Dynamic range extension of SiPM detectors with the time-gated operation

The silicon photomultiplier (SiPM) is a novel detector technology that has undergone a fast development in the last few years, owing to its single-photon resolution and ultra-fast response time. However, the typical high dark count rates of the sensor may prevent the detection of low intensity radiation fluxes. In this article, the time-gated operation with short active periods in the nanosecond range is proposed as a solution to reduce the number of cells fired due to noise and thus increase the dynamic range. The technique is aimed at application fields that function under a trigger command, such as gated fluorescence lifetime imaging microscopy

Faire face à l'hiver. Quelles réponses à l'hétérogénéité de la ressource en agroécosystème ? L'exemple de l'alouette des champs (Alauda arvensis)

La quantité et la qualité de la ressource alimentaire varient dans le temps et dans l'espace sous l'influence des conditions environnementales. Il est à présent reconnu qu'une diminution de cette ressource est à l'origine d'un déclin pour bon nombre d'espèces granivores inféodées aux milieux cultivés. Face à cette hétérogénéité, les individus mettent en place différentes stratégies individuelles ou collectives pour garantir leurs besoins énergétiques. Dans ce contexte, ce travail s'est attaché à comprendre les stratégies mise en place chez une espèce aviaire caractéristique des agrosystèmes. L'étude expérimentale du compromis alimentation/prédation révèle l'importance de variables environnementales, liées à la ressource, à la taille du groupe ou encore au risque de prédation sur leurs gains énergétiques des individus. Plus étonnamment, nos résultats ont mis en évidence des différences sexuelles dans les stratégies d'acquisitions d'énergie. Les choix effectués par les individus dans la réalisons de ce compromis ont des conséquences sur la sélection de l'habitat. L'étude de la réponse agrégative a ainsi souligné l'impact du type de culture ou de variables paysagères dans l'utilisation de l'habitat. Enfin, une étude sur le sex-ratio en fonction de la latitude en France a pu mettre en évidence une ségrégation spatiale entre les sexes, avec une forte proportion de mâles au nord, et un rééquilibrage vers le sud. Cette ségrégation sexuelle a pu être mise en relation avec des capacités physiologiques différentes (dépenses énergétiques et hypothermie), soulignant une plus forte tolérance des mâles aux faibles températures hivernales rencontrées dans les latitudes plus élevées.Both quantity and quality of food vary in time and space under the influence of environmental conditions. It is now recognized that a decrease of food is involving in a decline for many species of seed-eating farmland birds. According to this heterogeneity, individuals promote strategies to ensure individual and collective energy needs. In this context, this work has focused on understanding the strategies developed in an avian species characteristic of farmland. The experimental study of the trade-off between foraging and predation reveals the importance of environmental variables related to the resource, the group-size and group density, or the predation risk on the intake rate of individuals. More surprisingly, our results have shown sexual differences in energy acquisition strategies. The choices made by individuals under this trade-off have strong consequences on habitat selection. The study of the aggregative response has highlighted the impact crop type and different landscape variables in habitat use, more specially for foraging habitat. Finally, a study on the sex ratio in relationships with latitude in France has been able to demonstrate a spatial segregation between the sexes, with a high proportion of males in the north. This sexual segregation could be related with different physiological capabilities (energy expenditure and hypothermia), emphasizing a greater tolerance of males at low winter temperatures encountered in the higher latitudes during wintering period.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

Micro-Channel Plate Detectors Based on Hydrogenated Amorphous Silicon

A new type of micro-channel plate detector based on hydrogenated amorphous silicon is proposed which overcomes the fabrication and performance issues of glass or bulk silicon ones. This new type of detectors consists in 80-100 μm thick layers of amorphous silicon which are micro-machined by deep reactive ion etching to form the channels. This paper focuses on the structure and fabrication process and presents first results obtained with test devices on electron detection which demonstrate amplification effects. Fabrication and performance issues are also discussed

