Autoresonant control of the magnetization switching in single-domain nanoparticles

The ability to control the magnetization switching in nanoscale devices is a crucial step for the development of fast and reliable techniques to store and process information. Here we show that the switching dynamics can be controlled efficiently using a microwave field with slowly varying frequency (autoresonance). This technique allowed us to reduce the applied field by more than $30$ compared to competing approaches, with no need to fine-tune the field parameters. For a linear chain of nanoparticles the effect is even more dramatic, as the dipolar interactions tend to cancel out the effect of the temperature. Simultaneous switching of all the magnetic moments can thus be efficiently triggered on a nanosecond timescale

The price and trade effects of strict information requirements for genetically modified commodities: Under the Cartagena Protocol on Biosafety

This paper assesses the global economic implications of the proposed strict documentation requirements on traded shipments of potentially genetically modified (GM) commodities under the Cartagena Protocol on Biosafety. More specifically, we evaluate the trade diversion, price, and welfare effects of requiring all shipments to bear a list of specific GM events (the does contain rule) in the maize and soybean sectors. Using a spatial equilibrium model with 80 maize- and 53 soybean-trading countries, we show that information requirements would have a significant effect on the world market for maize and soybeans. But they would have even greater effects on trade, creating significant trade distortion that diverts exports from their original destination. The measure would also lead to significant negative welfare effects for all members of the Protocol and nonmembers that produce GM maize, soybeans, or both. While non-GM producers in Protocol member countries would benefit from this regulation, consumers and producers in many developing countries would have to pay a proportionally much heftier price for such a measure.Cartagena protocol on biosafety, Genetically modified food, International trade,

Capital Utilisation and Retirement

This empirical analysis aims at assessing the effect of the economic climate and the intensity of capital utilisation on companies' capital retirement behaviour. It is conducted using individual company data, as well as original data on the degree of utilisation of production factors. The sample includes 6,998 observations over the period 1996-2008. This database is, to our knowledge, unique for the empirical analysis of the intensity of capital utilisation on firms' capital retirement behaviour. We adjust for endogeneity biases by means of instrumental variables. The main results obtained from the estimation of capital retirement models may be summarised as follows: i) The retirement rate decreases with the variations in cyclical pressures measured by the changes in output and the workweek of capital; this relation corresponds to a countercyclical decelerator effect on capital retirement; ii) The capital retirement rate increases with the structural intensity of capital utilisation; this effect, which corresponds to a wear and tear one, is nevertheless small compared to the decelerator one; iii) The profit rate does not have a significant impact on the retirement rate. Compared with the existing literature, here mainly Mairesse and Dormont (1985), the contribution of these results is to show, through the use of unique survey data, that the effect of the intensity of capital utilisation on capital retirement is structurally positive, via a wear and tear effect, and cyclically negative, via a decelerator effect which completes that already taken into account via the effect of changes in value added.Capital; Capital measure; Capital retirement; Capital utilisation

From traffic and pedestrian follow-the-leader models with reaction time to first order convection-diffusion flow models

In this work, we derive first order continuum traffic flow models from a microscopic delayed follow-the-leader model. Those are applicable in the context of vehicular traffic flow as well as pedestrian traffic flow. The microscopic model is based on an optimal velocity function and a reaction time parameter. The corresponding macroscopic formulations in Eulerian or Lagrangian coordinates result in first order convection-diffusion equations. More precisely, the convection is described by the optimal velocity while the diffusion term depends on the reaction time. A linear stability analysis for homogeneous solutions of both continuous and discrete models are provided. The conditions match the ones of the car-following model for specific values of the space discretization. The behavior of the novel model is illustrated thanks to numerical simulations. Transitions to collision-free self-sustained stop-and-go dynamics are obtained if the reaction time is sufficiently large. The results show that the dynamics of the microscopic model can be well captured by the macroscopic equations. For non--zero reaction times we observe a scattered fundamental diagram. The scattering width is compared to real pedestrian and road traffic data

Genetically modified food and international trade: The case of India, Bangladesh, Indonesia, and the Philippines

"Genetically modified (GM) food crops have the potential to raise agricultural productivity in Asian countries, but they are also associated with the risk of market access losses in sensitive importing countries. We study the potential effects of introducing GM food crops in Bangladesh, India, Indonesia, and the Philippines in the presence of trade-related regulations of GM food in major importers. We focus on GM field crops (rice, wheat, maize, soybeans, and cotton) resistant to biotic and abiotic stresses, such as drought-resistant rice, and use a multi-country, multi-sector computable general equilibrium model. We build on previous international simulation models by improving the representation of the productivity shocks associated with GM crops, and by using an improved representation of the world market, accounting for the effects of GM food labeling policies in major importers and the possibility of segregation for non-GM products going toward sensitive importing countries. The results of our simulations first show that the gains associated with the adoption of GM food crops largely exceed any type of potential trade losses these countries may incur. Adopting GM crops also allows net importing countries to greatly reduce their imports. Overall, we find that GM rice is bound to be the most advantageous crop for the four countries. Second, we find that segregation of non-GM crops can help reduce any potential trade loss for GM adopters, such as India, that want to keep export opportunities in sensitive countries, even with a 5 percent segregation cost. Lastly, we find that the opportunity cost of segregation is much larger for sensitive importing countries than for countries adopting new GM crops, which suggests that sensitive importers will have the incentive to invest in separate non-GM marketing channels if exporting countries like India decide to adopt GM food crops." from Authors' AbstractGenetically modified food, International trade, Developing countries, Segregation,

From “May Contain” to “Does Contain”: The price and trade effects of strict information requirements for GM maize under the Cartagena Protocol on Biosafety

Replaced with revised version of paper 07/22/10.Genetically modified food, International Trade, Cartagena Protocol on Biosafety., Agricultural and Food Policy, Environmental Economics and Policy, International Relations/Trade, Political Economy, Research and Development/Tech Change/Emerging Technologies, Q17, Q18, F18,

Spin-torque switching and control using chirped oscillating currents

We propose to use oscillating spin currents with slowly varying frequency (chirp) to manipulate and control the magnetization dynamics in a nanomagnet. By recasting the Landau-Lifshitz-Slonczewski equation in a quantum-like two-level formalism, we show that a chirped spin current polarized in the direction normal to the anisotropy axis can induce a stable precession of the magnetic moment at any angle (up to $90^\circ$) with respect to the anisotropy axis. The drive current can be modest ($10^6\,\rm A/cm^2$ or lower) provided the chirp rate is sufficiently slow. The induced precession is stable against thermal noise, even for small nano-objects at room temperature. Complete reversal of the magnetization can be achieved by adding a small external magnetic field antiparallel to the easy axis. Alternatively, a combination of chirped ac and dc currents with different polarization directions can also be used to trigger the reversal

Quelle prise en compte des informations pour quelle hiérarchisation des mondes possibles ? Une typologie des démarches d'évaluation

Le traitement de l'information opéré dans le but de produire une expertise, et plus généralement un raisonnement en sciences sociales, peut être séparé en deux opérations logiques élémentaires : la prise en compte et la hiérarchisation. Nous nous inspirons sur cette question de la distinction établie par Latour (1999) entre prise en compte et ordonnancement à propos des modalités de la décision publique, mais nous proposons des définitions un peu différentes. Nous entendons ici par prise en compte la manière d'inclure des informations nouvelles dans le raisonnement. L'opération de prise en compte porte donc sur des informations. La hiérarchisation est une opération consistant à utiliser les informations prises en compte pour produire une hiérarchie des mondes possibles