840 research outputs found
On the dynamics of vortex modes within magnetic islands
Recent work investigating the interaction of magnetic islands with
micro-turbulence has uncovered the striking observation of large scale vortex
modes forming within the island structure [W.A. Hornsby {\it et al.}, Phys.
Plasmas {\bf 17} 092301 (2010)]. These electrostatic vortices are found to be
the size of the island and are oscillatory. It is this oscillatory behaviour
and the presence of turbulence that leads us to believe that the dynamics are
related to the Geodesic Acoustic Mode (GAM), and it is this link that is
investigated in this paper.
Here we derive an equation for the GAM in the MHD limit, in the presence of a
magnetic island modified three-dimensional axisymmetric geometry. The
eigenvalues and eigenfunctions are calculated numerically and then utilised to
analyse the dynamics of oscillatory large-scale electrostatic potential
structures seen in both linear and non-linear gyro-kinetic simulations
The linear tearing instability in three dimensional, toroidal gyrokinetic simulations
Linear gyro-kinetic simulations of the classical tearing mode in
three-dimensional toroidal geometry were performed using the global gyro
kinetic turbulence code, GKW . The results were benchmarked against a
cylindrical ideal MHD and analytical theory calculations. The stability, growth
rate and frequency of the mode were investigated by varying the current
profile, collisionality and the pressure gradients. Both collision-less and
semi-collisional tearing modes were found with a smooth transition between the
two. A residual, finite, rotation frequency of the mode even in the absense of
a pressure gradient is observed which is attributed to toroidal finite
Larmor-radius effects. When a pressure gradient is present at low
collisionality, the mode rotates at the expected electron diamagnetic
frequency. However the island rotation reverses direction at high
collisionality. The growth rate is found to follow a scaling with
collisional resistivity in the semi-collisional regime, closely following the
semi-collisional scaling found by Fitzpatrick. The stability of the mode
closely follows the stability using resistive MHD theory, however a
modification due to toroidal coupling and pressure effects is seen
Physiological Effects of Aquatic Exercise on Cognitive Function in the Aging Population
Neurocognitive decline, including Alzheimer’s disease and other forms of dementia, is considered to be the world’s fastest growing disease (Alzheimer\u27s Association, 2011). Due to this escalation, research focused on determining causes, accelerants, impeding factors, and preventative strategies has become a focus of interest within the field. One of the principal points of study is the role that exercise plays in the maintenance or fortification against neurocognitive decline. Though there is a robust library of research focused on the effects of land-based exercise on cognitive function, currently there is no research that discusses the impact of aquatic-based exercise on these parameters. This paper will examine the effects of land-based exercise on cognitive function while bridging these results to the aquatic environment
Effects of Degree and Configuration of Hearing Loss on the Contribution of High- and Low-Frequency Speech Information to Bilateral Speech Understanding
Objectives: The purpose of this study was to examine the effects of degree and configuration of hearing loss on the use of, and benefit from, information in amplified high- and low-frequency speech presented in background noise.
Design: Sixty-two adults with a wide range of high- and low-frequency sensorineural hearing loss (5 to 115+ dB HL) participated in the study. To examine the contribution of speech information in different frequency regions, speech understanding in noise was assessed in multiple low- and high-pass filter conditions, as well as a band-pass (713 to 3534 Hz) and wideband (143 to 8976 Hz) condition. To increase audibility over a wide frequency range, speech and noise were amplified based on each individual\u27s hearing loss. A stepwise multiple linear regression approach was used to examine the contribution of several factors to (1) absolute performance in each filter condition and (2) the change in performance with the addition of amplified high- and low-frequency speech components.
Results: Results from the regression analysis showed that degree of hearing loss was the strongest predictor of absolute performance for low- and high-pass filtered speech materials. In addition, configuration of hearing loss affected both absolute performance for severely low-pass filtered speech and benefit from extending high-frequency (3534 to 8976 Hz) bandwidth. Specifically, individuals with steeply sloping high-frequency losses made better use of low-pass filtered speech information than individuals with similar low-frequency thresholds but less high-frequency loss. In contrast, given similar high-frequency thresholds, individuals with flat hearing losses received more benefit from extending high-frequency bandwidth than individuals with more sloping losses.