Comparison of Two Cameras based on Single Photon Avalanche Diodes (SPADs) for Fluorescence Lifetime Imaging Application with Picosecond Resolution

We report on a comparative study of two time-resolved cameras based on digital Single Photon Avalanche Diodes (SPADs) for Fluorescen ce Lifetime Imaging applications. In contrast to standard imagers such as cameras, SPAD imagers provide intensity as well as direct access to the fluorescence decay temporal profile, from which lifetime contrast can be extracted. Intensity images provide physicians with anatomical information to localize cancerous tissue; lifetime maps on the other hand provide metabolic information on tissues and can help detect the presence and location of metastatic cells [1,2,3]. With a timing resolution better than 100ps in a compact setup, the SPAD camera represents an innovative solution to explore subnanosecond fluorescence mechanisms

Compact solid-state CMOS single-photon detector array for in vivo NIR fluorescence lifetime oncology measurements

In near infrared fluorescence-guided surgical oncology, it is challenging to distinguish healthy from cancerous tissue. One promising research avenue consists in the analysis of the exogenous fluorophores’ lifetime, which are however in the (sub-)nanosecond range. We have integrated a single-photon pixel array, based on standard CMOS SPADs (single-photon avalanche diodes), in a compact, time-gated measurement system, named FluoCam. In vivo measurements were carried out with indocyanine green (ICG)-modified derivatives targeting the avb3 integrin, initially on a genetically engineered mouse model of melanoma injected with ICG conjugated with tetrameric cyclic pentapeptide (ICG􀀀E[c(RGDfK)4]), then on mice carrying tumour xenografts of U87-MG (a human primary glioblastoma cell line) injected with monomeric ICG􀀀c(RGDfK). Measurements on tumor, muscle and tail locations allowed us to demonstrate the feasibility of in vivo lifetime measurements with the FluoCam, to determine the characteristic lifetimes (around 500 ps) and subtle lifetime differences between bound and unbound ICG-modified fluorophores (10% level), as well as to estimate the available photon fluxes under realistic conditions

Radiation hardness of amorphous silicon particle sensors

Radiation tests of 32 μm thick hydrogenated amorphous silicon n-i-p diodes have been performed using a high- energy 24 GeV proton beam up to fluences of 2x1016 protons/cm2. The results are compared to irradiation of similar 1 μm and 32 μm thick n-i-p diodes using a proton beam of 405 keV at a fluence of 3x1013 protons/cm2. All samples exhibited a drop of the photoconductivity and an increase in the dark leakage current under both high and low energy proton irradiation. An almost full recovery of the device performance was observed after a subsequent thermal annealing

Research on the Standard about Communication between Predecessor and Successor Auditors

近年来，审计师发生变更越发频繁，对审计师发生变更的原因学者们有多种看法，其中学者们公认的最主要原因是由于审计师与被审计单位的意见分歧所引发的，而这种意见分歧若是发展到被审计单位对审计师进行“意见购买”，则就会影响审计独立性和被审计单位披露信息的真实性。因此，监管部门应该此类动机进行监管，以保证市场运作的秩序。而加强前后任审计师沟通则是抑制上市公司“意见购买”动机，提高审计效率和审计质量的有效途径。美国1975年就出台了前后任审计师沟通准则SASNo.7，到了1998年出台SASNo.84代替原先的SASNo.7，SASNo.84在内容上和措辞上对比SASNo.7更加清晰，确实给审计师提供了对于...Recently, changes of auditors have taken place more and more frequently. Scholars have lots of opinions about the reasons which lead companies to change auditors. Most of scholars agree on that the disagreement about audit opinions between auditors and their clients is the major reason which leads to change auditors. And if this disagreement develops to be a new situation that the clients behave “...学位：管理学硕士院系专业：管理学院会计系_会计学学号：20031103

The requirements for natural Th17 cell development are distinct from those of conventional Th17 cells

A distinct population of Th17 cells develops in the thymus with innate immune cell characteristics, different selection requirements, and skewed TCR gene usage compared with peripheral Th17 cells