scholarly journals Changes in geometrical aspects of a simple model of cilia synchronization control the dynamical state, a possible mechanism for switching of swimming gaits in microswimmers

PLoS ONE ◽  
2021 ◽  
Vol 16 (4) ◽  
pp. e0249060
Author(s):  
Evelyn Hamilton ◽  
Pietro Cicuta

Active oscillators, with purely hydrodynamic coupling, are useful simple models to understand various aspects of motile cilia synchronization. Motile cilia are used by microorganisms to swim and to control the flow fields in their surroundings; the patterns observed in cilia carpets can be remarkably complex, and can be changed over time by the organism. It is often not known to what extent the coupling between cilia is due to just hydrodynamic forces, and neither is it known if it is biological or physical triggers that can change the dynamical collective state. Here we treat this question from a very simplified point of view. We describe three possible mechanisms that enable a switch in the dynamical state, in a simple scenario of a chain of oscillators. We find that shape-change provides the most consistent strategy to control collective dynamics, but also imposing small changes in frequency produces some unique stable states. Demonstrating these effects in the abstract minimal model proves that these could be possible explanations for gait switching seen in ciliated micro organisms like Paramecium and others. Microorganisms with many cilia could in principle be taking advantage of hydrodynamic coupling, to switch their swimming gait through either a shape change that manifests in decreased coupling between groups of cilia, or alterations to the beat style of a small subset of the cilia.

2002 ◽  
Vol 16 (3) ◽  
pp. 129-149 ◽  
Author(s):  
Boris Kotchoubey

Abstract Most cognitive psychophysiological studies assume (1) that there is a chain of (partially overlapping) cognitive processes (processing stages, mechanisms, operators) leading from stimulus to response, and (2) that components of event-related brain potentials (ERPs) may be regarded as manifestations of these processing stages. What is usually discussed is which particular processing mechanisms are related to some particular component, but not whether such a relationship exists at all. Alternatively, from the point of view of noncognitive (e. g., “naturalistic”) theories of perception ERP components might be conceived of as correlates of extraction of the information from the experimental environment. In a series of experiments, the author attempted to separate these two accounts, i. e., internal variables like mental operations or cognitive parameters versus external variables like information content of stimulation. Whenever this separation could be performed, the latter factor proved to significantly affect ERP amplitudes, whereas the former did not. These data indicate that ERPs cannot be unequivocally linked to processing mechanisms postulated by cognitive models of perception. Therefore, they cannot be regarded as support for these models.


1991 ◽  
Vol 279 (3) ◽  
pp. 855-861 ◽  
Author(s):  
S E Szedlacsek ◽  
R G Duggleby ◽  
M O Vlad

A new type of enzyme kinetic mechanism is suggested by which catalysis may be viewed as a chain reaction. A simple type of one-substrate/one-product reaction mechanism has been analysed from this point of view, and the kinetics, in both the transient and the steady-state phases, has been reconsidered. This analysis, as well as literature data and theoretical considerations, shows that the proposed model is a generalization of the classical ones. As a consequence of the suggested mechanism, the expressions, and in some cases even the significance of classical constants (Km and Vmax.), are altered. Moreover, this mechanism suggests that, between two successive enzyme-binding steps, more than one catalytic act could be accomplished. The reaction catalysed by alcohol dehydrogenase was analysed, and it was shown that this chain-reaction mechanism has a real contribution to the catalytic process, which could become exclusive under particular conditions. Similarly, the mechanism of glycogen phosphorylase is considered, and two partly modified versions of the classical mechanism are proposed. They account for both the existing experimental facts and suggest the possibility of chain-reaction pathways for any polymerase.


2020 ◽  
pp. 1-32
Author(s):  
ALEXEI KOCHETOV ◽  
LAURA COLANTONI ◽  
JEFFREY STEELE

The phonetic realization of the English word-final alveolar nasal /n/ is known to be highly variable. Previous articulatory work has reported both gradient and categorical nasal place assimilation including considerable between-speaker differences. This work, however, has largely focused on a small subset of place contexts (namely, preceding velar /k, ɡ/) in a limited number of English varieties. The present article uses electropalatography to study the articulatory realization of /n/ in a wider range of phonetic contexts and read texts as produced by three speakers of Canadian English. The results reveal considerable inter- and intra-speaker differences in the rates of assimilation. Consistent with previous work, we observed a high degree of variation, both gradient and categorical, before velars. Substantial rates of assimilation were also observed before labials, where the process is unexpected from the point of view of gestural phonology but predicted by traditional phonological analyses. The variation in the place and stricture of /n/ before coronals was more limited and typically gradient. Finally, some differences were observed across the text conditions, with more assimilation occurring in carrier sentences than in the read passage and, to a more limited extent, in function than in content words.


