Peac Institute of Multiscale science

Chengdu, China

Peac Institute of Multiscale science

Chengdu, China
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Chen S.,Peac Institute of Multiscale science | Juncheng E.,Peac Institute of Multiscale science | Luo S.-N.,Peac Institute of Multiscale science | Luo S.-N.,Southwest Jiaotong University
Journal of Applied Crystallography | Year: 2017

SLADS (, a parallel code for direct simulations of X-ray scattering of large anisotropic dense nanoparticle systems of arbitrary species and atomic configurations, is presented. Particles can be of arbitrary shapes and dispersities, and interactions between particles are considered. Parallelization is achieved in real space for the sake of memory limitation. The system sizes attempted are up to one billion atoms, and particle concentrations in dense systems up to 0.36. Anisotropy is explored in terms of superlattices. One- and two-dimensional small-angle scattering or diffraction patterns are obtained. SLADS is validated self-consistently or against cases with analytical solutions.SLADS is a parallel code for direct simulations of single-shot X-ray scattering of large anisotropic dense nanoparticle systems of arbitrary species and atomic configurations. Particles can be of arbitrary shapes and dispersities, and interactions between particles are considered. © International Union of Crystallography, 2017.

Hou H.,Peac Institute of Multiscale science | Hou H.,Lawrence Berkeley National Laboratory | Mao X.,Lawrence Berkeley National Laboratory | Zorba V.,Lawrence Berkeley National Laboratory | And 2 more authors.
Analytical Chemistry | Year: 2017

Recently, laser ablated molecular isotopic spectrometry (LAMIS) has expanded its capability to explore molecules formation mechanism in laser-induced plasma in addition to isotope analysis. LAMIS is a powerful tool for tracking the origination of atoms that is involved in formation of investigated molecules by labeling atoms with their isotopic substitution. The evolutionary formation pathways of organic molecules, especially of C2 dimers and CN radicals, were frequently reported. However, very little is known about the formation pathways for metallic radicals and heterodimers in laser ablated plasma. This research focuses on elucidating the formation pathways of AlO radicals in femtosecond laser ablated plasma from 18O-labeled Al2O3 pellet. Plasmas expanding with strong forward bias in the direction normal to the sample surface were generated in the wake of a weakly ionized channel created by a femtosecond laser. The formation mechanism of AlO and influence of air were investigated with multiple plasma diagnostic methods such as monochromatic fast gating imaging, spatiotemporal resolved optical emission spectroscopy, and LAMIS. An advanced LAMIS fitting procedure was used to deduce the spatiotemporal distributions of Al18O and Al16O number densities and also their ratios. We found that the Al16O/Al18O number density ratio is higher for plasma portion closer to the sample surface, which suggests that chemical reactions between the plasma plume and ambient air are more intense at the tail of the plasma. The results also reveals that direct association of free Al and O atoms is the main mechanism for the formation of AlO at the early stage of the plasma. To the contrast, chemical reactions between plasma materials and ambient oxygen molecules and the isotope exchange effect are the dominant mechanisms of the formation of AlO and evolution of Al16O/Al18O number density ratio at the late stage of the plasma. © 2017 American Chemical Society.

Wang M.C.,Peac Institute of Multiscale science | Wang M.C.,Southwest Jiaotong University | Qiao S.,CAS Shanghai Institute of Microsystem and Information Technology | Qiao S.,University of Shanghai for Science and Technology | And 5 more authors.
Physical Review Letters | Year: 2016

We report on a time-resolved ultrafast optical spectroscopy study of the topological insulator Bi2Se3. We unravel that a net spin polarization cannot only be generated using circularly polarized light via interband transitions between topological surface states (SSs), but also via transitions between SSs and bulk states. Our experiment demonstrates that tuning photon energy or temperature can essentially allow for photoexcitation of spin-polarized electrons to unoccupied topological SSs with two distinct spin relaxation times (∼25 and ∼300 fs), depending on the coupling between SSs and bulk states. The intrinsic mechanism leading to such distinctive spin dynamics is the scattering in SSs and bulk states which is dominated by Eg 2 and A1g 1 phonon modes, respectively. These findings are suggestive of novel ways to manipulate the photoinduced coherent spins in topological insulators. © 2016 American Physical Society.

