Complex frequencies in elastodynamics, with application to the Damping-Solvent Extraction method

This paper addresses the use of complex frequencies in problems of wave propagation and structural vibrations. The most common form of application is as artificial damping that is extracted after the response in the time domain has been obtained. Then again a rather unorthodox application is in the simulation of systems of infinite spatial extent by means of finite systems modeled with discrete methods such as finite elements, a task that can be accomplished even when no transmitting or absorbing boundaries are used. This latter application of complex frequencies, which goes by the name damping-solvent extraction method or its acronym DSE, is assessed herein by means of exact solutions to canonical problems that are used to establish the conditions that must be met by the finite models to work as intended, especially the size of the models, the magnitude of the imaginary component of frequency, and the limitations of the method

Number and location of zero-group-velocity modes

The frequency-wavenumber spectra of laminated media often exhibit anomalous modes with descending branches whose group velocity is negative, and these terminate at a minimum point at which the group velocity transitions from negative to positive. These minima are associated with resonant conditions in the medium, which have been clearly observed in experiments and in the nondestructive testing of laminated plates. Starting from first principles, this paper provides a theoretical analysis on the number and location of such zero-group-velocity (ZGV) modes for horizontally layered media bounded by any arbitrary combination of external boundaries. It is found that these ZGV points are few in number and show up mostly in low-order modes which are characterized by a negative second derivative at the cutoff frequencies, a condition that can readily be tested. It is also shown that the effective number of ZGVs is small even when the ratio of the dilatational and shear wave velocity is a rational number and there exist coincidences in cutoff frequencies, a condition that at first would suggest that the number of ZGVs is infinite. Finally, it is shown that the number of ZGVs decreases with the Poisson’s ratio

Are Groups more Rational than Individuals? A Review of Interactive Decision Making in Groups

Many decisions are interactive; the outcome of one party depends not only on its decisions or on acts of nature but also on the decisions of others. In the present article, we review the literature on decision making made by groups of the past 25 years. Researchers have compared the strategic behavior of groups and individuals in many games: prisoner’s dilemma, dictator, ultimatum, trust, centipede and principal-agent games, among others. Our review suggests that results are quite consistent in revealing that groups behave closer to the game-theoretical assumption of rationality and selfishness than individuals. We conclude by discussing future research avenues in this area.group decision making, interactive decision making, rationality, discontinuity effect

Dynamic Characteristics of Comares Palace in the Alhambra

This paper describes the geotechnical investigations that have been conducted to characterize the static and dynamic properties of the ground, the foundation and the structure\u27s material of the Comares tower in the Alhambra palace. The Gmax values of the different materials were determined using seismic refraction, P-wave transmission tomography, cross-hole and down-hole tests. To obtain the variation of the shear moduli with strain amplitude surface wave and cyclic horizontal plate loading tests were performed in several trenches excavated in the immediate neighborhood. The analysis of the structure response to M = 5 earthquakes recently recorded at the top and the bottom of the Tower allowed to check the dynamic properties of the materials estimated previously

Does overconfidence pay off when things go well?: CEO overconfidence, firm performance, and the business cycle

We investigate the moderating effect of the business cycle on the positive relationship between CEO overconfidence and firm performance. We propose that the expansion years of the business cycle enhance the positive impact of overconfident CEOs on firms’ performance. However, this effect is reduced during recession periods. We analyze the effect of CEO overconfidence on the Return on Equity of publicly listed US firms from 1992 to 2015, a period that includes the bursting of the dot-com bubble in 2001 and the Great Recession of 2008–2009. The empirical findings support the hypotheses that expansion periods increase the positive relationship between overconfident CEOs and firms’ performance, but this positive effect weakens during recessions.Fil: Reyes, Tomas. Pontificia Universidad Católica de Chile; ChileFil: Vassolo, Roberto Santiago. Universidad Austral. Instituto de Altos Estudios; Argentina. Pontificia Universidad Católica de Chile; Chile. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Kausel, Edgar E.. Pontificia Universidad Católica de Chile; ChileFil: Peña Torres, Diamela. Pontificia Universidad Católica de Chile; ChileFil: Zhang, Stephen. University of Adelaide; Australi