Bianchi type IX asymptotical behaviours with a massive scalar field: chaos strikes back

We use numerical integrations to study the asymptotical behaviour of a homogeneous but anisotropic Bianchi type IX model in General Relativity with a massive scalar field. As it is well known, for a Brans-Dicke theory, the asymptotical behaviour of the metric functions is ruled only by the Brans-Dicke coupling constant with respect to the value -3/2. In this paper we examine if such a condition still exists with a massive scalar field. We also show that, contrary to what occurs for a massless scalar field, the singularity oscillatory approach may exist in presence of a massive scalar field having a positive energy density.Comment: 31 pages, 7 figures (low resolution

An accurate formula for the period of a simple pendulum oscillating beyond the small-angle regime

A simple approximation formula is derived here for the dependence of the period of a simple pendulum on amplitude that only requires a pocket calculator and furnishes an error of less than 0.25% with respect to the exact period. It is shown that this formula describes the increase of the pendulum period with amplitude better than other simple formulas found in literature. A good agreement with experimental data for a low air-resistance pendulum is also verified and it suggests, together with the current availability/precision of timers and detectors, that the proposed formula is useful for extending the pendulum experiment beyond the usual small-angle oscillations.Comment: 15 pages and 4 figures. to appear in American Journal of Physic

Isotropisation of flat homogeneous Bianchi type I model with a non minimally coupled and massive scalar field

In previous works, we studied the isotropisation of Bianchi class A models with a minimally coupled scalar field. In this paper, we extend these results to the case of a non minimally coupled one. We first make the calculations in the Einstein frame where the scalar field is minimally coupled to the curvature but non minimally coupled to the perfect fluid. Then, we use a conformal transformation to generalise our results to a scalar field non minimally coupled to the curvature. Universe isotropisation for the Brans-Dicke and low energy string theories are studied.Comment: 32 pages, 9 figures (low resolution

Evaluation and management implications of uncertainty in a multispecies size-structured model of population and community responses to fishing

1. Implementation of an ecosystem approach to fisheries requires advice on trade-offs among fished species and between fisheries yields and biodiversity or food web properties. However, the lack of explicit representation, analysis and consideration of uncertainty in most multispecies models has limited their application in analyses that could support management advice. 2. We assessed the consequences of parameter uncertainty by developing 78 125 multispecies size-structured fish community models, with all combinations of parameters drawn from ranges that spanned parameter values estimated from data and literature. This unfiltered ensemble was reduced to 188 plausible models, the filtered ensemble (FE), by screening outputs against fish abundance data and ecological principles such as requiring species' persistence. 3. Effects of parameter uncertainty on estimates of single-species management reference points for fishing mortality (FMSY, fishing mortality rate providing MSY, the maximum sustainable yield) and biomass (BMSY, biomass at MSY) were evaluated by calculating probability distributions of estimated reference points with the FE. There was a 50% probability that multispecies FMSY could be estimated to within ±25% of its actual value, and a 50% probability that BMSY could be estimated to within ±40% of its actual value. 4. Signal-to-noise ratio was assessed for four community indicators when mortality rates were reduced from current rates to FMSY. The slope of the community size spectrum showed the greatest signal-to-noise ratio, indicating that it would be the most responsive indicator to the change in fishing mortality F. Further, the power of an ongoing international monitoring survey to detect predicted responses of size spectrum slope was higher than for other size-based metrics. 5. Synthesis and applications: Application of the ensemble model approach allows explicit representation of parameter uncertainty and supports advice and management by (i) providing uncertainty intervals for management reference points, (ii) estimating working values of reference points that achieve a defined reduction in risk of not breaching the true reference point, (iii) estimating the responsiveness of population, community, food web and biodiversity indicators to changes in F, (iv) assessing the performance of indicators and monitoring programmes and (v) identifying priorities for data collection and changes to model structure to reduce uncertainty

Dynamical study of the empty Bianchi type I model in generalised scalar-tensor theory

A dynamical study of the generalised scalar-tensor theory in the empty Bianchi type I model is made. We use a method from which we derive the sign of the first and second derivatives of the metric functions and examine three different theories that can all tend towards relativistic behaviours at late time. We determine conditions so that the dynamic be in expansion and decelerated at late time.Comment: 18 pages, 3 figures, to appear in General Relativity and Gravitatio

Dynamical study of the hyperextended scalar-tensor theory in the empty Bianchi type I model

The dynamics of the hyperextended scalar-tensor theory in the empty Bianchi type I model is investigated. We describe a method giving the sign of the first and second derivatives of the metric functions whatever the coupling function. Hence, we can predict if a theory gives birth to expanding, contracting, bouncing or inflationary cosmology. The dynamics of a string inspired theory without antisymetric field strength is analysed. Some exact solutions are found.Comment: 18 pages, 3 figure

Simultaneous measurement of Ca2+ release and influx into smooth muscle cells in response to caffeine. A novel approach for calculating the fraction of current carried by calcium

