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This paper presents performances achieved with InAlGaN/GaN HEMTs with 0.15 µm gate length on SiC substrate. Technology Computer Aided Design simulations were used to optimize the heterostructure. Special attention was paid to the design of the buffer structure. I-V measurements with DC and pulsed bias voltages were performed. CW measurements at millimeter waves were also carried out and are detailed in the following sections. The technology, optimized for power applications up to 45 GHz, demonstrates a current gain cut-off frequency FT of 70 GHz and a maximum available gain cut-off frequency FMAG of 140 GHz. CW Load-pull power measurements at 30 GHz enable to achieve a maximum PAE of 41% associated with an output power density of 3.5 W/mm when biased at VDS = 20 V. These devices, with an improved buffer structure show, reduced recovery time in pulsed operating conditions. These improved characteristics should have a positive impact for pulsed or modulated signal applications.
Atom probe has been developed for investigating materials at the atomic scale and in three dimensions by using either high-voltage (HV) pulses or laser pulses to trigger the field evaporation of surface atoms. In this paper, we propose an atom probe setup with pulsed evaporation achieved by simultaneous application of both methods. This provides a simple way to improve mass resolution without degrading the intrinsic spatial resolution of the instrument. The basic principle of this setup is the combination of both modes, but with a precise control of the delay (at a femtosecond timescale) between voltage and laser pulses. A home-made voltage pulse generator and an air-to-vacuum transmission system are discussed. The shape of the HV pulse presented at the sample apex is experimentally measured. Optimizing the delay between the voltage and the laser pulse improves the mass spectrum quality.
Euclid is a Europe-led cosmology space mission dedicated to a visible and near infrared survey of the entire extra-galactic sky. Its purpose is to deepen our knowledge of the dark content of our Universe. After an overview of the Euclid mission and science, this contribution describes how the community is getting organized to face the data analysis challenges, both in software development and in operational data processing matters. It ends with a more specific account of some of the main contributions of the Swiss Science Data Center (SDC-CH).
The influence of geomorphological features on rain-forest diversity has been reported in different Amazonian regions. Soil filtering is often assumed to underlie the observed geomorphic control on the floristic composition but other hypotheses related to biogeography or long-term forest dynamics are also possible. We tested relationships between geomorphology, soil properties and forest composition in French Guiana rain forest using a recent geomorphological map and a large dataset comprising 3132 0.2-ha plots and 421 soil cores. Soil properties were characterized by laboratory analyses and by field descriptions indicating drainage capacity and classification according to the World Reference Base (WRB). The influence of soils and geomorphology on beta-diversity was tested using variance partitioning and ANOVA-like tests. Our results confirm the hypothesis of a strong relationship between geomorphological landscapes and soil properties. Soil filtering significantly influenced the abundance of more than 40 species or groups of species. However geomorphic control of forest composition involves much more than the effects of the soil, which only explain a minor part of the broad-scale patterns of forest diversity related to geomorphological landscapes. These results reinforce the alternative hypotheses linking geomorphological landscapes to long-term forest change under the control of historical processes that shaped forest diversity.
Rapid changes in agricultural systems call for profound changes in agricultural research and extension practices. The Diagnosis, Design, Assessment, Training and Extension (DATE) approach was developed and applied to co-design Conservation Agriculture-based cropping systems in contrasted situations. DATE is a multi-scale, multi-stakeholder participatory approach that integrates scientific and local knowledge. It emerged in response to questions raised by and issues encountered in the design of innovative systems. A key feature of this approach is the high input of innovative systems which are often although not exclusively based on conservation agricultural practices. Prototyping of innovative cropping systems (ICSs) largely relies on a conceptual model of soil–plant–macrofauna–microorganism system functioning. By comparing the implementation of the DATE approach and conservation agriculture-based cropping systems in Madagascar, Lao PDR, and Cambodia, we show that: (i) the DATE approach is flexible enough to be adapted to local conditions; (ii) market conditions need to be taken into account in designing agricultural development scenarios; and (iii) the learning process during the transition to conservation agriculture requires time. The DATE approach not only enables the co-design of ICSs with farmers, but also incorporates training and extension dimensions. It feeds back practitioners’ questions to researchers, and provides a renewed and extended source of innovation to farmers.
Whereas broad-scale Amazonian forest types have been shown to influence the structure of the communities of medium- to large-bodied vertebrates, their natural heterogeneity at smaller scale or within the terra firme forests remains poorly described and understood. Diversity indices of such communities and the relative abundance of the 21 most commonly observed species were compared from standardized line-transect data across 25 study sites distributed in undisturbed forests in French Guiana. We first assessed the relevance of a forest typology based on geomorphological landscapes to explain the observed heterogeneity. As previously found for tree beta-diversity patterns, this new typology proved to be a non-negligible factor underlying the beta diversity of the communities of medium- to large bodied vertebrates in French Guianan terra firme forests. Although the species studied are almost ubiquitous across the region, they exhibited habitat preferences through significant variation in abundance and in their association index with the different landscape types. As terra firme forests represent more than 90% of the Amazon basin, characterizing their heterogeneity – including faunal communities – is a major challenge in neotropical forest ecology.
