Surface lattice dynamics and inelastic He scattering in Cu(111)

Summary We present a calculation of the Cu(111) surface dynamics in the framework of the multipole model. The electronic degrees of freedom include dipole and quadrupole deformabilities of the conduction electron density, the multipole expansion points being located at the midpoints between nearest-neighbour ions. The model accounts for the anomalous longitudinal resonance by an increase of dipolar deformability at the surface. Moreover the model explains in a straight-forward way the intense He scattering from the longitudinal resonance via the dipolar and quadrupolar modulations of the surface electron density. The surface dipolar contribution also explains the intense electron scattering from the optical surface resonance localized on the second layer.     

Surface phonon anomalies in superconducting transition metal compounds

The surface phonon dispersion curves of superconducting refractory materials are shown to present important anomalies induced by the electron-phonon interaction, similar to those appearing in the bulk phonon dispersion. A Green function calculation of surface dynamics for TiN(001), based on a cluster-deformability model, predicts anomalies in the Rayleigh wave, as well as in the surface quasi-longitudinal acoustic and optical branches. The Rayleigh wave anomaly turns out to be shifted down to one half of the zone with respect to the bulk anomaly occurring at $\text{2}\text{3}$ of the zone. Such shift is directly related to the surface-induced change in the average range of electron-phonon interaction. Recent He scattering data on NbSe₂(0001) are commented on in the light of the present theoretical prediction.     

Synthesis of mono- and dihydroxy-substituted 2-aminocyclooctanecarboxylic acid enantiomers

(1R,2S,6R)-2-Amino-6-hydroxycyclooctanecarboxylic acid (?)-10 was synthesized from (1R,2S)-2-aminocyclooct-5-enecarboxylic acid (+)-2 via an iodolactone intermediate, while (1R,2S,3R,4S)-2-amino-5,6-dihydroxycyclooctanecarboxylic acid (?)-12 was prepared by using the OsO₄-catalyzed oxidation of Boc-protected amino ester (?)-5. The stereochemistry and relative configurations of the synthesized compounds were determined by 1D and 2D NMR spectroscopy (based on 2D NOE cross-peaks and ³J(H,H) coupling constants) and X-ray crystallography.     

Quantum Monte Carlo calculations of the dissociation energy of the water dimer

We report diffusion quantum Monte Carlo (DMC) calculations of the equilibrium dissociation energy D(e) of the water dimer. The dissociation energy measured experimentally, D(0), can be estimated from D(e) by adding a correction for vibrational effects. Using the measured dissociation energy and the modern value of the vibrational energy Mas et al., [J. Chem. Phys. 113, 6687 (2000)] leads to D(e)=5.00+/-0.7 kcal mol(-1), although the result Curtiss et al., [J. Chem. Phys. 71, 2703 (1979)] D(e)=5.44+/-0.7 kcal mol(-1), which uses an earlier estimate of the vibrational energy, has been widely quoted. High-level coupled cluster calculations Klopper et al., [Phys. Chem. Chem. Phys. 2, 2227 (2000)] have yielded D(e)=5.02+/-0.05 kcal mol(-1). In an attempt to shed new light on this old problem, we have performed all-electron DMC calculations on the water monomer and dimer using Slater-Jastrow wave functions with both Hartree-Fock approximation (HF) and B3LYP density functional theory single-particle orbitals. We obtain equilibrium dissociation energies for the dimer of 5.02+/-0.18 kcal mol(-1) (HF orbitals) and 5.21+/-0.18 kcal mol(-1) (B3LYP orbitals), in good agreement with the coupled cluster results.     

Perturbation of Singular Equilibria of Hyperbolic Two-Component Systems: A Universal Hydrodynamic Limit

We consider one-dimensional, locally finite interacting particle systems with two conservation laws which under the Eulerian hydrodynamic limit lead to two-by-two systems of conservation laws:with where is a convex compact polygon in ². The system is typically strictly hyperbolic in the interior of with possible non-hyperbolic degeneracies on the boundary . We consider the case of an isolated singular (i.e. non-hyperbolic) point on the interior of one of the edges of , call it (₀,u₀). We investigate the propagation of small nonequilibrium perturbations of the steady state of the microscopic interacting particle system, corresponding to the densities (₀,u₀) of the conserved quantities. We prove that for a very rich class of systems, under a proper hydrodynamic limit the propagation of these small perturbations are universally driven by the two-by-two systemwhere the parameter is the only trace of the microscopic structure.The proof relies on the relative entropy method and thus, it is valid only in the regime of smooth solutions of the pde. But there are essential new elements: in order to control the fluctuations of the terms with Poissonian (rather than Gaussian) decay coming from the low density approximations we have to apply refined pde estimates. In particular Lax entropies of these pde systems play a not merely technical key role in the main part of the proof.     

Oscillations in the expansion of solid 4He into vacuum

The particle flux through a micron-sized orifice into vacuum from a source chamber filled with solid 4He exhibits a striking sequence of periodic bursts. The period increases (decreases) with pressure (temperature), vanishing at the melting point for temperatures above the upper lambda point at 1.76 K. The oscillations are attributed to a periodic collapse of the solid induced by the accumulation of excess vacancies injected at the orifice and the period provides information on vacancy diffusivity. Dramatic deviations from this behavior below 1.76 K suggest important modifications in the flow properties of solid 4He induced by the excess vacancies.     

Studies on the use of needle-free injection device on proteins

In the following communication we report the evaluation of 18 proteins that were processed by a specific needle free injection device. The processed protein samples were analyzed by two HPLC techniques, reversed-phase liquid chromatography (RPLC) and size-exclusion chromatography (SEC). These techniques are two of the most widely used analytical techniques in the biopharmaceutical industry for the characterization, integrity assessment and stability study of peptide and protein products. The results indicate that needle free injection, using the specific device of this study, is not damaging to the studied proteins and does not generate aggregates. We found no evidence of the predicted possible effects of needle free injections, and concluded that needle free delivery is in general not different than any other delivery system and that its use should be evaluated on a case by case basis. It has to be noted that there are various needle free device designs and our work was performed using an Iject from Bioject. Our conclusions therefore should be limited to the Iject design we used in this study. In the reported experiments we used commercially available (economical) model proteins, which facilitate the use of the results for future comparison and reference. The work reported here can serve as a reference to illustrate the benign nature of our needle free injection device. It also highlights an interesting analogy between a set of phobias that were seen to have plagued the early stages of biochemistry and HPLC, on the one hand, and some attitudes that appear to hinder the widespread acceptance of needle free injection at present time, on the other. These phobias were identified and named by Professor Csaba Horváth, the father of HPLC, as barophobia, siderophobia and lithophobia. Today a wealth of evidence is available to indicate that those phobias are ungrounded and that the negative observations can be explained in most cases by adsorption and prevented by proper formulations and solvent conditions.     

Highly enantioselective conjugate addition of nitromethane to chalcones using bifunctional cinchona organocatalysts

Cinchona alkaloid-derived chiral bifunctional thiourea organocatalysts were synthesized and applied in the Michael addition between nitromethane and chalcones with high ee and chemical yields.