust-faulting earthquakes. The correlation of stress drops with depth and faulting regime implies that stress drop is related to the applied shear stress. We compare the spatial distribution of stress drops on the Hayward fault to a model of creeping versus locked behavior of the fault and find that high stress drops are concentrated around the major locked patch near Oakland. This also suggests a connection between stress drop and applied shear stress, as the locked patch may experience higher applied shear stress as a result of the difference in cumulative slip or the presence of higher-strength material. The stress drops do not directly correlate with the strength of the proposed wall-rock geology at depth, suggesting that the relationship between fault strength and the strength of the wall rock is complex.

Seismic investigation of the Kunlun Fault: Analysis of the INDEPTH IV 2-D active-source seismic dataset

NASA Astrophysics Data System (ADS)

Seelig, William George

The Tibetan Plateau has experienced significant crustal thickening and deformation since the continental subduction and collision of the Asian and Indian plates in the Eocene. Deformation of the northern Tibetan Plateau is largely accommodated by strike-slip faulting. The Kunlun Fault is a 1000-km long strike-slip fault near the northern boundary of the Plateau that has experienced five magnitude 7.0 or greater earthquakes in the past 100 years and represents a major rheological boundary. Active-source, 2-D seismic reflection/refraction data, collected as part of project INDEPTH IV (International Deep Profiling of Tibet and the Himalaya, phase IV) in 2007, was used to examine the structure and the dip of the Kunlun fault. The INDEPTH IV data was acquired to better understand the tectonic evolution of the northeastern Tibetan Plateau, such as the far-field deformation associated with the continent-continent collision and the potential subduction of the Asian continent beneath northern Tibet. Seismic reflection common depth point (CDP) stacks were examined to look for reflectivity patterns that may be associated with faulting. A possible reflection from the buried North Kunlun Thrust (NKT) is identified at 18-21 km underneath the East Kunlun Mountains, with an estimated apparent dip of 15°S and thrusting to the north. Minimally-processed shot gathers were also inspected for reflections off near-vertical structures such as faults and information on first-order velocity structure. Shot offset and nearest receiver number to reflection was catalogued to increase confidence of picks. Reflections off the North Kunlun (NKF) and South Kunlun Faults (SKF) were identified and analyzed for apparent dip and subsurface geometry. Fault reflection analysis found that the North Kunlun Fault had an apparent dip of approximately 68ºS to an estimated depth of 5 km, while the South Kunlun Fault dipped at approximately 78ºN to an estimated 3.5 km depth. Constraints on apparent dip and geometry of the NKF/SKF and NKT provide information valuable for seismic hazard analysis.

Seismic imaging of the Waltham Canyon fault, California: comparison of ray‐theoretical and Fresnel volume prestack depth migration

USGS Publications Warehouse

Bauer, Klaus; Ryberg, Trond; Fuis, Gary S.; Lüth, Stefan

2013-01-01

Near‐vertical faults can be imaged using reflected refractions identified in controlled‐source seismic data. Often theses phases are observed on a few neighboring shot or receiver gathers, resulting in a low‐fold data set. Imaging can be carried out with Kirchhoff prestack depth migration in which migration noise is suppressed by constructive stacking of large amounts of multifold data. Fresnel volume migration can be used for low‐fold data without severe migration noise, as the smearing along isochrones is limited to the first Fresnel zone around the reflection point. We developed a modified Fresnel volume migration technique to enhance imaging of steep faults and to suppress noise and undesired coherent phases. The modifications include target‐oriented filters to separate reflected refractions from steep‐dipping faults and reflections with hyperbolic moveout. Undesired phases like multiple reflections, mode conversions, direct P and S waves, and surface waves are suppressed by these filters. As an alternative approach, we developed a new prestack line‐drawing migration method, which can be considered as a proxy to an infinite frequency approximation of the Fresnel volume migration. The line‐drawing migration is not considering waveform information but requires significantly shorter computational time. Target‐oriented filters were extended by dip filters in the line‐drawing migration method. The migration methods were tested with synthetic data and applied to real data from the Waltham Canyon fault, California. The two techniques are applied best in combination, to design filters and to generate complementary images of steep faults.

Fluid-rock interaction controlling clay-mineral crystallization in quartz-rich rocks and its influence on the seismicity of the Carboneras fault area (SE Spain)

NASA Astrophysics Data System (ADS)

Jimenez-Espinosa, R.; Abad, I.; Jimenez-Millan, J.; Lorite-Herrera, M.

2009-04-01

The Carboneras Fault zone is one of the longest fault in the Betic Cordillera (SE Spain) and it would be a good candidate to generate large magnitude earthquakes (Gracia et al., 2006). Seismicity in the region is characterised by low to moderate magnitude events, although large destructive earthquakes have occurred, which reveals significant earthquake and tsunami hazards (Masana et al., 2004). Due to the internal architecture of the fault zone, shear lenses of post-orogenic sediments of Miocene and Pliocene age including marls and sandstones sequences are juxtaposed to the predominant slaty gouges of the Alpine basement. Microcataclasites and gouges of the quartz-rich post-orogenic sediments are also developed as cm- to m-scale bands, allowing the comparison between the deformed materials and their protoliths. Red, yellow and white sandstones and their respective cataclasites can be identified. This communication is concerned with the clay mineral crystallization events in these materials and its possible influence on the seismicity model of the region. The presence of phyllosilicates in fault zones as either neoformed or inherited clays is commonly related with fluid circulation and a mechanically weak fault behaviour (e.g., Wang, 1984). A critical factor for the understanding of the mechanical role of clays in fault rocks is to determine the timing of formation of mineral assemblages and microstructure of fault rocks and protolith. The effects of post-faulting alteration limit inferences about fault behaviour that can be made from exhumed rocks. The Carboneras fault zone provides good opportunities to study mineral processes enhanced by deformation, given that it is located in a region of arid climate and shows outcroppings of quartzitic rocks included in slaty rocks. Combined XRD, optical microscopy and SEM analyses reveal that deformed quartzitic rocks are enriched in phyllosilicates, increasing especially the amount of chlorite. The samples strongly damaged are characterised also by the presence of dolomite and gypsum. The deformation is highly localized, developing phyllosilicate-rich bands highly foliated due to the presence of fine-sized aligned clays (chlorite and mica). In some undeformed lenses of the cataclastic rocks, variable-sized patches of phyllosilicates containing random oriented stacks of chlorite and mica are developed. BSE images reveal that the stacks are made of two intergrown compositional types of chlorite. These results lead to conclude that limited clay growth during faulting occurred. The absence of significant compositional differences between undeformed and deformed phyllosilicates suggests that whereas fluids were present during strike-slip faulting, fluids were not preferentially focused along the quartz-rich rocks of the fault zone by phyllosilicates avoiding the development of the synkinematic clay alteration process. However, clays played an important role for the mechanical behaviour of the quartzitic rocks in the fault zone. Deformation is highly localized in chlorite-rich sandstones. These sandstones show substantial clay crystallization which texture can be related with a hydrothermal origin before strike-slip faulting, likely associated with the volcanic activity of the area leading to form of chlorite/mica patches. These data indicate that, although elevated fluid pressure confined by clay fabric cannot be appealed for the mechanical behaviour of the sandstones of the Carboneras fault, clay fabrics developed during deformation dominated the fault-weakening mechanism. We consider that lubricating properties of phyllosilicates in the quartzitic rocks were an important factor controlling movement mechanisms promoting the predominance of creep as regards seismic stick-slip (Bedrosian et al., 2004) reducing the possibility of larger seismogenic events that nucleate on localized fault planes developed within quartzitic rocks contained within the fault zone. Finally the crystallization of dolomite and gypsum in the highly damaged areas of the microcataclasites could be related with recent low-temperature and high-salinity water circulation episodes, suggesting that cataclasis may control pathways and focus circulation of the current aquifer systems. References Bedrosian, P.A., Unsworth, M.J., Egbert, G.D., Thuerber, C.H. (2004): Geophysical images of creeping segment of the San Andreas Fault: Implications for the role of crustal fluids in the earthquake process. Tectonophysics, 385, 137-158. Gracia, E., Palla, R., Soto, J.I., Comas, M., Moreno, X., Masana, E., Santanach, P., Diez, S., García, M., Dañobeitia, J. & HITS scientific party (2006): Active faulting offshore SE Spain (Alboran Sea): Implications for earthquake hazard assessment in the Southern Iberian Margin. Earth and Planetary Science Letters, 241, 734-749. Masana E., Martínez-Díaz, J.J., Hernández-Enrile, J.L. & Santanach, P. (2004): The Alhama de Murcia fault (SE Spain), a seismogenic fault in a diffuse plate boundary: seismotectonic implications for the Ibero-Magrebian region. J. Geophys. Res., 109, 1-17. Wang, C.Y. (1984): On the constitution of the San Andreas fault zone in central California. J. Geophys. Res., 89, 5858-5866.

Multi-scale Investigation on Microstructure, Mechanical Properties, and Deformation Mechanisms in Mg Alloys

NASA Astrophysics Data System (ADS)

Zhang, Dalong

Mg and its alloys are promising candidates for light-weight structural applications, e.g., aircraft, automobile, electronic, etc. However, the inherent hexagonal close packed crystal structure makes the deformation of Mg anisotropic, namely deformation only occurs predominantly by dislocation slip in the close-packed (0001) plane (i.e., basal plane), or by deformation twinning in {101¯2} planes. Both basal slip and twinning cause the crystal to re-orient. Consequently, polycrystalline Mg alloys that have undergone thermomechanical processing usually contain strong texture, i.e., preferred crystallographic orientation in grains. The texture in turn leads to anisotropic deformation in wrought Mg alloys. For example, in extruded Mg alloys, the compressive yield strength is usually much lower than the tensile yield strength (so-called yield asymmetry and strength differential). It is the anisotropy that hinders the broader application of Mg alloys. Recent modeling studies on Mg predict that certain alloying elements, particularly rare-earth elements (e.g., Y, Ce, Nd, Gd, etc.), could alter the active deformation modes and enhance homogeneous deformation and overall mechanical properties in Mg. Therefore, the objective of this dissertation research is to investigate experimentally the effects of alloying element Y in reducing the intrinsic and extrinsic anisotropy, modifying texture, and enhancing the overall strength and ductility for Mg. In addition, the research also uncovered some unexpected "side effects" of Y and these phenomena were studied and explained from a fundamental perspective. The methodology used in this work is described as follows. Ultrafine grained Mg 2.5 at.% Y alloy (UFG Mg-2.5Y) was prepared by powder metallurgy method, including gas atomization for producing Mg-2.5Y powder, degassing and hot isostatic pressing (HIP), and hot extrusion. Both the as-HIPed and the as-extruded materials were characterized by electron back-scattered diffraction (EBSD), transmission electron microscopy (TEM), and/or atom probe tomography (APT). It is noted that different configurations of stacking faults (all in basal plane, i.e., basal stacking faults, BSFs for short) were observed in the as-extruded Mg-2.5Y, whereas no BSFs were documented in the as-HIPed alloy. Feasible models to explain the formation of BSFs were proposed based on the activity of different dislocations. Tension and compression tests were carried out along the extrusion direction (ED) for UFG Mg-2.5Y. Unlike common Mg alloys exhibiting yield asymmetry, the UFG Mg-2.5Y exhibits yield "symmetry" and significantly reduced strength differential. Namely, the deformation is more isotropic. In addition to post-mortem TEM characterization for deformed UFG Mg-2.5Y, in-situ TEM was also performed, in an effort to understand the fundamental deformation mechanisms in UFG Mg-Y that lead to reduced anisotropy. In-situ TEM for single-crystal Mg-Y nano-pillars reveals that deformation twinning is replaced by dislocation slip in non-basal planes (i.e., prismatic planes), which diametrically differs from any other Mg alloys. However, it is noted that deformation twinning still occurs in the polycrystalline UFG Mg-2.5Y occasionally, and a new type of stacking faults (i.e., prismatic stacking faults, PSFs for short) may be present in the vicinity of twins. Feasible mechanisms explaining the formation of PSFs are proposed.

Seismic images of a Grenvillian terrane boundary

USGS Publications Warehouse

Milkereit, B.; Forsyth, D. A.; Green, A.G.; Davidson, A.; Hanmer, S.; Hutchinson, Deborah R.; Hinze, W. J.; Mereu, R.F.

1992-01-01

A series of gently dipping reflection zones extending to mid-crustal depths is recorded by seismic data from Lakes Ontario and Erie. These prominent reflection zones define a broad complex of southeast-dipping ductile thrust faults in the interior of the Grenville orogen. One major reflection zone provides the first image of a proposed Grenvillian suture—the listric boundary zone between allochthonous terranes of the Central Gneiss and Central Metasedimentary belts. Curvilinear bands of reflections that may represent "ramp folds" and "ramp anticlines" that originally formed in a deep crustal-scale duplex abut several faults. Vertical stacking of some curvilinear features suggests coeval or later out-of-sequence faulting of imbricated and folded thrust sheets. Grenvillian structure reflections are overlain by a thin, wedge-shaped package of shallow-dipping reflections that probably originates from sediments deposited in a local half graben developed during a period of post-Grenville extension. This is the first seismic evidence for such extension in this region, which could have occurred during terminal collapse of the Grenville orogen, or could have marked the beginning of pre-Appalachian continental rifting.

Faulted shoreline and tidal deposits in the Moenkopi Formation of the Grassy Trail Creek field, Utah

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allison, M.L.; Lutz, S.J.

1991-06-01

The Grassy Trail Creek field produces 40{degrees} API oil and minor gas from shallow marine sandstones of the Triassic Moenkopi Formation on the north-plunging nose of the San Rafael swell in central Utah. Production is controlled by a combination of stratigraphic variations and minor north-south-trending faults. Although fracture permeability enhances production of the reservoir, some faults act as barriers to fluid migration, segmenting the area into productive and dry fault blocks. Horizontal drilling techniques developed in this field in the early 1980s resulted in significantly better production. Log analyses indicate the main reservoir is a complex stack of this thinmore » tidal channel sandstones. Isochore maps of the A and B zones indicate thickened meanders that form localized reservoir pods that are vertically offset. The distribution of isochore thicks appears to represent deposition along a northwest-southeast-trending shoreline fed by sediments from the northeast. There is potential for field extensions in similar deposits along this paleoshoreline. The Moenkopi Formation, long thought to be self-sourcing, may contain oil generated in Precambrian sediments equivalent to the Late Proterozoic Chuar Group. Presence of this older oil would have required migration from Precambrian sedimentary rocks surrounding the San Rafael swell.« less

Towards New Metrics for High-Performance Computing Resilience

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hukerikar, Saurabh; Ashraf, Rizwan A; Engelmann, Christian

Ensuring the reliability of applications is becoming an increasingly important challenge as high-performance computing (HPC) systems experience an ever-growing number of faults, errors and failures. While the HPC community has made substantial progress in developing various resilience solutions, it continues to rely on platform-based metrics to quantify application resiliency improvements. The resilience of an HPC application is concerned with the reliability of the application outcome as well as the fault handling efficiency. To understand the scope of impact, effective coverage and performance efficiency of existing and emerging resilience solutions, there is a need for new metrics. In this paper, wemore » develop new ways to quantify resilience that consider both the reliability and the performance characteristics of the solutions from the perspective of HPC applications. As HPC systems continue to evolve in terms of scale and complexity, it is expected that applications will experience various types of faults, errors and failures, which will require applications to apply multiple resilience solutions across the system stack. The proposed metrics are intended to be useful for understanding the combined impact of these solutions on an application's ability to produce correct results and to evaluate their overall impact on an application's performance in the presence of various modes of faults.« less

PVA/NaCl/MgO nanocomposites-microstructural analysis by whole pattern fitting method

NASA Astrophysics Data System (ADS)

Prashanth, K. S.; Mahesh, S. S.; Prakash, M. B. Nanda; Somashekar, R.; Nagabhushana, B. M.

2018-04-01

The nanofillers in the macromolecular matrix have displayed noteworthy changes in the structure and reactivity of the polymer nanocomposites. Novel functional materials usually consist of defects and are largely disordered. The intriguing properties of these materials are often attributed to defects. X-ray line profiles from powder diffraction reveal the quantitative information about size distribution and shape of diffracting domains which governs the contribution from small conventional X-ray diffraction (XRD) techniques to enumerate the microstructural information. In this study the MgO nanoparticles were prepared by solution combustion method and PVA/NaCl/MgO nanocomposite films were synthesized by the solvent cast method. Microstructural parameters viz crystal defects like stacking faults and twin faults, compositional inhomogeneity, crystallite size and lattice strain (g in %), were extracted using whole pattern fitting method.

Seismic Evidence for a Geosuture between the Yangtze and Cathaysia Blocks, South China

PubMed Central

He, Chuansong; Dong, Shuwen; Santosh, M.; Chen, Xuanhua

2013-01-01

South China, composed of the Yangtze and Cathaysia Blocks and the intervening Jiangnan orogenic belt, has been central to the debate on the tectonic evolution of East Asia. Here we investigate the crustal structure and composition of South China from seismic data employing the H-k stacking technique. Our results show that the composition and seismic structure of the crust in the Jiangnan orogenic belt are identical to those of the Cathaysia Block. Our data reveal a distinct contrast in the crustal structure and composition between the two flanks of the Jiujiang-Shitai buried fault. We propose that the Jiujiang-Shitai buried fault defines a geosuture between the Yangtze and Cathaysia Blocks, and that the felsic lower crust of the Cathaysia Block and the Jiangnan orogenic belt may represent fragments derived from the Gondwana supercontinent. PMID:23857499

The Effect of High Pressure - High Temperature Treatment on Neutron Irradiation Induced Defects in Czochralski Silicon

DTIC Science & Technology

2001-01-01

Spectra by the 830cm’ Localized Vibrational Mode (LVM) band. Upon annealing , this defect is converted to the V0 2 defect responsible for a LVM band at...887cmŕ. The purpose of this work is to study the effect of various combinations of HTHP treatment prior to irradiation on the annealing behaviour of...and stacking faults. Keywords: high temperature - high pressure treatments, annealing , neutron irradiation. 1. INTRODUCTION Oxygen is one of the two

Surface effects on the radiation response of nanoporous Au foams

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, E. G.; Caro, M.; Wang, Y. Q.

2012-11-05

We report on an experimental and simulation campaign aimed at exploring the radiation response of nanoporous Au (np-Au) foams. We find different defect accumulation behavior by varying radiation dose-rate in ion-irradiated np-Au foams. Stacking fault tetrahedra are formed when np-Au foams are irradiated at high dose-rate, but they do not seem to be formed in np-Au at low dose-rate irradiation. A model is proposed to explain the dose-rate dependent defect accumulation based on these results.

Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy

DOE PAGES

Luria, Justin; Kutes, Yasemin; Moore, Andrew; ...

2016-09-26

Polycrystalline photovoltaics comprising cadmium telluride (CdTe) represent a growing portion of the solar cell market, yet the physical picture of charge transport through the meso-scale grain morphology remains a topic of debate. It is unknown how thin film morphology affects the transport of electron-hole pairs. Accordingly this study is the first to generate three dimensional images of photocurrent throughout a thin-film solar cell, revealing the profound influence of grain boundaries and stacking faults on device efficiency.

Development of High Quality 4H-SiC Thick Epitaxy for Reliable High Power Electronics Using Halogenated Precursors

DTIC Science & Technology

2016-08-02

epitaxy platform, it is essential that malignant defects, such as in-grown stacking faults (IGSFs) and basal plane dislocations (BPDs), be...crystal quality. (5) Even though the inlet C/Si ratio is kept fixed , the C/Si ratio at the growth surface varies depending on the different gas...morphology, and quality (generation of additional defects). Two CVD reactor types, a chimney reactor and an inverted chimney reactor, are assembled; the

Atomistic Simulations of Surface Cross-Slip Nucleation in Face-Centered Cubic Nickel and Copper (Postprint)

DTIC Science & Technology

2013-02-15

molecular dynamics code, LAMMPS [9], developed at Sandia National Laboratory. The simulation cell is a rectangular parallelepiped, with the z-axis...with assigned energies within LAMMPs of greater than 4.42 eV (Ni) or 3.52 eV (Cu) (the energy of atoms in the stacking fault region), the partial...molecular dynamics code LAMMPS , which was developed at Sandia National Laboratory by Dr. Steve Plimpton and co-workers. This work was supported by the

Growth study of self-assembled GaN nanocolumns on silica glass by plasma assisted molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Liudi Mulyo, Andreas; Konno, Yuta; Nilsen, Julie S.; van Helvoort, Antonius T. J.; Fimland, Bjørn-Ove; Weman, Helge; Kishino, Katsumi

2017-12-01

We demonstrate GaN nanocolumn growth on fused silica glass by plasma-assisted molecular beam epitaxy. The effect of the substrate temperature, Ga flux and N2 flow rate on the structural and optical properties are studied. At optimum growth conditions, GaN nanocolumns are vertically aligned and well separated with an average diameter, height and density of 72 nm, 1.2 μm and 1.6 × 109 cm-2, respectively. The nanocolumns exhibit wurtzite crystal structure with no threading dislocations, stacking faults or twinning and grow in the [0 0 0 1] direction. At the interface adjacent to the glass, there is a few atom layers thick intermediate phase with ABC stacking order (zinc blende). Photoluminescence measurements evidence intense and narrow excitonic emissions, along with the absence of any defect-related zinc blende and yellow luminescence emission.

Elimination of trench defects and V-pits from InGaN/GaN structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Smalc-Koziorowska, Julita; Grzanka, Ewa; Czernecki, Robert

2015-03-09

The microstructural evolution of InGaN/GaN multiple quantum wells grown by metalorganic chemical vapor phase epitaxy was studied as a function of the growth temperature of the GaN quantum barriers (QBs). We observed the formation of basal stacking faults (BSFs) in GaN QBs grown at low temperature. The presence of BSFs terminated by stacking mismatch boundaries (SMBs) leads to the opening of the structure at the surface into a V-shaped trench loop. This trench may form above an SMB, thereby terminating the BSF, or above a junction between the SMB and a subsequent BSF. Fewer BSFs and thus fewer trench defectsmore » were observed in GaN QBs grown at temperatures higher than 830 °C. Further increase in the growth temperature of the GaN QBs led to the suppression of the threading dislocation opening into V-pits.« less

Evidence for submarine landslides and continental slope erosion related to fault reactivation during the last glaciation offshore eastern Canada

NASA Astrophysics Data System (ADS)

Saint-Ange, F.; Campbell, C.; MacKillop, K.; Mosher, D. C.; Piper, D. J.; Roger, J.

2012-12-01

Many studies have proposed that reactivation of dormant faults during deglaciation is a source of neotectonic activity in glaciated regions, but few have demonstrated the relationship to submarine landslides. In this study, seabed morphology and shallow geology of the outer continental margin adjacent to the Charlie Gibbs Fracture Zone off Newfoundland, Canada was investigated for evidence of this relationship. The glacial history and morphology of the margin suggest that the entire continental shelf in the area, coincident with major continental crustal lineaments, was ice-covered during the Last glacial cycle, and transverse troughs delineate the paleo-icestream drainage patterns. A recent investigation of Notre Dame Trough revealed the existence of large sediment failures on the shelf. The current study investigates complex seafloor erosion and widespread mass transport deposition (MTD) on the continental slope seaward of Notre Dame Trough, using recently-acquired high resolution seismic reflection data and piston cores. The new data reveal that a trough mouth fan (TMF) is present on the slope seaward of Notre Dame Trough. The Notre Dame TMF is characterized by a succession of stacked debris flows, but does not show a lobate shape in plan view like other classic TMFs. Instead, the Notre Dame TMF has abruptly-truncated margins suggesting post-depositional failure and erosion of the fan deposits. Seismic reflection data show that the locations of the failures along the TMF margin are coincident with a set of shallow faults; however the current dataset does not image the deeper portion of the faults. On the upper slope immediately south of the TMF, a narrow and deeply incised canyon is located along-trend with the Notre Dame Trough. The location of this canyon appears to be controlled by a fault. Downslope from this canyon, along the southern margin of the TMF, a 25 km wide, flat-floored, U-shaped valley was eroded into a succession of stacked MTD-filled channels. Seismic stratigraphic analysis shows that the valley developed around the same time as the adjacent TMF, however, the valley morphology and evidence for repeated slope failure suggests that the processes responsible for its formation were different than the processes that formed the nearby TMF. Age control provided from piston cores suggest that the last major slope failure that contributed to valley formation probably occurred at ~29 ka. Geotechnical measurements from piston cores show slightly underconsolidated sediments. The results indicate that this part of the margin is more unstable than Orphan Basin and Labrador slope regions. Given the low factor of safety and the complex fault system, low energy earthquake from the surrounding area could be enough to potentially trigger landslides.

Low-frequency earthquakes reveal punctuated slow slip on the deep extent of the Alpine Fault, New Zealand

USGS Publications Warehouse

Chamberlain, Calum J.; Shelly, David R.; Townend, John; Stern, T.A.

2014-01-01

We present the first evidence of low-frequency earthquakes (LFEs) associated with the deep extension of the transpressional Alpine Fault beneath the central Southern Alps of New Zealand. Our database comprises a temporally continuous 36 month-long catalog of 8760 LFEs within 14 families. To generate this catalog, we first identify 14 primary template LFEs within known periods of seismic tremor and use these templates to detect similar events in an iterative stacking and cross-correlation routine. The hypocentres of 12 of the 14 LFE families lie within 10 km of the inferred location of the Alpine Fault at depths of approximately 20–30 km, in a zone of high P-wave attenuation, low P-wave speeds, and high seismic reflectivity. The LFE catalog consists of persistent, discrete events punctuated by swarm-like bursts of activity associated with previously and newly identified tremor periods. The magnitudes of the LFEs range between ML – 0.8 and ML 1.8, with an average of ML 0.5. We find that the frequency-magnitude distribution of the LFE catalog both as a whole and within individual families is not consistent with a power law, but that individual families' frequency-amplitude distributions approximate an exponential relationship, suggestive of a characteristic length-scale of failure. We interpret this LFE activity to represent quasi-continuous slip on the deep extent of the Alpine Fault, with LFEs highlighting asperities within an otherwise steadily creeping region of the fault.

Molecular dynamics studies of defect formation during heteroepitaxial growth of InGaN alloys on (0001) GaN surfaces

DOE PAGES

Gruber, J.; Zhou, X. W.; Jones, R. E.; ...

