A Pore Scale Model for Osmotic Flow: Homogenization and Lattice Boltzmann Simulations

Transport in Porous Media - Osmosis is the phenomenon of spontaneous passage of solvents through a membrane that is permeable to the solvent but is completely or partially impermeable to solute...     

Reactivity of oximes of 1-aryl(hetaryl)-2-(hydroxyamino)propan-1-ones with ethyl glyoxylate

Chemistry of Heterocyclic Compounds - Alkyl(hetero)aromatic α-hydroxyamino oximes with the anti configuration of the oxime group reacted with ethyl glyoxylate to form...     

Coarse-graining the computations of surface reactions: Nonlinear dynamics from atomistic simulators

We review and discuss the use of equation-free computation in extracting coarse-grained, nonlinear dynamics information from atomistic (lattice-gas) models of surface reactions. The approach is based on circumventing the explicit derivation of macroscopic equations for the system statistics (e.g., average coverage). Short bursts of appropriately initialized computational experimentation with the lattice-gas simulator are designed “on demand” and processed in the spirit of the coarse timestepper introduced in Theodoropoulos et al. (2000) (K. Theodoropoulos, Y.-H. Qian, I.G. Kevrekidis, Proc. Natl. Acad. Sci. USA 97 (2000) 9840). The information derived from these computational experiments, processed through traditional, continuum numerical methods is used to solve the macroscopic equations without ever deriving them in closed form. The approach is illustrated through two computational examples: the CO oxidation reaction, and the NO + CO/Pt(1 0 0) reaction.     

Temperature‐dependent EXAFS study of the local structure and lattice dynamics in cubic Y2O3

The local structure and lattice dynamics in cubic Y₂O₃ were studied at the Y K‐edge by X‐ray absorption spectroscopy in the temperature range from 300 to 1273 K. The temperature dependence of the extended X‐ray absorption fine structure was successfully interpreted using classical molecular dynamics and a novel reverse Monte Carlo method, coupled with the evolutionary algorithm. The obtained results allowed the temperature dependence of the yttria atomic structure to be followed up to ～6 Å and to validate two force‐field models.     

Electronic transport through carbon nanotubes: effects of structural deformation and tube chirality

Atomistic simulations using a combination of classical force field and density-functional theory (DFT) show that carbon atoms remain essentially sp(2) coordinated in either bent tubes or tubes pushed by an atomically sharp atomic-force microscope (AFM) tip. Subsequent Green's-function-based transport calculations reveal that for armchair tubes there is no significant drop in conductance, while for zigzag tubes the conductance can drop by several orders of magnitude in AFM-pushed tubes. The effect can be attributed to simple stretching of the tube under tip deformation, which opens up an energy gap at the Fermi surface.     

Perturbation theory results for the diffuse scattering of light from two-dimensional randomly rough metal surfaces

Using the unitarity and reciprocity preserving formulation of Brown et al a perturbation treatment, correct to fourth order in the surface profile function, is given for the scattering of electromagnetic waves from a weakly rough, two-dimensional, random metal surface. In this formulation the boundary conditions on the electromagnetic fields are satisfied using the extinction theorem in conjunction with the Rayleigh hypothesis and the vector equivalent of the Kirchhoff integral. The theory is applied to, and results are presented for, several different types of rough surfaces which are characterized by power spectra that are extensions to two-dimensional random surfaces of the power spectrum of some one-dimensional random surfaces recently fabricated by West and O'Donnell. These surfaces, which can be realized experimentally, favor coherent, interferent, multiple scattering of electromagnetic waves via surface plasmon polaritons in intermediate states, and clearly exhibit enhanced backscattering caused by the surface plasmon polariton mechanism. Theoretical results are presented for silver surfaces at optical wavelengths.     

IR selective sensitivity of amorphous/crystalline silicon heterostructure

An IR detector based on a-Sin-type) /c-Si(p-type) heterostructure is reported to have selective sensitivity in the wavelength ranged for 1000–1100 nm with a maximum at 1080 nm. The energy band diagram of the heterostructure is considered taking into account the existence of the interfacial layer. The analysis of the photogeneration and carrier transport processes in the a-Si(n-type) / c-Si(p-type) heterostructure has been carried out. It is shown that the interfacial layer and defect on the a-Si/c-Si boundary control the spectral photosensitivity characteristic.     

Nusselt number measurements for turbulent Rayleigh-Bénard convection

We present high-precision measurements of the Nusselt number N as a function of the Rayleigh number R for a cylindrical sample of water (Prandtl number sigma=4.4) of height L approximately equal to 50 cm and aspect ratio Gamma identical with D/L approximately equal to 1 (D is the diameter) for 3 x 10(9)< or =R< or =6 x 10(10). For R approximately 3 x 10(9) the data are consistent with existing results for acetone (sigma=4.0, R< or =3 x 10(9)). There the measurements are also consistent with a model by Grossmann and Lohse (GL). As R increases, the measurements fall below the GL prediction. Near R=6 x 10(10) the prediction is 8% above the data.