1988 ◽  
Vol 16 (1) ◽  
pp. 11-17
Author(s):  
Michael E. Patch

A variety of social contingencies have been described in terms of the patterning of self and/or social causality along a chain of responses between two persons. Non-reciprocal (pseudo and asymmetrical) contingencies focus the researcher on the comparative implications of self and socially caused behavior as a matter of causal preference and relationship style. Two laboratory studies were conducted with this point of view in mind. In the first study it was shown that subjects who had indicated a preference for socially caused behavior were more likely to choose spontaneous interactions with strangers while those who preferred self causality were more likely to choose scripted or nonspontaneous interactions. In the second study it was found that subjects who preferred social causality were more accurate in assessing their own influence over in the behavior of others in a self disclosure task than were those who preferred self causality. The findings were discussed in terms of both the need for a causal preference assessment technique as well as further research into the phenomena of “pseudo relationships.“


2016 ◽  
Vol 27 (8) ◽  
pp. 1204-1209 ◽  
Author(s):  
Ramila S. Patel-King ◽  
Stephen M. King

WDR92 is a highly conserved WD-repeat protein that has been proposed to be involved in apoptosis and also to be part of a prefoldin-like cochaperone complex. We found that WDR92 has a phylogenetic signature that is generally compatible with it playing a role in the assembly or function of specifically motile cilia. To test this hypothesis, we performed an RNAi-based knockdown of WDR92 gene expression in the planarian Schmidtea mediterranea and were able to achieve a robust reduction in mRNA expression to levels undetectable under our standard RT-PCR conditions. We found that this treatment resulted in a dramatic reduction in the rate of organismal movement that was caused by a switch in the mode of locomotion from smooth, cilia-driven gliding to muscle-based, peristaltic contractions. Although the knockdown animals still assembled cilia of normal length and in similar numbers to controls, these structures had reduced beat frequency and did not maintain hydrodynamic coupling. By transmission electron microscopy we observed that many cilia had pleiomorphic defects in their architecture, including partial loss of dynein arms, incomplete closure of the B-tubule, and occlusion or replacement of the central pair complex by accumulated electron-dense material. These observations suggest that WDR92 is part of a previously unrecognized cytoplasmic chaperone system that is specifically required to fold key components necessary to build motile ciliary axonemes.


2018 ◽  
Vol XIX (1) ◽  
pp. 50-57

From the point of view of reliability theory, a system can have two stable states: functioning and defect (bivalent system). Any system is a set of elements. Each element in this set can be found in one of the following states: operating state and fault condition. A subset of elements in the running state is called a system link if they only ensure the system works. The length of a bivalent system is equal to the minimum number of elements that the system holds. In this paper we present an algorithm for automatic determination of dual system length to a bivalent system, a Matlab script, a case study and subsequent development directions.


2018 ◽  
Vol 24 (3) ◽  
pp. 83-88
Author(s):  
Paul Vasiliu

Abstract From the point of view of reliability theory, a system can have two stable states: functioning and defect (bivalent system). Any system is a set of elements. Each element in this set can be found in one of the following states: operating state and fault condition. A subset of elements in the running state is called a system link if they only ensure the system works. The length of a bivalent system is equal to the minimum number of elements that the system holds. In this paper we present an algorithm for the automatic determination of the length of a bivalent system, a Matlab script, a case study and subsequent development directions


Comunicar ◽  
2005 ◽  
Vol 13 (25) ◽  
Author(s):  
Lorena López-Font ◽  
Cristina González-Oñate

