776 research outputs found
Effect of Alloying and Ageing on Parameters of the B2↔R Transition in TiNi-Me Alloys
No full textSpecific splitting of the l/3(hkl) reflections along with the B2(CsCl)-matrix reflections at the B2↔IC↔C(R) transition at T≤TRcor was observed. Linear size of the R-phase needle-like domain structure λ1 correlates well in a reverse manner with degree of incommensurability δ1. The CDWs formation with coupling to longitudinal displacement wave is thought to be responsible for the B2↔R phase transition
Numerical Simulations of Cracks in Polycrystalline Aggregates
No full textCD-ROM, 0860International audienceFinite Element Crystal Plasticity is now a well developped field of research that allows the researchers to investigate global and local material behaviour. The initial attempts were devoted to homogenization: the goal was to determine the global properties by means of a description of the microstructures in terms of morphology and crystal orientations. A crude model of the microstructure is well adapted in that case, as, after averaging process, the details of the local fields just vanish at the macroscale. Even non realistic geometries with a new crystal orientation in each element of a cubic mesh is an acceptable solution in some cases. Nevertheless, this approach is now obsolete, due to the development of the experimental characterization of the microstructures (automated mapping of a surface, EBSD, microtomography). These new techniques are able to provide a quantitative analysis of the aggregate, that can be reproduced directly as it is, or as a statistically equivalent synthetic aggregate generated by morphological operations. Having such a type of mesh in hand, one can have an access to local stress and strain fields on the microstructural level. The purpose is now to investigate the strain localisation scheme [1], surface or grain boundary effects [2], or the influence of specific microstructures like for bainitic steels [3]. In these approaches, one has an evaluation of local pertinent fields, ready to use in local damage models to predict degradation and failure of the material element. This is why the next step must be prepared: the modelling of craks in aggregates. This paper shows three applications where cracks have been introduced in realistic agggregates. The first one deals with intergranular crack propagation in presence of stress corrosion cracking [4]. Special elements are introduced to represent the grain boundary affected zone in the grains. The behaviour of these elements is inherited from the grain they belong to and includes also three additional variables to represent damage, opening and sliding of the grain boundaries. Opening and sliding simulate relative motion of the grains and allow crack propagation to occur. They are promoted by damage, which evolution is linked to the mechanical state and to the environment, namely the presence of iodine. On the other hand, iodine adsorption is made easier in grain boundaries by damage, producing a catastrophic process. The second case study introduces cyclic loadings. It aims to characterise short crack propagation in fatigue. During the fatigue process, cracks initiate in surface grains, following maximum shear planes. In this “stage I” period, many initiation sites are present in the material element, and the crack occurrence is totally linked to the crystallography. The “micropropagation” regime corresponds then to mechanisms where cracks interact with the microstructure. The macroscopic crack initiation used by engineers takes place when the crack is large enough (several grains) to impose its own stress field. The goal of the study is to explain the transition between the crack in one grain and a long crack crossing several grains. The way the crack interact with grain boundaries is then simulated, and several arguments are proposed to decide if it is trapped or if it can go through. The last example is an application to fretting. A previous work has shown that crystal plasticity enhances strain localisation under the contact [5]. The new study wants to characterise the propagation angle of the cracks that initiate on both sides of the contact zone, and try to determine the condition they have to fill for stopping [6]. References: [1] C. Gérard, F. N'Guyen, N. Osipov, G. Cailletaud, M. Bornert, and D. Caldemaison, “Finite element simulation of strain localisation scheme and comparison with experimental results under cyclic loading paths,” submitted, 2009. [2] A. Musienko, A. Tatschl, K. Schmidegg, O. Kolednik, R. Pippan, and G. Cailletaud, “3D finite element simulation of a polycrystalline copper specimen,” Acta Mat., vol. 55,pp. 4121–4136, 2007. [3] N. Osipov, A.-F. Gourgues-Lorenzon, B. Marini, V. Mounoury, F. Nguyen, and G. Cailletaud, “FE modelling of bainitic steels using crystal plasticity,” Philosophical Magasine, vol. 88, no. 30–32, pp. 3757–3777, 2008. [4] A. Musienko and G. Cailletaud, “Simulation of inter and transgranular crack propagation in polycrystalline aggregates due to stress corrosion cracking,” submitted, 2009. [5] T. Dick and G. Cailletaud, “Fretting modelling with a crystal plasticity model of Ti6Al4V,” Computational Materials Science, vol. 38, pp. 113–125, 2006. [6] L. Sun, H. Proudhon, S. Basseville, and G. Cailletaud, “Effet de la microstructure sur la propagation des fissures de fretting,” in 9e colloque national en calcul de structures (C. Rey et al ed.), (Giens, France), may 25–29, 2009
Numerical Simulations of Cracks in Polycrystalline Aggregates
