Impact of Thermal Aging on the Microstructure Evolution and Mechanical Properties of Lanthanum-Doped Tin-Silver-Copper Lead-Free Solders

The authors would like to thank Ste´phanie Blanc (Electrical Engineer at Schlumberger) for her useful contribution to the project, Claude Guyomard and Olivier Naegelen (Arts et Me´tiers ParisTech) for the die design and sample casting, respectively, and Jean-Marc Raulot for his enriching discussions.An extensive study is made to analyze the impact of pure lanthanum on the microstructure and mechanical properties of Sn-Ag-Cu (SAC) alloys at high temperatures. Different compositions are tested; the temperature applied for the isothermal aging is 150 C, and aging times of 10 h, 25 h, 50 h, 100 h, and 200 h are studied. Optical microscopy with cross-polarized light is used to follow the grain size, which is refined from 8 mm to 1 mm for as-cast samples and is maintained during thermal aging. Intermetallic compounds (IMCs) present inside the bulk Sn matrix affect the mechanical properties of the SAC alloys. Due to high-temperature exposure, these IMCs grow and hence their impact on mechanical properties becomes more significant. This growth is followed by scanning electron microscopy, and energy-dispersive spectroscopy is used for elemental mapping of each phase. A significant refinement in the average size of IMCs of up to 40% is identified for the as-cast samples, and the coarsening rate of these IMCs is slowed by up to 70% with no change in the interparticle spacing. Yield stress and tensile strength are determined through tensile testing at 20 C for as-cast samples and after thermal aging at 150 C for 100 h and 200h. Both yield stress and tensile strength are increased by up to 20% by minute lanthanum doping

A mudança geopolítica do coronavírus e a queda do neoliberalismo

This paper examines the context of the spread of the new coronavirus, the correlation with the instability of world financial markets and the fall in oil prices, and concerns about the future of neorealist capitalism. The first part addresses several questions: was the pandemic caused by nature or by man? Can scientific research help to separate the truth from the conspiracy theses? The second part suggests that the coronavirus has imposed a de facto trickle-down economy on Reagan’s trickledown economy, and shows the economic disruptions it has caused in developed and developing countries. It is concluded that a tiny virus is forcing the dominant neoliberal system to review reality by force.Este artículo examina el contexto de propagación del nuevo coronavirus, la correlación con la inestabilidad de los mercados financieros mundiales y la caída de los precios del petróleo, y la preocupación por el futuro del capitalismo neorrealista. La primera parte aborda varias preguntas: ¿la pandemia fue provocada por la naturaleza o por el hombre?, ¿la investigación científica puede ayudar a separar la verdad de las tesis conspirativas? La segunda parte sugiere que el coronavirus impuso una economía de goteo de facto a la economía de goteo de Reagan, y muestra los trastornos económicos que ha provocado en países desarrollados y en desarrollo. Se concluye que un pequeño virus está obligando al sistema neoliberal dominante a revisar la realidad a la fuerza.Este artigo examina o contexto de disseminação do novo coronavírus, a correlação com a instabilidade dos mercados financeiros mundiais e a queda dos preços do petróleo, e as preocupações com o futuro do capitalismo neorrealista. A primeira parte aborda várias questões: A pandemia foi causada pela natureza ou pelo homem? A pesquisa científica pode ajudar a separar os verdade das teses da conspiração? A segunda parte sugere que o coronavírus impôs uma economia de gotejamento de fato à economia de gotejamento de Reagan e mostra as rupturas econômicas que causou nos países desenvolvidos e em desenvolvimento. Conclui-se que um pequeno vírus está forçando o sistema neoliberal dominante a rever a realidade pela força

Stress influence on high temperature oxide scale growth: modeling and investigation on a thermal barrier coating system.

International audienceIn thermal barrier coating (TBC) systems, an oxide layer develops at high temperature below the ceramic coating, leading at long term to the mechanical failure of the structure upon cooling. This study investigates a mechanism of stress-affected oxidation likely to induce the growth of a non-uniform oxide scale detrimental to the TBC lifetime. A continuum thermodynamics formulation is derived accounting for the influence of the stress and strain situation at the sharp metal/oxide phase boundary on the local oxidation kinetics. It specially includes the contributions of the large volumetric strain and the mass consumption associated with metal oxidation. A continuum mechanics/mass diffusion framework is used along with the developed formulation for the interface evolution to study the growth of an oxide layer coupled with local stress development. The implementation of the model has required the development of a specific simulation tool, based on a finite element method completed with an external routine for the phase boundary propagation. Results on an electron-beam physical vapor deposited (EB-PVD) TBC case are presented. The processes resulting in a non-uniform oxide scale growth are analyzed and the main influences are discussed

Physics of nail conditions: why do ingrown nails always happen in the big toes?

