Elasto-magnetic waves in metamaterials: physics and modelling

The present work is framed in the wide topic of metamaterials. New elements portray this investigation with respect to what already existing in the current worldwide scenario. Indeed, the attention is focused on elastic metamaterials, with the idea to control wave propagation within the structure in terms of wave targeting, wave stopping and wave absorption. This is a novelty, since the concept of metamaterials is usually related to electromagnetic applications, for which all the uncommon effects, as for instance the invisible cloaking, are mainly related to the negative refraction index. A simple one-dimensional structure is analysed. More than the short-range elastic constitutive relationship, a nonlocal new long-range elastic material is here considered. This deeply affects and changes the topology of the system, leading to unexpected propagation phenomena. A mathematical model, based on the nonlocal elasticity theory of Eringen, is considered. The long-range interaction term appears as an integral function that induces a nonlinear characteristic to the conventional equation of motion. Special types of forces are chosen to model the long-range term, as they not only accurately model the elastic forces, but also lend themselves to analysis by Fourier transform. Closed form analytical solutions are achieved and it is the first time that such type of problem is so exhaustively examined. Indeed, long-range interactions have already been investigated, first by V.E. Tarasov, then by Zingales. However, Tarasov developed an analysis on the purely static response of structures, whilst this work discusses its dynamic behaviour, and Zingales performed only numerical solutions, which prevent a thorough understanding, and is mainly interested in modal analysis. The results are discussed in terms of modal analysis, dispersion relationship and propagation. It can be seen how the introduction of unconventional connections affects the typical behaviour of the structure and new phenomena, as hypersonic and superluminal propagation and negative group velocity arise. The analysis has been extended to a twin system, composed by two identical waveguides, with no structural coupling, but mutually coupled only through the long-range characteristic. An experimental campaign concludes the work. A twin waveguide system has been realized by 3D printing; several magnet holders and metallic strips acting as springs are used so to reproduce the mathematical model. The magnetic coupling recreates the long-range interaction. Different types of excitations have been applied to the primary waveguide, so to retrace first the complex frequency response and secondly the dispersion relationship. First results, even though rough, exhibit a damped response on the main waveguide, and a more complex response in the secondary waveguide, in agreement with what analytically observed

Optimal control theory based design of elasto-magnetic metamaterial

A method to design a new type of metamaterial is presented. A two-step strategy to define an optimal long-range force distribution embedded in an elastic support to control wave propagation is considered. The first step uses a linear quadratic regulator (LQR) to produce an optimal set of long-range interactions. In the second step, a least square passive approximation of the LQR optimal gains is determined. The paper investigates numerical solutions obtained by the previously described procedure. Finally, we discuss physical and engineering implications and practical use of the present study

Twin-waves propagation phenomena in magnetically-coupled structures

The use of magnetic dipoles embedding in an elastic support introduces long-range interaction forces. This is a completely new paradigm in structural mechanics, classically based on local short-range particle interaction. The features of long-range forces produce very new mechanical coupling effects. This paper examines the case in which two identical rod-like structures, each with a dipole distribution embedded, vibrate side by side. Waves generated in one of the rods propagate also in the second and vice versa creating a new effect we name twin-waves. The present investigation unveils the existence of an infinite number of propagation modes even in one-dimensional infinite structures, a new and unus al behaviour in classical waveguides. The physics behind this phenomenon is further investigated also by numerical simulations

Long-range retarded elastic metamaterials: wave-stopping, negative, and hypersonic or superluminal group velocity

This paper investigates new phenomena in elastic wave propagation in metamaterials, characterised by long-range interactions. The kind of waves borne in this context unveil wave-stopping, negative group velocity, instability and hypersonic or superluminal effects, both for instantaneous and for nonlocal retarded actions. Closed form results are presented and a universal propagation map synthesizes the expected properties of these materials. Perspectives in physics, engineering and social dynamics are discussed

