Participatory scenario planning for sustainable irrigated agriculture when actors seldom communicate: an experiment in Morocco

ABSTRACT

In Morocco, agricultural activities based on groundwater use increasingly face risks of aquifer overdraft and market saturation. However, farmers and public organizations responsible for agriculture and water resources rarely communicate to identify how these risks could be overcome. A participatory scenario-planning process was organized in a small region to identify a pathway towards agricultural activities that are sustainable in terms of groundwater resource use and profitability. Actors jointly determined this pathway thanks to the organization of preparatory workshops held separately with each actor before they met together, and the progressive integration of agriculture development and groundwater use in scenario design.     

Unambiguous method for DLL BOC signals tracking

In this paper, we propose an efficient method for eliminating ambiguity in the acquisition and tracking processes of binary offset carrier (BOC)‐modulated signals. Our contribution is realized in two stages. The first one is based on the use, at the receiver end, of optimized locally generated subcarrier sequences to get a completely unambiguous composite correlation function (CF). This first stage is used to initialize and control the second stage of the proposed method designed on the basis of a maximum likelihood algorithm (MLA) to mitigate, specifically, multipath (MP) effect. In fact, the idea is to combine, in this second stage, the received signal (affected by noise and MP) with a set of locally generated ideal BOC(m,n)‐modulated signals, which are delayed and weighted by the MLA‐estimated parameters of delays, amplitudes, and phases of all the MP signals, to obtain an unambiguous CF with better performance. The simulation results, based on MATLAB tool, have demonstrated that the proposed method effectively eliminates the ambiguity problem. Besides, a comparative study with several methods has shown that the proposed method grants better performance than the most popular techniques.     

Lower bounds on the iteration time and the initiation interval of functional pipelining and loop folding

The performance of pipelined datapath implementations is measured basically by three parameters: the clock cycle length, the initiation interval between successive iterations (inverse of the throughput) and the iteration time (turn-around time). In this paper we present a new method for computing performance bounds of pipelined implementations:

Cybersecurity Issues in Wireless Sensor Networks: Current Challenges and Solutions

The spectrum is a scarce resource and shall be used efficiently. It is observed that fixed spectrum allocation techniques, currently in use, may not be able to accommodate increased number of users trying simultaneously to access the network. Researches suggest that this problem of spectrum scarcity can be addressed by cognitive radio networks; which permits the dynamic use of spectrum. One of the basic requirements of dynamic spectrum access in cognitive radio network is spectrum handoff. There is an associated issue with frequent spectrum handoffs and that is of the ping-pong ect. The ping-pong ect is caused due to the motion of mobile users between the adjacent cells, thus, initiating unnecessary spectrum handoffs. The purpose of this study is to develop and analyse a system that has the ability to perform cient decision about the execution of spectrum handoffs and in turn reduce the chances of ping-pong ect. Therefore, a fuzzy logic based system has been developed in a cognitive radio WLAN and UMTS environment and handoff is investigated between primary and secondary users. Our proposed hybrid system uses a two-stage fuzzy logic controller to reduce the number of ping-pong handoffs. In the rst stage, the system is designed to control the power of SU and to avoid any interference to PU. In the second stage, the system is designed to take the decision to execute handoff.

     

An accurate two dimensional Markov chain model for IEEE 802.11n DCF

According to the amendment 5 of the IEEE 802.11 standard, 802.11n still uses the distributed coordination function (DCF) access method as mandatory function in access points and wireless stations (essentially to assure compatibility with previous 802.11 versions). This article provides an accurate two dimensional Markov chain model to investigate the throughput performance of IEEE 802.11n networks when frame aggregation and block acknowledgements (Block-ACK) schemes are adopted. Our proposed model considered packet loss either from collisions or channel errors. Further, it took anomalous slots and the freezing of backoff counter into account. The contribution of this work was the analysis of the DCF performance under error-prone channels considering both 802.11n MAC schemes and the anomalous slot in the backoff process. To validate the accuracy of our proposed model, we compared its mathematical simulation results with those obtained using the 802.11n DCF in the network simulator (NS-2) and with other analytical models investigating the performance of 802.11n DCF. Simulation results proved the accuracy of our model.     

Écoulement de Taylor‐Couette en géométrie finie et à surface libre

The reactors of Taylor‐Couette type are relatively recent application in the engineering processes field. The stability and the flow structure in this device are examined under the effect combined of the free surface and the fluid's height in annular space. The exploitation of the flow regimes is carried out according to the number of Taylor for various values of aspect ration Γ. By means of ultrasonic velocimetry (UPV) we determine axial average velocity profile and the axial wavelength. We also carry out the spectral analysis by Fourier's fast transform of the fluctuations associated with the average velocity values in order to analyze the flow structure. We particularly aim for checking the presence or the absence of the azimuth wave according to the filling height and the rotational velocity imposed. We highlight the effects of free surface and aspect ratio on the conditions of appearance of the second instability ( wavy mode). The analysis of the fluctuation shows that the appearance of the azimuth wave regime (Wavy mode) is delayed when the aspect ration decreases. Below a critical value noted Γc = 10, the azimuth wave regime is not observed any more.     

