Girard F.,IRSTEA |
Vennetier M.,IRSTEA |
Vennetier M.,Aix - Marseille University |
Guibal F.,IMEP |
And 3 more authors.
European Journal of Forest Research | Year: 2012
The objectives of this study were to describe and quantify Aleppo pine aerial primary growth processes and to assess their relationships with climate. Primary growth (branch length growth, branching rate, polycyclism, needle number and size, fruiting), i. e. crown development and reproduction, was reconstructed for the last 16 years in Mediterranean France. From 1998 to 2007, climate has been far hotter and drier than normal in South-eastern France. All variables related to crown development and fruiting, as well as radial growth, significantly declined after 2003 heat wave and during repeated droughts from 2004 to 2007. A partial recovery of most parameters occurred from 2008 to 2010 on vigorous branches while frail branches showed less improvement. The limited crown development during unfavourable years may significantly hold back tree potential photosynthetic biomass for several following years and contribute to a slower than expected recovery of tree growth or to delayed die-back. © 2011 Springer-Verlag.
News Article | February 17, 2017
From the SPIE Photonics West Show Daily : The OPTO plenary talks at SPIE Photonics West explored the promise of technology from controlling thermal radiation, quantum dots, and LiFi - wireless communication using visible light. Everything, from your body to the universe itself, emits thermal radiation. "If we can control thermal radiation, we open new possibilities for technological applications," said Shanhui Fan of Stanford University who lead off the OPTO plenary session 30 January in San Francisco, CA (USA). One example is a passive cooling system. Almost any black material, surrounded by an insulator, radiates heat. By putting such a setup on a rooftop, you can passively cool buildings at night by as much as 15 degrees C below the ambient temperature. Recently, though, Fan and his colleagues have devised a way to cool a building even during the day. The researchers fabricated a structure made of multiple layers of dielectric materials, which reflect sunlight but still strongly emit infrared radiation in the 8 to 13 micron range. Using this structure, they built a module that cools running water to below ambient temperature. The water feeds into a condenser, resulting in an air-conditioning unit that doesn't require electricity. This method uses the ambient environment as a heat sink, so, in principle, if you use the universe itself as a heat sink, you could cool something down to 3 degrees kelvin, the temperature of the cosmos. "If you think about it, the sky is really the limit," Fan said. His group has already reached temperatures below the freezing point of water. These approaches, however, reflect visible light — which isn't always desired. By layering a silica photonic crystal on top of an absorber, the researchers created a material that emits heat and is transparent to the solar spectrum. Such a device could be used to cool photovoltaic cells even while they bake in the sun. For every 10-degree increase in temperature, solar cells drop in efficiency by 1%, so cooling is paramount. Such passive cooling can also generate electricity. If you place a diode next to a cooler object, photons will flow out from the diode via thermal radiation, generating electricity. Placing a fan-like optical chopper in front of the diode periodically blocks the thermal radiation, allowing the ability to encode signals into the electric current. Fan also described his work developing textiles for clothes that keep you as cool as if you're wearing nothing. Working with Yi Cui's group at Stanford, the researchers developed a material made of polyethylene, which is typically clear and nearly 100% transparent in infrared. But by embedding holes ranging in size from 500 nm to 10 microns in the material, they produced a nanoporous polyethylene that's as opaque as cotton, yet transparent to infrared. Quantum dots for encryption OPTO plenary speaker Dieter Bimberg of Technische University in Berlin described the benefits and potential of quantum dots in a variety of applications - and how they are vital for quantum cryptography and energy-efficient nanophotonics. Quantum dots can be fabricated via self-organizing processes. For example, indium arsenide dots are grown on and embedded in gallium arsenide. The dots, appearing as pyramids with a diameter of a few nanometers - 1010 times smaller than those in Egypt - act like individual atoms, with completely quantized energy levels. This allows them to emit light at discrete wavelengths. By embedding quantum dots in a waveguide, for example, you can create a nanophotonic device, like a laser or amplifier. A single quantum dot, Bimberg explained, can have important uses in quantum cryptography and communication. Within a quantum dot, a hole and an electron, bound together as a quasiparticle called an exciton, can recombine and emit one or at most two polarized photons. One photon can serve as a qubit for sending encrypted signals; two are useful for entanglement. Unlike in classical encryption, quantum encryption enables the sender and receiver to know immediately if an interloper has broken the coded signal. Quantum dot technology, Bimberg said, is also relatively simple and inexpensive, since it is based on classical semiconductor technology. A single qubit emitter is just a LED with one single quantum dot inside. A single quantum dot behaves like an individual atom. But in a large assembly of them - say, several million in a semiconductor device - their discrete properties are hidden. But that's what makes them advantageous for creating or transmitting optical signals through communication networks. Not every quantum dot is identical, so a big collection of them will have a range of sizes and shapes, which means they emit light with a Gaussian distribution of wavelengths. A laser based on quantum dots exploits this broad emission. The broader the emission, the faster the laser can fire pulses - pulses narrower than one picosecond, Bimberg said. Because quantum dots have both a ground state and an excited state, quantum-dot lasers can generate pulses at different wavelengths. Lastly, such lasers allow for quantum techniques to suppress the slight fluctuations in arrival times of signals called jitter, down to as little as 200 femtoseconds, which would otherwise be very difficult with conventional lasers. Using quantum-dot technology for other network devices like amplifiers will reduce energy consumption and cost, he said. For instance, devices like an erbium-doped fiber amplifier (EDFA) compensate for the intensity loss of a signal that travels through kilometers of fiber-optic cables. But these amplifiers are complex and expensive and do not operate in the O-band around 1310 nm, which is the range where local and metropolitan area networks operate. Instead, amplifiers based on quantum-dot technology are a cheaper and simpler solution. Quantum-dot amplifiers have several other advantages. A single device can amplify multiple signals with different wavelengths and does this wavelength division multiplexing without crosstalk between signals. These devices can even change the wavelength of signals, which is sometimes necessary in a network because signals of the same wavelength can interfere with one another. In general, quantum-dot technology is more energy efficient, which is increasingly important given the rising energy demands of the internet. "We really have to work on energy-efficient devices," Bimberg said. "Quantum-dot-based lasers and amplifiers are absolutely essential." A quantum-dot laser, for instance, has a threshold current density three to four times lower than that of a conventional quantum well laser, which means it requires much less electricity. Such a device is also more thermally stable, not changing its threshold current density up to 70-80 degrees C, and thus doesn't need an energy-consuming cooling system. Because a quantum-dot amplifier works for both upstream and downstream signals, a network can cut the number of devices — and thus energy demand — by half. Conventional technology would require a separate amplifier for upstream and downstream signals. Concluding the plenary session, Harald Haas of the University of Edinburgh discussed the possibilities of LiFi, wireless communication using visible light. The technology could potentially be revolutionary, playing a role in everything from driverless cars and industrial robots to delivering the internet to remote areas and the Internet of Things. Haas is chair of mobile communications and director of the LiFi Research and Development Center at University of Edinburgh. He is also the founder of pureLiFi, a startup he created after discovering how to use a simple LED to stream data to a computer. LiFi installations are proliferating across the globe and are even used for solar panels, he said. "Commercial activity is increasing all the time," Haas said. "The more pilot projects we have, the more we can show that this technology improves our lives." More than five years ago, Haas demonstrated how he used an LED lamp fitted with a transmitter driver chipset to modulate the light, encode, and then transmit data to a desktop. High-definition video was transmitted through the light beam and LiFi was born. Since 2011, progress has been as rapid as LiFi's data rates. In the lab, as part of the Ultra-Parallel Visible Light Communications Project (UP-VLC), Haas and colleagues have reached blisteringly fast 10Gbit/s data transmission speeds. They developed micro-LED arrays to transmit 3.5Gbit/s via each red, green and blue micro-LEDs in parallel. They also applied novel spatial modulation orthogonal frequency divisional multiplexing so the micro-LED elements within the array could beam thousands of streams of light in parallel, multiplying the volume of data transmitted at any one time. "LEDs have been the bottleneck in data rate. So as part of this project, we wanted to develop a technology that would unlock the vast amount of data rates available in the visible light spectrum," according to Haas. "We've achieved 10Gbit/s with these LEDs, but can reach 100Gbit/s using red, green and blue laser diodes." Chairs for the OPTO symposium were SPIE Fellow Shibin Jiang of AdValue Photonics (USA) and Jean-Emmanuel Broquin of Institut de Microélectronique Électromagnétisme Photonique/Lab. d'Hyperfréquence et Caractérisation (IMEP-LAHC) in France. Connie J. Chang-Hasnain of UC, Berkeley and SPIE Fellow Graham T. Reed of University of Southampton (UK) were the OPTO cochairs. Photonics West 2017, 28 January through 2 February at the Moscone Center, encompassed more than 4700 presentations on light-based technologies across more than 95 conferences. It was also the venue for dozens of technical courses for professional development, the Prism Awards for Photonics Innovation, the SPIE Startup Challenge, a two-day job fair, two major exhibitions, and a diverse business program with more than 25 events. SPIE Photonics West 2018 will run 27 January through 1 February at Moscone Center.
