Voltage sensing in ion channels: Mesoscale simulations of biological devices

Electrical signaling via voltage-gated ion channels depends upon the function of a voltage sensor (VS), identified with the S1-S4 domain in voltage-gated K+ channels. Here we investigate some energetic aspects of the sliding-helix model of the VS using simulations based on VS charges, linear dielectrics and whole-body motion. Model electrostatics in voltage-clamped boundary conditions are solved using a boundary element method. The statistical mechanical consequences of the electrostatic configurational energy are computed to gain insight into the sliding-helix mechanism and to predict experimentally measured ensemble properties such as gating charge displaced by an applied voltage. Those consequences and ensemble properties are investigated for two alternate S4 configurations, \alpha- and 3(10)-helical. Both forms of VS are found to have an inherent electrostatic stability. Maximal charge displacement is limited by geometry, specifically the range of movement where S4 charges and counter-charges overlap in the region of weak dielectric. Charge displacement responds more steeply to voltage in the \alpha-helical than the 3(10)-helical sensor. This difference is due to differences on the order of 0.1 eV in the landscapes of electrostatic energy. As a step toward integrating these VS models into a full-channel model, we include a hypothetical external load in the Hamiltonian of the system and analyze the energetic in/output relation of the VS.Comment: arXiv admin note: substantial text overlap with arXiv:1112.299

Around Gaia Alerts in 20 questions

Gaia is a European Space Agency (ESA) astrometry space mission, and a successor to the ESA Hipparcos mission. Gaia's main goal is to collect high-precision astrometric data (i.e. positions, parallaxes, and proper motions) for the brightest 1 billion objects in the sky. These data, complemented with multi-band, multi-epoch photometric and spectroscopic data collected from the same observing platform, will allow astronomers to reconstruct the formation history, structure, and evolution of the Galaxy. Gaia will observe the whole sky for 5 years, providing a unique opportunity for the discovery of large numbers of transient and anomalous events, e.g. supernovae, novae and microlensing events, GRB afterglows, fallback supernovae, and other theoretical or unexpected phenomena. The Photometric Science Alerts team has been tasked with the early detection, classification and prompt release of anomalous sources in the Gaia data stream. In this paper, we discuss the challenges we face in preparing to use Gaia to search for transient phenomena at optical wavelengths.Comment: Text of the poster presented at the IAU Symposium #285 "New Horizons in Time Domain Astronomy", Oxford, UK, 19-23 September 2011, included in the proceedings Eds. R.E.M. Griffin, R.J. Hanisch & R. Seaman. Original poster is available under this link: http://www.ast.cam.ac.uk/ioa/wikis/gsawgwiki/images/3/33/AroundGaiaPoster2011.pd

Optimization of the leak conductance in the squid giant axon

We report on a theoretical study showing that the leak conductance density, \GL, in the squid giant axon appears to be optimal for the action potential firing frequency. More precisely, the standard assumption that the leak current is composed of chloride ions leads to the result that the experimental value for \GL is very close to the optimal value in the Hodgkin-Huxley model which minimizes the absolute refractory period of the action potential, thereby maximizing the maximum firing frequency under stimulation by sharp, brief input current spikes to one end of the axon. The measured value of \GL also appears to be close to optimal for the frequency of repetitive firing caused by a constant current input to one end of the axon, especially when temperature variations are taken into account. If, by contrast, the leak current is assumed to be composed of separate voltage-independent sodium and potassium currents, then these optimizations are not observed.Comment: 9 pages; 9 figures; accepted for publication in Physical Review

Learning About Being a Scientist from the Vitamin B-12 Structure Collaboration

This historical note reviews the work that resulted in the publication of the structure of Vitamin B12. The collaborations and resulting friendships that developed during this time made a strong impression on the author and encouraged her to pursue a scientific career

Book review: critical theory of communication: new readings of Lukacs, Adorno, Marcuse, Honneth and Habermas in the age of the internet by Christian Fuchs

In Critical Theory of Communication, Christian Fuchs explores how the theories of five key thinkers from the Frankfurt School – Georg Lukács, Theodor Adorno, Herbert Marcuse, Axel Honneth and Jürgen Habermas – can contribute to a critical understanding of contemporary media. While the book succeeds in underscoring the need to continue re-examining the vital contributions of these theorists, it does not always fully convince of their relevance to more specific aspects of the digital age, argues Adam Hodgkin

Popular Attitudes to Taxation in Britain, c.1945- 1992

There has been a general view among British historians that popular opposition to tax increased dramatically in the 1970s. However, no study has looked in detail at the available evidence. This view has been based largely on politicians’ statements and a few isolated studies from the 1980s, most of which did not focus on Britain specifically. This thesis attempts to construct a more detailed picture of the development of popular attitudes to tax in Britain c1945 to 1992. To do this it first examines the available quantitative evidence, variable and unreliable as much of it is before the 1980s and draws some cautious conclusions about how this suggests popular attitudes to tax developed. The following chapters look at discussions in the major national newspapers and political magazines, two main political parties, the civil service, Trades Union Congress, and Federation of British Industries, later Confederation of British Industry, in a series of case studies. These focus on moments when tax was a particularly high-profile issue: the 1949 budget and 1950 election; the 1959 election and 1961 budget; the 1964 election and 1965 budget, the late 1960s and 1970 election; the late 1970s and 1979 election; and the 1987 and 1992 elections. The findings do not indicate that opposition increased significantly in the 1970s. On the contrary, the quantitative evidence suggests that popular opposition to taxation was consistently at a relatively low level throughout the period studied, potentially even decreasing through the 1980s, when the evidence is more methodologically reliable. Similarly, although there is evidence that some Labour politicians, in particular, were slightly more concerned about opposition to tax from the 1970s onwards, they were also convinced of opposition in the 1940s and 1950s, supposedly the high point of popular support for high taxation. Even in 1992, the evidence indicates that most Labour politicians remained convinced that perceptions of fairness in taxation were crucial and that support for public spending was also extensive. The views expressed by Labour and Conservative politicians’ during the 1980s indicate that they did not think at that time that popular opposition to tax had increased unprecedentedly in the 1970s. Instead, that idea first appeared in the press in 1987, becoming pervasive by 1992. Among the various organisations studied here, the research therefore indicates that this idea of opposition to tax increasing in the 1970s was found initially only among journalists in the late 1980s and early 1990s – and that it was circulated without supporting evidence

Pupils’ Expectations and Experiences of PE across the Primary–secondary Transition in South Wales

This paper explores the experiences of physical education (PE) among a group of 10–11-year-old pupils who made the transition to an inner-city secondary school in south Wales from one of its feeder primary schools during 2013. The primary–secondary transition concerning PE is marked by significant changes in resource provision, and a mode of delivery from (mainly) non-specialist teachers to subject specialists (Capel and Piotrowski, 2000). Identified as a source of discontinuity at a time of potential risk, the impact of PE has been neglected with educational research (Dismore and Bailey, 2010). As a qualitative exploratory study, an ethnographic approach was adopted with 'pupil voice' a distinctive and central feature. Two six-week phases of fieldwork were conducted which examined the holistic impact of PE across transition in a secondary school and its feeder primary school (June–October 2013). Twenty-five pupils' expectations and experiences of PE across the transition were explored: first prior to transition (primary school) and then post-transition (secondary school). Thematic analysis of pupil interviews, staff interviews and classroom drawings was conducted and created three super ordinate findings which relate to pupils' perception of the process of transition and specifically in terms of PE; the notion of 'being good enough'; social implications of transition and gender; teachers and teaching were all highlighted as significant issues across the transitional process