Operationalising factors that explain the emergence of infectious diseases : A case study of the human campylobacteriosis epidemic

Peer reviewedPublisher PD

Vestibular contributions to lateral stabilization are bilaterally dependent during split belt walking

Vestibular information is critical for maintaining balance during locomotion, and is known to be attenuated with increasing locomotor velocity and cadence. This attenuation is muscle and phase dependent, and is thought to reflect the functional contribution of each muscle to balance control during each stride of the gait cycle. Bilaterally, the vestibular coupling is mirrored relative to the gait cycle as each leg undergoes similar modulation with variation in phase, velocity and cadence. Here, we asked whether the modulation of the vestibular contribution to each limb is bilaterally dependent. By using a split-belt treadmill with asymmetric belt speeds, we can control the locomotion properties of each leg and compare the vestibular modulation to symmetric conditions. We hypothesized that bilaterally symmetric vestibular modulation would indicate leg independent vestibular influence while bilaterally asymmetric vestibular modulation would indicate leg dependent vestibular influence. Subjects were exposed to binaural bipolar stochastic vestibular stimulation (0-25 Hz) during symmetric and asymmetric walking conditions. Symmetric trials were performed at belt speeds of 0.4 and 0.8 m/s and for 10 min. The asymmetric trial was performed at belt speeds of 0.4 and 0.8 m/s for 16 min. Subjects walked with a cadence of 78 steps/min which was easily maintained in both limbs. EMG of the bilateral medial gastrocnemii and three-dimensional ground reaction force and torques were collected. Only the last 340 strides (~ 9 min of data) were used in the analysis to avoid the adaptation that typically occurs within the first 250 strides (~ 6 min) of asymmetric walking. Significant muscle activity and lateral ground reaction forces (P < 0.01) were correlated to the input stimuli in all trials. Stimulus-EMG and -lateral ground reaction force correlations decreased at higher belt speeds during symmetric walking, as previously reported. During the split belt condition, the magnitude of correlations stimulus-EMG and -force were bilaterally asymmetric and different from their symmetric counterparts. During the asymmetric condition correlations decreased for the slow leg, but more closely resembled the responses observed during slow symmetric walking, and increased for the fast leg, but more closely resembled the responses observed during fast symmetric walking. These results indicate that the modulation of vestibular reflexes is dependent upon the specific kinematics of each leg but bilaterally linked to respond to the properties of the locomotion pattern

Variance based weighting of multisensory head rotation signals for verticality perception

We tested the hypothesis that the brain uses a variance-based weighting of multisensory cues to estimate head rotation to perceive which way is up. The hypothesis predicts that the known bias in perceived vertical, which occurs when the visual environment is rotated in a vertical-plane, will be reduced by the addition of visual noise. Ten healthy participants sat head-fixed in front of a vertical screen presenting an annulus filled with coloured dots, which could rotate clockwise or counter-clockwise at six angular velocities (1, 2, 4, 6, 8, 16°/s) and with six levels of noise (0, 25, 50, 60, 75, 80%). Participants were required to keep a central bar vertical by rotating a hand-held dial. Continuous adjustments of the bar were required to counteract low-amplitude low-frequency noise that was added to the bar's angular position. During visual rotation, the bias in verticality perception increased over time to reach an asymptotic value. Increases in visual rotation velocity significantly increased this bias, while the addition of visual noise significantly reduced it, but did not affect perception of visual rotation velocity. The biasing phenomena were reproduced by a model that uses a multisensory variance-weighted estimate of head rotation velocity combined with a gravito-inertial acceleration signal (GIA) from the vestibular otoliths. The time-dependent asymptotic behaviour depends on internal feedback loops that act to pull the brain's estimate of gravity direction towards the GIA signal. The model's prediction of our experimental data furthers our understanding of the neural processes underlying human verticality perception

Coronal mass ejections as expanding force-free structures

We mode Solar coronal mass ejections (CMEs) as expanding force-fee magnetic structures and find the self-similar dynamics of configurations with spatially constant \alpha, where {\bf J} =\alpha {\bf B}, in spherical and cylindrical geometries, expanding spheromaks and expanding Lundquist fields correspondingly. The field structures remain force-free, under the conventional non-relativistic assumption that the dynamical effects of the inductive electric fields can be neglected. While keeping the internal magnetic field structure of the stationary solutions, expansion leads to complicated internal velocities and rotation, induced by inductive electric field. The structures depends only on overall radius R(t) and rate of expansion \dot{R}(t) measured at a given moment, and thus are applicable to arbitrary expansion laws. In case of cylindrical Lundquist fields, the flux conservation requires that both axial and radial expansion proceed with equal rates. In accordance with observations, the model predicts that the maximum magnetic field is reached before the spacecraft reaches the geometric center of a CME.Comment: 19 pages, 9 Figures, accepted by Solar Physic

Cognitive Reserve in Parkinson’s Disease: The Effects of Welsh-English Bilingualism on Executive Function

PublishedJournal ArticleObjective. Bilingualism has been shown to benefit executive function (EF) and delay the onset of Alzheimer's disease. This study aims at examining whether a bilingual advantage applies to EF in Parkinson's disease (PD). Method. In a cross-sectional outpatient cohort of monolingual English (n = 57) and bilingual Welsh/English (n = 46) speakers with PD we evaluated the effects of bilingualism compared with monolingualism on performance on EF tasks. In bilinguals we also assessed the effects of the degree of daily usage of each language and the degree of bilingualism. Results. Monolinguals showed an advantage in performance of language tests. There were no differences in performance of EF tests in monolinguals and bilinguals. Those who used Welsh less in daily life had better performance on one test of English vocabulary. The degree of bilingualism correlated with one test of nonverbal reasoning and one of working memory but with no other tests of EF. Discussion. The reasons why the expected benefit in EF in Welsh-English bilinguals with PD was not found require further study. Future studies in PD should include other language pairs, analysis of the effects of the degree of bilingualism, and longitudinal analysis of cognitive decline or dementia together with structural or functional neuroimaging.This study was funded by Economic and Social Research Council Grant RES-062-23-1931 awarded to Linda Clare (PI), John V. Hindle, Virginia C. Mueller Gathercole, Enlli M. Thomas, Ellen Bialystok, Fergus I. M. Craik, and Christopher J. Whitaker