Although surgical treatment of nail conditions can be traced back centuries to the writings of Paul Aegineta (625–690 AC), little is known about the physical laws governing nail growth. Such a poor understanding together with the increasing number of nail salons in the high street should raise legitimate concerns regarding the different procedures applied to nails. An understanding of the physics of nail growth is therefore essential to engage with human medicine and to understand the aetiology of nail conditions. In this context, a theory of nail plate adhesion, including a physical description of nail growth can be used to determine the transverse and longitudinal curvatures of the nail plate that are so important in the physical diagnosis of some nail conditions. As a result physics sheds light on: (a) why/how nails/hooves adhere strongly, yet grow smoothly; (b) why hoof/claw/nail growth rates are similar across species; (c) potential nail damage incurred by poor trimming; (d) the connection between three previously unrelated nail conditions, i.e. spoon-shaped, pincer and ingrown nails and; last but not least, (e) why ingrown nails occur preferentially in the big toes

Efficient Multi-task offloading with energy and computational resources optimization in a mobile edge computing node

With the fifth-generation (5G) networks, Mobile edge computing (MEC) is a promising paradigm to provide near computing and storage capabilities to smart mobile devices. In addition, mobile devices are most of the time battery dependent and energy constrained while they are characterized by their limited processing and storage capacities. Accordingly, these devices must offload a part of their heavy tasks that require a lot of computation and are energy consuming. This choice remains the only option in some circumstances, especially when the battery drains off. Besides, the local CPU frequency allocated to processing has a huge impact on devices energy consumption. Additionally, when mobile devices handle many tasks, the decision of the part to offload becomes critical. Actually, we must consider the wireless network state, the available processing resources at both sides, and particularly the local available battery power. In this paper, we consider a single mobile device that is energy constrained and that retains a list of heavy offloadable tasks that are delay constrained. Therefore, we formulated the corresponding optimization problem, and proposed a Simulated Annealing based heuristic solution scheme. In order to evaluate our solution, we carried out a set of simulation experiments. Finally, the obtained results in terms of energy are very encouraging. Moreover, our solution performs the offloading decisions within an acceptable and feasible timeframes

Time and resource constrained offloading with multi-task in a mobile edge computing node

In recent years, the importance of the mobile edge computing (MEC) paradigm along with the 5G, the Internet of Things (IoT) and virtualization of network functions is well noticed. Besides, the implementation of computation-intensive applications at the mobile device level is limited by battery capacity, processing capabalities and execution time. To increase the batteries life and improve the quality of experience for computationally intensive and latency-sensitive applications, offloading some parts of these applications to the MEC is proposed. This paper presents a solution for a hard decision problem that jointly optimizes the processing time and computing resources in a mobile edge-computing node. Hence, we consider a mobile device with an offloadable list of heavy tasks and we jointly optimize the offloading decisions and the allocation of IT resources to reduce the latency of tasks’ processing. Thus, we developped a heuristic solution based on the simulated annealing algorithm, which can improve the offloading rate and reduce the total task latency while meeting short decision time. We performed a series of experiments to show its efficiency. Finally, the obtained results in terms of full-time treatrement are very encouraging. In addition, our solution makes offloading decisions within acceptable and achievable deadlines

Energy and Processing Time Efficiency for an Optimal Offloading in a Mobile Edge Computing Node

This article describes a processing time, energy and computing resources optimization in a Mobile Edge Computing (MEC). We consider a mobile user MEC system, where a smart mobile device (SMD) demand computation offloading to a MEC server. For that, we consider a SMD contains a set of heavy tasks that can be offloadable. The formulated optimization problem takes into account both the dedicated energy capacity and the processing times. We proposed a heuristic solution schema. To evaluate our solution, we realized a range of simulation experiments. The results obtained in terms of treatment time and energy consumption are very

Offloading Decisions in a Mobile Edge Computing Node with Time and Energy Constraints

This article describes a simulated annealing based offloading decision with processing time, energy consumption and resource constraints in a Mobile Edge Computing Node. Edge computing mostly deals with mobile devices subject to constraints. Especially because of their limited processing capacity and the availability of their battery, these devices have to offload some of their heavy tasks, which require a lot of calculations. We consider a single mobile device with a list of heavy tasks that can be offloadable. The formulated optimization problem takes into account both the dedicated energy capacity and the total execution time. We proposed a heuristic solution schema. To evaluate our solution, we performed a set of simulation experiments. The results obtained in terms of processing time and energy consumption are very encouraging