Intrinsic character of Stokes matrices

Two germs of linear analytic differential systems $x^{k+1}Y^\prime=A(x)Y$ with a non resonant irregular singularity are analytically equivalent if and only if they have the same eigenvalues and equivalent collections of Stokes matrices. The Stokes matrices are the transition matrices between sectors on which the system is analytically equivalent to its formal normal form. Each sector contains exactly one separating ray for each pair of eigenvalues. A rotation in $S$ allows supposing that $\mathbb R^+$ lies in the intersection of two sectors. Reordering of the coordinates of $Y$ allows ordering the real parts of the eigenvalues, thus yielding triangular Stokes matrices. However, the choice of the rotation in $x$ is not canonical. In this paper we establish how the collection of Stokes matrices depends on this rotation, and hence on a chosen order of the projection of the eigenvalues on a line through the origin.Comment: 10 pages, 3 figure

The median of a jittered Poisson distribution

Let $N_\lambda$ and $U$ be two independent random variables respectively distributed as a Poisson distribution with parameter $\lambda >0$ and a uniform distribution on $(0,1)$. This paper establishes that the median, say $M$, of $N_\lambda+U$ is close to $\lambda +1/3$ and more precisely that $M-\lambda-1/3=o(\lambda^{-1})$ as $\lambda\to \infty$. This result is used to construt a very simple robust estimator of $\lambda$ which is consistent and asymptotically normal. Compared to known robust estimates, this one can still be used with large datasets ($n\simeq 10^9$)

Développement d'une biotechnologie verte innovatrice par ingénierie métabolique pour la valorisation des résidus fromagers

De nombreuses recherches sont menées de par le monde pour valoriser la biomasse résiduelle en sources d'énergie alternatives ou en diverses molécules d’intérêt commercial. Au Québec, parmi les secteurs industriels produisant des résidus potentiellement valorisables, l'industrie de la transformation du lait génère des quantités importantes de lactosérum et de perméat. Notre projet vise à évaluer la possibilité de créer par génie métabolique des microorganismes capables de produire des molécules d’intérêt commercial à partir du lactose contenu dans ces substances. Plus spécifiquement, ce projet vise l’obtention de diols, constitués de (2,3)-butanediol (2,3BD) ainsi que d’acétoïne (AC), par l’intermédiaire d’un procédé de fermentation qui met en œuvre une souche génétiquement modifiée de la bactérie Escherichia coli. Les diols sont des substances permettant de nombreuses applications industrielles, dont la fabrication de polymères, d’explosifs et de produits pharmaceutiques, pour le 2,3BD, ainsi que la fabrication d’agents de saveur, de parfum, pour l’AC. Puisque les enzymes nécessaires à la production de diols ne se retrouvent pas chez E. coli, nous avons d’abord identifié trois produits de gènes permettant successivement de transformer le pyruvate provenant de la glycolyse en 1) acétolactate puis en 2) AC et finalement en 3) 2,3BD. Ces gènes ont été synthétisés puis intégrés au chromosome d’E. coli. Nous avons ensuite validé que la souche obtenue permettait la production des molécules attendues avant de créer une série de délétions inactivant les cinq voies de fermentation principales chez E. coli pouvant potentiellement compétitionner la production de diols. Nos résultats montrent que l’ajout de la voie métabolique des diols couplé à la délétion de certaines voies de fermentation endogènes à E. coli apporte de meilleurs rendements. Nos résultats ont aussi démontré que la surexpression de la voie métabolique des diols via l’utilisation d’un plasmide augmentait la productivité maximale de la souche d’environ 10 fois, pour atteindre 35.3 mM*h-1 ou encore 3.11 g/L*h-1

Un fleuve sous pression : l'hydroélectricité et le transport fluvial dans le bassin supérieur du Lancang-Mékong

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal

SPECTRAL CLUSTERING BASED PARCELLATION OF FETAL BRAIN MRI

Many neuroimaging studies are based on the idea that there are distinct brain regions that are functionally or micro-anatomically homogeneous. Obtaining such regions in an au-tomatic way is a challenging task for fetal data due to the lack of strong and consistent anatomical features at the early stages of brain development. In this paper we propose the use of an automatic approach for parcellating fetal cerebral hemi-spheric surfaces into K regions via spectral clustering. Unlike previous methods, our technique has the crucial advantage of only relying on intrinsic geometrical properties of the corti-cal surface and thus being unsupervised. Results on a data-set of fetal brain MRI acquired in utero demonstrated a convinc-ing parcellation reproducibility of the cortical surfaces across fetuses with varying gestational ages and folding magnitude

Intracerebral delivery of Carboplatin in combination with either 6 MV Photons or monoenergetic synchrotron X-rays are equally efficacious for treatment of the F98 rat glioma.

