Combinatorial signal processing in an insect

Human language is combinatorial: phonemes are grouped into syllables, syllables are grouped into words, and so on. The capacity for combinatorial processing is present, in different degrees, in some mammals and birds. We used vibrational insects, Enchenopa treehoppers, to test the hypothesis of basic combinatorial processing against two competing hypotheses: beginning rule (where the early signal portions play a stronger role in acceptability) and no ordering rule (where the order of signal elements plays no role in signal acceptability). Enchenopa males use plant-borne vibrational signals that consist of a whine followed by pulses. We tested the above hypotheses with vibrational playback experiments in which we presented Enchenopa females with stimuli varying in signal element combinations. We monitored female responses to these playbacks with laser vibrometry. We found strong support for combinatorial processing in Enchenopa: in brief, females preferred natural-combination signals regardless of the beginning element and discriminated against reverse-order signals or individual elements. Finding support for the combinatorial rule hypothesis in insects suggests that this capability represents a common solution to the problems presented by complex communication.Publisher PDFPeer reviewe

Temperature dependence of the magnetic Casimir-Polder interaction

We analyze the magnetic dipole contribution to atom-surface dispersion forces. Unlike its electrical counterpart, it involves small transition frequencies that are comparable to thermal energy scales. A significant temperature dependence is found near surfaces with a nonzero DC conductivity, leading to a strong suppression of the dispersion force at T > 0. We use thermal response theory for the surface material and discuss both normal metals and superconductors. The asymptotes of the free energy of interaction and of the entropy are calculated analytically over a large range of distances. Near a superconductor, the onset of dissipation at the phase transition strongly changes the interaction, including a discontinuous entropy. We discuss the similarities with the Casimir interaction beween two surfaces and suggest that precision measurements of the atom-surface interaction may shed new light upon open questions around the temperature dependence of dispersion forces between lossy media.Comment: 11 figure

Lifetime of the first and second collective excitations in metallic nanoparticles

We determine the lifetime of the surface plasmon in metallic nanoparticles under various conditions, concentrating on the Landau damping, which is the dominant mechanism for intermediate-size particles. Besides the main contribution to the lifetime, which smoothly increases with the size of the particle, our semiclassical evaluation yields an additional oscillating component. For the case of noble metal particles embedded in a dielectric medium, it is crucial to consider the details of the electronic confinement; we show that in this case the lifetime is determined by the shape of the self-consistent potential near the surface. Strong enough perturbations may lead to the second collective excitation of the electronic system. We study its lifetime, which is limited by two decay channels: Landau damping and ionization. We determine the size dependence of both contributions and show that the second collective excitation remains as a well defined resonance.Comment: 18 pages, 5 figures; few minor change

Theory of Vibrationally Inelastic Electron Transport through Molecular Bridges

Vibrationally inelastic electron transport through a molecular bridge that is connected to two leads is investigated. The study is based on a generic model of vibrational excitation in resonant transmission of electrons through a molecular junction. Employing methods from electron-molecule scattering theory, the transmittance through the molecular bridge can be evaluated numerically exactly. The current through the junction is obtained approximately using a Landauer-type formula. Considering different parameter regimes, which include both the case of a molecular bridge that is weakly coupled to the leads, resulting in narrow resonance structures, and the opposite case of a broad resonance caused by strong interaction with the leads, we investigate the characteristic effects of coherent and dissipative vibrational motion on the electron transport. Furthermore, the validity of widely used approximations such as the wide-band approximation and the restriction to elastic transport mechanisms is investigated in some detail.Comment: Submited to PRB, revised version according to comments of referees (minor text changes and new citations

Passive acoustic monitoring provides a fresh perspective on fundamental ecological questions