2017-05-15

Here, we investigate the formation of extended defects during molecular-dynamics (MD) simulations of GaN and InGaN growth on (0001) and (11more » $$\\bar{2}$$0) wurtzite-GaN surfaces. The simulated growths are conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN surface; we apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the vapor-phase, the near-surface solid-phase, and the bulk-like regions of the growing layer. The simulations employ newly optimized Stillinger-Weber In-Ga-N-system potentials, wherein multiple binary and ternary structures are included in the underlying density-functional-theory training sets, allowing improved treatment of In-Ga-related atomic interactions. To examine the effect of growth conditions, we study a matrix of >30 different MD-growth simulations for a range of InxGa1-xN-alloy compositions (0 ≤ x ≤ 0.4) and homologous growth temperatures [0.50 ≤ T/T* m(x) ≤ 0.90], where T* m(x) is the simulated melting point. Growths conducted on polar (0001) GaN substrates exhibit the formation of various extended defects including stacking faults/polymorphism, associated domain boundaries, surface roughness, dislocations, and voids. In contrast, selected growths conducted on semi-polar (11$$\\bar{2}$$0) GaN, where the wurtzite-phase stacking sequence is revealed at the surface, exhibit the formation of far fewer stacking faults. We discuss variations in the defect formation with the MD growth conditions, and we compare the resulting simulated films to existing experimental observations in InGaN/GaN. Finally, while the palette of defects observed by MD closely resembles those observed in the past experiments, further work is needed to achieve truly predictive large-scale simulations of InGaN/GaN crystal growth using MD methodologies.« less

Molecular dynamics studies of defect formation during heteroepitaxial growth of InGaN alloys on (0001) GaN surfaces

NASA Astrophysics Data System (ADS)

Gruber, J.; Zhou, X. W.; Jones, R. E.; Lee, S. R.; Tucker, G. J.

2017-05-01

We investigate the formation of extended defects during molecular-dynamics (MD) simulations of GaN and InGaN growth on (0001) and ( 11 2 ¯ 0 ) wurtzite-GaN surfaces. The simulated growths are conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN surface; we apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the vapor-phase, the near-surface solid-phase, and the bulk-like regions of the growing layer. The simulations employ newly optimized Stillinger-Weber In-Ga-N-system potentials, wherein multiple binary and ternary structures are included in the underlying density-functional-theory training sets, allowing improved treatment of In-Ga-related atomic interactions. To examine the effect of growth conditions, we study a matrix of >30 different MD-growth simulations for a range of InxGa1-xN-alloy compositions (0 ≤ x ≤ 0.4) and homologous growth temperatures [0.50 ≤ T/T*m(x) ≤ 0.90], where T*m(x) is the simulated melting point. Growths conducted on polar (0001) GaN substrates exhibit the formation of various extended defects including stacking faults/polymorphism, associated domain boundaries, surface roughness, dislocations, and voids. In contrast, selected growths conducted on semi-polar ( 11 2 ¯ 0 ) GaN, where the wurtzite-phase stacking sequence is revealed at the surface, exhibit the formation of far fewer stacking faults. We discuss variations in the defect formation with the MD growth conditions, and we compare the resulting simulated films to existing experimental observations in InGaN/GaN. While the palette of defects observed by MD closely resembles those observed in the past experiments, further work is needed to achieve truly predictive large-scale simulations of InGaN/GaN crystal growth using MD methodologies.

Molecular dynamics studies of defect formation during heteroepitaxial growth of InGaN alloys on (0001) GaN surfaces.

PubMed

Gruber, J; Zhou, X W; Jones, R E; Lee, S R; Tucker, G J

2017-05-21

We investigate the formation of extended defects during molecular-dynamics (MD) simulations of GaN and InGaN growth on (0001) and ([Formula: see text]) wurtzite-GaN surfaces. The simulated growths are conducted on an atypically large scale by sequentially injecting nearly a million individual vapor-phase atoms towards a fixed GaN surface; we apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the vapor-phase, the near-surface solid-phase, and the bulk-like regions of the growing layer. The simulations employ newly optimized Stillinger-Weber In-Ga-N-system potentials, wherein multiple binary and ternary structures are included in the underlying density-functional-theory training sets, allowing improved treatment of In-Ga-related atomic interactions. To examine the effect of growth conditions, we study a matrix of >30 different MD-growth simulations for a range of In x Ga 1-x N-alloy compositions (0 ≤  x  ≤ 0.4) and homologous growth temperatures [0.50 ≤  T/T * m ( x ) ≤ 0.90], where T * m ( x ) is the simulated melting point. Growths conducted on polar (0001) GaN substrates exhibit the formation of various extended defects including stacking faults/polymorphism, associated domain boundaries, surface roughness, dislocations, and voids. In contrast, selected growths conducted on semi-polar ([Formula: see text]) GaN, where the wurtzite-phase stacking sequence is revealed at the surface, exhibit the formation of far fewer stacking faults. We discuss variations in the defect formation with the MD growth conditions, and we compare the resulting simulated films to existing experimental observations in InGaN/GaN. While the palette of defects observed by MD closely resembles those observed in the past experiments, further work is needed to achieve truly predictive large-scale simulations of InGaN/GaN crystal growth using MD methodologies.

Formation of an 18R long-period stacking ordered structure in rapidly solidified Mg{sub 88}Y{sub 8}Zn{sub 4} alloy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Garcés, Gerardo, E-mail: ggarces@cenim.csic.es

The formation of the long-period stacking ordered structure (LPSO) in a Mg{sub 88}Y{sub 8}Zn{sub 4}(at%) ribbon produced by melt spinning was studied using high energy X-ray synchrotron radiation diffraction during in-situ isochronal heating and transmission electron microscopy. The microstructure of the rapidly solidified ribbons is characterised by fine magnesium grains with yttrium and zinc in solid solution and primary 18R LPSO-phase segregated at grain boundaries. Using differential scanning calorimetry, a strong exothermal peak was observed around 300 °C which was associated with the development of the 18R-type LPSO-phase in the magnesium grains. The apparent activation energy calculated using the Kissingermore » model was 125 KJmol{sup −1} and it is related to simultaneous diffusion of Y and Zn through magnesium basal plane. - Highlights: •The formation of the LPSO phase in rapidly solidified ribbons was studied. •The formation of the 18R LPSO starts at around 300 °C. •LPSO formation have to steps: Stacking faults along basal plane and then growth of 18R structure along the c direction.« less

How to build and teach with QuakeCaster: an earthquake demonstration and exploration tool

USGS Publications Warehouse

Linton, Kelsey; Stein, Ross S.

2015-01-01

QuakeCaster is an interactive, hands-on teaching model that simulates earthquakes and their interactions along a plate-boundary fault. QuakeCaster contains the minimum number of physical processes needed to demonstrate most observable earthquake features. A winch to steadily reel in a line simulates the steady plate tectonic motions far from the plate boundaries. A granite slider in frictional contact with a nonskid rock-like surface simulates a fault at a plate boundary. A rubber band connecting the line to the slider simulates the elastic character of the Earth’s crust. By stacking and unstacking sliders and cranking in the winch, one can see the results of changing the shear stress and the clamping stress on a fault. By placing sliders in series with rubber bands between them, one can simulate the interaction of earthquakes along a fault, such as cascading or toggling shocks. By inserting a load scale into the line, one can measure the stress acting on the fault throughout the earthquake cycle. As observed for real earthquakes, QuakeCaster events are not periodic, time-predictable, or slip-predictable. QuakeCaster produces rare but unreliable “foreshocks.” When fault gouge builds up, the friction goes to zero and fault creep is seen without large quakes. QuakeCaster events produce very small amounts of fault gouge that strongly alter its behavior, resulting in smaller, more frequent shocks as the gouge accumulates. QuakeCaster is designed so that students or audience members can operate it and record its output. With a stopwatch and ruler one can measure and plot the timing, slip distance, and force results of simulated earthquakes. People of all ages can use the QuakeCaster model to explore hypotheses about earthquake occurrence. QuakeCaster takes several days and about $500.00 in materials to build.

Early Tertiary Anaconda metamorphic core complex, southwestern Montana

USGS Publications Warehouse

O'Neill, J. M.; Lonn, J.D.; Lageson, D.R.; Kunk, Michael J.

2004-01-01

A sinuous zone of gently southeast-dipping low-angle Tertiary normal faults is exposed for 100 km along the eastern margins of the Anaconda and Flint Creek ranges in southwest Montana. Faults in the zone variously place Mesoproterozoic through Paleozoic sedimentary rocks on younger Tertiary granitic rocks or on sedimentary rocks older than the overlying detached rocks. Lower plate rocks are lineated and mylonitic at the main fault and, below the mylonitic front, are cut by mylonitic mesoscopic to microscopic shear zones. The upper plate consists of an imbricate stack of younger-on-older sedimentary rocks that are locally mylonitic at the main, lowermost detachment fault but are characteristically strongly brecciated or broken. Kinematic indicators in the lineated mylonite indicate tectonic transport to the east-southeast. Syntectonic sedimentary breccia and coarse conglomerate derived solely from upper plate rocks were deposited locally on top of hanging-wall rocks in low-lying areas between fault blocks and breccia zones. Muscovite occurs locally as mica fish in mylonitic quartzites at or near the main detachment. The 40Ar/39Ar age spectrum obtained from muscovite in one mylonitic quartzite yielded an age of 47.2 + 0.14 Ma, interpreted to be the age of mylonitization. The fault zone is interpreted as a detachment fault that bounds a metamorphic core complex, here termed the Anaconda metamorphic core complex, similar in age and character to the Bitterroot mylonite that bounds the Bitterroot metamorphic core complex along the Idaho-Montana state line 100 km to the west. The Bitterroot and Anaconda core complexes are likely components of a continuous, tectonically integrated system. Recognition of this core complex expands the region of known early Tertiary brittle-ductile crustal extension eastward into areas of profound Late Cretaceous contractile deformation characterized by complex structural interactions between the overthrust belt and Laramide basement uplifts, overprinted by late Tertiary Basin and Range faulting. ?? 2004 NRC Canada.

The crustal structure along the 1999 Izmit/Düzce rupture of the North-Anatolian Fault

NASA Astrophysics Data System (ADS)

Sebastian, Rost; David, Cornwell; David, Thompson; Greg, Houseman; Metin, Kahraman; Ugur, Teoman; Selda, Altuncu-Poyraz; Niyazi, Turkelli; Andrew, Frederiksen; Stephane, Rondenay; Tim, Wright

2015-04-01

Deformation along continental strike-slip faults is localized onto narrow fault zones at the surface, which may slip suddenly and catastrophically in earthquakes. On the other hand, strain in the upper mantle is more broadly distributed and is thought to occur by continuous ductile creep. The transition between these two states is poorly understood although it controls the behaviour of the fault zone during the earthquake loading cycle. To understand the structure of and strain distribution across the North-Anatolian Fault Zone (NAFZ) we deployed temporary seismic stations in the region of the 1999 Izmit (M7.5) and Düzce (M7.2) earthquakes. The rectangular array consisted of 66 seismic stations with a nominal station spacing of 7 km and seven additional stations forming a semi-circular ring towards the east (Dense Array for Northern Anatolia - DANA). Using this very dense seismic dataset and a combination of established (e.g. H-k stacking and common conversion point migration) and novel (scattering migration and scattering inversion) seismic processing techniques allows unprecedented resolution of the crustal structure in this region. This study resolves sharp changes in crustal structure across and along the surface expression of the two branches of the NAFZ at scale lengths less than 10 km at mid to lower-crustal depths. The results indicate that the northern NAFZ branch depth extent varies from the mid-crust to the upper mantle and it is likely to be less than 5 km wide throughout the crust. We furthermore resolve a high velocity lower crust and a region of crustal underthrusting that might add strength to a heterogeneous crust and may play a role in dictating the variation in faulting style and postseismic deformation in this region of the NAFZ. The results are consistent with a narrow fault zone accommodating postseismic deformation in the lower crust, as opposed to a broad ductile region below the seismogenic region of the fault.

Geomorphology and Kinematics of the Nobi-Ise Active Fault Zone, Central Japan: Implications for the kinematic growth of tectonic landforms within an active thrust belt

NASA Astrophysics Data System (ADS)

Ishiyama, T.; Mueller, K. J.; Togo, M.; Takemura, K.; Okada, A.

2002-12-01

We present structural models constrained by tectonic geomorphology, surface geologic mapping and high-resolution seismic reflection profiles to define the kinematic evolution and geometry of active fault-related folds along the Nobi-Ise active fault zone (NAFZ). The NAFZ is an active intraplate fault system in central Japan, and consists of a 110-km-long array of active, east-verging reverse faults. We focus on the northern half of the NAFZ, where we use the kinematic evolution of active fault-related folds to constrain rates of slip on underlying blind thrusts and the rate of contraction across the belt since early Quaternary time. Fluvial terraces folded across the east-dipping forelimb, and west-dipping backlimb of the frontal Kuwana anticline suggest that it grows above a stacked sequence of thin-skinned wedge thrusts. Numerous secondary, bedding-parallel thrusts also deform the terraces and are interpreted to form by flexural slip folding that acts to consume slip on the primary blind thrusts across synclinal axial surfaces. Late Holocene fold scarps formed in the floodplain of the Ibi River east of Kuwana anticline coincide with the projected surface trace of the east-vergent wedge thrust tip and indicate the structure has accommodated coseismic (?) kink-band migration of a fault-bend fold during a historic blind thrust earthquake in 1586. A topographic cross-section based on a detailed photogrammetric map suggests 111 m of uplift of ca. 50-80 ka fluvial terraces deposited across the forelimb. For a 35° thrust, this yields the minimum slip rate of 2.7-4.8 mm/yr on the deepest wedge thrust beneath Kuwana anticline. Kinematic analysis for the much larger thrust defined to the west (the Fumotomura fault) suggests that folding of fluvial terraces occurred by trishear fault-propagation folding above a more steeply-dipping (54°), basement-involved blind thrust that propagated upward from the base of the seismogenic crust (about 12 km). Pleistocene growth strata defined by tephra (ca. 1.6 Ma) suggest the Fumotomura fault slips at a rate of 0.7-0.9 mm/yr.

The Lithosphere-asthenosphere Boundary beneath the South Island of New Zealand

NASA Astrophysics Data System (ADS)

Hua, J.; Fischer, K. M.; Savage, M. K.

2017-12-01

Lithosphere-asthenosphere boundary (LAB) properties beneath the South Island of New Zealand have been imaged by Sp receiver function common-conversion point stacking. In this transpressional boundary between the Australian and Pacific plates, dextral offset on the Alpine fault and convergence have occurred for the past 20 My, with the Alpine fault now bounded by Australian plate subduction to the south and Pacific plate subduction to the north. This study takes advantage of the long-duration and high-density seismometer networks deployed on or near the South Island, especially 29 broadband stations of the New Zealand permanent seismic network (GeoNet). We obtained 24,980 individual receiver functions by extended-time multi-taper deconvolution, mapping to three-dimensional space using a Fresnel zone approximation. Pervasive strong positive Sp phases are observed in the LAB depth range indicated by surface wave tomography (Ball et al., 2015) and geochemical studies. These phases are interpreted as conversions from a velocity decrease across the LAB. In the central South Island, the LAB is observed to be deeper and broader to the west of the Alpine fault. The deeper LAB to the west of the Alpine fault is consistent with oceanic lithosphere attached to the Australian plate that was partially subducted while also translating parallel to the Alpine fault (e.g. Sutherland, 2000). However, models in which the Pacific lithosphere has been underthrust to the west past the Alpine fault cannot be ruled out. Further north, a zone of thin lithosphere with a strong and vertically localized LAB velocity gradient occurs to the west of the fault, juxtaposed against a region of anomalously weak LAB conversions to the east of the fault. This structure, similar to results of Sp imaging beneath the central segment of the San Andreas fault (Ford et al., 2014), also suggests that lithospheric blocks with contrasting LAB properties meet beneath the Alpine fault. The observed variations in LAB properties indicate strong modification of the LAB by the interplay of convergence and strike-slip deformation along and across this transpressional plate boundary.

Decadal strain along creeping faults in the Needles District, Paradox Basin Utah determined with InSAR Time Series Analysis

NASA Astrophysics Data System (ADS)

Kravitz, K.; Furuya, M.; Mueller, K. J.

2013-12-01

The Needles District, in Canyonlands National Park in Utah exposes an array of actively creeping normal faults that accommodate gravity-driven extension above a plastically deforming substrate of evaporite deposits. Previous interferogram stacking and InSAR analysis of faults in the Needles District using 35 ERS satellite scenes from 1992 to 2002 showed line-of-sight deformation rates of ~1-2 mm/yr along active normal faults, with a wide strain gradient along the eastern margin of the deforming region. More rapid subsidence of ~2-2.5 mm/yr was also evident south of the main fault array across a broad platform bounded by the Colorado River and a single fault scarp to the south. In this study, time series analysis was performed on SAR scenes from Envisat, PALSAR, and ERS satellites ranging from 1992 to 2010 to expand upon previous results. Both persistent scatterer and small baseline methods were implemented using StaMPS. Preliminary results from Envisat data indicate equally distributed slip rates along the length of faults within the Needles District and very little subsidence in the broad region further southwest identified in previous work. A phase ramp that appears to be present within the initial interferograms creates uncertainty in the current analysis and future work is aimed at removing this artifact. Our new results suggest, however that a clear deformation signal is present along a number of large grabens in the northern part of the region at higher rates of up to 3-4 mm/yr. Little to no creep is evident along the single fault zone that bounds the southern Needles, in spite of the presence of a large and apparently active fault. This includes a segment of this fault that is instrumented by a creepmeter that yields slip rates on the order of ~1mm/yr. Further work using time series analysis and a larger sampling of SAR scenes will be used in an effort to determine why differences exist between previous and current work and to test mechanics-based modeling of extension in the region.

The time-dependence of the defective nature of ice Ic (cubic ice) and its implications for atmospheric science

NASA Astrophysics Data System (ADS)

Sippel, Christian; Koza, Michael M.; Hansen, Thomas C.; Kuhs, Werner F.

2010-05-01

The possible atmospheric implication of ice Ic (cubic ice) has already been suggested some time ago in the context of snow crystal formation [1]. New findings from air-borne measurements in cirrus clouds and contrails have put ice Ic into the focus of interest to understand the so-called "supersaturation puzzle" [2,3,4]. Our recent microstructural work on ice Ic [5,6] appears to be highly relevant in this context. We have found that ice Ic is characterized by a complex stacking fault pattern, which changes as a function of temperature as well as time. Indeed, from our own [7] and other group's work [8] one knows that (in contrast to earlier believe) ice Ic can form up to temperatures at least as high as 240K - thus in the relevant range for cirrus clouds. We have good preliminary evidence that the "cubicity" (which can be related to stacking fault probabilities) as well as the particle size of ice Ic are the relevant parameters for this correlation. The "cubicity" of stacking faulty ice Ic (established by diffraction) correlates nicely with the increased supersaturation at decreasing temperatures observed in cirrus clouds and contrails, a fact, which may be considered as further evidence for the presence of ice Ic. Recently, we have studied the time-dependency of the changes in both "cubicity" and particle size at various temperatures of relevance for cirrus clouds and contrails by in-situ neutron powder diffraction. The timescales over which changes occur (several to many hours) are similar to the life-time of cirrus clouds and contrails and suggest that the supersaturation situation may change within this time span in the natural environment too. Some accompanying results obtained by cryo-SEM (scanning electron microscopy) work will also be presented and suggest that stacking-faulty ice Ic has kinky surfaces providing many more active centres for heterogeneous reactions on the surface than in the usually assumed stable hexagonal form of ice Ih with its rather flat low-indexed crystal faces. [1] T Kobayashi & T Kuroda (1987) Snow Crystals. In: Morphology of Crystals (ed. I Sunagawa), Terra Scientific Publishing, Tokyo, pp.649-743. [2] RS Gao & 19 other authors (2004) Evidence that nitric acid increases relative humidity in low-temperature cirrus clouds. Science 303, 516-520. [3] T Peter, C Marcolli, P Spichtinger, T Corti, MC Baker & T Koop (2006) When dry air is too humid. Science 314, 1399-1402. [4] JE Shilling, MA Tolbert, OB Toon, EJ Jensen, BJ Murray & AK Bertram (2006) Measurements of the vapor pressure of cubic ice and their implications for atmospheric ice clouds. Geophys.Res.Lett. 33, 026671. [5] TC Hansen, MM Koza & WF Kuhs (2008) Formation and annealing of cubic ice: I Modelling of stacking faults. J.Phys.Cond.Matt. 20, 285104. [6] TC Hansen, MM Koza, P Lindner & WF Kuhs (2008) Formation and annealing of cubic ice: II. Kinetic study. J.Phys.Cond.Matt. 20, 285105. [7] WF Kuhs, G Genov, DK Staykova & AN Salamatin, T Hansen (2004) Ice perfection and the onset of anomalous preservation of gas hydrates. Phys.Chem.Chem.Phys. 6, 4917-4920. [8] BJ Murray, DA Knopf & AK Bertram (2005) The formation of cubic ice under conditions relevant to Earth's atmosphere. Nature 434, 292-205.

A High-Resolution Seismic Survey Across the State Line fault, NV

NASA Astrophysics Data System (ADS)

Beachly, M.; Cox, C. M.; Saldana, S. C.; Snelson, C. M.; Taylor, W. J.; Robins, C.; Davis, R.; Stropky, M.; Phillips, R.; Cothrun, C.

2007-12-01

During the summer of 2007, an investigation of the faulting in Stewart Valley was under taken, located within the central Basin and Range province ~90 km west of Las Vegas, Nevada. The goal of this study was to resolve the seismic hazard potential of the State Line fault, a right-lateral strike-slip fault that runs the length of Stewart Valley. Four seismic reflection lines were acquired, two perpendicular and two parallel to the State Line fault. What is presented is an analysis of the western and eastern seismic lines parallel to the State Line fault. The western line was acquired utilizing a 144-channel geode system with each of the 4.5 Hz vertical geophones set out at 5 m intervals to form a 715 m long profile. The eastern line employed 120 of these geophones in a 595 m long profile. A mini-vibroseis served as the seismic source every ten meters, between geophones. The vibroseis was programmed to produce an 8 s linear sweep from 20-160 Hz. Three sweeps were recorded at each shot location without acquisition filters at a sampling rate of 0.5 ms. The three shot gathers were then stacked at each location to reduce noise. The data collected had minimal noise, although; during the processing of the eastern line a notch filtered was used to remove the 60 Hz noise created by adjacent power line. These lines, acquired parallel to the State Line fault, contain matching features that serve to determine how much lateral displacement the fault has undergone. The amount of the displacement can indicate how active the fault is, and thus, what magnitude of earthquake can be expected in the future. This will in turn contribute to determining the seismic hazard potential for southern Nevada. A preliminary interpretation of the seismic reflection sections indicates an average displacement of about 20 - 38 m with greater displacement in the deeper sections of the image. The shallow depth displacement calculations are consistent with previous work in the area. The State Line fault is believed to be a result of strain partitioning from the San Andreas Fault. By studying this more localized active strike-slip fault system the results of this study can contribute to a model that provides a better understanding of the tectonics in the central Basin and Range.

Sediment Accretion During Horst and Graben Subduction associated with the Tohoku Oki M9 Earthquake, Northern Japan

NASA Astrophysics Data System (ADS)

Moore, J. C.; Chester, F. M.

2015-12-01

The stratigraphic sequence within the frontal accretionary prism of the Japan Trench, the site of large slip during the Tohoku earthquake, is unique due to horst and graben subduction. Boreholes at IODP Site C0019, penetrating the toe of the Tohoku accretionary prism, document a younger over older intraprism thrust contact with a 9 Ma age gap across the basal plate boundary fault. The anomalously young (Quaternary to Pliocene), fault-bounded sediment package is 130 m thick, of a total of 820 m of sediment above the plate boundary fault. In contrast, typical accretionary prism structure consists of stacked sediment packages on imbricate faults above the basal decollement resulting in an overall increase in age downward. Site C0019 penetrates the prism directly above a horst of the subducting Pacific oceanic crust. Here the plate-boundary fault consists of a thin, weak smectitic pelagic clay that is probably the principal slip surface of ~50 m offset in the 2011 Tohoku earthquake. The fault continues seaward deepening off the seaward edge of the horst and beneath the sediment fill of the adjacent graben, dying out at the landward base of the next incoming horst. The plate boundary fault and its splays in the graben form a narrow-taper protoprism and a small sedimentary basin of trench fill marking the seaward edge of the upper plate. The modern fault and sediment distributions within the graben are used to motivate a viable model for the presence of anomalously young sediments directly above the plate boundary fault. In this model sediments in the trench are thrust over the incoming horst by propagation of the plate boundary thrust up the landward-dipping fault of the incoming horst and along the smectitic clay layer to emplace Quaternary and Pliocene trench deposits directly on top of the incoming horst. These young deposits are in turn overlain by sediments 9 Ma or older that have been transported out of the graben along imbricate faults associated with the necessary increase in the taper of the prism above the graben. The Quaternary to Pliocene units thicken due to internal deformation accounting for the 130 m thickness now observed over the plate boundary fault at Site C0019. Conversely emplacement of very young sediment directly above a basal detachment would be unexpected in accretionary prisms subducting smoother oceanic crust.

Lack of Dependence of Dynamic Triggering on the Timing within the Seismic Cycle

NASA Astrophysics Data System (ADS)

Cattania, C.; McGuire, J. J.; Collins, J. A.

2009-12-01

Numerical models predict that dynamic triggering of earthquakes is more likely when faults are close to failure (e.g. late in their earthquake cycle), and laboratory experiments have supported this hypothesis. We attempted to test this idea by analysing data on three adjacent transform faults of the East Pacific Rise which have a relatively well defined, quasiperiodic seismic cycle with a median repeat time of 5 years. Moreover, the Gofar, Discovery and Quebrada transform faults share several seismicity properties with continental geothermal areas, including high geothermal gradients, high seismicity rates, and frequent earthquake swarms, that suggest they may be prone to dynamic triggering. We analyze an earthquake catalog of over 100,000 events recorded in 2008 by a network of 38 Ocean Bottom Seismometers. We extract Mw>6.3 mainshocks from the Global CMT catalog, and perform the β test for an array of time intervals covering from 5 hours before to 10 hours after the low-frequency Rayleigh wave arrival. To verify the presence of common seismicity patterns, β plots are also stacked for multiple earthquakes. We observe triggering after the May 12th Wenchuan earthquake. On the Quebrada transform a burst of seismicity starts during the wavetrain; in Gofar there is no response during the wave, but an increase in seismicity (β=5.08) starts about 2 h later; no triggering is visible on the Discovery fault. A Mw=6.0 earthquake ruptured the Gofar transform on September 18th, and triggered seismicity on Discovery: ~60 earthquakes (β=15.3), starting 1h after the wave arrival. We have no data from Quebrada for this period. Other instances of triggering are dubious. Stacked β plots suggest delayed triggering (Δt>1h) in Gofar and Discovery, but the statistical significance of these results is unclear. From a comparison of different fault segments, triggering does not appear to be more common at late stages in the seismic cycle. Instead, the events triggered by the largest dynamic stresses concentrate in the regions between rupture zones. This suggests that changes in rock composition or fluid content may make these areas act as barriers to rupture propagation as well as facilitating dynamic triggering. Using the Rate-and-State seismicity model, we estimate that the effective normal stress where triggering occurs: is extremely low (σ<0.1MPa in Quebrada and σ<0.5MPa on Discovery), implying a nearly lithostatic pore pressure.