The Spanish televising scene is, at the present time, the center of a social and cultural discussion.Before the critic carried out towards as daily means as it is it the television, are many, (including the hearing), those that demand a reform that structures all the televising scene with the purpose of constructing an educative television and of quality. But, what it is happening from the point of view of the own television networks before the critical panorama which they face?. Which is its reaction, its strategies and their techniques to create a positive image of the own means and, most important, to transmit it to the spectator and to seduce to him?. The television networks have chosen to reframe their identity to reform the image that grant to the hearing. They have begun to be unmarked, to create a differentiating positioning before a hearing that every day is more demanding due to the supply that the technology offers to him. One of the most effective instruments fortify a position, to consolidate a position of the television companies before a heterogenous and more and more complex hearing, is the development of the televising continuity, with peculiar discursivas forms like cardboards of continuity, self-promotions, heads of programs, syntonies, bursts, etc., that contribute to fix the image of mark of the different companies, before the eyes of the spectator. This communication will be placed in the plane of the televisions like organizations to reflect from the side of televising means before the emergent problems, and to analyze the methods that are carrying out the different chains to create that positioning that differentiates from the others, centering to us in the autopromociones like the used advertising tool more, nowadays, by the television networks. The transmitted values, the corporative image and communicative identity and, really, all those aspects that in the autopromociones are expressed, will be analyzed to be able to understand the reactions caused by the chains of the Spanish televising panorama. In sum: 20 seconds of publicity of self-promotion so that a chain can transmit a new image, full of positive values for a society that, nowadays, questions own televising means, that is to say, to analyze how the televising means make use of its own channel to trasmitir and to create value of mark. El panorama televisivo español se encuentra, desde su pasado reciente hasta la actualidad, en el centro de un debate social y cultural. La audiencia, reclama ya, una reforma de contenidos que construya una televisión con mayor diversidad y equilibrio de contenidos. Esa audiencia alza la voz ante la evidente necesidad de recibir una televisión de mayor calidad. Pero, ¿qué está ocurriendo desde el punto de vista de las propias cadenas de televisión ante el panorama crítico al que se enfrentan? ¿Cuál es su reacción, sus estrategias y sus técnicas para crear una imagen positiva del propio medio? y, lo más importante para esta comunicación, ¿cómo están transmitiéndola al espectador para seducirle? Las cadenas de televisión han optado por replantearse su identidad con el objetivo de reformar la imagen que otorgan a la audiencia. Han comenzado a desmarcarse, a crear un posicionamiento diferenciador ante segmentos de audiencias que cada día son más exigentes debido a la saturación de la oferta. Uno de los instrumentos más efectivos para consolidar la posición de las empresas de televisión ante una audiencia cada vez más heterogénea y compleja, es el desarrollo de la continuidad televisiva, con formas discursivas peculiares como los cartones de continuidad, autopromociones, cabeceras de programas, sintonías, ráfagas, etc., que contribuyen a fijar la imagen de marca de las distintas empresas audiovisuales, ante los ojos del espectador. Esta comunicación se colocará en el plano de las televisiones como entidades para reflexionar desde el lado del medio televisivo ante los problemas emergentes, y analizar los métodos que están llevando a cabo las diferentes cadenas para crear ese posicionamiento que diferencie las unas de las otras, centrándonos en las autopromociones como la herramienta publicitaria más usada, hoy en día, por las cadenas de televisión. Los valores transmitidos, la imagen e identidad corporativas y, en definitiva, todos aquellos aspectos comunicativos que en las autopromociones se expresan, serán analizados para poder entender las reacciones provocadas por las cadenas del panorama televisivo español. En suma: 20 segundos de publicidad de autopromoción para que una cadena pueda transmitir una imagen nueva, llena de valores positivos para una sociedad que, hoy en día, cuestiona el propio medio. Concretamente y con esta investigación, se analizarán las últimas telepromociones de TVE-1, es decir, cómo esta cadena trasmite y crea valor de marca.


2012 ◽  
Vol 40 (3/4) ◽  
pp. 385-404
Author(s):  
Katalin Kroó

The paper raises the theoretical question of the cultural mediational nature of literary intertexts from the point of view of generic and transformational dynamics. The intertextual complex as mediational operator is examined at two levels – (1) in the context of cultural diachrony by observing how the literary work establishes its place in the history of literature closely connected to the metapoiesis of the text; (2) at various kinds of intratextual interlevel movements regulating the evolution of a whole intertextual system within the work. Differentiating the ontological, generative and transformational conceptualization of intertextual poetics, an attempt is made to define the basic textual modes of the pretext, the intext and the intertext by describing their functionality in the building of an intersemiotic literary system. The relevant functions are grasped by shedding light upon the types of the sign of which the given signifying structures consist (here a terminological clarification and re-evaluation are added) and their textual semantics in terms of referential and relational quality (cf. the different versions of referential and relational semantics). In the first place, however, the paper aims at outlining the structure and content of the generic-transformational semiotic processes in which the dynamic aspects of intertextual semiosis are revealed. Within this framework, the processuality of the development of the intertextual signifying structure is elucidated, shown as a chain of reciprocal sign activities resulting in constantly evolving semantic shifts within the intra- and intertextual semiosis processes, all relying on mediational operations. Text examples are taken from and references made to works by A. S. Pushkin, I. S. Turgenev, F. M. Dostoevsky and J. M. Coetzee.


2015 ◽  
Vol 77 (21) ◽  
Author(s):  
Mohammad Hazrin Ismail ◽  
Shamsul Anuar Shamsudin ◽  
Mohd Nizam Sudin

Airframe noise reduction becomes a main interest among researchers who study the performance of aircrafts. The airframe noise can occur between the high-lift systems and main body of the airfoil. The proposed shape-changing airfoil is one of many ideas to reduce airframe noise by eliminating the gap between the main body and high-lift systems. This paper presents a new design of 30P30N airfoil, which converts the three-element airfoil (slat, main body and flap) into two-element airfoil (combination of slat and main body as an element and flap) by installing a shape-changing slat into the systems. This work applies a chain of rigid bodies connected by revolute and prismatic joints that are capable of approximating a shape change defined by a set of morphed slat design profiles. To achieve a single degree of freedom (DOF), a building-block approach is employed to mechanize the fixed-end shape-changing chain with the helped of Geometric Constraint Programming technique as an effective method to develop the mechanism. The conventional and shape-change 30P30N airfoils are compared to study the performances of airfoils with the velocity and angle of attack are constant.


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