Conforming discretizations of boundary element solutions to the electroencephalography forward problem
We report on the fact that several standardly used discretizations of these formulations are consistent only with an L 2 -framework, requiring the expansion term to be a square integrable function (i.e., in a Petrov–Galerkin scheme with expansion and testing functions). Instead, those techniques are not consistent when a more appropriate mapping in terms of fractional-order Sobolev spaces is considered. Such a mapping allows the expansion function term to be a less regular function, thus sensibly reducing the need for mesh refinements and low-precisions handling strategies that are currently required. These more favor...
Source: Comptes Rendus Physique - April 14, 2018 Category: Physics Source Type: research
Historical perspective on the physics of artificial lighting
We describe the evolution of lighting technologies used throughout the ages, and how the need for improvements was such that any new technology giving better and cheaper lighting was immediately implemented. Thus, every revolution in energy sources – gas, petrol electricity – was first put to large-scale use in lighting. We describe in some detail several “ancient” techniques of scientific interest, along with their physical limitations. Electroluminescence – the phenomenon by which LEDs directly convert electricity into light – was long thought to only be of use for indicators or flat panel displays supposed t...
Source: Comptes Rendus Physique - April 14, 2018 Category: Physics Source Type: research
LED-based white light
This article discusses the use of light-emitting diodes to generate white light – a research forefront in Physics and Ergonomics. We first present various technological approaches to white-light generation. After a general introduction to the human vision system, we discuss two key aspects of the quality of white light: the color of the light itself, and the color rendering of illuminated objects. We present the tools underlying modern color science, and review key color rendering metrics, from the well-known color rendering index to the latest improvements in the field. (Source: Comptes Rendus Physique)
Source: Comptes Rendus Physique - April 14, 2018 Category: Physics Source Type: research
Invention, development, and status of the blue light-emitting diode, the enabler of solid-state lighting
Publication date: Available online 9 January 2018 Source:Comptes Rendus Physique Author(s): Daniel Feezell, Shuji Nakamura The realization of the first high-brightness blue-light-emitting diodes (LEDs) in 1993 sparked a more than twenty-year period of intensive research to improve their efficiency. Solutions to critical challenges related to material quality, light extraction, and internal quantum efficiency have now enabled highly efficient blue LEDs that are used to generate white light in solid-state lighting systems that surpass the efficiency of conventional incandescent lighting by 15–20×. Here we discuss the ...
Source: Comptes Rendus Physique - January 9, 2018 Category: Physics Source Type: research
LED advances accelerate universal access to electric lighting
Publication date: Available online 5 January 2018 Source:Comptes Rendus Physique Author(s): Peter Alstone, Arne Jacobson A rapid increase in the performance and quality of white LED light sources has changed the dynamics of electricity access in the last 10 years, reaching tens of millions of people with electric light who previously had no viable alternatives to fuel-based lighting, which is dangerous and expensive. Eliminating fuel-based lighting is a key public health, safety, social equality, and environmental opportunity that is now achievable. Technology advances in LEDs, other super-efficient appliances, solar p...
Source: Comptes Rendus Physique - January 5, 2018 Category: Physics Source Type: research
LED lighting efficacy: Status and directions
Publication date: Available online 28 December 2017 Source:Comptes Rendus Physique Author(s): Paul Morgan Pattison, Monica Hansen, Jeffrey Y. Tsao A monumental shift from conventional lighting technologies (incandescent, fluorescent, high intensity discharge) to LED lighting is currently transpiring. The primary driver for this shift has been energy efficiency and associated cost savings. LED lighting is now more efficacious than any of the conventional lighting technologies with room to still improve. Near term, phosphor-converted LED packages have the potential for efficacy improvement between 160 lm/W (now) to 255 ...
Source: Comptes Rendus Physique - December 29, 2017 Category: Physics Source Type: research
LED lighting, ultra-low-power lighting schemes for new lighting applications
Publication date: Available online 28 December 2017 Source:Comptes Rendus Physique Author(s): Marc Fontoynont In 2018, Solid-State Lighting (SSL) can totally outperform, if properly designed, most of other lighting products used for general lighting applications. This concerns various attributes such as luminous efficacy, life, spectral qualities, dimming potential, and more and more total cost of ownership. SSL can also mimic a large variety of reference light sources from candlelight to sunlight. The absence of international standards concerning LED modules remains the major difficulty for luminaire manufacturers and ...
