Dynamique spatio-temporelle des épidémies de la tordeuse des bourgeons de l'épinette dans la pessière à mousses au cours XXième siècle

À l'aide de données dendrochronologiques provenant d'une dizaine de bases de données différentes, et réparties sur 35 sites d'épinettes noires au travers de la pessière à mousse, nous avons étudié la dynamique spatio-temporelle des épidémies de la tordeuse des bourgeons de Pépinette (Chroristoneura fumiferana). Les périodes épidémiques ont été identifiées à l'aide d'une interprétation multicritères prenant en compte l'indice de croissance, le pourcentage d'arbres affectés ainsi qu'un algorithme de somme cumulée (CUSUM chart). Les données ont été cartographiées et soumises à un test d'autocorrélation spatiale (global et local). Nous avons ainsi identifié deux épidémies au cours du XXe siècle qui présentent une emprise significative sur le domaine de la pessière mousses. Parmi ces deux épidémies, la première a émergé dans la zone en 1904 pour atteindre un maximum autour de 1914 et semble avoir progressé du sud vers le nord, appuyant ainsi l'hypothèse d'un débordement des épidémies en provenance des sapinières plus au sud. La deuxième quant à elle présente une emprise plus importante ainsi qu'une structure spatiale plus marquée, notamment à l'échelle régionale. De plus, les premières réductions de croissances attribuées à la tordeuse des bourgeons de l'épinette ont été enregistrées au nord-est de la zone ce qui suppose une dynamique d'émergence propre à la pessière à mousses pour cette épidémie. Enfin, la différence d'impact enregistrée entre les deux épidémies suggère un déplacement vers le nord de la zone propice au développement des épidémies, et donc une plus grande susceptibilité de la pessière à mousses

Evolution of landslide activity, and the origin of debris flows in the El Niño affected Payhua Creek basin, Matucana area, Huarochiri, Peru

Matucana, Perú (population 5800; elevation 2390 m), is located in Andes Occidental, approximately 75 km east of Lima. Matucana shares the Río Rimac (RR) flood plain with a strategic highway and railway. Debris flow-prone Quebrada Payhua (Payhua Creek (QP) joins RR at the upstream end of Matucana. Debris flows from QP dammed the RR and diverted it through Matucana in 1959 and 1983. These large debris flows originated in different parts of the QP basin. The steep ravine systems that produced them are supply-limited with respect to debris flow generation. Based on the volumes of debris flows that were produced by ravine systems in 1983, and channel surveys, a maximum volume of ~250 000 m3 is estimated for the total discharge of a basin-wide debris flow event. Large debris flow events that are conditioned by regional rains are the greatest threat during an El Niño year and in the following year. The area of active landslides near Payhua village, has increased by a factor of five since 1951. Although landslide movement in the recent past has been slow and channel blockage by landslides has not been linked to large destructive debris flows, past events cannot be regarded as confident predictors of future events in this case

A Holocene landscape dynamic multiproxy reconstruction: How do interactions between fire and insect outbreaks shape an ecosystem over long time scales?

At a multi-millennial scale, various disturbances shape boreal forest stand mosaics and the distribution of species. Despite the importance of such disturbances, there is a lack of studies focused on the long-term dynamics of spruce budworm (Choristoneura fumiferana (Clem.)) (SBW) outbreaks and the interaction of insect outbreaks and fire. Here, we combine macrocharcoal and plant macrofossils with a new proxy-lepidopteran scalesto describe the Holocene ecology around a boreal lake. Lepidopteran scales turned out to be a more robust proxy of insect outbreaks than the traditional proxies such as cephalic head capsules and feces. We identified 87 significant peaks in scale abundance over the last 10 000 years. These results indicate that SBW outbreaks were more frequent over the Holocene than suggested by previous studies. Charcoal accumulation rates match the established fire history in eastern Canada: A more fire-prone early and late Holocene and reduced fire frequency during the mid-Holocene. Although on occasion, both fire and insect outbreaks were coeval, our results show a generally inverse relationship between fire frequency and insect outbreaks over the Holocene

Nonnegative matrix factorization: a blind spectra separation method for in vivo fluorescent optical imaging

