Résumé -La tomographie par ultrasons a été utilisée pour détecter l'état de dégradation de la section transversale d'un tronc de hêtre, attaqué par une pourriture blanche. La reconstitution de l'image du tronc en 2D a été faite à partir d'un logiciel qui utilise les valeurs de vitesses de propagation des ultrasons à travers la section de l'arbre. Le bois dégradé est caractérisé par des valeurs faibles des vitesses. Les mesures ont été effectuées à travers l'écorce de l'arbre, à trois hauteurs du sol, avec des transducteurs spéciaux de fréquence d'émission de 1 MHz. Dans le cas d'un signal trop entaché par le bruit, une analyse en fréquence a été effectuée. Les tomogrammes ultrasonores ainsi obtenus ont été comparés avec les photographies des sections correspondantes et avec les données obtenues par mesure de résistance à la pénétration d'une aiguille, avec un « Résistograph ». Aux faibles valeurs de la résistance à la pénétration correspondent des valeurs faibles de vitesses. Une bonne correspondance entre les tomogrammes et les photographies a été constatée. La résolution de l'image tomographique est comprise entre 4 et 5 cm. À l'état actuel du développement des techniques de détection non destructives acoustiques des défauts sur les arbres sur pied, cette résolution est la meilleure jamais obtenue. détection non destructive / tomographie ultrasonore / pourriture du bois / évaluation de la stabilité des arbres Abstract -Ultrasonic tomography on standing trees. Ultrasonic tomography was used for the detection of degradation of transversal section of a beech, attacked by white decay. The image reconstruction of the transversal section of the tree in 2D was obtained with a software, which used the values of ultrasonic velocities measured at different heights from the ground. The attacked wood is characterised by low velocities. The measurements were performed with special transducers of 1 MHz, without damaging the bark of the tree. To improve the readings of the signals, a frequency analysis was performed. The ultrasonic tomographies were compared with the corresponding photographic images and with data obtained with a "Resistograph". A good agreement between ultrasonic tomographies and photographs was observed. The image resolution is between 4 and 5 cm. Presently, this is the best resolution ever obtained with an acoustic nondestructive method on a standing tree. non invasive wood testing / ultrasonic tomography / wood decay / tree stability assessment

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United States, does not automatically lead to Washington's desired outcomes, and American delegates must competently perform a certain number of practices for their power advantage to take its full effect. The article also illustrates how looking at practices helps to explain policy decisions, such as NATO's decision to go to Afghanistan, the establishment of an ISAF strategy and the wording of policy papers. By studying a case of military diplomacy, the article contributes to the emerging scholarship aimed at bridging the gap between diplomatic studies and practice-based approaches to International Relations. How did NATO manage the Afghanistan campaign? I argue that the "classical narrative" of the war in Afghanistan, which explains shifts in strategy as an adjustment to shifting US interests, does not fully explain the political dynamics at play within the International Security and Assistance Force (ISAF) and NATO. The problem is not that the classical narrative is wrong, but rather that it only tells a limited aspect of the story. Most scholarship on the Afghanistan war has focused on strategic debates such as the utility and effectiveness of a counter-insurgency (COIN) approach or the soundness of the strategic conceptions behind the overall campaign (Farrell and Chaudhuri, 2011; Bird and Marshall, 2011). Research on multilateral war-fighting in Afghanistan observes that the United States' reliance on coalition partners grew over time, and explains this change by: the government structure and party politics of NATO allies or principal-agent problems (Auerswald and Saideman, 2014); the larger time horizon of the United States which had thus more incentives to seek multilateral cooperation (Kreps, 2012); or the evolution of the way institutional design facilitates multinational military cooperation (Weitsman, 2013). However, few of these studies explain and illustrate how these incentives are translated into actual social dynamics and thus lead to outcomes. They often take for granted a linear relation between state's preferences, power distribution and political outcomes. In short, little is known about NATO's

There is a growing consensus that multinational military operations are often less militarily effective than the theoretical sum of their constitutive parts. At the strategic level, multiple chains of command and demands of consensus can undermine both integration and responsiveness. At the tactical and operational levels, problems such as sector assignments and liaison teams, restriction on intelligence sharing and capability aggregation problems can reduce integration and fighting skills. However, partners may be necessary to provide legitimacy to an intervention. As such, most studies assume that the most powerful state leading a coalition (usually the United States) has to accept a degree of operational ineffectiveness in order to gain political benefits from the participation of junior partners to a multinational military operation. However, such analysis encompasses all « junior partners » under the same broad category, without taking into account the differentiated contributions those junior partners can bring based on their relative military power and international status. This article explores such variations between the junior partners' contributions to multinational military operations and their impact on coalition political and military dynamics, and teases out the theoretical and policy implications of adopting a fine-grained analysis of junior partners.