Neuromuscular and functional adaptations to whole body vibration exercise in older adults

University of Technology, Sydney. Faculty of Business.The ageing process is associated with sarcopema: a reduction in muscle mass, strength and power. Sarcopenia is responsible for diminished physical performance; it affects the ability to perform activities of daily living and can severely impact quality of life in older age. There is potentially no age group that can benefit more from interventions to combat reduced muscle strength and power than an older population. Whole body vibration (WBV) is a relatively new exercise intervention. WBV is suggested to improve strength and power by stimulating the neuromuscular system and inducing reflex muscle contractions. The potential for WBV to be used as a strength training intervention for an older population was the rationale behind this thesis. Study one was an investigation of the effects of eight weeks WBV on a range of physical perfonnance measures in a healthy, older population. Forty three, older adults (73.5 ± 4.5 yr, 168.2 ± 10.5 cm, 74.5 ± 11.1 kg) were divided into three groups: 15 to a WBV group (VIB), 13 to an exercise without vibration group (EX) and 15 into a control group (CONT). The VIB and EX group interventions consisted of three sessions per week for eight weeks. Outcome measures included isokinetic flexor and extensor strength of the hip, knee and ankle, one-legged postural steadiness (OLPS), sit-to-stand performance (STS), fast walk time and stair mobility. Following the eight week intervention, the VIB group significantly improved OLPS compared to the EX and CONT groups (p<0.05). The improvements in OLPS were significantly affected by baseline values, with the largest changes evident for VIB participants with a poorer initial score (p<0.01). WBV exercise can improve OLPS in a healthy, older population. As improvements in OLPS were related to baseline values, WBV as an intervention would appear to serve the most benefit for those that exhibit diminished postural control. The VIB group significantly improved ankle plantar flexor strength compared to the EX and CONT group (18.2%, 5.0%, 0.9%) (p<0.05). The VIB and EX groups both significantly improved knee extension strength compared to the CONT (8.1 %, 7.2%, - 2.0%) (p<0.05). There were no effects for hip flexor or extensor strength. The VIB and EX groups both showed improved STS (12.4%, 10.2%) and Sm fast walk (3.0%, 3.7%) compared to the control (p<0.05). There were no effects for stair mobility performance. While WBV exercise can be considered a plantar flexor strength training intervention, it appears to have a disproportional effect on lower limb strength. WB V did not facilitate knee extensor strength or physical performance measures to a greater degree than the same exercise program without vibration. The comparable change in physical perfonnance measures between the VIB and EX groups appears linked to similar gains in knee extensor strength. Further, these similar knee extensor strength improvements appears linked to the same body weight squats performed by both the VIB and EX groups. To explore the disproportional change in lower limb strength found in study one, study two was designed to investigate the neuromuscular activation of the ankle, knee and hip flexors and extensors during WBV. Ten healthy, older male participants (70.4 ± 4.9 yr, 176.9 ± 7.8 cm, 78.6 ± 12.0 kg) completed a number of static exercises with and without WBV. Activation of the soleus, gastrocnemius, tibialis anterior, vastus medialis, rectus femoris, biceps femoris, iliopsoas and gluteus maximus were recorded unilaterally with electromyography (EMG). EMG amplitude was normalised and analysed with respect to each individual's maximum isometric strength values. The absolute increases in EMG with vibration, above the non-vibration condition, were compared between muscle groups and exercise conditions. The increase in neuromuscular activity with WBV was significantly larger in the soleus and gastrocnemius than muscles higher up the leg (p<0.05). Furthermore, the increase in gastrocnemius neuromuscular activity was greatest when participants maintained a heel raise position. It appears that WBV should be prescribed as an exercise intervention that intends to specifically train the triceps surae musculature. The results of study one and two suggested WBV be considered a localised strength training intervention for older individuals which predominately targeted the plantar flexors. The aim of study three was to examine the efficacy of WBV for a frail, elderly population; to validate plantar flexor strength improvement with WBV and examine the neuromuscular mechanisms associated with this adaptation. Seventeen frail, older participants (88.2 ± 3.6 yr, 166.8 ± 8.2 cm, 71.7 ± 11.4 kg) were divided into two groups: ten to a WBV group (VIB) and seven to a control group (CONT). The VIB group undertook WBV three times per week for four weeks. Outcome measures included isometric and isokinetic plantar flexor strength, single leg balance performance and EMG of the gastrocnemius. The EMG signal was analysed for amplitude and median power frequency. EMG amplitude was normalised with respect to each individual's maximum isometric strength values. WBV had no effects on single leg balance performance in a frail , older population. This result is in contrast to study one that found significant improvements in OLPS in a population of healthy, older adults. In contrast to study one participants, the frail older adults in study three were unable to exercise on the WBV platform without firmly grasping the handlebars for support. The difficulty maintaining balance whilst undertaking WBV exercise is suggested to be a mediating factor behind the improvements in balance observed in study one but not three. Following the WBV intervention, the VIB group significantly improved isometric (40.5%) and isokinetic (32.4%) plantar flexor strength compared to the CONT group (1.5%, 2.9% respectively) group (p<0.05). The WBV group displayed a significant 32.3% increase and a 8.3% decrease in right medial gastrocnemius EMG peak amplitude and EMG median power frequency respectively during isometric plantar flexion (p<0.05). WBV can be considered an effective training intervention to improve plantar flexor strength in frail, older adults. It is speculated that increased plantar flexor strength with WBV exercise be explained at least in part by an improvement in motor unit synchronisation and efficiency