International audienceFluorescence imaging in diffusive media is an emerging imaging modality for medical applications that uses injected fluorescent markers that bind to specific targets, e.g., carcinoma. The region of interest is illuminated with near-IR light and the emitted back fluorescence is analyzed to localize the fluorescence sources. To investigate a thick medium, as the fluorescence signal decreases with the light travel distance, any disturbing signal, such as biological tissues intrinsic fluorescence (called autofluorescence) is a limiting factor. Several specific markers may also be simultaneously injected to bind to different molecules, and one may want to isolate each specific fluorescent signal from the others. To remove the unwanted fluorescence contributions or separate different specific markers, a spectroscopic approach is explored. The nonnegative matrix factorization (NMF) is the blind positive source separation method we chose. We run an original regularized NMF algorithm we developed on experimental data, and successfully obtain separated in vivo fluorescence spectra

In vivo fluorescence spectra unmixing and autofluorescence removal by sparse Non-negative Matrix Factorization

International audienceFluorescence imaging locates fluorescent markers that specifically bind to targets, as tumors: markers are injected to a patient, optimally excited with near infrared light, and located thanks to emitted back fluorescence analysis. To investigate thick and diffusive media, as the fluorescence signal decreases with the light travel distance, the autofluorescence of biological tissues comes to be a limiting factor. To remove autofluorescence and isolate specific fluorescence, a spectroscopic approach, based on Non-negative Matrix Factorization (NMF), is explored. To improve results on spatially sparse markers detection, we suggest a new constrained NMF algorithm which takes sparsity constraints into account. A comparative study between both algorithms is proposed on simulated and in vivo data

Application de la Factorisation en Matrices Non-négatives pour l'amélioration de la localisation de tumeurs en tomographie optique diffusive de fluorescence

National audienceL'imagerie optique de fluorescence permet de localiser des marqueurs fluorescents spécifiques injectés au patient qui s'accumulent autour de tumeurs cancéreuses. Une fois les régions dŠintérêt illuminées, un signal de fluorescence est émis par les marqueurs mais également par les tissus sains environnants. Lors de l'analyse de tissus épais, alors que le signal de fluorescence décroit avec le parcours de la lumière, l'autofluorescence des tissus prévient la détection des marqueurs profonds. Un approche spectroscopique basée sur la Factorisation en Matrices Non-négatives (FMN) est proposée pour séparer les spectres de fluorescence et éliminer l'autofluorescence des tissus. Afin de limiter le problème de non-unicité de la décomposition, l'ajout d'a priori à la méthode classique développée par Lee et Seung est proposé; la pertinence de ces contraintes est illustrée sur des exemples d'acquisitions de fluorescence in vivo

Non-negative Matrix Factorization under sparsity constraints to unmix in vivo spectrally resolved acquisitions

International audienceFluorescence imaging in diffusive media is an emerging imaging modality for medical applications which uses injected fluorescent markers (several ones may be simultaneously injected) that bind to specific targets, as tumors. The region of interest is illuminated with near infrared light and the emitted back fluorescence is analyzed to localize the fluorescence sources. To investigate thick medium, as the fluorescence signal decreases with the light travel distance, any disturbing signal, such as biological tissues intrinsic fluorescence - called autofluorescence -, is a limiting factor. To remove autofluorescence and isolate each specific fluorescent signal from the others, a spectroscopic approach, based on Non-negative Matrix Factorization, is explored. We ran an NMF algorithm with sparsity constraints on experimental data, and successfully obtained separated in vivo fluorescence spectra

Regularized non negative matrix factorization for autofluorescence removal in fluorescence optical imaging

International audienceFluorescence imaging in diffusive media locates cancers thanks to injected fluorescent markers specific to the tumors. The region of interest is illuminated with red light and the emitted back fluorescence is analyzed to locate the fluorescence sources. To detect accurately the markers signal and be able to explore thick media (breast, prostate), autofluorescence emitted by biological tissues has to be removed. We propose a spectroscopic approach, based on Non-negative Matrix Factorization (NMF) method, and present interest of regularized NMF algorithms on unmixing results. In vivo autofluorescence removal and tumor detection enhancement results on mice will be presented

