910 research outputs found
Effects of central sympathetic inhibition on heart rate variability during steady-state exercise in healthy humans
No full textThe profound reduction in heart rate variability (HRV) that occurs during exercise is thought to be, at least in part, the result of sympathetic nervous system activation. Moxonidine is a centrally acting anti-sympathetic drug, which suppresses sympathetic nervous system outflow by stimulation of central imidazoline receptors located in the rostral ventro-lateral medulla. This study was designed to investigate the combined effects of central sympathetic inhibition with moxonidine and steady-state dynamic exercise on HRV. Ten normal males participated in a double-blind cross-over study, taking either placebo or 0·4 mg of moxonidine. The subjects were studied at rest and during steady-state exercise. HRV was measured considering both time and frequency domain parameters. As a non-linear measure, the Poincaré scatter-plot was measured and analysed quantitatively. Ventilation and gas exchange were also measured during exercise. In addition, plasma catecholamines were measured at rest and during exercise. The only parameter changed, at rest, by moxonidine was the blood pressure which was reduced. During exercise, moxonidine reduced plasma noradrenaline (NA), compared with the placebo (P<0·01). The only change observed in HRV during exercise was a significant reduction of the continuous long-term standard deviation (SD2) of the Poincaré scatter-plot of the R-R interval (P<0·05). However, the potential and prognostic significance of this result needs to be further assessed
Dispersion of material by wind and tide in shallow seas
No full textMixing processes in shallow seas are of particular importance in the dispersion of pollution (e.g. oil slicks) as well as in the distribution of sediment and biological material (e.g. phytoplankton and fish larvae). This study aims to further investigate the processes of wind-driven Langmuir circulation and bottom-generated turbulence and to quantify the effects they have on the dispersion of buoyant material. A numerical and analytical study is made of the dispersion of a plume of floating particles under the combined action of Langmuir circulation and a mean current. The numerical simulations show the general patterns the plume will form, with initial meanders leading to the formation of distinct windrows. The analytical model shows that the lateral diffusivity, the rate of across-current dispersion of the particles, is greatest when the angle between the direction of the wind and current is between 30° and 120°, and when the wind speed is large in comparison to the current speed. Further, it is found that the effects of Langmuir circulation will dominate the dispersion process when the wind speed is greater than about 10 times the current speed. Acoustic and visual observations of the surface effects of bottom-generated turbulence in a tidally-influenced and well-mixed region of the North Sea are presented. Although the sea bed in the area is flat, it is found that at any one time 20-30% of the water surface is affected by boils - circular regions of local upwelling - of diameter 0.9±0.2 times the water depth. The signature of individual boils persists for at least 7 minutes and, in accordance with laboratory and numerical studies, shows the appearance of eddies. Again, analytical and numerical models are constructed to estimate the effects of the boils on the dispersion of floating particles. The numerical simulations provide good qualitative agreement with the patterns observed in visual images of the dispersion of oil. Further, the horizontal diffusivities calculated by both them and the analytical methods show that the presence of boils can account for the dispersion measured by experimental methods in shallow tidal seas. In summarising and discussing the main findings of this work, particular emphasisis placed on the need for further observations of these two processes, in particular the boils and eddies and their interaction with the Langmuir circulation, to further improve the estimates of dispersion
Skeletal muscle ATP turnover and muscle fiber conduction velocity are elevated at higher muscle temperatures during maximal power output development in humans
No full textThe effect of exercise on plasma soluble IL-6 receptor concentration: a dichotomous response
No full textThe aim of this article is to review current literature on the response of soluble interleukin-6 receptor to exercise and identify a potential role for sIL-6R in skeletal muscle function. We also provide novel data on the impact of eccentric exercise on circulating levels. The aim of the research study was to investigate changes in plasma concentration of soluble interleukin-6 receptor (sIL-6R) and soluble glycoprotein 130 (sgp130) during recovery from exercise-induced muscle damage (EIMD) up to 72 h and their relationship with delayed onset muscle soreness (DOMS) and muscle function. 18 participants attended the laboratory on 4 consecutive days. On the first day, participants completed 6 sets of 10 repetitions of unilateral eccentric-concentric knee flexions at a test speed of 1.05 rad.s(-1) using a Cybex Isokentic dynamometer to induce muscle damage of the hamstrings. Prior to the eccentric exercise bout and each subsequent morning, following an overnight fast, participants had a venous blood sample taken which was centrifuged immediately and plasma frozen at -80 degrees C until later analysis. Plasma IL-6 and sgp130 were unchanged at any time point during recovery but sIL-6R was significantly reduced at 48 h and 72 h post-exercise (p < 0.05). Plasma sIL-6R was correlated with DOMS at 48 h post EIMD (r = 0.45, p < 0.05) and peak muscle torque at 24 h and 48 h following EIMD (r = -.42; p < 0.05; r = -.57; p < 0.01 respectively). Our novel finding that sIL-6R concentrations are decreased 2-3 days following a single bout of EIMD may reflect a regulatory mechanism controlling the influx of different leukocyte subpopulations into damaged tissue, although this needs to be confirmed by future studies. Our data suggests an association between sIL-6R, perception of pain and reduced peak muscle performance post-EIMD but further investigation is warranted to explore this relationship and implications for exercise performance
Methods for wavelet-based autonomous discrimination of multiple partial discharge sources
