Animal Avatars: Reconstructing Animatable 3D Animals from Casual Videos

We present a method to build animatable dog avatars from monocular videos. This is challenging as animals display a range of (unpredictable) non-rigid movements and have a variety of appearance details (e.g., fur, spots, tails). We develop an approach that links the video frames via a 4D solution that jointly solves for animal's pose variation, and its appearance (in a canonical pose). To this end, we significantly improve the quality of template-based shape fitting by endowing the SMAL parametric model with Continuous Surface Embeddings, which brings image-to-mesh reprojection constaints that are denser, and thus stronger, than the previously used sparse semantic keypoint correspondences. To model appearance, we propose an implicit duplex-mesh texture that is defined in the canonical pose, but can be deformed using SMAL pose coefficients and later rendered to enforce a photometric compatibility with the input video frames. On the challenging CoP3D and APTv2 datasets, we demonstrate superior results (both in terms of pose estimates and predicted appearance) to existing template-free (RAC) and template-based approaches (BARC, BITE)

Assessing variations in water availability to vegetation and its consequences on the riparian forest of the arid southwestern USA in service of ecosystem conservation

As Earth’s climate changes, a solid understanding of ecosystems’ sensitivity and reactivity to climatic and environmental controls is critical. Vegetation is considered a key structural element of habitats and ecosystems. By studying changes in vegetation communities’ (specific species assemblages) distribution, health, and timing of main life events, compared with potential controls, such as water availability, it is possible to infer important information on the interactions between vegetation communities (an indicator of habitat integrity) and a changing climate. This comprehension of vegetation dynamics is also crucial for the conservation of species vulnerable to changes and their habitat, even more so in the case of species that are already considered endangered. To fulfil their conservation mission, natural resources managers of lands, regardless of ownership, need a regional-scale understanding of climatic and environmental controls on habitat distribution, condition and vulnerability to climate change. They also need to be able to monitor habitat condition and distribution efficiently and accurately with limited resources. This thesis examines the case of riparian habitats in drylands. Intermittent streams and their streamside vegetation act as moist and cool refuges, support a high species richness and buffer sensitive populations from drought. But they are also rare, isolated, and highly sensitive to changes in water availability. My goal is to reconstruct the complex links between water distribution, water availability to vegetation, and vegetation distribution across a diverse landscape covering a range of elevation, topography and geology, supporting diverse ecosystems. To achieve this landscape-scale overview, I use remote sensing to map the main vegetation communities distribution, their long-term evolution, health, and sensitivity to drought, and conductivity sensors to detect flow and open water presence in-non perennial streams. These methods provide high spatiotemporal resolution datasets that can cover wide areas. The resulting information on vegetation and flow is then compared to climatic and environmental factors, including local geology and rainfall, to better understand their potential vulnerability to drought. This work is focused on applied research and is set in a wider context of providing knowledge and tools for natural resources managers to keep track of rare and sensitive habitats’ condition and extent. The methods and tools used were chosen to test their suitability as accessible and efficient monitoring tools. This thesis focuses on an area in the Southwest USA, covering the upper basin of the San Pedro River (an intermittent river of the Colorado basin), the Huachuca Mountains (an isolated mountain range) and the semi-arid valley in between. My research was conducted on military lands and, as such, the natural resources management side of this work is seen through the lens of military installations and their specific approach to ecosystem conservation. However, the findings of my thesis, both on the ecosystem functioning and the management implications sides, can be more widely applied to monitoring of isolated ecosystems in drylands. This work provides an overall understanding of water availability to vegetation across a diverse landscape, and how this availability controls vegetation distribution and health, from rainfall-supported grassland to groundwater-fed dense riparian forests. I study the differences in long-term, interannual vegetation density variations between ephemeral and perennial reaches along a dryland river, showing how local geology and groundwater levels can buffer riparian ecosystems against drought. I also describe the spatiotemporal distribution of flow in mountain ephemeral streams, from perennial springs to rainfall-fed washes. I link flow permanence to underlying geology, consider how different reaches might be impacted by prolonged drought, and the consequences on local flora and fauna. Finally, I look at short-term, intra-annual changes in vegetation phenology along mountain streams and show how droughts, with higher temperatures and lower precipitation, might shorten the growing season and negatively impact vegetation leaf density. Throughout the thesis, I relate my findings to natural resources management questions and needs, with the goal of providing tools and conclusions useful for endangered and critical habitat monitoring

On the pulsating instability of two-dimensional flames

We consider a well-known thermo-diffusive model for the propagation of a premixed, adiabatic flame front in the large-activation-energy limit. That model depends only on one nondimensional parameter β, the reduced Lewis number. Near the pulsating instability limit, as β↓β0= 32/3, we obtain an asymptotic model for the evolution of a quasi-planar flame front, via a multi-scale analysis. The asymptotic model consists of two complex Ginzburg–Landau equations and a real Burgers equation, coupled by non-local terms. The model is used to analyse the nonlinear stability of the flame front

Helium precipitation study in UO2 by Transmission Electron Microscopy

International audienc

On the origins and the evolution of the fuel-cladding bonding phenomenon in PWR fuel rods