4pi Models of CMEs and ICMEs

Coronal mass ejections (CMEs), which dynamically connect the solar surface to the far reaches of interplanetary space, represent a major anifestation of solar activity. They are not only of principal interest but also play a pivotal role in the context of space weather predictions. The steady improvement of both numerical methods and computational resources during recent years has allowed for the creation of increasingly realistic models of interplanetary CMEs (ICMEs), which can now be compared to high-quality observational data from various space-bound missions. This review discusses existing models of CMEs, characterizing them by scientific aim and scope, CME initiation method, and physical effects included, thereby stressing the importance of fully 3-D ('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication in Solar Physics (SUN-360 topical issue

Reconstructing the 3-D Trajectories of CMEs in the Inner Heliosphere

A method for the full three-dimensional (3-D) reconstruction of the trajectories of coronal mass ejections (CMEs) using Solar TErrestrial RElations Observatory (STEREO) data is presented. Four CMEs that were simultaneously observed by the inner and outer coronagraphs (COR1 and 2) of the Ahead and Behind STEREO satellites were analysed. These observations were used to derive CME trajectories in 3-D out to ~15Rsun. The reconstructions using COR1/2 data support a radial propagation model. Assuming pseudo-radial propagation at large distances from the Sun (15-240Rsun), the CME positions were extrapolated into the Heliospheric Imager (HI) field-of-view. We estimated the CME velocities in the different fields-of-view. It was found that CMEs slower than the solar wind were accelerated, while CMEs faster than the solar wind were decelerated, with both tending to the solar wind velocity.Comment: 17 pages, 10 figures, 1 appendi

The impact on human health of car-related air pollution in the UK, 1995-2005

We have analysed the impact on human health of emissions produced by the UK car fleet in the years 1995 and 2005. Calculations were based on reported measurements of pollutant concentration, literature values of exposure response coefficients and data for mortality and morbidity. A share was attributed to the car fleet based on emissions data. Although the total distance driven in the UK increased by 16% over this period to 460 billion km, there was a significant fall in engine emissions as increasingly stringent regulations (EURO standards) were introduced. As a result there was a decrease of some 25% in the number of deaths attributable to car-related air pollution – down to 5589 in 2005. The estimated number of years of life lost at 65 000 (England and Wales) in 2005, was about half that caused by road accidents involving cars in the same year. We report further calculations which show the effect of car-related pollution on hospital admissions. Our method is straightforward, providing acceptable estimates for health impacts on the predominantly urban population of the UK. There remains a need for more work, particularly cohort studies of morbidity, to establish the long-term effects of air pollution

3D evolution of a filament disappearance event observed by STEREO

A filament disappearance event was observed on 22 May 2008 during our recent campaign JOP 178. The filament, situated in the southern hemisphere, showed sinistral chirality consistent with the hemispheric rule. The event was well observed by several observatories in particular by THEMIS. One day before the disappearance, H$\alpha$ observations showed up and down flows in adjacent locations along the filament, which suggest plasma motions along twisted flux rope. THEMIS and GONG observations show shearing photospheric motions leading to magnetic flux canceling around barbs. STEREO A, B spacecraft with separation angle 52.4 degrees, showed quite different views of this untwisting flux rope in He II 304 \AA\ images. Here, we reconstruct the 3D geometry of the filament during its eruption phase using STEREO EUV He II 304 \AA\ images and find that the filament was highly inclined to the solar normal. The He II 304 \AA\ movies show individual threads, which oscillate and rise to an altitude of about 120 Mm with apparent velocities of about 100 km s$^{-1}$, during the rapid evolution phase. Finally, as the flux rope expands into the corona, the filament disappears by becoming optically thin to undetectable levels. No CME was detected by STEREO, only a faint CME was recorded by LASCO at the beginning of the disappearance phase at 02:00 UT, which could be due to partial filament eruption. Further, STEREO Fe XII 195 \AA\ images showed bright loops beneath the filament prior to the disappearance phase, suggesting magnetic reconnection below the flux rope

Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003

We present and interpret observations of two morphologically homologous flares that occurred in active region (AR) NOAA 10501 on 20 November 2003. Both flares displayed four homologous H-alpha ribbons and were both accompanied by coronal mass ejections (CMEs). The central flare ribbons were located at the site of an emerging bipole in the center of the active region. The negative polarity of this bipole fragmented in two main pieces, one rotating around the positive polarity by ~ 110 deg within 32 hours. We model the coronal magnetic field and compute its topology, using as boundary condition the magnetogram closest in time to each flare. In particular, we calculate the location of quasiseparatrix layers (QSLs) in order to understand the connectivity between the flare ribbons. Though several polarities were present in AR 10501, the global magnetic field topology corresponds to a quadrupolar magnetic field distribution without magnetic null points. For both flares, the photospheric traces of QSLs are similar and match well the locations of the four H-alpha ribbons. This globally unchanged topology and the continuous shearing by the rotating bipole are two key factors responsible for the flare homology. However, our analyses also indicate that different magnetic connectivity domains of the quadrupolar configuration become unstable during each flare, so that magnetic reconnection proceeds differently in both events.Comment: 24 pages, 10 figures, Solar Physics (accepted