No full textRecent years have seen increased interest in the application of on-line condition monitoring of medium voltage networks as the need to maintain and operate ageing cable networks increases. Detection and analysis of partial discharge (PD) activity is generally used as an indicator of pre-breakdown processes that may be indicative of insulation degradation over time. A significant challenge for on-line monitoring is discrimination between multiple partial discharge sources that will often naturally exist in the data. To discriminate between PD sources each PD signal is represented as a feature vector and a clustering algorithm is used to identify clusters in the resulting feature vector space, often after dimensional reduction. Each cluster identified in the data corresponds to a distinct PD source. In this work a comparison of clustering algorithms and dimensional reduction techniques is performed to identify clusters for a variety of PD data sets, in all cases the feature vector is created using wavelet decomposition energies. The three clustering algorithms used were Density Based Spatial Clustering of Applications with Noise (DBSCAN), Ordering Points to Identify Clustering Structure (OPTICS) and Simple Statistics-based Near Neighbour clustering technique (SSNN). The two dimensional reduction techniques considered were Principal Component Analysis (PCA) and t Distributed Stochastic Neighbour Embedding (t SNE). At present the most commonly used combination of dimensional reduction technique and clustering algorithm for PD data are PCA and DBSCAN respectively. From the comparison performed in this work it was found that t SNE combined with OPTICS or SSNN were the most successful at clustering PD data. For use in practical situations SSNN is preferred over OPTICS as it requires only a single input parameter, which generally be hardcoded, leading to a completely autonomous technique. It is therefore suggested that a combination of t SNE and SSNN is particularly appropriate for discriminating PD sources
Inhibition of neurogenic inflammation attenuates the inflammatory response following traumatic brain injury in rats
No full text© 2004 by MEDIMOND The document attached has been archived with permission from the Medimond International Proceedings Division. An external link to the publisher’s web site is included.A profound inflammatory response is initiated following traumatic brain injury (TBI). It has been proposed that serum IL-6 levels may serve as a marker for the severity of the injury. Using the rat impact-acceleration model of TBI, the study examined whether drugs which are able to inhibit neurogenic inflammation (capsaicin, NK1 antagonist), might influence the post-traumatic inflammatory response. In non-treated animals, TBI resulted in a significant increase in serum IL-6 levels. However, in animals pre-treated with capsaicin prior to injury, or treated with an NK1 antagonist following injury, this rise in IL-6 levels was not observed. We conclude that the inhibition of neurogenic inflammation may attenuate the inflammatory reaction associated with TBI, and help improve outcome.K. Reardon, D. Heath, A. Nimmo, R. Vink and K. Whitfieldhttp://www.medimond.com/proceedings/moreinfo/20040912.ht
Neurogenic inflammation is associated with development of edema and functional deficits following traumatic brain injury in rats
No full textAvailable online 10 February 2004.The present study has used capsaicin-induced neuropeptide depletion to examine the role of neurogenic inflammation in the development of edema and functional deficits following traumatic brain injury (TBI). Adult, male rats were treated with capsaicin (neuropeptide-depleted) or equal volume vehicle (controls) 14 days prior to induction of moderate/severe diffuse TBI. Injury in vehicle treated control animals resulted in acute (4–5 h) edema formation, which was confirmed as being vasogenic in origin by diffusion weighted magnetic resonance imaging and the presence of increased permeability of the blood–brain barrier (BBB) to Evans blue dye. There was also a significant decline in brain magnesium concentration, as assessed by phosphorus magnetic resonance spectroscopy, and the development of profound motor and cognitive deficits. In contrast, capsaicin pre-treatment resulted in a significant reduction in post-traumatic edema formation (p<0.001), BBB permeability (p<0.001), free magnesium decline (p<0.01) and both motor and cognitive deficits (p<0.001). We conclude that neurogenic inflammation may play an integral role in the development of edema and functional deficits following TBI, and that neuropeptides may be a novel target for development of interventional pharmacological strategies.A. J. Nimmo, I. Cernak, D. L. Heath, X. Hu, C. J. Bennett and R. Vinkhttp://www.elsevier.com/wps/find/journaldescription.cws_home/623063/description#descriptio
Yang-Baxter maps and the discrete KP hierarchy
No full textWe present a systematic construction of the discrete KP hierarchy in terms of Sato–Wilson-type shift operators. Reductions of the equations in this hierarchy to 1+1-dimensional integrable lattice systems are considered, and the problems that arise with regard to the symmetry algebra underlying the reduced systems as well as the ultradiscretizability of these systems are discussed. A scheme for constructing ultradiscretizable reductions that give rise to Yang–Baxter maps is explained in two explicit examples
GRAIL Crustal Thickness Archive
No full text<p>This archive contains crustal thickness models of the Moon derived from GRAIL (Gravity Recovery And Interior Laboratory) gravity. The original crustal thickness data were published in map form in <em>Wieczorek et al. </em>(2013).</p>
<p>Wieczorek, M. A., G. A. Neumann, F. Nimmo, W. S. Kiefer, G. J. Taylor, H. J. Melosh, R. J. Phillips, S. C. Solomon, J. C. Andrews-Hanna, S. W. Asmar, A. S. Konopliv, F. G. Lemoine, D. E. Smith, M. M. Watkins, J. G. Williams, M. T. Zuber, The crust of the Moon as seen by GRAIL, <em>Science</em>, <strong>339</strong>, 671-675, doi:10.1126/science.1231530, 2013.</p>
Bäcklund transformations for noncommutative anti-self-dual Yang-Mills equations
No full textWe present Bäcklund transformations for the non-commutative anti-self-dual Yang–Mills equations where the gauge group is G = GL(2) and use it to generate a series of exact solutions from a simple seed solution. The solutions generated by this approach are represented in terms of quasi-determinants and belong to a non-commutative version of the Atiyah–Ward ansatz. In the commutative limit, our results coincide with those by Corrigan, Fairlie, Yates and Goddard
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