Daux V.,French Climate and Environment Sciences Laboratory |
Edouard J.L.,French National Center for Scientific Research |
Masson-Delmotte V.,French Climate and Environment Sciences Laboratory |
Stievenard M.,French Climate and Environment Sciences Laboratory |
And 5 more authors.
Earth and Planetary Science Letters | Year: 2011
Larch wood has been used for centuries as a building material. Hence, the study of the tree-ring width, the latewood maximal density, and the oxygen and carbon isotope composition of the cellulose of this tree provides potential and valuable insights when reconstructing past climate variability. We explore the qualities and limitations of these proxies, focusing on a forest standing the Névache valley (French Alps). The analysis of 15 trees demonstrates a small intra-tree variability in comparison with the inter-tree variability of δ13C and δ18O, and shows that 6 trees, at least, must be pooled to make a population-representative sample.Our results show no juvenile effect for δ13C. Unlike tree-ring width and density, δ13C and δ18O are not altered by budmouth outbreaks. These two parameters therefore appear well suited for climate reconstructions, and depict a strong correlation with July-August temperature and relative humidity. The δ18O of larch cellulose is also strongly linked with the previous winter (December-March) oxygen isotopic composition of the precipitation. This is consistent with a winter water recharge of soil and ground.The past variations of July-August maximum temperature and relative humidity were established using two different combinations of the isotopic ratios. Uncertainties on the reconstructions are estimated respectively at ± 1.4°C and 3.6%. Inter-annual variations of temperature and relative humidity are well reproduced.However, the reconstructed July-August temperature series diverges from the instrumental one, being lower, after ca. 1990. The effects of the variation through time of the depth of source water and of the ecophysiological response of trees to rising CO2 on the isotope composition are discussed as possible causes of divergence.This 'divergence problem' strongly questions the possibility of producing appropriate isotope-based temperature calibration.The relationships between isotopes and the July-August relative humidity are more stationary than those with temperature. This may reflect the first order control of the relative humidity on δ13C via the stomatal conductance and its influence on the evaporative enrichment of the oxygen of the leaf-water. Our study suggests that past variations of relative humidity in the French Alps can be accurately estimated using the stable isotope composition of larch cellulose. © 2011 Elsevier B.V..
News Article | December 17, 2015
« $12B EV deal: NEVS to provide Panda with 150K 9-3 EVs through 2020, 100K other EV products and services | Main | DOE BETO seeking input on Optima initiative for co-optimization of fuels and engines » Achates Power will work with Delphi Automotive and Argonne National Laboratory on its ARPA-E-funded project to develop an innovative opposed-piston, gasoline compression ignition (OPGCI) engine. (Earlier post.) The engine should yield fuel efficiency gains of more than 50% compared to a downsized, turbo-charged gasoline direct injection engine, while reducing the overall cost of the powertrain system, said Fabien Redon, Vice President, Technology Development at Achates Power. ARPA-E will provide initial funding of $9 million to this project over three years; Achates Power, Argonne and Delphi expect to spend a total of $13 million on the program, including cost share. The $9-million award is “one of the largest single ARPA-E awards ever made,” noted Chris Atkinson, the ARPA-E program manager for the Achates project. Broadly, the 30-month Achates ARPA-E project will deliver a three-cylinder, 3.0-liter opposed-piston, gasoline compression ignition engine applicable to large passenger vehicles, pick-up trucks, SUVs and minivans. It could also be the first of a family of OPGCI engines spanning 1.0 to 4.0L displacements, said Redon. The smaller displacement engine (1.0L) could be extremely interesting as a range extender, he suggested. The specific scope of the project is still being worked through with the partners and the ARPA-E team. Gasoline compression ignition uses high cylinder temperatures and pressures to spontaneously combust gasoline fuel without requiring spark plugs. The Achates Power opposed-piston engine has leveraged two-stroke engine design to develop a flexible air handling and scavenging capability, which provides the necessary high temperature for stable combustion even at low loads. In addition, the combustion system design uses diametrically opposed dual injectors to enable superior control of fuel penetration and mixture stratification for robust ignition and controlled in-cylinder heat release. Argonne National Laboratory has been developing gasoline compression in a series of conventional development engines for nearly 10 years. Their expertise in gasoline compression, computational fluid dynamics and engine modeling and simulation will be a key to the success of this project. Delphi GDCI. Delphi has been working on gasoline direct-injection compression-ignition (GDCI) technology for a number of years (e.g., earlier post). At SAE World Congress 2015 earlier this year, Delphi’s Mark Sellnau and his colleagues presented the latest results from their work for a 1.8L GDCI engine over a wide range of engine speeds and loads using RON91 gasoline. The engine was operated with a new low-temperature combustion process for gasoline partially-premixed compression ignition without combustion mode switching. Injection parameters controlled mixture stratification and