Steady-state solutions of rupture propagation in an earthquake simulator governed by rate and state dependent friction

Earthquake simulators become increasingly important with respect to seismic hazard assessment. It is, therefore, a crucial question whether the imposed simplifications, e.g. reducing fully dynamic to quasi-dynamic rupture propagation, may lead to unrealistic results. In the present study, we focus on the role of rupture velocity v _r in an earthquake simulator governed by rate-and-state dependent friction as proposed by [8]. In particular, we investigate the range of possible values of v _r within the model. As an end-member scenario, we consider the existence of a steady-state solution of a one-dimensional rupture front propagating with v _r on an idealized two-dimensional fault of infinite dimension discretized into uniform cells. We find that, in principle, values of v _r between 0 and ∞ are possible depending on the values of slip speed δ₀ and pre-stress τ₀ ahead of the rupture front. In this view, values of δ₀ close to the slip speed during an earthquake δ _EQ lead to small values of the time-to-failure and can thus generate ruptures with unrealistic high values of v _r , if the model is close to the steady-state conditions. These results are useful to provide constraints for the parameter space of a reasonable earthquake simulator.     

Auger-induced rearrangement of an ion-bombarded/SiO2 surface: Influence of electron energy

Ion bombardment of SiO₂ produces an understoichiometric surface layer containing a distribution of bonding states: SiO₂, SiO _x and free Si. Under the electron beam probe, a redistribution occurs, favoring the SiO₂ and free Si states at the expense of SiO _x , without loss of oxygen. The free Si yield exhibits the same energy dependence as the Auger yield of the Si LVV transition, thus pointing to Auger-induced bond rupture as the primary damaging event.     

A density functional theory study of formaldehyde adsorption and oxidation on CeO2(1 1 1) surface

The effects of different oxygen species and vacancies on the adsorption and oxidation of formaldehyde over CeO₂(1 1 1) surface were systematically investigated by using density functional theory (DFT) method. On the stoichiometric CeO₂(1 1 1) surface, the C-H bond rupture barriers of chemisorbed formaldehyde are much higher than that of formaldehyde desorption. On the reduced CeO₂(1 1 1) surface, the energy barriers of C-H bond ruptures are less than those on the stoichiometric CeO₂(1 1 1) surface. If the C-H bond rupture occurs, CO and H₂ form quickly with low energy barriers. When O₂ adsorbs on the reduced (1 1 1) surface (O₂/O_v species), the C-H bond rupture barriers of formaldehyde are greatly reduced in comparison with those on the stoichiometric CeO₂(1 1 1) surface. If O₂ adsorbs on oxygen vacancy at sub-layer surface, its oxidative roles on formaldehyde are much similar to that of O₂/O_v species.     

The Decomposition of Methane,Ethane, Ethylene and n-Butane in Electrical Discharges of Moderate Pressures

The decomposition of CH₄, C₂H₆, C₂H₄, and n-C₄H₁₀ has been investigated in radiofrequency plasmas operated at power levels of 1–8 cal cm^?3 sec^?1, 10–40 torr and flow rates of the hydrocarbons between 2 and 20 1 (STP) min^?1. It is shown that values of the rate constants are very close for all the hydrocarbons investigated and several orders of magnitude greater than those observed in their pyrolisis at comparable gas temperatures. Energy yields up to 30% can be observed for all hydrocarbons. It is suggested that the rate determining step for the decomposition process of all hydrocarbons investigated involves the rupture of a C-H bond in vibrotationally excited molecules.     

Microstructural aspects of long-term creep ductility of AISI 316 LN steel

Microstructural aspects of the creep plasticity and impact strength of non-stabilized austenitic CrNiMo steels with two different nitrogen contents have been evaluated. During creep exposure an intergranular precipitation of the sigma phase, M₂₃C₆ or/and Cr₂N particles produce favourable conditions for transition from typically intergranular fracture to ductile shear fractures or to intergranular ductile fractures with characteristic dimple morphology. A given type of fractures is accompanied with high values of the relative creep rupture elongation (up to 100%) dependent on temperature and time to rupture.     

Implementation of visual data mining for unsteady blood flow field in an aortic aneurysm

Abstract  

This study was performed to determine the relations between the features of wall shear stress and aneurysm rupture. For this purpose, visual data mining was performed in unsteady blood flow simulation data for an aortic aneurysm. The time-series data of wall shear stress given at each grid point were converted to spatial and temporal indices, and the grid points were sorted using a self-organizing map based on the similarity of these indices. Next, the results of cluster analysis were mapped onto the real space of the aortic aneurysm to specify the regions that may lead to aneurysm rupture. With reference to previous reports regarding aneurysm rupture, the visual data mining suggested specific hemodynamic features that cause aneurysm rupture.     

