Indentation d'une membrane fortement précontrainte par un poinçon plat\\ et modèle de type JKR avec tension de surface

The contact between a cylindrical flat indenter and a highly prestressed membrane is considered. The behavior is totally controlled by the assumed constant surface tension. The analytical solution is developed to describe the shape of the surface as a function of the applied force as well as the strain energy. A Griffith/JKR type energy analysis makes then possible to approach the adhesion measurement.Le contact entre un indenteur plat cylindrique et d'une membrane fortement précontrainte est considéré. Le comportement est totalement contrôlé par la tension de surface supposée constante. La solution analytique est développée pour décrire la forme de la surface en fonction de la force appliquée ainsi que l'énergie de déformation. Une analyse énergétique de type Griffith/JKR permet ensuite d'aborder la mesure d'adhésion

Extension du modèle de Hertz pour la prise en compte de la tension de surface dans les essais de nano-indentation des matériaux souples

International audienceThe contact between a spherical indenter and a solid is considered. A numerical finite element model (F. E. M) to taking into account the surface tension of the solid is presented and assessed. It is shown that for nano-indentation of soft materials, the surface tension of the solid influences significantly the reaction force due to indentation. The validity of the classical Hertz model is defined. In very good approximation, the force vs. indentation depth curve can be fitted by a power law function F = a d where F denotes the force acting on the indentor, d the indentation depth, a and b in ]1, 1.5] are constants depending on the materials and the size of the indentor.Le contact entre un indenteur sphérique et un solide élastique est considéré. Un modèle par éléments finis permettant de prendre en compte la tension de surface du solide est présenté et validé. Il est montré que pour la nano-indentation de matières souples, la tension de surface du solide peut influencer considérablement la courbe force vs. profondeur d’indentation. Il est ainsi définit quand le modèle de Hertz classique ne convient plus. En très bonne approximation, la courbe force vs. profondeur d’indentation peux être décrite par une croissance allométrique F = a  d où F désigne la force agissant sur l'indenteur, d la profondeur d’indentation, a et b dans ]1, 1.5] sont des constantes qui dépendent du matériau et du rayon de pointe

INDENTATION, ELASTICITE ET TENSION DE SURFACE

International audienceThe classical models of Hertz, Sneddon and Boussinesq provide solutions for problems of indentation of a semi-infinite elastic massif by a sphere, a sphere or a cone and a flat punch. Although these models have been widely tested, it appears that at small scales and for flexible materials, surface tension can contribute to considerably to the mechanical response to indentation. The scales are typically those of the less than one micron for an elastomer and less than one millimetre for a gel. The exploitation of certain experimental results of microscopy or nanoindentation remain approximate due to the absence of models incorporating the effect of surface tension.Les modèles classiques de Hertz, Sneddon et Boussinesq fournissent des solutions pour les problèmes de l'indentation d'un massif élastique semi-infini par respectivement une sphère, un cône et un poinçon plat. Bien que ces modèles aient été largement éprouvés, il s'avère qu'à petites échelles et pour des matériaux souples, la tension de surface peut contribuer considérablement à la réponse mécanique à l'indentation. Les échelles sont typiquement celles inférieures au micron pour un élastomère et celles inférieures au millimètre pour un gel. L'exploitation de certains résultats expérimentaux de microscopie ou de nanoindentation demeurent approximatifs en raison de l'absence de modèles intégrant l'effet de la tension de surface

Viscoplasticité des polymères amorphes et mécanismes de déformation

Les polymères amorphes tels que le polyméthacrylate de méthyle (PMMA), le polycarbonate (PC) et le polystyrène (PS) sont à l'état vitreux à température ambiante. Ils sont utilisés, entre autres, pour leur transparence mais présentent une transition ductile-fragile qui limite leurs utilisations. Cette fragilité intrinsèque est la conséquence de la visco-élasto-plasticité des polymères. En effet, on constate que la ténacité est considérablement dépendante de la vitesse de chargement du sommet de fissure. En conséquence de la transition adiabatique isotherme et des effets inertiels en sommet de fissures on montre que l'énergie de rupture varie avec la vitesse de fissuration et les mécanismes de fissuration

