Tribological study of a press-fit assembling process

International audienceA particular case of press-fitting of two metal parts is studied, with high fit interference inducing high contact pressures and plastic deformation of the bushing and collar. Furthermore, the female piece is polymer-coated by cataphoresis, and the coating evolution by damage and wear during sliding promotes significant changes of friction with sliding length. These particular frictional properties impact the structural mechanics behaviour of the system during assembling

Etude expérimentale et modélisation de l'évolution couplée du frottement et de l'usure dans un contact entre une surface métallique et un revêtement polymère

International audienceDans une jonction statique, le frottement a la particularité de devoir atteindre un fort niveau en fin d'assemblage, car il représente la majeure partie de la force de résistance de la jonction en service. Ce niveau de frottement est conféré par le procédé d'assemblage. Nous nous intéressons ici aux relations entre frottement et usure pour un assemblage polymère - métal caractérisé par un contact sous haute pression (localement, plus de 500 MPa), mais à basse vitesse (quelques mm.s-1) et avec une faible longueur de glissement (inférieure à 10 mm). Pour simuler ce contact, des essais tribologiques en régime linéaire alternatif ont été mis au point, dans lequel ont été utilisés des objets les plus proche possible des pièces réelles. Le polymère est celui qui reste en contact permanent, le métal voyant, lui, défiler la zone de contact. Le frottement augmente fortement au début de l'essai, puis se stabilise. En observant les surfaces en microscopie optique et électronique, on montre qu'une forte usure du polymère se produit, et que les particules d'usure se déposent pour une grande part dans la rugosité de la surface métallique. Des essais complémentaires montrent que ce piégeage de particules d'usure est la cause principale de l'augmentation du frottement. Un paramètre essentiel est la rugosité du métal, dont l'usure et la croissance du frottement sont fonctions croissantes. La croissance du frottement est modélisée sur la base du concept de troisième corps et d'un bilan de la circulation des particules d'usure. La comparaison aux courbes expérimentales de frottement montre la pertinence de ce modèle

Modulation of interferon-[alpha] secretion by activated platelets in systemic lupus erythematosus.

Type I interferons play a key role in systemic lupus erythematosus (SLE) pathogenesis as an "IFN signature" is found in the majority of patients with active SLE. Immune complexes are internalized by plasmacytoid dendritic cells (DC) via Fc-[gamma] ReceptorIIA, reach the endosomal compartment and activate IFN-[alpha] secretion through TLR7/9-dependent pathways. Naturally occurring differences in expression of the TLR7/9 gene as well as factors that modulate TLR7/9 expression, including CD154 could therefore contribute to SLE pathogenesis. Although its origin is not elucidated CD154 is hyperexpressed in SLE patients, and is important for the differentiation of autoantibody-secreting cells. We hypothesized that platelets which are an abundant source of CD154, and which can mediate proinflammatory effects could be an actor involved in SLE pathogenesis. Platelets from SLE patients are activated _in vivo_ by circulating immune complexes which are abundant in SLE sera, via a CD32-dependent mechanism. Activated platelets formed aggregates with antigen-presenting cells in SLE patients and enhanced interferon-[alpha] secretion induced by immune-complexes stimulated plasmacytoid DCs. Finally, _in vivo_ depletion of platelets and megakaryocytes in NZBxNZW(F1) lupus prone mice improved all parameters assessing disease activity, whereas transfusion of activated platelets worsened the disease course. Altogether, these data identify platelets as a mediator of SLE pathogenesis and a new therapeutical target

Etude de l'évolution couplée du frottement et de l'usure dans un contact entre une surface métallique et un revêtement polymère

National audienceDans une jonction statique, le frottement a la particularité de devoir atteindre un fort niveau car il représente la majeure partie de la force de résistance de la jonction. Ce niveau de frottement est conféré par le procédé d'assemblage. Nous nous intéressons ici aux relations entre frottement et usure pour un assemblage polymère - métal caractérisé par un contact sous haute pression (localement, plus de 500 MPa), mais à basse vitesse (quelques mm.s-1) et avec une faible longueur de glissement (inférieure à 10 mm). Pour simuler ce contact, des essais tribologiques bille - plan en régime linéaire alternatif ont été mis au point, sous deux formes duales : le revêtement " usable ", polymère, est soit en contact permanent (bille revêtue sur tôle métallique plane et rugueuse), soit en contact transitoire (bille métallique rugueuse sur tôle plane revêtue de polymère)