Long-term high frequency monitoring of a large borehole heat exchanger array

Borehole heat exchangers are a key technological element of geothermal energy systems and modelling their behaviour has received much attention. The aim in the work reported here has been to produce a reference data set that can be used in analysis of large borehole heat exchanger systems and validation of models of such. A monitoring exercise to collect high frequency data from a large ground heat exchanger array consisting of 56 boreholes over 38 months since the start of operations is reported. The system is associated with a mixed-use university building that has both heating and cooling loads. Ground heat exchange was found to be dominated by rejection of heat over the monitoring period and modest seasonal increases in temperatures. The ground heat exchanger installation has been additionally characterised by analysis of thermal response test data to estimate the effective ground and grout thermal properties. The utility of the measurements as a reference data set by presenting a model validation study is furthermore demonstrated. This has highlighted some features of the data that are more significant in systems of larger scale. These reference data are being made openly available for further work on performance analysis and model validation

Performance analysis of a large geothermal heating and cooling system

Ground Source Heat Pump systems can play an important role in reducing carbon emissions associated with building heating and cooling. The efficiencies and carbon emission savings achieved, partly depend on the optimization of the design, the control of the system and its reliability during extended operation. This paper reports the detailed investigation of the performance of a large system that includes fifty-six vertical borehole heat exchangers and four large heat pumps that provide both heating and cooling. High frequency data have been collected during the initial three years of operation that allow seasonal performance factors to be derived and detailed analysis of system operation. Annual performance has been found to be satisfactory overall but is highly variable depending on operating conditions and control system actions. A series of analyses have been carried out to investigate the roles of circulating pump energy, control system operation and dynamic behaviour. A series of recommendations concerned with better design for part-load operation, reduction in pump energy demands and more robust control systems, are made with a view to improved system design and operation. Data from the study are being made available for further work on performance analysis and model validation studies

Fermion correlators in non-abelian holographic superconductors

We consider fermion correlators in non-abelian holographic superconductors. The spectral function of the fermions exhibits several interesting features such as support in displaced Dirac cones and an asymmetric distribution of normal modes. These features are compared to similar ones observed in angle resolved photoemission experiments on high T_c superconductors. Along the way we elucidate some properties of p-wave superconductors in AdS_4 and discuss the construction of SO(4) superconductors.Comment: 49 pages, 11 figure

Visual population receptive fields in people with schizophrenia have reduced inhibitory surrounds

People with schizophrenia (SZ) experience abnormal visual perception on a range of visual tasks, which have been linked to abnormal synaptic transmission and an imbalance between cortical excitation and inhibition. However differences in the underlying architecture of visual cortex neurons, which might explain these visual anomalies, have yet to be reported in vivo. Here, we probe the neural basis of these deficits by using functional MRI (fMRI) and population receptive field (pRF) mapping to infer properties of visually responsive neurons in people with SZ. We employed a Difference-of-Gaussian (DoG) model to capture the centre-surround configuration of the pRF, providing critical information about the spatial scale of the pRFs inhibitory surround. Our analysis reveals that SZ is associated with reduced pRF size in early retinotopic visual cortex as well as a reduction in size and depth of the inhibitory surround in V1, V2 and V4. We consider how reduced inhibition might explain the diverse range of visual deficits reported in SZ. SIGNIFICANCE STATEMENT: People with schizophrenia (SZ) experience abnormal perception on a range of visual tasks, which has been linked to abnormal synaptic transmission and an imbalance between cortical excitation/inhibition. However associated differences in the underlying architecture of visual cortex neurons have yet to be reported in vivo. We used fMRI and population receptive field (pRF) mapping to demonstrate that the fine-grained functional architecture of visual cortex in people with SZ differs from unaffected controls. SZ is associated with reduced pRF size in early retinotopic visual cortex, largely due to reduced inhibitory surrounds. An imbalance between cortical excitation and inhibition could drive such a change in the centre-surround pRF configuration, and ultimately explain the range of visual deficits experienced in SZ

