On Discrete Killing Vector Fields and Patterns on Surfaces

Symmetry is one of the most important properties of a shape, unifying form and function. It encodes semantic information on one hand, and affects the shape's aesthetic value on the other. Symmetry comes in many flavors, amongst the most interesting being intrinsic symmetry, which is defined only in terms of the intrinsic geometry of the shape. Continuous intrinsic symmetries can be represented using infinitesimal rigid transformations, which are given as tangent vector fields on the surface – known as Killing Vector Fields. As exact symmetries are quite rare, especially when considering noisy sampled surfaces, we propose a method for relaxing the exact symmetry constraint to allow for approximate symmetries and approximate Killing Vector Fields, and show how to discretize these concepts for generating such vector fields on a triangulated mesh. We discuss the properties of approximate Killing Vector Fields, and propose an application to utilize them for texture and geometry synthesis.     

From synthetic to natural nanoparticles: monitoring the biodegradation of SPIO (P904) into ferritin by electron microscopy

A strong focus on Superparamagnetic Iron Oxide Nanoparticles (SPIOs) has been appreciated recently especially for their use in Magnetic Resonance Imaging (MRI). However, some questions are being raised over these particles due to their long-term toxicity related to the production of toxic free iron during their biodegradation. Here we show by Electron Microscopy how SPIOs (P904) (Guerbet, Paris) are degraded after they are taken up by macrophages, so that iron from the SPIO core is progressively incorporated into the iron-storing protein ferritin (a nontoxic form of iron).     

The redox thermodynamics and kinetics of flavonoid rutin adsorbed at glassy carbon electrodes by stripping square wave voltammetry

The adsorptive accumulation of rutin (RU) at glassy carbon (GC) electrodes in 10% ethanol + 90% 1 mol dm⁻³ HClO₄ aqueous solution is studied by using cyclic (CV) and square wave (SWV) voltammetries. The Frumkin adsorption isotherm best described the specific interaction of rutin with carbon electrodes. By fitting the experimental data, values of −31.9 kJ mol⁻¹ and 0.54 ± 0.02 were obtained for the Gibbs free energy of adsorption and the interaction parameter, respectively. SWV fully characterized the thermodynamics and kinetics of the surface redox process, using a combination of the “quasi-reversible maximum” and the “splitting of SW peaks” methods. Average values of 0.644 ± 0.003 V and 0.44 ± 0.02 were obtained for the formal potential and the anodic transfer coefficient, respectively. Moreover, a formal rate constant of 6.1 × 10² s⁻¹ was obtained. SWV was also employed to generate calibration curves. The lowest concentration of RU experimentally measured for a signal-to-noise ratio of 3:1 was 2 × 10⁻⁸ mol dm⁻³ (12 ppb).     

Stereochemistry of Neolignans - A Revised Structure for a Neolignan Isolated from the Roots of Piper capense

The erythro8-O-4′ neolignan IIIb was synthesized and was found to have identical ¹H and ¹³C NMR characteristics to a neolignan reported as a component of the roots of Nardostachys jatamansi. The NMR spectral characteristics of compound IIIb were also identical with those of a neolignan previously obtained from the roots of Piper capense, for which the unlikely 8-O-3′ structure IVa had been proposed. Two further erythro 8-O-4′ compounds IIIc and IIId were prepared, and their assigned ¹³C NMR signals were consistent with those of IIIb. At this time, there appears to be no evidence for the existence of 8-0-3′ neolignans as plant extracts.     

New Epoxy-Anhydride Thermosets Modified with Multiarm Stars with Hyperbranched Polyester Cores and Poly(ϵ-caprolactone) Arms

Multiarm star polymers with hyperbranched aromatic or aromatic-aliphatic cores and poly(?-caprolactone) arms have been used as toughness modifiers in epoxy-anhydride formulations catalyzed by benzyldimethylamine. The curing process has been studied by dynamic scanning calorimetry, demonstrating little influence of the mobility of the reactive species and the hydroxyl content on the kinetics of this process. The obtained materials were characterized by thermal and mechanical tests and the microstructure by electron microscopy. Homogeneous thermosets have been obtained with a remarkable increase in impact strength without compromising glass transition temperature, thermal stability or hardness.     

Identification of heat integration retrofit opportunities for crude distillation and residue cracking units

This study investigates improving the energy efficiency of two key refining processes: the Crude Distillation Unit (CDU) and the Residue Cracking Unit (RCU). The research methodology followed the ‘targeting before design’ approach. The CDU is a ‘tightly pinched’ system, with limited opportunities for further energy savings. The RCU actual ΔT_min is around 55 °C indicating a low level of current heat recovery. The Total-Site analysis shows that theoretically 18 MW of heat could be transferred from the RCU to the CDU, reducing CDU requirements by 40% for a new or grass roots design. RCU retrofit designs were developed to increase steam generation by up to 35% and in line with targeting estimates would appear to have economic potential. The alternative CDU-RCU retrofit design was developed to decrease CDU hot utility use. Although the Total-Site profile demonstrated strong potential for heat integration, this retrofit design is not commercially attractive, as the decrease in CDU fuel does not offset the cost of reduced steam generation. This demonstrates the need to consider the different fuel and steam costs in the Total-Site analysis.     

Hydrogen Spillover in Ga2O3–Pd/SiO2 Catalysts for Methanol Synthesis from CO2/H2

The hydrogenation of CO₂ was investigated on Ga₂O₃-promoted Pd/SiO₂ catalyts and mechanical mixtures of Ga₂O₃/SiO₂ and Pd/SiO₂ catalysts (H₂/CO₂ = 3; P = 3.0 MPa; T = 523 K). By means of the latter it was possible to demonstrate that atomic hydrogen, H_s, can be generated by Pd⁰ far from Ga₂O₃, and move (spill-over) there to reach the other reactive species (formates) and complete the reaction cycle. The reaction results indicate that (as also evidenced by in situ FTIR) the Ga₂O₃-Pd/SiO₂ catalyst works as a true bi-functional system. The metal-promoter intimacy is not decisive in terms of the catalytic chemistry of the system, but the closeness between the Pd crystallites and the Ga₂O₃ surface patches boost the activity, owing to a minimized effort in the H_s supply to the latter.     

High temperature oxidation of SiC under helium with low-pressure oxygen. Part 2: CVD β-SiC

In the frame of the Generation IV International Forum, Gas-cooled Fast Reactor (GFR) is one system studied by CEA (France). Helium pressurized at 7 MPa is the coolant and the nominal temperature of use is about 1300 K. The cladding materials currently considered is a SiC/SiC composite with a β-SiC coating. In case of accident, reactor temperatures can reach 1900–2300 K. A previous study was carried out to determine the physico-chemical behavior of another polytype, α-SiC, for comparison on the position of the active to passive transition and of the mass loss rates under active conditions to simulate a typical accident. Experimental oxidation tests at high temperature (1400–2300 K) on massive β-SiC samples processed by Chemical Vapor Deposition (CVD) coupled to mass variation, SEM, XPS, AFM and roughness analyses enabled to determine the transition between passive and active oxidation regimes, and to study the resistance to oxidation of such material in some conditions that might be encountered in case of accident (high temperature increase up to 2300 K). Finally, the experimental results have shown that the transition from passive to active regime occurs at higher temperature for β-SiC than for α-SiC and that the mass loss rate of β-SiC is lower than the one measured for α-SiC on the common temperature range investigated (up to 2100 K).