Source Parameters and Rupture Directivities of Earthquakes Within the Mendocino Triple Junction

NASA Astrophysics Data System (ADS)

Allen, A. A.; Chen, X.

2017-12-01

The Mendocino Triple Junction (MTJ), a region in the Cascadia subduction zone, produces a sizable amount of earthquakes each year. Direct observations of the rupture properties are difficult to achieve due to the small magnitudes of most of these earthquakes and lack of offshore observations. The Cascadia Initiative (CI) project provides opportunities to look at the earthquakes in detail. Here we look at the transform plate boundary fault located in the MTJ, and measure source parameters of Mw≥4 earthquakes from both time-domain deconvolution and spectral analysis using empirical Green's function (EGF) method. The second-moment method is used to infer rupture length, width, and rupture velocity from apparent source duration measured at different stations. Brune's source model is used to infer corner frequency and spectral complexity for stacked spectral ratio. EGFs are selected based on their location relative to the mainshock, as well as the magnitude difference compared to the mainshock. For the transform fault, we first look at the largest earthquake recorded during the Year 4 CI array, a Mw5.72 event that occurred in January of 2015, and select two EGFs, a Mw1.75 and a Mw1.73 located within 5 km of the mainshock. This earthquake is characterized with at least two sub-events, with total duration of about 0.3 second and rupture length of about 2.78 km. The earthquake is rupturing towards west along the transform fault, and both source durations and corner frequencies show strong azimuthal variations, with anti-correlation between duration and corner frequency. The stacked spectral ratio from multiple stations with the Mw1.73 EGF event shows deviation from pure Brune's source model following the definition from Uchide and Imanishi [2016], likely due to near-field recordings with rupture complexity. We will further analyze this earthquake using more EGF events to test the reliability and stability of the results, and further analyze three other Mw≥4 earthquakes within the array.

Tectono-stratigraphic evolution of normal fault zones: Thal Fault Zone, Suez Rift, Egypt

NASA Astrophysics Data System (ADS)

Leppard, Christopher William

The evolution of linkage of normal fault populations to form continuous, basin bounding normal fault zones is recognised as an important control on the stratigraphic evolution of rift-basins. This project aims to investigate the temporal and spatial evolution of normal fault populations and associated syn-rift deposits from the initiation of early-formed, isolated normal faults (rift-initiation) to the development of a through-going fault zone (rift-climax) by documenting the tectono-stratigraphic evolution of the Sarbut EI Gamal segment of the exceptionally well-exposed Thai fault zone, Suez Rift, Egypt. A number of dated stratal surfaces mapped around the syn-rift depocentre of the Sarbut El Gamal segment allow constraints to be placed on the timing and style of deformation, and the spatial variability of facies along this segment of the fault zone. Data collected indicates that during the first 3.5 My of rifting the structural style was characterised by numerous, closely spaced, short (< 3 km), low displacement (< 200 m) synthetic and antithetic normal faults within 1 - 2 km of the present-day fault segment trace, accommodating surface deformation associated with the development of a fault propagation monocline above the buried, pre-cursor strands of the Sarbut El Gamal fault segment. The progressive localisation of displacement onto the fault segment during rift-climax resulted in the development of a major, surface-breaking fault 3.5 - 5 My after the onset of rifting and is recorded by the death of early-formed synthetic and antithetic faults up-section, and thickening of syn-rift strata towards the fault segment. The influence of intrabasinal highs at the tips of the Sarbut EI Gamal fault segment on the pre-rift sub-crop level, combined with observations from the early-formed structures and coeval deposits suggest that the overall length of the fault segment was fixed from an early stage. The fault segment is interpreted to have grown through rapid lateral propagation and early linkage of the precursor fault strands at depth before the fault segment broke surface, followed by the accumulation of displacement on the linked fault segment with minimal lateral propagation. This style of fault growth contrasts conventional fault growth models by which growth occurs through incremental increases in both displacement and length through time. The evolution of normal fault populations and fault zones exerts a first- order control on basin physiography and sediment supply, and therefore, the architecture and distribution of coeval syn-rift stratigraphy. The early syn-rift continental, Abu Zenima Formation, to shallow marine, Nukhul Formation show a pronounced westward increase in thickness controlled by the series of synthetic and antithetic faults up to 3 km west of present day Thai fault. The orientation of these faults controlled the location of fluvial conglomerates, sandstones and mudstones that shifted to the topographic lows created. The progressive localisation of displacement onto the Sarbut El Gamal fault segment during rift-climax resulted in an overall change in basin geometry. Accelerated subsidence rates led to sedimentation rates being outpaced by subsidence resulting in the development of a marine, sediment-starved, underfilled hangingwall depocentre characterised by slope-to-basinal depositional environments, with a laterally continuous slope apron in the immediate hangingwall, and point-sourced submarine fans. Controls on the spatial distribution, three dimensional architecture, and facies stacking patterns of coeval syn-rift deposits are identified as: I) structural style of the evolution and linkage of normal fault populations, ii) basin physiography, iii) evolution of drainage catchments, iv) bedrock lithology, and v) variations in sea/lake level.

Crustal Deformation along San Andreas Fault System revealed by GPS and Sentinel-1 InSAR

NASA Astrophysics Data System (ADS)

Xu, X.; Sandwell, D. T.

2017-12-01

We present a crustal deformation velocity map along the San Andreas Fault System by combining measurements from Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) velocity models (CGM V1). We assembled 5 tracks of descending Sentinel-1 InSAR data spanning 2014.11-2017.02, and produced 545 interferograms, each of which covers roughly 250km x 420km area ( 60 bursts). These interferograms are unwrapped using SNAPHU [Chen & Zebker, 2002], with the 2Npi unwrapping ambiguity corrected with a sparse recovery method. We used coherence-based small baseline subset (SBAS) method [Tong & Schmidt, 2016] together with atmospheric correction by common-point stacking [Tymofyeyeva and Fialko, 2015] to construct deformation time series [Xu et. al., 2017]. Then we project the horizontal GPS model and vertical GPS data into satellite line-of-sight directions separately. We first remove the horizontal GPS model from InSAR measurements and perform elevation-dependent atmospheric phase correction. Then we compute the discrepancy between the remaining InSAR measurements and vertical GPS data. We interpolate this discrepancy and remove it from the residual InSAR measurements. Finally, we restore the horizontal GPS model. Preliminary results show that fault creep over the San Jacinto fault, the Elsinore fault, and the San Andreas creeping section is clearly resolved. During the period of drought, the Central Valley of California was subsiding at a high rate (up to 40 cm/yr), while the city of San Jose is uplifting due to recharge, with a quaternary fault acting as a ground water barrier. These findings will be reported during the meeting.

The structure of crystallographic damage in GaN formed during rare earth ion implantation with and without an ultrathin AlN capping layer

NASA Astrophysics Data System (ADS)

Gloux, F.; Ruterana, P.; Wojtowicz, T.; Lorenz, K.; Alves, E.

2006-10-01

The crystallographic nature of the damage created in GaN implanted by rare earth ions at 300 keV and room temperature has been investigated by transmission electron microscopy versus the fluence, from 7×10 13 to 2×10 16 at/cm 2, using Er, Eu or Tm ions. The density of point defect clusters was seen to increase with the fluence. From about 3×10 15 at/cm 2, a highly disordered 'nanocrystalline layer' (NL) appears on the GaN surface. Its structure exhibits a mixture of voids and misoriented nanocrystallites. Basal stacking faults (BSFs) of I 1, E and I 2 types have been noticed from the lowest fluence, they are I 1 in the majority. Their density increases and saturates when the NL is observed. Many prismatic stacking faults (PSFs) with Drum atomic configuration have been identified. The I 1 BSFs are shown to propagate easily through GaN by folding from basal to prismatic planes thanks to the PSFs. When implanting through a 10 nm AlN cap, the NL threshold goes up to about 3×10 16 at/cm 2. The AlN cap plays a protective role against the dissociation of the GaN up to the highest fluences. The flat surface after implantation and the absence of SFs in the AlN cap indicate its high resistance to the damage formation.

Size effect, critical resolved shear stress, stacking fault energy, and solid solution strengthening in the CrMnFeCoNi high-entropy alloy.

PubMed

Okamoto, Norihiko L; Fujimoto, Shu; Kambara, Yuki; Kawamura, Marino; Chen, Zhenghao M T; Matsunoshita, Hirotaka; Tanaka, Katsushi; Inui, Haruyuki; George, Easo P

2016-10-24

High-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equatomic CrMnFeCoNi with the face-centered cubic (FCC) structure is noteworthy because its ductility and strength increase with decreasing temperature while maintaining outstanding fracture toughness at cryogenic temperatures. Here we report for the first time by single-crystal micropillar compression that its bulk room temperature critical resolved shear stress (CRSS) is ~33-43 MPa, ~10 times higher than that of pure nickel. CRSS depends on pillar size with an inverse power-law scaling exponent of -0.63 independent of orientation. Planar ½ < 110 > {111} dislocations dissociate into Shockley partials whose separations range from ~3.5-4.5 nm near the screw orientation to ~5-8 nm near the edge, yielding a stacking fault energy of 30 ± 5 mJ/m 2 . Dislocations are smoothly curved without any preferred line orientation indicating no significant anisotropy in mobilities of edge and screw segments. The shear-modulus-normalized CRSS of the HEA is not exceptionally high compared to those of certain concentrated binary FCC solid solutions. Its rough magnitude calculated using the Fleischer/Labusch models corresponds to that of a hypothetical binary with the elastic constants of our HEA, solute concentrations of 20-50 at.%, and atomic size misfit of ~4%.

Size effect, critical resolved shear stress, stacking fault energy, and solid solution strengthening in the CrMnFeCoNi high-entropy alloy

PubMed Central

Okamoto, Norihiko L.; Fujimoto, Shu; Kambara, Yuki; Kawamura, Marino; Chen, Zhenghao M. T.; Matsunoshita, Hirotaka; Tanaka, Katsushi; Inui, Haruyuki; George, Easo P.

2016-01-01

High-entropy alloys (HEAs) comprise a novel class of scientifically and technologically interesting materials. Among these, equatomic CrMnFeCoNi with the face-centered cubic (FCC) structure is noteworthy because its ductility and strength increase with decreasing temperature while maintaining outstanding fracture toughness at cryogenic temperatures. Here we report for the first time by single-crystal micropillar compression that its bulk room temperature critical resolved shear stress (CRSS) is ~33–43 MPa, ~10 times higher than that of pure nickel. CRSS depends on pillar size with an inverse power-law scaling exponent of –0.63 independent of orientation. Planar ½ < 110 > {111} dislocations dissociate into Shockley partials whose separations range from ~3.5–4.5 nm near the screw orientation to ~5–8 nm near the edge, yielding a stacking fault energy of 30 ± 5 mJ/m2. Dislocations are smoothly curved without any preferred line orientation indicating no significant anisotropy in mobilities of edge and screw segments. The shear-modulus-normalized CRSS of the HEA is not exceptionally high compared to those of certain concentrated binary FCC solid solutions. Its rough magnitude calculated using the Fleischer/Labusch models corresponds to that of a hypothetical binary with the elastic constants of our HEA, solute concentrations of 20–50 at.%, and atomic size misfit of ~4%. PMID:27775026

Compression-induced stacking fault tetrahedra around He bubbles in Al

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Jian-Li, E-mail: shao-jianli@iapcm.ac.cn; Wang, Pei; He, An-Min

Classic molecular dynamics methods are used to simulate the uniform compression process of the fcc Al containing He bubbles. The formation of stacking fault tetrahedra (SFTs) during the collapse of He bubbles is found, and their dependence on the initial He bubble size (0.6–6 nm in diameter) is presented. Our simulations indicate only elastic deformation in the samples for the He bubble size not more than 2 nm. Instead, increasing the He bubble size, we detect several small SFTs forming on the surface of the He bubble (3 nm), as well as the two intercrossed SFTs around the He bubbles (4–6 nm). All thesemore » SFTs are observed to be stable under further compression, though there may appear some SF networks outside the SFTs (5–6 nm). Furthermore, the dynamic analysis on the SFTs shows that the yield pressure keeps a near-linear increase with the initial He bubble pressure, and the potential energy of Al atoms inside the SFTs is lower than outside because of their gliding inwards. In addition, the pressure increments of 2–6 nm He bubbles with strain are less than that of Al, which just provides the opportunity for the He bubble collapse and the SFTs formation. Note that the current work only focuses on the case that the number ratio between He atoms and Al vacancies is 1:1.« less

The temporal distribution of seismic radiation during deep earthquake rupture

USGS Publications Warehouse

Houston, H.; Vidale, J.E.

1994-01-01

The time history of energy release during earthquakes illuminates the process of failure, which remains enigmatic for events deeper than about 100 kilometers. Stacks of teleseismic records from regional arrays for 122 intermediate (depths of 100 to 350 kilometers) and deep (depths of 350 to 700 kilometers) earthquakes show that the temporal pattern of short-period seismic radiation has a systematic variation with depth. On average, for intermediate depth events more radiation is released toward the beginning of the rupture than near the end, whereas for deep events radiation is released symmetrically over the duration of the event, with an abrupt beginning and end of rupture. These findings suggest a variation in the style of rupture related to decreasing fault heterogeneity with depth.The time history of energy release during earthquakes illuminates the process of failure, which remains enigmatic for events deeper than about 100 kilometers. Stacks of teleseismic records from regional arrays for 122 intermediate (depths of 100 to 350 kilometers) and deep (depths of 350 to 700 kilometers) earthquakes show that the temporal pattern of short-period seismic radiation has a systematic variation with depth. On average, for intermediate depth events more radiation is released toward the beginning of the rupture than near the end, whereas for deep events radiation is released symmetrically over the duration of the event, with an abrupt beginning and end of rupture. These findings suggest a variation in the style of rupture related to decreasing fault heterogeneity with depth.

Detection of small earthquakes with dense array data: example from the San Jacinto fault zone, southern California

NASA Astrophysics Data System (ADS)

Meng, Haoran; Ben-Zion, Yehuda

2018-01-01

We present a technique to detect small earthquakes not included in standard catalogues using data from a dense seismic array. The technique is illustrated with continuous waveforms recorded in a test day by 1108 vertical geophones in a tight array on the San Jacinto fault zone. Waveforms are first stacked without time-shift in nine non-overlapping subarrays to increase the signal-to-noise ratio. The nine envelope functions of the stacked records are then multiplied with each other to suppress signals associated with sources affecting only some of the nine subarrays. Running a short-term moving average/long-term moving average (STA/LTA) detection algorithm on the product leads to 723 triggers in the test day. Using a local P-wave velocity model derived for the surface layer from Betsy gunshot data, 5 s long waveforms of all sensors around each STA/LTA trigger are beamformed for various incident directions. Of the 723 triggers, 220 are found to have localized energy sources and 103 of these are confirmed as earthquakes by verifying their observation at 4 or more stations of the regional seismic network. This demonstrates the general validity of the method and allows processing further the validated events using standard techniques. The number of validated events in the test day is >5 times larger than that in the standard catalogue. Using these events as templates can lead to additional detections of many more earthquakes.

TEM studies of plasma nitrided austenitic stainless steel.

PubMed

Stróz, D; Psoda, M

2010-03-01

Cross-sectional transmission electron microscopy and X-ray phase analysis were used to study the structure of a layer formed during nitriding the AISI 316L stainless steel at temperature 440 degrees C. It was found that the applied treatment led to the formation of 6-microm-thick layer of the S-phase. There is no evidence of CrN precipitation. The X-ray diffraction experiments proved that the occurred austenite lattice expansion - due to nitrogen atoms - depended on the crystallographic direction. The cross-sectional transmission electron microscopy studies showed that the layer consisted of a single cubic phase that contained a lot of defects such as dislocations, stacking faults, slip bands and twins. The high-resolution electron microscopy observations were applied to study the defect formation due to the nitriding process. It was shown that the presence of great number of stacking faults leads to formation of nanotwins. Weak, forbidden {100} reflections were still another characteristic feature of the S-phase. These were not detected in the X-ray spectra of the phase. Basing on the high-resolution electron microscopy studies it can be suggested that the short-range ordering of the nitrogen atoms in the octahedral sites inside the f.c.c. matrix lattice takes place and gives rise to appearance of these spots. It is suggested that the cubic lattice undergoes not only expansion but also slight rombohedral distortion that explains differences in the lattice expansion for different crystallographic directions.

High temperature deformation mechanisms of L12-containing Co-based superalloys

NASA Astrophysics Data System (ADS)

Titus, Michael Shaw

Ni-based superalloys have been used as the structural material of choice for high temperature applications in gas turbine engines since the 1940s, but their operating temperature is becoming limited by their melting temperature (Tm =1300degrees C). Despite decades of research, no viable alternatives to Ni-based superalloys have been discovered and developed. However, in 2006, a ternary gamma' phase was discovered in the Co-Al-W system that enabled a new class of Co-based superalloys to be developed. These new Co-based superalloys possess a gamma-gamma' microstructure that is nearly identical to Ni-based superalloys, which enables these superalloys to achieve extraordinary high temperature mechanical properties. Furthermore, Co-based alloys possess the added benefit of exhibiting a melting temperature of at least 100degrees C higher than commercial Ni-based superalloys. Superalloys used as the structural materials in high pressure turbine blades must withstand large thermomechanical stresses imparted from the rotating disk and hot, corrosive gases present. These stresses induce time-dependent plastic deformation, which is commonly known as creep, and new superalloys must possess adequate creep resistance over a broad range of temperature in order to be used as the structural materials for high pressure turbine blades. For these reasons, this research focuses on quantifying high temperature creep properties of new gamma'-containing Co-based superalloys and identifying the high temperature creep deformation mechanisms. The high temperature creep properties of new Co- and CoNi-based alloys were found to be comparable to Ni-based superalloys with respect to minimum creep rates and creep-rupture lives at 900degrees C up to the solvus temperature of the gamma' phase. Co-based alloys exhibited a propensity for extended superlattice stacking fault formation in the gamma' precipitates resulting from dislocation shearing events. When Ni was added to the Co-based compositions, this mode of shearing altered such that extended antiphase boundaries formed in the gamma' precipitates. These high temperature shearing mechanisms differ from Ni-based superalloys, where shearing occurs via APB-coupled dislocations. High resolution electron microscopy studies revealed chemical fluctuations of solute near stacking faults and antiphase boundaries in the gamma' phases. These chemical fluctuations were found to significantly reduce the stacking fault energy, which was calculated via first-principles. The implications for these chemical fluctuations on creep strength were determined, and new models for precipitate shearing will be presented. Furthermore, the implications for the design of new Co- and CoNi-based compositions will be discussed.

Shockwave-Induced Plasticity Via Large-Scale Nonequilibrium Molecular Dynamics

NASA Astrophysics Data System (ADS)

Holian, Brad Lee

1997-07-01

In nonequilibrium molecular-dynamics (MD) simulations of shock waves in single crystals, carried out in 1979 at Los Alamos,(B.L. Holian and G.K. Straub, Phys. Rev. Lett. 43), 1598 (1979). we discovered that, above a threshold strength, strongly shocked crystals deform in a very simple way. Rather than experiencing massive deformation, a simple slippage occurs at the shock front, relieving the peak shear stress, and leaving behind a stacking fault. We realized, of course, that real materials could yield at much lower thresholds, and speculated then that pre-existing defects could nucleate plastic flow at lower shock strengths than those characteristic of pure single crystals. (Historical note: at about the same time as our earliest dynamical shockwave simulations, Mogilevsky, working independently in the Soviet Union, carried out relaxation MD calculations under uniaxial strain, and observed spontaneous production of dislocations.(M.A. Mogilevsky, in Shock Waves and High Strain Rate Phenomena in Metals) (Plenum, New York, 1981), p.531.) Further Los Alamos calculations, carried out nearly a decade later in five-times larger systems (up to 10,000 atoms), confirmed this observation and quantified the threshold strength, namely the yield strength of the perfect crystal.(B.L. Holian, Phys. Rev. A 37), 2562 (1988); for a review, see B.L. Holian, Shock Waves 5, 149 (1995). Subsequently, Zaretskii and co-workers,(E.B. Zaretskii, G.I. Kanel, P.A. Mogilevskii, and V.E. Fortov, Sov. Phys. Dokl. 36), 76 (1991). using x-ray diffraction of shocked single crystals, confirmed our MD observations of stacking faults produced by shockwave passage. With the advent of massively parallel computers, we have recently studied systems with over six-times larger cross-sectional area and four-times longer distance of run to the steady state (approximately 270,000 atoms). We have seen that the increased cross-section allows the system to slip along both available forward slip systems, in different places along the now non-planar shock front, though only one stacking fault survives. This leads us to attempt simulations with even larger cross-sectional areas, and with pre-existing defects embedded in the sample, such as those we will report on here (36-times larger cross-sectional area: 10 million atoms). We report on shock waves in fcc copper, where the atoms interact via an EAM (embedded-atom-method) many-body potential, as well as pair-potential materials.(B.L. Holian, P.S. Lomdahl, S.J. Zhou, D.M. Beazley, and A.F. Voter, (1997, unpublished).)

Fault zone architecture of a major oblique-slip fault in the Rawil depression, Western Helvetic nappes, Switzerland

NASA Astrophysics Data System (ADS)

Gasser, D.; Mancktelow, N. S.

2009-04-01

The Helvetic nappes in the Swiss Alps form a classic fold-and-thrust belt related to overall NNW-directed transport. In western Switzerland, the plunge of nappe fold axes and the regional distribution of units define a broad depression, the Rawil depression, between the culminations of Aiguilles Rouge massif to the SW and Aar massif to the NE. A compilation of data from the literature establishes that, in addition to thrusts related to nappe stacking, the Rawil depression is cross-cut by four sets of brittle faults: (1) SW-NE striking normal faults that strike parallel to the regional fold axis trend, (2) NW-SE striking normal faults and joints that strike perpendicular to the regional fold axis trend, and (3) WNW-ESE striking normal plus dextral oblique-slip faults as well as (4) WSW-ENE striking normal plus dextral oblique-slip faults that both strike oblique to the regional fold axis trend. We studied in detail a beautifully exposed fault from set 3, the Rezli fault zone (RFZ) in the central Wildhorn nappe. The RFZ is a shallow to moderately-dipping (ca. 30-60˚) fault zone with an oblique-slip displacement vector, combining both dextral and normal components. It must have formed in approximately this orientation, because the local orientation of fold axes corresponds to the regional one, as does the generally vertical orientation of extensional joints and veins associated with the regional fault set 2. The fault zone crosscuts four different lithologies: limestone, intercalated marl and limestone, marl and sandstone, and it has a maximum horizontal dextral offset component of ~300 m and a maximum vertical normal offset component of ~200 m. Its internal architecture strongly depends on the lithology in which it developed. In the limestone, it consists of veins, stylolites, cataclasites and cemented gouge, in the intercalated marls and limestones of anastomosing shear zones, brittle fractures, veins and folds, in the marls of anastomosing shear zones, pressure solution seams and veins and in the sandstones of coarse breccia and veins. Later, straight, sharp fault planes cross-cut all these features. In all lithologies, common veins and calcite-cemented fault rocks indicate the strong involvement of fluids during faulting. Today, the southern Rawil depression and the Rhone Valley belong to one of the seismically most active regions in Switzerland. Seismogenic faults interpreted from earthquake focal mechanisms strike ENE-WSW to WNW-ESE, with dominant dextral strike-slip and minor normal components and epicentres at depths of < 15 km. All three Neogene fault sets (2-4) could have been active under the current stress field inferred from the current seismicity. This implies that the same mechanisms that formed these fault zones in the past may still persist at depth. The Rezli fault zone allows the detailed study of a fossil fault zone that can act as a model for processes still occurring at deeper levels in this seismically active region.

Updated mapping and seismic reflection data processing along the Queen Charlotte fault system, southeast Alaska

NASA Astrophysics Data System (ADS)

Walton, M. A. L.; Gulick, S. P. S.; Haeussler, P. J.; Rohr, K.; Roland, E. C.; Trehu, A. M.

2014-12-01

The Queen Charlotte Fault (QCF) is an obliquely convergent strike-slip system that accommodates offset between the Pacific and North America plates in southeast Alaska and western Canada. Two recent earthquakes, including a M7.8 thrust event near Haida Gwaii on 28 October 2012, have sparked renewed interest in the margin and led to further study of how convergent stress is accommodated along the fault. Recent studies have looked in detail at offshore structure, concluding that a change in strike of the QCF at ~53.2 degrees north has led to significant differences in stress and the style of strain accommodation along-strike. We provide updated fault mapping and seismic images to supplement and support these results. One of the highest-quality seismic reflection surveys along the Queen Charlotte system to date, EW9412, was shot aboard the R/V Maurice Ewing in 1994. The survey was last processed to post-stack time migration for a 1999 publication. Due to heightened interest in high-quality imaging along the fault, we have completed updated processing of the EW9412 seismic reflection data and provide prestack migrations with water-bottom multiple reduction. Our new imaging better resolves fault and basement surfaces at depth, as well as the highly deformed sediments within the Queen Charlotte Terrace. In addition to re-processing the EW9412 seismic reflection data, we have compiled and re-analyzed a series of publicly available USGS seismic reflection data that obliquely cross the QCF. Using these data, we are able to provide updated maps of the Queen Charlotte fault system, adding considerable detail along the northernmost QCF where it links up with the Chatham Strait and Transition fault systems. Our results support conclusions that the changing geometry of the QCF leads to fundamentally different convergent stress accommodation north and south of ~53.2 degrees; namely, reactivated splay faults to the north vs. thickening of sediments and the upper crust to the south. We also highlight areas where additional data are needed and would be ideal targets for future study.

Structural imaging of the East Beni Sueif Basin, north eastern Desert, Egypt

NASA Astrophysics Data System (ADS)

Salem, E.; Sehim, A.