Variational control approach to energy extraction from a fluid flow

Energy harvesting from the environment is an important aspect of many technologies. The scale of energy capturing and storage can involve the power range from mWatt up to MWatt, depending on the used devices and the considered environments (from ambient acoustic and vibration to ocean wave motion, or wind). In this paper, the wind turbine energy harvesting problem is approached as an optimal control problem, where the objective function is the absorption of an amount of energy in a given time interval by a fluid-flow environment, that should be maximized. The interest relies on outlining general control models of fluid-flow-based extraction plants and identifying an optimum strategy for the regulation of an electrical machine to obtain a maximum-efficiency process for the related energy storage. The mathematical tools are found in the light of optimal control theory, where solutions to the fundamental equations are in the frame of Variational Control (the basis of the Pontryagin optimal control theory). A special problem, named Optimally Controlled Betz’s Machine OCBM-optimal control steady wind turbine, is solved in closed form, and it is shown that, in the simpler steady case, it reproduces the maximum efficiency machine developed in Betz’s theory

accuracy and precision of statistical descriptors obtained from multidimensional diffusion signal inversion algorithms

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An unusual case of an intramuscular lipoma of the biceps brachii

Lipomas are common benign neoplasms consisting of mature fatty tissue. They are usually of roundish or ovoid shape and are situated in a single anatomical region. They most frequently occur on the back and in the extremities. Most lipomas are subcutaneous and require no imaging evaluation. When deep, large and unusual in location, MRI can identify and localise these tumours and is the best exploration to differentiate lipoma and lipo-sarcoma. We describe a case of a patient with an intramuscular lipoma of the biceps brachii.Key words: Intramuscular, lipoma, biceps brachi

OPTYRE—Real time estimation of rolling resistance for intelligent tyres

The study of the rolling tyre is a problem framed in the general context of nonlinear elasticity. The dynamics of the related phenomena is still an open topic, even though few examples and models of tyres can be found in the technical literature. The interest in the dissipation effects associated with the rolling motion is justified by their importance in fuel-saving and in the context of an eco-friendly design. However, a general lack of knowledge characterizes the phenomenon, since not even direct experience on the rolling tyre can reveal the insights of the correlated different dissipation effects, as the friction between the rubber and the road, the contact kinematics and dynamics, the tyre hysteretic behaviour and the grip. A new technology, based on fibre Bragg grating strain sensors and conceived within the OPTYRE project, is illustrated for the specific investigation of the tyre dissipation related phenomena. The remarkable power of this wireless optical system stands in the chance of directly accessing the behaviour of the inner tyre in terms of stresses when a real-condition-rolling is experimentally observed. The ad hoc developed tyre model has allowed the identification of the instant grip conditions, of the area of the contact patch and allows the estimation of the instant dissipated power, which is the focus of this paper

Androgens and cardiac diseases

Although androgens have been considered deleterious for the cardiovascular system, recent data have demonstrated favourable testosterone effects on cardiac and vascular remodeling and clinical outcome. However, the cardiovascular risk-benefit profile of testosterone therapy remains largely elusive due to lack of well-designed and adequately powered randomized clinical trials. In any case, a large body of clinical evidence underlines that low plasma testosterone levels should be considered a risk factor for cardiovascular disease, and that the evaluation of sex steroids should be included in the routine clinical evaluation of cardiac patients. A better understanding of the mechanism regulating the effects of testosterone on cardiovascular system could lead to novel therapeutic strategies in several cardiac patient populations, such as chronic heart failure patients and those who recently underwent cardiac surgery

Un cas de fracture luxation négligée du coude avec conservation de la fonction du coude

Les fractures luxations du coude sont rares et souvent mal tolérées chez les sujets jeunes actifs. Nous rapportons un cas de fracture-luxation du coude remontant à 20 ans. C'est un jeune de 35 ans, victime il y a 20 ans d'un traumatisme fermé, suite à une chute lors d'un match du football, de son coude gauche occasionnant une fracture-luxation du coude. Le patient a  refusé une intervention chirurgicale avec une auto-rééducation. L'examen a mis en évidence une conservation de la fonction du coude. Un bilan  radiologique a montré une fracture luxation du coude avec remaniement de la palette humérale. Une abstention thérapeutique a été décidée devant l'ancienneté de la fracture-luxation et la gêne fonctionnelle minime  engendrée. Contrairement aux autres séries, la fracture-luxation dans notre cas était bien tolérée malgré le jeune âge du patient