International audienceABSTRACT: BACKGROUND: The purpose of the present study was to compare side-by-side the therapeutic efficacy of a 6-day infusion of carboplatin, followed by X-irradiation with either 6 MV photons or synchrotron X-rays, tuned above the K-edge of Pt, for treatment of F98 glioma bearing rats. METHODS: Carboplatin was administered intracerebrally (i.c.) to F98 glioma bearing rats over 6 days using AlzetTM osmotic pumps starting 7 days after tumor implantation. Radiotherapy was delivered in a single 15 Gy fraction on day 14 using a conventional 6 MV linear accelerator (LINAC) or 78.8 keV synchrotron X-rays. RESULTS: Untreated control animals had a median survival time (MeST) of 33 days. Animals that received either carboplatin alone or irradiation alone with either 78.8 keV or 6 MV had a MeSTs 38 and 33 days, respectively. Animals that received carboplatin in combination with X-irradiation had a MeST of > 180 days with a 55% cure rate, irrespective of whether they were irradiated with either 78.8 KeV synchrotron X-rays or 6MV photons. CONCLUSIONS: These studies have conclusively demonstrated the equivalency of i.c. delivery of carboplatin in combination with X-irradiation with either 6 MV photons or synchrotron X-rays

Atlas-Free Surface Reconstruction of the Cortical Grey-White Interface in Infants

BACKGROUND: The segmentation of the cortical interface between grey and white matter in magnetic resonance images (MRI) is highly challenging during the first post-natal year. First, the heterogeneous brain maturation creates important intensity fluctuations across regions. Second, the cortical ribbon is highly folded creating complex shapes. Finally, the low tissue contrast and partial volume effects hamper cortex edge detection in parts of the brain. METHODS AND FINDINGS: We present an atlas-free method for segmenting the grey-white matter interface of infant brains in T2-weighted (T2w) images. We used a broad characterization of tissue using features based not only on local contrast but also on geometric properties. Furthermore, inaccuracies in localization were reduced by the convergence of two evolving surfaces located on each side of the inner cortical surface. Our method has been applied to eleven brains of one- to four-month-old infants. Both quantitative validations against manual segmentations and sulcal landmarks demonstrated good performance for infants younger than two months old. Inaccuracies in surface reconstruction increased with age in specific brain regions where the tissue contrast decreased with maturation, such as in the central region. CONCLUSIONS: We presented a new segmentation method which achieved good to very good performance at the grey-white matter interface depending on the infant age. This method should reduce manual intervention and could be applied to pathological brains since it does not require any brain atlas

Intracerebral delivery of 5-iodo-2'-deoxyuridine in combination with synchrotron stereotactic radiation for the therapy of the F98 glioma.

International audienceIodine-enhanced synchrotron stereotactic radiotherapy takes advantage of the radiation dose-enhancement produced by high-Z elements when irradiated with mono-energetic beams of synchrotron X-rays. In this study it has been investigated whether therapeutic efficacy could be improved using a thymidine analogue, 5-iodo-2'-deoxyuridine (IUdR), as a radiosentizing agent. IUdR was administered intracerebrally over six days to F98 glioma-bearing rats using Alzet osmotic pumps, beginning seven days after tumor implantation. On the 14th day, a single 15 Gy dose of 50 keV synchrotron X-rays was delivered to the brain. Animals were followed until the time of death and the primary endpoints of this study were the mean and median survival times. The median survival times for irradiation alone, chemotherapy alone or their combination were 44, 32 and 46 days, respectively, compared with 24 days for untreated controls. Each treatment alone significantly increased the rats' survival in comparison with the untreated group. Their combination did not, however, significantly improve survival compared with that of X-irradiation alone or chemotherapy alone. Further studies are required to understand why the combination of chemoradiotherapy was no more effective than X-irradiation alone