Subnanosecond multiphonon relaxation of divalent copper impurities in LiTaO3

The temperature dependence of the lifetime of the excited ²T₂ state of the Cu²⁺ ion in a LiTaO₃ crystalline host has been measured with picosecond optical pulses. Its value ranges from 450 psec at 22°K to 10 psec at 423°K. Consistent with this result is the observation of weak fluorescence at 1.75 μm having a low temperature quantum efficiency of ～ 10^?6. The experimental results are in reasonably good agreement with recent theoretical models based on strong coupling of the Cu²⁺ impurities to the host lattice.     

Interfacial Wave Motions Due to Marangoni Instability

Collisions and reflections of solitary waves and (periodic) wave trains driven by surface tension gradients (Marangoni stresses) exhibit a wealth of astonishing features. Depending on the angle between the incoming wave crests, the outgoing waves show in their trajectories after collision negative phase shift for small enough angles, no phase shift at about pi/2 and hence no appreciable change in their trajectories, or positive phase shift, accompanied by the appearance of a phase-locked third wave or Mach-Russell stem at wider crossing angles. Synchronous wave collisions exhibit regular but complex dynamic network patterns whose formation and dependence on the size and the shape of the container are discussed. Although wave reflections share some of these features, corresponding apparently to the outcome of the virtual collision of a wave with its mirror image, there are significant differences that are described here. Copyright 2001 Academic Press.     

Towards the european strategy for particle physics: The briefing book

This document was prepared as part of the briefing material for the Workshop of the CERN Council Strategy Group, held in DESY Zeuthen from 2nd to 6th May 2006. It gives an overview of the physics issues and of the technological challenges that will shape the future of the field, and incorporates material presented and discussed during the Symposium on the European Strategy for Particle Physics, held in Orsay from 30th January to 2nd February 2006, reflecting the various opinions of the European community as recorded in written submissions to the Strategy Group and in the discussions at the Symposium.     

Combining Enzymatic Esterification with Conventional Alkaline Transesterification in an Integrated Biodiesel Process

An integrated biodiesel process that combines enzymatic esterification and alkaline transesterification is suggested. With focus on the enzymatic step, the paper provides proof of concept and suggestions for further process development. Hence, palm fatty acid distillate (PFAD) has been enzymatically converted to fatty acid methyl esters in a two-step process using the immobilized lipase Novozym 435 in packed-bed columns. With only a small excess of methanol, the first reaction stage could reduce the free fatty acid (FFA) content from 85% to 5%. After removal of water by simple phase separation, it was possible to lower the FFA content to 2.5% in a second reaction stage. Both reaction stages are relatively fast with suggested reaction times of 15 min in column 1 (productivity 10 kg/kg/h) and 30 min in column 2 (productivity 5 kg/kg/h), resulting in 15% FFA after column 1 and 5% FFA after column 2. A lifetime study indicated that approximately 3,500 kg PFAD/kg Novozym 435 can be treated in the first reaction stage before the enzyme has become fully inactivated. With further optimization, the enzymatic process could be a real alternative to today’s sulfuric acid catalyzed process.     

Gas‐Phase Reactions of Cationic Vanadium‐Phosphorus Oxide Clusters with C2Hx (x=4, 6): A DFT‐Based Analysis of Reactivity Patterns

The reactivities of the adamantane‐like heteronuclear vanadium‐phosphorus oxygen cluster ions [V_xP_4?xO₁₀]^.+ (x=0, 2–4) towards hydrocarbons strongly depend on the V/P ratio of the clusters. Possible mechanisms for the gas‐phase reactions of these heteronuclear cations with ethene and ethane have been elucidated by means of DFT‐based calculations; homolytic C? H bond activation constitutes the initial step, and for all systems the P? O^. unit of the clusters serves as the reactive site. More complex oxidation processes, such as oxygen‐atom transfer to, or oxidative dehydrogenation of the hydrocarbons require the presence of a vanadium atom to provide the electronic prerequisites which are necessary to bring about the 2e^? reduction of the cationic clusters.     

A practical synthesis of [C4] N-benzylpiperazine from [C2] glycine

A high yielding gram-scale synthesis of [¹³C₄] N-benzylpiperazine for use as a convenient and versatile building block in isotope labeling studies of clinical drug candidates is reported.     

Control of the electrical conductivity of composites of antimony doped tin oxide (ATO) nanoparticles and acrylate by grafting of 3-methacryloxypropyltrimethoxysilane (MPS)

The effect of the addition of antimony doped tin oxide (ATO) nanoparticles on the electrical conductivity of acrylate films is described. To enable dispersing of ATO in acrylate matrices, 3-methacryloxypropyltrimethoxysilane (MPS) was grafted on the surface of the filler. The amount of MPS used for this surface modification was found to strongly affect the electrical conductivity. Surface modification with a large amount of MPS resulted in colloidally stable dispersions of ATO, leading to a homogeneous distribution. Surface modification with small amounts of MPS led to instable ATO dispersions and aggregation of ATO into a fractal type network, which gives a much higher conductivity especially at low-volume fractions. For composites with a fractal type ATO network a second effect was found. Decreasing the amount of on ATO grafted MPS resulted in an increase of the electrical conduction between the ATO particles.