The Relationship between Parkin and Protein Aggregation in Neurodegenerative Diseases

The most prominent changes in neurodegenerative diseases are protein accumulation and inclusion formation. Several neurodegenerative diseases, including Alzheimer's, the Synucleinopathies and Tauopathies share several overlapping clinical symptoms manifest in Parkinsonism, cognitive decline and dementia. As degeneration progresses in the disease process, clinical symptoms suggest convergent pathological pathways. Biochemically, protein cleavage, ubiquitination and phosphorylation seem to play fundamental roles in protein aggregation, inclusion formation and inflammatory responses. In the following we provide a synopsis of the current knowledge about protein accumulation and astrogliosis as a common denominator in neurodegenerative diseases, and we propose insights into protein degradation and anti-inflammation. We review the E3-ubiquitin ligase and other possible functions of parkin as a suppressant of inflammatory signs and a strategy to clear amyloid proteins in neurodegenerative diseases

A Lagrangian vortex method for vortex evolution

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About quantitative EBSD analysis of deformation and recovery substructures in pure Tantalum

International audienceThe aim of this work is to present a quantitative analysis of features involved in recovery during annealing of deformed Tantalum. In pure metals where crystalline defects usually have high mobility, dislocation annihilation and rearrangement occur to a great extent prior to recrystallization. Therefore a complete understanding of recrystallization cannot be accomplished without an advanced knowledge of the recovery phenomenon. Depending on whether dislocations induce a measurable curvature in the crystal lattice or not, they are called Geometrically Necessary Dislocations (GNDs) or Statistically Stored Dislocations (SSDs) respectively. In the present work only GNDs are considered. For this purpose electron backscatter diffraction (EBSD) is an advantageous technique to obtain statistically representative results when compared to Transmission Electron Microscopy (TEM). However, a quantitative analysis of GNDs from EBSD data is not straightforward. Since local misorientations are induced by the curvature of the crystal lattice caused by GNDs, GNDs analysis can be done using local misorientations. However the values obtained from this analysis are step size dependent and influenced by the measurement noise. Reasoning on the basis that when the step size tends to zero, local misorientation should also tend to zero, measurement noise can be estimated [1]. The measurement noise appears to notably be very much dependent on the amplitude of local misorientations, which must be considered in the perspective of GND density calculatio

Comparaison entre les déformations représentatives de l'indentation Vickers et de l'indentation sphérique Comparison between representative deformations in Vickers indentation and spherical indentation

National audienceThe application of the concept of the representative strain is often used in the stress-strain curve determination from indentation test. A new methodology for determining the representative strain for spherical and for Vickers indentation is presented in this article. The results obtained from this methodology show that there is no universal value of representative strain independent of the mechanical parameters of materials indented by Vickers indentation and spherical indentation. It is also shown that the representative strain, obtained by Vickers or by spherical indentation, is much lower when it is obtained from the relationship between the applied force and the penetration depth, F-h, rather than from the relationship between the applied force and the contact radius, F-a. By choosing the same representative strain value in spherical indentation and in Vickers indentation, the results show that the same constraint factor is obtained. Hence, it is possible to determine a perfect analogy between the two types of indentation. For Vickers indentation, the values of the calculated representative strains show that simultaneous measurement of relationships F-a and F-h allows to characterize the hardening law with two unknown parameters. In the case of the spherical indentation, the identification of a material hardening law from simultaneous measurements relationships F-a and F-h should lead to a more accurate determination of the stress-strain curve

Identification of macroscopic hardening law through spherical indentation: definition of an average representative strain and a confidence domain.

The instrumented indentation test is widely used for the identification of the stress-strain curve. One of the disadvantages of the indentation test is that the plastic strain field in the deformed sample is not homogenous which makes it difficult to identify the hardening law of the material from an indentation curve. This difficulty can lead to some complications such as the uniqueness of the solution due to the sensitivity of the indentation test. The use of the concept of the representative strain can simplify the analysis of the indentation response and has often been used in the stress-strain curve identification. In the present work, a new method based on the definition of an “average representative strain”, εaR, is developed for the determination of the hardening law using the load displacement curve, F-h, of a spherical indentation test. The advantage of the proposed εaR is that it is directly obtained from the material’s response to the indentation test. This method consists to calculate the error between an experimental indentation curve and a number of FE simulation curves. For the smaller values of these errors, the error distribution shape is a valley, which is defined with an analytical equation. Based on a sensitivity study, the εaR and the corresponding value of stress σaR can be calculated for every penetration depth. Hence, the hardening law is constructed with no assumptions on its mathematical form. Because of the local aspect of the indentation test, materials heterogeneities can lead to differences between several indentation curves obtained under the same conditions. The proposed method allows the determination of a confidence domain that takes into account the experimental imprecision and the material heterogeneity using several indentation curves1, 2. The present method points out the limitation od the indentation test to characterize the mechanical behavior for large deformations. The uniqueness of the solution and the sensitivity of the indentation test are also discussed. The results obtained for a 20MnB5 steel alloy show that the identified hardening law (and confidence domain) is in agreement with the tensile test curve (Figure 1). A similar approach can be used for Vickers indentation for determining the representative strain3. Results obtained for Vickers indentation are discussed and compared to the literature. Please click Additional Files below to see the full abstract

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

Continuous dynamic recrystallization in a Zn–Cu–Ti sheet subjected to bilinear tensile strain

Research on zinc sheet formability, relevant for its technological applications, requires deeper understanding of the microstructural features that govern the plastic response of the material. In this work, a microstructural analysis by means of electron back-scattered diffraction (EBSD) technique was conducted on a commercial Zn?Cu?Ti sheet subjected to a bilinear tensile test at room temperature and low strain rate (5 × 10−4 s−1). The refinement of the granular structure is analyzed in terms of the development of subgrains within initially large grains, which eventually evolve into high angle boundary grains. This continuous dynamic recrystallization (CDRX) mechanism appears as a key factor in order to explain the grain fragmentation process and the weakening of the texture observed during straining of this alloy.---La investigación de la conformabilidad de chapas de zinc, relevante para sus aplicaciones tecnológicas, requiere una comprensión más profunda de las características microestructurales que rigen la respuesta plástica del material. En este trabajo se realizó un análisis microestructural mediante la técnica de difracción de electrones retrodispersados (EBSD) en una chapa comercial de Zn-Cu-Ti sometida a un ensayo de tracción bilineal a temperatura ambiente y a baja velocidad de deformación. El afinamiento de la estructura granular se analiza en términos del desarrollo de subgranos dentro de granos inicialmente grandes, que eventualmente evolucionan en granos con bordes de ángulo alto. Este mecanismo de recristalización dinámica continua (CDRX) aparece como un factor clave para explicar el proceso de fragmentación sufrido por los granos y la atenuación de la textura cristalográfica observados durante la deformación de esta aleación.Fil: Leonard, Martin Eduardo. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Moussa, Charbel. Centre National de la Recherche Scientifique; Francia. Ecole Des Mines de Paris. Centre de Mise En Forme Des Materiaux; FranciaFil: Roatta, Analía. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; ArgentinaFil: Seret, Anthony. Technical University of Denmark; DinamarcaFil: Signorelli, Javier Walter. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina. Universidad Nacional de Rosario. Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Argentin

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