During the last two years the COVID-19 pandemic has affected the world population in several ways. An important increase in mental health problems is a consequence of this pandemic that is ubiquitous worldwide. In this work we study the effect of the pandemic on the mental health of a population of teenagers and youth based on the analysis of natural language processing, machine learning algorithms and expert knowledge. The data analysed was obtained from a chat helpline called Safe time from theIt Get’s Better Foundation in Chile. The data consists of 10,986 conversations gathered from 2018 until 2020 between volunteers from the foundation and users of the platform. We compared the conversationsbefore and during the pandemic in terms of their thematic content. Our analysis found: a significantdecrease in self-image appreciation during the pandemic; a significant decrease in the quality of personalrelationships during the pandemic, and a significant increase of performance appreciation.

A model used previously to study collective back scattering from fish schools [Feuillade et al., J. Acoust. Soc. Am. 99(1), 196-208 (1996)], is used to analyze the forward scattering properties of these objects. There is an essential physical difference between back and forward scattering from fish schools. Strong frequency dependent interference effects, which affect the back scattered field amplitude, are absent in the forward scattering case. This is critically important for data analysis. There is interest in using back scattering and transmission data from fish schools to study their size, the species and abundance of fish, and fish behavior. Transmission data can be processed to determine the extinction of the field by a school. The extinction of sound depends on the forward scattering characteristics of the school, and data inversion to provide information about the fish should be based upon a forward scattering paradigm. Results are presented of an analysis of transmission data obtained in September 1995 during an experiment performed in the Gulf of Lion in the Mediterranean Sea [Diachok, J. Acoust. Soc. Am. 105(4), 2107-2128 (1999)]. The analysis shows that using forward scattering leads to significantly larger estimates of fish abundance than previous analysis based upon back scattering approaches.

Assessing the validity of measurement/model comparison in fisheries acoustics is difficult, due to the uncertainty in ground truth for acoustic measurements obtained in the open water. One way to overcome this is to utilize laboratory measurements, where fish school parameters may be more well known. The primary purpose of this work was to investigate the feasibility of measuring the acoustic properties of a small group of live fish in a laboratory tank using a steady state subtraction method [J. Acoust. Soc. Am. 112, 1366–1376 (2002)]. Transfer function measurements were obtained in a fresh water tank that contained an enclosed group of goldfish (Carassius auratus auratus), in order to describe their resonance scattering behavior. The experimental results were compared with an existing predictive model [J. Acoust. Soc. Am. 99, 196–208 (1996)], which incorporates both multiple scattering effects between fish, and coherent interaction of their individual scattered fields. Computational modeling, experimental details and data/model comparison will be presented. This technique can be extended to larger tanks and other fish species. [Work supported by ONR.]

Low frequency acoustic scattering from swim bladder fish is dominated by the monopole resonance response of the bladder. A school scattering model has previously been developed [Feuillade et al., J. Acoust. Soc. Am. 99(1), 196–208 (1996)] to predict levels of scattering from schools of bladder fish, which includes multiple scattering effects among the fish, and coherent summation of their radiated fields. In order to incorporate these acoustic interactions, the relative locations of the individual fish within the school are required as an input. To provide a realistic description of fluctuating levels of scattering from schools, a self-organizing model of group formation in three-dimensional space has been developed, based on biological principles of collective animal behavior [Couzin et al., J. Theor. Biol. 218, 1–11 (2002)]. In this model, organization within the school is a function of alignment, and repulsive and attractive tendencies based upon the position and orientation of the individual fish. The results of using this model to simulate the fish behavior demonstrate the spatial and temporal dynamics of the fish school, and indicate how these influence the statistical variability of the acoustic scattering response as a function of frequency. [Work supported by ONR.]

The collective back scattering behavior of fish schools has previously been described by a school scattering model [J. Acoust. Soc. Am., 99(1), 196-208 (1996)], which incorporates both multiple scattering effects between neighboring fish, and coherent interactions of their individual scattered fields. In the present work, the school scattering model has been extended, and used to investigate the back- and forward-scattering properties of the acoustic field, and transmission through, large schools of swim bladder fish, at frequencies close to the swim bladder resonance frequency. Results show that their frequency and spatially-varying scattering behavior depends strongly upon the number of fish in the school ensemble, the species specific swim bladder size, the average spacing between fish, and the size and shape of the school. Results will also be presented of a comparison between the school model and fish absorption data obtained during the experiment Modal Lion, performed in the Gulf of Lion in September 1995, and reported by Diachok [J. Acoust. Soc. Am., 105(4), 2107-2128 (1999)]. [Work supported by ONR.]