Stability analysis of gravity driven shear flows with free surface for power-law fluids

Summary We study the stability of thin films of fluids subject to gravity along inclined planes, obeying a power-law constitutive relation of the Ostwald-de Waele type. A first analysis, in which the inertia terms are ignored, shows such flow to be stable against small, linear perturbations; a second analysis, in which the inertia terms are included, proves that there are stable and unstable regimes that are separated by a critical Ostwald-de Waele number O. Numerical computations for selected values of O demonstrate the decay and growth rate behavior of some finite amplitude disturbances. Received 12 May 1997; accepted for publication 23 July 1997     

Empirical method for the prediction of business executive jet cabin noise levels

As a result of flight noise measurements made at various locations in the cabin of the standard lined/no interior Westwind model 1124 business executive jet, it was possible to develop an empirical method for predicting the overall sound pressure level (OASPL) at any required location in the cabin. The cabin overall sound level in decibels (linear) may be found from nomographs related to aircraft altitude, mach number or velocity. The noise spectrum at any location may be found from a reference spectrum shape corrected for local parameters. The accuracy of the prediction method, verified by additional tests, was found to be ± 1 dB.     

Nickelmodifiedlarge poremesoporoussilicas ascatalysts for methanol decomposition

Summary Ni-modifiedlarge poremesoporous silicasarecharacterized by XRD, N₂physisorption and TPR with H₂. Theeffectof the supportpore structure on their catalytic behaviorin methanol decomposition to H₂, CO and CH₄is studied.     

Maximum entropy deconvolution of AFM and STM images

The Maximum Entropy Method (MEM) has been applied successfully to the deconvolution of images obtained by Atomic Force (AFM) and Scanning Tunneling Microscopy (STM) using a NanoScope III system. The images have been taken on graphite (STM) and NaCl (AFM) substrates. Image processing has been performed running the Cambridge MaxEnt Fortran 77 library MEMSYS-5 on an IBM RISC 6000/360. Among the possible hypotheses the optimal solution was selected using the standard entropy method. ICF and response function have been generated artificially to fit the correlation of physical structures for atomically resolved images. Comparison of MEM and FFT revealed, that the main advantage of MEM is its ability to reproduce atomic defects on regular structures, whereas FFT deconvolution tends to eliminate these perturbations.     

Ionic liquids from Car-Parrinello simulations, part I: liquid AlCl3

The properties of isolated AlCl3 clusters and the bulk system are investigated by means of static and dynamic electronic structure methods. We find important structural motifs with the edge connectivity dominant in a dimer and the corner connectivity dominant in a trimer. Furthermore, the trimer cluster exhibits an interesting ring structure with large cooperative effects relative to the dimer. Comparing the found structural motifs in isolated molecule calculations with the structure of the liquid allows us to determine the dominance of edge connectivity in the liquid. The size of the clusters present in the liquid indicates indeed that the dimer is the most abundant species, but there are also trimers, tetramers, and pentamers present. From the local dipole analysis both for the isolated clusters as well as for the liquid, further proof for the edge connectivity is given. However, all results point to the fact that there is also some small percentage of corner connectivity present that might be attributed to the most stable corner-connected cluster, namely the trimer. Importantly, we find that energetic considerations of isolated (static) clusters only do not represent the findings in liquid phase. Instead, a quantum cluster equilibrium approach or simulations are needed.     

Synthetic and computational assessment of a chiral metal–organic framework catalyst for predictive asymmetric transformation

Understanding and controlling molecular recognition mechanisms at a chiral solid interface is a continuously addressed challenge in heterogeneous catalysis. Here, the molecular recognition of a chiral peptide-functionalized metal–organic framework (MOF) catalyst towards a pro-chiral substrate is evaluated experimentally and in silico. The MIL-101 metal–organic framework is used as a macroligand for hosting a Noyori-type chiral ruthenium molecular catalyst, namely (benzene)Ru@MIL-101-NH-Gly-Pro. Its catalytic perfomance toward the asymmetric transfer hydrogenation (ATH) of acetophenone into R- and S-phenylethanol are assessed. The excellent match between the experimentally obtained enantiomeric excesses and the computational outcomes provides a robust atomic-level rationale for the observed product selectivities. The unprecedented role of the MOF in confining the molecular Ru-catalyst and in determining the access of the prochiral substrate to the active site is revealed in terms of highly face-specific host–guest interactions. The predicted surface-specific face differentiation of the prochiral substrate is experimentally corroborated since a three-fold increase in enantiomeric excess is obtained with the heterogeneous MOF-based catalyst when compared to its homogeneous molecular counterpart.

Understanding and controlling molecular recognition mechanisms at a chiral solid interface has been addressed in metal–organic framework catalysts for the asymmetric transfer hydrogenation reaction.