Recognition of diffraction-grating profile using a neural network classifier in optical scatterometry

Optical scatterometry has been given much credit during the past few years in the semiconductor industry. The geometry of an optical diffracted structure is deduced from the scattered intensity by solving an inverse problem. This step always requires a previously defined geometrical model. We develop an artificial neural network classifier whose purpose is to identify the structural geometry of a diffraction grating from its measured ellipsometric signature. This will take place before the characterization stage. Two types of geometry will be treated: sinusoidal and symmetric trapezoidal. Experimental results are performed on two manufactured samples: a sinusoidal photoresist grating deposited on a glass substrate and a trapezoidal grating etched on a SiO2 substrate with periods of 2 microm and 0.565 microm, respectively.     

Enhanced heat exchanger design for hydrogen storage using high-pressure metal hydride: Part 1. Design methodology and computational results

This study explores the use of a high-pressure metal hydride (HPMH), Ti_1.1CrMn, to store hydrogen at high pressures (up to 310 bar) and temperatures below 60 °C, conditions that are suitable for automobile fuel cells. However, the exothermic reaction of hydrogen with this material releases large amounts of heat, and the reaction rate depends on the metal hydride temperature, decreasing significantly if the heat is not removed quickly. Therefore, a powerful heat exchanger constitutes the most crucial component of a HPMH hydrogen storage system. For automobiles, this heat exchanger must enable fueling 5 kg of hydrogen in less than 5 min. This is a formidable challenge considering the enormous amount of heat that must be released and the stringent limits on the heat exchanger’s weight and volume, let alone a host of manufacturing requirements. Unlike conventional heat exchangers that are designed to exchange heat between two fluids, this heat exchanger is quite unique in that it must dissipate heat between a reacting powder and a coolant. In this first of a two-part study, a systematic heat exchanger design methodology is presented, starting with a 1-D criterion and progressing through a series of engineering decisions supported by computations of fill time. A final design is arrived at that meets the 5-min fill time requirement corresponding to minimum heat exchanger mass, supported by a 2-D computational model of the heat exchanger’s thermal and kinetic response.     

Application of the Analytical Strip Method to Antisymmetric Laminates

The analytical strip method is presented in this paper for the analysis of the bending-extension coupling problem of antisymmetric thin laminates. A system of three equations of equilibrium, governing the general response of antisymmetric laminates, is reduced to a single eighth-order partial differential equation (PDE) in terms of a displacement function. The PDE is then solved in a single series form to determine the displacement response of antisymmetric cross-ply and angle-ply laminates. The solution is applicable to rectangular laminates with two opposite edges simply supported and the other edges being simply supported, clamped, or free. The laminate can be subjected to any combination of concentrated, uniform, line, and patch loads. This method overcomes the limitations of other analytical methods (e.g., Navier’s and Levy’s) and provides an alternative to numerical, seminumerical, and approximate methods for rectangular plates with two parallel edges simply supported. The results obtained from this method compare very well with the ones derived using the finite-element program ANSYS and, where applicable, the existing classical laminated plate theory.     

Single-phase hybrid micro-channel/micro-jet impingement cooling

A new hybrid cooling scheme is proposed for high-flux thermal management of electronic and power devices. This scheme combines the cooling benefits of micro-channel flow and micro-jet impingement with those of indirect refrigeration cooling. Experiments were performed to assess single-phase cooling performance using HFE 7100 as working fluid. Excellent predictions were achieved using the standard k–ε model. The proposed cooling scheme is shown to involve complex interactions of impinging jets with micro-channel flow. Increasing jet velocity allows jets to penetrate the micro-channel flow toward the heated surface, especially in shallow micro-channels, greatly decreasing wall temperature. Despite the relatively poor thermophysical properties of HFE 7100, the proposed cooling scheme facilitated the dissipation of 304.9 W/cm² without phase change; further improvement is possible by increasing jet velocity and/or decreasing coolant temperature. In addition to the numerical predictions, a superpositioning technique is introduced that partitions the heat transfer surface into zones that are each dominated by a different heat transfer mechanism, and assigning a different heat transfer coefficient value to each zone. Using this technique, a new correlation is developed that fits the data with a mean absolute error of 6.04%.