Design of modified plastic surfaces for antimicrobial applications: Impact of ionizing radiation on the physical and mechanical properties of polypropylene

Surface modification of polypropylene (PP) sheets was carried out by radiation induced graft polymer- ization of hydrophilic functional molecules such as N,N-dimethylacrylamide (DMA) and [2-methacry- loyloxy)ethyl] trimethylammonium chloride, which is a quaternary ammonium salt (QAS). Polypropylene sheets were activated prior to the grafting reaction by using electron beam radiation. The changes in morphology, crystallinity and tensile parameters like deformation and stress at yield and deformation at break of PP after irradiation were investigated. The results showed that a minor crystalline reorganization takes place during the irradiation of PP at 100 kGy. The grafting has been observed to be strongly dependent on the monomer dilution in the reaction medium. After grafting of QAS (40%) and DMA (20%) it was possible to develop highly hydrophilic surfaces (water contact angle comprised between 30 and 411). The surfaces of virgin, irradiated and grafted PP were studied using polarized optical microscopy (POM) and scanning electron microscopy (SEM). Spherical particles (i.e. polystyrene or silica beads) adhering to the modified samples were studied according to the surface parameters. Adhesion tests confirmed the strong influence of substrate type (mainly hydrophilicity and roughness) and to a lesser extent underlined the role of electrostatic interactions for the design of plastic surfaces for antimicrobial applications

Simulation de la mise en forme et de la tenue mécanique de pièces obtenues par semi-découpe

National audienceLe procédé de semi-découpe de tôles d'acier est utilisé pour la mise en forme de composants de sièges d'automobiles. La tenue mécanique sous sollicitation radiale de pièces semi- découpées est étudiée par la réalisation d'essais de mise en forme et d'arrachement. La réponse des pièces aux sollicitations est prédite par simulation numérique. La prise en compte de la mise en forme dans la simulation de l'arrachement entraîne un gain de rigidité en adéquation avec l'expérience. La rupture des pièces intervient dans une zone de faible triaxialite.See http://hal.archives-ouvertes.fr/docs/00/59/27/17/ANNEX/r_VB1CWP70.pd

Identification of the hardening law of materials with spherical indentation using the average representative strain for several penetration depths

International audienceThe identification of plastic properties with spherical indentation has been the subject of many studies in last decades. In the present work, a new method for the determination of the hardening law of materials using the load-displacement curve of a spherical indentation test is proposed. This method is based on the use of an average representative strain. The advantage of the proposed average representative strain is that it is strictly obtained from the material response to the indentation test. By using various values of penetration depth, the proposed method gives the range of strain for which the hardening law is precisely identified and allows determining a confidence domain that takes into account experimental imprecision and material heterogeneity. The influence of penetration depth and the error formula on the identified Hollomon hardening law are discussed in the present study. The present study clarifies many problems that were observed in previous studies such as the uniqueness solution and the sensitivity of the indentation test to the plastic parameters of the Hollomon hardening law

Revue bibliographique sur la caractérisation mécanique des matériaux utilisant la déformation représentative en indentation sphérique Literature review on mechanical characterization of materials using a representative strain in spherical indentation

National audienceThe instrumented indentation provides access to several mechanical properties of materials, leading in particular to the knowledge of their hardening law. In front of the lack of a standard procedure, many techniques have been proposed in recent decades. The present work is a literature review on the methods of mechanical characterization based on the instrumented indentation, and using a representative strain. There are two families of methods. The first, based on the Meyer hardness, includes methods of conducting hardness tests with different loads and determine, from the hardness and measuring the radius of the corresponding imprint, a representative deformation and the corresponding stress leading to the construction of the work hardenning curve "point by point" of the tested material. The second includes the methods giving the 2 plastic parameters of the Hollomon law that minimize the difference between the experimental indentation F(h) curve, and a model based on a representative deformation, linking the measured quantities (F, h) and the parameters of the Hollomon law. Each family of methods has advantages and disadvantages that should be known for choosing the most suitable method to the studied case and thus makes best use of instrumented indentation testing

Evaluation of the tensile properties of a material through spherical indentation: definition of an average representative strain and a confidence domain.

International audienceIn the present article, a new method for the determination of the hardening law using the load displacement curve, F-h, of a spherical indentation test is developed. This method is based on the study of the error between an experimental indentation curve and a number of finite elements simulation curves. For the smaller values of these errors, the error distribution shape is a valley, which is defined with an analytic equation. Except for the fact that the identified hardening law is a Hollomon type, no assumption was made for the proposed identification method. A new representative strain of the spherical indentation, called "average representative strain," ε aR was defined in the proposed article. In the bottom of the valley, all the stress-strain curves that intersect at a point of abscissa ε aR lead to very similar indentation curves. Thus, the average representative strain indicates the part of the hardening law that is the better identified from spherical indentation test. The results show that a unique material parameter set (yield stress σ y, strain hardening exponent n) is identified when using a single spherical indentation curve. However, for the experimental cases, the experimental imprecision and the material heterogeneity lead to different indentation curves, which makes the uniqueness of solution impossible. Therefore, the identified solution is not a single curve but a domain that is called "solution domain" in the yield stress-work hardening exponent diagram, and "confidence domain" in the stress-strain diagram. The confidence domain gives clear answers to the question of uniqueness of the solution and on the sensitivity of the indentation test to the identified hardening laws parameters

