We investigate the effects of bottom roughness on bottom boundary-layer (BBL) instability beneath internal solitary waves (ISWs) of depression. Applying both two-dimensional (2-D) numerical simulations and linear stability theory, an extensive parametric study explores the effect of the Reynolds number, pressure gradient, roughness (periodic bump) height $h_b$ and roughness wavelength $\lambda _b$ on BBL instability. The simulations show that small $h_b$, comparable to that of laboratory-flume materials ($\sim$100 times less than the thickness of the viscous sublayer $\delta _v$), can destabilize the BBL and trigger vortex shedding at critical Reynolds numbers much lower than what occurs for numerically smooth surfaces. We identify two mechanisms of vortex shedding, depending on $h_b/\delta _v$. For $h_b/\delta _v \gtrapprox 1$, vortices are forced directly by local flow separation in the lee of each bump. Conversely, for $h_b/\delta _v \lessapprox 10^{-1}$ the roughness seeds perturbations in the BBL, which are amplified by the BBL flow. Roughness wavelengths close to those associated with the most unstable BBL mode, as predicted by linear instability theory, are preferentially amplified. This resonant amplification nature of the BBL flow, beneath ISWs, is consistent with what occurs in a BBL driven by surface solitary waves and by periodic monochromatic waves. Using the $N$-factor method for Tollmien–Schlichting waves, we propose an analogy between the roughness height and seed noise required to trigger instability. Including surface roughness, or more generally an appropriate level of seed noise, reconciles the discrepancies between the vortex-shedding threshold observed in the laboratory versus that predicted by otherwise smooth-bottomed 2-D spectral simulations.

We investigated the stability of the bottom boundary layer (BBL) beneath periodic internal solitary waves (ISWs) of depression over a flat bottom through two-dimensional direct numerical simulations. We explored the convective versus absolute/global nature of the BBL instability in response to changes in Reynolds number, and the sensitivity of the instability to seeding noise in the front of the ISW – spanning laboratory to geophysical scales. The BBL was laminar at $Re_{ISW}=90$ and convectively unstable at $Re_{ISW}=300$. At laboratory-scale $Re_{ISW}=300$, the convective wave packet was periodically amplified by each successive ISW, until vortex shedding occurred. The associated noise-amplification behaviour potentially explains the discrepancies of the critical $Re_{ISW}$ between the lock–release laboratory experiments and our Dubreil–Jacotin–Long-initialized numerical simulations as the result of the difference in background noise. Instability energy decreased under the front shoulder of the ISW, analogous to flow relaminarization under a favourable pressure gradient. At geophysical-scale $Re_{ISW}=900$, the BBL was initially convectively unstable, and then the instability tracked with the ISW, appearing phenomenologically similar to a global instability. The simulated initial convective instability at both $Re_{ISW}=300$ and $Re_{ISW}=900$ is in agreement with local linear stability analysis which predicts that the instability group speed is always lower than the ISW celerity. Increased free stream perturbations in front of the ISW and larger $Re_{ISW}$ shift the location of vortex shedding (and enhanced bed shear stress) beneath the wave, closer to the ISW trough, thereby potentially changing the location of maximum sediment resuspension, in agreement with field observations at higher $Re_{ISW}$.

In this article we examine the intertwined relationship between taste and mining culture in early modern Spanish worlds, highlighting descriptions of metals and minerals through which taste appears as an epistemic marker with symbolic dimensions. Drawing on different documents regarding mining practices, mineral vocabulary and metal appreciation in Spain, New Spain, Peru and the New Kingdom of Granada (c.1550–1640), our article contends that knowing minerals through taste in the Spanish worlds was part of a practice engaged with the senses, the body politic and its cosmological order.

Los primeros grupos humanos habrían ingresado al actual territorio de Colombia hacia ~15.000 cal aP durante el Pleistoceno final. Posteriormente, entre finales del Pleistoceno y el Holoceno temprano, el registro arqueológico indica su expansión por gran parte de la diversa geografía colombiana. Sin embargo, el noroccidente de Colombia carecía de datos relativos a este último proceso. Esta es una región clave para entender procesos de poblamiento y movimientos humanos tempranos entre el Istmo de Panamá, incluyendo las tierras bajas del Darién y la cuenca del Río Atrato hacia las tierras altas de la Cordillera Occidental (Andes colombianos). En este artículo presentamos los resultados de excavaciones efectuadas en el sitio Tabladito, localizado en la cuenca alta del Río Sucio en la Cordillera Occidental, el único sitio hasta ahora datado para comienzos del Holoceno temprano en el noroccidente colombiano. Se presentan los resultados obtenidos (fechas de radiocarbono, proceso de formación de sitio, tecnología lítica y datos arqueobotánicos) con el objetivo de integrarlos al contexto supraregional sobre establecimiento de poblaciones tempranas y el origen del cultivo de plantas en los Andes colombianos.

Word order is one of the earliest aspects of grammar that the child acquires, because her early utterances already respect the basic word order of the target language. However, the question of the nature of early syntactic representations is subject to debate. Approaches inspired by formal syntax assume that the head–complement order, differentiating verb–object and object–verb languages, is represented very early on in an abstract, rulelike format. In contrast, constructivist theories assume that it is initially encoded as lexicalized, verb-specific knowledge. In order to address this issue experimentally, we combined the preferential looking paradigm using pseudoverbs with the weird word order paradigm adapted to comprehension. The results, based on highly reliable, coder-independent eye-tracking measures, provide the first direct evidence that as early as 19 months French-speaking infants have an abstract representation of the word order of their language.