The Energetic Cost of Activation of White Muscle Fibres from the Dogfish Scyliophinus Canicula

Link to the publisher's site: http://jeb.biologists.org/The energetic cost of activation was measured during an isometric tetanus of white muscle fibres from the dogfish Scyliorhinus canicula. The total heat production by the fibres was taken as a measure of the total energetic cost. This energy consists of two parts. One is due to crossbridge interaction which produces isometric force, and this part varies linearly with the degree of filament overlap in the fibres. The other part of the energy is that associated with activation of the crossbridges by Ca2+, mainly with uptake of Ca2+ into the sarcoplasmic reticulum by the ATP-driven Ca2+ pump. Total heat production was measured at various degrees of filament overlap beyond the optimum for force development. Extrapolation of heat versus force production data to evaluate the heat remaining at zero force gave a value of 34±5 % (mean ± S.E.M., N=24) for activation heat as a percentage of total heat production in a 2.0 s isometric tetanus. Values for 0.4 and 1.0 s of stimulation were similar. Comparison with values in the literature shows that the energetic cost of activation in dogfish muscle is very similar to that of frog skeletal muscle and it cannot explain the lower maximum efficiency of dogfish muscle compared with frog muscle. The proportion of energy for activation (Ca2+ turnover) is similar to that expected from a simple model in which Ca2+ turnover was varied to minimize the total energy cost for a contraction plus relaxation cycle.Peer reviewe

Intimacy between men in modern women's writing

This thesis sets out to investigate, and concludes by defining, a genre of modern women's writing. This genre, which 1 have called 'intimatopia' for its depiction of fictional worlds which centre around intimacy, explores close relationships between men, I use this thesis to elucidate the ideological assumptions which underlie this genre, as well as to consider the textual features which are commonly used to support them. My investigation is facilitated by my choice to focus on the appropriative fictions which form a significant part of the intimatopic genre. The appropriative text is particularly apposite to any project which, like this one, seeks to investigate distinctive ideologies, for in a comparison between the text and its source the ideological perspectives of the writer can be glimpsed. As a result of this approach one of the central features of this thesis is a comparison between hegemonic and intimatopic ideologies, which are found to be markedly different. Central to the intimatopic text, which may be sexually explicit, sexually discreet, or sexually ambiguous, is the assumption that there exists a fluid link between love, friendship and intimacy. This ideological perspective is one which many theoreticians, in fields as diverse as literary criticism, psychology and biology, have connected to feminine, rather than masculine, ways of thinking. Although it is therefore unsurprising to find that this is a feature of a predominantly feminine genre, its application to relationships between men runs counter to ideological assumptions about masculine interaction. From examining a variety of appropriative literature 1 move on to less overtly appropriative texts in which the by now familiar intimatopic features can be identified. Following this, 1 discuss the interpretive communities which produce intimatopic texts, using the example of slash fiction, where the interpretive community is readily accessible, I begin to investigate the ideological assumptions about human interaction which underpin the interpretations typical of intimatopic writing. Finally, I consider the genre's antecedents, and mention other texts which, although they do not take male intimacy as their theme, nonetheless share intimatopic features. Thus this thesis offers an insight into an area of women's writing which has received little critical attention and which I have been able to crystallise into the genre of intimatopia. Whilst it is clearly inaccurate to describe all women's writing as intimatopic, this genre accounts for a significant number of texts by women and should be recognised alongside other feminine genres as part of the varied field of women's literature