Source: Comptes Rendus Physique - December 28, 2017 Category: Physics Source Type: research
Buildings: The new energy nexus
Publication date: September–October 2017 Source:Comptes Rendus Physique, Volume 18, Issues 7–8 Author(s): Daniel Quénard Buildings are the largest contributors to households' energy footprints. If both the energy for household mobility and the embodied energy are added to the energy for heating/cooling, domestic hot water, lighting, buildings are by far the main problem of energy consumption in France. This paper presents a review of the evolution of the main drivers of CO2 emissions by buildings in France. Eventually, the paradox of the effect of density is discussed. Lower density of cities increases the energy s...
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
Storage of thermal solar energy
Publication date: September–October 2017 Source:Comptes Rendus Physique, Volume 18, Issues 7–8 Author(s): Benoît Stutz, Nolwenn Le Pierres, Frédéric Kuznik, Kevyn Johannes, Elena Palomo Del Barrio, Jean-Pierre Bédécarrats, Stéphane Gibout, Philippe Marty, Laurent Zalewski, Jerome Soto, Nathalie Mazet, Régis Olives, Jean-Jacques Bezian, Doan Pham Minh Solar thermal energy storage is used in many applications, from building to concentrating solar power plants and industry. The temperature levels encountered range from ambient temperature to more than 1000 °C, and operating times range from a few...
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
The discovery of the neutron and its consequences (1930 –1940)
Publication date: November–December 2017 Source:Comptes Rendus Physique, Volume 18, Issues 9–10 Author(s): Valery Nesvizhevsky, Jacques Villain In 1930, Walther Bothe and Herbert Becker performed an experiment, which was further improved by Irène and Frédéric Joliot-Curie. These authors, however, misinterpreted their results and believed to have observed γ-rays while they had seen neutrons. After additional experimental verifications, James Chadwick gave the correct interpretation of these experiments in 1932. Immediately, the new particle, the neutron, became an essential actor of nuclear and elementary partic...
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
Henri B énard and pattern-forming instabilities
Publication date: November–December 2017 Source:Comptes Rendus Physique, Volume 18, Issues 9–10 Author(s): Stéphan Fauve The first quantitative experimental study of thermal convection has been performed by Henri Bénard, who presented his results in two articles published in the Comptes rendus in 1900. After describing the first experiments of Bénard and the ones he performed later with his students, we discuss some theoretical steps that led to the full understanding of Bénard's experiments more than fifty years later. We then shortly review some more recent aspects of pattern-forming instabilities that are dir...
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
Foucault and the rotation of the Earth
Publication date: November–December 2017 Source:Comptes Rendus Physique, Volume 18, Issues 9–10 Author(s): Joël Sommeria In February 1851, Léon Foucault published in the Comptes rendus his famous pendulum experiment performed at the “Observatoire de Paris”. This ended two centuries of quest for an experimental demonstration of Earth rotation. One month later, the experiment was reproduced at larger scale in the Panthéon and, as early as the summer of 1851, it was being repeated in many places across the world. The next year, Foucault invented the gyroscope to get a still more direct proof of Earth rotation. T...
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
Des premiers travaux de Le Verrier à la découverte de Neptune
Publication date: November–December 2017 Source:Comptes Rendus Physique, Volume 18, Issues 9–10 Author(s): Jacques Laskar Urbain-Jean-Joseph Le Verrier was born in Saint-Lô on March 11, 1811. He entered the “École polytechnique” in 1831, from which he was to emerge eighth of his class two years later. After first devoting himself to chemistry, in 1836 he obtained a position as an astronomy assistant at the “École polytechnique”. This choice will decide his future career, which culminates with the discovery of Neptune in 1846. Le Verrier wrote more than 200 contributions to the Comptes rendus de l'Académi...
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
From Huygens' waves to Einstein's photons: Weird light
Publication date: November–December 2017 Source:Comptes Rendus Physique, Volume 18, Issues 9–10 Author(s): Alain Aspect From Huygens to Kastler, the members of the Académie des sciences have played an important role in the development and/or the thorough understanding of the models of light. This has paved the way to modern Quantum Optics. (Source: Comptes Rendus Physique)
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
Science in the making: The Comptes rendus de l'Acad émie des sciences throughout history (1835–1966)
Publication date: November–December 2017 Source:Comptes Rendus Physique, Volume 18, Issues 9–10 Author(s): Jacques Villain (Source: Comptes Rendus Physique)
Source: Comptes Rendus Physique - December 16, 2017 Category: Physics Source Type: research
