Size-dependent mechanical properties of molybdenum nanopillars

We report the deformation behavior of single crystalline molybdenum nanopillars in uniaxial compression, which exhibits a strong size effect called the “smaller is stronger” phenomenon. We show that higher strengths arise from the increase in the yield strength rather than through postyield strain hardening. We find the yield strength at nanoscale to depend strongly on sample size and not on the initial dislocation density, a finding strikingly different from that of the bulk metal

B0→D0Dˉ0K0B^0 \to D^0 \bar D^0 K^0, B+→D0Dˉ0K+B^+ \to D^0 \bar D^0 K^+ and the scalar DDˉD \bar D bound state

We study the $B^0$ decay to $D^0 \bar D^0 K^0$ based on the chiral unitary model that generates the X(3720) resonance, and make predictions for the $D^0 \bar D^0$ invariant mass distribution. From the shape of the distribution, the existence of the resonance below threshold could be induced. We also predict the rate of production of the X(3720) resonance to the $D^0 \bar D^0$ mass distribution with no free parameters.Comment: 9 pages, 17 figure

Applying mesh conformation on shape analysis with missing data

A mesh conformation approach that makes use of deformable generic meshes has been applied to establishing correspondences between 3D shapes with missing data. Given a group of shapes with correspondences, we can build up a statistical shape model by applying principal component analysis (PCA). The conformation at first globally maps the generic mesh to the 3D shape based on manually located corresponding landmarks, and then locally deforms the generic mesh to clone the 3D shape. The local deformation is constrained by minimizing the energy of an elastic model. An algorithm was also embedded in the conformation process to fill missing surface data of the shapes. Using synthetic data, we demonstrate that the conformation preserves the configuration of the generic mesh and hence it helps to establish good correspondences for shape analysis. Case studies of the principal component analysis of shapes were presented to illustrate the successes and advantages of our approach

Search for Supermassive Black Hole Binaries in the Sloan Digital Sky Survey Spectroscopic Sample

Supermassive black hole (SMBH) binaries are expected in a Lambda CDM cosmology given that most (if not all) massive galaxies contain a massive black hole at their center. So far, however, direct evidence for such binaries has been elusive. We use cross-correlation to search for temporal velocity shifts in the MgII broad emission lines of 0.36 < z < 2 quasars with multiple observations in the Sloan Digital Sky Survey. For ~ 10^9 Msun BHs in SMBH binaries, we are sensitive to velocity drifts for binary separations of ~ 0.1 pc with orbital periods of ~100 years. We find seven candidate sub-pc--scale binaries with velocity shifts > 3.4 sigma ~ 280 km/s, where sigma is our systematic error. Comparing the detectability of SMBH binaries with the number of candidates (N < 7), we can rule out that most 10^9 Msun BHs exist in ~ 0.03-0.2 pc scale binaries, in a scenario where binaries stall at sub-pc scales for a Hubble time. We further constrain that < one-third of quasars host SMBH binaries after considering gas-assisted sub-pc evolution of SMBH binaries, although this result is very sensitive to the assumed size of the broad line region. We estimate the detectability of SMBH binaries with ongoing or next-generation surveys (e.g., BOSS, Subaru Prime Focus Spectrograph), taking into account the evolution of the sub-parsec binary in circumbinary gas disks. These future observations will provide longer time baselines for searches similar to ours and may in turn constrain the evolutionary scenarios of SMBH binaries.Comment: Resubmitted to ApJ after referee's comments. 21 pages, 9 figure