1,721,026 research outputs found
Plastic Behavior of Laser-Deposited Inconel 718 Superalloy at High Strain Rate and Temperature
Full text linkNickel-based superalloys have several applications for components exposed to high temperatures and high strain rate loading conditions during services. The objective of this study was to investigate the tensile properties of Inconel 718 produced using the laser metal deposition technique. Specimens with different heat treatments were investigated. Experimental tests were performed at the DYNLab at Politecnico di Torino (Italy). The temperature sensitivity was investigated between 20 °C and 1000 °C on a Hopkinson bar setup at a nominal strain rate of 1500 s−1. The specimens heating was obtained by means of an induction heating system, and the temperature control was performed by thermocouples, an infrared pyrometer, and a high-speed infrared camera. The thermal images were analyzed to check the uniformity of the heating and to investigate the presence of adiabatic self-heating. The results showed that the materials strength exhibited a significant drop starting from 800 °C. The strain rate influence was investigated at room temperature, and limited sensitivity was found covering six orders of magnitude in the strain rate. A preliminary analysis of the fracture mode was performed. Finally, different solutions for the strength material modeling were proposed and discussed with the aim of identifying models to be used in finite element simulations
Thermo-mechanical modelling of Dynamic Tensile Extrusion test
No full textRecently, the researchers of the Los Alamos National Laboratory (LANL) have been developed a technique to investigate high strain-rates in which a sphere is launched at high speed (300-800 m/s) through a conical die (Dynamic Tensile Extrusion test). The system can use a set-up similar to a Taylor test (like a light gusgun) but induces in the material high levels of tensile stresses and allows to investigate the fracture and damage of the material in these extreme conditions. Due to the high strain-rates and hydrostatic component of stress that occur during the extrusion in the die, the material is also subject to a rapid heating. In this work, the DTE test has been simulated with the explicit Lagrangian code LSDYNA. In order to correctly reproduce the various aspects of the test it is necessary to use an elasto-plastic material model that takes into account strain-rate, thermal softening, pressure influence and damage and that adequately describes the thermal coupling effects and the equation of state (EOS) of the material. Besides, due to the high distortion of the Lagrangian mesh, the use of a mesh adapting technique is absolutely necessar
Numerical simulations of components produced by fused deposition 3D printing
Full text linkThree-dimensional printing technology using fused deposition modeling processes is becoming more and more widespread thanks to the improvements in the mechanical properties of materials with the addition of short fibers into the polymeric filaments. The final mechanical properties of the printed components depend, not only on the properties of the filament, but also on several printing parameters. The main purpose of this study was the development of a tool for designers to predict the real mechanical properties of printed components by performing finite element analyses. Two different materials (nylon reinforced with glass or carbon fibers) were investigated. The experimental identification of the elastic material model parameters was performed by testing printed fully filled dog bone specimens in two different directions. The obtained parameters were used in numerical analyses to predict the mechanical response of simple structures. Blocks of 20 mm × 20 mm × 160 mm were printed in four different percentages of a triangular infill pattern. Experimental and numerical four-point bending tests were performed, and the results were compared in terms of load versus curvature. The analysis of the results demonstrated that the purely elastic transversely isotropic material model is adequate for predicting behavior, at least before nonlinearities occur
Adrenaline potentiates type 2B von Willebrand factor-induced activation of human platelets by enhancing both the formation and action of thromboxanes.
No full textAbstract
Von Willebrand factor (vWF) is a large plasma glycoprotein that mediates platelet adhesion at sites of vascular injury. We have previously reported that the pathological type 2B (formerly named type IIB) variant of vWF promotes platelet activation through phospholipase A(2)-mediated release of arachidonic acid. The present report shows that adrenaline (1 microM) potentiates type 2B vWF-induced platelet aggregation, serotonin secretion, rise in cytosolic Ca(2+) concentration, and pleckstrin phosphorylation, as well as thromboxane B(2) production. The hormone also increases the partially inhibited release of serotonin observed in platelets pretreated with the anti-GPIIb-IIIa antibody LJCP8 but does remove the total inhibition on the secretion caused by the anti-GPIb antibody LJIB1. Adrenaline also increases type 2B vWF-elicited tyrosine phosphorylation of proteins with apparent molecular masses of 60 and 80 kDa. Furthermore, adrenaline potentiates the rise in cytosolic Ca(2+) and the release of thromboxane B(2) in platelets stimulated with arachidonic acid (2 microM) as well as the increase in Ca(2+) induced by the thromboxane mimetic U46619 (0.3 microM). Platelet pretreatment with yohimbine or 13-azaprostanoic acid, which are antagonists of the alpha(2)-adrenergic and thromboxane receptors, respectively, or with acetylsalicylate and indomethacin, both of which act as inhibitors of thromboxane formation, abolishes the potentiating effect of adrenaline. These observations lead to the conclusion that the potentiating action of adrenaline on type 2B vWF-promoted platelet responses is due to an increase in both the formation and activating action of thromboxanes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Behaviour of Al6061-T6 alloy at different temperatures and strain-rates: Experimental characterization and material modelling
Full text linkThe simulation of impact scenario against a structure requires the use of material models able to reproduce all aspects of the mechanical behaviour of the involved materials; plastic flow is one of the main aspects to be reproduced. In more detail, attention has to be paid to the investigation of strain-rate and temperature sensitivities, as well as their interaction, which necessitates the use of a reverse engineering approach. The present paper mainly focuses on the tensile behaviour and an ad-hoc testing campaign was performed on cylindrical dog-bone specimens made in Al6061T6 at different temperatures and strain-rates extending the range up to a level where, at present, there is a lack in the scientific literature. The thermal softening effect was investigated in quasi-static as well as in dynamic loading conditions from room temperature up to 400 °C; while the material strength dependence on the strain-rate was studied up to 104 s−1 on miniaturized samples. Microstructure analyses were performed to better investigate the mechanical response at different loading conditions. The parameters of the Johnson-Cook model were identified starting from experimental data via a numerical inverse approach based on FEM simulations. These parameters can be used for simulations of extreme loading scenario like ballistic impact events
Arterial and venous thrombosis in patients with von Willebrand's disease: a critical review of the literature.
No full textAll patients with von Willebrand's disease (vWD) who showed an arterial or venous thrombosis and were reported in the literature have been evaluated. 11 patients had arterial thrombosis while 19 had venous thrombosis for a total of 30 cases. 9 out the 11 cases with arterial thrombosis had myocardial infarction. Two had cerebral thrombosis. Associated risk factors for arterial thrombosis were available only for three patients who showed, respectively, smoking and dyslipidemia (2 cases) and smoking and intravenous desmopressin infusion (1 case). The majority of patients with venous thrombosis showed DVT with or without PE. Four patients presented with apparently isolated PE. In two instances thrombosis occurred in unusual sites (central retinal vein and portal vein, respectively). Several associated risk factors were present, mainly: infusion of FVIII or FVIII + vWF concentrates in 7 cases; surgery in 8 cases, pregnancy in 1, desmopressin infusion in 1, variable coagulation defects or polymorphisms in 5. More than one of these associated conditions were present in a few patients. The majority of vWD patients who showed thrombotic phenomena were type I patient, but in 6 cases were also type 3. The type of defect was not reported in 6 patients. As a conclusion of this review it seems safe to assume that both arterial and venous thrombosis appear rare in vWD. This is confirmed by the fact that arterial or venous thrombosis appears slightly more frequent in hemophilia A and B
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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