combustion phasing using a multiple-late injection strategy with injection pressures similar to that for gasoline direct injection systems. Central to these advancements was a fuel injection system and injection strategy combined with a new piston design. Using multiple late injections and GDi-like fuel pressure, the fuel-air mixture could be stratified but sufficiently mixed. This produced robust ignition with very clean, efficient, and stable combustion within constraints for combustion noise. At idle and low loads, rebreathing of hot exhaust gases provided stable compression ignition with very low engine-out NO and PM emissions. Rebreathing enabled reduced boost pressure, while greatly increasing exhaust temperature. Hydrocarbon and carbon monoxide emissions after the oxidation catalyst were very low. Brake specific fuel consumption (BSFC) of 267 g/kWh was measured at the 2000 rpm-2bar BMEP global test point. At medium load to maximum torque, rebreathing was not used and cooled EGR enabled low-temperature combustion with very low NO and PM, while meeting combustion noise targets. MAP was reduced to minimize boost parasitics. Minimum BSFC was measured at 213 g/kWh at 1800 rpm—12 bar IMEP. Full load torque characteristics of the engine were developed using alternative injection strategies. Maximum BMEP of 20.3 bar was measured at 2000 rpm, with 17.4 bar BMEP achieved at 1500 rpm. While the team reported very good low-speed and medium-speed BMEP, more work is needed to develop output characteristics of the engine, they concluded. Achates compression-ignition OP2S. Once widely used for a range of applications—ground, marine and aviation—the conventional opposed-piston two-stroke (OP2S) engine suffered from poor emissions and oil control. Since its founding in 2004, Achates Power has enhanced the compression-ignition OP2S engine and has worked to resolve its challenges: wrist pin and power durability; piston and cylinder thermal management; piston ring integrity; and oil management. The company—which is an IP (intellectual property) company, not a high-volume engine manufacturer—has some 10 customer projects currently under way, ranging from the very small to the very large (with partner Fairbanks-Morse, earlier post). The first production engine stemming from one of its customer relationships will be out next year, and Achates is also moving to vehicle trials with other customers—all using diesel. In 2014, Achates presented results of an in-depth study on OP2S performance and emissions in a light-duty truck application in an SAE paper. (Earlier post.) The results showed that the Achates Power two-stroke opposed piston engine could meet and exceed—with no hybridization—the final 2025 light-truck CAFE fuel economy regulation for a full-size 5,500 lb pick-up truck and had the potential to achieve the engine-out emissions targets to meet the fully phased in LEV III/Tier 3 emissions with the appropriate aftertreatment. Furthermore, the study showed the potential for a 30% improvement in fuel economy over the equivalent performance Cummins ATLAS Tier 2 Bin 2 engine as well as a significant improvement in NO and PM (42-74%, depending upon drive cycle and pollutant). In April of this year, Achates presented initial test results of the transient control and exhaust temperature management capability of its opposed piston (OP) two-stroke diesel engine showing that under a typical transient maneuver—25% to 100% load step at low and constant engine speed—the engine can control both NO and soot with a minimal torque lag. Test results also showed that the air system control flexibility and robust combustion system that Achates Power developed for the OP engine can be used to achieve high exhaust gas temperatures for a diesel engine at idle-like speeds and load, thereby assisting catalyst light-off. (Earlier post.) Those results followed a paper published in January 2015 detailing steady-state testing results that showed the research 4.9L three-cylinder engine was able to achieve 43% brake thermal efficiency at the best point and almost 42% on average over the modes of the SET (Supplemental Emission Test) cycle. The results from this test confirmed the modeling predictions and pointed to a 48% best BTE and 46.6% average over the cycle for a production design of this engine, the Achates team concluded. OPGCI. In a discussion about the ARPA-E award at Achates main office in San Diego, Redon said that the partners expected to see the same efficiencies as delivered by the diesel version of the opposed-piston engine, but with the additional benefit of a lower cost fuel and aftertreatment system. Overall, they expect about a 50% improvement in fuel efficiency over a downsized, gasoline direct injection engine. Opposed-piston is perfect platform for GCI because of the lower peak loads, Redon noted. In terms of high load operation or max BMEP, the OP levels are 14-15 bar; the downsized four-stroke engines are at 20-25 bar for the 4 stroke. It is a challenge for GCI to achieve the very high BMEP levels in a 4-stroke. Managing the air-fuel mixture is critical for GCI; typically, there is portion of the fuel that is premixed and a portion the fuel that is stratified. For example, Redon said, with an injection that starts early in compression stroke, most of the initial fuel is almost fully premixed by the end of compression—it provides a base for combustion. Another injection that occurs closer to the time of ignition creates stratification and some pockets where ignition can happen, all requiring the right temperature, composition and pressure. The project will result in two purpose-built OPGCI engines: a single-cylinder version to be tested at Argonne, and a multi-cylinder version to be tested at Achates in San Diego.