Modelado de flujos de lodo usando FLO-2D en la quebrada Paihua: Impacto en la ciudad de Matucana, Lima

Se propone un modelo bidimensional de diferencias finitas FLO -2D para simular flujo de fluidos no-newtonianos, como aludes torrenciales en conos de deyección, que permita la estimación de la descarga de los huaycos en la Cuenca de la Quebrada Paihua, asumiendo valores de precipitación de 24 horas, para un período de retorno de 100 años como evento detonador. Las características del modelo permiten simular flujos en topografías complejas, como áreas urbanizadas, terrazas, intercambio de fluido entre canales y el cono de deyección. Considera flujos de agua y flujos hiperconcetrados (detritos, lodo, etc.), homogéneo y de concentración variable. Los datos de entrada requieren topografía digital del terreno, la geometría del canal, valores de la rugosidad del canal y de la planicie de inundación, hidrogramas de entrada de líquidos y sólidos, precipitación y propiedades reológicas de la mezcla agua-sedimento. Se establece la caracterización de la Quebrada a nivel topográfico, hidrológico, geológico y de geodinámica. Asimismo se definen los parámetros, como la concentración volumétrica de sedimentos (C), la gravedad específica del sedimento (G¿), resistencia al flujo laminar (K), entre otros. La metodología analiza dos escenarios; 1) el huayco de la quebrada con un flujo presente en el Río Rímac (27.2 m¿/s, caudal estimado del último huayco); 2) un análisis simulando el huayco en la quebrada y con una avenida de 80 m¿/s en el Río Rímac, a fin de poder presentar el fenómeno de desborde e inundación por colmatación. Se toma en cuenta el encauzamiento actual del río. El modelo permite elaborar un mapa de amenaza por niveles

EOT sub-nanométrico y degradación de la movilidad: ¿hacia un límite físico con las técnicas de fabricación modernas?

In this article we investigate the major problem of the micro/nano-electronic: How to redu­ce the Equivalent Oxide Thickness (EOT) in the sub-nanometric range and improving the MOSFET performance? To reduce the EOT it is necessary that the semiconductor indus­try introduce the high-K material as the Hafnium (Hf) in the dielectric layer. However the Hf produces a reduction of the mobility and therefore a reduction of the MOSFET speed. We explain through a simple semi-empirical model this mobility degradation in order to familiarize the reader with the concept of mobility for the high-K MOSFET. Afterward we focus on two optimized processing methods for the EOT reduction yielding the best gate stack quality. These processing methods are the Fully-Silicide (FuSi) gate with HfSiON dielectric and the Metal Gate with HfO2 which are both “gate first” based integration sche­me. The important results we found is that first we can obtain a sub-1nm EOT in the both cases although it was thought impossible to make it with high thermal budget process such as the FuSi method. Second, the mobility degradation is very similar in the both case in spite of the very different chemistries we use to form the gate stack. We conclude that the modern deposition technique does not allow controlling the dielectric quality as of 0.8 nm and we suggest using the “gate last” based integration scheme to improve further the gate stack quality.En este artículo investigamos un problema mayor de la microelectrónica moderna. Para reducir el EOT y aumentar el desempeño del MOSFET, la industria tiene que introducir el material high-K, como el Hf. Pero eso genera una degradación de la movilidad y una pérdida de la rapidez de los dispositivos. Explicamos esta degradación con un modelo muy sencillo para familiarizar al lector con el concepto de movilidad. Después nos enfocamos en dos procesamientos optimizados (Fully-Silicid con HfSiON y Metal Gate con HfO2) para reducir el EOT y causar un mínimo de defectos en el film. Un resultado muy impor­tante es que podemos lograr un EOT sub-nanométrico en los dos casos ya que esto fue considerado imposible con el FuSi/HfSiON. Otro resultado importante es que en los dos casos la degradación de la movilidad es muy parecida a pesar de que los dos procesamien­tos generan una pila de compuerta de naturaleza química muy diferente. Concluimos que con las técnicas de deposición moderna no se controla la calidad del dieléctrico a partir de 0.8 nm y sugerimos cambiar el esquema de integración con un “gate last”