Stochastic Representations of Ion Channel Kinetics and Exact Stochastic Simulation of Neuronal Dynamics

In this paper we provide two representations for stochastic ion channel kinetics, and compare the performance of exact simulation with a commonly used numerical approximation strategy. The first representation we present is a random time change representation, popularized by Thomas Kurtz, with the second being analogous to a "Gillespie" representation. Exact stochastic algorithms are provided for the different representations, which are preferable to either (a) fixed time step or (b) piecewise constant propensity algorithms, which still appear in the literature. As examples, we provide versions of the exact algorithms for the Morris-Lecar conductance based model, and detail the error induced, both in a weak and a strong sense, by the use of approximate algorithms on this model. We include ready-to-use implementations of the random time change algorithm in both XPP and Matlab. Finally, through the consideration of parametric sensitivity analysis, we show how the representations presented here are useful in the development of further computational methods. The general representations and simulation strategies provided here are known in other parts of the sciences, but less so in the present setting.Comment: 39 pages, 6 figures, appendix with XPP and Matlab cod

Ultra Bright LED Light Injection Calibration System for MINOS

We describe here a proposal for a light injection calibration system for the MINOS detectors based on ultra bright blue LEDs as the light source. We have shown that these LEDs are bright enough to span over two orders of magnitude in light intensity, commensurate with that expected in a single scintillator strip in the MINOS neutrino detectors.Comment: 9 pages, 13 figures, Submitted to NI

Reproductive Status of an Upland Population of Masked Shrews

Author Institution: Department of Zoology, Miami UniversityMasked shrew (Sorex cinereus Kerr) populations in upland hardwood forests of Upper Michigan were studied to determine their breeding status during the dry year of 1976. These populations lacked pregnant adult females and the younger age classes of juveniles. Other age/sex groups were well represented when conditions were moist. Apparently, masked shrews do not breed in upland hardwoods during dry conditions and may entirely abandon uplands during excessively dry periods

Asia-Pacific food markets and trade in 2005: a global, economy-wide perspective

Rapid industrialization in East Asia, particularly China, is raising questions about who will feed the region in the next century and how Asia will be able to pay for its food imports. The paper ®rst reviews existing food sector projections and then takes an economy-wide perspective using projections to 2005, based on the global CGE model known as GTAP. After showing the impact of implementing the Uruguay Round, the paper explores several alternative scenarios. A slowdown in farm productivity growth is shown to be costly to the world economy, as is slower economic growth in China. Failure to honour Uruguay Round obligations to open textile and clothing markets in OECD countries would reduce East Asia's industrialization and thereby slow its net imports of food. On the other hand, the trade reform that is likely to accompany China's (and hence Taiwan's) member- ship of the World Trade Organization (WTO) adds 30 per cent to estimated global gains from the Uruguay Round. Their WTO accession is projected to boost exports of manufactures and strengthen food import demand by not only China but also its densely populated neighbours with whom it trades intensively.International Relations/Trade,

Insights from unifying modern approximations to infections on networks

Networks are increasingly central to modern science owing to their ability to conceptualize multiple interacting components of a complex system. As a specific example of this, understanding the implications of contact network structure for the transmission of infectious diseases remains a key issue in epidemiology. Three broad approaches to this problem exist: explicit simulation; derivation of exact results for special networks; and dynamical approximations. This paper focuses on the last of these approaches, and makes two main contributions. Firstly, formal mathematical links are demonstrated between several prima facie unrelated dynamical approximations. And secondly, these links are used to derive two novel dynamical models for network epidemiology, which are compared against explicit stochastic simulation. The success of these new models provides improved understanding about the interaction of network structure and transmission dynamics

Social encounter networks : collective properties and disease transmission

A fundamental challenge of modern infectious disease epidemiology is to quantify the networks of social and physical contacts through which transmission can occur. Understanding the collective properties of these interactions is critical for both accurate prediction of the spread of infection and determining optimal control measures. However, even the basic properties of such networks are poorly quantified, forcing predictions to be made based on strong assumptions concerning network structure. Here, we report on the results of a large-scale survey of social encounters mainly conducted in Great Britain. First, we characterize the distribution of contacts, which possesses a lognormal body and a power-law tail with an exponent of −2.45; we provide a plausible mechanistic model that captures this form. Analysis of the high level of local clustering of contacts reveals additional structure within the network, implying that social contacts are degree assortative. Finally, we describe the epidemiological implications of this local network structure: these contradict the usual predictions from networks with heavy-tailed degree distributions and contain public-health messages about control. Our findings help us to determine the types of realistic network structure that should be assumed in future population level studies of infection transmission, leading to better interpretations of epidemiological data and more appropriate policy decisions

