On Riemann-problem-based methods for detonations in solid energetic materials

This paper compares several high-resolution schemes for the computation of detonation waves in solid explosives. The essential difficulty in comparison with the usual application domain of these schemes is due to the complexity and variety of the equations of state which are used. The HLLC Riemann solver is used in the context of an Eulerian MUSCL scheme and in conjunction with a shock-tracking scheme. The motivation and justification for the various choices in the building of these schemes are discussed. The accuracy of both schemes, full Eulerian and shock-tracking variant, is clearly demonstrated. In addition, the validity of the results is shown. For one-dimensional applications the shock-tracking scheme is very accurate and relatively simple. For multidimensional applications it is recommended that the full Eulerian version be used. © 1998 John Wiley & Sons, Ltd.     

Characterization of the surface of­bulk‐molded compounds

The automotive industry more and more frequently uses composite materials such as molded compounds (sheet‐molded compounds, SMC, or bulk‐molded compounds, BMC). Bonding is then the only way of assembling two pieces. Consequently, and in order tentatively to predict the adhesive behavior of such materials, it is necessary to have a good knowledge of their surface properties. Here, different complementary techniques of surface analysis allowed us, on the one hand, to reach this aim for BMCs prepared by compression molding and, on the other hand, to show the influence on the surface properties of the concentration and composition of the internal release agent added to the blend. The surface heterogeneity and the organic nature of the surface of the compounds are shown and no phase separation occurs there as in the bulk. Mold release agents remain in the surface layer and induce some acid–base character to the surface material which depends on the type of stearate introduced in the blend. Copyright © 1999 John Wiley & Sons, Ltd.     

A Validated HPLC-PDA-HRMS Method to Investigate the Biological Stability and Metabolism of Antiparasitic Triterpenic Esters

Pentacyclic triterpenes (PTs) are commonly found in medicinal plants with well-known antiparasitic effects. Previous research on C-3 and C-27 triterpenic esters showed effective and selective in vitro antiparasitic activities and in vivo effectiveness by parenteral routes. The aim of this study was to determine triterpenic esters’ stability in different biological-like media and the main microsomal degradation products. An HPLC-PDA method was developed and validated to simultaneously analyze and quantify bioactive triterpenic esters in methanol (LOQ: 2.5 and 1.25–100 µg/mL) and plasma (LOQ: 5–125 µg/mL). Overall, both triterpenic esters showed a stable profile in aqueous and buffered solutions as well as in entire plasma, suggesting gaining access to the ester function is difficult for plasma enzymes. Conversely, after 1 h, 30% esters degradation in acidic media was observed with potential different hydrolysis mechanisms. C-3 (15 and 150 µM) and C-27 esters (150 µM) showed a relatively low hepatic microsomal metabolism (<23%) after 1 h, which was significantly higher in the lowest concentration of C-27 esters (15 µM) (>40% degradation). Metabolic HPLC-PDA-HRMS studies suggested hydrolysis, hydroxylation, dehydration, O-methylation, hydroxylation and/or the reduction of hydrolyzed derivatives, depending on the concentration and the position of the ester link. Further permeability and absorption studies are required to better define triterpenic esters pharmacokinetic and specific formulations designed to increase their oral bioavailability.     

The uptake of Mn-DPDP by hepatocytes is not mediated by the facilitated transport of pyridoxine

Manganese-dipyridoxal diphosphate (Mn-DPDP) is a liver-selective contrast agent selectively taken up by the hepatocytes. Because of the analogy of structure with pyridoxine (vitamin B₆), it was previously suggested that this compound can be selectively taken up by the facilitated transport of vitamers B₆. To understand the uptake mechanism, an in vivo binding study was performed based on a competition between ⁵⁴Mn-DPDP and pyridoxine on the one hand, and Mn-DPDP and [³H]pyridoxine on the other. We found that the [³H]pyridoxine levels in the liver were not significantly different 5 min after intravenous administration of several doses of Mn-DPDP (5 nmol/kg to 50 μmol/kg): 5.0 ± 0.3% of the injected dose/g tissue. The content of ⁵⁴Mn (administered as ⁵⁴Mn-DPDP) in the liver was not affected by a saturation dose of pyridoxine (1 mmol/kg) and was found to be constant (±10% of the injected dose/g tissue) for 60 min. These experiments showed that the uptake of Mn-DPDP is not mediated by the transporter of pyridoxine.     

Application of a modified EHMO-ASED formalism to the determination of the structural parameters of organometallics

The parametrization of the EHMO-ASED method we have recently suggested for organometallics is shown to be also applicable, in principle without any modification, to derive the major structural parameters of second-row transition metal systems such as carbonyls or metallocenes. Furthermore, this model leads to satisfactory results when used to calculate the structure of compounds as large as (N-methylindole)tricarbonylchromium(0) or (phenylo.xazoline) tricarbonylchromlum(0) with full geometry optimization of the ligands.     

Limiting speed for jumping

General mechanical considerations provide an upper bound for the take-off velocity of any jumper, animate or inanimate, rigid or soft body, animal or vegetal. The take-off velocity is driven by the ratio of released energy to body mass. Further, the mean reaction force on a rigid platform during push-off is inversely proportional to the characteristic size of the jumper. These general considerations are illustrated in the context of Alexander's jumper model, which can be solved exactly and which shows an excellent agreement with the mechanical results.     

Data-driven curvilinear reconstructions of 3D MR images: application to cryptogenic extratemporal epilepsy

This paper presents a data-driven method for the reconstruction and visualisation of curvilinear slices from three-dimensional (3D) magnetic resonance (MR) scans of the head. Visualisation of curvilinear slices, rather than standard planar slices, produces symmetrical views of the cortex and allows small abnormalities to be detected by comparing the two hemispheres of the brain. In our method, the surface defined by the upper half of the brain is used as a reference shape for curvilinear reconstructions. The brain is first segmented from the 3D scan using a 3D region growing method associated to an unsupervised threshold selection technique. The upper half of the segmented brain is then extracted and fitted by a deformable surface model. This surface is finally interactively moved by the operator in the 3D scan, to visualise the desired curvilinear slice, which is projected on the screen as a two-dimensional image. We show an application of this visualisation technique to the localisation of cerebral epileptogenic lesions. The procedure has proven efficient and handy in clinical use.     

Poly(ethylene oxide) macromonomer based hydrogels as a template for the culture of hepatocytes

Macromonomer based poly(ethylene oxide) (PEO) hydrogels were tested with respect to their ability to serve as a template for the survival and the growth of hepatocytes. Two systems were considered : either the surface of preexisting hydrogels, with controlled structural parameters, were seeded with isolated rat hepatocytes or the hepatocytes were dispersed in physiological medium containing the macromonomer/initiator and heated to 37°C. In the first case, cells were examined at given times after spreading over two days. The results were compared to those observed for the dispersion of fibroblasts onto a surface of the same type of hydrogels. The effects of the structure of the hydrogels and its chemical nature on the extent of hepatocyte attachment (or encapsulation) and the morphology were investigated.