Serotonin drives a novel GABAergic synaptic current recorded in rat cerebellar purkinje cells: a lugaro cell to purkinje cell synapse

We recorded a novel fast GABAergic synaptic current in cerebellar Purkinje cells in rat brain slices using patch-clamp techniques. Because of a relatively low sensitivity to bicuculline, these currents can be recorded under conditions in which basket and stellate cell inputs are blocked. The observations that the novel synaptic currents occur spontaneously only in the presence of serotonin, and the specific limited positions in the slice from which they can be electrically evoked, suggest that the presynaptic cell is the Lugaro cell. Cell-attached recordings confirm that the Lugaro cell is the only interneuron in the cerebellar cortex with firing behavior consistent with the spontaneous activity recorded in Purkinje cells. The input shows a strong presynaptic modulation mediated by GABAA receptors, resulting in a dynamic range from almost 0 to >90% release probability. Modeling GABAA receptor responses to different GABA transients suggests that the relatively low sensitivity of the synaptic currents to bicuculline, compared with the higher affinity GABAA receptor antagonist SR-95531 (2-(3-carboxypropyl)-3-amino-6-(4-methoxyphenyl) pyridazinium), is attributable to an unusually long GABA dwell time and/or high GABA concentration in the synaptic cleft. The significance of this novel input is discussed in relation to other GABAergic synapses impinging on Purkinje cells. We suggest that the release of GABA onto Purkinje cells from Lugaro cells would primarily occur during motor activity under conditions in which the activity of basket and stellate cells might be inhibited

Uncertainty Analyses in the Finite-Difference Time-Domain Method

Providing estimates of the uncertainty in results obtained by Computational Electromagnetic (CEM) simulations is essential when determining the acceptability of the results. The Monte Carlo method (MCM) has been previously used to quantify the uncertainty in CEM simulations. Other computationally efficient methods have been investigated more recently, such as the polynomial chaos method (PCM) and the method of moments (MoM). This paper introduces a novel implementation of the PCM and the MoM into the finite-difference time -domain method. The PCM and the MoM are found to be computationally more efficient than the MCM, but can provide poorer estimates of the uncertainty in resonant electromagnetic compatibility data

Null point distribution in global coronal potential field extrapolations

SJE would like to thank the Isle of Man Government for support during her PhD and also for the financial support of the STFC.Magnetic null points are points in space where the magnetic field is zero. Thus, they can be important sites for magnetic reconnection by virtue of the fact that they are weak points in the magnetic field and also because they are associated with topological structures, such as separators, which lie on the boundary between four topologically distinct flux domains and therefore are also locations where reconnection occurs. The number and distribution of nulls in a magnetic field acts as a measure of the complexity of the field. In this article, the numbers and distributions of null points in global potential field extrapolations from high-resolution synoptic magnetograms are examined. Extrapolations from magnetograms obtained with the Michelson Doppler Imager (MDI) are studied in depth and compared with those from high-resolution SOlar Long-time Investigations of the Sun (SOLIS) and Heliospheric Magnetic Imager (HMI). The fall-off in the density of null points with height is found to follow a power law with a slope that differs depending on whether the data are from solar maximum or solar minimum. The distribution of null points with latitude also varies with the cycle as null points form predominantly over quiet-Sun regions and avoid active-region fields. The exception to this rule are the null points that form high in the solar atmosphere, and these null points tend to form over large areas of strong flux in active regions. From case studies of data acquired with the MDI, SOLIS, and HMI, it is found that the distribution of null points is very similar between data sets, except, of course, that there are far fewer nulls observed in the SOLIS data than in the cases from MDI and HMI due to its lower resolution.PostprintPeer reviewe

Axion-photon conversion in neutron star magnetospheres:The role of the plasma in the Goldreich-Julian model

The most promising indirect search for the existence of axion dark matter uses radio telescopes to look for narrow spectral lines generated from the resonant conversion of axions in the magnetospheres of neutron stars. Unfortunately, a large list of theoretical uncertainties has prevented this search strategy from being fully accepted as robust. In this work we attempt to address major outstanding questions related to the role and impact of the plasma, including: $(i)$ does refraction and reflection of radio photons in the magnetosphere induce strong inhomogeneities in the flux, $(ii)$ can refraction induce premature axion-photon de-phasing, $(iii)$ to what extent do photon-plasma interactions induce a broadening of the spectral line, $(iv)$ does the flux have a strong time dependence, and $(v)$ can radio photons sourced by axions be absorbed by the plasma. We present an end-to-end analysis pipeline based on ray-tracing that exploits a state-of-the-art auto-differentiation algorithm to propagate photons from the conversion surface to asymptotically large distances. Adopting a charge symmetric Goldreich-Julian model for the magnetosphere, we show that for reasonable parameters one should expect a strong anisotropy of the signal, refraction induced axion-photon de-phasing, significant line-broadening, a variable time-dependence of the flux, and, for large enough magnetic fields, anisotropic absorption. Our simulation code is flexible enough to serve as the basis for follow-up studies with a large range of magnetosphere models.Comment: v2: Accepted for publication PRD. Convergence improved, plots updated, minor bugs and typos corrected. No major changes to results/conclusions. v1: 9 pages + Appendi

