La peche dans le fleuve Niger

The fish production of the River Niger can best be estimated from a country by country evaluation of the tonnage exported and that consumed locally. All exported and some locally consumed fish are preserved by smoking or sun drying, a process which entails a loss of weight. Coefficients to correct for this of between 2.6 to 4 have been calculated depending on the type of product. A further loss occurs due to handling and to insect attack, which may account for up to 40% of the production. Taking the above factors into account the productions estimated for the various countries of the Niger River basin are as follows: Guinea (3,600 t), Mali (90,000 t), Upper Volta and Ivory Coast (negligible), Niger (5,200 t), Dahomey (1,200 t), Nigeria (25,000 t), Cameroon (3,000 t). A total production of 128,000 t is, therefore, obtained for the basin as a whole, excluding the Kainji Reservoir. At this level of production, there have been no intimations of overfishing from any part of the basin, and there is unanimity that fishing could be intensified. On the basis of the estimates of existing production and local estimates of potential production it is possible that up to 200,000 t of fish could be produced annually from the basin as a whole.

Le斑马鱼nanos1基因在配子发生中的原位杂交研究

利用组织原位杂交技术,以地高辛标记的反义RNA为探针,检测了斑马鱼(Daniorerio)nanos1基因在卵子发生及精子发生中的表达分布特点,初步探讨了该基因在斑马鱼配子发生中可能的功能。结果表明:在斑马鱼卵子发生中,nanos1mRNA均匀分布于卵原细胞和各时期卵母细胞的胞质中;在卵原细胞和Ⅰ、Ⅱ期卵母细胞中,nanos1mRNA的杂交信号十分强烈,而较晚期卵母细胞中信号明显减弱。在斑马鱼精子发生中,nanos1mRNA可在精原细胞和初级精母细胞中检测到。nanos1mRNA的阳性信号在精原细胞中极为

Stable dynamic walking over uneven terrain

We propose a constructive control design for stabilization of non-periodic trajectories of underactuated robots. An important example of such a system is an underactuated "dynamic walking" biped robot traversing rough or uneven terrain. The stabilization problem is inherently challenging due to the nonlinearity, open-loop instability, hybrid (impact) dynamics, and target motions which are not known in advance. The proposed technique is to compute a transverse linearization about the desired motion: a linear impulsive system which locally represents "transversal" dynamics about a target trajectory. This system is then exponentially stabilized using a modified receding-horizon control design, providing exponential orbital stability of the target trajectory of the original nonlinear system. The proposed method is experimentally verified using a compass-gait walker: a two-degree-of-freedom biped with hip actuation but pointed stilt-like feet. The technique is, however, very general and can be applied to a wide variety of hybrid nonlinear systems. © The Author(s) 2011.

Minimalistic control of biped walking in rough terrain

Toward our comprehensive understanding of legged locomotion in animals and machines, the compass gait model has been intensively studied for a systematic investigation of complex biped locomotion dynamics. While most of the previous studies focused only on the locomotion on flat surfaces, in this article, we tackle with the problem of bipedal locomotion in rough terrains by using a minimalistic control architecture for the compass gait walking model. This controller utilizes an open-loop sinusoidal oscillation of hip motor, which induces basic walking stability without sensory feedback. A set of simulation analyses show that the underlying mechanism lies in the "phase locking" mechanism that compensates phase delays between mechanical dynamics and the open-loop motor oscillation resulting in a relatively large basin of attraction in dynamic bipedal walking. By exploiting this mechanism, we also explain how the basin of attraction can be controlled by manipulating the parameters of oscillator not only on a flat terrain but also in various inclined slopes. Based on the simulation analysis, the proposed controller is implemented in a real-world robotic platform to confirm the plausibility of the approach. In addition, by using these basic principles of self-stability and gait variability, we demonstrate how the proposed controller can be extended with a simple sensory feedback such that the robot is able to control gait patterns autonomously for traversing a rough terrain. © 2010 Springer Science+Business Media, LLC.

Stable dynamic walking over rough terrain: Theory and experiment

We propose a constructive control design for stabilization of non-periodic trajectories of underactuated mechanical systems. An important example of such a system is an underactuated "dynamic walking" biped robot walking over rough terrain. The proposed technique is to compute a transverse linearization about the desired motion: a linear impulsive system which locally represents dynamics about a target trajectory. This system is then exponentially stabilized using a modified receding-horizon control design. The proposed method is experimentally verified using a compass-gait walker: a two-degree-of-freedom biped with hip actuation but pointed stilt-like feet. The technique is, however, very general and can be applied to higher degree-of-freedom robots over arbitrary terrain and other impulsive mechanical systems. © 2011 Springer-Verlag.

Motor control optimization of compliant one-legged locomotion in rough terrain

While underactuated robotic systems are capable of energy efficient and rapid dynamic behavior, we still do not fully understand how body dynamics can be actively used for adaptive behavior in complex unstructured environment. In particular, we can expect that the robotic systems could achieve high maneuverability by flexibly storing and releasing energy through the motor control of the physical interaction between the body and the environment. This paper presents a minimalistic optimization strategy of motor control policy for underactuated legged robotic systems. Based on a reinforcement learning algorithm, we propose an optimization scheme, with which the robot can exploit passive elasticity for hopping forward while maintaining the stability of locomotion process in the environment with a series of large changes of ground surface. We show a case study of a simple one-legged robot which consists of a servomotor and a passive elastic joint. The dynamics and learning performance of the robot model are tested in simulation, and then transferred the results to the real-world robot. ©2007 IEEE.

Parametros operacionais da irrigacao por sulcos em contorno em LE argiloso de cerrado.

2001

Strat?gie et id?ologie: le haut commandement fran?ais et la guerre civile espagnole?

Jackson, Peter, 'Strat?gie et id?ologie: le haut commandement fran?ais et la guerre civile espagnole ', Guerres Mondiales et Conflits Contemporains - Revue Trimestrielle d'Histoire (2001) 199 pp.111-133 RAE2008

Le Cheval de Mazeppa, un cas d'intertextualit? franco-anglaise

Sibona, Bruno, Le Cheval de Mazeppa, un cas d'intertextualit? franco-anglaise (L'Harmattan, 2006)