Residual stresses in aluminium alloy friction stir welds

Residual stresses are detrimental to the fatigue, fracture and corrosion resistance of welds. The literature on residual stress measurements in aluminium alloy friction stir welds is reviewed. The results of a large number of longitudinal residual stress measurements performed by the slitting method on friction stir welds in 2024-T3, 6082-T6 and 5754-H111 aluminium alloys are compared and their origin discussed. From the current investigation, it can be derived that the type of machine used for welding has only little influence on the residual stress profile. The influence of alloy type and welding parameters on the magnitude of the residual stresses and the shape of their distribution across the weld is investigated. Their magnitude is far below the room temperature yield strength of the base material. A distribution with an ??M-shape?? is always found on age hardenable structural alloys (albeit more pronounced in 6082-T6 alloy than in 2024-T3 alloy), while a ??plateau?? is found in the case of the strain hardenable 5754 H111 alloy. The low magnitude and the differences in distribution of the longitudinal residual stress are attributed mainly to the microstructural changes in the weld centre and are discussed based on the hardness profiles performed across the welds. The paper also discusses the reasons why those results are in disagreement with a number of numerical simulations from the literature that do not account for the influence of the welding thermomechanical history on the material microstructure and properties.     

Photoinduced Fluidity and Viscoelasticity in Chalcogenide Glasses

This work is an attempt to apply conventional mechanical testing to characterize the photoinduced viscoelastic behavior of chalcogenide glasses. Creep or relaxation-recovery experiments are usually performed to characterize the delayed elastic contribution to deformation, during thermally activated flow. In this article, relaxation-recovery is used to characterize delayed elasticity under irradiation condition and to investigate the influence of the photon irradiation on the viscoelastic behavior. It is showed that thermally activated processes and photoinduced ones are decoupled. The viscoplastic deformation under irradiation is the sum of thermally activated and photoinduced processes. As soon as the irradiation ceases, chalcogenide glasses behave exactly as if they had never been irradiated. The photoinduced viscoelastic behavior seems to be solely due to transient photoinduced structural defects.     

Solution of Strongly Coupled Multiphysics Problems Using Space-Time Separated Representations—Application to Thermoviscoelasticity

The space-time separated representation method (Ladevèze, C. R. Acad. Sci. Paris 309(II):1095–1099, 1989; Ammar et al., J. Non-Newton. Fluid Mech. 144:98–121, 2007) is here extended to solve strongly coupled multiphysics problems. The feasibility of the method for dealing with strongly coupled multiphysics problems with different characteristic times is here discussed and a new strategy to solve the nonlinear system for the basis enrichment is proposed. The method is validated in the case of a strongly coupled thermoviscoelastic model.     

Buffer occupancy and link state opportunistic routing for wireless mesh networks

Wireless Networks - Providing a high level of Quality of Service is essential for future wireless networks. This article presents a new multihop wireless routing protocol that opportunistically...     

Dense on Porous Solid LATP Electrolyte System: Preparation and Conductivity Measurement

A dense membrane of lithium aluminum titanium phosphate Li_1+xAl_xTi_2?x(PO₄)₃, x = 0.3 (LATP) is deposited on a porous LATP substrate via wet chemistry. In the polymerized complex process, phosphate precursors with different active groups and steric hindrance are selected to tune precursor's reactivity. Rheological studies and microstructural observations lead to the selection of an LATP powder slurry charged with lithium, aluminum, titanium, and phosphate ion precursors. The optimized formulation is impregnated into a porous LATP substrate. After thermal treatment, dense LATP membranes on top of a porous LATP substrate are obtained with conductivities as high as 3 × 10^?4 S/cm for the dense part, the porous part acting as a mechanical support. An original Van der Pauw impedance setup is validated for the measurement of the ionic conductivity of such dense/porous systems.     

SUN Database: Exploring a Large Collection of Scene Categories

Progress in scene understanding requires reasoning about the rich and diverse visual environments that make up our daily experience. To this end, we propose the Scene Understanding database, a nearly exhaustive collection of scenes categorized at the same level of specificity as human discourse. The database contains 908 distinct scene categories and 131,072 images. Given this data with both scene and object labels available, we perform in-depth analysis of co-occurrence statistics and the contextual relationship. To better understand this large scale taxonomy of scene categories, we perform two human experiments: we quantify human scene recognition accuracy, and we measure how typical each image is of its assigned scene category. Next, we perform computational experiments: scene recognition with global image features, indoor versus outdoor classification, and “scene detection,” in which we relax the assumption that one image depicts only one scene category. Finally, we relate human experiments to machine performance and explore the relationship between human and machine recognition errors and the relationship between image “typicality” and machine recognition accuracy.     

Reaching with multi-referential dynamical systems

We study a reaching movement controller for a redundant serial arm manipulator, based on two principles believed to be central to biological motion control: multi-referential control and dynamical system control. The resulting controller is based on two concurrent dynamical systems acting on different, yet redundant variables. The first dynamical system acts on the end-effector location variables and the second one acts on the joint angle variables. Coherence constraints are enforced between those two redundant representations of the movement and can be used to modulate the relative influence of each dynamical system. We illustrate the advantages of such a redundant representation of the movement regarding singularities and joint angle avoidance.     

Discovery and Characterization of ACT‐451840: an Antimalarial Drug with a Novel Mechanism of Action

More than 40 % of the world's population is at risk of being infected with malaria. Most malaria cases occur in the countries of sub‐Saharan Africa, Central and South America, and Asia. Resistance to standard therapy, including artemisinin combinations, is increasing. There is an urgent need for novel antimalarials with new mechanisms of action. In a phenotypic screen, we identified a series of phenylalanine‐based compounds that exhibit antimalarial activity via a new and yet unknown mechanism of action. Our optimization efforts culminated in the selection of ACT‐451840 [(S,E)‐N‐(4‐(4‐acetylpiperazin‐1‐yl)benzyl)‐3‐(4‐(tert‐butyl)phenyl)‐N‐(1‐(4‐(4‐cyanobenzyl)piperazin‐1‐yl)‐1‐oxo‐3‐phenylpropan‐2‐yl)acrylamide] for clinical development. Herein we describe our optimization efforts from the screening hit to the potential drug candidate with respect to antiparasitic activity, drug metabolism and pharmacokinetics (DMPK) properties, and in vivo pharmacological efficacy.     

Correlation Between Thermal and Mechanical Relaxation in Chalcogenide Glass Fibers

Enthalpy relaxation processes in chalcogenide fibers at room temperature are investigated by differential scanning calorimetry and compared with bending-stress relaxation measurements obtained by rolling fibers on a mandrel and recording the viscoelastic relaxation parameters. While the kinetics of the two processes is very different, several qualitative correlations are demonstrated between the enthalpy state and the mechanical properties of chalcogenide glass fibers. It is observed that the ability to undergo stress relaxation is dependent upon the fictive temperature of the glass. Stress relaxation in a glass far from thermodynamic equilibrium is contingent upon its ability to undergo enthalpy relaxation and is minimal in glasses that have already relaxed enthalpy or in which relaxation time is overwhelmingly large.