2017-12-01

The East Beni Sueif Basin is the only tested hydrocarbon-bearing basin on the eastern side of the Nile in Egypt. The basin is located around 150 km to the south of Cairo. This work introduces the first attempt of seismic interpretation and structural patterns of this basin, for which subsurface published works are lacking. Structural imaging of the area is achieved through interpretation of pre-stack time migration (PSTM) seismic cube and data sets of seven wells. The penetrated sedimentary section is represented by Albian-Middle Eocene sediments. The East Beni Sueif Basin is a type of the whole graben-system and is bounded by two NW-SE bounding faults. These faults had continued activity in an extensional regime associated with fault-propagating folds. The basin is traversed by a N75°E-trending fault system at basement level. This fault system separates the basin into two structural provinces. The Northwestern Province is deeper and shows more subsidence with a predominance of NW-trending longitudinal faults and N60·W oblique faults to the basin trend. The Southeastern Province is shallow and crossed by N14·W-trending faults which are slightly oblique to the basin axis. Albian time had witnessed the main extensional tectonic phase and resulted in major subsidence along basin-bounding faults associated with growth thickening of basal deposits. During Senonian time, the basin experienced a mild phase of transtensional tectonics, which formed negative-flower structures entrapping different folds along the N75°E and N60·W faults. The timing and style of these structures are similar to the Syrian-Arc structures in several Western Desert oil fields. The basin emerged during the Paleocene with scoured and eroded top Cretaceous sediments. Subsidence was resumed during the Early Eocene and resulted in 1500 m-thick carbonate sediments. Lastly, a mild extensional activity possibly occurred during the Oligocene-Miocene time. Despite the possible restricted potentiality of the source rock, the main hydrocarbon accumulation risk is attributed to retention in traps of long-span tectonic history. Reaching of main faults to surface through brittle carbonate cap rocks and limited thickness of the shale in the reservoir section risk hydrocarbon sealing. Buried structures of passive setting during the Tertiary show a minor trapping risk.

An integrated multi-sensor fusion-based deep feature learning approach for rotating machinery diagnosis

NASA Astrophysics Data System (ADS)

Liu, Jie; Hu, Youmin; Wang, Yan; Wu, Bo; Fan, Jikai; Hu, Zhongxu

2018-05-01

The diagnosis of complicated fault severity problems in rotating machinery systems is an important issue that affects the productivity and quality of manufacturing processes and industrial applications. However, it usually suffers from several deficiencies. (1) A considerable degree of prior knowledge and expertise is required to not only extract and select specific features from raw sensor signals, and but also choose a suitable fusion for sensor information. (2) Traditional artificial neural networks with shallow architectures are usually adopted and they have a limited ability to learn the complex and variable operating conditions. In multi-sensor-based diagnosis applications in particular, massive high-dimensional and high-volume raw sensor signals need to be processed. In this paper, an integrated multi-sensor fusion-based deep feature learning (IMSFDFL) approach is developed to identify the fault severity in rotating machinery processes. First, traditional statistics and energy spectrum features are extracted from multiple sensors with multiple channels and combined. Then, a fused feature vector is constructed from all of the acquisition channels. Further, deep feature learning with stacked auto-encoders is used to obtain the deep features. Finally, the traditional softmax model is applied to identify the fault severity. The effectiveness of the proposed IMSFDFL approach is primarily verified by a one-stage gearbox experimental platform that uses several accelerometers under different operating conditions. This approach can identify fault severity more effectively than the traditional approaches.

Lithostratigraphy and depositional environments in the Waterberg-Erongo area, central Namibia, and correlation with the main Karoo Basin, South Africa

NASA Astrophysics Data System (ADS)

Holzförster, Frank; Stollhofen, Harald; Stanistreet, Ian G.

1999-07-01

The dissected landscape of the Waterberg-Erongo area, central Namibia, exposes Karoo-equivalent strata deposited in basins that occur throughout sub-Saharan Africa. Although many are of economic interest, including coal-bearing strata, their depositional history is not well understood. This study of the Waterberg-Erongo area provides detailed lithostratigraphical data, which suggest sedimentation from the late Early Triassic to the Early Jurassic in a fault-bounded depository. Subsidence and sediment supply were controlled predominantly by the northeast-southwest trending Waterberg-Omaruru Fault Zone, which defines the northwestern margin of the depository. Facies development and thickness distribution of the Karoo strata in the Waterberg-Erongo area, perhaps the most continuous of any of the Karoo basins, indicate a northeastwardly-migrating depocentre alongside that fault, in response to major extensional movements in the early pre-South Atlantic rift zone. Periodic fault movements repeatedly caused basinward progradation of the alluvial facies, which are reflected by stacked fining-upward cycles in the lithological record. On a broader scale, the results of this study suggest that the northward propagation of the rift zone between Southern Africa and South America, was partially accommodated by transfer lineaments. Local depocentres developed along these lineaments, such as those in the Waterberg-Erongo area, with localised enhanced subsidence greater than that revealed in other Namibian onshore exposures, dominated by the rifting itself.

Preliminary paleoseismic observations along the western Denali fault, Alaska

NASA Astrophysics Data System (ADS)

Koehler, R. D.; Schwartz, D. P.; Rood, D. H.; Reger, R.; Wolken, G. J.

2013-12-01

The Denali fault in south-central Alaska, from Mt. McKinley to the Denali-Totschunda fault branch point, accommodates ~9-12 mm/yr of the right-lateral component of oblique convergence between the Pacific/Yakutat and North American plates. The eastern 226 km of this fault reach was part of the source of the 2002 M7.9 Denali fault earthquake. West of the 2002 rupture there is evidence of two large earthquakes on the Denali fault during the past ~550-700 years but the paleoearthquake chronology prior to this time is largely unknown. To better constrain fault rupture parameters for the western Denali fault and contribute to improved seismic hazard assessment, we performed helicopter and ground reconnaissance along the southern flank of the Alaska Range between the Nenana Glacier and Pyramid Peak, a distance of ~35 km, and conducted a site-specific paleoseismic study. We present a Quaternary geologic strip map along the western Denali fault and our preliminary paleoseismic results, which include a differential-GPS survey of a displaced debris flow fan, cosmogenic 10Be surface exposure ages for boulders on this fan, and an interpretation of a trench across the main trace of the fault at the same site. Between the Nenana Glacier and Pyramid Peak, the Denali fault is characterized by prominent tectonic geomorphic features that include linear side-hill troughs, mole tracks, anastamosing composite scarps, and open left-stepping fissures. Measurements of offset rills and gullies indicate that slip during the most recent earthquake was between ~3 and 5 meters, similar to the average displacement in the 2002 earthquake. At our trench site, ~ 25 km east of the Parks Highway, a steep debris fan is displaced along a series of well-defined left-stepping linear fault traces. Multi-event displacements of debris-flow and snow-avalanche channels incised into the fan range from 8 to 43 m, the latter of which serves as a minimum cumulative fan offset estimate. The trench, excavated into the fan across the main fault scarp and adjacent graben, exposed sheared debris fan parent material at its north and south ends, separated by a central zone of stacked scarp-derived colluvium and weakly developed peaty soils. Stratigraphic relations and upward fault terminations clearly record the occurrence of the past three surface-faulting earthquakes and suggest four or more such events. Results of pending 14C analyses are expected to provide new information on earthquake timing and recurrence. A Holocene slip rate for this section of the fault will be developed using back-slip models and an estimate of the age of the fan constrained by our detailed surveys of channel offsets and pending cosmogenic 10Be exposure ages for surface boulders, respectively.

3D P and S Wave Velocity Structure and Tremor Locations in the Parkfield Region

NASA Astrophysics Data System (ADS)

Zeng, X.; Thurber, C. H.; Shelly, D. R.; Bennington, N. L.; Cochran, E. S.; Harrington, R. M.

2014-12-01

We have assembled a new dataset to refine the 3D seismic velocity model in the Parkfield region. The S arrivals from 184 earthquakes recorded by the Parkfield Experiment to Record MIcroseismicity and Tremor array (PERMIT) during 2010-2011 were picked by a new S wave picker, which is based on machine learning. 74 blasts have been assigned to four quarries, whose locations were identified with Google Earth. About 1000 P and S wave arrivals from these blasts at permanent seismic network were also incorporated. Low frequency earthquakes (LFEs) occurring within non-volcanic tremor (NVT) are valuable for improving the precision of NVT location and the seismic velocity model at greater depths. Based on previous work (Shelley and Hardebeck, 2010), waveforms of hundreds of LFEs in same family were stacked to improve signal qualify. In a previous study (McClement et al., 2013), stacked traces of more than 30 LFE families at the Parkfileld Array Seismic Observatory (PASO) have been picked. We expanded our work to include LFEs recorded by the PERMIT array. The time-frequency Phase Weight Stacking (tf-PWS) method was introduced to improve the stack quality, as direct stacking does not produce clear S-wave arrivals on the PERMIT stations. This technique uses the coherence of the instantaneous phase among the stacked signals to enhance the signal-to-noise ratio (SNR) of the stack. We found that it is extremely effective for picking LFE arrivals (Thurber et al., 2014). More than 500 P and about 1000 S arrivals from 58 LFE families were picked at the PERMIT and PASO arrays. Since the depths of LFEs are much deeper than earthquakes, we are able to extend model resolution to lower crustal depths. Both P and S wave velocity structure have been obtained with the tomoDD method. The result suggests that there is a low velocity zone (LVZ) in the lower crust and the location of the LVZ is consistent with the high conductivity zone beneath the southern segment of the Rinconada fault that was revealed in the 3D magnetotelluric inversion of Tietze and Ritter(2013).

Monoclinic crystal structure of α - RuCl 3 and the zigzag antiferromagnetic ground state

DOE PAGES

Johnson, R. D.; Williams, S. C.; Haghighirad, A. A.; ...

2015-12-10

We have proposed the layered honeycomb magnet α - RuCl 3 as a candidate to realize a Kitaev spin model with strongly frustrated, bond-dependent, anisotropic interactions between spin-orbit entangled j eff = 1/2 Ru 3 + magnetic moments. We report a detailed study of the three-dimensional crystal structure using x-ray diffraction on untwinned crystals combined with structural relaxation calculations. We consider several models for the stacking of honeycomb layers and find evidence for a parent crystal structure with a monoclinic unit cell corresponding to a stacking of layers with a unidirectional in-plane offset, with occasional in-plane sliding stacking faults, inmore » contrast with the currently assumed trigonal three-layer stacking periodicity. We also report electronic band-structure calculations for the monoclinic structure, which find support for the applicability of the j eff = 1/2 picture once spin-orbit coupling and electron correlations are included. Of the three nearest-neighbor Ru-Ru bonds that comprise the honeycomb lattice, the monoclinic structure makes the bond parallel to the b axis nonequivalent to the other two, and we propose that the resulting differences in the magnitude of the anisotropic exchange along these bonds could provide a natural mechanism to explain the previously reported spin gap in powder inelastic neutron scattering measurements, in contrast to spin models based on the three-fold symmetric trigonal structure, which predict a gapless spectrum within linear spin wave theory. Our susceptibility measurements on both powders and stacked crystals, as well as magnetic neutron powder diffraction, show a single magnetic transition upon cooling below T N ≈ 13 K. Our analysis of our neutron powder diffraction data provides evidence for zigzag magnetic order in the honeycomb layers with an antiferromagnetic stacking between layers. Magnetization measurements on stacked single crystals in pulsed field up to 60 T show a single transition around 8 T for in-plane fields followed by a gradual, asymptotic approach to magnetization saturation, as characteristic of strongly anisotropic exchange interactions.« less

The Eocene-Miocene tectonic evolution of the Rif chain (Morocco): new data from the Jebha area

NASA Astrophysics Data System (ADS)

D'Assisi Tramparulo, Francesco; Ciarcia, Sabatino; El Ouaragli, Bilal; Vitale, Stefano; Najib Zaghloul, Mohamed

2016-04-01

Keywords: structural analysis, tectonics, shear bands, Miocene, Jebha Fault The Jebha area, located in the Central Rif, is a key sector to understand the orogenic evolution of the Rif chain. Here, the left lateral Jebha-Chrafate transfer fault, allowed, in the Miocene time, the westward migration of the internal thrust front. The structural analysis of the area revealed a complex tectonic history. The Eocene orogenic pulse produced the tectonic stacking of the Ghomaride thrust sheets. During the late Aquitanian and Langhian, under a dominant ENE-WSW shortening, imbrication of several Internal Dorsale Calcaire slices occurred. The following orogenic stage, characterized by a main SE tectonic transport, allowed the External Dorsale Calcaire to overthrust the Maghrebian Flysch Basin Units by means of a dominant thin-skinned tectonics. Synchronously with the buttressing following the collision of the allochthonous wedge against the External Rif domain, an out-of-sequence thrusting stage involved the Ghomaride and Dorsale Calcaire Units and a general back-thrusting deformed the entire tectonic pile. A renewal of the NE-SW shortening produced strike-slip faults and SW-verging folds and finally a radial extension affected the whole chain.

The Investigation of Active Tectonism Offshore Cide-Sinop, Southern Black Sea by Seismic Reflection and Bathymetric Data

NASA Astrophysics Data System (ADS)

Alp, Y. I.; Ocakoglu, N.; Kılıc, F.; Ozel, A. O.

2017-12-01

The active tectonism offshore Cide-Sinop at the Southern Black Sea shelf area was first time investigated by multi-beam bathymetric and multi-channel seismic reflection data under the Research Project of The Scientific and Technological Research Council of Turkey (TUBİTAK-ÇAYDAG-114Y057). The multi-channel seismic reflection data of about 700 km length were acquired in 1991 by Turkish Petroleum Company (TP). Multibeam bathymetric data were collected between 2002-2008 by the Turkish Navy, Department of Navigation, Hydrography and Oceanography (TN-DNHO). Conventional data processing steps were applied as follows: in-line geometry definition, shot-receiver static correction, editing, shot muting, gain correction, CDP sorting, velocity analysis, NMO correction, muting, stacking, predictive deconvolution, band-pass filtering, finite-difference time migration, and automatic gain correction. Offshore area is represented by a quite smooth and large shelf plain with an approx. 25 km wide and the water depth of about -100 m. The shelf gently deepens and it is limited by the shelf break with average of -120 m contour. The seafloor morphology is charasterised by an erosional surface. Structurally, E-W trending strike-slip faults with generally compression components and reverse/thrust faults have been regionally mapped for the first time. Most of these faults deform all seismic units and reach the seafloor delimiting the morphological highs and submarine plains. Thus, these faults are intepreted as active faults. These results support the idea that the area is under the active compressional tectonic regime

Core evidence of paleoseismic events in Paleogene deposits of the Shulu Sag in the Bohai Bay Basin, east China, and their petroleum geologic significance

NASA Astrophysics Data System (ADS)

Zheng, Lijing; Jiang, Zaixing; Liu, Hui; Kong, Xiangxin; Li, Haipeng; Jiang, Xiaolong

2015-10-01

The Shulu Sag, located in the southwestern corner of the Jizhong Depression, Bohai Bay Basin of east China, is a NE-SW trending, elongate Cenozoic half-graben basin. The lowermost part of the third member of the Shahejie Formation in this basin is characterized by continental rudstone and calcilutite to calcisiltite facies. Based on core observation and regional geologic analysis, seismites are recognized in these lacustrine deposits, which include soft-sediment deformation structures (sedimentary dikes, hydraulic shattering, diapir structures, convolute lamination, load-flame structures, ball-and-pillow structures, loop bedding, and subsidence structures), synsedimentary faults, and seismoturbidites. In addition, mixed-source rudstones, consisting of the Paleozoic carbonate clasts and in situ calcilutite clasts in the lowermost submember of Shahejie 3, appear in the seismites, suggesting an earthquake origin. A complete representative vertical sequence in the lowermost part of the third member found in well ST1H located in the central part of the Shulu Sag shows, from the base to the top: underlying undeformed layers, synsedimentary faults, liquefied carbonate rocks, allogenetic seismoturbidites, and overlying undeformed layers. Seismites are widely distributed around this well and there are multiple sets of stacked seismites separated by undeformed sediment. The nearby NW-trending Taijiazhuang fault whose fault growth index is from 1.1 to 1.8 and the NNE-trending Xinhe fault with a fault growth index of 1.3-1.9 may be the source of the instability to create the seismites. These deformed sedimentary layers are favorable for the accumulation of oil and gas; for example, sedimentary dikes can cut through many layers and serve as conduits for fluid migration. Sedimentary faults and fractures induced by earthquakes can act as oil and gas migration channels or store petroleum products as well. Seismoturbidites and mixed-source rudstones are excellent reservoirs due to their abundant primary or dissolved pores.

Anisotropy of electrical resistivity in PVT grown WSe2-x crystals

NASA Astrophysics Data System (ADS)

Solanki, G. K.; Patel, Y. A.; Agarwal, M. K.

2018-05-01

Single crystals of p-type WSe2 and WSe1.9 were grown by a physical vapour transport technique. The anisotropy in d.c. electrical resistivity was investigated in these grown crystals. The off-stoichiometric WSe1.9 exhibited a higher anisotropy ratio as compared to WSe2 crystals. The electron microscopic examination revealed the presence of a large number of stacking faults in these crystals. The resistivity enhancement along the c-axis and anisotropic effective mass ratio explained on the basis of structural disorder introduced due to off-stoichiometry.

Structure of nickel-copper alloys subjected to high-pressure torsion to saturation stage

NASA Astrophysics Data System (ADS)

Popov, V. V.; Stolbovsky, A. V.; Popova, E. N.

2017-11-01

Transmission electron microscopy and microhardness measurements were used to study the structure of Ni-Cu alloys subjected to high-pressure torsion (to saturation state) at room-temperature using five revolutions. It was shown that, when passing from copper to nickel, the submicrocrystalline structure becomes substantially refined, and the microhardness increases by more than 1.5 times. This is related to differences in the melting temperature and stacking fault energy. The simultaneous effect of these two factors leads to the nonlinearity of the composition dependences of the crystallite size and microhardness.

Dislocation core structures of tungsten with dilute solute hydrogen

NASA Astrophysics Data System (ADS)

Wang, Yinan; Li, Qiulin; Li, Chengliang; Shu, Guogang; Xu, Ben; Liu, Wei

2017-12-01

In this paper, a combination of quantum mechanical and interatomic potential-based atomistic calculations are used to predict the core structures of screw and edge dislocations in tungsten in the presence of a particular concentration of hydrogen atoms. These configurations of the core structures are the results of two competing energies: the interaction between the partial dislocations and the corresponding generalized stacking fault energy in between the two partial dislocations, which are presented in this work. With this, we can precisely predict the configurations of the hydrogen-doped dislocation core structures.

Effects of Cobalt Concentration on the Relative Resistance to Octahedral and Cube Slip in Nickel-Base Superalloys

NASA Technical Reports Server (NTRS)

Bobeck, Gene E.; Miner, R. V.

1988-01-01

Compression yielding tests were performed at 760 C on crystals of the Ni base superalloys Rene 150 and a modified MAR-M247, both having two different Co concentrations. For both alloy bases, increasing Co concentration was shown to decrease the critical resolved shear stress for octahedral slip, but to have little effect on that for cube slip. The results suggest that decreasing complex stacking fault energy in the gamma-prime with increasing Co could account for the observed effects.

Theoretical prediction and direct observation of the 9R structure in Ag

NASA Astrophysics Data System (ADS)

Ernst, F.; Finnis, M. W.; Hofmann, D.; Muschik, T.; Schönberger, U.; Wolf, U.; Methfessel, M.

1992-07-01

Molecular-dynamics simulations of the Σ3<110>(211) twin boundary in Ag predict a thin (1 nm) boundary phase of the 9R (α-Sm) structure. High-resolution electron microscopy shows the presence of the predicted structure. We also calculate the energy ab initio for several hypothetical structures of Cu and Ag. Low energies of the 9R structure and other polytypes, low experimental stacking-fault energies, and the hcp-fcc energy difference are correlated and explained in terms of an effective nearest-neighbor Ising interaction.

Compositional modulated atomic layer stacking and uniaxial magnetocrystalline anisotropy of CoPt alloy sputtered films with close-packed plane orientation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Saito, Shin, E-mail: ssaito@ecei.tohoku.ac.jp; Nozawa, Naoki; Hinata, Shintaro

An atomic layer stacking structure in hexagonal close packed (hcp) Co{sub 100−x}Pt{sub x} alloy films with c-plane sheet texture was directly observed by a high-angle annular dark-field imaging scanning transmission electron microscopy. The analysis of sequential and/or compositional atomic layer stacking structure and uniaxial magnetocrystalline anisotropy (K{sub u} = K{sub u1} + K{sub u2}) revealed that (1) integrated intensity of the superlattice diffraction takes the maximum at x = 20 at. % and shows broadening feature against x for the film fabricated under the substrate temperature (T{sub sub}) of 400 °C. (2) Compositional separation structure in atomic layers is formed for the films fabricated under T{sub sub} = 400 °C.more » A sequential alternative stacking of atomic layers with different compositions is hardly formed in the film with x = 50 at. %, whereas easily formed in the film with x = 20 at. %. This peculiar atomic layer stacking structure consists of in-plane-disordered Pt-rich and Pt-poor layers, which is completely different from the so-called atomic site ordered structure. (3) A face centered cubic atomic layer stacking as faults appeared in the host hcp atomic layer stacking exists in accompanies with irregularities for the periodicity of the compositional modulation atomic layers. (4) K{sub u1} takes the maximum of 1.4 × 10{sup 7 }erg/cm{sup 3} at around x = 20 at. %, whereas K{sub u2} takes the maximum of 0.7 × 10{sup 7 }erg/cm{sup 3} at around x = 40 at. %, which results in the maximum of 1.8 × 10{sup 7 }erg/cm{sup 3} of K{sub u} at x = 30 at. % and a shoulder in compositional dependence of K{sub u} in the range of x = 30–60 at. %. Not only compositional separation of atomic layers but also sequential alternative stacking of different compositional layers is quite important to improve essential uniaxial magnetocrystalline anisotropy.« less

Modes of orogen-parallel stretching and extensional exhumation in response to microplate indentation and roll-back subduction (Tauern Window, Eastern Alps)

NASA Astrophysics Data System (ADS)

Scharf, A.; Handy, M. R.; Favaro, S.; Schmid, S. M.; Bertrand, A.

2013-09-01

The Tauern Window exposes a Paleogene nappe stack consisting of highly metamorphosed oceanic (Alpine Tethys) and continental (distal European margin) thrust sheets. In the eastern part of this window, this nappe stack (Eastern Tauern Subdome, ETD) is bounded by a Neogene system of shear (the Katschberg Shear Zone System, KSZS) that accommodated orogen-parallel stretching, orogen-normal shortening, and exhumation with respect to the structurally overlying Austroalpine units (Adriatic margin). The KSZS comprises a ≤5-km-thick belt of retrograde mylonite, the central segment of which is a southeast-dipping, low-angle extensional shear zone with a brittle overprint (Katschberg Normal Fault, KNF). At the northern and southern ends of this central segment, the KSZS loses its brittle overprint and swings around both corners of the ETD to become subvertical, dextral, and sinistral strike-slip faults. The latter represent stretching faults whose displacements decrease westward to near zero. The kinematic continuity of top-east to top-southeast ductile shearing along the central, low-angle extensional part of the KSZS with strike-slip shearing along its steep ends, combined with maximum tectonic omission of nappes of the ETD in the footwall of the KNF, indicates that north-south shortening, orogen-parallel stretching, and normal faulting were coeval. Stratigraphic and radiometric ages constrain exhumation of the folded nappe complex in the footwall of the KSZS to have begun at 23-21 Ma, leading to rapid cooling between 21 and 16 Ma. This exhumation involved a combination of tectonic unroofing by extensional shearing, upright folding, and erosional denudation. The contribution of tectonic unroofing is greatest along the central segment of the KSZS and decreases westward to the central part of the Tauern Window. The KSZS formed in response to the indentation of wedge-shaped blocks of semi-rigid Austroalpine basement located in front of the South-Alpine indenter that was part of the Adriatic microplate. Northward motion of this indenter along the sinistral Giudicarie Belt offsets the Periadriatic Fault and triggered rapid exhumation of orogenic crust within the entire Tauern Window. Exhumation involved strike-slip and normal faulting that accommodated about 100 km of orogen-parallel extension and was contemporaneous with about 30 km of orogen-perpendicular, north-south shortening of the ETD. Extension of the Pannonian Basin related to roll-back subduction in the Carpathians began at 20 Ma, but did not affect the Eastern Alps before about 17 Ma. The effect of this extension was to reduce the lateral resistance to eastward crustal flow away from the zone of greatest thickening in the Tauern Window area. Therefore, we propose that roll-back subduction temporarily enhanced rather than triggered exhumation and orogen-parallel motion in the Eastern Alps. Lateral extrusion and orogen-parallel extension in the Eastern Alps have continued from 12 to 10 Ma to the present and are driven by northward push of Adria.

The magnetic ground state and relationship to Kitaev physics in α-RuCl3

NASA Astrophysics Data System (ADS)

Banerjee, Arnab

The 2D Kitaev candidate alpha-RuCl3 consists of stacked honeycomb layers weakly coupled by Van der Waals interactions. Here we report the measurements of bulk properties and neutron diffraction in both powder and single crystal samples. Our results show that the full three dimensional magnetic ground state is highly pliable with at least two dominant phases corresponding to two different out-of-plane magnetic orders. They have different Neel temperatures dependent on the stacking of the 2D layers, such as a broad magnetic transition at TN = 14 K as observed in phase-pure powder samples, or a sharp magnetic transition at a lower TN = 7 K as observed in homogeneous single crystals with no evidence for stacking faults. The magnetic refinements of the neutron scattering data will be discussed, which in all cases shows the in-plane magnetic ground state is the zigzag phase common in Kitaev related materials including the honeycomb lattice Iridates. Inelastic neutron scattering in all cases shows that this material consistently exhibit strong two-dimensional magnetic fluctuations leading to a break-down of the classical spin-wave picture. Work performed at ORNL is supported by U.S. Dept. of Energy, Office of Basic Energy Sciences and Office of User Facilities Division.

Evolution of long-period stacking order (LPSO) in Mg97Zn1Gd2 cast alloys viewed by HAADF-STEM multi-scale electron tomography

NASA Astrophysics Data System (ADS)

Sato, Kazuhisa; Tashiro, Shunya; Matsunaga, Shuhei; Yamaguchi, Yohei; Kiguchi, Takanori; Konno, Toyohiko J.

2018-07-01

We have studied three-dimensional (3D) structures and growth processes of 14H-type long-period stacking order (LPSO) formed in Mg97Zn1Gd2 cast alloys by single tilt-axis electron tomography (ET) using high-angle annular dark-field scanning transmission electron microscopy. Evolution of the solute-enriched stacking faults (SFs) and the 14H LPSO by ageing were visualised in 3D with a high spatial resolution in multi-scale fields of views from a few nanometres to 10 μm. Lateral growth of the solute-enriched SFs and the LPSO in the (0 0 0 1)Mg plane is notable compared to the out-of-plane growth in the [0 0 0 1]Mg direction. The 14H LPSO grows at the cost of decomposition of the (Mg, Zn)3Gd-type precipitates, and accompany a change of in-plane edge angles from 30 to 60°. We have updated the Time-Temperature-Transformation diagram for precipitation in Mg97Zn1Gd2 alloys: starting temperatures of both solute-enriched SFs and LPSO formation shifted to a shorter time side than those in the previous diagram.