This study proposes a new and detailed description of the fuel-cladding bonding phenomenon occurring in PWR fuel rods. Very early and late bonding states were characterized on specimens of 35.3 GWd.tU−1 moderate burnup and of 64.5 GWd.tU−1 high burnup respectively. Results were then compared with those achieved on a re-created bonded situation obtained on a Zircaloy-4/hyper-stoichiometric UO2+x model materials diffusion couple. These results tend to indicate that a chemical adhesion is probably at the origin of the PWR fuel-cladding bonding. In addition, the progressive formation of ZrO2/UO2 interfacial circumvolutions observed with increasing burnup, which lead to the physical anchorage of ZrO2 and UO2, is likely to lead to their mechanical adhesion. Thus, the in-reactor ZrO2/UO2 bonding could be considered, since the occurrence of the first bonded situations, as an adhesion phenomenon owning two components: an initial chemical progressively strengthened by a second mechanical

Vegetation responses to climatic and geologic controls on water availability in southeastern Arizona

Vegetation distribution, composition and health in arid regions are largely dependent on water availability controlled by climate, local topography and geology. Despite a general understanding of climatic and geologic drivers in plant communities, trends in plant responses to water distribution and storage across areas under different local controls are poorly understood. Here we investigate the multi-decadal interactions between spatial heterogeneity of geologic controls and temporal variation of climate, and their impacts on water availability to vegetation and plant responses (via normalized difference vegetation index, NDVI) in a monsoon-driven arid region of southeastern Arizona. We find that grasslands display low NDVI and respond directly to monsoonal rainfall. In the uplands, vegetation on west-facing slopes and in canyons share similar NDVI averages and variability, suggesting that they both use water from surface-groundwater flow paths through fractured rocks. Along the San Pedro River, streamflow, groundwater, and NDVI in deciduous riparian woodlands are strongly responsive to monsoonal rainfall, but water availability stratifies between wet (perennial), intermediate, and dry reaches, underlain by different local geologic controls that affect water table elevation. These controls interact with the driving climate to affect water availability in the shallow alluvial aquifer of the riparian zone, a primary water source to the gallery phreatophytes. A recent shift toward a strengthened monsoon in the region has led to an increase in water availability for grasslands and for dry reaches of the San Pedro, while the benefit is more muted along wetter reaches, where the riparian forest shows signs of having reached its maturity, with diminished trends in NDVI. These results have implications for the future vulnerability of dryland vegetation to climate change, which may be either dampened or intensified by local controls such as geology

Finite size effects near the onset of the oscillatory instability

A system of two complex Ginzburg - Landau equations is considered that applies at the onset of the oscillatory instability in spatial domains whose size is large (but finite) in one direction; the dependent variables are the slowly modulated complex amplitudes of two counterpropagating wavetrains. In order to obtain a well posed problem, four boundary conditions must be imposed at the boundaries. Two of them were already known, and the other two are first derived in this paper. In the generic case when the group velocity is of order unity, the resulting problem has terms that are not of the same order of magnitude. This fact allows us to consider two distinguished limits and to derive two associated (simpler) sub-models, that are briefly discussed. Our results predict quite a rich variety of complex dynamics that is due to both the modulational instability and finite size effects

Drought onset and propagation into soil moisture and grassland vegetation responses during the 2012–2019 major drought in Southern California

Despite clear signals of regional impacts of the recent severe drought in California, e.g., within Californian Central Valley groundwater storage and Sierra Nevada forests, our understanding of how this drought affected soil moisture and vegetation responses in lowland grasslands is limited. In order to better understand the resulting vulnerability of these landscapes to fire and ecosystem degradation, we aimed to generalize drought-induced changes in subsurface soil moisture and to explore its effects within grassland ecosystems of Southern California. We used a high-resolution in situ dataset of climate and soil moisture from two grassland sites (coastal and inland), alongside greenness (Normalized Difference Vegetation Index) data from Landsat imagery, to explore drought dynamics in environments with similar precipitation but contrasting evaporative demand over the period 2008–2019. We show that negative impacts of prolonged precipitation deficits on vegetation at the coastal site were buffered by fog and moderate temperatures. During the drought, the Santa Barbara region experienced an early onset of the dry season in mid-March instead of April, resulting in premature senescence of grasses by mid-April. We developed a parsimonious soil moisture balance model that captures dynamic vegetation–evapotranspiration feedbacks and analyzed the links between climate, soil moisture, and vegetation greenness over several years of simulated drought conditions, exploring the impacts of plausible climate change scenarios that reflect changes to precipitation amounts, their seasonal distribution, and evaporative demand. The redistribution of precipitation over a shortened rainy season highlighted a strong coupling of evapotranspiration to incoming precipitation at the coastal site, while the lower water-holding capacity of soils at the inland site resulted in additional drainage occurring under this scenario. The loss of spring rains due to a shortening of the rainy season also revealed a greater impact on the inland site, suggesting less resilience to low moisture at a time when plant development is about to start. The results also suggest that the coastal site would suffer disproportionally from extended dry periods, effectively driving these areas into more extreme drought than previously seen. These sensitivities suggest potential future increases in the risk of wildfires under climate change, as well as increased grassland ecosystem vulnerability