IN SITU TEM INVESTIGATION OF DEFORMATION AND FRACTURE MECHANISM IN NANOCRYSTALLINE NICKEL

The strength of a material is known to increase with the decreasing grain size and will reach its peak strength at certain critical grain size. It was proposed and has been widely accepted that this results from the deformation mechanism crossover, i.e. a continuous transition from dislocation nucleation and motion to grain boundary mediated plasticity. Evidence for this has been sought for many years, however, to date, direct experimental confirmation remains elusive. By solving the challenging problems encountered in previous studies, in situ dynamic dark field transmission electron microscope (TEM) investigations combined with in situ high resolution TEM observations have been performed successfully on high purity nanocrystalline nickel samples with an average grain size about 10nm, which show: 1) grain agglomerates formed very frequently and rapidly in many locations apparently independently of one another under influence of the applied stress, 2) both inter- and intra-grain agglomerate fractures are observed in response to the deformation, 3) trapped dislocations are frequently observed in grains which may be still in a strained state and no deformation twinning was detected, 4) trapped lattice dislocations were observed to move and annihilate during the stress relaxation. These TEM observations i) for the first time provide conclusive experimental evidence that grain boundary mediated plasticity, such as grain boundary sliding and grain rotation, has become a prominent deformation mode for as deposited Ni. Theoretical analysis suggested that the deformation mechanism crossover resulted from the competition between the deformation controlled by nucleation and motion of dislocations and the deformation controlled by grain boundary related deformation accommodated mainly by grain boundary diffusion with decreasing grain size, ii) confirmed the speculation that dislocations are most probably observed in stressed grains, iii) suggested that the dimpled fracture surface of nanocrystalline materials may result from those newly formed grain agglomerates. Additionally, direct measurement of lattice distortions during straining revealed that grain interiors may experience ultra-high elastic distortions during tensile deformation

Experimental implementation of generalized Grover's algorithm of multiple marked states and its application

Generalized Grover's searching algorithm for the case in which there are multiple marked states is demonstrated on a nuclear magnetic resonance (NMR) quantum computer. The entangled basis states (EPR states) are synthesized using the algorithm.Comment: 20 pages,3 figure

Elastic strain engineering for unprecedented materials properties

“Smaller is stronger.” Nanostructured materials such as thin films, nanowires, nanoparticles, bulk nanocomposites, and atomic sheets can withstand non-hydrostatic (e.g., tensile or shear) stresses up to a significant fraction of their ideal strength without inelastic relaxation by plasticity or fracture. Large elastic strains, up to ∼10%, can be generated by epitaxy or by external loading on small-volume or bulk-scale nanomaterials and can be spatially homogeneous or inhomogeneous. This leads to new possibilities for tuning the physical and chemical properties of a material, such as electronic, optical, magnetic, phononic, and catalytic properties, by varying the six-dimensional elastic strain as continuous variables. By controlling the elastic strain field statically or dynamically, a much larger parameter space opens up for optimizing the functional properties of materials, which gives new meaning to Richard Feynman’s 1959 statement, “there’s plenty of room at the bottom.”National Science Foundation (U.S.) (DMR-1240933)National Science Foundation (U.S.) (DMR-1120901

Is the large-scale structure traced by the BOSS LOWZ galaxies consistent with Planck\textit{Planck}?

Recently, several studies reported a significant discrepancy between the clustering and lensing of the Baryon Oscillation Spectroscopic Survey (BOSS) galaxies in the $\textit{Planck}$ cosmology. We construct a simple yet powerful model based on the linear theory to assess whether this discrepancy points toward deviations from $\textit{Planck}$. Focusing on scales $10<R<30$ $h^{-1}\mathrm{Mpc}$, we model the amplitudes of clustering and lensing of BOSS LOWZ galaxies using three parameters: galaxy bias $b_\mathrm{g}$, galaxy-matter cross-correlation coefficient $r_\mathrm{gm}$, and $A$, defined as the ratio between the true and $\textit{Planck}$ values of $\sigma_8$. Using the cross-correlation matrix as a diagnostic, we detect systematic uncertainties that drive spurious correlations among the low-mass galaxies. After building a clean LOWZ sample with $r_\mathrm{gm}\sim1$, we derive a joint constraint of $b_\mathrm{g}$ and $A$ from clustering+lensing, yielding $b_\mathrm{g}=2.47_{-0.30}^{+0.36}$ and $A=0.81_{-0.09}^{+0.10}$, i.e., a $2\sigma$ tension with $\textit{Planck}$. However, due to the strong degeneracy between $b_\mathrm{g}$ and $A$, systematic uncertainties in $b_\mathrm{g}$ could masquerade as a tension with $A=1$. To ascertain this possibility, we develop a new method to measure $b_\mathrm{g}$ from the cluster-galaxy cross-correlation and cluster weak lensing using an overlapping cluster sample. By applying the independent bias measurement ($b_\mathrm{g}=1.76\pm0.22$) as a prior, we successfully break the degeneracy and derive stringent constraints of $b_\mathrm{g}=2.02_{-0.15}^{+0.16}$ and $A=0.96\pm0.07$. Therefore, our result suggests that the large-scale clustering and lensing of LOWZ galaxies are consistent with $\textit{Planck}$, while the different bias estimates may be related to some observational systematics in the target selection.Comment: 8 pages, 5 figures, comments welcome

Preliminary study of predation of the multi-colored lady beetle, Leis axyridis (Pallas), on two species of aphids

Adults of multi-colored lady beetle, Leis axyridis were starved for 24- hour, and allowed to prey on soybean aphid, Aphis glycines Matsumura, and corn leaf aphid, Rhopalosiphum maidis(Fitch) which were at various densities. By comparing and analyzing its predatory potential, we consider that both L. axyridis’ preying on A. glycines and on R. maidis were fitted with type II response, which can be simulated by Holling disc equation, and expressed as: Na 0.6792N/ (1 0.0022N) corn ? ? and Na 0.9463N/ (1 0.0023N) soybean ? ? , respectively. In addition, by comparing its functional parameters, we found that L. axyridis’ ability to control A. glycines is significantly stronger than that of R. maidis.Originating text in Chinese.Citation: Lin, Zhiwei, Wang, Liyan, Sun, Qiang, Nan, Shan. (1999). Preliminary study of predation of the multi-colored lady beetle, Leis axyridis (Pallas), on two species of aphids. Journal of Heilongjiang August First Land Reclamation University, 11(1), 26-28

Inflating hollow nanocrystals through a repeated Kirkendall cavitation process.

The Kirkendall effect has been recently used to produce hollow nanostructures by taking advantage of the different diffusion rates of species involved in the chemical transformations of nanoscale objects. Here we demonstrate a nanoscale Kirkendall cavitation process that can transform solid palladium nanocrystals into hollow palladium nanocrystals through insertion and extraction of phosphorus. The key to success in producing monometallic hollow nanocrystals is the effective extraction of phosphorus through an oxidation reaction, which promotes the outward diffusion of phosphorus from the compound nanocrystals of palladium phosphide and consequently the inward diffusion of vacancies and their coalescence into larger voids. We further demonstrate that this Kirkendall cavitation process can be repeated a number of times to gradually inflate the hollow metal nanocrystals, producing nanoshells of increased diameters and decreased thicknesses. The resulting thin palladium nanoshells exhibit enhanced catalytic activity and high durability toward formic acid oxidation