Mechanical characterization of carbonitrided steel with spherical indentation using the average representative strain

International audienceThis paper investigates the identification of mechanical properties of carbonitrided steels using the spherical indentation test. The proposed procedure consists in performing the Vickers microindentation hardness test across the carbonitrided steel in order to obtain the thickness of the hardened layers. Thus, with the assumption of a linear variation of the plastic properties in the intermediate layers between surface and substrate, two spherical macroindentation tests, performed on the substrate and on the surface of the carbonitrided steel, are necessary to identify the work hardening laws' variation through the thickness of the carbonitrided steel. The proposed method does not call for inverse analysis but is based on the use of a database of finite element simulation F–h curves obtained by simulating indentation tests on the surface of various pseudo-carbonitrided materials. The advantage of this method compared to those based on inverse analysis is that it allows a representative strain and a confidence domain of the solution to be determined. The confidence domain of the identified solution takes into account the experimental imprecision of the indentation test and of the case depth variability often encountered in carbonitrided parts

Learning smoothing models of copy number profiles using breakpoint annotations

Many models have been proposed to detect breakpoints in chromosomal copy number profiles, but it is usually not obvious to decide which is most effective for a given data set. Furthermore, most methods have a smoothing parameter that determines the number of breakpoints and must be chosen using various heuristics. We present three contributions toward automatic training of smoothing models. First, we propose to select the model and degree of smoothness that maximizes agreement with visual breakpoint region annotations. Second, we develop cross-validation procedures to estimate the error of the trained models. Third, we apply these methods to a new database of annotated neuroblastoma copy number profiles, which we make available as a public benchmark for testing new algorithms. Whereas previous studies have been qualitative or limited to simulated data, our approach is quantitative and suggests which algorithms are fastest and most accurate in practice on real data

MYBL2 (B-Myb): a central regulator of cell proliferation, cell survival and differentiation involved in tumorigenesis

Limitless cell proliferation, evasion from apoptosis, dedifferentiation, metastatic spread and therapy resistance: all these properties of a cancer cell contribute to its malignant phenotype and affect patient outcome. MYBL2 (alias B-Myb) is a transcription factor of the MYB transcription factor family and a physiological regulator of cell cycle progression, cell survival and cell differentiation. When deregulated in cancer cells, MYBL2 mediates the deregulation of these properties. In fact, MYBL2 is overexpressed and associated with poor patient outcome in numerous cancer entities. MYBL2 and players of its downstream transcriptional network can be used as prognostic and/or predictive biomarkers as well as potential therapeutic targets to offer less toxic and more specific anti-cancer therapies in future. In this review, we summarize current knowledge on the physiological roles of MYBL2 and highlight the impact of its deregulation on cancer initiation and progression

JUN Oncogene Amplification and Overexpression Block Adipocytic Differentiation in Highly Aggressive Sarcomas

SummaryThe human oncogene JUN encodes a component of the AP-1 complex and is consequently involved in a wide range of pivotal cellular processes, including cell proliferation, transformation, and apoptosis. Nevertheless, despite extensive analyses of its functions, it has never been directly involved in a human cancer. We demonstrate here that it is highly amplified and overexpressed in undifferentiated and aggressive human sarcomas, which are blocked at an early step of adipocyte differentiation. We confirm by cellular and xenograft mouse models recapitulating these sarcoma genetics that the failure to differentiate is dependent upon JUN amplification/overexpression

Anaplastic oligodendrogliomas with 1p19q codeletion have a proneural gene expression profile

<p>Abstract</p> <p>Background</p> <p>In high grade gliomas, 1p19q codeletion and <it>EGFR </it>amplification are mutually exclusive and predictive of dramatically different outcomes. We performed a microarray gene expression study of four high grade gliomas with 1p19q codeletion and nine with <it>EGFR </it>amplification, identified by CGH-array.</p> <p>Results</p> <p>The two groups of gliomas exhibited very different gene expression profiles and were consistently distinguished by unsupervised clustering analysis. One of the most striking differences was the expression of normal brain genes by oligodendrogliomas with 1p19q codeletion. These gliomas harbored a gene expression profile that partially resembled the gene expression of normal brain samples, whereas gliomas with <it>EGFR </it>amplification expressed many genes in common with glioblastoma cancer stem cells. The differences between the two types of gliomas and the expression of neuronal genes in gliomas with 1p19q codeletion were both validated in an independent series of 16 gliomas using real-time RT-PCR with a set of 22 genes differentiating the two groups of gliomas (<it>AKR1C3</it>, <it>ATOH8</it>, <it>BMP2</it>, <it>C20orf42</it>, <it>CCNB1</it>, <it>CDK2</it>, <it>CHI3L1</it>, <it>CTTNBP2</it>, <it>DCX, EGFR, GALNT13, GBP1, IGFBP2, IQGAP1, L1CAM, NCAM1, NOG, OLIG2, PDPN, PLAT, POSTN, RNF135</it>). Immunohistochemical study of the most differentially expressed neuronal gene, alpha-internexin, clearly differentiated the two groups of gliomas, with 1p19q codeletion gliomas showing specific staining in tumor cells.</p> <p>Conclusion</p> <p>These findings provide evidence for neuronal differentiation in oligodendrogliomas with 1p19q codeletion and support the hypothesis that the cell of origin for gliomas with 1p19q codeletion could be a bi-potential progenitor cell, able to give rise to both neurons and oligodendrocytes.</p