Domengie F.,STMicroelectronics |
Morin P.,STMicroelectronics |
Electronic Device Failure Analysis | Year: 2012
Complementary metal-oxide semiconductor (CMOS) image sensors, which include millions of pixels, are wonderful tools for very low doses of metallic contamination detection. They represent an active volume of a few cubic micrometers where the charge generated by the contaminant defects will be collected and read by the sensor, constituting their fingerprint for identification. Statistics over millions of pixels can be exploited not only for identification consolidation but also for contaminant-mode evaluation, contaminant diffusivity, and electrical activity. Providing detection limits below 10 10 atcm -3 makes DCS a very efficient technique for monitoring the so-called invisible defect.
Arens D.,IMEP |
Bodart F.,IMEP |
Guillemette M.,IMEP |
Amouh T.,University of Namur |
Chemseddine M.,University of Namur
IHM'10 - 22nd Conference Francophone sur l'Interaction Homme-Machine | Year: 2010
The aim of the Kulitta research project is the creation of innovative software to develop the learning of the different characteristics of sounds in order to improve the musical hearing. This paper describes the principles of the Kulitta software. Copyright © 2010 ACM.
News Article | February 5, 2016
« Researchers create graphene-like structure with transition metal atoms | Main | NREL patents method for continuous monitoring of materials during manufacturing; benefits for fuel cell components, semiconductor wafers » A team at the Engine Research Center (ERC), University of Wisconsin-Madison has demonstrated the viability of reactivity-controlled compression ignition (RCCI) in a two-stroke engine. (Earlier post.) A paper on their work is published in Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering. RCCI is a dual-fuel combustion technology developed by Dr. Rolf Reitz and colleagues at the ERC. RCCI, a variant of Homogeneous Charge Compression Ignition (HCCI), provides more control over the combustion process and has been shown to have the potential to lower fuel use and emissions significantly. The RCCI process uses in-cylinder fuel blending with at least two fuels of different reactivity and multiple injections to control in-cylinder fuel reactivity to optimize combustion phasing, duration and magnitude. The process involves introduction of a low reactivity fuel into the cylinder to create a well-mixed charge of low reactivity fuel, air and recirculated exhaust gases. For their study, the ERC team modified a two-stroke outboard engine to accommodate two direct fuel injectors for RCCI combustion in one cylinder, while the production direct-injection spark ignition combustion system was maintained in the other cylinder for comparison of performances at equivalent operating conditions. The team found that using gasoline and diesel as the two RCCI fuels resulted in unstable combustion and rapid accumulation of particulate matter in the emissions-sampling equipment. However, RCCI experiments with gasoline and n-heptane (higher volatility) proved to be successful. They found that the low-reactivity fuel fraction and the high-reactivity start-of-injection timing were independent combustion-control levers. At 1500 rpm, an IMEP (indicated mean effective pressure) of 2.5 bar and NO emissions of 1.25 g/kWh, reactivity-controlled compression ignition resulted in a lower coefficient of variation in the indicated mean effective pressure, lower carbon monoxide emissions and a significantly higher gross indicated efficiency than those for the direct-injection spark ignition homogeneous mode and the direct-injection spark ignition stratified mode (36.3% versus 27.0% and 25.7% respectively). At 1200 rpm, IMEP of 2.0 bar and hydrocarbon + NO emissions of about 16.5 g/kW h, the reactivity-controlled compression ignition efficiency was still significantly better than those for the direct-injection spark ignition homogeneous mode and the direct-injection spark ignition stratified mode (32.9% versus 25.2% and 26.6% respectively). The researchers suggested that further design optimization might enable the use of a standard diesel fuel instead of n-heptane.