Do Forward- and Backward-Traveling Waves Occur Within the Cochlea? Countering the Critique of Nobili et al.

The question of whether or not forward- and backward-traveling waves occur within the cochlea constitutes a long-standing controversy in cochlear mechanics recently brought to the fore by the problem of understanding otoacoustic emissions. Nobili and colleagues articulate the opposition to the traveling-wave viewpoint by arguing that wave-equation formulations of cochlear mechanics fundamentally misrepresent the hydrodynamics of the cochlea [e.g., Nobili et al. (2003) J. Assoc. Res. Otolaryngol. 4:478–494]. To correct the perceived deficiencies of the wave-equation formulation, Nobili et al. advocate an apparently altogether different approach to cochlear modeling—the so-called “hydrodynamic” or “Green’s function” approach—in which cochlear responses are represented not as forward- and backward-traveling waves but as weighted sums of the motions of individual basilar membrane oscillators, each interacting with the others via forces communicated instantaneously through the cochlear fluids. In this article, we examine Nobili and colleagues’ arguments and conclusions while attempting to clarify the broader issues at stake. We demonstrate that the one-dimensional wave-equation formulation of cochlear hydrodynamics does not misrepresent long-range fluid coupling in the cochlea, as claimed. Indeed, we show that the long-range component of Nobili et al.’s three-dimensional force propagator is identical to the hydrodynamic Green’s function representing a one-dimensional tapered transmission line. Furthermore, simulations that Nobili et al. use to discredit wave-equation formulations of cochlear mechanics (i.e., cochlear responses to excitation at a point along the basilar membrane) are readily reproduced and interpreted using a simple superposition of forward- and backward-traveling waves. Nobili and coworkers’ critique of wave-equation formulations of cochlear mechanics thus appears to be without compelling foundation. Although the traveling-wave and hydrodynamic formulations impose strikingly disparate conceptual and computational frameworks, the two approaches ultimately describe the same underlying physics

The long-term (1979-2005) effects of the North Atlantic Oscillation on wind-induced wave mixing in Loch Leven (Scotland)

We report on long-term covariation (1979-2005) between indices of the North Atlantic Oscillation (NAO) and wind speed and direction in Loch Leven. The effects of the observed variations in wind speed and direction were combined to produce modelled wave mixed depths (Zc). Positive correlations were observed between seasonal and annual wind speeds, and westerly frequency, and indices of the NAO that are in line with general perception: positive NAO was correlated with stronger, more westerly winds and these effects were strongest in winter and spring. Correlations between NAO and estimates of Zc were strongest in the most westerly exposed site in spring (r2 = 0.701; Zcspring versus spring NAO index). On average, over a 25-year period Zc was deeper in spring and shallower in summer. Major anomalies from the 25-year seasonal means were observed in 1982, 1979, and 1991. Annual average Zc was low in the late 1970s and early 1980s (shallowest average annual Zc of 1.0 m (1984)), high in the late 1980s and early 1990s (deepest average annual Zc of 1.9 m (1990)) and moderate in recent years (up to 2005). This work has major implications for our understanding of potential climate change drivers and the related responses of shallow lake ecosystems, including alterations to littoral habitat quality and benthic-pelagic coupling

Averting Child Maltreatment: Individual, Economic, Social, and Community Resources that Promote Resilient Parenting

This study explores the influence of promotive factors in achieving resilience to child abuse and neglect among 524 at-risk mothers, an indicator that has substantial implications for the child\u27s development and long-term outcomes. We include in our analyses measures of each ofthe potential qualities or resources discussed in the literature: characteristics of the child, maternal characteristics, socioeconomic resources, social resources and supportive networks, and perceived neighborhood safety. The analyses suggest the importance of a diverse array of factors in the sustained and successful avoidance of child abuse and neglect among a sample of women at risk to maltreat. The explanatory power of promotive factors individually and collectively indicates that resilience does not simply represent the other end of a risk continuum but reflects the presence of considerable and accessible resources that compensate for a range of adversities. These resources include characteristics and activities of the mother, socioeconomic resources, and social resources available in the community in which she and her child live