No full textCD-ROM, 0860International audienceFinite Element Crystal Plasticity is now a well developped field of research that allows the researchers to investigate global and local material behaviour. The initial attempts were devoted to homogenization: the goal was to determine the global properties by means of a description of the microstructures in terms of morphology and crystal orientations. A crude model of the microstructure is well adapted in that case, as, after averaging process, the details of the local fields just vanish at the macroscale. Even non realistic geometries with a new crystal orientation in each element of a cubic mesh is an acceptable solution in some cases. Nevertheless, this approach is now obsolete, due to the development of the experimental characterization of the microstructures (automated mapping of a surface, EBSD, microtomography). These new techniques are able to provide a quantitative analysis of the aggregate, that can be reproduced directly as it is, or as a statistically equivalent synthetic aggregate generated by morphological operations. Having such a type of mesh in hand, one can have an access to local stress and strain fields on the microstructural level. The purpose is now to investigate the strain localisation scheme [1], surface or grain boundary effects [2], or the influence of specific microstructures like for bainitic steels [3]. In these approaches, one has an evaluation of local pertinent fields, ready to use in local damage models to predict degradation and failure of the material element. This is why the next step must be prepared: the modelling of craks in aggregates. This paper shows three applications where cracks have been introduced in realistic agggregates. The first one deals with intergranular crack propagation in presence of stress corrosion cracking [4]. Special elements are introduced to represent the grain boundary affected zone in the grains. The behaviour of these elements is inherited from the grain they belong to and includes also three additional variables to represent damage, opening and sliding of the grain boundaries. Opening and sliding simulate relative motion of the grains and allow crack propagation to occur. They are promoted by damage, which evolution is linked to the mechanical state and to the environment, namely the presence of iodine. On the other hand, iodine adsorption is made easier in grain boundaries by damage, producing a catastrophic process. The second case study introduces cyclic loadings. It aims to characterise short crack propagation in fatigue. During the fatigue process, cracks initiate in surface grains, following maximum shear planes. In this “stage I” period, many initiation sites are present in the material element, and the crack occurrence is totally linked to the crystallography. The “micropropagation” regime corresponds then to mechanisms where cracks interact with the microstructure. The macroscopic crack initiation used by engineers takes place when the crack is large enough (several grains) to impose its own stress field. The goal of the study is to explain the transition between the crack in one grain and a long crack crossing several grains. The way the crack interact with grain boundaries is then simulated, and several arguments are proposed to decide if it is trapped or if it can go through. The last example is an application to fretting. A previous work has shown that crystal plasticity enhances strain localisation under the contact [5]. The new study wants to characterise the propagation angle of the cracks that initiate on both sides of the contact zone, and try to determine the condition they have to fill for stopping [6]. References: [1] C. Gérard, F. N'Guyen, N. Osipov, G. Cailletaud, M. Bornert, and D. Caldemaison, “Finite element simulation of strain localisation scheme and comparison with experimental results under cyclic loading paths,” submitted, 2009. [2] A. Musienko, A. Tatschl, K. Schmidegg, O. Kolednik, R. Pippan, and G. Cailletaud, “3D finite element simulation of a polycrystalline copper specimen,” Acta Mat., vol. 55,pp. 4121–4136, 2007. [3] N. Osipov, A.-F. Gourgues-Lorenzon, B. Marini, V. Mounoury, F. Nguyen, and G. Cailletaud, “FE modelling of bainitic steels using crystal plasticity,” Philosophical Magasine, vol. 88, no. 30–32, pp. 3757–3777, 2008. [4] A. Musienko and G. Cailletaud, “Simulation of inter and transgranular crack propagation in polycrystalline aggregates due to stress corrosion cracking,” submitted, 2009. [5] T. Dick and G. Cailletaud, “Fretting modelling with a crystal plasticity model of Ti6Al4V,” Computational Materials Science, vol. 38, pp. 113–125, 2006. [6] L. Sun, H. Proudhon, S. Basseville, and G. Cailletaud, “Effet de la microstructure sur la propagation des fissures de fretting,” in 9e colloque national en calcul de structures (C. Rey et al ed.), (Giens, France), may 25–29, 2009
FINANCIAL ANALYSIS AND FORECASTING OF THE RESULTS OF SMALL BUSINESSES PERFORMANCE BASED ON REGRESSION MODEL
No full textObjective: to develop the economic-mathematical model of the dependence of revenue on other balance sheet items, taking into account the sectoral affiliation of the companies.Methods: using comparative analysis, the article studies the existing approaches to the construction of the company management models. Applying the regression analysis and the least squares method, which is widely used for financial management of enterprises in Russia and abroad, the author builds a model of the dependence of revenue on other balance sheet items, taking into account the sectoral affiliation of the companies, which can be used in the financial analysis and prediction of small enterprises’ performance.Results: the article states the need to identify factors affecting the financial management efficiency. The author analyzed scientific research and revealed the lack of comprehensive studies on the methodology for assessing the small enterprises’ management, while the methods used for large companies are not always suitable for the task. The systematized approaches of various authors to the formation of regression models describe the influence of certain factors on the company activity. It is revealed that the resulting indicators in the studies were revenue, profit, or the company relative profitability. The main drawback of most models is the mathematical, not economic approach to the definition of the dependent and independent variables. Basing on the analysis, it was determined that the most correct is the model of dependence between revenues and total assets