Structurally controlled 'teleconnection' of large-scale mass wasting (Eastern Alps)

NASA Astrophysics Data System (ADS)

Ostermann, Marc; Sanders, Diethard

2015-04-01

In the Brenner Pass area (Eastern Alps) , closely ahead of the most northward outlier ('nose') of the Southern-Alpine continental indenter, abundant deep-seated gravitational slope deformations and a cluster of five post-glacial rockslides are present. The indenter of roughly triangular shape formed during Neogene collision of the Southern-Alpine basement with the Eastern-Alpine nappe stack. Compression by the indenter activated a N-S striking, roughly W-E extensional fault northward of the nose of the indenter (Brenner-normal fault; BNF), and lengthened the Eastern-Alpine edifice along a set of major strike-slip faults. These fault zones display high seismicity, and are the preferred locus of catastrophic rapid slope failures (rockslides, rock avalanches) and deep-seated gravitational slope deformations. The seismotectonic stress field, earthquake activity, and structural data all indicate that the South-Alpine indenter still - or again - exerts compression; in consequence, the northward adjacent Eastern Alps are subject mainly to extension and strike-slip. For the rockslides in the Brenner Pass area, and for the deep-seated gravitational slope deformations, the fault zones combined with high seismic activity predispose massive slope failures. Structural data and earthquakes mainly record ~W-E extension within an Eastern Alpine basement block (Oetztal-Stubai basement complex) in the hangingwall of the BNF. In the Northern Calcareous Alps NW of the Oetztal-Stubai basement complex, dextral faults provide defacement scars for large rockfalls and rockslides. Towards the West, these dextral faults merge into a NNW-SSE striking sinistral fault zone that, in turn, displays high seismic activity and is the locus of another rockslide cluster (Fern Pass cluster; Prager et al., 2008). By its kinematics dictated by the South-Alpine indenter, the relatively rigid Oetztal-Stubai basement block relays faulting and associated mass-wasting over a N-S distance of more than 60 kilometers - from the Brenner Pass area located along the crestline of the Alps to mount Zugspitze near the northern fringe of the Northern Calcareous Alps. Major fault zones and intercalated rigid blocks thus can 'teleconnect' zones of preferred mass-wasting over large lateral distances in orogens. Reference: Prager, C., Zangerl, C., Patzelt, G., Brandner, R., 2008. Age distribution of fossil landslides in the Tyrol (Austria) and its surrounding areas. Natural Hazards and Earth System Science 8, 377-407.

Near transferable phenomenological n-body potentials for noble metals

NASA Astrophysics Data System (ADS)

Pontikis, Vassilis; Baldinozzi, Gianguido; Luneville, Laurence; Simeone, David

2017-09-01

We present a semi-empirical model of cohesion in noble metals with suitable parameters reproducing a selected set of experimental properties of perfect and defective lattices in noble metals. It consists of two short-range, n-body terms accounting respectively for attractive and repulsive interactions, the former deriving from the second moment approximation of the tight-binding scheme and the latter from the gas approximation of the kinetic energy of electrons. The stability of the face centred cubic versus the hexagonal compact stacking is obtained via a long-range, pairwise function of customary use with ionic pseudo-potentials. Lattice dynamics, molecular statics, molecular dynamics and nudged elastic band calculations show that, unlike previous potentials, this cohesion model reproduces and predicts quite accurately thermodynamic properties in noble metals. In particular, computed surface energies, largely underestimated by existing empirical cohesion models, compare favourably with measured values, whereas predicted unstable stacking-fault energy profiles fit almost perfectly ab initio evaluations from the literature. All together the results suggest that this semi-empirical model is nearly transferable.

Near transferable phenomenological n-body potentials for noble metals.

PubMed

Pontikis, Vassilis; Baldinozzi, Gianguido; Luneville, Laurence; Simeone, David

2017-09-06

We present a semi-empirical model of cohesion in noble metals with suitable parameters reproducing a selected set of experimental properties of perfect and defective lattices in noble metals. It consists of two short-range, n-body terms accounting respectively for attractive and repulsive interactions, the former deriving from the second moment approximation of the tight-binding scheme and the latter from the gas approximation of the kinetic energy of electrons. The stability of the face centred cubic versus the hexagonal compact stacking is obtained via a long-range, pairwise function of customary use with ionic pseudo-potentials. Lattice dynamics, molecular statics, molecular dynamics and nudged elastic band calculations show that, unlike previous potentials, this cohesion model reproduces and predicts quite accurately thermodynamic properties in noble metals. In particular, computed surface energies, largely underestimated by existing empirical cohesion models, compare favourably with measured values, whereas predicted unstable stacking-fault energy profiles fit almost perfectly ab initio evaluations from the literature. All together the results suggest that this semi-empirical model is nearly transferable.

Bridging the pressure gap: In situ atomic-level investigations of model platinum catalyst surfaces under reaction conditions by scanning tunneling microscopy

DOE Office of Scientific and Technical Information (OSTI.GOV)

McIntyre, Brian James

1994-05-01

Results of this thesis show that STM measurements can provide information about the surfaces and their adsorbates. Stability of Pt(110) under high pressures of H 2, O 2, and CO was studied (Chap. 4). In situ UHV and high vacuum experiments were carried out for sulfur on Pt(111) (Chap.5). STM studies of CO/S/Pt(111) in high CO pressures showed that the Pt substrate undergoes a stacking-fault-domain reconstruction involving periodic transitions from fcc to hcp stacking of top-layer atoms (Chap.6). In Chap.7, the stability of propylene on Pt(111) and the decomposition products were studied in situ with the HPSTM. Finally, in Chap.8,more » results are presented which show how the Pt tip of the HPSTM was used to locally rehydrogenate and oxidize carbonaceous clusters deposited on the Pt(111) surface; the Pt tip acted as a catalyst after activation by short voltage pulses.« less

Extensional faulting in the southern Klamath Mountains, California

USGS Publications Warehouse

Schweickert, R.A.; Irwin, W.P.

1989-01-01

Large northeast striking normal faults in the southern Klamath Mountains may indicate that substantial crustal extension occurred during Tertiary time. Some of these faults form grabens in the Jurassic and older bedrock of the province. The grabens contain continental Oligocene or Miocene deposits (Weaverville Formation), and in two of them the Oligocene or Miocene is underlain by Lower Cretaceous marine formations (Great Valley sequence). At the La Grange gold placer mine the Oligocene or Miocene strata dip northwest into the gently southeast dipping mylonitic footwall surface of the La Grange fault. The large normal displacement required by the relations at the La Grange mine is also suggested by omission of several kilometers of structural thickness of bedrock units across the northeast continuation of the La Grange fault, as well as by significant changes in bedrock across some northeast striking faults elsewhere in the Central Metamorphic and Eastern Klamath belts. The Trinity ultramafic sheet crops out in the Eastern Klamath terrane as part of a broad northeast trending arch that may be structurally analogous to the domed lower plate of metamorphic core complexes found in eastern parts of the Cordillera. The northeast continuation of the La Grange fault bounds the southeastern side of the Trinity arch in the Eastern Klamath terrane and locally cuts out substantial lower parts of adjacent Paleozoic strata of the Redding section. Faults bounding the northwestem side of the Trinity arch generally trend northeast and juxtapose stacked thrust sheets of lower Paleozoic strata of the Yreka terrane against the Trinity ultramafic sheet. Geometric relations suggest that the Tertiary extension of the southern Klamath Mountains was in NW-SE directions and that the Redding section and the southern part of the Central Metamorphic terrane may be a large Tertiary allochthon detached from the Trinity ultramafic sheet. Paleomagnetic data indicate a lack of rotation about a vertical axis during the extension. We propose that the Trinity ultramafic sheet is structurally analogous to a metamorphic core complex; if so, it is the first core complex to be described that involves ultramafic rocks. We infer that Mesozoic terrane accretion produced a large gravitational instability in the crust that spread laterally during Tertiary extension

Cenozoic stratigraphy and structure of the Chesapeake Bay region

USGS Publications Warehouse

Powars, David S.; Edwards, Lucy E.; Kidwell, Susan M.; Schindler, J. Stephen

2015-01-01

The Salisbury embayment is a broad tectonic downwarp that is filled by generally seaward-thickening, wedge-shaped deposits of the central Atlantic Coastal Plain. Our two-day field trip will take us to the western side of this embayment from the Fall Zone in Washington, D.C., to some of the bluffs along Aquia Creek and the Potomac River in Virginia, and then to the Calvert Cliffs on the western shore of the Chesapeake Bay. We will see fluvial-deltaic Cretaceous deposits of the Potomac Formation. We will then focus on Cenozoic marine deposits. Transgressive and highstand deposits are stacked upon each other with unconformities separating them; rarely are regressive or lowstand deposits preserved. The Paleocene and Eocene shallow shelf deposits consist of glauconitic, silty sands that contain varying amounts of marine shells. The Miocene shallow shelf deposits consist of diatomaceous silts and silty and shelly sands. The lithology, thickness, dip, preservation, and distribution of the succession of coastal plain sediments that were deposited in our field-trip area are, to a great extent, structurally controlled. Surficial and subsurface mapping using numerous continuous cores, auger holes, water-well data, and seismic surveys has documented some folds and numerous high-angle reverse and normal faults that offset Cretaceous and Cenozoic deposits. Many of these structures are rooted in early Mesozoic and/or Paleozoic NE-trending regional tectonic fault systems that underlie the Atlantic Coastal Plain. On Day 1, we will focus on two fault systems (stops 1–2; Stafford fault system and the Skinkers Neck–Brandywine fault system and their constituent fault zones and faults). We will then see (stops 3–5) a few of the remaining exposures of largely unlithified marine Paleocene and Eocene strata along the Virginia side of the Potomac River including the Paleocene-Eocene Thermal Maximum boundary clay. These exposures are capped by fluvial-estuarine Pleistocene terrace deposits. On Day 2, we will see (stops 6–9) the classic Miocene section along the ~25 miles (~40 km) of Calvert Cliffs in Maryland, including a possible fault and structural warping. Cores from nearby test holes will also be shown to supplement outcrops.

Reflection seismic characterization of the Grängesberg iron deposit and its mining-induced structures, central Sweden

NASA Astrophysics Data System (ADS)

Place, Joachim; Malehmir, Alireza; Högdahl, Karin; Juhlin, Christopher; Persson Nilsson, Katarina

2014-05-01

Reflection seismic investigation has been conducted on the Grängesberg apatite iron deposit where over 150 Mt of iron ore were produced until the mine closed in 1989. The mine infrastructure with shafts and tunnels extend down to ca. 650 m below the surface. Both natural and mine induced fracture and fault systems are today water-filled (some of them extending to the surface). The disputed ore genesis of the apatite-iron ores and its exploration potential due to large remaining quantities once again attracts both scientific and commercial interests. A good understanding of the geometry of mineral deposits and their hostrock structures at depth is essential for optimizing their exploration and exploitation. In addition, deep understanding of the fracture system is vital if mining activity is resumed as these may impact the terrain stability and seismicity, which may put at risk new populated and industrial areas. To address some of these challenging issues related to the past mining and also to obtain information about the depth continuation of the existing deposit, two E-W oriented reflection lines with a total length of 3.5 km were acquired in May 2013 by Uppsala University. A weight drop mounted on an hydraulic bobcat truck (traditionally used for concrete breaking in demolition sector) was used to generate seismic signal. In order to increase the signal-to-noise ratio, several impacts were generated at each shot point and stacked together. The seismic lines intersect at high angle the Grängesberg ore body and open pit, as well as several mining-induced faults. A combination of cabled and wireless receivers placed at every 10 m was used for the data recording. Use of wireless receivers was necessary as deploying cabled sensors was not possible due to city infrastructures, roads and houses. A careful analysis of the data suggested that several field-related issues such as (1) the crooked geometry of the lines (due to the available path and road network), (2) electric and vibration noise due to populated areas and roads, as well as a rock crusher working close to the line, (3) significant static variations (due to the variable nature of the terrain: forest, roads, open pit filled with 10s of meters of unconsolidated materials...), make this dataset similar to a city-kind dataset. Preprocessing of the data first required the cable- and wireless- recorded sub-datasets to be merged using GPS time stamps (nanoseconds accuracy) registered in the active data. Vertical shift and stack was then carried out to stack all data available at each shot point. Preliminary results from brute stacks exhibit evidences of reflections or diffractions. It is anticipated that further processing, involving especially appropriate static corrections and velocity analysis, would help interpreting such seismic events in relation to the ore body and its surrounding structures. Possible along-profile compartmentalization is also detected; further processing is however necessary before interpreting such features in terms of recent faulting. Acknowledgements: Formas, Grängesberg Iron AB, Spendrups and Geological Survey of Sweden

Shear-induced mechanical failure of β -G a2O3 from quantum mechanics simulations

NASA Astrophysics Data System (ADS)

An, Qi; Li, Guodong

2017-10-01

Monoclinic gallium oxide (β -G a2O3 ) has important applications in power devices and deep UV optoelectronic devices because of such novel properties as a wide band gap, high breakdown electric field, and a wide range of n -type doping conductivity. However, the intrinsic failure mechanisms of β -G a2O3 remain unknown, which limits the fabrication and packaging of β -G a2O3 -based electronic devices. Here we used density-functional theory at the Perdew-Burke-Ernzerhof level to examine the shear-induced failure mechanisms of β -G a2O3 along various plausible slip systems. We found that the (001 )/〈010 〉 slip system has the lowest ideal shear strength of 3.8 GPa among five plausible slip systems, suggesting that (001 )/〈010 〉 is the most plausible activated slip system. This slip leads to an intrinsic failure mechanism arising from breaking the longest Ga-O bond between octahedral Ga and fourfold-coordinated O. Then we identified the same failure mechanism of β -G a2O3 under biaxial shear deformation that mimics indentation stress conditions. Finally, the general stacking fault energy (SFE) surface is calculated for the (001) surface from which we concluded that there is no intrinsic stacking fault structure for β -G a2O3 . The deformation modes and SFE calculations are essential to understand the intrinsic mechanical processes of this semiconductor material, which provides insightful guidance for designing high-performance semiconductor devices.

Stratal stacking patterns and tectono-sedimentary evolution of hyperextended magma-poor rifted margins

NASA Astrophysics Data System (ADS)

Ribes, C.; Gillard, M.; Epin, M. E.; Ghienne, J. F.; Manatschal, G.; Karner, G. D.; Johnson, C. A.

2016-12-01

Research on the formation and evolution of deep-water rifted margins has undergone a major paradigm shift in recent years. An increasing number of studies of present-day and fossil rifted margins allow us to identify and characterize the structural architecture of the most distal parts of rifted margins, the so-called hyperextended, magma-poor rifted margins. However, at present, little is known about the depositional environments, sedimentary facies, stacking patterns, subsidence and thermal history within these domains. In this context, characterizing the stratal stacking patterns and understanding their spatial and temporal evolution is a new challenge. The major difficulty comes from the fact that the observed stratigraphic geometries and facies relationships are a result of the complex interplay between sediment supply and available accommodation, which is controlled by not only the regional generation of accommodation, but also by local tectono-magmatic processes. These parameters are poorly constrained or even sufficiently known in these tectonic settings. Indeed, the complex structural evolution of hyperextended magma-poor rifted margins, including the development of poly-phase in-sequence and out of sequence extensional detachment faults and associated mantle exhumation and magmatic activity, can generate complex accommodation patterns over a highly structured top basement. The presentation summarizes early results concerning the controlling parameters on ultra-deep water stratigraphic stacking patterns and to provide a conceptual framework. This observation-driven approach combines fieldwork from fossil Alpine Tethys margins exposed in the Alps and the analysis of seismic reflection data from present-day deep water rifted margins such as the Australian-Antarctic, East India and Iberia-Newfoundland margins.

3D Fault Network of the Murchison Domain, Yilgarn Craton

NASA Astrophysics Data System (ADS)

Murdie, Ruth; Gessner, Klaus

2014-05-01

The architecture of Archean granite-greenstone terranes is often controlled by networks of 10 km to 100 km-scale shear zones that record displacement under amphibolite facies to greenschist facies metamorphic conditions. The geometry of such crustal scale 'fault networks' has been shown to be highly relevant to understand the tectonic and metamorphic history of granite-greenstone terranes, as well as the availability of structural controlled fluid pathways related to magmatic and hydrothermal mineralization. The Neoarchean Yilgarn Craton and the Proterozoic orogens around its margins constitute one of Earth's greatest mineral treasure troves, including iron, gold, copper and nickel mineral deposits. Whereas the Yilgarn Craton is one of the best studied Archean cratons, its enormous size and limited outcrop are detrimental to the better understanding of what controls the distribution of these vast resources and what geodynamic processes were involved the tectonic assembly of this part of the Australian continent. Here we present a network of the major faults of the NW Yilgarn Craton between the Yalgar Fault, Murchison's NW contact with the Narryer Terrane to the Ida Fault, its boundary with the Eastern Goldfields Superterrane. The model has been constructed from various geophysical and geological data, including potential field grids, Geological Survey of Western Australia map sheets, seismic reflection surveys and magnetotelluric traverses. The northern extremity of the modelled area is bounded by the Proterozoic cover and the southern limit has been arbitrarily chosen to include various greenstone belts. In the west, the major faults in the upper crust, such as the Carbar and Chundaloo Shear Zones, dip steeply towards the west and then flatten off at depth. They form complex branching fault systems that bound the greenstone belts in a series of stacked faults. East of the Ida, the far east of the model, the faults have been integrated with Geoscience Australia's pmd*CRC Eastern Goldfields model. In the central portion, the major faults such as the Youanmi and Wattle Creek, dip to the east and can be followed into the fabric of the Yarraquin Seismic Province. The Wattle Creek Shear Zone in particular can be traced on all three of the Youanmi seismic lines. The greenstones are cradled between these major faults and antithetic westward dipping subsidiary faults such as the Edale Shear Zone. While the Ida Fault cannot be located with great confidence, the slight drop in Moho depth toward the east and the overall change of seismic texture delineate the Youanmi-Eastern Goldfields boundary. The Lawler's Anticline, presumably located in the hanging wall of the Ida Fault, again changes the style of faulting with the Lawler's tonalite forming the core of a 10 km-scale antiform. The fault network presented here is a milestone to a craton-wide integrated structural model and will hopefully contribute to provide a better spatial context for geological, geochemical and geophysical data in our quest to understand the tectonics and mineral potential of the Yilgarn craton.

Nonlocal sparse model with adaptive structural clustering for feature extraction of aero-engine bearings

NASA Astrophysics Data System (ADS)

Zhang, Han; Chen, Xuefeng; Du, Zhaohui; Li, Xiang; Yan, Ruqiang

2016-04-01

Fault information of aero-engine bearings presents two particular phenomena, i.e., waveform distortion and impulsive feature frequency band dispersion, which leads to a challenging problem for current techniques of bearing fault diagnosis. Moreover, although many progresses of sparse representation theory have been made in feature extraction of fault information, the theory also confronts inevitable performance degradation due to the fact that relatively weak fault information has not sufficiently prominent and sparse representations. Therefore, a novel nonlocal sparse model (coined NLSM) and its algorithm framework has been proposed in this paper, which goes beyond simple sparsity by introducing more intrinsic structures of feature information. This work adequately exploits the underlying prior information that feature information exhibits nonlocal self-similarity through clustering similar signal fragments and stacking them together into groups. Within this framework, the prior information is transformed into a regularization term and a sparse optimization problem, which could be solved through block coordinate descent method (BCD), is formulated. Additionally, the adaptive structural clustering sparse dictionary learning technique, which utilizes k-Nearest-Neighbor (kNN) clustering and principal component analysis (PCA) learning, is adopted to further enable sufficient sparsity of feature information. Moreover, the selection rule of regularization parameter and computational complexity are described in detail. The performance of the proposed framework is evaluated through numerical experiment and its superiority with respect to the state-of-the-art method in the field is demonstrated through the vibration signals of experimental rig of aircraft engine bearings.

Late Miocene extensional systems in northern Tunisia and their relation with SE directed delamination of the African subcontinental mantle lithosphere

NASA Astrophysics Data System (ADS)

Booth-Rea, Guillermo; Gaidi, Seif; Melki, Fetheddine; Pérez-Peña, Vicente; Marzougui, Wissem; Azañón, Jose Miguel; Galve, Jorge Pedro

2017-04-01

Recent work has proposed the delamination of the subcontinental mantle lithosphere under northern Tunisia during the late Miocene. This process is required to explain the present location of the Tunisian segment of the African slab, imaged by seismic tomography, hanging under the Gulf of Gabes to the south of Tunisia. Thus, having retreated towards the SE several hundred km from its original position under the Tellian-Atlas nappe contact that crops out along the north of Tunisia. However, no tectonic structures have been described which could be related to this mechanism of lithospheric mantle peeling. Here we describe for the first time extensional fault systems in northern Tunisia that strongly thinned the Tellian nappes, exhuming rocks from the Tunisian Atlas in the core of folded extensional detachments. Two normal fault systems with sub-orthogonal extensional transport occur. These were active during the late Miocene associated to the extrusion of 13 Ma granodiorite and 9 Ma rhyodacite in the footwall of the Nefza detachment. We have differentiated an extensional system formed by low-angle normal faults with NE- and SW-directed transport cutting through the Early to Middle Miocene Tellian nappen stack and a later system of low and high-angle normal faults that cuts down into the underlying Tunisian Atlas units with SE-directed transport, which root in the Nefza detachment. Both normal fault systems have been later folded and cut by thrusts during Plio-Quaternary NW-SE directed compression. These findings change the interpretation of the tectonic evolution of Tunisia that has always been framed in a transpressive to compressive setting, manifesting the extensional effects of Late Miocene lithospheric mantle delamination under northern Tunisia.

Subsurface architecture of a strike-slip collapse structure: insights from Ilopango caldera, El Salvador

NASA Astrophysics Data System (ADS)

Saxby, Jennifer; Gottsmann, Joachim; Cashman, Katherine; Gutierrez, Eduardo

2016-04-01

While most calderas are created by roof collapse along ring-like faults into an emptying magma reservoir during a large and violent explosive eruption, an additional condition for caldera formation may be tectonically induced extensional stresses. Here we provide geophysical insights into the shallow sub-volcanic plumbing system of a collapse caldera in a major strike-slip tectonic setting by inverting Bouguer gravity data from the Ilopango caldera in El Salvador. Despite a long history of catastrophic eruptions with the most recent in 500 A.D., the internal architecture of the caldera has not been investigated, although studies of the most recent eruption have not identified the ring faults commonly associated with caldera collapse. The gravity data show that low-density material aligned along the principal stress orientations of the El Salvador Fault Zone (ESFZ) forms a pronounced gravity low beneath the caldera. Extending to around 6 km depth, the low density structure likely maps a complex stacked shallow plumbing system composed of magmatic and fractured hydrothermal reservoirs. A substantial volume of the plumbing system must be composed of a vapour phase to explain the modeled negative density contrasts. We use these constraints to map the possible multi-phase parameter space contributing to the subsurface architecture of the caldera and propose that the local extension along the complex ESFZ controls accumulation, ascent and eruption of magma at Ilopango. The data further suggest that future eruptions at Ilopango could be facilitated by rapid rise of magma along conjugate fault damage zones through a mechanically weak crust under tension. This may explain the absence of clear ring fault structures at the caldera.

Architecture and tectono-stratigraphic evolution of the intramontane Baza Basin (Bétics, SE-Spain): Constraints from seismic imaging

NASA Astrophysics Data System (ADS)

Haberland, Christian; Gibert, Luis; Jurado, María José; Stiller, Manfred; Baumann-Wilke, Maria; Scott, Gary; Mertz, Dieter F.

2017-07-01

The Baza basin is a large Neogene intramontane basin in the Bétic Cordillera of southern Spain that formed during the Tortonian (late Miocene). The Bétic Cordillera was produced by NW-SE oblique convergence between the Eurasian and African Plates. Three seismic reflection lines (each 18 km long; vibroseis method) were acquired across the Baza basin to reveal the architecture of the sedimentary infill and faulting during basin formation. We applied rather conventional CDP data processing followed by first arrival P-wave tomography to provide complementary structural information and establish velocity models for the post-stack migration. These images show a highly asymmetric structure for the Basin with sediments thickening westward, reaching a maximum observed thickness of > 2200 m near the governing Baza Fault zone (BFZ). Three major seismic units (including several subunits) on top of the acoustic basement could be identified. We use stratigraphic information from the uplifted block of the BFZ and other outcrops at the basin edges together with available information from neighboring Bétic basins to tentatively correlate the seismic units to the known stratigraphy in the area. Until new drilling or surface outcrop data is not available, this interpretation is preliminary. The seismic units could be associated to Tortonian marine deposits, and latest Miocene to Pleistocene continental fluvio-lacustrine sediments. Individual strands of the BFZ truncate the basin sediments. Strong fault reflections imaged in two lines are the product of the large impedance contrast between sedimentary fill and basement. In the central part of the Basin several basement faults document strong deformation related to the early stages of basin formation. Some of these faults can be traced up to the shallowest imaged depth levels indicating activity until recent times.

Fault Diagnosis Based on Chemical Sensor Data with an Active Deep Neural Network

PubMed Central

Jiang, Peng; Hu, Zhixin; Liu, Jun; Yu, Shanen; Wu, Feng

2016-01-01

Big sensor data provide significant potential for chemical fault diagnosis, which involves the baseline values of security, stability and reliability in chemical processes. A deep neural network (DNN) with novel active learning for inducing chemical fault diagnosis is presented in this study. It is a method using large amount of chemical sensor data, which is a combination of deep learning and active learning criterion to target the difficulty of consecutive fault diagnosis. DNN with deep architectures, instead of shallow ones, could be developed through deep learning to learn a suitable feature representation from raw sensor data in an unsupervised manner using stacked denoising auto-encoder (SDAE) and work through a layer-by-layer successive learning process. The features are added to the top Softmax regression layer to construct the discriminative fault characteristics for diagnosis in a supervised manner. Considering the expensive and time consuming labeling of sensor data in chemical applications, in contrast to the available methods, we employ a novel active learning criterion for the particularity of chemical processes, which is a combination of Best vs. Second Best criterion (BvSB) and a Lowest False Positive criterion (LFP), for further fine-tuning of diagnosis model in an active manner rather than passive manner. That is, we allow models to rank the most informative sensor data to be labeled for updating the DNN parameters during the interaction phase. The effectiveness of the proposed method is validated in two well-known industrial datasets. Results indicate that the proposed method can obtain superior diagnosis accuracy and provide significant performance improvement in accuracy and false positive rate with less labeled chemical sensor data by further active learning compared with existing methods. PMID:27754386

Experimental evaluation of the certification-trail method

NASA Technical Reports Server (NTRS)

Sullivan, Gregory F.; Wilson, Dwight S.; Masson, Gerald M.; Itoh, Mamoru; Smith, Warren W.; Kay, Jonathan S.

