2,797 research outputs found
Mechanisms of high-frequency song generation in brachypterous crickets and the role of ghost frequencies
Sound production in crickets relies on stridulation, the well-understood rubbing together of a pair of specialised wings. As the file of one wing slides over the scraper of the other, a series of rhythmic impacts cause harmonic oscillations, usually resulting in the radiation of pure tones delivered at low frequencies (2-8 kHz). In the short winged crickets of the Lebinthini tribe, acoustic communication relies on signals with remarkably high frequencies (> 8 kHz) and rich harmonic content. Using several species of the subfamily Eneopterinae, we characterise the morphological and mechanical specialisations supporting the production of high frequencies, and demonstrate that higher harmonics are exploited as dominant frequencies. These specialisations affect the structure of the stridulatory file, the motor control of stridulation and the resonance of the sound radiator. We place these specialisations in a phylogenetic framework and show that they serve to exploit high frequency vibrational modes pre-existing in the phylogenetic ancestor. In Eneopterinae, the lower frequency components are harmonically related to the dominant peak, suggesting they are relicts of ancestral carrier frequencies. Yet, such ghost frequencies still occur in the wings' free resonances, highlighting the fundamental mechanical constraints of sound radiation. These results support the hypothesis that such high frequency songs evolved stepwise, by a form of punctuated evolution which could be related to functional constraints, rather than by the progressive increase of the ancestral fundamental frequency
Biomechanics of hearing in katydids
Animals have evolved a vast diversity of mechanisms to detect sounds. Auditory
organs are used to detect intraspecific communicative signals and environmental
sounds relevant to survival. To hear, terrestrial animals must convert the acoustic
energy contained in the airborne sound pressure waves into neural signals. In
mammals, spectral quality is assessed by the decomposition of incoming sound waves
into elementary frequency components using a sophisticated cochlear system. Some
neotropical insects like katydids (bushcrickets) have evolved biophysical mechanisms
for auditory processing that are remarkably equivalent to those of mammals. Located
on their front legs, katydid ears are small, yet are capable of performing several of the
tasks usually associated with mammalian hearing. These tasks include air-to-liquid
impedance conversion, signal amplification, and frequency analysis. Impedance
conversion is achieved by a lever system, a mechanism functionally analogous to the
mammalian middle ear ossicles, yet morphologically distinct. In katydids, the exact
mechanisms supporting frequency analysis seem diverse, yet are seen to result in
dispersive wave propagation phenomenologically similar to that of cochlear systems.
Phylogenetically unrelated, katydids and tetrapods have evolved remarkably different
structural solutions to common biophysical problems. Here, we discuss the biophysics
of hearing in katydids and the variations observed across different species
A Ghost Workers' Bill of Rights: How to Establish a Fair and Safe Gig Work Platform
Many of us assume that all the free editing and sorting of online content we ordinarily rely on is carried out by AI algorithms — not human persons. Yet in fact, that is often not the case. This is because human workers remain cheaper, quicker, and more reliable than AI for performing myriad tasks where the right answer turns on ineffable contextual criteria too subtle for algorithms to yet decode. The output of this work is then used for machine learning purposes to generate algorithms constructed from large data sets containing thousands of correctly coded observations. The fact that ghost workers are treated as consumers distorts the basic logic of the employment relationship, effectively placing the worker-as-consumer in the worst of both worlds, in which they hold the legal rights of neither group. This puts them in a regulatory limbo position in which they have little or no protection, control, or guarantee of return on investment. This is because the platforms that facilitate ghost work have orchestrated a three-way virtual relationship that absolves all parties of responsibility, while placing nearly all the risks and opportunity costs squarely on the shoulders of the workers. As a result, we believe such a work arrangement as it stands, does not uphold basic standards of Rawlsian justice as fairness
On the effects of firing memory in the dynamics of conjunctive networks
Boolean networks are one of the most studied discrete models in the context
of the study of gene expression. In order to define the dynamics associated to
a Boolean network, there are several \emph{update schemes} that range from
parallel or \emph{synchronous} to \emph{asynchronous.} However, studying each
possible dynamics defined by different update schemes might not be efficient.
In this context, considering some type of temporal delay in the dynamics of
Boolean networks emerges as an alternative approach. In this paper, we focus in
studying the effect of a particular type of delay called \emph{firing memory}
in the dynamics of Boolean networks. Particularly, we focus in symmetric
(non-directed) conjunctive networks and we show that there exist examples that
exhibit attractors of non-polynomial period. In addition, we study the
prediction problem consisting in determinate if some vertex will eventually
change its state, given an initial condition. We prove that this problem is
{\bf PSPACE}-complete
Measurement of turbulent correlations in a coaxial flow of dissimilar fluids
Axial turbulence measurements in coaxial flow of dissimilar gase
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