Intimacy between men in modern women's writing

This thesis sets out to investigate, and concludes by defining, a genre of modern women's writing. This genre, which 1 have called 'intimatopia' for its depiction of fictional worlds which centre around intimacy, explores close relationships between men, I use this thesis to elucidate the ideological assumptions which underlie this genre, as well as to consider the textual features which are commonly used to support them. My investigation is facilitated by my choice to focus on the appropriative fictions which form a significant part of the intimatopic genre. The appropriative text is particularly apposite to any project which, like this one, seeks to investigate distinctive ideologies, for in a comparison between the text and its source the ideological perspectives of the writer can be glimpsed. As a result of this approach one of the central features of this thesis is a comparison between hegemonic and intimatopic ideologies, which are found to be markedly different. Central to the intimatopic text, which may be sexually explicit, sexually discreet, or sexually ambiguous, is the assumption that there exists a fluid link between love, friendship and intimacy. This ideological perspective is one which many theoreticians, in fields as diverse as literary criticism, psychology and biology, have connected to feminine, rather than masculine, ways of thinking. Although it is therefore unsurprising to find that this is a feature of a predominantly feminine genre, its application to relationships between men runs counter to ideological assumptions about masculine interaction. From examining a variety of appropriative literature 1 move on to less overtly appropriative texts in which the by now familiar intimatopic features can be identified. Following this, 1 discuss the interpretive communities which produce intimatopic texts, using the example of slash fiction, where the interpretive community is readily accessible, I begin to investigate the ideological assumptions about human interaction which underpin the interpretations typical of intimatopic writing. Finally, I consider the genre's antecedents, and mention other texts which, although they do not take male intimacy as their theme, nonetheless share intimatopic features. Thus this thesis offers an insight into an area of women's writing which has received little critical attention and which I have been able to crystallise into the genre of intimatopia. Whilst it is clearly inaccurate to describe all women's writing as intimatopic, this genre accounts for a significant number of texts by women and should be recognised alongside other feminine genres as part of the varied field of women's literature.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Transformation of dynamical fluctuation into coherent energy

Studies of noise-induced motions are showing that coherent energy can be extracted from some kinds of noise in a periodic ratchet. Recently, energetics of Langevin dynamics is formulated by Sekimoto [J.Phys.Soc.Jpn, 66 1234 (1997)], which can be applied to ratchet systems described by Fokker-Planck equation. In this paper, we derive an energetics of ratchet systems that can be applied to dynamical-noise-induced motion in a static potential. Analytical efficiency of the energy transformation is derived for the dynamical noise in an overdumping limit of the system. Comparison between analytical and numerical studies is performed for chaotic noise.Comment: 3 pages, 2 figures; submitted to Phys. Rev. Let

Exact solution of a linear molecular motor model driven by two-step fluctuations and subject to protein friction

We investigate by analytical means the stochastic equations of motion of a linear molecular motor model based on the concept of protein friction. Solving the coupled Langevin equations originally proposed by Mogilner et al. (A. Mogilner et al., Phys. Lett. {\bf 237}, 297 (1998)), and averaging over both the two-step internal conformational fluctuations and the thermal noise, we present explicit, analytical expressions for the average motion and the velocity-force relationship. Our results allow for a direct interpretation of details of this motor model which are not readily accessible from numerical solutions. In particular, we find that the model is able to predict physiologically reasonable values for the load-free motor velocity and the motor mobility.Comment: 12 pages revtex, 6 eps-figure

Energetics of Forced Thermal Ratchet

Molecular motors are known to have the high efficiency of energy transformation in the presence of thermal fluctuation. Motivated by the surprising fact, recent studies of thermal ratchet models are showing how and when work should be extracted from non-equilibrium fluctuations. One of the important finding was brought by Magnasco where he studied the temperature dependence on the fluctuation-induced current in a ratchet (multistable) system and showed that the current can generically be maximized in a finite temperature. The interesting finding has been interpreted that thermal fluctuation is not harmful for the fluctuation-induced work and even facilitates its efficiency. We show, however, this interpretation turns out to be incorrect as soon as we go into the realm of the energetics [Sekimoto,J.Phys.Soc.Jpn.66,1234-1237(1997)]: the efficiency of energy transformation is not maximized at finite temperature, even in the same system that Magnasco considered. The maximum efficiency is realized in the absence of thermal fluctuation. The result presents an open problem whether thermal fluctuation could facilitate the efficiency of energetic transformation from force-fluctuation into work.Comment: 3pages, 4sets of figure

Biomechanics of predator–prey arms race in lion, zebra, cheetah and impala

The fastest and most manoeuvrable terrestrial animals are found in savannah habitats, where predators chase and capture running prey. Hunt outcome and success rate are critical to survival, so both predator and prey should evolve to be faster and/or more manoeuvrable. Here we compare locomotor characteristics in two pursuit predator–prey pairs, lion–zebra and cheetah–impala, in their natural savannah habitat in Botswana. We show that although cheetahs and impalas were universally more athletic than lions and zebras in terms of speed, acceleration and turning, within each predator–prey pair, the predators had 20% higher muscle fibre power than prey, 37% greater acceleration and 72% greater deceleration capacity than their prey. We simulated hunt dynamics with these data and showed that hunts at lower speeds enable prey to use their maximum manoeuvring capacity and favour prey survival, and that the predator needs to be more athletic than its prey to sustain a viable success rate