159,142 research outputs found
A mesoscale finite element simulation of intermittent plastic flow of micropillar compression under hybrid loading mode
The plastic deformation of the micropillar proceeds as a series of strain bursts, showing an intermittent plastic flow. In this work, we present a stochastic finite element method in crystal plasticity to describe the intermittent characteristic of crystal deformation under the hybrid loading mode (HLM). The microscopic boundary conditions(MBCs) using the HLM are studied and they are demonstrated to be different in various deformation periods such as loading stage, burst slip and holding stage, which occur alternatively as the plastic flow proceeds. In order to determine the MBCs, we use the Monte Carlo (MC) stochastic model to predict the amplitude of the burst displacement and then incorporate such model into our established continuum framework accounting for the characteristics of the strain burst. By implementing this continuum model into the finite element analysis, we predict the plastic flow of single crystal nickel micropillars that deform under uniaxial compression along the [2 6 9] crystalline direction. The simulation results indicate clearly visible strain bursts in the course of plastic deformation, producing a stair-case like stress-strain behavior that agrees well with experimental observations. The computational results reveal that the intermittent flow in the micrometer-scale is intensified due to the increasing amplitude of the strain burst, as well as the occurrence of successive strain bursts rather than the discrete strain bursts, with decreasing of the specimen size. In addition, the micropillar displacement in the context of burst activity predicted from our simulations is similar to the experimental observations. We demonstrate that our simulation method could provide further insights into the intermittent plastic flow characteristics such as burst time duration, micropillar velocity; plus, it is feasible to apply this method to investigate the plastic flow behaviors under complex loading conditions
Effect of distribution of stickers along backbone on temperature-dependent structural properties in associative polymer solutions
Effect of distribution of stickers along the backbone on structural
properties in associating polymer solutions is studied using self-consistent
field lattice model. Only two inhomogeneous morphologies, i.e.,
microfluctuation homogenous (MFH) and micelle morphologies, are observed. If
the system is cooled, the solvent content within the aggregates decreases. When
the spacing of stickers along the backbone is increased the
temperature-dependent range of aggregation in MFH morphology and half-width of
specific heat peak for homogenous solutions-MFH transition increase, and the
symmetry of the peak decreases. However, with increasing spacing of stickers,
the above three corresponding quantities related to micelles behave
differently. It is demonstrated that the broad nature of the observed
transitions can be ascribed to the structural changes which accompany the
replacement of solvents in aggregates by polymer, which is consistent with the
experimental conclusion. It is found that different effect of spacing of
stickers on the two transitions can be interpreted in terms of intrachain and
interchain associations.Comment: 10 pages, 4 figures. arXiv admin note: text overlap with
arXiv:1202.459
Interdecadal variability of winter precipitation in Southeast China
Interdecadal variability of observed winter precipitation in Southeast China (1961–2010) is characterized by the first empirical orthogonal function of the three-monthly Standardized Precipitation Index (SPI) subjected to a 9-year running mean. For interdecadal time scales the dominating spatial modes represent monopole features involving the Arctic Oscillation (AO) and the sea surface temperature (SST) anomalies. Dynamic composite analysis (based on NCEP/NCAR reanalyzes) reveals the following results: (1) Interdecadal SPI-variations show a trend from a dryer state in the 1970s via an increase during the 1980s towards stabilization on wetter conditions commencing with the 1990s. (2) Increasing wetness in Southeast China is attributed to an abnormal anticyclone over south Japan, with northward transport of warm and humid air from the tropical Pacific to South China. (3) In mid-to-high latitudes the weakened southward flow of polar airmasses induces low-level warming over Eurasia due to stronger AO by warmer zonal temperature advection. This indicates that AO is attributed to the Southeast China precipitation increase influenced by circulation anomalies over the mid-to-high latitudes. (4) The abnormal moisture transport along the southwestern boundary of the abnormal anticyclone over south Japan is related to anomalous south-easterlies modulated by the SST anomalies over Western Pacific Ocean; a positive (negative) SST anomaly will strengthen (weaken) warm and humid air transport, leading to abundant (reduced) precipitation in Southeast China. That is both AO and SST anomalies determine the nonlinear trend observed in winter precipitation over Southeast China
Evolution of binary stars and its implications for evolutionary population synthesis
Most stars are members of binaries, and the evolution of a star in a close
binary system differs from that of an ioslated star due to the proximity of its
companion star. The components in a binary system interact in many ways and
binary evolution leads to the formation of many peculiar stars, including blue
stragglers and hot subdwarfs. We will discuss binary evolution and the
formation of blue stragglers and hot subdwarfs, and show that those hot objects
are important in the study of evolutionary population synthesis (EPS), and
conclude that binary interactions should be included in the study of EPS.
