A nyquist criterion for time-varying periodic systems, with application to a hydraulic test bench

In this paper, stability results dedicated to sampled periodic systems are applied to a mechanical system whose stiffness exhibits quick variations: a hydraulic test bench used to achieve mechanical test on complex structures. To carry out this application, time-varying w transformation representation of sampled periodic systems are first introduced. An extension of the Nyquist Criterion to sampled periodic systems is then given. Finally, this theorem is applied to evaluate the stability degree of the hydraulic test bench controlled using CRONE control methodology

Toughening and hardening in double-walled carbon nanotube/nanostructured magnesia composites

Dense double-walled carbon nanotube (DWCNT)/nanostructured MgO composites were prepared using an in situ route obviating any milling step for the synthesis of powders and consolidation by spark-plasma-sintering. An unambiguous increase in both toughness and microhardness is reported. The mechanisms of crack-bridging on an unprecedented scale, crack-deflection and DWCNT pullout have been evidenced. The very long DWCNTs, which appear to be mostly undamaged, are very homogeneously dispersed at the grain boundaries of the matrix, greatly inhibiting the grain growth during sintering. These results arise because the unique microstructure (low content of long DWCNTs, nanometric matrix grains and grain boundary cohesion) provides the appropriate scale of the reinforcement to make the material tough

Payments for Environmental Services: To whom, where, and how much?

In this paper we consider different strategies for implementing a payment for environmental services (PES) program to mitigate deforestation in Mexican common property forests (ejidos). We begin by discussing the policy context within which PES programs find themselves, highlighting other possible interventions to help preserve environmental amenities in Mexico. We then discuss some basic principles of environmental payment schemes, formalizing these into three that we simulate: payment of the opportunity cost for forests at risks; payment for environmental benefits provided by forests at risk; a flat payment scheme with a cap on allowable hectares, similar to the type of program often applied in developing countries; and a program of opportunity cost payments for forest at risk with highest environmental benefit per dollar paid. We find that, of these three, the last is most efficient and the second most egalitarian. We also repeat a simulation of the third scheme using predicted, rather than actual risk, which circumvents the problem of strategic behavior on the part of recipient communities but introduces some error into the targeting process. Finally, we consider the characteristics of communities that receive payments from the most efficient program, finding that larger and more remote ejidos receive the lion's share of the budget, but that payments to them are not necessarily more efficient. This scheme also gives more, though smaller on a per capita basis, payments to poor and indigenous communities, where they are more efficient than those to non-poor and non-indigenous ejidos.Environmental Economics and Policy,

Spark-plasma-sintering of double-walled carbon nanotube–magnesia nanocomposites

A double-walled carbon nanotube–MgO powder is prepared without any mixing. The applied pressure is the main parameter acting on densification. Increasing the maximum temperature and holding time is marginally beneficial. The nanotubes are blocking the matrix grain growth. The nanocomposite prepared using the most severe spark plasma sintering conditions (1700 °C, 150 MPa) shows mostly undamaged nanotubes and a higher microhardness than the other materials, reflecting a better bonding between nanotubes and matrix. The electrical conductivity of all nanocomposites is over 12 S/cm

Synthesis of Fe-ZrO2 nanocomposite powders by reduction in H2 of a nanocrystalline (Zr, Fe)O2 solid solution

The formation of Fe-ZrO2 nanocomposite powders by reduction in hydrogen of a nanocrystalline totally stabilized Zr0.9Fe0.1O1.95 solid solution was investigated by X-ray diffraction (XRD), field-emission-gun scanning electron microscopy (FEG-SEM) and Mössbauer spectroscopy. The reduction of the stabilized Zr0.9Fe0.1O1.95 solid solution and the formation of metallic particles precedes the transformation of zirconia into the monoclinic phase, which becomes the major zirconia phase upon reduction at 950 °C. α-Fe particles with a size distribution slightly increasing from 10–50 to 20–70 nm upon the increase in reduction temperature are observed and a second population of smaller (<5 nm) γ-Fe nanoparticles is also noticed when the reduction is performed at 1000 °C. Another metallic phase with a hyperfine field of not, vert, similar200 kOe at RT (not, vert, similar250 kOe at 80 K) is detected, which could account for an Fe/Zr phase. It could be formed by the reduction on an Fe2+-rich transient phase incorporating a small fraction of the Zr4+ ions, formed by a phase partitioning process superimposed to the reduciton processes