Charge radii of high-spin isomers measured using laser spectroscopy methods

The overview of experimental data on charge radii differences between the ground and the high-spin isomeric states is presented. Methods of high-resolution laser spectroscopy were used for measurements. Charge radii differences obtained in two ways are compared: from measurements of isomeric shifts of atomic levels of nuclei under study and from measurements of quadrupole moments in both states under the assumption that the radii differences are determined by the difference of their quadrupole deformations. Isomers formed at a rupture of one or several nucleon pairs and isomers with the configuration of the odd neutron 1h _11/2 for the nuclear region Cd-Ba and 1i _13/2 for the region Hg-Pb are considered. Observed deviations of the above charge radii differences for isomeric states of a different nature are discussed.     

Bipolar resistive switching effect and mechanism of solution-processed orthorhombic Bi2SiO5 thin films

Orthorhombic Bi₂SiO₅ thin films with dense surface were synthesized by using a chemical solution deposition method. The crystallized films were first utilized to implement resistive memory cells with Pt/Bi₂SiO₅/Pt sandwich architecture. It exhibited outstanding switching parameters including concentrated distributions of low and high resistance states, uniform switching voltages, cycling endurance, and long retention. Furthermore, the model of formation and rupture of conductive filaments consisted of oxygen vacancies was used to well explain resistive switching behavior. The results revealed that the solution-processed Bi₂SiO₅ thin film devices have great potential for forefront application in nonvolatile memory.     

Angular and spin distributions of primary fission fragments

It is demonstrated that the formation of the fissile nucleus prescission configuration with two fission prefragments connected by a neck is possible only with the simultaneous appearance of high values of relative orbital moments [(L)\vec]\vec L of the abovementioned prefragments, independently of their form. It is found that conservation of the fissile nucleus spin when its values are low leads to the formation of high values of prefragment spins [(J)\vec]₁\vec J_1, [(J)\vec]₂\vec J_2 that are oriented antiparallel to the moment [(L)\vec]\vec L and perpendicular to the fissile nucleus symmetry axis. It is shown that for two deformed fission prefragments, the pumping mechanism of high values of their relative moments [(L)\vec]\vec L and spins [(J)\vec]₁\vec J_1, [(J)\vec]₂\vec J_2 is due to the combined influence of bending- and wriggling- vibrations, the latter predominating. It is found that the high values of spherical fission prefragments are not related to thermal excitations but is determined by the excitation of the initial high-spin double quasiparticle states, due to the nonadiabatic collective deformation motion of the fissile nucleus in the vicinity of its rupture point.     

A DFT periodic study of the vanadyl pyrophosphate (1 0 0) surface

The unique ability of the vanadyl pyrophosphate (1 0 0) surface to activate n-butane and then selectively oxidise the hydrocarbon to maleic anhydride was investigated using modern quantum chemical methods. Bulk (VO)₂P₂O₇, together with stoichiometric and phosphorus-enriched (1 0 0) surfaces, were analysed using periodic density functional theory calculations. Also simulated was surface ionic relaxation from bulk geometry, and surface hydration. Density of states (DOS) plots show that, whether stoichiometric or phosphorus-enriched, bulk terminated or relaxed, bare or hydrated, local covalent reactivity at the (1 0 0) surface is controlled by vanadium species. Terminal P-O oxygen species are the most nucleophilic surface oxygens, as indicated by their predominance of sub-vanadium high-lying valence band levels. A periodic treatment of (VO)₂P₂O₇(1 0 0) hence gives results qualitatively identical to those obtained from earlier cluster calculations. Simulation of surface ionic relaxation shows that in-plane P-O-V oxygens may also be involved in rupture of substrate C-H bonds for mild oxidation, while surface hydration calculations indicate that dissociative chemisorption of water may play a key role in perpetuation of the selective oxidation cycle.     

Precipitation and fracture behaviour of Fe–Mn–Ni–Al alloys

The effects of Al addition on the precipitation and fracture behaviour of Fe–Mn–Ni alloys were investigated. With the increasing of Al concentration, the matrix and grain boundary precipitates changed from L1₀ θ-MnNi to B2 Ni₂MnAl phase, which is coherent and in cube-to-cube orientation relationship with the α′-matrix. Due to the suppression of the θ-MnNi precipitates at prior austenite grain boundaries (PAGBs), the fracture mode changed from intergranular to transgranular cleavage fracture. Further addition of Al resulted in the discontinuous growth of Ni₂MnAl precipitates in the alloy containing 4.2?wt.% Al and fracture occurred by void growth and coalescence, i.e. by ductile dimple rupture. The transition of the fracture behaviour of the Fe–Mn–Ni–Al alloys is discussed in relation to the conversion of the precipitates and their discontinuous precipitation behaviour at PAGBs.     