The effect of EMAT coil geometry on the Rayleigh wave frequency behaviour

Understanding of optimal signal generation and frequency content for electromagnetic acoustic transducers (EMATs) is key to improving their design and signal to noise ratio. Linear and meander coil designs are fairly well understood, but other designs such as racetrack or focused coils have recently been proposed. Multiple transmission racetrack coil EMATs, with focused and unfocused designs, were constructed. The optimum driving frequency for maximum detected signal was found to range between 1.1 and 1.4 MHz on aluminium for a 1.5 mm width coil. A simple analytical model based on the instantaneous velocity of a wave predicts a maximum signal at 1.44 MHz. Modelling the detection coil as a spatial square wave agrees with this, and predicts a general relation of fP = 0.761v / L between the optimum frequency fP , the wave velocity v, and the coil width L. A time domain model of the detection coil predicts a 1.4 to 1.5 MHz peak for continuous wave excitation, with a frequency that decreases as the length of the wavepacket is decreased, consistent with the experimental data. Linear coil modelling using the same technique is shown to be consistent with previous work, with improving detection at lower wave frequencies, and signal minima at every integer multiple of the wavelength. Finite Element Analysis (FEA) is used to model the effects of the spatial width of the racetrack generation coil and focused geometry, and no significant difference is found between the focused and the unfocused EMAT response. This highlights the importance of designing the EMAT coil for the correct lift-off and desired frequency of operation

‘Trust the experts!’ Risk definitions in Dutch online forums about the ‘swine flu’

Citizens are becoming increasingly likely to challenge the knowledge bases underlying policy programmes that deal with risks. This paper investigates how participants in online discussions engage in interactions between expert knowledge, ‘commons knowledge’ and policy assumptions. The concept of ‘boundary objects’, arrangements that allow different groups to work together without consensus, is used to analyse the role of online discussions in these interactions. Discussions on three Dutch online forums about the swine flu are investigated according to a framework for policy argumentation. Interaction between knowledge domains was limited, and it varied in focus and nature across the three forums. Each discussion functioned as a partial approximation of a boundary object. Government organizations should be more aware of the variety of online forums in which discussions about societal risks take place. Several practical options are presented for policy-making with regard to risks

Optimising landmark-based route guidance for older drivers

In-vehicle navigation systems (IVNS) have the potential to benefit older drivers, reducing stress associated with way-finding and providing on-trip support, especially in unfamiliar locations. However, existing IVNS present challenges to usability, resulting in lack of uptake and over-reliance on pre-trip planning. This paper presents research aimed at identifying features that make IVNS user-friendly and appropriate for older drivers. Studying navigational performance within a simulated driving environment, it focuses on the use of landmarks with route guidance information, and the most appropriate method of information provision (audio only, visual only or a combination of audio and visual). It also assesses potential gender differences that might arise with landmark-based navigational information. Solutions include use of appropriate roadside landmarks, and information delivered through a combination of audio and icon-based visual format. These features result in lower workload and fewer navigational errors. The audio/visual modality reduces the hazard of distraction by landmarks resulting in fewer visual glances and lower glance duration to the roadside compared to other modalities. Design and provision of IVNS tailored to older drivers’ needs can make a considerable contribution to maintaining individual mobility for longer

Two-dimensional modelling of a towed transient magnetic dipole-dipole sea floor EM system

The discovery of massive sulphide deposits along mid-ocean ridges has prompted the development of towed sea floor electromagnetic mapping tools. One suitable configuration of transmitter and receiver is the in-line, coaxial, magnetic dipole-dipole. The step response of this system to a double half-space model has two distinct parts. The position in time of the initial event is indicative of the conductivity of the sea floor. A reduction in dimensionality greatly simplifies the analytic and numerical computation of more complicated cases. The transmitter is reduced to a pair of horizontal line sources carrying equal but opposite currents and separated by a small vertical distance. The transient responses of the simplified system and the coaxial system to the double half-space model are remarkably similar, even though the electromagnetic mode characterised by vertical current flow is excluded by the simplification. The analytic form of the sensitivity function enables a simple expression for a depth of investigation beneath the sea floor to be derived as a function of time. The magnetic effects of currents impressed in a two-dimensional conductive target embedded in the sea floor by a horizontal magnetic point dipole transmitter may be represented approximately by a system of vortex currents only. Since vortex current flow is the type of current flow induced in a two-dimensional target by a two-dimensional magnetic source, the principal characteristics of the three-dimensional problem can be studied by two-dimensional modelling. The scattered fields from a thin conductive dike and a thin conductive sill are evaluated by setting up and solving a boundary element integral equation in the electric field. Transient response curves are presented for a limited range of models. The sea floor conductivity is fixed at 1/30 that of seawater, a typical value for recent basalt. The array size and plate depth extent are fixed at 100 m and 25 m, respectively, while the depth of burial is allowed to vary from 4 m to 25 m. The ratio of the inductive response parameter of the plate to the response parameter of the crust, which determines the degree of influence of the plate conductor on the combined step response, is varied from 0.4 to 10. Increasing the relative effect of the target delays the onset and decreases the gradient of the initial part of the response. Pronounced minima in the response as a function of array location are observed when either the transmitter or the receiver cross over the target. The minimum field over a wide range of times is close to zero for a shallow dike due to the combined shielding effect of the dike and the seawater. The shallow dike may be distinguished from a shallow sill by the shape of the minima.           ARK: https://n2t.net/ark:/88439/y079019 Permalink: https://geophysicsjournal.com/article/123 &nbsp