WTC2005-63582 MECHANICAL ANALYSIS OF THE DAMAGE OF A THIN POLYMERIC COATING DURING SCRATCHING

ABSTRACT Coating is a common way of improving the scratch behaviour of polymeric glasses. A thin coating will prevent the micro-scratches created by the roughness of a diamond tip at the surface of the macro-groove left on the substrate and allow recovery of the groove. The ratio of the thickness of the coating to the roughness of the tip is a critical parameter, which enables one to increase the scratch resistance in the case of a thin coating. A single value of the critical load cannot describe the damage behaviour of a coating on a polymeric material. It is generally assumed that cracking appears at the rear edge of the contact area and is related to the tensile stress, whereas we observed that cracking of the coating appears within the contact area. The mechanical behaviour of a coating on a viscoelastic material should be analysed in terms of the shape of the stress field, modified by the effect of the local friction between a scratching tip and the coat, where this local friction will depend on the roughness of the tip. Some numerical simulations were performed to attempt to elucidate the cracking mechanism

C-Reactive Protein as a Peripheral Biomarker in Schizophrenia. An Updated Systematic Review

Objectives: The objective of this systematic review was to synthetize the published data on the relationships between elevated blood C-reactive protein (CRP) levels and schizophrenia (SZ) onset risk, illness characteristics and treatments, cognition and physical health.Method: The systematic bibliographic searches have been carried out according to the Cochrane methodology. Medline, web of science, Google Scholar with each database being searched from inception to November 2017.Results: 53 studies were included in the present review. While meta-analyses including case-control studies suggest a clear association between CRP and SZ, one other study has suggested that CRP-associated genes were associated with a lower risk of SZ onset. Increased CRP has been significantly associated with positive symptoms in acute phase psychosis, while studies including community-dwelling stabilized subjects did not find such an association. Abnormal CRP has been associated with a wide range of cognitive impairment in SZ stabilized individuals. Body Mass index has been extensively associated with increased CRP in SZ subjects; and increased CRP has been identified as a risk factor for metabolic syndrome and cardiovascular risk in SZ subjects. Increased CRP has also been associated with high nicotine dependence in SZ smokers and one study has suggested that increased CRP was associated with sedentary behavior.Conclusion: In the light of the above-mentioned studies, increased hs-CRP may be reasonably suggested as a marker for SZ onset risk, as well as a risk factor for increased positive symptoms, cognitive impairment, hypovitaminosis D, microbiota disturbances, cardiovascular and metabolic syndrome risk in SZ subjects, and increased nicotine dependence in SZ smokers. In case of increased CRP levels, anti-inflammatory strategies (add-on anti-inflammatory drugs including aspirin and omega 3 fatty acids, vitamin D supplementation, physical activity, probiotics) should be also further evaluated.Limits: Most of the studies were cross-sectional and cohort studies are needed to determine the temporal relationship between increased CRP and the psychiatric outcomes

A self-affine geometrical model of dynamic RT-PMMA fractures: implications for fracture energy measurements

Profilometric imaging of fracture surfaces of rubber toughened polymer has been performed at two different resolutions (a) at large scales [10 μ\upmu m–25 mm] using an opto-mechanical profilometer and (b) at small scales [0.195 μ\upmu m–0.48 mm] using an interferometric optical microscope. We introduced a self-affine geometrical model using two parameters: the Hurst exponent and the topothesy. We showed that for rubber toughened materials the approximation of the created surface by a mean flat plane leads to a poor estimation of the dynamic fracture energy GIdcG_{Idc}. The description of the created rough fracture surface by a self-affine model is shown to provide a significantly better approximation. A new and original geometrical method is introduced to estimate self-affine parameters: the 3D surface scaling method. Hurst exponents are shown to be unique, χ=0.6±0.1\chi =0.6\pm 0.1 for the different fracture zones and measurement scales. Topothesy ratios indicate a significant difference of fracture surface roughness amplitude depending on the observation resolution when the detrending technique is not correctly introduced.ANR Carenc

