Bifurcations in rotorcraft flight dynamics

La dynamique du vol des hélicoptères est fortement non-linéaire à cause de la dynamique complexe du rotor principal et des nombreux couplages entre les différents éléments et variables physiques. La théorie des bifurcations examine les changements qualitatifs de types des trajectoires solution d'un système dynamique. Grâce à elle, plusieurs phénomènes physiques concrets seront analysés (état d'anneaux tourbillonnaires,  roulis hollandais). La pertinence de diverses modélisations sera évaluée

Conceptual Design of Environmentally Friendly Rotorcraft - A Comparison of NASA and ONERA Approaches

In 2011, a task was initiated under the US-French Project Agreement on rotorcraft studies to collaborate on design methodologies for environmentally friendly rotorcraft. This paper summarizes the efforts of that collaboration. The French and US aerospace agencies, ONERA and NASA, have their own software toolsets and approaches to rotorcraft design. The first step of this research effort was to understand how rotorcraft impact the environment, with the initial focus on air pollution. Second, similar baseline helicopters were developed for a passenger transport mission, using NASA and ONERA rotorcraft design software tools. Comparisons were made between the designs generated by the two tools. Finally, rotorcraft designs were generated targeting reduced environmental impact. The results show that a rotorcraft design that targets reduced environmental impact can be significantly different than one that targets traditional cost drivers, such as fuel burn and empty weight

C-fos and c-jun Proto-Oncogene Expression Is Decreased in Psoriasis: an In Situ Quantitative Analysis

Psoriasis is a common, sometimes sevcre, non-malignant skin disease characterized by hyperproliferation and abnormal differentiation of keratinocytes. Because proto-oncogenes are implicated in both cell proliferation and differentiation, their expression could be modified in skin diseases such as psoriasis. The c-fos and c-jun proto-oncogenes, whose products associate to form a heterodimeric transcription factor, are among the first genes to be expressed when certain cells are stimulated to either proliferate or differentiate. Recent studies in our laboratory have shown that the c-fos protooncogene is highly expressed in normal human adult skin. In the present study, we used in situ hybridization with RNA to compare the expression and localization of c-fos and c-jun transcripts in 15 lesional and non-lesional psoriatic skin samples. Two clinical variants of psoriasis were studied: the most severe and chronic form or plaque-type psoriasis (N = 10) and rapidly resolutive guttate-type psoriasis (N = 5). Quantitative analysis was performed using a semi-automatic image analyzer and the “Starwise grain” software program. Our control samples included 10 normal skins and eight specimens from other benign hyperproliferative non-psoriatic skin diseases, consisting of three with inflammation (seborrheic dermatitis and atopic dermatitis), and 5 without inflammation (seborrheic keratoses). Control genes we used for in situ hybridization and RNA integrity were keratin 14, which is expressed in the epidermis and was normally expressed in all tissue analyzed, and ribosomal RNA. Our data showed that c-fos and c-jun were expressed to an equivalent extent, both spatially and quantitatively, in all specimens tested. Expression was significantly decreased in plaque-type but not in guttate-type psoriasis. It was also decreased in the three other benign inflammatory cutaneous hyperproliferative disorders, but not in the five non-inflammatory cases. These results were surprising because hyperproliferation was here associated with a decrease in proto-oncogene expression, thus suggesting that c-fos and c-jun do not play a crucial role in the control of keratinocyte proliferation in vivo. However, their reduced expression in some abnormally differentiated skins indicates that both c-fos and c-jun proto-oncogenes may play a key role in keratinocyte differentiation. Their altered expression correlated with severity of the disease and the presence of an inflammatory infiltrate. These data offer a new insight into the role and regulation of these proto-oncogenes in vivo in humans

Inhibition of the Proprotein Convertases Represses the Invasiveness of Human Primary Melanoma Cells with Altered p53, CDKN2A and N-Ras Genes