Passive acoustic monitoring (PAM) has emerged as a transformative tool for applied ecology, conservation and biodiversity monitoring, but its potential contribution to fundamental ecology is less often discussed, and fundamental PAM studies tend to be descriptive, rather than mechanistic. Here, we chart the most promising directions for ecologists wishing to use the suite of currently available acoustic methods to address long-standing fundamental questions in ecology and explore new avenues of research. In both terrestrial and aquatic habitats, PAM provides an opportunity to ask questions across multiple spatial scales and at fine temporal resolution, and to capture phenomena or species that are difficult to observe. In combination with traditional approaches to data collection, PAM could release ecologists from myriad limitations that have, at times, precluded mechanistic understanding. We discuss several case studies to demonstrate the potential contribution of PAM to biodiversity estimation, population trend analysis, assessing climate change impacts on phenology and distribution, and understanding disturbance and recovery dynamics. We also highlight what is on the horizon for PAM, in terms of near-future technological and methodological developments that have the potential to provide advances in coming years. Overall, we illustrate how ecologists can harness the power of PAM to address fundamental ecological questions in an era of ecology no longer characterised by data limitation

Ecoacoustics and multispecies semiosis: naming, semantics, semiotic characteristics, and competencies

Biosemiotics to date has focused on the exchange of signals between organisms, in line with bioacoustics; consideration of the wider acoustic environment as a semiotic medium is under-developed. The nascent discipline of ecoacoustics, that investigates the role of environmental sound in ecological processes and dynamics, fills this gap. In this paper we introduce key ecoacoustic terminology and concepts in order to highlight the value of ecoacoustics as a discipline in which to conceptualise and study intra- and interspecies semiosis. We stress the inherently subjective nature of all sensory scapes (vivo-, land-, vibro- and soundscapes) and propose that they should always bear an organismic attribution. Key terms to describe the sources (geophony, biophony, anthropophony, technophony) and scales (sonotopes, soundtopes, sonotones) of soundscapes are described. We introduce epithets for soundscapes to point to the degree to which the global environment is implicated in semiosis (latent, sensed and interpreted soundscapes); terms for describing key ecological structures and processes (acoustic community, acoustic habitat, ecoacoustic events) and examples of ecoacoustic events (choruses and noise) are described. The acoustic eco-field is recognized as the semiotic model that enables soniferous species to intercept core resources like food, safety and roosting places. We note that whilst ecoacoustics to date has focused on the critical task of the development of metrics for application in conservation and biodiversity assessment, these can be enriched by advancing conceptual and theoretical foundations. Finally, the mutual value of integrating ecoacoustic and biosemiotics perspectives is considered

The relationship between a combinatorial processing rule and a continuous mate preference function in an insect

Mate choice involves processing signals that can reach high levels of complexity and feature multiple components, even in small animals with tiny brains. This raises the question of whether and how such organisms deal with this complexity. One solution involves combinatorial processing, whereby different signal elements are processed as single units. Combinatorial processing has been described in several mammals and birds, and recently in a vibrationally signalling insect, Enchenopa treehoppers. Here, we ask about the relationship between combinatorial rules and mate preferences for continuously varying signal features. Enchenopa male advertisement signals are composed of two elements: a ‘whine’ followed by a set of pulses. The dominant frequency of the whine and element combination both matter to females. We presented synthetic signals varying in element order (natural [whine-pulses], reverse [pulses-whine]) and in frequency to Enchenopa females and recorded their responses. The reverse combination resulted in a decrease in attractiveness of the signals, and also slightly changed the shape of the preference for frequency. We found that females could be classified into three ‘types’: females with both a strong preference and a strong combinatorial rule, females with both a weak preference and weak rule, and females with a strong preference but a weak rule. Our results suggest that in Enchenopa signal processing, the mate preference for a continuous signal feature ‘takes precedence’ over, but also interacts with, the combinatorial rule. The relationship between the preference and the rule could evolve to take different forms according to selection on mate choice decisions. We suggest that exploring the relationship between such preferences and rules in species with more complex signals will bring insight into the evolution of the multi-component communication systems

Hidden surface states on pristine and H-passivated Ni(111): Angle-resolved photoemission and density-functional calculations

By means of angle-resolved photoemission, we have uncovered surface related states on the pristine and hydrogen saturated Ni(111) surfaces. Near normal emission spectra were recorded at room temperature as a function of photon energy. A hidden Tamm surface state is found on the clean Ni(111) surface at a binding energy of ~1.19 eV, completely masked by the Lambda1 bulk d band. The existence of this surface state is in agreement with the density-functional theory calculations presented here. On the other hand, a surface state related to hydrogen adsorbed on the surface has been identified at a binding energy of ~0.22 eV. Under hydrogen exposure, it grows at the same rate as the three other surface states of the clean Ni(111) vanish