Integrating the geodesic equations in the Schwarzschild and Kerr space-times using Beltrami's "geometrical" method

We revisit a little known theorem due to Beltrami, through which the integration of the geodesic equations of a curved manifold is accomplished by a method which, even if inspired by the Hamilton-Jacobi method, is purely geometric. The application of this theorem to the Schwarzschild and Kerr metrics leads straightforwardly to the general solution of their geodesic equations. This way of dealing with the problem is, in our opinion, very much in keeping with the geometric spirit of general relativity. In fact, thanks to this theorem we can integrate the geodesic equations by a geometrical method and then verify that the classical conservation laws follow from these equations.Comment: 12 pages; corrected typos, journal-ref adde

THE IMPACT OF TECHNICAL BARRIERS ON US-EU AGRO-FOOD TRADE

Controversial aspects exist in the current debate on the application of Non Tariff Measures (NTMs) on agro-food trade. This study intends to offer an evaluation of the trade impact of both non-technical and technical NTMs on the US-EU bilateral trade, the two major players in WTO negotiations. The results show two main structural differences between the EU and US borders: technical NTMs are preferred in the US, while in the EU the opposite is true; agro-food imports in the US face a number of NTMs more than double that of the EU. Gravity model estimates confirm the negative impact of NTMs on trade. However, safety technical requirements seem to have a positive effect on trade, probably as a consequence of lower transaction, monitoring and enforcing costs.International Relations/Trade,

THE IMPACT OF EU AND US AGRO-FOOD NON TARIFF MEASURES ON EXPORTS FROM DEVELOPING COUNTRIES

Aim of the paper is to appraise the impact of EU and US non tariff measures on agro-food exports from African, Asian and South-American developing countries. After an inventory description of these measures, a gravity model is estimated. The results offer a measure of the impact of the different type of technical (i.e. labeling and standard requirement for both safety and non safety matters) and non-technical (i.e. import licensing and authorization requirements) provisions and of the different degree of application of the same measures, on the agro-food export from developing countries.International Relations/Trade,

The NAFTA Agreement and Market Integration Among Canada, US and Mexico: The Role of Non-Tariff Measures

The aim of this study is to evaluate the impact of non-tariff measures (NTM) on NAFTA agro-food trade comparing the measures implemented at the borders of participating countries, Canada, United States and Mexico, and evaluating the impact of those NTM still implemented within the NAFTA area on agro-food market integration by estimating different gravity models for the agro-food industry as a whole and for particularly relevant product categories. The overall results from the gravity model offer a measure of the impact of the different types of technical provisions and of the different degree of application of the same measure, on the agro-food trade in the NAFTA area. The picture emerging from the estimates is quite complex: overall, a net trade creation effect seems to prevail, even though the results cannot be unambigously generalized, because they are conditional to product groups and country-specific measures.International Relations/Trade,

Concurrent enhancement of percolation and synchronization in adaptive networks

Co-evolutionary adaptive mechanisms are not only ubiquitous in nature, but also beneficial for the functioning of a variety of systems. We here consider an adaptive network of oscillators with a stochastic, fitness-based, rule of connectivity, and show that it self-organizes from fragmented and incoherent states to connected and synchronized ones. The synchronization and percolation are associated to abrupt transitions, and they are concurrently (and significantly) enhanced as compared to the non-adaptive case. Finally we provide evidence that only partial adaptation is sufficient to determine these enhancements. Our study, therefore, indicates that inclusion of simple adaptive mechanisms can efficiently describe some emergent features of networked systems' collective behaviors, and suggests also self-organized ways to control synchronization and percolation in natural and social systems.Comment: Published in Scientific Report

Consumer's Attitude Towards Labeled and Unlabeled GM Food Products in Italy

Based on survey data collected on a sample of 500 Italian consumers, this paper evaluates the consumer's attitude towards foods obtained from the application of biotechnologies and foods labeled as "GM free". Results from the application of probit models shows that the probability to purchase GM products is lower for individuals more adverse to risk, older, with higher education and less confident in institutional guarantees. Willingness to Pay for GM free products is positively related to information, risk aversion, age, trust in institutional environment, negatively to the degree of agreement with the application of biotechnologies.Food Consumption/Nutrition/Food Safety, Research and Development/Tech Change/Emerging Technologies,