An Q.,California Institute of Technology | Goddard W.A.,California Institute of Technology | Zybin S.V.,California Institute of Technology | Luo S.-N.,Peac Institute of Multiscale science
Journal of Physical Chemistry C | Year: 2014

In order to elucidate how shocks in heterogeneous materials affect decomposition and reactive processes, we used the ReaxFF reactive force field in reactive molecules dynamics (RMD) simulations of the effects of strong shocks (2.5 and 3.5 km/s) on a prototype polymer bonded explosive (PBX) consisting of cyclotrimethylene trinitramine (RDX) bonded to hydroxyl-terminated polybutadiene (HTPB). We showed earlier that shock propagation from the high density RDX to the low density polymer (RDX → Poly) across a nonplanar periodic interface (sawtooth) leads to a hotspot at the initial asperity but no additional hotspot at the second asperity. This hotspot arises from shear along the interface induced by relaxation of the stress at the asperity. We now report the case for shock propagation from the low density polymer to the high density RDX (Poly → RDX) where we find a hotspot at the initial asperity and a second more dramatic hotspot at the second asperity. This second hotspot is enhanced due to shock wave convergence from shock wave interaction with nonplanar interfaces. We consider that this second hotspot is likely the source of the detonation in realistic PBX systems. We showed how these hotspots depend on the density mismatch between the RDX and polymer and found that decreasing the density by a factor of 2 dramatically reduces the hotspot. These results suggest that to make PBX less sensitive for propellants and explosives, the binder should be designed to provide low density at the asperity in contact with the RDX. Based on these simulations, we propose a new design for an insensitive PBX in which a low density polymer coating is deposited between the RDX and the usual polymer binder. To test this idea, we simulated shock wave propagation from two opposite directions (RDX → Poly and Poly → RDX) through the interface matched PBX (IM-PBX) material containing a 3 nm coating of low density (0.48 g/cm 3) polymer. These simulations showed that this IM-PBX design dramatically suppresses hotspot formation. © 2014 American Chemical Society.

Huang J.W.,Peac Institute of Multiscale science | Huang J.W.,Southwest Jiaotong University | Huang J.Y.,Peac Institute of Multiscale science | Huang J.Y.,Southwest Jiaotong University | And 4 more authors.
Journal of Synchrotron Radiation | Year: 2016

Dynamic compression experiments are performed on single-crystal Si under split Hopkinson pressure bar loading, together with simultaneous high-speed (250-350?ns resolution) synchrotron X-ray Laue diffraction and phase-contrast imaging. A methodology is presented which determines crystal rotation parameters, i.e. instantaneous rotation axes and angles, from two unindexed Laue diffraction spots. Two-dimensional translation is obtained from dynamic imaging by a single camera. High-speed motion of crystals, including translation and rotation, can be tracked in real time via simultaneous imaging and diffraction.

Cai Y.,Anhui University of Science and Technology | Huang J.Y.,Anhui University of Science and Technology | Wu H.A.,Anhui University of Science and Technology | Zhu M.H.,Southwest Jiaotong University | And 3 more authors.
Journal of Physical Chemistry Letters | Year: 2016

It is well known that strain rate and size effects are both important in material failure, but the relationships between them are poorly understood. To establish this connection, we carry out molecular dynamics (MD) simulations of cavitation in Lennard-Jones and Cu liquids over a very broad range of size and strain rate. These studies confirm that temporal and spatial scales play equivalent roles in the tensile strengths of these two liquids. Predictions based on smallest-scale MD simulations of Cu for larger temporal and spatial scales are consistent with independent simulations, and comparable to experiments on liquid metals. We analyze these results in terms of classical nucleation theory and show that the equivalence arises from the role of both size and strain rate in the nucleation of a daughter phase. Such equivalence is expected to hold for a wide range of materials and processes and to be useful as a predictive bridging tool in multiscale studies. © 2016 American Chemical Society.

Liu H.K.,University of Electronic Science and Technology of China | Liu H.K.,Peac Institute of Multiscale science | Lin Y.,University of Electronic Science and Technology of China | Luo S.N.,Peac Institute of Multiscale science
Journal of Physical Chemistry C | Year: 2014

We investigate with molecular dynamics simulations the dependences of thermal conductivity (κ) of polycrystalline graphene on grain boundary (GB) energy and grain size. Hexagonal grains and grains with random shapes and sizes are explored, and their thermal properties and phonon densities of states are characterized. It is found that κ decreases exponentially with increasing GB energy, and decreasing grain size reduces κ. GB-induced phonon softening and scattering, as well as reduction in the number of heat conducting phonons, contribute to the decrease in thermal conductivity. © 2014 American Chemical Society.