Lessons from end-of-life care among schizophrenia patients with cancer: a population- based cohort study from the French national hospital database Running title: End-of-life care among patients with schizophrenia and cancer

International audienceBackgroundPatients with schizophrenia represent a vulnerable, underserved, and undertreated population who have been neglected in health disparities work. Understanding of end-of-life care in patients with schizophrenia and cancer is poor. We aimed to establish whether end-of-life care delivered to patients with schizophrenia and cancer differed from that delivered to patients with cancer who do not have diagnosed mental illness.MethodsWe did a population-based cohort study of all patients older than 15 years who had a diagnosis of advanced cancer and who died in hospital in France between Jan 1, 2013, and Dec 31, 2016. We divided this population into cases (ie, patients with schizophrenia) and controls (ie, patients without a diagnosis of mental illness) and compared access to palliative care and indicators of high-intensity end-of-life care between groups. In addition to unmatched analyses, we also did matched analyses (matched in terms of age at death, sex, and site of primary cancer) between patients with schizophrenia and matched controls (1:4). Multivariable generalised linear models were done with adjustment for social deprivation, year of death, time from cancer diagnosis to death, metastases, comorbidity, and hospital type (ie, specialist cancer centre vs non-specialist centre).FindingsThe main analysis included 2481 patients with schizophrenia and 222 477 controls. The matched analyses included 2477 patients with schizophrenia and 9896 controls. Patients with schizophrenia were more likely to receive palliative care in the last 31 days of life (adjusted odds ratio 1·61 [95% CI 1·45–1·80]; p<0·0001) and less likely to receive high-intensity end-of-life care—such as chemotherapy and surgery—than were matched controls without a diagnosis of mental illness. Patients with schizophrenia were also more likely to die younger, had a shorter duration between cancer diagnosis and death, and were more likely to have thoracic cancers and comorbidities than were controls.InterpretationOur findings suggest the existence of disparities in health and health care between patients with schizophrenia and patients without a diagnosis of mental illness. These findings underscore the need for better understanding of health inequalities so that effective interventions can be developed for this vulnerable population

Schizophrenia Bulletin Open

Treatment-resistant schizophrenia (TRS) affects around 30% of patients with schizophrenia (SZ) resulting in poor functioning, relapses, and reduced quality of life. Convergent findings show that inflammation could contribute to resistance. We thus search for immune signatures of patients with TRS/ultra TRS (UTRS) in a sample of community-dwelling outpatients with SZ. In total, 195 stabilized SZ patients (mean age = 31.2 years, 73% male gender) were consecutively included in the network of the FondaMental Expert Centers for Schizophrenia in France and received a thorough clinical assessment. At inclusion, psychotic symptomatology was evaluated by the Positive and Negative Syndrome Scale (PANSS) for schizophrenia. Circulating serum/plasma levels of a large panel of markers reflecting the main inflammatory pathways were evaluated. TRS was defined by current treatment by clozapine (CLZ) and UTRS by current CLZ treatment + PANSS total score ≥ 70. The frequency of TRS and UTRS patients was, respectively, 20% and 7.7% and was defined using multivariable analysis elevated by high levels of interleukin (IL)-12/IL-23p40, IL-17A, IL-10, and beta 2 microglobulin (B2M) and IL-12/IL-23p40, IL-17A, IL-6, IL-10, IFNγ, and B2M, respectively. These observations suggest that resistance and ultra resistance to CLZ treatment are underpinned by pro-inflammatory molecules mainly belonging to the T helper 17 pathway, a finding making sense given the interplay between inflammation and antipsychotic treatment responses. If confirmed, our findings may allow us to consider IL-23/IL-17 pathway as a therapeutic target for patients with resistance to antipsychotics.Sorbonne Universités à Paris pour l'Enseignement et la RechercheFondaMental-Cohorte