Improved predictions of the standard model and the detection of new physics in neutron beta decay

We improve the current predictions of the standard model for neutron beta decay observables and compare them with the currently available ones. Next we study their implications in the possible detection of new physics. We discuss where the limitations are and where further efforts should be directed.Comment: 8 pages, 3 figures, to appear in Physics Letters

Neoclassical Growth, Environment and Technological Change: The Environmental Kuznets Curve

The paper investigates socially optimal patterns of economic growth and environmental quality in a neoclassical growth model with endogenous technological progress. In the model, the environmental quality affects positively not only to utility but also to production. However, cleaner technologies can be used in the economy whether a part of the output is used in environmentally oriented R&D. In this framework, if the initial level of capital is low then the shadow price of a cleaner technology is low relative to the cost of developing it given by the marginal utility of consumption and it is not worth investing in R&D. Thus, there will be a first stage of growth based only on the accumulation of capital with a decreasing environmental quality until the moment that pollution is great enough to make profitable the investment in R&D. After this turning point, if the new technologies are efficient enough, the economy can evolve along a balanced growth path with an increasing environmental quality. The result is that the optimal investment pattern supports an environmental Kuznets curve.Neoclassical Growth Model, Endogenous Technological Progress, External Effects, Environmental Kuznets Curve

Choice of Metrics used in Collaborative Filtering and their Impact on Recommender Systems

The capacity of recommender systems to make correct predictions is essentially determined by the quality and suitability of the collaborative filtering that implements them. The common memory-based metrics are Pearson correlation and cosine, however, their use is not always the most appropriate or sufficiently justified. In this paper, we analyze these two metrics together with the less common mean squared difference (MSD) to discover their advantages and drawbacks in very important aspects such as the impact when introducing different values of k-neighborhoods, minimization of the MAE error, capacity to carry out a sufficient number of predictions, percentage of correct and incorrect predictions and behavior when attempting to recommend the n-best items. The paper lists the results and practical conclusions that have been obtained after carrying out a comparative study of the metrics based on 135 experiments on the MovieLens database of 100,000 ratios

Squeezing enhancement by competing nonlinearities: Almost perfect squeezing without instabilities

4 págs.; 3 figs.; PACS number~s!: 42.50.Dv, 42.50.Lc, 42.65.KyThe competition between the χ(2) nonlinearity of a resonant second-harmonic-generation (SHG) system and an added χ(3) nonlinearity shifts the Hopf bifurcation of the standard SHG towards higher photon numbers eventually completely stabilizing the system. Remarkably, perfect squeezing survives the stabilization. Two important consequences are discussed, namely, efficient bright squeezing generation and strong suppression of the excess noise which, for parameters corresponding to an experiment reported in the literature, can be reduced by two orders of magnitude without diminishing the squeezing. Possible experimental implementations are finally discussed. ©1997 American Physical SocietyThis work was supported in part by Project No. TIC95- 0563-C05-03 (CICYT, Spain).Peer Reviewe

Economic evaluation of small desalination plants from brackish aquifers. Application to Campo de Cartagena (SE Spain)

The Campo de Cartagena (Eastern Spain) is one of Europe’s driest areas with a mean precipitation of around 300 mm. One of the main challengesin the region is to secure a reliable water supply in both quantity and quality terms, to provide a water supply and agricultural irrigation, while water desalination has become an extensively applied solution, and one of the most sustainable solutions to the water scarcity problem. As water availability is lacking and groundwater quality is poor, the agricultural sector in Campo de Cartagena has developed small private brackish groundwater desalination plants (15-20 m3/h) through already existing agricultural wells. Costs and benefits (C-B) for citrus cultivation (1 ha) in three such plants have been assessed. The results indicate that for the studied cases, current agricultural management is feasible and costs outweigh benefits, with a positive NPV and a cost/benefit ratio higher than 1. The internal rate of return is also positive and higher than 11%. The results evidence practical and theoretical implications as to how to increase water resources in areas where water is scarce by closing the loop, ensuring farmers’ profitability and encouraging private sector investments.Peer ReviewedPostprint (author's final draft

Laser Shock Microforming of Thin Metal Sheets

Continuous and long-pulse lasers have been used for the forming of metal sheets in macroscopic mechanical applications. However, for the manufacturing of micro-electromechanical systems (MEMS), the applicability of such type of lasers is limited by the long-relaxation-time of the thermal fields responsible for the forming phenomena. As a consequence of such slow relaxation, the final sheet deformation state is attained only after a certain time, what makes the generated internal residual stress fields more dependent on ambient conditions and might make difficult the subsequent assembly process from the point of view of residual stresses due to adjustment. The use of ns laser pulses provides a suitable parameter matching for the laser forming of an important range of sheet components used in MEMS that, preserving the short interaction time scale required for the predominantly mechanic (shock) induction of deformation residual stresses, allows for the successful processing of components in a medium range of miniaturization, particularly important according to its frequent use in such systems. In the present paper, a discussion is presented on the physics of laser shock microforming and the influence of the different effects on the net bending angle. The experimental setup used for the experiments, sample fabrication and experimental results of influence of number of laser pulses on the net bending angle are also presented

Quantum Ratchets at High Temperatures

Using the continued-fraction method we solve the Caldeira-Leggett master equation in the phase-space (Wigner) representation to study Quantum ratchets. Broken spatial symmetry, irreversibility and periodic forcing allows for a net current in these systems. We calculate this current as a function of the force under adiabatic conditions. Starting from the classical limit we make the system quantal. In the quantum regime tunnel events and over-barrier wave reflection phenomena modify the classical result. Finally, using the phase-space formalism we give some insights about the decoherence in these systems.Comment: submitted to Physia E (proceedings of conference "Frontiers of Quantum and Mesoscopic Thermodynamics", Prague 26-29 July 2004