Some chemical and microstructural factors influencing creep cavitation resistance of austenitic stainless steels

Creep cavitation in materials is greatly influenced by trace elements. To enhance creep cavitation resistance, the chemical composition of 304, 321, 347 austenitic stainless steels was modified with the addition of minute amounts of boron and cerium. The addition of boron and cerium to type 304 stainless steel led to an increase in its creep rupture life with an associated decrease in creep rupture ductility. The addition of boron and cerium to the titanium-containing 321 steel and niobium-containing 347 steel was found to increase their creep rupture life and ductility. Creep cavitation was highly suppressed in the 347 and 321 steels with the addition of boron and cerium. The chemistry of the grain boundary and creep cavity surface was analyzed by Auger electron spectroscopy. Extensive sulphur segregation was observed on the grain boundary and cavity surface of the steels without boron and cerium addition and even in the 304 steel containing boron and cerium. In the boron- and cerium-containing 347 and 321 steels, respectively, segregation of elemental boron and the BN compound on the cavity surface were observed. These segregations reduced cavity growth rate substantially in these steels and BN segregation was found to be more effective in reducing cavity growth rate than boron segregation. Cerium acts as a getter for soluble sulphur in the steels by precipitation of ceriumoxysulfide (Ce₂O₂S) to facilitate the segregation of boron on the cavity surface.     

Cohesive zone modelling of anodic dissolution stress corrosion cracking induced by corrosion product films

Damage mechanics based on the cohesive zone model were applied to study the anodic dissolution stress corrosion cracking (SCC) in flat and U-shaped edge-notched specimens. The simulation results show that corrosion product films (CPFs) facilitate crack initiation in SCC due to the CPF-induced stress and CPF rupture. In the flat specimen, SCC susceptibility increases with the CPF thickness and CPF Young’s modulus, while it decreases with CPF fracture strength. For the U-shaped edge-notched specimen, the normalised threshold stress intensity factor K_ISCC/K_IC decreases with the CPF thickness and notch depth.     

Computer simulations in the study of gold nanowires: the effect of impurities

Suspended gold nanowires have recently been made in an ultra-high vacuum ambient and were imaged by electron microscopy. Two puzzles were presented: one atom thick wires are produced and some of the atomic distances between these atoms before their breaking were too large. Simulations using realistic molecular dynamics method were able to unveil some processes to explain the mechanisms of formation, evolution, and breaking of these atomically thin Au nanowires under stress. The calculations showed how defects induce the formation of constrictions that eventually will form the one-atom chains. Atomically thin chains, five atoms long were obtained, before breaking. The results were in excellent agreement with experimental results except for the large Au-Au distances. In fact no theoretical calculation of pure gold nanowires have been able to produce such large distances. Light impurities that cannot be imaged in these experiments may be responsible for these large Au-Au distances. Using ab initio total energy calculations based on the density functional theory, we have studied the effect of H, C, O, N, B, S, CH, CH₂, and H₂ impurities on the nanowire’s electronic and structural properties, in particular how they affect the rupture of the nanowire. We find that the impurities tend to locally increase the nanowire’s strength, in such a way that its rupture always occurs at an Au-Au bond and never at an Au-X bond (X being an impurity). In particular, oxygen seems to form very stable bonds that may be used to pull longer Au chains. Regarding the observed large Au-Au bond lengths, it was found, based on quasi-static calculations, that the best candidate to explain the large distances is H. However, some particular experimental conditions may lead to different results. PACS 68.65.-k; 68.37.Lp; 71.15.Pd     

Reversible resistance switching properties in Ti-doped polycrystalline Ta2O5 thin films

Unipolar reversible resistance switching effects were found in 5 at% Ti-doped polycrystalline Ta₂O₅ films with the device structure of Pt/Ti–Ta₂O₅/Pt. Results suggest that the recovery/rupture of the conductive filaments which are involved in the participation of oxygen vacancies and electrons leads to the resistance switching process. Ti-doped Ta₂O₅ thin films possess higher resistance whether in low-resistance state or high-resistance state and higher resistance switching ratio than Ta₂O₅ thin films, where Ti addition plays an important role in the resistance switching process by suppressing the migration of oxygen vacancies via forming an electrically inactive Ti/O–vacancy complex. Excellent retention properties of the high and low resistances under constant stress of applied voltage were obtained.     

