A further study on Palatini f(R)-theories for polytropic stars

After briefly reviewing the results about polytropic stars in Palatini f(R)-theories, we first show how these results rely on the assumption of a regular function f(R). In particular, singular models allow to extend the parameter interval in which no singularity is formed. Furthermore, we present how the conformal metric can be matched smoothly in the cases where the original metric generates a singularity. In fact, the singularity comes from a singular conformal factor which is continuous though not differentiable at the stellar surface. This suggests that the correct metric to be considered as physical is the conformal metric. This is relevant because, even also when matching the original metric is possible, the use of the conformal metric generates different stellar models.Comment: 18 pages (refs added and typos corrected

Low-Cost Laser-Based Localization System for Agricultural Machines

This paper describes the design and test of a low-cost localization system for agricultural applications, which determines a tractor position in fields up to 0.5 km with an uncertainty of about 1 m. The proposed system employs a standard unmodified laser head, which is commonly used for field leveling, plus a reference ground-fixed laser receiver and requires neither laser modulation nor expensive time-of-flight measurements of light beam

Universality of Einstein Equations for the Ricci Squared Lagrangians

It has been recently shown that, in the first order (Palatini) formalism, there is universality of Einstein equations and Komar energy-momentum complex, in the sense that for a generic nonlinear Lagrangian depending only on the scalar curvature of a metric and a torsionless connection one always gets Einstein equations and Komar's expression for the energy-momentum complex. In this paper a similar analysis (also in the framework of the first order formalism) is performed for all nonlinear Lagrangians depending on the (symmetrized) Ricci square invariant. The main result is that the universality of Einstein equations and Komar energy-momentum complex also extends to this case (modulo a conformal transformation of the metric).Comment: 21 pages, Late

Ultrasonic distance sensor improvement using a two-level neural network

This paper discusses the performance improvement that a neural network can provide to a contactless distance sensor based on the measurement of the time of flight (TOF) of an ultrasonic (US) pulse. The sensor, which embeds a correction system for the temperature effect, achieves a distance uncertainty (rms) of less than 0.5 mm over 0.5 m by using a two-level neural network to process the US echo and determine the TOF in the presence of environmental acoustic noise. The network embeds a "guard" neuron that guards against gross measurement errors, which would be possible in the presence of high environmental noise

A Web-Based Distributed Virtual Educational Laboratory

Evolution and cost of measurement equipment, continuous training, and distance learning make it difficult to provide a complete set of updated workbenches to every student. For a preliminary familiarization and experimentation with instrumentation and measurement procedures, the use of virtual equipment is often considered more than sufficient from the didactic point of view, while the hands-on approach with real instrumentation and measurement systems still remains necessary to complete and refine the student's practical expertise. Creation and distribution of workbenches in networked computer laboratories therefore becomes attractive and convenient. This paper describes specification and design of a geographically distributed system based on commercially standard components

Low-cost electrochemical impedance spectroscopy system for corrosion monitoring of metallic antiquities and works of art

Electrochemical impedance spectroscopy (EIS) is recognized to be a powerful and noninvasive technique to test the integrity of protective coatings on memorials, but commercial EIS systems are rather costly though versatile devices. This paper describes a low cost and portable EIS system that is based on a compact digital signal processor (DSP) board and embeds the potentiostatic function so that it can be used without requiring an external potentiostat. The software that runs on the DSP is designed to analyze the electrochemical impedance only in a reduced frequency range in order to produce a simple corrosion alert result. The device is equipped with a digital interface and can be connected to a personal computer to carry out a complete frequency analysis and perform a more complex data processing

Lagrangian Symmetries of Chern-Simons Theories

This paper analyses the Noether symmetries and the corresponding conservation laws for Chern-Simons Lagrangians in dimension $d=3$. In particular, we find an expression for the superpotential of Chern-Simons gravity. As a by-product the general discussion of superpotentials for 3rd order natural and quasi-natural theories is also given.Comment: 16 pages in LaTeX, some comments and references added. to appear in Journal of Physics A: Mathematical and Genera

Exposure-Tolerant Imaging Solution forCultural Heritage Monitoring

This paper describes a simple and cheap solution specifically designed for monitoring the degradation of thin coatings employed for metal protection. The proposed solution employs a commercial photocamera and a frequency-domain-based approach that is capable of highlighting the surface uniformity changes due to initial corrosion. Even though the proposed solution is specifically designed to monitor the long-time performance of protective coatings employed for the restoration of silver artifacts, it can be successfully used also for assessing the conservation state of other ancient metallic works of art. The proposed solution is made tolerant to exposure changes by using a procedure for sensor nonlinearity identification and correction, does not require a precise lighting control, and employs only free open-source software, so that its overall cost is very low and can be used also by not specifically trained operator