Conclusions: Consistent with previous work, benefit from speech information in a given frequency region generally decreases as degree of hearing loss in that frequency region increases. However, given a similar degree of loss, the configuration of hearing loss also affects the ability to use speech information in different frequency regions. Except for individuals with steeply sloping high-frequency losses, providing high-frequency amplification (3534 to 8976 Hz) had either a beneficial effect on, or did not significantly degrade, speech understanding. These findings highlight the importance of extended high-frequency amplification for listeners with a wide range of high-frequency hearing losses, when seeking to maximize intelligibility
Global gyrokinetic simulations of intrinsic rotation in ASDEX Upgrade Ohmic L-mode plasmas
Non-linear, radially global, turbulence simulations of ASDEX Upgrade (AUG)
plasmas are performed and the nonlinear generated intrinsic flow shows
agreement with the intrinsic flow gradients measured in the core of Ohmic
L-mode plasmas at nominal parameters. Simulations utilising the kinetic
electron model show hollow intrinsic flow profiles as seen in a predominant
number of experiments performed at similar plasma parameters. In addition,
significantly larger flow gradients are seen than in a previous flux-tube
analysis (Hornsby et al {\it Nucl. Fusion} (2017)). Adiabatic electron model
simulations can show a flow profile with opposing sign in the gradient with
respect to a kinetic electron simulation, implying a reversal in the sign of
the residual stress due to kinetic electrons. The shaping of the intrinsic flow
is strongly determined by the density gradient profile. The sensitivity of the
residual stress to variations in density profile curvature is calculated and
seen to be significantly stronger than to neoclassical flows (Hornsby et al
{\it Nucl. Fusion} (2017)). This variation is strong enough on its own to
explain the large variations in the intrinsic flow gradients seen in some AUG
experiments. Analysis of the symmetry breaking properties of the turbulence
shows that profile shearing is the dominant mechanism in producing a finite
parallel wave-number, with turbulence gradient effects contributing a smaller
portion of the parallel wave-vector
Improved Coinfection with Amphotropic Pseudotyped Retroviral Vectors
Amphotropic pseudotyped retroviral vectors have typically been used to infect target cells without prior concentration. Although this can yield high rates of infection, higher rates may be needed where highly efficient coinfection of two or more vectors is needed. In this investigation we used amphotropic retroviral vectors produced by the Plat-A cell line and studied coinfection rates using green and red fluorescent proteins (EGFP and dsRed2). Target cells were primary human fibroblasts (PHF) and 3T3 cells. Unconcentrated vector preparations produced a coinfection rate of ∼4% (defined as cells that are both red and green as a percentage of all cells infected). Optimized spinoculation, comprising centrifugation at 1200 g for 2 hours at 15°C, increased the coinfection rate to ∼10%. Concentration by centrifugation at 10,000 g or by flocculation using Polybrene increased the coinfection rate to ∼25%. Combining the two processes, concentration by Polybrene flocculation and optimized spinoculation, increased the coinfection rate to 35% (3T3) or >50% (PHF). Improved coinfection should be valuable in protocols that require high transduction by combinations of two or more retroviral vectors
Addressing the Confusion Within Periodization Research
In this editorial, we focus on recent problematic developments in sport science, and more specifically, problems related to periodization research. Primary areas discussed are (1) appreciation of history, (2) considerations for training studies, (3) the development of concepts, and (4) programming-driven training models
Addressing the Confusion within Periodization Research
In this editorial, we focus on recent problematic developments in sport science, and more specifically, problems related to periodization research. Primary areas discussed are (1) appreciation of history, (2) considerations for training studies, (3) the development of concepts, and (4) programming-driven training models
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