Hudspeth M.,Purdue University | Sun T.,Argonne National Laboratory | Parab N.,Purdue University | Guo Z.,Purdue University | And 3 more authors.
Journal of Synchrotron Radiation | Year: 2015

Using a high-speed camera and an intensified charge-coupled device (ICCD), a simultaneous X-ray imaging and diffraction technique has been developed for studying dynamic material behaviors during high-rate tensile loading. A Kolsky tension bar has been used to pull samples at 1000s-1 and 5000s-1 strain-rates for super-elastic equiatomic NiTi and 1100-O series aluminium, respectively. By altering the ICCD gating time, temporal resolutions of 100ps and 3.37μs have been achieved in capturing the diffraction patterns of interest, thus equating to single-pulse and 22-pulse X-ray exposure. Furthermore, the sample through-thickness deformation process has been simultaneously imaged via phase-contrast imaging. It is also shown that adequate signal-to-noise ratios are achieved for the detected white-beam diffraction patterns, thereby allowing sufficient information to perform quantitative data analysis diffraction via in-house software (WBXRD-GUI). Of current interest is the ability to evaluate crystal d-spacing, texture evolution and material phase transitions, all of which will be established from experiments performed at the aforementioned elevated strain-rates. © 2015 International Union of Crystallography.

Wang L.,Peac Institute of Multiscale science | E J.C.,Peac Institute of Multiscale science | Cai Y.,Peac Institute of Multiscale science | Cai Y.,Anhui University of Science and Technology | And 3 more authors.
Journal of Applied Physics | Year: 2015

We investigate shock-induced deformation of columnar nanocrystalline Al with large-scale molecular dynamics simulations and implement orientation mapping (OM) and selected area electron diffraction (SAED) for microstructural analysis. Deformation mechanisms include stacking fault formation, pronounced twinning, dislocation slip, grain boundary (GB) sliding and migration, and lattice or partial grain rotation. GBs and GB triple junctions serve as the nucleation sites for crystal plasticity including twinning and dislocations, due to GB weakening, and stress concentrations. Grains with different orientations exhibit different densities of twins or stacking faults nucleated from GBs. GB migration occurs as a result of differential deformation between two grains across the GB. High strain rates, appropriate grain orientation and GBs contribute to deformation twinning. Upon shock compression, intra-grain dislocation and twinning nucleated from GBs lead to partial grain rotation and the formation of subgrains, while whole grain rotation is not observed. During tension, stress gradients associated with the tensile pulse give rise to intra-grain plasticity and then partial grain rotation. The simulated OM and SAED are useful to describe lattice/grain rotation, the formation of subgrains, GB migration and other microstructures. © 2015 AIP Publishing LLC.

Li B.,Anhui University of Science and Technology | Li B.,Peac Institute of Multiscale science | Zhao F.P.,Anhui University of Science and Technology | Zhao F.P.,Peac Institute of Multiscale science | And 2 more authors.
Journal of Applied Physics | Year: 2014

We investigate with large-scale molecular dynamics simulations shock-induced surface jetting from grooved Cu as regards microstructure effects, including jetting mass/velocity ratios, directionality, jetting phase diagram, secondary jetting, and underlying mechanisms. The grooves are of wedged, cylindrical, and rectangular shapes. Other microstructure features explored are half angles, crystal structure asymmetry as represented by grain boundaries, geometrical asymmetry, and deformation heterogeneity. The common fundamental mechanism is that jetting is driven by stress gradients due to transverse mass collision. For symmetrical wedged grooves, the velocity ratio (maximum jet head velocity/free surface velocity of flat surface) increases linearly with decreasing half angle, with a slope similar for different materials and at nano- to macroscales, as indicated by our simulations and previous experiments. However, the jetting factor or mass ratio reaches the maximum at certain intermediate half angle. An impact strength vs. half angle phase diagram is established for a typical case of wedged grooves, useful for predicting the critical parameters for jetting (e.g., the critical impact velocity for a given half angle, as well as deducing yield strength). Small asymmetries, including crystal structure and geometrical asymmetries as well as deformation inhomogeneities, may induce considerable deviation of the jetting direction. Wedged, cylindrical, and rectangular grooves form a geometrical hierarchy. Primary jetting can be well described with wedged grooves, and secondary jetting is a result of collision of primary jets. Rectangular grooves may yield pronounced, velocity-enhanced, secondary jetting. © 2014 AIP Publishing LLC.

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