1993-01-01

Certification trails are a recently introduced and promising approach to fault-detection and fault-tolerance. A comprehensive attempt to assess experimentally the performance and overall value of the method is reported. The method is applied to algorithms for the following problems: huffman tree, shortest path, minimum spanning tree, sorting, and convex hull. Our results reveal many cases in which an approach using certification-trails allows for significantly faster overall program execution time than a basic time redundancy-approach. Algorithms for the answer-validation problem for abstract data types were also examined. This kind of problem provides a basis for applying the certification-trail method to wide classes of algorithms. Answer-validation solutions for two types of priority queues were implemented and analyzed. In both cases, the algorithm which performs answer-validation is substantially faster than the original algorithm for computing the answer. Next, a probabilistic model and analysis which enables comparison between the certification-trail method and the time-redundancy approach were presented. The analysis reveals some substantial and sometimes surprising advantages for ther certification-trail method. Finally, the work our group performed on the design and implementation of fault injection testbeds for experimental analysis of the certification trail technique is discussed. This work employs two distinct methodologies, software fault injection (modification of instruction, data, and stack segments of programs on a Sun Sparcstation ELC and on an IBM 386 PC) and hardware fault injection (control, address, and data lines of a Motorola MC68000-based target system pulsed at logical zero/one values). Our results indicate the viability of the certification trail technique. It is also believed that the tools developed provide a solid base for additional exploration.

Fault Diagnosis Based on Chemical Sensor Data with an Active Deep Neural Network.

PubMed

Jiang, Peng; Hu, Zhixin; Liu, Jun; Yu, Shanen; Wu, Feng

2016-10-13

Big sensor data provide significant potential for chemical fault diagnosis, which involves the baseline values of security, stability and reliability in chemical processes. A deep neural network (DNN) with novel active learning for inducing chemical fault diagnosis is presented in this study. It is a method using large amount of chemical sensor data, which is a combination of deep learning and active learning criterion to target the difficulty of consecutive fault diagnosis. DNN with deep architectures, instead of shallow ones, could be developed through deep learning to learn a suitable feature representation from raw sensor data in an unsupervised manner using stacked denoising auto-encoder (SDAE) and work through a layer-by-layer successive learning process. The features are added to the top Softmax regression layer to construct the discriminative fault characteristics for diagnosis in a supervised manner. Considering the expensive and time consuming labeling of sensor data in chemical applications, in contrast to the available methods, we employ a novel active learning criterion for the particularity of chemical processes, which is a combination of Best vs. Second Best criterion (BvSB) and a Lowest False Positive criterion (LFP), for further fine-tuning of diagnosis model in an active manner rather than passive manner. That is, we allow models to rank the most informative sensor data to be labeled for updating the DNN parameters during the interaction phase. The effectiveness of the proposed method is validated in two well-known industrial datasets. Results indicate that the proposed method can obtain superior diagnosis accuracy and provide significant performance improvement in accuracy and false positive rate with less labeled chemical sensor data by further active learning compared with existing methods.

Kinematics of syn- and post-exhumational shear zones at Lago di Cignana (Western Alps, Italy): constraints on the exhumation of Zermatt-Saas (ultra)high-pressure rocks and deformation along the Combin Fault and Dent Blanche Basal Thrust

NASA Astrophysics Data System (ADS)

Kirst, Frederik; Leiss, Bernd

2017-01-01

Kinematic analyses of shear zones at Lago di Cignana in the Italian Western Alps were used to constrain the structural evolution of units from the Piemont-Ligurian oceanic realm (Zermatt-Saas and Combin zones) and the Adriatic continental margin (Dent Blanche nappe) during Palaeogene syn- and post-exhumational deformation. Exhumation of Zermatt-Saas (U)HP rocks to approximately lower crustal levels at ca. 39 Ma occurred during normal-sense top-(S)E shearing under epidote-amphibolite-facies conditions. Juxtaposition with the overlying Combin zone along the Combin Fault at mid-crustal levels occurred during greenschist-facies normal-sense top-SE shearing at ca. 38 Ma. The scarcity of top-SE kinematic indicators in the hanging wall of the Combin Fault probably resulted from strain localization along the uppermost Zermatt-Saas zone and obliteration by subsequent deformation. A phase of dominant pure shear deformation around 35 Ma affected units in the direct footwall and hanging wall of the Combin Fault. It is interpreted to reflect NW-SE crustal elongation during updoming of the nappe stack as a result of underthrusting of European continental margin units and the onset of continental collision. This phase was partly accompanied and followed by ductile bulk top-NW shearing, especially at higher structural levels, which transitioned into semi-ductile to brittle normal-sense top-NW deformation due to Vanzone phase folding from ca. 32 Ma onwards. Our structural observations suggest that syn-exhumational deformation is partly preserved within units and shear zones exposed at Lago di Cignana but also that the Combin Fault and Dent Blanche Basal Thrust experienced significant post-exhumational deformation reworking and overprinting earlier structures.

Passive recording of an active transform, an example from the Levant continental margin and the Dead Sea Fault

NASA Astrophysics Data System (ADS)

Lang, Guy; Lazar, Michael; Schattner, Uri

2017-04-01

Transform faults accommodate lateral motion between two adjacent plates. Records of plate motion and consequent boundary development on land is, at times, scarce and limited to structures along the fault axis. Investigation of a passive continental margin adjacent to the plate boundary might broaden the scope and provide estimates for its structural development. To examine this hypothesis, we analyzed depth and time migrated 3D seismic data together with four boreholes located along the southern Levant continental margin, ca. 100 Km from the continental Dead Sea fault (DSF). The analysis focus on the Plio-Pleistocene sequence, a key period in the development of the DSF. It includes formation of structural maps, stacking pattern investigation and calculation of sedimentation rates based on decompacted 3D depth data. These, in turn, enabled the reconstruction of margin development. This includes Messinian-earliest Zanclean NNE-SSW sinistral strike-slip faulting followed by Zanclean-Late Gelasian syn-depositional folding striking in the same direction. Abrupt change is marked by the Top Gelasian surface that shows indications of regional mass slumping. Successive Mid-Late Pleistocene progradation marks a basinward shift of the depocenter. Progradation controls margin sedimentation rates during the mid-late Pleistocene. These were found to increase throughout the whole Plio-Pleistocene, in contrast to reported sediment discharge from the Nile, which was shown to decrease after the Gelasian. Correlations to onshore findings, suggest that the continental margin records strain localization on the DSF during the Pliocene-Gelasian. This trend peaked at 1.8 Ma when short wavelength strain ceased along the margin, and differential subsidence commenced basinwards. This is attributed to consequent deepening of the DSF plate boundary.

Structure of the Suasselkä postglacial fault in northern Finland obtained by analysis of local events and ambient seismic noise

NASA Astrophysics Data System (ADS)

Afonin, Nikita; Kozlovskaya, Elena; Kukkonen, Ilmo; Dafne/Finland Working Group

2017-04-01

Understanding the inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of local seismic events and ambient seismic noise recorded by the temporary DAFNE array in the northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä postglacial fault (SPGF), which was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised an area of about 20 to 100 km and consisted of eight short-period and four broadband three-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September 2011-May 2013. Recordings of the array have being analysed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä gold mine. As a result, we found a number of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single-station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green's functions between pairs of stations in the frequency band of 0.1-1 Hz and to calculate corresponding surface wave dispersion curves. The S-wave velocity models were obtained as a result of dispersion curve inversion. The results suggest that the area of the SPGF corresponds to a narrow region of low S-wave velocities surrounded by rocks with high S-wave velocities. We interpret this low-velocity region as a non-healed mechanically weak fault damage zone (FDZ) formed due to the last major earthquake that occurred after the last glaciation.

Characterization of high-quality kerfless epitaxial silicon for solar cells: Defect sources and impact on minority-carrier lifetime

DOE PAGES

Kivambe, Maulid M.; Powell, Douglas M.; Castellanos, Sergio; ...

2017-11-14

We investigate the types and origins of structural defects in thin (<100 μm) kerfless epitaxial single crystal silicon grown on top of reorganized porous silicon layers. Although the structural defect density is low (has average defect density < 10 4 cm -2), localized areas with a defect density > 10 5 cm -2 are observed. Cross-sectional and systematic plan-view defect etching and microscopy reveals that the majority of stacking faults and dislocations originate at the interface between the porous silicon layer and the epitaxial wafer. Localised dislocation clusters are observed in regions of collapsed/deformed porous silicon and at decorated stackingmore » faults. In localized regions of high extended defect density, increased minority-carrier recombination activity is observed. Evidence for impurity segregation to the extended defects (internal gettering), which is known to exacerbate carrier recombination is demonstrated. In conclusion, the impact of the defects on material performance and substrate re-use is also discussed.« less

Superconducting shielded core reactor with reduced AC losses

DOEpatents

Cha, Yung S.; Hull, John R.

2006-04-04

A superconducting shielded core reactor (SSCR) operates as a passive device for limiting excessive AC current in a circuit operating at a high power level under a fault condition such as shorting. The SSCR includes a ferromagnetic core which may be either closed or open (with an air gap) and extends into and through a superconducting tube or superconducting rings arranged in a stacked array. First and second series connected copper coils each disposed about a portion of the iron core are connected to the circuit to be protected and are respectively wound inside and outside of the superconducting tube or rings. A large impedance is inserted into the circuit by the core when the shielding capability of the superconducting arrangement is exceeded by the applied magnetic field generated by the two coils under a fault condition to limit the AC current in the circuit. The proposed SSCR also affords reduced AC loss compared to conventional SSCRs under continuous normal operation.

Analyzing checkpointing trends for applications on the IBM Blue Gene/P system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Naik, H.; Gupta, R.; Beckman, P.

Current petascale systems have tens of thousands of hardware components and complex system software stacks, which increase the probability of faults occurring during the lifetime of a process. Checkpointing has been a popular method of providing fault tolerance in high-end systems. While considerable research has been done to optimize checkpointing, in practice the method still involves a high-cost overhead for users. In this paper, we study the checkpointing overhead seen by applications running on leadership-class machines such as the IBM Blue Gene/P at Argonne National Laboratory. We study various applications and design a methodology to assist users in understanding andmore » choosing checkpointing frequency and reducing the overhead incurred. In particular, we study three popular applications -- the Grid-Based Projector-Augmented Wave application, the Carr-Parrinello Molecular Dynamics application, and a Nek5000 computational fluid dynamics application -- and analyze their memory usage and possible checkpointing trends on 32,768 processors of the Blue Gene/P system.« less

Evolution of microstructure and residual stress during annealing of austenitic and ferritic steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wawszczak, R.; Baczmański, A., E-mail: Andrzej.Baczmanski@fis.agh.edu.pl; Marciszko, M.

2016-02-15

In this work the recovery and recrystallization processes occurring in ferritic and austenitic steels were studied. To determine the evolution of residual stresses during material annealing the nonlinear sin{sup 2}ψ diffraction method was used and an important relaxation of the macrostresses as well as the microstresses was found in the cold rolled samples subjected to heat treatment. Such relaxation occurs at the beginning of recovery, when any changes of microstructure cannot be detected using other experimental techniques. Stress evolution in the annealed steel samples was correlated with the progress of recovery process, which significantly depends on the value of stackingmore » fault energy. - Highlights: • X-ray diffraction was used to determine the first order and second order stresses. • Diffraction data were analyzed using scale transition elastoplastic models model. • Stress relaxation in annealed ferritic and austenitic steels was correlated with evolution of microstructure. • Influence of stacking fault energy on thermally induced processes was discussed.« less

Characterization of high-quality kerfless epitaxial silicon for solar cells: Defect sources and impact on minority-carrier lifetime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kivambe, Maulid M.; Powell, Douglas M.; Castellanos, Sergio

We investigate the types and origins of structural defects in thin (<100 μm) kerfless epitaxial single crystal silicon grown on top of reorganized porous silicon layers. Although the structural defect density is low (has average defect density < 10 4 cm -2), localized areas with a defect density > 10 5 cm -2 are observed. Cross-sectional and systematic plan-view defect etching and microscopy reveals that the majority of stacking faults and dislocations originate at the interface between the porous silicon layer and the epitaxial wafer. Localised dislocation clusters are observed in regions of collapsed/deformed porous silicon and at decorated stackingmore » faults. In localized regions of high extended defect density, increased minority-carrier recombination activity is observed. Evidence for impurity segregation to the extended defects (internal gettering), which is known to exacerbate carrier recombination is demonstrated. In conclusion, the impact of the defects on material performance and substrate re-use is also discussed.« less

Rock formation characterization for CO2-EOR and carbon geosequestration; 3D seismic amplitude and coherency anomalies, Wellington Field, Kansas, USA

USGS Publications Warehouse

Ohl, D.; Raef, A.; Watnef, L.; Bhattacharya, S.

2011-01-01

In this paper, we present a workflow for a Mississipian carbonates characterization case-study integrating post-stack seismic attributes, well-logs porosities, and seismic modeling to explore relating changes in small-scale "lithofacies" properties and/or sub-seismic resolution faulting to key amplitude and coherency 3D seismic attributes. The main objective of this study is to put emphasis on reservoir characterization that is both optimized for and subsequently benefiting from pilot tertiary CO2-EOR in preparation for future carbon geosequestration in a depleting reservoir and a deep saline aquifer. The extracted 3D seismic coherency attribute indicated anomalous features that can be interpreted as a lithofacies change or a sub-seismic resolution faulting. A 2D finite difference modeling has been undertaken to understand and potentially build discriminant attributes to map structural and/or lithofacies anomalies of interest especially when embarking upon CO2-EOR and/or carbon sequestration monitoring and management projects. ?? 2011 Society of Exploration Geophysicists.

Focal mechanisms and tidal modulation for tectonic tremors in Taiwan

NASA Astrophysics Data System (ADS)

Ide, S.; Yabe, S.; Tai, H. J.; Chen, K. H.

2015-12-01

Tectonic tremors in Taiwan have been discovered beneath the southern Central Range, but their hosting structure has been unknown. Here we constrain the focal mechanism of underground deformation related to tremors, using moment tensor inversion in the very low frequency band and tidal stress analysis. Three types of seismic data are used for two analysis steps: detection of tremors and the moment tensor inversion. Short-period seismograms from CWBSN are used for tremor detection. Broadband seismograms from BATS and the TAIGER project are used for both steps. About 1000 tremors were detected using an envelope correlation method in the high frequency band (2-8 Hz). Broadband seismograms are stacked relative to the tremor timing, and inverted for a moment tensor in the low frequency band (0.02-0.05 Hz). The best solution was obtained at 32 km depth, as a double-couple consistent with a low-angle thrust fault dipping to the east-southeast, or a high-angle thrust with a south-southwest strike. Almost all tremors occur when tidal shear stress is positive and normal stress is negative (clamping). Since the clamping stress is high for a high-angle thrust fault, the low-angle thrust fault is more likely to be the fault plane. Tremor rate increases non-linearly with increasing shear stress, suggesting a velocity strengthening friction law. The high tidal sensitivity is inconsistent with horizontal slip motion suggested by previous studies, and normal faults that dominates regional shallow earthquakes. Our results favor thrust slip on a low-angle fault dipping to the east-southeast, consistent with the subduction of the Eurasian plate. The tremor region is characterized by a deep thermal anomaly with decrease normal stress. This region has also experienced enough subduction to produce metamorphic fluids. A large amount of fluid and low vertical stress may explain the high tidal sensitivity.

Energy investigation of effects of O on mechanical properties of NiAl intermetallics.

PubMed

Hu, Xue-Lan; Liu, Li-Hua; Zhang, Ying; Lu, Guang-Hong; Wang, Tianmin

2011-01-19

We have investigated effects of O on mechanical properties of NiAl by calculating the cleavage energy (γ(C)) and the unstable stacking fault energy (γ(us)) using a first-principles method. O is shown to reduce γ(C)/γ(us) for the [001](110) and [100](001) slip systems, indicating that the presence of O should be associated with the ductility reduction of NiAl. Further, γ(C)/γ(us) of the NiAl-O system can be increased by Cr, suggesting the possibility to suppress the negative effect of O via alloying elements.

Scalable cloud without dedicated storage

NASA Astrophysics Data System (ADS)

Batkovich, D. V.; Kompaniets, M. V.; Zarochentsev, A. K.

2015-05-01

We present a prototype of a scalable computing cloud. It is intended to be deployed on the basis of a cluster without the separate dedicated storage. The dedicated storage is replaced by the distributed software storage. In addition, all cluster nodes are used both as computing nodes and as storage nodes. This solution increases utilization of the cluster resources as well as improves fault tolerance and performance of the distributed storage. Another advantage of this solution is high scalability with a relatively low initial and maintenance cost. The solution is built on the basis of the open source components like OpenStack, CEPH, etc.

New adatom model for Si(11) 7X7 and Si(111)Ge 5X5 reconstructed surfaces

NASA Technical Reports Server (NTRS)

Chadi, D. J.

1985-01-01

A new adatom model differing from the conventional model by a reconstruction of the substrate is proposed. The new adatom structure provides an explanation for the 7x7 and 5x5 size of the unit cells seen on annealed Si(111) and Si(111)-Ge surfaces, respectively. The model is consistent with structural information from vacuum-tunneling microscopy. It also provides simple explanations for stacking-fault-type features expected from Rutherford backscattering experiments and for similarities in the LEED and photoemission spectra of 2x1 and 7x7 surfaces.

Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sedao, Xxx; Garrelie, Florence, E-mail: florence.garrelie@univ-st-etienne.fr; Colombier, Jean-Philippe

2014-04-28

The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

Incommensurateness in nanotwinning models of modulated martensites

NASA Astrophysics Data System (ADS)

Benešová, Barbora; Frost, Miroslav; Kampschulte, Malte; Melcher, Christof; Sedlák, Petr; Seiner, Hanuš

2015-11-01

We study the formation of modulated martensites in ferromagnetic shape memory alloys by a mathematical model originating from the nanotwinning concept. The results show that the incommensurateness, systematically observed in experiments for the modulated phases, may be understood as a precursor effect of the intermartensitic transitions, and its appearance does not contradict the nanotwinning concept itself. The model sufficiently explains the different levels of incommensurateness reported from different experimental observations for the 14-layered and 10-layered martensites of the Ni-Mn-Ga alloy and outlines the mechanism of formation of faults in the stacking sequences of these materials.

MEANS 2: Microstructure- and Micromechanism-Sensitive Property Models for Advanced Turbine Disk and Blade Systems

DTIC Science & Technology

2009-12-31

f„„„,„ -L...-J..— - —I 1 / f+_—=p / —j \\-\\- 4A 14 4A»4 / 4A C4 M / »4.4C A4, «i »A OWOLC $-ISF s - csr !•» ’ML...Materials Society) Publications. 23. S . Ma, L. Carroll and T.M. Pollock, "Development of y Phase Stacking Faults during High Temperature Creep of Ru...into the design of advanced disk and blade systems 6. AUTHOR( S ) Michael J Mills 5. FUNDING NUMBERS FA9550-05-1-0135 7. PERFORMING ORGANIZATION

Lonsdaleite has been used as an indicator of shock from cratering events, but does it exist?

NASA Astrophysics Data System (ADS)

Nemeth, P.; Garvie, L. A.; Buseck, P. R.

2013-12-01

In 1967 a new diamond polymorph was described from the Canyon Diablo iron meteorite [1] and called lonsdaleite (also referred to as hexagonal diamond. It was identified from reflections (e.g., at 0.218, 0.193, and 0.150 nm), additional to those in diamond, that were indexed in terms of a hexagonal cell [1]. Lonsdaleite was attributed to shock-induced transformation of graphite within the iron meteorite upon impact [1, 2] and has subsequently been used as an indicator of shock and meteorite impact [3, 4, 5]. Given the importance of lonsdaleite, we reinvestigated the structure of the shock-formed diamond and lonsdaleite from the Canyon Diablo meteorite with an aberration-corrected ultra-high-resolution scanning transmission electron microscope (STEM), with the view of providing further insights into the shock-forming mechanism. The STEM images allowed direct structural interpretation at 0.1-nm resolution and showed that the samples consist of single-crystal and twinned diamond, as well as graphite intimately associated at the nanoscale. A characteristic feature of the STEM images is stacking faults and twins (111, 200, 113) that interrupt the regularity of the crystal structure. Uncommon, subnanometer-sized regions occur with two- and four-layer hexagonal symmetry, though these regions merge into diamond with stacking faults. Although we did not find lonsdaleite, the defects can give rise to extra reflections like those attributed to lonsdaleite. For example, the (113) diamond twin results in a 0.216-nm spacing that matches that of the broad 0.218-nm lonsdaleite peak. Our observations from Canyon Diablo provide a new understanding of shocked diamond structures and question the existence of lonsdaleite and its inferred geologic implication, although the abundance of diamond twinning and stacking faults may be indicative of shock metamorphism. [1] Frondel, C. & Marvin, U.B. (1967) Lonsdaleite, a hexagonal polymorph of diamond. Nature 217, 587-589. [2] Lipschutz, M. & Anders, E. (1961) The record in the meteorites-IV: Origin of diamonds in iron meteorites. Geochimica et Cosmochimica Acta 24, 83-105. [3] Kennet, D. J., Kennet, J. P., West, A., Mercer, C., Que Hee, S. S., Bement, L., Bunch, T. E., Sellers, M., & Wolbach, W. S. (2009) Nanodiamonds in the Younger Dryas boundary sediment layers. Science 323, 94. [4] Le Guillou, C., Rouzaud, J.N., Remusat, L., Jambon, A., & Bourot-Denise, M. (2010) Structures, origin and evolution of various carbon phases in the ureilite Northwest Africa 4742 compared with laboratory-shocked graphite. Geochimica Et Cosmochimica Acta 74(14), 4167-4185. [5] Hough, R.M., Gilmour, I., Pillinger, C.T., Arden, J.W., Gilkes, K.W.R., Yuan, J. & Milledge, H.J. (1995) Diamond and silicon carbide in an impact melt rock from the Ries impact crater. Nature 378, 41-44.

Structures, microfabrics and textures of the Cordilleran-type Rechnitz metamorphic core complex, Eastern Alps☆

PubMed Central

Cao, Shuyun; Neubauer, Franz; Bernroider, Manfred; Liu, Junlai; Genser, Johann

2013-01-01

Rechnitz window group represents a Cordilleran-style metamorphic core complex, which is almost entirely located within nearly contemporaneous Neogene sediments at the transition zone between the Eastern Alps and the Neogene Pannonian basin. Two tectonic units are distinguished within the Rechnitz metamorphic core complex (RMCC): (1) a lower unit mainly composed of Mesozoic metasediments, and (2) an upper unit mainly composed of ophiolite remnants. Both units are metamorphosed within greenschist facies conditions during earliest Miocene followed by exhumation and cooling. The internal structure of the RMCC is characterized by the following succession of structure-forming events: (1) blueschist relics of Paleocene/Eocene age formed as a result of subduction (D1), (2) ductile nappe stacking (D2) of an ophiolite nappe over a distant passive margin succession (ca. E–W to WNW–ESE oriented stretching lineation), (3) greenschist facies-grade metamorphism annealing dominant in the lower unit, and (4) ductile low-angle normal faulting (D3) (with mainly NE–SW oriented stretching lineation), and (5) ca. E to NE-vergent folding (D4). The microfabrics are related to mostly ductile nappe stacking to ductile low-angle normal faulting. Paleopiezometry in conjunction with P–T estimates yield high strain rates of 10− 11 to 10− 13 s− 1, depending on the temperature (400–350 °C) and choice of piezometer and flow law calibration. Progressive microstructures and texture analysis indicate an overprint of the high-temperature fabrics (D2) by the low-temperature deformation (D3). Phengitic mica from the Paleocene/Eocene high-pressure metamorphism remained stable during D2 ductile deformation as well as preserved within late stages of final sub-greenschist facies shearing. Chlorite geothermometry yields two temperature groups, 376–328 °C, and 306–132 °C. Chlorite is seemingly accessible to late-stage resetting. The RMCC underwent an earlier large-scale coaxial deformation accommodated by a late non-coaxial shear with ductile low-angle normal faulting, resulting in subvertical thinning in the extensional deformation regime. The RMCC was rapidly exhumed during ca. 23–18 Ma. PMID:27065502

Pre-stack depth Migration imaging of the Hellenic Subduction Zone

NASA Astrophysics Data System (ADS)

Hussni, S. G.; Becel, A.; Schenini, L.; Laigle, M.; Dessa, J. X.; Galve, A.; Vitard, C.

2017-12-01

In 365 AD, a major M>8-tsunamignic earthquake occurred along the southwestern segment of the Hellenic subduction zone. Although this is the largest seismic event ever reported in Europe, some fundamental questions remain regarding the deep geometry of the interplate megathrust, as well as other faults within the overriding plate potentially connected to it. The main objective here is to image those deep structures, whose depths range between 15 and 45 km, using leading edge seismic reflection equipment. To this end, a 210-km-long multichannel seismic profile was acquired with the 8 km-long streamer and the 6600 cu.in source of R/V Marcus Langseth. This was realized at the end of 2015, during the SISMED cruise. This survey was made possible through a collective effort gathering labs (Géoazur, LDEO, ISTEP, ENS-Paris, EOST, LDO, Dpt. Geosciences of Pau Univ). A preliminary processing sequence has first been applied using Geovation software of CGG, which yielded a post-stack time migration of collected data, as well as pre-stack time migration obtained with a model derived from velocity analyses. Using Paradigm software, a pre-stack depth migration was subsequently carried out. This step required some tuning in the pre-processing sequence in order to improve multiple removal, noise suppression and to better reveal the true geometry of reflectors in depth. This iteration of pre-processing included, the use of parabolic Radon transform, FK filtering and time variant band pass filtering. An initial velocity model was built using depth-converted RMS velocities obtained from SISMED data for the sedimentary layer, complemented at depth with a smooth version of the tomographic velocities derived from coincident wide-angle data acquired during the 2012-ULYSSE survey. Then, we performed a Kirchhoff Pre-stack depth migration with traveltimes calculated using the Eikonal equation. Velocity model were then tuned through residual velocity analyses to flatten reflections in common reflection point gathers. These new results improve the imaging of deep reflectors and even reveal some new features. We will present this work, a comparison with our previously obtained post-stack time migration, as well as some insights into the new geological structures revealed by the depth imaging.