of the company using the decimal logarithm. The model was built using data on the activities of the 507 small businesses operating in three spheres of economic activity. Using the presented model, it was proved that there is direct dependence between the sales proceeds and the main items of the asset balance, as well as differences in the degree of this effect depending on the economic activity of small enterprises.Scientific novelty: the article presents a regression model of dependence of revenues on the major categories of assets for small businesses based on the principles of economic expediency, not of mathematically correct dependencies.Practical significance: the main findings of this paper can be useful in the practical management of small businesses, for financial analysis and forecasting, in particular in the benchmarking of companies in certain sectors. In addition, the results of this research can be used in scientific and teaching activities in covering the issues of financial management of small businesses
Corticospinal neuroprostheses to restore locomotion after spinal cord injury
No full textIn this conceptual review, we highlight our strategy for, and progress in the development of corticospinal neuroprostheses for restoring locomotor functions and promoting neural repair after thoracic spinal cord injury in experimental animal models. We specifically focus on recent developments in recording and stimulating neural interfaces, decoding algorithms, extraction of real-time feedback information, and closed-loop control systems. Each of these complex neurotechnologies plays a significant role for the design of corticospinal neuroprostheses. Even more challenging is the coordinated integration of such multifaceted technologies into effective and practical neuroprosthetic systems to improve movement execution, and augment neural plasticity after injury. In this review we address our progress in rodent animal models to explore the viability of a technology-intensive strategy for recovery and repair of the damaged nervous system. The technical, practical, and regulatory hurdles that lie ahead along the path toward clinical applications are enormous - and their resolution is uncertain at this stage. However, it is imperative that the discoveries and technological developments being made across the field of neuroprosthetics do not stay in the lab, but instead reach clinical fruition at the fastest pace possible. © 2013 Elsevier Ireland Ltd and the Japan Neuroscience Society
Restoring voluntary control of locomotion after paralyzing spinal cord injury
No full textHalf of human spinal cord injuries lead to chronic paralysis. Here, we introduce an electrochemical neuroprosthesis and a robotic postural interface designed to encourage supraspinally mediated movements in rats with paralyzing lesions. Despite the interruption of direct supraspinal pathways, the cortex regained the capacity to transform contextual information into task-specific commands to execute refined locomotion. This recovery relied on the extensive remodeling of cortical projections, including the formation of brainstem and intraspinal relays that restored qualitative control over electrochemically enabled lumbosacral circuitries. Automated treadmill-restricted training, which did not engage cortical neurons, failed to promote translesional plasticity and recovery. By encouraging active participation under functional states, our training paradigm triggered a cortex-dependent recovery that may improve function after similar injuries in humans
Parameters of the preproduction series SiPMs for the CMS HCAL phase I upgrade
No full textIn 2012 the HCAL SiPM photo sensor upgrade was approved for the increased luminosity (5*10 34 ) of SLHC. The upgrade will replace the current hybrid photodiodes (HPDs) with multi-pixel Geiger-mode avalanche photodiodes, also known as silicon photomultipliers (SiPMs). A key aspect of the upgrade to SiPMs is to add longitudinal segmentation and improve signal to noise to compensate for scintillator radiation damage. After 5 years of R&D; with multiple companies we developed custom large dynamic range SiPMs with large PDE and small ENC. To ensure good mechanical alignment and easy handling of the large number of production channels (>20,000) we have developed a custom ceramic package with a very thin 0.3 mm quartz window with Kyocera. Each package holds 8 channels of SiPMs
Pharmacological stimulation to facilitate and restore standing and walking functions in spinal cord motor disorders
No full textThe invention relates to the selective targeting of specific α2 adrenergic receptor subtypes for facilitating and also restoring standing and walking in a subject affected by spinal cord disorders, in particular spinal cord injury. In particular, the improvement of locomotion by targeting specific receptor subtypes can be achieved by stimulation of the α2c receptor subtype using an α2c specific agonist or by blocking the α2a receptor subtype using α2a antagonists. A combination of an α2c agonist and an α2a antagonist is also provided for a synergistic effect. Alternatively, a large α2 agonist can be used in combination with an α2a antagonist to achieve specific stimulation of the α2c receptor. Pharmaceutical compositions, kit-of-parts and therapeutic systems comprising said agonists/antagonists as active agents are objects of the present invention. A robotic interface and epidural electric stimulation can also be used in combination with the compositions of the invention for restoring voluntary control of locomotion.AVP-R-TTOUPCOURTINEAlternative title(s) :
(de) Pharmakologische stimulation zur unterstützung und wiederherstellung von steh- und gehfunktionen bei rückenmarkserkrankungen
(fr) Stimulation pharmacologique afin de faciliter et restaurer des fonctions pour se tenir debout et marcher dans des troubles de la moelle épinière
(en) Pharmacological stimulation to facilitate and restore standing and walking functions in spinal cord disorder
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