Surface Rebound of Relativistic Dislocations Directly and Efficiently Initiates Deformation Twinning

Under ultrahigh stresses (e.g., under high strain rates or in small-volume metals) deformation twinning (DT) initiates on a very short time scale, indicating strong spatial-temporal correlations in dislocation dynamics. Using atomistic simulations, here we demonstrate that surface rebound of relativistic dislocations directly and efficiently triggers DT under a wide range of laboratory experimental conditions. Because of its stronger temporal correlation, surface rebound sustained relay of partial dislocations is shown to be dominant over the conventional mechanism of thermally activated nucleation of twinning dislocations.National Science Foundation (U.S.) (Grant DMR-1410636

In situ TEM study of deformation-induced crystalline-to-amorphous transition in silicon

The mechanism responsible for deformation-induced crystalline-to-amorphous transition (CAT) in silicon is still under considerable debate, owing to the absence of direct experimental evidence. Here we have devised a novel core/shell configuration to impose confinement on the sample to circumvent early cracking during uniaxial compression of submicron-sized Si pillars. This has enabled large plastic deformation and in situ monitoring of the CAT process inside a transmission electron microscope. We demonstrate that diamond cubic Si transforms into amorphous silicon through slip-mediated generation and storage of stacking faults (SFs), without involving any intermediate crystalline phases. By employing density functional theory simulations, we find that energetically unfavorable single-layer SFs create very strong antibonding interactions, which trigger the subsequent structural rearrangements. Our findings thus resolve the interrelationship between plastic deformation and amorphization in silicon, and shed light on the mechanism underlying deformation-induced CAT in general.National Natural Science Foundation of China (grant 51231005)National Natural Science Foundation of China (grant 51321003)National Natural Science Foundation of China (grant 11132006

Tetra­aqua­(2-hy­droxy­acetato-κ2 O 1,O 2)magnesium nitrate

In the title complex, [Mg(C2H3O3)(H2O)4]NO3, the MgII cation is hexa­coordinated by four O atoms from water mol­ecules and two O atoms from a 2-hy­droxy­acetate ligand in a distorted octa­hedral coordination geometry. The structure exhibits a three-dimensional supra­molecular network, which is stabilized by nine different O—H⋯O hydrogen bonds

A new regime for mechanical annealing and strong sample-size strengthening in body centred cubic molybdenum

Because of crystal symmetry, body centred cubic (BCC) metals have large differences in lattice friction between screw and edge dislocations, and manifest generally different mechanical behaviours from face centred cubic (FCC) metals. Although mechanical annealing (significant drop in stored dislocation density in response to applied stress) has been observed in FCC metals, it has not been observed in BCC metals so far. Here we show that significant mechanical annealing does occur in BCC Mo pillars, when their diameters decrease to hundreds of nanometers. In addition, there exists a critical diameter for focused ion beam milled pillars, below which the strengthening exponent increases dramatically, from ~0.3 to ~1. Thus, a new regime of size effects in BCC metals is discovered that converges to that of FCC metals, revealing deep connection in the dislocation dynamics of the two systems.National Natural Science Foundation (China) (Grant 50925104)National Natural Science Foundation (China) (Grant 50720145101)National Natural Science Foundation (China) (Grant 50831004)National Basic Research Program of China (973 Program) (Grant 2010CB631003)National Basic Research Program of China (973 Program) (Grant 2012CB619402)National Science Foundation (U.S.) (CMMI-0728069)National Science Foundation (U.S.) (DMR-1008104)National Science Foundation (U.S.) (DMR-1120901)United States. Air Force Office of Scientific Research (FA9550-08-1-0325

Distributed Impulsive Consensus of the Multiagent System without Velocity Measurement

This paper deals with the distributed consensus of the multiagent system. In particular, we consider the case where the velocity (second state) is unmeasurable and the communication among agents occurs at sampling instants. Based on the impulsive control theory, we propose an impulsive consensus algorithm that extends some of our previous work to account for the lack of velocity measurement. By using the stability theory of the impulsive system, some necessary and sufficient conditions are obtained to ensure the consensus of the controlled multiagent system. It is shown that the control gains, the sampled period and the eigenvalues of Laplacian matrix of communication graph play key roles in achieving consensus. Finally, a numerical simulation is provided to illustrate the effectiveness of the proposed algorithm

Tetra-μ-acetato-κ4 O:O′;κ3 O,O′:O′;κ3 O:O,O′-bis­[(acetato-κ2 O,O′)(1,10-phenanthroline-κ2 N,N′)europium(III)]

In the title centrosymmetric dinuclear EuIII complex, [Eu2(CH3COO)6(C12H8N2)2], each EuIII cation is coordinated by seven O atoms from five acetate anions and two N atoms from one phenanthroline ligand in a distorted tricapped trigonal-prismatic geometry. Four acetate anions bridge two EuIII cations to form the dinuclear complex, with an Eu⋯Eu distance of 3.9409 (8) Å. Weak inter­molecular C—H⋯O hydrogen bonding is present in the crystal structure