Activation of ryanodine receptors on the sarcoplasmic reticulum of single smooth muscle cells from the stomach muscularis of Bufo marinus by caffeine is accompanied by a rise in cytoplasmic [Ca2+] ([Ca2+]i), and the opening of nonselective cationic plasma membrane channels. To understand how each of these pathways contributes to the rise in [Ca2+]i, one needs to separately monitor Ca2+ entry through them. Such information was obtained from simultaneous measurements of ionic currents and [Ca2+]i by the development of a novel and general method to assess the fraction of current induced by an agonist that is carried by Ca2+. Application of this method to the currents induced in these smooth muscle cells by caffeine revealed that approximately 20% of the current passing through the membrane channels activated following caffeine application is carried by Ca2+. Based on this information we found that while Ca2+ entry through these channels rises slowly, release of Ca2+ from stores, while starting at the same time, is much faster and briefer. Detailed quantitative analysis of the Ca2+ release from stores suggests that it most likely decays due to depletion of Ca2+ in those stores. When caffeine was applied twice to a cell with only a brief (30 s) interval in between, the amount of Ca2+ released from stores was markedly diminished following the second caffeine application whereas the current carried in part by Ca2+ entry across the plasma membrane was not significantly affected. These and other studies described in the preceding paper indicate that activation of the nonselective cation plasma membrane channels in response to caffeine was not caused as a consequence of emptying of internal Ca2+ stores. Rather, it is proposed that caffeine activates these membrane channels either by direct interaction or alternatively by a linkage between ryanodine receptors on the sarcoplasmic reticulum and the nonselective cation channels on the surface membrane

Caffeine activates a Ca(2+)-permeable, nonselective cation channel in smooth muscle cells

The effects of caffeine on cytoplasmic [Ca2+] ([Ca2+]i) and plasma membrane currents were studied in single gastric smooth muscle cells dissociated from the toad, Bufo marinus. Experiments were carried out using Fura-2 for measuring [Ca2+]i and tight-seal voltage-clamp techniques for recording membrane currents. When the membrane potential was held at -80 mV, in 15% of the cells studied caffeine increased [Ca2+]i without having any effect on membrane currents. In these cells ryanodine completely abolished any caffeine induced increase in [Ca2+]i. In the other cells caffeine caused both an increase in [Ca2+]i and activation of an 80-pS nonselective cation channel. In this group of cells ryanodine only partially blocked the increase in [Ca2+]i induced by caffeine; moreover, the change in [Ca2+]i that did occur was tightly coupled to the time course and magnitude of the cation current through these channels. In the presence of ryanodine, blockade of the 80-pS channel by GdCl3 or decreasing the driving force for Ca2+ influx through the plasma membrane by holding the membrane potential at +60 mV almost completely blocked the increase in [Ca2+]i induced by caffeine. Thus, the channel activated by caffeine appears to be permeable to Ca2+. Caffeine activated the cation channel even when [Ca2+]i was clamped to below 10 nM when the patch pipette contained 10 mM BAPTA suggesting that caffeine directly activates the channel and that it is not being activated by the increase in Ca2+ that occurs when caffeine is applied to the cell. Corroborating this suggestion were additional results showing that when the membrane was depolarized to activate voltage-gated Ca2+ channels or when Ca2+ was released from carbachol-sensitive internal Ca2+ stores, the 80-pS channel was not activated. Moreover, caffeine was able to activate the channel in the presence of ryanodine at both positive and negative potentials, both conditions preventing release of Ca2+ from stores and the former preventing its influx. In summary, in gastric smooth muscle cells caffeine transiently releases Ca2+ from a ryanodine-sensitive internal store and also increases Ca2+ influx through the plasma membrane by activating an 80-pS cation channel by a mechanism which does not seem to involve an elevation of [Ca2+]i

Memory, learning and language in autism spectrum disorder

Background and aims: The ‘dual-systems’ model of language acquisition has been used by Ullman and colleagues to explain patterns of strength and weakness in the language of higher-functioning people with autism spectrum disorder (ASD). Specifically, intact declarative/explicit learning is argued to compensate for a deficit in non-declarative/implicit procedural learning, constituting an example of the so-called ‘see-saw’ effect. Ullman and Pullman (2015) extended their argument concerning a see-saw effect on language in ASD to cover other perceived anomalies of behaviour, including impaired acquisition of social skills. The aim of this paper is to present a critique of Ullman and colleagues’ claims, and to propose an alternative model of links between memory systems and language in ASD. Main contribution: We argue that a 4-systems model of learning, in which intact semantic and procedural memory are used to compensate for weaknesses in episodic memory and perceptual learning, can better explain patterns of language ability across the autistic spectrum. We also argue that attempts to generalise the ‘impaired implicit learning/spared declarative learning’ theory to other behaviours in ASD are unsustainable. Conclusions: Clinically significant language impairments in ASD are under-researched, despite their impact on everyday functioning and quality of life. The relative paucity of research findings in this area lays it open to speculative interpretation which may be misleading. Implications: More research is need into links between memory/learning systems and language impairments across the spectrum. Improved understanding should inform therapeutic intervention, and contribute to investigation of the causes of language impairment in ASD with potential implications for prevention

Isotropisation of Generalized Scalar-Tensor theory plus a massive scalar field in the Bianchi type I model

In this paper we study the isotropisation of a Generalized Scalar-Tensor theory with a massive scalar field. We find it depends on a condition on the Brans-Dicke coupling function and the potential and show that asymptotically the metric functions always tend toward a power or exponential law of the proper time. These results generalise and unify these of De Sitter in the case of a cosmological constant and of Cooley and Kitada in the case of an exponential potential.Comment: 10 page