Shock wave equations of state of chondritic meteorites

We have obtained shock compression data for Murchison and Bruderheim chondritic meteorites. Data for Murchison suggest that the Hugoniot states are described by a smooth curve to ≥90 GPa, having ρ_0=2.656 Mg/m^3, K_(S0)=24.2±.7 GPa, K′=4.17±.10, and constant γ=1.0. The data for Bruderheim suggest more complicated behavior. A mineral mixture model consistent with the Bruderheim data suggests that the Hugoniot state is a low pressure phase below 25 GPa, with ρ_0=3.555 Mg/m^3, K_(S0)=146 GPa, K′=2.53, and constant ργ=7.11 Mg/m^3; and a high pressure phase above 65 GPa, with ρ_0=4.40 Mg/m^3, K_(S0)=225 GPa, K′=3.25, and constant ργ=7.485 Mg/m^3

Childhood IQ and risk of bipolar disorder in adulthood: prospective birth cohort study

Background: Intellectual ability may be an endophenotypic marker for bipolar disorder. Aims: Within a large birth cohort, we aimed to assess whether childhood IQ (including both verbal IQ (VIQ) and performance IQ (PIQ) subscales) was predictive of lifetime features of bipolar disorder assessed in young adulthood. Method: We used data from the Avon Longitudinal Study of Parents and Children (ALSPAC), a large UK birth cohort, to test for an association between measures of childhood IQ at age 8 years and lifetime manic features assessed at age 22–23 years using the Hypomania Checklist-32 (HCL-32; n=1881 individuals). An ordinary least squares linear regression model was used, with normal childhood IQ (range 90–109) as the referent group. We adjusted analyses for confounding factors, including gender, ethnicity, handedness, maternal social class at recruitment, maternal age, maternal history of depression and maternal education. Results: There was a positive association between IQ at age 8 years and lifetime manic features at age 22–23 years (Pearson's correlation coefficient 0.159 (95% CI 0.120–0.198), P>0.001). Individuals in the lowest decile of manic features had a mean full-scale IQ (FSIQ) which was almost 10 points lower than those in the highest decile of manic features: mean FSIQ 100.71 (95% CI 98.74–102.6) v. 110.14 (95% CI 107.79–112.50), P>0.001. The association between IQ and manic features was present for FSIQ, VIQ and for PIQ but was strongest for VIQ. Conclusions: A higher childhood IQ score, and high VIQ in particular, may represent a marker of risk for the later development of bipolar disorder. This finding has implications for understanding of how liability to bipolar disorder may have been selected through generations. It will also inform future genetic studies at the interface of intelligence, creativity and bipolar disorder and is relevant to the developmental trajectory of bipolar disorder. It may also improve approaches to earlier detection and treatment of bipolar disorder in adolescents and young adults

Physics of interplanetary dust capture via impact into organic polymer foams

The physics of hypervelocity impacts into foams is of interest because of the possible application to interplanetary dust particle (IDP) capture by spacecraft. We present a model for the phenomena occurring in such impacts into low-density organic polymer foams. Particles smaller than foam cells behave as if the foam is a series of solid slabs and are fragmented and, at higher velocities, thermally altered. Particles much larger than the foam cells behave as if the foam were a continuum, allowing the use of a continuum mechanics model to describe the effects of drag and ablation. Fragmentation is expected to be a major process, especially for aggregates of small grains. Calculations based on these arguments accurately predict experimental data and, for hypothetical IDPs, indicate that recovery of organic materials will be low for encounter velocities greater than 5 km s^(−1). For an organic particle 100 μm in diameter, ∼35% of the original mass would be collected in an impact at 5 km s^(−1), dropping to ∼10% at 10 km s^(−1) and ∼0% at 15 km s^(−1). For the same velocities the recovery ratios for troilite (FeS) are ∼95%, 65%, and 50%, and for olivine (Mg_2SiO_4) they are ∼98%, 80%, and 65%, demonstrating that inorganic materials are much more easily collected. The density of the collector material has only a second-order effect, changing the recovered mass by <10% of the original mass