Indeed, binary interactions make a stellar population younger (hotter), and the
far-ultraviolet (UV) excess in elliptical galaxies is shown to be most likely
resulted from binary interactions. This has major implications for
understanding the evolution of the far-UV excess and elliptical galaxies in
general. In particular, it implies that the far-UV excess is not a sign of age,
as had been postulated prviously and predicts that it should not be strongly
dependent on the metallicity of the population, but exists universally from
dwarf ellipticals to giant ellipticals.Comment: Oral talk on IAUS 262, Brazi
X-Ray Flares from Postmerger Millisecond Pulsars
Recent observations support the suggestion that short-duration gamma-ray
bursts are produced by compact star mergers. The X-ray flares discovered in two
short gamma-ray bursts last much longer than the previously proposed postmerger
energy release time scales. Here we show that they can be produced by
differentially rotating, millisecond pulsars after the mergers of binary
neutron stars. The differential rotation leads to windup of interior poloidal
magnetic fields and the resulting toroidal fields are strong enough to float up
and break through the stellar surface. Magnetic reconnection--driven explosive
events then occur, leading to multiple X-ray flares minutes after the original
gamma-ray burst.Comment: 10 pages, published in Scienc
Superconductivity and Phase Diagram in (LiFe)OHFeSeS
A series of (LiFe)OHFeSeS (0 x 1)
samples were successfully synthesized via hydrothermal reaction method and the
phase diagram is established. Magnetic susceptibility suggests that an
antiferromagnetism arising from (LiFe)OH layers coexists with
superconductivity, and the antiferromagnetic transition temperature nearly
remains constant for various S doping levels. In addition, the lattice
parameters of the both a and c axes decrease and the superconducting transition
temperature T is gradually suppressed with the substitution of S for Se,
and eventually superconductivity vanishes at = 0.90. The decrease of T
could be attributed to the effect of chemical pressure induced by the smaller
ionic size of S relative to that of Se, being consistent with the effect of
hydrostatic pressure on (LiFe)OHFeSe. But the detailed
investigation on the relationships between and the crystallographic
facts suggests a very different dependence of on anion height from
the Fe2 layer or -Fe2- angle from those in FeAs-based superconductors.Comment: 6 pages, 6 figure
What does a bacterial genome sequence represent? Mis-assignment of MAFF 303099 to the genospecies Mesorhizobium loti
Morphological characterization of shocked porous material
Morphological measures are introduced to probe the complex procedure of shock
wave reaction on porous material. They characterize the geometry and topology
of the pixelized map of a state variable like the temperature. Relevance of
them to thermodynamical properties of material is revealed and various
experimental conditions are simulated. Numerical results indicate that, the
shock wave reaction results in a complicated sequence of compressions and
rarefactions in porous material. The increasing rate of the total fractional
white area roughly gives the velocity of a compressive-wave-series.
When a velocity is mentioned, the corresponding threshold contour-level of
the state variable, like the temperature, should also be stated. When the
threshold contour-level increases, becomes smaller. The area increases
parabolically with time during the initial period. The curve goes
back to be linear in the following three cases: (i) when the porosity
approaches 1, (ii) when the initial shock becomes stronger, (iii) when the
contour-level approaches the minimum value of the state variable. The area with
high-temperature may continue to increase even after the early
compressive-waves have arrived at the downstream free surface and some
rarefactive-waves have come back into the target body. In the case of energetic
material ... (see the full text)Comment: 3 figures in JPG forma
- …