Microstructure, optical and static recording properties of AgOx film, and near-field simulation of sub-wavelength aperture based on the AgOx marks’ formation

Structures, spectra and surface topographies of as-deposited and annealed AgO_x films have been investigated by an X-ray diffractometer, a spectrophotometer and an atomic force microscopy (AFM). X-ray diffraction and spectrum results show that the as-deposited AgO_x films with high oxygen ratios (x≥0.5) are in amorphous states and Ag crystalline particles will separate out after annealed. AFM results show that the film surface will become much rougher and film thickness will increase greatly after annealed due to the decomposition of AgO_x with release of oxygen. Static recording results show that two microstructures of the recording marks can be produced: one is the bubble mark at a low recording power and the other is the rupture bubble with an ablated aperture (hole) in the center at a high recording power. Based on the formation of rupture bubble marks, the near-field optical distribution of a focused Gaussian laser beam through a sub-wavelength aperture (200 nm in diameter) has been simulated using finite-difference-time-domain (FDTD) method. Results show that the spot size can be greatly squeezed with still highly transmitted intensity, which may lead to the super-resolution readout.     

Combined effects of high pressure and sodium hydrogen carbonate treatment on pork ham: improvement of texture and palatability

In this study, the combined effects of high pressure and sodium hydrogen carbonate (NaHCO₃) treatment on the physical and chemical properties, and palatability of pork ham, a tough and under-utilized meat, were investigated. Assessment of meat properties with heat treatment, after exposure to NaHCO₃ and high pressure treatment, revealed an increase in water content, and decreased weight reduction and rupture stress. The free amino acid content of meat samples increased with NaHCO₃ and high pressure treatment. The effect of high pressure processing was especially notable at a pressure of 300 MPa. Sensory evaluation showed that meat subjected to high pressure processing after NaHCO₃ treatment was tender and juicy. In addition, the sample produced minimal residue in the mouth and was characterized by a good taste.     

Thermodynamics of the rupture in a Morse lattice

The rupture of a Morse lattice is considered in the presentpaper. The critical rupture force F _cr is found todecrease with the number of particles N as F _cr ~ 1/\(\sqrt{N}\). The partition function is obtained for two states ofthe lattice – with all equal bond lengths and one broken bond.In the first case an accurate expressions for thermodynamicparameters are obtained, and thermodynamic expressions arederived in the harmonic approximation in the latter case. Theanalytical predictions are confirmed by extensive MD simulations.Cis-trans isomerization is considered as an example. Volumefractions of trans- and cis-isomers versus number ofmonomer units N are found depending on the torsion stiffnesses.     

Molecular dynamics simulations of Ar gas ejection from a ruptured subsurface bubble in Cu(100) induced by impact of 200 eV Ar atoms

We present a molecular dynamics simulation of the rupture of a subsurface Ar bubble in Cu(100) and the ejection of Ar atoms and Ar₂ dimers. A cavity in the subsurface region was pressurised by inserting Ar atoms until a stability condition was met and the bubble rupture was initiated by the impact of a 200 eV Ar atom. We calculate local temperature and pressure profiles inside the Ar bubble, the angular and energy distributions of emitted Ar atoms and Ar₂ dimers and compare with experiments.     

The Tensile Properties of Uncoated and TiO2 Coated Bombyx Mori Silk Yarns Exposed to Thermal Treatment

Bombyx mori silk yarns were coated with a TiO₂ network by sol-gel processing. The tensile properties of TiO₂ coated silk yarns heated at various temperatures were examined and compared with those of uncoated silk yarns. The thermal properties of uncoated silk yarns and TiO₂ coated silk yarns were also discussed. Prominent changes were seen in the rigidity and Young's modulus. The Young's modulus of TiO₂ coated silk yarn increased by 13% at room condition and remained higher than that of uncoated silk yarns with increasing temperature. The shape of the stress–strain curve of TiO₂ coated silk yarns became the same as uncoated silk yarns and showed a similar tendency of change to uncoated silk yarns with increasing temperature. The rupture values of uncoated silk yarns and TiO₂ coated silk yarns decreased significantly, e.g., the breaking extension decreased from 17.28 to 2.44% and from 15.25 to 1.96% for uncoated silk yarns and TiO₂ coated silk yarns, respectively, when the temperature was increased from 25 to 225°C. Structural changes and degradation processes due to thermal effects for both uncoated and TiO₂ coated silk yarns are discussed.