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In this review, we present the results on sub-wavelength perfect acoustic absorption using acoustic metamaterials made of Helmholtz resonators with different setups. Low frequency perfect absorption requires to increase the number of states at low frequencies and finding the good conditions for impedance matching with the background medium. If, in addition, one wishes to reduce the geometric dimensions of the proposed structures for practical issues, one can use properly designed local resonators and achieve sub-wavelength perfect absorption. Helmholtz resonators have been shown good candidates due to their easy tunability of the geometry, so of the resonance frequency, the energy leakage and the intrinsic losses. When plugged to a waveguide or a surrounding medium they behave as open, lossy and resonant systems characterized by their energy leakage and intrinsic losses. The balance between these two represents the critical coupling condition and gives rise to maximum energy absorption. The critical coupling mechanism is represented here in the complex frequency plane in order to interpret the impedance matching condition. In this review we discuss in detail the possibility to obtain perfect absorption by these critical coupling conditions in different systems such as reflection (one-port), transmission (two-ports) or three-ports systems.

Context: “Analytical frameworks” and “practical tools” referring extensively to values and principles have been developed since the 1990’s to provide guidance for public health decision makers and practitioners in ethical reasoning., Objective: This study aimed at identifying the values and principles in public health ethics “frameworks” and “tools”, at classifying them by theme, and at characterizing them by questioning their meanings and articulations., Method: We conducted a systematic review according to PRISMA-S guidelines. It used 3 databases and gathered documents published during the last thirty years. This corpus was analyzed following a multidisciplinarily defined interpretive framework., Results: We included 51 publications. More than a half was issued by North American organizations and 7 by European organizations. We identified 110 values and 153 principles referring to the themes of justice, autonomy, beneficence and non-maleficence, governance and evaluation of actions., Limitations: There are likely other unpublished frameworks and tools used by public health actors and decision makers., Conclusion: Although the most cited values and principles appear to correspond to several fundamental characteristics of public health, it is still early to talk about an ethics specific to public health.

In the present investigation the "in vitro" behaviour of three morphologically different types of embryoid bodies of the teratocarcinoma OTT 6050, which were isolated by means of a Ficoll's density gradient, was analyzed. The study of the results obtained from the culture in suspension and in monolayer show that these morphologically different types represent three different stages of one evolutional cycle which tends to reproduce them as well as creating a variety of potentially more malign embryoid body.