This paper presents an original characterization method of trapping phenomena in gallium nitride high electron mobility transistors (GaN HEMTs). This method is based on the frequency dispersion of the output-admittance that is characterized by low-frequency S-parameter measurements. As microwave performances of GaN HEMTs are significantly affected by trapping effects, trap characterization is essential for this power technology. The proposed measurement setup and the trap characterization method allow us to determine the activation energy Ea and the capture cross-section σn of the identified traps. Three original characterizations are presented here to investigate the particular effects of bias, ageing, and light, respectively. These measurements are illustrated through different technologies such as AlGaN/GaN and InAlN/GaN HEMTs with non-intentionally doped or carbon doped GaN buffer layers. The extracted trap signatures are intended to provide an efficient feedback to the technology developments
Cognitive-behavioral therapy (CBT) using traditional exposure techniques (i.e. imaginal and in vivo) seems less effective to treat anxiety in older adults than in younger ones. This is particularly true when imaginal exposure is used to confront the older patient to inaccessible (e.g. fear of flying) or less tangible/controllable anxiety triggers (e.g. fear of illness). Indeed, imaginal exposure may become less effective as the person gets older since normal aging is characterized by the decline in cognitive functions involved in the creation of vivid/detailed mental images. One way to circumvent this difficulty is to expose the older patient to a virtual environment that does not require the ability to imagine the frightening situation. In virtuo exposure has proven to be efficient to treat anxiety in working-age people. In virtuo exposure could be employed to improve the efficacy of CBT with exposure sessions in the treatment of late-life anxiety? The current paper explores this question and suggests new research avenues.
This paper presents power results of L-band packaged hybrid amplifiers using InAlN/GaN/SiC HEMT power dies. The high-power densities achieved both in pulsed and continuous wave (cw) modes confirm the interest of such technology for high-frequency, high-power, and high-temperature operation. We present here record RF power measurements for different versions of amplifiers. Up to 260 W, i.e. 3.6 W/mm, in pulsed (10 µs/10%) conditions, and 105 W, i.e. 2.9 W/mm, in cw conditions were achieved. Such results are made possible thanks to the impressive performances of InAlN/GaN transistors, even when operating at high temperatures. Unit cell transistors deliver output powers of 4.3 W/mm at Vds = 40 V in the cw mode of operation at the frequency of 2 GHz. The transistor process is described here, as well as the amplifiers design and measurements, with a particular focus to the thermal management aspects.
In this paper, we report a new high-speed and high-power switching circuit based on GaN HEMT's. The elementary switching cell, composed of two GaN HEMT's and two resistors, acts like a power threshold comparator with high-output voltage. Theoretical analysis of static and dynamic circuit operation points out the dependence of efficiency and switching speed to the main circuit elements. Four switching cells are then combined together thanks to SiC Schottky diodes to design a multi-level power switch that can be used as a power supply modulator for envelope tracking power amplifiers. The designed four-level supply modulator, based on Nitronex GaN HEMT's, exhibits more than 75% of efficiency for an envelope signal up to 4 MHz, a switching frequency of 20 MHz and output voltages in the range of 12–30 V.
The Mekong River runs through or along Myanmar, Laos, Thailand, Cambodia, and Vietnam. In these “Mekong countries”, agriculture provides a livelihood for a larger proportion of the population than the proportion of GDP derived from agriculture. Agriculture also functions as a safety net for the cities: many workers return to the country to work on farms when there is a rise in unemployment. But the degradation of the environment (soil fertility, erosion, increased population density) and climate change threaten the agriculture sector's ability to play these two roles. Plans must be implemented to keep the agriculture sector sustainable and competitive. Such plans must be adapted to the fact that farmers are financially fragile. Most of their revenue is absorbed by day-to-day expenses, and their investment capacity is low. Also, population growth has saturated the available cultivable lands. As the capacity of urban areas to accommodate rural migration has in most cases reached its limit, crop cultivation is being extended to less fertile areas, often with slopes where erosion happens. Such areas are typically in the peripheral region of Cambodia, the hilly areas of Sayaboury in Laos, and the highlands of Vietnam. As more and more marginal land is being cropped, the sustainability of this activity decreases and the rate of rural poverty increases. Within the Mekong countries rural poverty usually is higher than the national average, and it is higher than rural poverty elsewhere in Asia.