Do mobile phones help expand social capital? An empirical case study

The rapid adoption of mobile phones, particularly in developing countries, has led a number of researchers to investigate their impact on socioeconomic activity in the developing world. However, until the recent advent of smart communication devices, mobile phones were primarily a relations management technology that enabled people to stay connected with each other. In this article, we focus on this basic function and analyze how people use this technology as a tool to expand their social capital. We use a dataset containing more than three billion call detail records from Rwanda’s largest telecommunication operator, covering the whole country during the period from 1 July 2014 to 31 March 2015, and combine these records with data from the fourth Integrated Household Living Conditions Survey conducted by the National Institute of Statistics of Rwanda in 2015. We found that people’s calling patterns significantly correlated with the income level of their region, which also dictated the destinations of their calls, with middle-income regions acting as a link between the richest and the poorest regions. From these results, we propose a framework for understanding the role of mobile phones in the development of social capital

Capacity Dimensioning for Aeronautical Communications in North Atlantic Corridor

In the context of the Internet everywhere paradigm, aircraft passengers expect to get connectivity during flights. Several solutions based either on cellular networks in continental area or on satellite links have been designed and even deployed for some of them. But to face the increasing number of users and expected services, a migration to future satellite system such as Inmarsat's Ka band Global Xpress system have been planned. The considered geographical area of the present study is the north Atlantic corridor. In this service zone, the specific structure of aeronautical traffic must be taken into account. NAT (North Atlantic Tracks) are oceanic routes between North America and Europe that are periodically defined considering weather and wind conditions. This explains why the exact locations of the tracks change daily according to weather and also traffic demands. On each continent, specific air traffic control is provided in order to manage entrance and movement along these tracks. The proposed study makes the assumption of a flexible global coverage provided by multi beam Ka band satellites that operate in geosynchronous orbit. Aircraft flying in the north Atlantic corridor use the system in order to offer in-flight connectivity for airline passengers. Doing so, passengers may access common Internet services, namely web browsing, electronic mail, or file transfer. More specific applications for pilots and companies are also taken in consideration enhanced with new services such as real time black box data streaming. In order to assess induced traffic load and instantaneous required capacities in each spot beam, a simulation model has been specifically developed by ENAC and ISAE with Opnet Modeler software

Iron-stabilized nanocrystalline ZrO2 solid solutions: Synthesis by combustion and thermal stability

The synthesis of Fe3+-stabilized zirconia by the nitrate/urea combustion route was investigated. Using several characterization techniques, including X-ray diffraction, field-emission-gun scanning electron microscopy and notably Mo¨ ssbauer spectroscopy, it was possible to determine the appropriate amount of urea that allows to obtain a totally stabilized Zr0.9Fe0.1O1.95 solid solution. The nanocrystalline zirconia solid solution is mostly tetragonal, but the presence of the cubic phase could not be ruled out. An indepth study of the thermal stability in air showed that the Fe3+ solubility in the stabilized solid solution starts to decrease at about 875 8C which results in the formation of hematite (possibly containing some Zr4+) at the surface of the zirconia grains and further provokes the progressive transformation into the monoclinic zirconia phase

Tetragonal-(Zr,Co)O2 solid solution: Combustion synthesis, thermal stability in air and reduction in H2, H2–CH4 and H2–C2H4 atmospheres

The synthesis of Co2+-stabilized zirconia by the nitrate/urea combustion route is investigated. Using seven times the so-called stoichiometric urea proportion allows to obtain for the first time the Zr0.9Co0.1O1.9 solid solution fully stabilized in tetragonal form. The thermal stability in air and the reduction in H2, H2–CH4 and H2–C2H4 atmospheres are studied. The carbon forms obtained upon reduction are investigated. Reduction in H2–CH4 produces many carbon species including short carbon nanofibers, nanoribbons, hollow particles often forming bamboo structures, carbon-encapsulated Co particles and carbon nanotubes. Reduction in H2–C2H4 produces 15–30 nm nanofibers