Combined interpretation of 3D seismic reflection attributes for geothermal exploration in the Polish Basin using self-organizing maps

NASA Astrophysics Data System (ADS)

Bauer, Klaus; Pussak, Marcin; Stiller, Manfred; Bujakowski, Wieslaw

2014-05-01

Self-organizing maps (SOM) are neural network techniques which can be used for the joint interpretation of multi-disciplinary data sets. In this investigation we apply SOM within a geothermal exploration project using 3D seismic reflection data. The study area is located in the central part of the Polish basin. Several sedimentary target horizons were identified at this location based on fluid flow rate measurements in the geothermal research well Kompina-2. The general objective is a seismic facies analysis and characterization of the major geothermal target reservoir. A 3D seismic reflection experiment with a sparse acquisition geometry was carried out around well Kompina-2. Conventional signal processing (amplitude corrections, filtering, spectral whitening, deconvolution, static corrections, muting) was followed by normal-moveout (NMO) stacking, and, alternatively, by common-reflection-surface (CRS) stacking. Different signal attributes were then derived from the stacked images including root-mean-square (RMS) amplitude, instantaneous frequency and coherency. Furthermore, spectral decomposition attributes were calculated based on the continuous wavelet transform. The resulting attribute maps along major target horizons appear noisy after the NMO stack and clearly structured after the CRS stack. Consequently, the following SOM-based multi-parameter signal attribute analysis was applied only to the CRS images. We applied our SOM work flow, which includes data preparation, unsupervised learning, segmentation of the trained SOM using image processing techniques, and final application of the learned knowledge. For the Lower Jurassic target horizon Ja1 we derived four different clusters with distinct seismic attribute signatures. As the most striking feature, a corridor parallel to a fault system was identified, which is characterized by decreased RMS amplitudes and low frequencies. In our interpretation we assume that this combination of signal properties can be explained by increased fracture porosity and enhanced fluid saturation within this part of the Lower Jurassic sandstone horizon. Hence, we suggest that a future drilling should be carried out within this compartment of the reservoir.

Detailed Velocity and Density models of the Cascadia Subduction Zone from Prestack Full-Waveform Inversion

NASA Astrophysics Data System (ADS)

Fortin, W.; Holbrook, W. S.; Mallick, S.; Everson, E. D.; Tobin, H. J.; Keranen, K. M.

2014-12-01

Understanding the geologic composition of the Cascadia Subduction Zone (CSZ) is critically important in assessing seismic hazards in the Pacific Northwest. Despite being a potential earthquake and tsunami threat to millions of people, key details of the structure and fault mechanisms remain poorly understood in the CSZ. In particular, the position and character of the subduction interface remains elusive due to its relative aseismicity and low seismic reflectivity, making imaging difficult for both passive and active source methods. Modern active-source reflection seismic data acquired as part of the COAST project in 2012 provide an opportunity to study the transition from the Cascadia basin, across the deformation front, and into the accretionary prism. Coupled with advances in seismic inversion methods, this new data allow us to produce detailed velocity models of the CSZ and accurate pre-stack depth migrations for studying geologic structure. While still computationally expensive, current computing clusters can perform seismic inversions at resolutions that match that of the seismic image itself. Here we present pre-stack full waveform inversions of the central seismic line of the COAST survey offshore Washington state. The resultant velocity model is produced by inversion at every CMP location, 6.25 m laterally, with vertical resolution of 0.2 times the dominant seismic frequency. We report a good average correlation value above 0.8 across the entire seismic line, determined by comparing synthetic gathers to the real pre-stack gathers. These detailed velocity models, both Vp and Vs, along with the density model, are a necessary step toward a detailed porosity cross section to be used to determine the role of fluids in the CSZ. Additionally, the P-velocity model is used to produce a pre-stack depth migration image of the CSZ.

Structural Properties, Order–Disorder Phenomena, and Phase Stability of Orotic Acid Crystal Forms

PubMed Central

2016-01-01

Orotic acid (OTA) is reported to exist in the anhydrous (AH), monohydrate (Hy1), and dimethyl sulfoxide monosolvate (SDMSO) forms. In this study we investigate the (de)hydration/desolvation behavior, aiming at an understanding of the elusive structural features of anhydrous OTA by a combination of experimental and computational techniques, namely, thermal analytical methods, gravimetric moisture (de)sorption studies, water activity measurements, X-ray powder diffraction, spectroscopy (vibrational, solid-state NMR), crystal energy landscape, and chemical shift calculations. The Hy1 is a highly stable hydrate, which dissociates above 135 °C and loses only a small part of the water when stored over desiccants (25 °C) for more than one year. In Hy1, orotic acid and water molecules are linked by strong hydrogen bonds in nearly perfectly planar arranged stacked layers. The layers are spaced by 3.1 Å and not linked via hydrogen bonds. Upon dehydration the X-ray powder diffraction and solid-state NMR peaks become broader, indicating some disorder in the anhydrous form. The Hy1 stacking reflection (122) is maintained, suggesting that the OTA molecules are still arranged in stacked layers in the dehydration product. Desolvation of SDMSO, a nonlayer structure, results in the same AH phase as observed upon dehydrating Hy1. Depending on the desolvation conditions, different levels of order–disorder of layers present in anhydrous OTA are observed, which is also suggested by the computed low energy crystal structures. These structures provide models for stacking faults as intergrowth of different layers is possible. The variability in anhydrate crystals is of practical concern as it affects the moisture dependent stability of AH with respect to hydration. PMID:26741914

The nature of the structural phase transition from the hexagonal (4H) phase to the cubic (3C) phase of silver.

PubMed

Chakraborty, Indrani; Shirodkar, Sharmila N; Gohil, Smita; Waghmare, Umesh V; Ayyub, Pushan

2014-03-19

The phase transition from the hexagonal 4H polytype of silver to the commonly known 3C (fcc) phase was studied in detail using x-ray diffraction, electron microscopy, differential scanning calorimetry and Raman spectroscopy. The phase transition is irreversible and accompanied by extensive microstructural changes and grain growth. Detailed scanning and isothermal calorimetric analysis suggests that it is an autocatalytic transformation. Though the calorimetric data suggest an exothermic first-order phase transition with an onset at 155.6 °C (for a heating rate of 2 K min(-1)) and a latent heat of 312.9 J g(-1), the microstructure and the electrical resistance appear to change gradually from much lower temperatures. The 4H phase shows a Raman active mode at 64.3 cm(-1) (at 4 K) that undergoes mode softening as the 4H → 3C transformation temperature is approached. A first-principles density functional theory calculation shows that the stacking fault energy of 4H-Ag increases monotonically with temperature. That 4H-Ag has a higher density of stacking faults than 3C-Ag, implies the metastability of the former at higher temperatures. Energetically, the 4H phase is intermediate between the hexagonal 2H phase and the 3C ground state, as indicated by the spontaneous transformation of the 2H to the 4H phase at -4 °C. Our data appear to indicate that the 4H-Ag phase is stabilized at reduced dimensions and thermally induced grain growth is probably responsible for triggering the irreversible transformation to cubic Ag.

Prediction and characterization of an Mg-Al intermetallic compound with potentially improved ductility via orbital-free and Kohn-Sham density functional theory

NASA Astrophysics Data System (ADS)

Zhuang, Houlong L.; Chen, Mohan; Carter, Emily A.

2017-10-01

Magnesium-aluminum (Mg-Al) intermetallic compounds that form as precipitates can significantly influence the mechanical properties of Mg-Al alloys. A computational evaluation of known and unknown Mg-Al intermetallic compounds could help design new Mg-Al alloy microstructures with optimal properties. Here, we employ the cluster-expansion method with energies efficiently calculated with orbital-free density functional theory (OFDFT) and predict a new, metastable intermetallic compound Mg3Al with a D019 hexagonal structure that is slightly more stable than an alternative L12 cubic structure. We apply Kohn-Sham DFT (KSDFT) to accurately evaluate various metastability criteria for D019 and L12 Mg3Al, including Born’s criterion and phonon dispersion. We show that both Mg3Al crystalline phases satisfy the metastability criteria and hence should be at least metastable. We further compare ductility metrics for D019 and L12 Mg3Al to that of hexagonal-close-packed Mg by computing Pugh’s ratio and generalized stacking fault energies. The ductility is predicted to follow the order: D019 Mg3Al > L12 Mg3Al > Mg, based on the highest Pugh’s ratio and the lowest unstable stacking and twinning fault energies of D019 Mg3Al compared to that of Mg. We also predict a very low antiphase boundary energy for Mg3Al and therefore expect D019 Mg3Al to be beneficial for improving the ductility of Mg-rich Mg-Al alloys. A computational design of Mg-Al alloy microstructures may become possible by combining the strengths of both OFDFT and KSDFT, i.e., the efficiency of the former and the accuracy of the latter, as demonstrated here.

The key role of dislocation dissociation in the plastic behaviour of single crystal nickel-based superalloy with low stacking fault energy: Three-dimensional discrete dislocation dynamics modelling

NASA Astrophysics Data System (ADS)

Huang, Minsheng; Li, Zhenhuan

2013-12-01

To model the deformation of single crystal nickel based superalloys (SCNBS) with low stacking fault energy (SFE), three-dimensional discrete dislocation dynamics (3D-DDD) is extended by incorporating dislocation dissociation mechanism. The present 3D-DDD simulations show that, consistent with the existing TEM observation, the leading partial can enter the matrix channel efficiently while the trailing partial can hardly glide into it when the dislocation dissociation is taken into account. To determine whether the dislocation dissociation can occur or not, a critical percolation stress (CPS) based criterion is suggested. According to this CPS criterion, for SCNBS there exists a critical matrix channel width. When the channel width is lower than this critical value, the dislocation tends to dissociate into an extended configuration and vice versa. To clarify the influence of dislocation dissociation on CPS, the classical Orowan formula is improved by incorporating the SFE. Moreover, the present 3D-DDD simulations also show that the yielding stress of SCNBSs with low SFE may be overestimated up to 30% if the dislocation dissociation is ignored. With dislocation dissociation being considered, the size effect due to the width of γ matrix channel and the length of γ‧ precipitates on the stress-strain responses of SCNBS can be enhanced remarkably. In addition, due to the strong constraint effect by the two-phase microstructure in SCNBS, the configuration of formed junctions is quite different from that in single phase crystals such as Cu. The present results not only provide clear understanding of the two-phase microstructure levelled microplastic mechanisms in SCNBSs with low SFE, but also help to develop new continuum-levelled constitutive laws for SCNBSs.

Atomistic simulation study of influence of Al2O3-Al interface on dislocation interaction and prismatic loop formation during nano-indentation on Al2O3-coated aluminum.

PubMed

Mishra, Srishti; Meraj, Md; Pal, Snehanshu

2018-06-19

A large-scale molecular dynamics (MD) simulation of nano-indentation was carried out to provide insight into the influence of the Al-Al 2 O 3 interface on dislocation evolution and deformation behavior of Al substrate coated with Al 2 O 3 thin film. Adaptive common neighbor analysis (a-CNA), centro-symmetry parameter (CSP) estimation, and dislocation extraction algorithm (DXA) were implemented to represent structural evolution during nano-indentation deformation. The absence of elastic regime was observed in the P-h curve for this simulated nano-indentation test of Al 2 O 3 thin film coated Al specimen. The displacement of oxygen atoms from Al 2 O 3 to Al partly through the interface greatly influences the plastic deformation behavior of the specimen during nano-indentation. Prismatic dislocation loops, which are formed due to pinning of Shockley partials (1/6 < 112>) by Stair-rod (1/6 < 110>) and Hirth dislocation (1/3 < 001>), were observed in all cases studied in this work. Pile-up of atoms was also observed and the extent of the pile-up was found to vary with the test temperature. A distorted stacking fault tetrahedron (SFT) is formed when a nano-indentation test is carried out at 100 K. The presence of a prismatic dislocation loop, SFT and dislocation forest caused strain hardening and, consequently, there is an increase in hardness as indentation depth increases. Graphical abstract Figure illustrates nano-indentation model set up along with load vs. depth curve and distorted stacking fault tetrahedron.

Neogene evolution of northern Mahakam Delta, East Kalimantan, Indonesia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armin, R.A.; Abdoerrias, R.; Boer, W.D. de

1996-01-01

A regional sequence-stratigraphic study of the lower Kutei basin, embracing present coastal and offshore East Kalimantan, was undertaken to decipher the Neogene history of an important oil-producing province. The chronostratigraphic framework developed during this study was applied to facies analyses, organic geochemistry, and 2-D basin modeling. Integration of these disciplines powerfully illuminated the relationships between structuring, sedimentation, and hydrocarbon migration, Sedimentation in the lower Kutei basin since the late Middle Miocene has been dominated by the tidal-fluvial Mahakam delta system. During this time the principal river transport system has remained in about the same location as the present-day Mahakam River.more » Thick successions of monotonously similar deltaic facies were stacked vertically, punctuated by progradational or backstepping (flooding) units. Middle to Upper Miocene shelf edges of the delta platform, which are commonly sites of carbonate buildups, offlap from west to east towards the present-day shelf edge. Growth faults active during ca. 12-9 Ma are clustered just basinward of a prominent aggradational Middle Miocene shelf margin, and they exerted profound control on facies distribution. Tectonic quiescence prevailed during ca. 9-4 Ma, and in this period widespread regressive deltaic deposition over a broad, stable delta platform created the most important reservoirs. Subsequently, during Late Pliocene and younger time, many early growth faults were reactivated, and new faults also formed eastward toward the present shelf margin. Here, economically significant intervals consist mainly of lowstand deposits that accumulated in shelf-margin half-grabens created by these Plio-Pleistocene faults.« less

Neogene evolution of northern Mahakam Delta, East Kalimantan, Indonesia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Armin, R.A.; Abdoerrias, R.; Boer, W.D. de

1996-12-31

A regional sequence-stratigraphic study of the lower Kutei basin, embracing present coastal and offshore East Kalimantan, was undertaken to decipher the Neogene history of an important oil-producing province. The chronostratigraphic framework developed during this study was applied to facies analyses, organic geochemistry, and 2-D basin modeling. Integration of these disciplines powerfully illuminated the relationships between structuring, sedimentation, and hydrocarbon migration, Sedimentation in the lower Kutei basin since the late Middle Miocene has been dominated by the tidal-fluvial Mahakam delta system. During this time the principal river transport system has remained in about the same location as the present-day Mahakam River.more » Thick successions of monotonously similar deltaic facies were stacked vertically, punctuated by progradational or backstepping (flooding) units. Middle to Upper Miocene shelf edges of the delta platform, which are commonly sites of carbonate buildups, offlap from west to east towards the present-day shelf edge. Growth faults active during ca. 12-9 Ma are clustered just basinward of a prominent aggradational Middle Miocene shelf margin, and they exerted profound control on facies distribution. Tectonic quiescence prevailed during ca. 9-4 Ma, and in this period widespread regressive deltaic deposition over a broad, stable delta platform created the most important reservoirs. Subsequently, during Late Pliocene and younger time, many early growth faults were reactivated, and new faults also formed eastward toward the present shelf margin. Here, economically significant intervals consist mainly of lowstand deposits that accumulated in shelf-margin half-grabens created by these Plio-Pleistocene faults.« less

Imaging the Alpine Fault to depths of more than 2 km - Initial results from the 2011 WhataDUSIE seismic reflection profile, Whataroa Valley, New Zealand

NASA Astrophysics Data System (ADS)

Kovacs, A.; Gorman, A. R.; Buske, S.; Schmitt, D. R.; Eccles, J. D.; Toy, V. G.; Sutherland, R.; Townend, J.; Norris, R.; Pooley, B.; Cooper, J.; Bruce, C.; Smillie, M.; Bain, S.; Hellwig, O.; Hlousek, F.; Hellmich, J.; Riedel, M.; Schijns, H. M.

2011-12-01

The Alpine Fault is a major plate-bounding fault that is thought to fail in large earthquakes (Mw~7.9) every 200-400 years and to have last ruptured in AD 1717. It is the principal geological structure accommodating transpressional motion between the Australian and Pacific plates on the South Island, with a long-term horizontal motion over the last 1-2 million years of 21-27 mm/yr. Determining the Alpine Fault zone structure at depths of several kilometres beneath the Earth's surface is crucial for understanding not only what conditions govern earthquake rupture but also how ongoing faulting produces mountain ranges such as the Southern Alps. The valley of the Whataroa River, in the central sector of the Alpine Fault, provides rare access to the SE (hanging wall) side of the fault for the purpose of a seismic survey. During January and February 2011, a ~5-km-long seismic reflection line was collected that aimed to image the Alpine Fault at depth. The acquisition was undertaken with the use of 21 Geode seismographs and two Seistronix seismographs with a total capacity of 552 channels. Geophone spacing varied from 4 m in the north (close to the surface trace of the fault) to 8 m in the south (farther from the surface trace.) Sources were 400-g Pentex charges buried in 1.5-2.0 m deep holes of which ~100 were dug by an excavator and ~100 were dug by hand tools where heavy equipment could not access shot locations. Single shots had a nominal separation of 25 m at the north end of the line. At the south end of the line, shots were deployed in patterns of five with a nominal spacing of 125 m. Acquisition system requirements and surface morphology (meanders in the Whataroa River) required five separate acquisition systems. Timing of shots for these systems was accomplished with a radio-controlled firing system, GPS clocks linked to co-located Reftek seismographs, and overlapping traces between acquisition systems. Shot records have been merged and processed through to stacks using the GLOBE Claritas seismic processing package. Initial observations and interpretations of the data are presented. The hanging wall of the Alpine Fault beneath the Whataroa Valley contains at least two major units, a lower basement of Alpine Schist rocks overlain by a substantial layer of glacial sediments that are as much as 700 m thick in places. A sharp reflection marks the boundary between the two units. In places, the Alpine Fault is interpreted as a dipping reflection in the seismic data. The strength of the reflection varies, perhaps as a result of changes in the rocks of the footwall or changes in the geometry of the fault or fault zone.

Superresolution near-field imaging with surface waves

NASA Astrophysics Data System (ADS)

Fu, Lei; Liu, Zhaolun; Schuster, Gerard

2018-02-01

We present the theory for near-field superresolution imaging with surface waves and time reverse mirrors (TRMs). Theoretical formulae and numerical results show that applying the TRM operation to surface waves in an elastic half-space can achieve superresolution imaging of subwavelength scatterers if they are located less than about 1/2 of the shear wavelength from the source line. We also show that the TRM operation for a single frequency is equivalent to natural migration, which uses the recorded data to approximate the Green's functions for migration, and only costs O(N4) algebraic operations for post-stack migration compared to O(N6) operations for natural pre-stack migration. Here, we assume the sources and receivers are on an N × N grid and there are N2 trial image points on the free surface. Our theoretical predictions of superresolution are validated with tests on synthetic data. The field-data tests suggest that hidden faults at the near surface can be detected with subwavelength imaging of surface waves by using the TRM operation if they are no deeper than about 1/2 the dominant shear wavelength.

Detailed Northern Anatolian Fault Zone crustal structure from receiver functions

NASA Astrophysics Data System (ADS)

Cornwell, D. G.; Kahraman, M.; Thompson, D. A.; Houseman, G. A.; Rost, S.; Turkelli, N.; Teoman, U.; Altuncu Poyraz, S.; Gülen, L.; Utkucu, M.

2013-12-01

We present high resolution images derived from receiver functions of the continental crust in Northern Turkey that is dissected by two fault strands of the Northern Anatolian Fault Zone (NAFZ). The NAFZ is a major continental strike-slip fault system that is comparable in length and slip rate to the San Andreas Fault Zone. Recent large earthquakes occurred towards the western end of the NAFZ in 1999 at Izmit (M7.5) and Düzce (M7.2). As part of the multi-disciplinary Faultlab project, we aim to develop a model of NAFZ crustal structure and locate deformation by constraining variations in seismic properties and anisotropy in the upper and lower crust. The crustal model will be an input to test deformation scenarios in order to match geodetic observations from different phases of the earthquake loading cycle. We calculated receiver functions from teleseismic earthquakes recorded by a rectangular seismometer array spanning the NAFZ with 66 stations at a nominal inter-station spacing of 7 km and 7 additional stations further afield. This Dense Array for North Anatolia (DANA) was deployed from May 2012 until September 2013 and we selected large events (Mw>5.5) from the high quality seismological dataset to analyze further. Receiver functions were calculated for different frequency bands then collected into regional stacks before being inverted for crustal S-wave velocity structure beneath the entire DANA array footprint. In addition, we applied common conversion point (CCP) migration using a regional velocity model to construct a migrated 3D volume of P-to-S converted and multiple energy in order to identify the major crustal features and layer boundaries. We also performed the CCP migration with transverse receiver functions in order to identify regions of anisotropy within the crustal layers. Our preliminary results show a heterogeneous crust above a flat Moho that is typically at a depth of 33 km. We do not observe a prominent step in the Moho beneath the surface locations at either of the NAFZ fault branches. We observe first-order differences in crustal structure between the crustal blocks that are separated by the faults. Each crustal block also contains regions of strong anisotropy at various depths that will be analyzed further with the full seismological dataset and compared to petrofabric analyses of exhumed fault segments. We will compare our results with other seismological imaging techniques to attempt to resolve the distribution of fault zone deformation with respect to depth. This information will be useful to other complementary Faultlab techniques that will add a detailed insight into the fault structure and dynamics of the NAFZ and contribute more broadly into ongoing research into major strike-slip fault zones.

Structural short-range order of the β-Ti phase in bulk Ti-Fe-(Sn) nanoeutectic composites

NASA Astrophysics Data System (ADS)

Das, J.; Eckert, J.; Theissmann, R.

2006-12-01

The authors report lattice distortion and "ω-like" structural short-range order (SRO) of the β-Ti phase in a Ti-Fe-(Sn) bulk nanoeutectic composite prepared by slow cooling from the melt. The nanoeuetctic phases are chemically homogeneous, but the addition of Sn releases the local lattice strain, modifies the structural SRO, and prevents the formation of stacking faults in the body centered cubic (bcc) β-Ti phase resulting in improved plastic deformability. The elastic properties and the structural SRO of the β-Ti phase are proposed to be important parameters for developing advanced high strength, ductile Ti-base nanocomposite alloys.

Impact of temperature and nitrogen composition on the growth of GaAsPN alloys

NASA Astrophysics Data System (ADS)

Yamane, Keisuke; Mugikura, Shun; Tanaka, Shunsuke; Goto, Masaya; Sekiguchi, Hiroto; Okada, Hiroshi; Wakahara, Akihiro

2018-03-01

This paper presents the impact of temperature and nitrogen-composition on the growth mode and crystallinity of GaAsPN alloys. Reflection high-energy electron diffraction results combined with transmission electron microscopy analysis revealed that maintaining two-dimensional (2-D) growth required higher temperatures when nitrogen composition increased. Outside the 2-D growth windows, stacking faults and micro-twins were preferentially formed at {1 1 1} B planes rather than at the {1 1 1} A planes and anomalous growth was observed. The photoluminescence spectra of GaAsPN layers implies that the higher temperature growth is effective for reducing the nitrogen-related point defects.

Nanocrystalline copper films are never flat

NASA Astrophysics Data System (ADS)

Zhang, Xiaopu; Han, Jian; Plombon, John J.; Sutton, Adrian P.; Srolovitz, David J.; Boland, John J.

2017-07-01

We used scanning tunneling microscopy to study low-angle grain boundaries at the surface of nearly planar copper nanocrystalline (111) films. The presence of grain boundaries and their emergence at the film surface create valleys composed of dissociated edge dislocations and ridges where partial dislocations have recombined. Geometric analysis and simulations indicated that valleys and ridges were created by an out-of-plane grain rotation driven by reduction of grain boundary energy. These results suggest that in general, it is impossible to form flat two-dimensional nanocrystalline films of copper and other metals exhibiting small stacking fault energies and/or large elastic anisotropy, which induce a large anisotropy in the dislocation-line energy.

Transparently wrap-gated semiconductor nanowire arrays for studies of gate-controlled photoluminescence

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nylund, Gustav; Storm, Kristian; Torstensson, Henrik

2013-12-04

We present a technique to measure gate-controlled photoluminescence (PL) on arrays of semiconductor nanowire (NW) capacitors using a transparent film of Indium-Tin-Oxide (ITO) wrapping around the nanowires as the gate electrode. By tuning the wrap-gate voltage, it is possible to increase the PL peak intensity of an array of undoped InP NWs by more than an order of magnitude. The fine structure of the PL spectrum reveals three subpeaks whose relative peak intensities change with gate voltage. We interpret this as gate-controlled state-filling of luminescing quantum dot segments formed by zincblende stacking faults in the mainly wurtzite NW crystal structure.

Stability of vacancy-type defect clusters in Ni based on first-principles and molecular dynamics simulations

DOE PAGES

Zhao, Shijun; Zhang, Yanwen; Weber, William J.

2017-10-17

Using first-principles calculations based on density-functional theory, the energetics of different vacancy-type defects, including voids, stacking fault tetrahedra (SFT) and vacancy loops, in Ni are investigated. It is found that voids are more stable than SFT at 0 K, which is also the case after taking into account the volumetric strains. By carrying out ab initio molecular dynamics simulations at temperatures up to 1000 K, direct transformations from vacancy loops and voids into SFT are observed. Our results suggest the importance of temperature effects in determining thermodynamic stability of vacancy clusters in face-centered cubic metals.

Dislocation structures of Σ3 {112} twin boundaries in face centered cubic metals

NASA Astrophysics Data System (ADS)

Wang, J.; Anderoglu, O.; Hirth, J. P.; Misra, A.; Zhang, X.

2009-07-01

High resolution transmission electron microscopy of nanotwinned Cu films revealed Σ3 {112} incoherent twin boundaries (ITBs), with a repeatable pattern involving units of three {111} atomic planes. Topological analysis shows that Σ3 {112} ITBs adopt two types of atomic structure with differing arrangements of Shockley partial dislocations. Atomistic simulations were performed for Cu and Al. These studies revealed the structure of the two types of ITBs, the formation mechanism and stability of the associated 9R phase, and the influence of stacking fault energies on them. The results suggest that Σ3 {112} ITBs may migrate through the collective glide of partial dislocations.

Application of Oxidation to the Structural Characterization of Sic Epitaxial Films

NASA Technical Reports Server (NTRS)

Powell, J. A.; Petit, J. B.; Edgar, J. H.; Jenkins, I. G.; Matus, L. G.

1991-01-01

Both 3C-SiC and 6H-SiC single-crystal films can be grown on vicinal (0001) 6H-SiC wafers. It is found that oxidation can be a powerful diagnostic process for (1) 'color mapping' the 3C and 6H regions of these films, (2) decorating stacking faults in the films, (3) enhancing the decoration of double positioning boundaries, and (4) decorating polishing damage. Contrary to previously published oxidation results, proper oxidation conditions can yield interference colors that provide a definitive map of the polytype distribution for both the Si face and C face of SiC films.