Altered tumor suppressor p53 and/or CDKN2A as well as Ras genes are frequently found in primary and metastatic melanomas. These alterations were found to be responsible for acquisition of invasive and metastatic potential through their defective regulatory control of metalloproteinases and urokinase genes.Using primary human melanoma M10 cells with altered p53, CDKN2A and N-Ras genes, we found that inhibition of the proprotein convertases (PCs), enzymes involved in the proteolytic activation of various cancer-related protein precursors resulted in significantly reduced invasiveness. Analysis of M10 cells and their gastric and lymph node derived metastatic cells revealed the presence of all the PCs found in the secretory pathway. Expression of the general PCs inhibitor alpha1-PDX in these cells in a stable manner (M10/PDX) had no effect on the mRNA expression levels of these PCs. Whereas, in vitro digestion assays and cell transfection experiments, revealed that M10/PDX cells display reduced PCs activity and are unable to process the PCs substrates proIGF-1R and proPDGF-A. These cells showed reduced migration and invasion that paralleled decreased gelatinase MMP-2 activity and increased expression and secretion of tissue inhibitor of metalloproteinase-1 (TIMP-1) and TIMP-2. Furthermore, these cells showed decreased levels of urokinase-type plasminogen activator receptor (uPAR) and increased levels of plasminogen activator inhibitor-1 (PAI-1).Taken together, these data suggest that inhibition of PCs activity results in decreased invasiveness of primary human melanoma cells despite their altered p53, CDKN2A and N-Ras genes, suggesting that PCs may serve as novel therapeutic targets in melanoma

A Reliable Method for the Selection of Exploitable Melanoma Archival Paraffin Embedded Tissues for Transcript Biomarker Profiling

The source tissue for biomarkers mRNA expression profiling of tumors has traditionally been fresh-frozen tissue. The adaptation of formalin-fixed, paraffin-embedded (FFPE) tissues for routine mRNA profiling would however be invaluable in view of their abundance and the clinical information related to them. However, their use in the clinic remains a challenge due to the poor quality of RNA extracted from such tissues. Here, we developed a method for the selection of melanoma archival paraffin-embedded tissues that can be reliably used for transcript biomarker profiling. For that, we used qRT-PCR to conduct a comparative study in matched pairs of frozen and FFPE melanoma tissues of the expression of 25 genes involved in angiogenesis/tumor invasion and 15 housekeeping genes. A classification method was developed that can select the samples with a good frozen/FFPE correlation and identify those that should be discarded on the basis of paraffin data for four reference genes only. We propose therefore a simple and inexpensive assay which improves reliability of mRNA profiling in FFPE samples by allowing the identification and analysis of “good” samples only. This assay which can be extended to other genes would however need validation at the clinical level and on independent tumor series

Théorie des bifurcations appliquée à l'analyse de la dynamique du vol des hélicoptères