Classifying global catastrophic risks

We present a novel classification framework for severe global catastrophic risk scenarios. Extending beyond existing work that identifies individual risk scenarios, we propose analysing global catastrophic risks along three dimensions: the critical systems affected, global spread mechanisms, and prevention and mitigation failures. The classification highlights areas of convergence between risk scenarios, which supports prioritisation of particular research and of policy interventions. It also points to potential knowledge gaps regarding catastrophic risks, and provides an interdisciplinary structure for mapping and tracking the multitude of factors that could contribute to global catastrophic risks

Probes on D3-D7 Quark-Gluon Plasmas

We study the holographic dual model of quenched flavors immersed in a quark-gluon plasma with massless dynamical quarks in the Veneziano limit. This is modeled by embedding a probe D7 brane in a background where the backreaction of massless D7 branes has been taken into account. The background, and hence the effects, are perturbative in the Veneziano parameter N_f/N_c, therefore giving small shifts of all magnitudes like the constituent mass, the quark condensate, and several transport coefficients. We provide qualitative results for the effect of flavor degrees of freedom on the probes. For example, the meson melting temperature is enhanced, while the screening length is diminished. The drag force is also enhanced.Comment: 31 pages, 17 figure

Zero Sound in Strange Metallic Holography

One way to model the strange metal phase of certain materials is via a holographic description in terms of probe D-branes in a Lifshitz spacetime, characterised by a dynamical exponent z. The background geometry is dual to a strongly-interacting quantum critical theory while the probe D-branes are dual to a finite density of charge carriers that can exhibit the characteristic properties of strange metals. We compute holographically the low-frequency and low-momentum form of the charge density and current retarded Green's functions in these systems for massless charge carriers. The results reveal a quasi-particle excitation when z<2, which in analogy with Landau Fermi liquids we call zero sound. The real part of the dispersion relation depends on momentum k linearly, while the imaginary part goes as k^2/z. When z is greater than or equal to 2 the zero sound is not a well-defined quasi-particle. We also compute the frequency-dependent conductivity in arbitrary spacetime dimensions. Using that as a measure of the charge current spectral function, we find that the zero sound appears only when the spectral function consists of a single delta function at zero frequency.Comment: 20 pages, v2 minor corrections, extended discussion in sections 5 and 6, added one footnote and four references, version published in JHE

MHD models of Pulsar Wind Nebulae

Pulsar Wind Nebulae (PWNe) are bubbles or relativistic plasma that form when the pulsar wind is confined by the SNR or the ISM. Recent observations have shown a richness of emission features that has driven a renewed interest in the theoretical modeling of these objects. In recent years a MHD paradigm has been developed, capable of reproducing almost all of the observed properties of PWNe, shedding new light on many old issues. Given that PWNe are perhaps the nearest systems where processes related to relativistic dynamics can be investigated with high accuracy, a reliable model of their behavior is paramount for a correct understanding of high energy astrophysics in general. I will review the present status of MHD models: what are the key ingredients, their successes, and open questions that still need further investigation.Comment: 18 pages, 5 figures, Invited Review, Proceedings of the "ICREA Workshop on The High-Energy Emission from Pulsars and their Systems", Sant Cugat, Spain, April 12-16, 201

Lepton Acceleration in Pulsar Wind Nebulae

Pulsar Wind Nebulae (PWNe) act as calorimeters for the relativistic pair winds emanating from within the pulsar light cylinder. Their radiative dissipation in various wavebands is significantly different from that of their pulsar central engines: the broadband spectra of PWNe possess characteristics distinct from those of pulsars, thereby demanding a site of lepton acceleration remote from the pulsar magnetosphere. A principal candidate for this locale is the pulsar wind termination shock, a putatively highly-oblique, ultra-relativistic MHD discontinuity. This paper summarizes key characteristics of relativistic shock acceleration germane to PWNe, using predominantly Monte Carlo simulation techniques that compare well with semi-analytic solutions of the diffusion-convection equation. The array of potential spectral indices for the pair distribution function is explored, defining how these depend critically on the parameters of the turbulent plasma in the shock environs. Injection efficiencies into the acceleration process are also addressed. Informative constraints on the frequency of particle scattering and the level of field turbulence are identified using the multiwavelength observations of selected PWNe. These suggest that the termination shock can be comfortably invoked as a principal injector of energetic leptons into PWNe without resorting to unrealistic properties for the shock layer turbulence or MHD structure.Comment: 19 pages, 5 figures, invited review to appear in Proc. of the inaugural ICREA Workshop on "The High-Energy Emission from Pulsars and their Systems" (2010), eds. N. Rea and D. Torres, (Springer Astrophysics and Space Science series