Are the cohesive laws of interfaces sufficient for modelling fracture in polycrystals using the cohesive zone model? We examine this question by comparing a fully atomistic simulation of a silicon polycrystal with a finite element simulation with a similar overall geometry. The cohesive laws used in the finite element simulation are measured atomistically. We describe in detail how to convert the output of atomistic grain boundary fracture simulations into the piecewise linear form needed by a cohesive zone model.

In solid-state physics two different paradigms are typically applied. The first is a local picture, in which one visualizes the quantum states of electrons in atomic orbitals or at impurity atoms in real space (r-space). The second is the momentum or reciprocal space (k-space) picture, where electrons are viewed as de Broglie waves completely delocalized throughout the material.

Using spin density functional theory, we study the electronic and magnetic properties of atomically thin, suspended chains containing silver and oxygen atoms in an alternating sequence. Chains longer than 4 atoms develop a half-metallic ground state implying fully spin-polarized charge carriers. The conductances of the chains exhibit weak even-odd oscillations around an anomalously low value of 0.1G0 (G0=2e2/h) which coincide with the averaged experimental conductance in the long chain limit.

We demonstrate that a monolayer graphene membrane is impermeable to standard gases including helium. By applying a pressure difference across the membrane, we measure both the elastic constants and the mass of a single layer of graphene. This pressurized graphene membrane is the world's thinnest balloon and provides a unique separation barrier between 2 distinct regions that is only one atom thick. © 2008 American Chemical Society.

We introduce a new technique of probing the local potential inside a nanostructure employing Au nanoparticles as electrometers and using single-electron force microscopy to sense the charge states of the Au electrometers, which are sensitive to local potential variations. The Au nanoelectrometers are weakly coupled to a carbon nanotube through high-Impedance molecular junctions. We demonstrate the operation of the Au nanoelectrometer, determine the impedance of the molecular junctions, and measure the local potential profile in a looped nanotube. © 2008 American Chemical Society.

We model the impact of final-state interactions on the radio frequency spectrum of a strongly interacting two-component superfluid Fermi gas. In addition to a broad asymmetric peak coming from the breakup of Cooper pairs, we find that, for appropriate parameters, one can observe a sharp symmetric "bound-bound" spectral line coming from the conversion of Cooper pairs in one channel to pairs or molecules in another. © 2008 The American Physical Society.

Two likely causes of Type C Damping in highly entangled polymers are interfacial slip and shear banding. To isolate these mechanisms, we use confocal microscopy and particle image velocimetry to visualize flow in a planar-Couette shear. Polybutadiene (Mw=200K, 1.1 M) solutions with different entanglement densities (8≤Z≤56) are sheared in narrow gaps ∼35μm. Not only does the velocity at the boundaries violate the no-slip condition, but the velocity profiles are linear. This is inconsistent with shear banding. The measured shear rates and stresses are used to characterize interfacial slip.

Capillary tubes have many advantages over multi-well plates for macromolecular crystal growth and handling, including the possibility of in situ structure determination. To obtain complete high-resolution X-ray data sets, cryopreservation protocols must be developed to prevent crystalline ice formation and preserve macromolecular crystal order. The minimum glycerol concentrations required to vitrify aqueous solutions during plunging into liquid nitrogen and liquid propane have been determined for capillary diameters from 3.3 mm to 150 μm.