The Mekong countries agriculture is based on irrigated rice, but this system has reached its limits. For rain-fed agriculture, even on sloppy areas, direct sowing (or seeding) mulch-based cropping (DMC), also known as “no tillage” systems, is a better choice. This method was originally developed for tropical upland agriculture in central-west regions of Brazil. For some years, the Agence Française de Développement (AFD) funded research and development projects based on DMC. These projects were implemented with the technical and scientific support of the Centre de Coopération Internationale en Recherche Agronomique pour le Développement (CIRAD) in Cambodia, Laos, and Vietnam.
Scanning Thermal Microscopy measurements with a resistive microprobe electrically heated were performed for different probe temperatures, for probe free in air and in contact with various specimens. The measured relative difference of Joule power dissipated in the probe when tip is in contact with a sample and when it is free in air is studied for different magnitude of the electrical current that heats the probe. A variation of this signal, never outlined before, is observed. A predictive modeling is used to explain these results and identify from the experimental data the global thermal conductance of the probe-sample thermal exchange for experiments performed in ambient conditions.
We observe the heat flux exchanged by the hot tip of a scanning thermal microscope, which is an instrument based on the atomic force microscope. We first vary the pressure in order to analyze the impact on the hot tip temperature. Then the distance between the tip and a cold sample is varied down to few nanometers, in order to reach the ballistic regime. We observe the cooling of the tip due to the tip-sample heat flux and compare it to the current models in the literature.
A major uncertainty in models for photoionised outflows in AGN is the distance of the gas to the central black hole. We present the results of a massive multiwavelength monitoring campaign on the bright Seyfert 1 galaxy Mrk 509 to constrain the location of the outflow components dominating the soft X-ray band. Mrk 509 was monitored by XMM-Newton, Integral, Chandra, HST/COS and Swift in 2009. We have studied the response of the photoionised gas to the changes in the ionising flux produced by the central regions. We were able to put tight constraints on the variability of the absorbers from day to year time scales. This allowed us to develop a model for the time-dependent photoionisation in this source. We find that the more highly ionised gas producing most X-ray line opacity is at least 5 pc away from the core; upper limits to the distance of various absorbing components range between 20 pc up to a few kpc. The more lowly ionised gas producing most UV line opacity is at least 100 pc away from the nucleus. These results point to an origin of the dominant, slow (v<1000 km s−1) outflow components in the NLR or torus-region of Mrk 509. We find that while the kinetic luminosity of the outflow is small, the mass carried away is likely larger than the 0.5 Solar mass per year accreting onto the black hole. We also determined the chemical composition of the outflow as well as valuable constraints on the different emission regions. We find for instance that the resolved component of the Fe-K line originates from a region 40–1000 gravitational radii from the black hole, and that the soft excess is produced by Comptonisation in a warm (0.2–1 keV), optically thick (τ~ 10–20) corona near the inner part of the disk.
A study of the electrical performances of AlInN/GaN High Electron Mobility Transistors (HEMTs) on SiC substrates is presented in this paper. Four different wafers with different technological and epitaxial processes were characterized. Thanks to intensive characterizations as pulsed-IV, [S]-parameters, and load-pull measurements from S to Ku bands, it is demonstrated here that AlInN/GaN HEMTs show excellent power performances and constitute a particularly interesting alternative to AlGaN/GaN HEMTs, especially for high-frequency applications beyond the X band. The measured transistors with 250 nm gate lengths from different wafers delivered in continuous wave (cw): 10.8 W/mm with 60% associated power added efficiency (PAE) at 3,5 GHz, 6.6 W/mm with 39% associated PAE at 10.24 GHz, and 4.2 W/mm with 43% associated PAE at 18 GHz.
We report synthesis, and optical properties, of dihexyl-fluorene-co-3,4-ethylene- dioxythiophene (DHF-co-EDOT) random copolymers obtained from mixture, in various ratios, of the two corresponding dibrominated monomers. Infra-red studies coupled with 1H NMR clearly indicate, as expected, that the amount of each monomer unit in the materials is strongly connected to the feed composition. It clearly appears that even a low 3,4-ethylene- dioxythiophene (EDOT) content, i.e. 15 %, within a poly(dihexyl fluorene) main chain induces significant changes in the electronic properties of the corresponding material, denoted COPO1, compared with the fluorene-based homopolymer. Higher EDOT contents lead to less soluble copolymers which are not or only to a slight extent suitable to investigate their use as luminescent semiconducting ∼-conjugated materials in Organic Light-Emitting Diodes (OLEDs). Green organic light emitting devices based on COPO1, exhibiting no significant spectral evolution, have been demonstrated and showed improved hole-injection properties when compared to the ones using poly(dihexyl fluorene). The use of an additional PEDOT- PSS layer on the ITO anode has also been investigated leading to improved operating lifetime.