Ultra-low noise front-end electronics for air-coupled ultrasonic non-destructive evaluation

Air-coupled ultrasonic inspection has been demonstrated to be a non-contact method of great interest in non-destructive evaluation (NDE) applications. The absence of direct contact or a liquid couplant provides this technique very attractive benefits in front of the well-known and well-developed liquid-coupled ultrasonic inspection systems. A wide range of defects can be detected by means of ultrasound coupled to and harvested from the specimen in absence of contact when using appropriate transducers designed for their operation in air.This paper presents an easy way to integrate air-coupled piezoelectric transducers in conventional ultrasonic NDE equipment. The design of a specific front-end electronics by using an ultra-low noise amplifier enables existing inspection systems to be used for the dry-coupled ultrasonic test of materials and structures. The amplifier provides the receiver with a signal-to-noise ratio large enough for good quality signal processing and imaging. System dynamic ranges of more than 100 dB are achieved.     

A new route to graphene starting from heavily ozonized fullerenes: Part 3 – an electron spin resonance study

It is shown that graphite oxide (GO) and both heavily ozonized C₆₀ and C₇₀ fullerenes, known as “fullerene ozopolymers,” are paramagnetic materials with a very strong electron spin resonance (ESR) signal at room temperature. When thermally annealed, the paramagnetic centers are gradually lost in large part. This occurs at 350°C in the case of GO, while for fullerene ozopolymers, a higher temperature is required, reaching the same results in the end. The half-width of ESR signal is linked to the distribution of paramagnetic centers. Once again, striking analogies were found in the half-width of the ESR signal measured on GO and fullerene ozopolymers, at least in the temperature range of 25–450°C. Similarly, the same g-factor values, which are diagnostic for understanding the chemical nature of paramagnetic centers, were found on both GO and fullerene ozopolymers in all ranges of temperature considered.     

SOLVING THE SAILING PROBLEM WITH A NEW PRIORITIZED VALUE ITERATION

In this paper we tackle the sailing strategies problem, a stochastic shortest-path Markov decision process. The problem of solving large Markov decision processes accurately and quickly is challenging. Because the computational effort incurred is considerable, current research focuses on finding superior acceleration techniques. For instance, the convergence properties of current solution methods depend, to a great extent, on the order of backup operations. On one hand, algorithms such as topological sorting are able to find good orderings, but their overhead is usually high. On the other hand, shortest path methods, such as Dijkstra's algorithm, which is based on priority queues, have been applied successfully to the solution of deterministic shortest-path Markov decision processes. Here, we propose improved value iteration algorithms based on Dijkstra's algorithm for solving shortest path Markov decision processes. The experimental results on a stochastic shortest-path problem show the feasibility of our approach.     

Handling qualitative aspects in Unequal Area Facility Layout Problem: An Interactive Genetic Algorithm

The Unequal Area Facility Layout Problem (UA-FLP) has been addressed using several methods. However, the UA-FLP has only been solved for criteria that can be quantified. Our approach includes subjective features in the UA-FLP, which are difficult to take into account with a more classical heuristic optimization. In this respect, we propose an Interactive Genetic Algorithm (IGA) that allows an interaction between the algorithm and the Decision Maker (DM). Involving the DM's knowledge in the approach guides the search process, adjusting it to his/her preferences at each generation of the algorithm. In this paper, we are concerned with assisting the DM in finding a good solution according with criteria that can be: subjective, unknown at the beginning or changed during the process, so that, the problem addressed differs from a classic optimization problem. In order to avoid overloading the DM, the whole population is classified into clusters by the fuzzy c-means clustering algorithm and only one representative element of each cluster is directly evaluated by the DM. A memory of the best solutions chosen by the DM is kept as a reference. The tests carried out show that the proposed IGA is capable of capturing DM preferences.     

Residual stresses in cold drawn pearlitic rods

Residual stress profiles in the three principal directions in a cold-drawn pearlitic rod were calculated by a three-dimensional finite element simulation and measured by synchrotron X-ray diffraction. It has been shown that anisotropy of cold-drawn pearlite has to be considered for accurate simulations of residual stresses of steel wires.     

Designing amplifiers with very low output noise for high impedance piezoelectric transducers

An analytical output noise voltage model of an ultra low noise amplifier for high impedance ultrasonic transducers is presented. Operational amplifier with low input bias current is needed to avoid using compensation resistance that considerably increases the noise at the input of the operational amplifier. The proposed analytical model, including the ultrasonic transducer, provides a useful tool to design, compare and select component values.     

A low complexity time-scaling expansion algorithm of speech signals suitable for real time implementation

This paper presents the development and implementation of a variable rate time-scaling expansion system for speech signals, based on the pitch information, in which only the voiced segments are expanded, keeping the unvoiced and silence segments unchanged. The proposed system was first evaluated by computer simulation and then implemented on a digital signal processor (DSP). Time-domain, frequency-domain, mean opinion score (MOS) and diagnostic rhyme test (DRT) evaluations were done to test the actual performance of developed algorithm, which show that the proposed system allows improving the learning level of foreign language students as well as the understanding ability of elderly people. Objective tests also were carried out in order to probe similarity between the original and the expanded signals. Applying an iterative refinement of the C source code it was possible to obtain a real-time implementation. The current implemented algorithm requires 11 kwords program memory and about 9 million of floating point operations per second (MFLOPS).     

New prioritized value iteration for Markov decision processes

The problem of solving large Markov decision processes accurately and quickly is challenging. Since the computational effort incurred is considerable, current research focuses on finding superior acceleration techniques. For instance, the convergence properties of current solution methods depend, to a great extent, on the order of backup operations. On one hand, algorithms such as topological sorting are able to find good orderings but their overhead is usually high. On the other hand, shortest path methods, such as Dijkstra’s algorithm which is based on priority queues, have been applied successfully to the solution of deterministic shortest-path Markov decision processes. Here, we propose an improved value iteration algorithm based on Dijkstra’s algorithm for solving shortest path Markov decision processes. The experimental results on a stochastic shortest-path problem show the feasibility of our approach.     

Lamb wave generation with an air-coupled piezoelectric concave array using square-wave burst excitation

In this paper, an improved pulse generator is proposed to emit a low-voltage square-wave burst. This generator will be used to excite a concave piezoelectric transducer array. Unlike classical single-pulse excitation circuits, this generator is also able to generate a square-wave burst signal. The Lamb waves generated in an aluminium plate with the square-wave burst generator are compared with those obtained using a classical single-pulse generator. Also, the signal conditioning system for all the transducer array elements has been implemented and tested.     

Acenes adducts with C70 fullerene: Anthracene,tetracene and pentacene

The mono-adducts of C₇₀ fullerene with pentacene, tetracene and antracene were synthesized. The C₇₀/acene adducts were studied with FT-IR and the electronic absorption spectroscopy. Thermogravimetric analysis (TGA) in combination with derivative thermogravimetry (DTG) and differential thermal analysis (DTA) were employed to determine the quantitative composition of the adducts and their relative thermal stability. Differential scanning calorimetry (DSC) was employed as well for the determination of the stability of the adducts. It was found that the C₇₀/acene adducts decompose with endothermal reactions. The enthalpy of the decomposition reaction and the decomposition temperatures were determined and found in agreement with the DTG and DTA results.