CAD-based calibration and shape measurement with stereoDIC

A new calibration procedure is proposed for a stereovision setup. It uses the object of interest as the calibration target, provided the observed surface has a known definition (e.g., its CAD model). In a first step, the transformation matrices needed for the calibration of the setup are determined assuming that the object conforms to its CAD model. Then the 3D shape of the surface of interest is evaluated by deforming the a priori given freeform surface. These two steps are performed via an integrated approach to stereoDIC. The measured 3D shape of a machined Bézier patch is validated against data obtained by a coordinate measuring machine. The feasibility of the calibration method’s application to large surfaces is shown with the analysis of a 2-m² automotive roof panel.     

Relay catalysis: combined metal catalyzed oxidation and asymmetric iminium catalysis for the synthesis of bi- and tricyclic chromenes

A catalytic asymmetric oxidative iminium-allenamine cascade allows the use of propargyl alcohols as stable substrates and yields valuable chiral bicyclic 4H-chromenes. A subsequent Michael addition-condensation domino reaction provides complex tricyclic 4H-chromenes in a highly enantioselective fashion.     

Influence of the crystallite size on the phase transformation of yttria irradiated with swift heavy ions

The irradiation effects induced by swift heavy ions are now widely described in `bulk' materials. It is shown here that the behaviour of matter under irradiation depends on its crystalline state in the sense that a given material is all the more sensitive to swift heavy ion irradiations as the mean crystallite size L is small. The present paper relates the experimental results obtained in yttrium oxide from `in situ' X-ray diffraction measurements. Three kinds of sample have been irradiated: sintered samples (L = 1μm), non-ground powders (L = 45 nm) and ground powders (L = 28 nm). A cubic to monoclinic phase transformation appears if the electronic energy loss of the incident particle is higher than a threshold. The comparison between the different kinds of samples reveals that this phase transformation is all the easier as the mean crystallite size of the target is weak. Received 27 January 2000 and Received in final form 13 December 2000     

Design and development of a new program for data processing of mass spectra acquired by means of a high-resolution double-focusing glow-discharge mass spectrometer

An new program has been developed and implemented for data analysis of mass spectra obtained by use of the VG9000 glow-discharge mass spectrometer. The program, designed to run in a Windows 9X environment includes several tools for import and export of data, cluster generators, etc. An automated technique for the interpretation of mass spectra is also built into the program; this enables faster and operator-independent interpretation. When major interferences or not-well defined signals are involved, the automated technique might fail to find the correct result. Therefore, a manual, VG9000 software-like, bypass is at hand. A comparison of the different techniques and programs shows, in general, comparable results. An installable version of the software is available on the university FTP-server (ftp://PLASMA-FTP.uia.ac.be/ private/imsas/).     

Application of comprehensive multidimensional gas chromatography combined with time-of-flight mass spectrometry (GC x GC-TOFMS) for high resolution analysis of hop essential oil

The selection and quality of hops is a major determinant in beer flavour. Brewers acknowledge that distinctive characteristics of different hop varieties can be traced to the composition of their essential oils. The difficulty in characterising complex mixtures such as hop oil using 1-D chromatography is that many compounds co-elute. With the introduction of comprehensive multidimensional capillary gas chromatography (GC x GC), there is a tremendous improvement in the separation power or peak capacity. Recent work using GC x GC with flame ionisation detection has suggested that there may be over 1,000 compounds in hop oil. This work describes the use of GC x GC combined with TOFMS detection (Leco Pegasus 4D instrument) to analyse Target hop oil. The TOFMS spectral acquisition rate of 60 Hz provided sufficient spectra per peak (2-D peak base width of 0.1-0.2 s) for identification (119 components were identified with 45 previously unreported compounds). When analysing results, an advantage of GC x GC coupled to TOFMS is that 2-D chromatograms can be viewed for individual masses that are characteristic of particular functional groups. This allows the analyst to view the various homologous series of compounds although in certain cases coelution may still be present as shown by the esters with mass 75.     

Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.     

Nambu Structures and Integrable 1-Forms

Some years ago Moshé Flato pointed out that it would be interesting to develop Nambu's idea to generalize Hamiltonian mechanics. An interesting new formalism in that direction was proposed by L. Takhtajan. His theory gave new perspectives concerning deformation quantization, and many authors have developed its mathematical features. The purpose of this Letter is to show that this theory, at first dedicated to physics, presents a new point of view for the study of singularities of integrable 1-forms. Namely, we will prove that any integrable 1-form which vanishes at a point and has a nonzero linear part at this point is, up to multiplication by a nonvanishing function, the formal pull-back of a two-dimensional 1-form. We also obtain a classification of quadratic integrable 1-forms.     

Theory of chemical equilibrium in a lattice

The chemical equilibrium is studied for the reactionA+B?C, assuming that, initially, the particlesB form a lattice and the particlesA are statistically distributed on interstices. A mass action law is derived which defines the numbersn _A, n_B, n_C of particlesA, B,C in the chemical equilibrium assuming the initial distribution to be known. It predicts a considerably larger numbern _C of fused particlesC compared to the mass action law for the gaseous phase. The result holds for an ordinary as well as for a nuclear lattice. Its possible relevance for the production of proton-rich isotopes in the universe is discussed.