Rituximab Efficacy during a Refractory Polyarteritis Nodosa Flare

Polyarteritis nodosa (PAN) is a systemic vasculitis whose severe forms are treated with glucocorticoids and cyclophosphamide. Refractory patients are exposed to many complications, notably accelerated atherosclerosis. We report a case report of 71-year-old man followed for polyarteritis nodosa refractory to glucocorticoids and cyclosphosphamide. Systemic vasculitis relapses are followed to accelerated atherosclerosis: severe ischemic lesions led to amputation of lower limbs. Remission of refractory PAN is obtained with rituximab. Disappearance of biological inflammatory is allowed to regression of ischemic lesions in upper limbs. In this situation, we recommend a systematic vascular work-up for patients suffered from refractory vasculitis. On the other hand, therapeutic trials are needed to determine the real efficacy and place of rituximab in the treatment of polyarteritis nodosa

Locoregional treatments for digital ulcers in systemic sclerosis: A systematic review

The management of digital ulcers in systemic sclerosis is difficult. While the 2017 European League Against Rheumatism (EULAR) guidelines clearly defined the use of systemic therapies for digital ulcers, little is known about the efficacy of locoregional treatments. The aim of this review is to systematically assess the spectrum of published locoregional therapies for digital ulcers. A total of 58 studies were included. Among the different locoregional treatment strategies descri-bed, injections of fat-derived cells and botulinum toxin showed promising results in the reduction of pain and the number of digital ulcers. By contrast, this review found that sympathectomy yielded disappointing re-sults, with low rates of effectiveness and frequent recurrence. For other treatments, such as hyperbaric oxygen therapy, phototherapy (ultraviolet A), low-level light therapy, intermittent compression, Waon therapy, extracorporeal shockwave, vitamin E gel, and topical dimethyl sulphoxide, the conflicting results or limited published data reflected the low level of evi-dence. Larger randomized clinical trials are required to confirm the validity of promising techniques

T Follicular Helper Cells in Autoimmune Disorders

T follicular helper (Tfh) cells are a distinct subset of CD4+ T lymphocytes, specialized in B cell help and in regulation of antibody responses. They are required for the generation of germinal center reactions, where selection of high affinity antibody producing B cells and development of memory B cells occur. Owing to the fundamental role of Tfh cells in adaptive immunity, the stringent control of their production and function is critically important, both for the induction of an optimal humoral response against thymus-dependent antigens but also for the prevention of self-reactivity. Indeed, deregulation of Tfh activities can contribute to a pathogenic autoantibody production and can play an important role in the promotion of autoimmune diseases. In the present review, we briefly introduce the molecular factors involved in Tfh cell formation in the context of a normal immune response, as well as markers associated with their identification (transcription factor, surface marker expression, and cytokine production). We then consider in detail the role of Tfh cells in the pathogenesis of a broad range of autoimmune diseases, with a special focus on systemic lupus erythematosus and rheumatoid arthritis, as well as on the other autoimmune/inflammatory disorders. We summarize the observed alterations in Tfh numbers, activation state, and circulating subset distribution during autoimmune and some other inflammatory disorders. In addition, central role of interleukin-21, major cytokine produced by Tfh cells, is discussed, as well as the involvement of follicular regulatory T cells, which share characteristics with both Tfh and regulatory T cells

Imaging practice in low-grade gliomas among European specialized centers and proposal for a minimum core of imaging

Objective: Imaging studies in diffuse low-grade gliomas (DLGG) vary across centers. In order to establish a minimal core of imaging necessary for further investigations and clinical trials in the field of DLGG, we aimed to establish the status quo within specialized European centers. Methods: An online survey composed of 46 items was sent out to members of the European Low-Grade Glioma Network, the European Association of Neurosurgical Societies, the German Society of Neurosurgery and the Austrian Society of Neurosurgery. Results: A total of 128 fully completed surveys were received and analyzed. Most centers (n=96, 75%) were academic and half of the centers (n=64, 50%) adhered to a dedicated treatment program for DLGG. There were national differences regarding the sequences enclosed in MRI imaging and use of PET, however most included T1 (without and with contrast, 100%), T2 (100%) and TIRM or FLAIR (20, 98%). DWI is performed by 80% of centers and 61% of centers regularly performed PWI.ConclusionA minimal core of imaging composed of T1 (w/wo contrast), T2, TIRM/FLAIR, PWI and DWI could be identified. All morphologic images should be obtained in a slice thickness of 3mm. No common standard could be obtained regarding advanced MRI protocols and PET. Importance of the study: We believe that our study makes a significant contribution to the literature because we were able to determine similarities in numerous aspects of LGG imaging. Using the proposed minimal core of imaging in clinical routine will facilitate future cooperative studies