Structure of Suasselkä Postglacial Fault in northern Finland obtained by analysis of ambient seismic noise

NASA Astrophysics Data System (ADS)

Afonin, Nikita; Kozlovskaya, Elena

2016-04-01

Understanding inner structure of seismogenic faults and their ability to reactivate is particularly important in investigating the continental intraplate seismicity regime. In our study we address this problem using analysis of ambient seismic noise recorded by the temporary DAFNE array in northern Fennoscandian Shield. The main purpose of the DAFNE/FINLAND passive seismic array experiment was to characterize the present-day seismicity of the Suasselkä post-glacial fault (SPGF) that was proposed as one potential target for the DAFNE (Drilling Active Faults in Northern Europe) project. The DAFNE/FINLAND array comprised the area of about 20 to 100 km and consisted of 8 short-period and 4 broad-band 3-component autonomous seismic stations installed in the close vicinity of the fault area. The array recorded continuous seismic data during September, 2011-May, 2013. Recordings of the array have being analyzed in order to identify and locate natural earthquakes from the fault area and to discriminate them from the blasts in the Kittilä Gold Mine. As a result, we found several dozens of natural seismic events originating from the fault area, which proves that the fault is still seismically active. In order to study the inner structure of the SPGF we use cross-correlation of ambient seismic noise recorded by the array. Analysis of azimuthal distribution of noise sources demonstrated that that during the time interval under consideration the distribution of noise sources is close to the uniform one. The continuous data were processed in several steps including single station data analysis, instrument response removal and time-domain stacking. The data were used to estimate empirical Green's functions between pairs of stations in the frequency band of 0.1-1 Hz and to calculate correspondent surface wave dispersion curves. After that S-wave velocity models were obtained as a result of dispersion curves inversion using Geopsy software. The results suggest that the area of the SPGF corresponds to a narrow region of low S-wave velocities surrounded by rocks with high S-wave velocities. We interpret this low velocity region as a non-healed mechanically weak fault damage zone (FDZ) remained after the last major earthquake that occurred after the last glaciation. Seismic instruments for the DAFNE/FINLAND experiment were provided by the institute of Seismology of the University of Helsinki and by the Sodankylä Geophysical Observatory. The study was partly funded by Posiva Oy and Geological Survey of Finland. DAFNE/FINLAND Working Group: Ilmo Kukkonen Pekka Heikkinen Kari Komminaho Elena Kozlovskaya Riitta Hurskainen Tero Raita Hanna Silvennoinen

Morphology and tectonics of the Andaman Forearc, northeastern Indian Ocean

NASA Astrophysics Data System (ADS)

Cochran, James R.

2010-08-01

The Andaman Sea has developed as the result of highly oblique subduction at the western Sunda Trench, leading to partitioning of convergence into trench-perpendicular and trench-parallel components and the formation of a northward-moving sliver plate to accommodate the trench parallel motion. The Andaman forearc contains structures resulting from both components of motion. The main elements of the forearc are the accretionary prism and outerarc ridge, a series of forearc basins and major N-S faults. The accretionary prism is an imbricate stack of fault slices and folds consisting of ophiolites and sediments scrapped off the subducting Indian Plate. The western, outer slope of the accretionary prism is very steep, rising to depths of 1500-2000 m within a distance of 30 km. There is a difference in the short wavelength morphology between the western and eastern portions of the accretionary prism. The outer portion consists of a series of faulted anticlines and synclines with amplitudes of a few 100 to ~1000 m and widths of 5-15 km resulting from ongoing deformation of the sediments. The inner portion is smoother with lower slopes and forms a strong backstop. The width of the deforming portion of the accretionary prism narrows from 80 to 100 km in the south to about 40 km between 10°N and 11° 30'N. It remains at about 40 km to ~14°40'N. North of there, the inner trench wall becomes a single steep slope up to the Myanmar shelf. The eastern edge of the outerarc ridge is fault bounded and, north of the Nicobar Islands, a forearc basin is located immediately to the east. A deep gravity low with very steep gradients lies directly over the forearc basin. The West Andaman Fault (WAF) and/or the Seulimeum strand of the Sumatra Fault System form the boundary between the Burma and Sunda plates south of the Andaman spreading centre. The WAF is the most prominent morphologic feature of the Andaman Sea and divides the sea into a shallow forearc and a deeper backarc region. The Diligent Fault runs through the forearc basin east of Little Andaman Island. Although it has the general appearance of a normal fault, multichannel seismic data show that it is a compressional feature that probably resulted from deformation of the hanging wall of the Eastern Margin Fault. This could occur if the forearc basins were formed by subduction erosion of the underlying crust rather than by east-west extension.

The Seismic Stratigraphic Record of Quaternary Deformation Across the North Anatolian Fault System in Southern Marmara Sea, Turkey

NASA Astrophysics Data System (ADS)

Sorlien, C. C.; Seeber, L.; Diebold, J.; Shillington, D.; Steckler, M. S.; Gurcay, S.; Kucuk, H. M.; Akhun, S. D.; Timur, D.; Dondurur, D.; Kurt, H.; Perincek, E.; Ozer, P.; Imren, C.; Coskun, S.; Buyukasik, E.; Cevatoglu, M.; Cifci, G.; Demirbag, E.

2008-12-01

We collected high-resolution multichannel seismic reflection (MCS) and chirp seismic data across the North Anatolian Fault (NAF) system in the Marmara Sea aboard the R/V K. Piri Reis during July 2008. Three 1200+ m-deep bathymetric basins are arrayed along the North strand of the NAF. This strand passes closest to Istanbul and is considered to carry most of the current and late Holocene plate motion, but other strands to the south are active and may have been more important in the past. The transverse Central Marmara Ridge, formed by a contractional anticline, separates two of the basins. Filled sedimentary basins underlie the southern shelf, and, adjacent to that shelf, the partly-filled North Imrali basin underlies a 400 m-deep platform. Our chirp data image several strands of the southern fault system, 50 km south of the northern NAF on the inner (southern) shelf, that offset strata which postdate the ~12 ka marine transgression. Another W-striking fault that deforms post-12 ka strata cuts the mid-southern shelf. A WNW-striking segment of the Imrali fault system is associated with normal-separation, 300 m-high sea floor scarps that separate the shelf from the North Imrali basin. This basin is cut by numerous NW-striking normal-separation faults, some deforming the sea floor. At least 4 complexes of shelf edge deltas, whose tops were formed near sea level or lake level, are stacked between 500 and 900 m depth in this downthrown block of the Imrali fault. The originally sub- horizontal tops of each delta are now locally progressively tilted and folded near an ENE-striking branch of the Imrali fault (known as the Yalova fault). Lacking stratigraphic control, we infer that the deltas represent glacial intervals spaced at 100 ka during the late Pleistocene. Assuming a locally constant subsidence rate, with lowstands near -90 m, and the observed 130 m vertical spacing between the deltas, subsidence rates would be ~1.3 mm/yr, and the youngest well-preserved delta would be ~320 ka (MIS10). Alternatively, it corresponds to the pronounced 420 ka glacial (MIS12). Younger deltas did not form in this area, at least not with prograding geometries, because the water depth became too great. Possibly, outer shelf anticlinal growth may have diverted the river westward, where younger deltas are preserved on the shelf. The slope between the 400 m platform and the lower flank of the NE-trending Central Marmara Ridge is dominated by north-trending and northeast-trending 1 km-wavelength folds. These folds grew through the late Quaternary interval of deposition of the imaged deltas, and they deform the seafloor. They could be secondary shortening structures, forced folds above blind normal faults, or both. Farther east along the same slope, low-angle normal faults also grew through much of late Quaternary time. These faults root above unfaulted strata, and represent a slow collapse of the escarpment into the deep basin. NE-trending thrust- folds, NW-striking normal faults, WNW-striking transtensional faults, and ENE-striking transpressional faults are all consistent with the E-W right-lateral continental transform fault system.

Deformation Measurement In The Hayward Fault Zone Using Partially Correlated Persistent Scatterers

NASA Astrophysics Data System (ADS)

Lien, J.; Zebker, H. A.

2013-12-01

Interferometric synthetic aperture radar (InSAR) is an effective tool for measuring temporal changes in the Earth's surface. By combining SAR phase data collected at varying times and orbit geometries, with InSAR we can produce high accuracy, wide coverage images of crustal deformation fields. Changes in the radar imaging geometry, scatterer positions, or scattering behavior between radar passes causes the measured radar return to differ, leading to a decorrelation phase term that obscures the deformation signal and prevents the use of large baseline data. Here we present a new physically-based method of modeling decorrelation from the subset of pixels with the highest intrinsic signal-to-noise ratio, the so-called persistent scatters (PS). This more complete formulation, which includes both phase and amplitude scintillations, better describes the scattering behavior of partially correlated PS pixels and leads to a more reliable selection algorithm. The new method identifies PS pixels using maximum likelihood signal-to-clutter ratio (SCR) estimation based on the joint interferometric stack phase-amplitude distribution. Our PS selection method is unique in that it considers both phase and amplitude; accounts for correlation between all possible pairs of interferometric observations; and models the effect of spatial and temporal baselines on the stack. We use the resulting maximum likelihood SCR estimate as a criterion for PS selection. We implement the partially correlated persistent scatterer technique to analyze a stack of C-band European Remote Sensing (ERS-1/2) interferometric radar data imaging the Hayward Fault Zone from 1995 to 2000. We show that our technique achieves a better trade-off between PS pixel selection accuracy and network density compared to other PS identification methods, particularly in areas of natural terrain. We then present deformation measurements obtained by the selected PS network. Our results demonstrate that the partially correlated persistent scatterer technique can attain accurate deformation measurements even in areas that suffer decorrelation due to natural terrain. The accuracy of phase unwrapping and subsequent deformation estimation on the spatially sparse PS network depends on both pixel selection accuracy and the density of the network. We find that many additional pixels can be added to the PS list if we are able to correctly identify and add those in which the scattering mechanism exhibits partial, rather than complete, correlation across all radar scenes.

An advanced SEU tolerant latch based on error detection

NASA Astrophysics Data System (ADS)

Xu, Hui; Zhu, Jianwei; Lu, Xiaoping; Li, Jingzhao

2018-05-01

This paper proposes a latch that can mitigate SEUs via an error detection circuit. The error detection circuit is hardened by a C-element and a stacked PMOS. In the hold state, a particle strikes the latch or the error detection circuit may cause a fault logic state of the circuit. The error detection circuit can detect the upset node in the latch and the fault output will be corrected. The upset node in the error detection circuit can be corrected by the C-element. The power dissipation and propagation delay of the proposed latch are analyzed by HSPICE simulations. The proposed latch consumes about 77.5% less energy and 33.1% less propagation delay than the triple modular redundancy (TMR) latch. Simulation results demonstrate that the proposed latch can mitigate SEU effectively. Project supported by the National Natural Science Foundation of China (Nos. 61404001, 61306046), the Anhui Province University Natural Science Research Major Project (No. KJ2014ZD12), the Huainan Science and Technology Program (No. 2013A4011), and the National Natural Science Foundation of China (No. 61371025).

Understanding checkpointing overheads on massive-scale systems : analysis of the IBM Blue Gene/P system.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, R.; Naik, H.; Beckman, P.

Providing fault tolerance in high-end petascale systems, consisting of millions of hardware components and complex software stacks, is becoming an increasingly challenging task. Checkpointing continues to be the most prevalent technique for providing fault tolerance in such high-end systems. Considerable research has focussed on optimizing checkpointing; however, in practice, checkpointing still involves a high-cost overhead for users. In this paper, we study the checkpointing overhead seen by various applications running on leadership-class machines like the IBM Blue Gene/P at Argonne National Laboratory. In addition to studying popular applications, we design a methodology to help users understand and intelligently choose anmore » optimal checkpointing frequency to reduce the overall checkpointing overhead incurred. In particular, we study the Grid-Based Projector-Augmented Wave application, the Carr-Parrinello Molecular Dynamics application, the Nek5000 computational fluid dynamics application and the Parallel Ocean Program application-and analyze their memory usage and possible checkpointing trends on 65,536 processors of the Blue Gene/P system.« less

A Viscoplastic Stress Relaxation Model for Predicting Variations of the Least Principal Stress With Depth in Unconventional Reservoirs

NASA Astrophysics Data System (ADS)

Zoback, M. D.; Xu, S.; Rassouli, F.; Ma, X.

2016-12-01

In this paper we extend the viscoplastic stress relaxation model of Sone and Zoback (Jour. Petrol. Sci. and Eng., 2014) for predicting variations of least principal stress with stress and its impact on the vertical propagation of hydraulic fractures. Viscoplastic stress relaxation in clay-rich (or diagenetically immature) sedimentary rocks makes the stress field more isotropic. In normal faulting and strike-slip faulting environments, this causes the least principal stress to increase making such formations likely barriers to vertical hydraulic fracture growth. In order to predict the magnitude of viscoplastic stress relaxation in different unconventional formations, we generalize a constitutive law developed from a wide range of creep experiments in our lab over the past several years and apply it to areas of stacked pay in Oklahoma and Texas. Using frac gradients were measured from minifrac and DFIT (Diagnostic Fracture Injection Test) experiments. The viscoplastic model does a good job of explaining vertical hydraulic fracture propagation, as indicated by the distribution of microseismic events recorded during stimulation.

From 2012 HAITI-SIS Survey: thick-skin versus thin-skin tectonics partitioned along offshore strike-slip Faults-Haïti

NASA Astrophysics Data System (ADS)

Ellouz, N.; Leroy, S. D.; Momplaisir, R.; Mercier de Lepinay, B.

2013-12-01

The characterization of the deformation along large strike-slip fault-systems like transpressive boundaries between N. Caribbean/N America is a challenging topic, which requires a multi-scale approach. Thanks to Haiti-sis new data, the precise description of the fault segmentation pattern, the sedimentogical distribution, the uplift/subsidence rates, the along-fault and intra-basin fluids circulations, allows to actualize the evolution of the deformation history up to present-day . All the co-seismic surface to near-surface events, have to be also identified in order to integrate geophysical solutions for the earthquake, within the present-day geological and structural pattern. These two approaches, ranging from geological to instantaneous time-scales have been used during multi-tools Haiti-Sis oceanographic survey, allowing to document and image these different aspects at a large scale. The complex strike-slip North Caribbean boundary registered significative stress partitioning. Oblique convergence is expressed by along-strike evolution; from rifted segments (Cayman Through) to transpressive ones (Haiti, Dominican Rep.), to subduction (Porto Rico). In the Haiti-Sis survey, we acquired new offshore data surrounding the active fault areas, in the Gonâve Bay, the Jamaica Channel and along Southern Peninsula. Mapping the sea-floor, and HR seismic acquisition were our main objectives, in order to characterize the fault and fold architecture, with a new delineation of active segments. Offshore piston cores, have been used as representative of the modern basin sedimentation, and to document the catastrophic events (earthquakes, massive flood or sudden destabilization of the platform ) represented by turbiditic or mass-flow sequences, with the objective to track the time recurrence of seismic events by dating some of these catastrophic sediment deposition. At surface, the other markers of the fault activity are linked with along-fault permeability and fluid circulation pathway changes. Geochemical signature and temperature of the fluids and gas, change drastically depending on location and depth provenance. Our first results show that 1) the present-day EPGF geometry results from oblique shortening processes along different segments of the fault. Deep basins previously localized south and north of the fault are inverted at different degrees, 2) the Gonâve Island is only the emerged part of a NW-SE, either growing large " anti-formal stack" or basement inversion responsible for the large present-day fold amplitude, or both of them successively. It separates two sub-basins South and North Gonâve with independant sedimentary and deformation evolution 3) the Jeremie Basin probably has a specific long-living evolution, allowing to precise the geodynamic evolution of the Western Hispaniola Margin.

Constraints on Shallow Crustal Structure across the San Andreas Fault Zone, Coachella Valley, Southern California: Results from the Salton Seismic Imaging Project (SSIP)

NASA Astrophysics Data System (ADS)

Hernandez, A.; Persaud, P.; Bauer, K.; Stock, J. M.; Fuis, G. S.; Hole, J. A.; Goldman, M.

2015-12-01

The strong influence of basin structure and crustal heterogeneities on seismic wave propagation suggests that these factors should be included in calculations of strong ground shaking. Knowledge of the shallow subsurface is thus essential for an accurate seismic hazard estimate for the densely populated Coachella Valley, the region north of the potential M7.8 rupture near the Salton Sea. Using SSIP data, we analyzed first arrivals from nine 65-911 kg explosive shots recorded along a profile in the Coachella Valley in order to evaluate the interpretation of our 2D tomographic results and give added details on the structural complexity of the shallow crust. The line extends 37 km from the Peninsular Ranges to the Little San Bernardino Mountains crossing the major strands of the San Andreas Fault Zone. We fit traveltime curves to our picks with forward modeling ray tracing, and determined 1D P-wave velocity models for traveltime arrivals east and west of each shot, and a 2D model for the line. We also inferred the geometry of near-vertical faults from the pre-stack line migration method of Bauer et al. (2013). In general, the 1D models east of individual shots have deeper basement contacts and lower apparent velocities, ~5 km/s at 4 km depth, whereas the models west of individual shots have shallower basement and velocities up to 6 km/s at 2 km depth. Mismatches in basement depths (assuming 5-6 km/s) between individual 1D models indicate a shallowly dipping basement, deepening eastward towards the Banning Fault and shoaling abruptly farther east. An east-dipping structure in the 2D model also gives a better fit than horizontal layers. Based on high velocity zones derived from traveltimes at 9-20 km from the western end of the line, we included an offset from ~2 km to 4 km depth near the middle of the line, which significantly improved the 2D model fit. If fault-related, this offset could represent the Garnet Hill Fault if it continues southward in the subsurface.

Dual-vergence structure from multiple migration of widely spaced OBSs

NASA Astrophysics Data System (ADS)

Yelisetti, Subbarao; Spence, George D.; Scherwath, Martin; Riedel, Michael; Klaeschen, Dirk

2017-10-01

The detailed structure of the northern Cascadia basin and frontal ridge region was obtained using data from several widely spaced ocean bottom seismometers (OBSs). Mirror imaging was used in which the downgoing multiples (mirror signal) are migrated as they provide information about a much larger area than imaging with primary signal alone. Specifically, Kirchhoff time migration was applied to hydrophone and vertical geophone data. Our results indicate remarkable structures that were not observed on the northern Cascadia margin in previous single-channel or multi-channel seismic (MCS) data. Results show that, in these water depths (2.0-2.5 km), an OBS can image up to 5 km on either side of its position on the seafloor and hence an OBS spacing of 5 km is sufficient to provide a two-fold migration stack. Results also show the top of the igneous oceanic crust at 5-6 km beneath the seafloor using only a small airgun source (120 in.3). Specifically, OBS migration results clearly show the continuity of reflectors which enabled the identification of frontal thrusts and a main thrust fault. These faults indicate, for the first time on this margin, the presence of a dual-vergence structure. These kinds of structures have so far been observed in < 0.5% of modern convergent margins and could be related to horizontal compression associated with subduction and low basal shear stress resulting from over-pressure. Reanalysis of previous MCS data from this region augmented the OBS migration results and further suggests that the vergence switches from seaward to landward around central Vancouver Island. Furthermore, fault geometry analyses indicate that the total amount of shortening accommodated due to faulting and folding is about 3 km, which suggest that thrusting would have started at least ∼ 65 ky ago.

Intelligent condition monitoring method for bearing faults from highly compressed measurements using sparse over-complete features

NASA Astrophysics Data System (ADS)

Ahmed, H. O. A.; Wong, M. L. D.; Nandi, A. K.

2018-01-01

Condition classification of rolling element bearings in rotating machines is important to prevent the breakdown of industrial machinery. A considerable amount of literature has been published on bearing faults classification. These studies aim to determine automatically the current status of a roller element bearing. Of these studies, methods based on compressed sensing (CS) have received some attention recently due to their ability to allow one to sample below the Nyquist sampling rate. This technology has many possible uses in machine condition monitoring and has been investigated as a possible approach for fault detection and classification in the compressed domain, i.e., without reconstructing the original signal. However, previous CS based methods have been found to be too weak for highly compressed data. The present paper explores computationally, for the first time, the effects of sparse autoencoder based over-complete sparse representations on the classification performance of highly compressed measurements of bearing vibration signals. For this study, the CS method was used to produce highly compressed measurements of the original bearing dataset. Then, an effective deep neural network (DNN) with unsupervised feature learning algorithm based on sparse autoencoder is used for learning over-complete sparse representations of these compressed datasets. Finally, the fault classification is achieved using two stages, namely, pre-training classification based on stacked autoencoder and softmax regression layer form the deep net stage (the first stage), and re-training classification based on backpropagation (BP) algorithm forms the fine-tuning stage (the second stage). The experimental results show that the proposed method is able to achieve high levels of accuracy even with extremely compressed measurements compared with the existing techniques.

Splay Fault Branching from the Hikurangi Subduction Shear Zone: Implications for Slow Slip and Fluid Flow

NASA Astrophysics Data System (ADS)

Henrys, S. A.; Plaza-Faverola, A. A.; Pecher, I. A.; Klaeschen, D.; Wallace, L.

2016-12-01

Seismic reflection data along the East Coast of the New Zealand North Island are used to map the offshore character and geometry of the central Hikurangi subduction thrust and outer wedge in a region of short term ( 2-3 weeks duration) geodetically determined slow-slip events (SSEs). Pre-stack depth migration of line 05CM-38 was used to derive subducting slab geometry and upper crustal structure together with a Vp image of the crust that is resolved to 14 km depth. The subduction interface is a shallow dipping thrust at < 7 km deep near the trench and steps down to 14 km depth along an approximately 18 km long ramp, beneath Porangahau Ridge. This bend in the subducted plate is associated with splay fault branching and coincides with the zone of maximum slip (90 mm) inferred on the subduction interface during slow slip events in June and July 2011. We infer that the step down in the décollement transfers slip on the plate interface from the top of subducting sediments to the oceanic crust and drives underplating beneath the inner margin of central Hikurangi margin. Low-velocity subducting sediments (LVZ) beneath the plate interface, updip of the plate interface ramp, are interpreted as being capped with a low permeability condensed layer of chalk and interbedded mudstones. We interpret this LVZ as fluid-rich overpressured sediments that have been displaced and later imbricated by splay faults in a region that may mark the up-dip transition from seismic to aseismic behavior. Further, we hypothesize that fluids derived from the overpressured sediment are channeled along splay faults to the shallow sub-seafloor near Porangahau Ridge where seafloor seepage and an upwarping of the gas hydrate Bottom-Simulating Reflector have been documented.

Observation of ‘hidden’ planar defects in boron carbide nanowires and identification of their orientations

PubMed Central

2014-01-01

The physical properties of nanostructures strongly depend on their structures, and planar defects in particular could significantly affect the behavior of the nanowires. In this work, planar defects (twins or stacking faults) in boron carbide nanowires are extensively studied by transmission electron microscopy (TEM). Results show that these defects can easily be invisible, i.e., no presence of characteristic defect features like modulated contrast in high-resolution TEM images and streaks in diffraction patterns. The simplified reason of this invisibility is that the viewing direction during TEM examination is not parallel to the (001)-type planar defects. Due to the unique rhombohedral structure of boron carbide, planar defects are only distinctive when the viewing direction is along the axial or short diagonal directions ([100], [010], or 1¯10) within the (001) plane (in-zone condition). However, in most cases, these three characteristic directions are not parallel to the viewing direction when boron carbide nanowires are randomly dispersed on TEM grids. To identify fault orientations (transverse faults or axial faults) of those nanowires whose planar defects are not revealed by TEM, a new approach is developed based on the geometrical analysis between the projected preferred growth direction of a nanowire and specific diffraction spots from diffraction patterns recorded along the axial or short diagonal directions out of the (001) plane (off-zone condition). The approach greatly alleviates tedious TEM examination of the nanowire and helps to establish the reliable structure–property relations. Our study calls attention to researchers to be extremely careful when studying nanowires with potential planar defects by TEM. Understanding the true nature of planar defects is essential in tuning the properties of these nanostructures through manipulating their structures. PMID:24423258

Observation of 'hidden' planar defects in boron carbide nanowires and identification of their orientations.

PubMed

Guan, Zhe; Cao, Baobao; Yang, Yang; Jiang, Youfei; Li, Deyu; Xu, Terry T

2014-01-15

The physical properties of nanostructures strongly depend on their structures, and planar defects in particular could significantly affect the behavior of the nanowires. In this work, planar defects (twins or stacking faults) in boron carbide nanowires are extensively studied by transmission electron microscopy (TEM). Results show that these defects can easily be invisible, i.e., no presence of characteristic defect features like modulated contrast in high-resolution TEM images and streaks in diffraction patterns. The simplified reason of this invisibility is that the viewing direction during TEM examination is not parallel to the (001)-type planar defects. Due to the unique rhombohedral structure of boron carbide, planar defects are only distinctive when the viewing direction is along the axial or short diagonal directions ([100], [010], or 1¯10) within the (001) plane (in-zone condition). However, in most cases, these three characteristic directions are not parallel to the viewing direction when boron carbide nanowires are randomly dispersed on TEM grids. To identify fault orientations (transverse faults or axial faults) of those nanowires whose planar defects are not revealed by TEM, a new approach is developed based on the geometrical analysis between the projected preferred growth direction of a nanowire and specific diffraction spots from diffraction patterns recorded along the axial or short diagonal directions out of the (001) plane (off-zone condition). The approach greatly alleviates tedious TEM examination of the nanowire and helps to establish the reliable structure-property relations. Our study calls attention to researchers to be extremely careful when studying nanowires with potential planar defects by TEM. Understanding the true nature of planar defects is essential in tuning the properties of these nanostructures through manipulating their structures.

Receiver function analysis of the Texas Gulf Coast to better understand the Ouachita Orogeny, opening of the Gulf of Mexico, and current state of the southern margin of North America

NASA Astrophysics Data System (ADS)

Knuppel, M.; Pratt, K. W.; Evanzia, D.; Gurrola, H.; Pulliam, J.

2012-12-01

For the past two years, Texas Tech and Baylor universities have been operating 21 broadband seismic stations extending from Matagorda Island, crossing the Gulf Coast plain and Balcones fault, ending in the middle of the Llano Uplift at Johnson City, Texas. The goal of this project is to image the basement to better understand the opening of the Gulf of Mexico (GOM) and the stabilization of the southern lithosphere of North America. In this presentation we will present preliminary results of receiver function analysis of data recorded by our broadband array. Using 18 months' of data we performed common conversion point (CCP) stack imaging of the crust and lithosphere along the profile and have produced a cross section showing receiver function derived Vp/Vs ratios along the profile. The strongest phase on the CCP stack is the Ps phase from the base of a 15 to 20-km-deep (at the shoreline) sedimentary basin that shallows to approximately 1 km deep at the Balcones fault. Vp/Vs analysis shows that this sedimentary unit has Vp/Vs ratios between 1.9 and 2.0. This unusually high Vp/Vs ratio is consistent with the basin being dominated by poorly consolidated, relatively young clastic sediment. This layer pinches out to the northwest. No clear Ps phase is observed from base of the Mesozoic carbonates and Ouachita-related sediments that we believe is several kilometers thick, based on observed Vp/Vs ratios of 1.85 to 1.9 (which is more consistent with carbonate rock than granitic basement). The pattern of Vp/Vs implies near-vertical, crust-wide displacement along the Balcones Fault. The Moho appears to be 15 to 20 km deep near the ocean but descends to more than 40 km beneath the Llano uplift. There is a strong Ps phase from about 70 km depth near the coastline that we interpret as remnant depleted mantle from the rifting of the GOM. The region between this P70s phase and the Moho appear to have a low Vp/Vs ratio (~1.75), which would be consistent with mantle depleted in iron as a result of rifting during the opening of the Gulf of Mexico.