Cette étude consiste à explorer les possibilités offertes par la théorie des bifurcations pour l'analyse concrète de la dynamique du vol des hélicoptères. Un état de l'art permet de montrer en quoi la méthodologie a fait ses preuves dans le cas de la mécanique du vol des avions et présente quelques phénomènes fortement non-linéaires issus du domaine des hélicoptères. Dans un premier temps, il s'agit de mettre en place la problématique. Des travaux informatiques aboutissent au couplage du code HOST de mécanique du vol des hélicoptères d'EUROCOPTER et du code ASDOBl d'analyse des systèmes dynamiques de l'ONERA. Un modèle analytique d'hélicoptère complètement dédié et adapté à cette application est également développé. Par ailleurs, il est mis en évidence que la bonne formulation mathématique des problèmes évoqués est celle d'un système algébrico-différentiel. Dans un second temps, trois cas illustratifs de la démarche sont étudiés. Tout d'abord, l'instabilité aérodynamique liée à la formation d'anneaux tourbillonnaires à la périphérie du rotor dans certains cas de vol est analysée et des bifurcations de valeur propre réelle sont diagnostiquées. Un nouveau critère pour délimiter la région d'instabilité est donné par le calcul du lieu des points de ces bifurcations. Ensuite, le cas du roulis hollandais est examiné montrant que la bifurcation de Hopf (supercritique) sous-jacente s'avère donner naissance à des cycles limites stables. Enfin, l'étude porte son attention sur le couplage aéronef-pilote. Des oscillations induites par le pilote sont constatées pour la chaîne de commande choisie. Des bifurcations nœuds-selles de cycles limites et des sauts d'orbites périodiques correspondent aux changements brusques de qualités de vol observésThis study aims at exploring the interest of using bifurcation theory to analyse concretely helicopter flight dynamics. A state-of-the-art allows to show how the methodology was applied with success in the case of fixed-wings aircrafts flight dynamics and presents some phenomenons highly nonlinear coming from the helicopter world. The first step is to set up the issue. lnformatical works end up with the coupling of the HOST code of helicopter flight mechanics from EUROCOPTER and the ASDOBl code of dynamical systems analysis from ONERA. An analytical helicopter model absolutely dedicated and adapted to this application is also developed. Moreover, it is shown that the required mathematical formulation of the evoked problems is based on a differential algebraic system representation. ln a second step, three illustrative cases of this approach are studied. Firstly, the aerodynamic instability due to the vortex rings formation at the rotor periphery in some flight cases is analysed and bifurcations of real eigenvalues are diagnosed. A new criterion to delimit the region of instability is given by the calculation of the locus of these bifurcations. Then, the case of the Dutch roll is examined showing that the underlying (supercritical) Hopf bifurcation turns out to give rise to stable limit cycles. Finally, the study is interested in aircraft-pilot coupling. Pilot induced oscillations are determined for the chosen command channel. Saddle-node bifurcations of limit cycles and jumps of periodical orbits corresponds to the handling qualities cliffs observedGRENOBLE1-BU Sciences (384212103) / SudocSudocFranceF

SELECTIVE HYDROGENATION ON PLATINUM NANOPARTICLES STABILIZED BY ORGANOSILANES

Nanoparticles are widely used in heterogeneous catalysis and generally, they are supported on oxides such as silica or alumina. Unfortunately, strong interactions between support and particles exist and lead to the modification of the particles’ properties which means that no unique active sites are obtained. Other side phenomena like diffusion or migration of adsorbed atoms towards the support surface are observed and undesired reactions (isomerization, cyclization,…) with the acid sites take place. Unsupported metal nanoparticles do not interact with a support. Their properties can be modified depending on their size especially in the order of magnitude between 1 and 10 nm. This makes unsupported nanoparticles interesting candidates for fine chemical catalytic applications since no side phenomena occur and active sites are well defined. Surface Organometallic Chemistry on Metals allows controlling the coordination sphere of the active metal by an organometallic fragment. By changing “at will” the steric and electronic properties of the organometallic fragment, it is possible to influence the chemio- , stereo- and regio-selectivity of reactions catalyzed by metallic surfaces. Pt is considered to be a very good catalyst for selective hydrogenation; in particular for enantioselective hydrogenation of alpha ketoesters and it is believed to be less hydrolyzing than Ru. Unsupported Pt nanoparticles were prepared following the procedure already described for Ru, using Pt(dba)2 as precursor and octylsilane (C8SiH3) or vinylphenylmethylsilane (VPMSiH) as stabilizer. The size and the structure of the nanoparticles were determined by TEM and the grafted organometallic fragments were characterized by solid state 1H and 13C CP-MAS NMR, IR and elementary analysis. Crystalline Pt nanoparticles (see Figure) of about 2 nm corresponding to a cubo-octahedron with 3 edge atoms, covered by organosilane fragments were obtained. These nanoparticles are active and chemio-selective in the hydrogenation of cetopentoylactone into the corresponding alcohol and their properties were compared to silica supported Pt