No description available.

The prediction of grain entrainment rates in river flows is of great importance to an engineer, as the movement of sediment can cause permanent changes to the form and character of a river. One of the key elements in achieving accurate prediction of grain entrainment rates is the understanding of the near bed flow regime, as research has revealed the existence of a number of organised flow structures which are thought to control the magnitude of shear stress applied to the bed surface. However, most of the knowledge gained on these turbulent flow structures has been from experiments conducted over smooth walls often at low Reynolds numbers. Many geophysical flows differ greatly from this scenario, having flows with high Reynolds numbers and boundaries which are rough and deformable. A series of flume experiments have therefore been conducted to investigate whether the flow structures identified over smooth walls are also present over mixed grain sized sediment beds. The first experiment used a new flow measurement technique known as particle image velocimetry to record flow field measurements over a fixed bed. Both horizontal and vertical planes of the flow were investigated (at different times) in order to obtain an understanding of the three dimensional nature of the flow. A second set of experiments was conducted over the same fixed bed, but also involved the introduction of sediment grains into the flow upstream of the measurement area. The same techniques were used to examine the flow in this case, thus enabling significant differences between the circumstances to be identified. A third set of experiments was conducted over a natural sediment and in this case flow field measurements were taken at periods of high and low transport rates, a difference in transport rate being associated with bed armouring. A short time series of near instantaneous velocity field measurements were recorded for each experimental condition to aid the identification of the flow structures. Visual inspection of the time series revealed that sweeps and ejections occur at different scales, the smallest scaling with grain size or bed features and the largest scaling with flow depth.

No description available.

The exact mechanism underlying the coupling between breathing and locomotion is still unknown; the visceral piston theory is a putative mechanism but has gone largely untested. The study assessed the visceral piston theory by examining the effect of perturbations (vocalization and fluid ingestion) on the coupling of breathing and locomotion. 10 experienced runners performed a speed running trial (6.5 to 8.0 mph in 0.5 mph increments), followed by a vocalization trial and a fluid ingestion trial at their preferred running speed while on a treadmill. Continuous recordings of respiratory flow and single leg, tibial acceleration was acquired (500 Hz). Rating of perceived exertion for breathing (RPEB), effort (RPEE), stitch (RPES) and heart rate (HR) were also recorded during the trials. The magnitude (SIFTMAG) and timing (SIFTT) of step induced flow transients were determined, along with the breath cycle duration (BCD) and respiratory locomotor entrainment (RLE) ratios. RPEB, and HR showed an increase in all three trials, RPEE showed an increase in the speed trial and the fluid ingestion trial but not the vocalization trial. SIFTMAG had a significant increase post perturbation (vocalization and fluid ingestion). SIFTT increased significantly post fluid ingestion but not after the vocalization perturbation. RLE ratios were increased post fluid ingestion but not post vocalization perturbation, however BCD was reduced after vocalization trials. The SIFTMAG was increased as result of perturbations corresponding to respiratory flow suppression which could lead to increased respiratory load. A shift in timing after fluid ingestion is consistent with an increased mass of a visceral spring mass system. Four of ten runners experienced a stitch after fluid ingestion. These findings strongly support the visceral piston theory of RLE, and this becomes a plausible mechanism for the induction of a stitch in the side.

The exact mechanism underlying the coupling between breathing and locomotion is still unknown; the visceral piston theory is a putative mechanism but has gone largely untested. The study assessed the visceral piston theory by examining the effect of perturbations (vocalization and fluid ingestion) on the coupling of breathing and locomotion. 10 experienced runners performed a speed running trial (6.5 to 8.0 mph in 0.5 mph increments), followed by a vocalization trial and a fluid ingestion trial at their preferred running speed while on a treadmill. Continuous recordings of respiratory flow and single leg, tibial acceleration was acquired (500 Hz). Rating of perceived exertion for breathing (RPEB), effort (RPEE), stitch (RPES) and heart rate (HR) were also recorded during the trials. The magnitude (SIFTMAG) and timing (SIFTT) of step induced flow transients were determined, along with the breath cycle duration (BCD) and respiratory locomotor entrainment (RLE) ratios. RPEB, and HR showed an increase in all three trials, RPEE showed an increase in the speed trial and the fluid ingestion trial but not the vocalization trial. SIFTMAG had a significant increase post perturbation (vocalization and fluid ingestion). SIFTT increased significantly post fluid ingestion but not after the vocalization perturbation. RLE ratios were increased post fluid ingestion but not post vocalization perturbation, however BCD was reduced after vocalization trials. The SIFTMAG was increased as result of perturbations corresponding to respiratory flow suppression which could lead to increased respiratory load. A shift in timing after fluid ingestion is consistent with an increased mass of a visceral spring mass system. Four of ten runners experienced a stitch after fluid ingestion. These findings strongly support the visceral piston theory of RLE, and this becomes a plausible mechanism for the induction of a stitch in the side.

archives@tulane.edu / 1 / Miguel Velasquez

Neural entrainment is a phenomenon whereby neural oscillations adjust their frequency to synchronize with the periodic vibration of external stimuli. Research suggests that neural entrainment may help explain the relationship between music education and more optimal cognitive performance later in development. This dissertation tested whether sensory entrainment caused short-term cognitive and motor performance benefits in a young adult sample, and whether entrainment or performance were impacted by stimulus parameters like modality or rhythm or individual differences in attentional ability and music training. Participants (N= 47) were asked to report the extent and type (e.g. instrumental, vocal) of music experience and severity of ADHD symptoms, and then were exposed to repetitive 1.25-Hz or arrhythmic visual or auditory stimuli with interlaced Flanker test items, while EEG was recorded. At some points in the experiment participants were additionally tasked with tapping along to the 1.25-Hz beat through both beat stimuli and gaps. Some entrainment and performance effects were congruent with findings from prior literature, while many other hypotheses regarding entrainment effects were not supported. In terms of individual differences, neither music training nor ADHD symptoms impacted entrainment, but ADHD did impact the effects of entrainment stimuli on Flanker reaction time, with higher ADHD symptoms predicting worse performance during periods of rhythmic stimulation. Lastly and surprisingly, while neither entrainment, music training, nor ADHD symptoms impacted beat-keeping performance in general, ADHD symptoms predicted better beat-keeping during stimulus gap periods. Results in general paint a complicated picture of acute entrainment effects and individual differences. / Doctor of Philosophy / Neural entrainment is a phenomenon whereby neural oscillations adjust their frequency to synchronize with the periodic vibration of external stimuli. Research suggests that neural entrainment may help explain the relationship between music education and more optimal cognitive performance later in development. This dissertation tested whether sensory entrainment caused short-term cognitive and motor performance benefits in a young adult sample, and whether entrainment or performance were impacted by stimulus parameters like modality or rhythm or individual differences in attentional ability and music training. Participants (N= 47) were asked to report the extent and type (e.g. instrumental, vocal) of music experience and severity of ADHD symptoms, and then were exposed to repetitive 1.25-Hz or arrhythmic visual or auditory stimuli with interlaced Flanker test items, while EEG was recorded. At some points in the experiment participants were additionally tasked with tapping along to the 1.25-Hz beat through both beat stimuli and gaps. Some entrainment and performance effects were congruent with findings from prior literature, while many other hypotheses regarding entrainment effects were not supported. In terms of individual differences, neither music training nor ADHD symptoms impacted entrainment, but ADHD did impact the effects of entrainment stimuli on Flanker reaction time, with higher ADHD symptoms predicting worse performance during periods of rhythmic stimulation. Lastly and surprisingly, while neither entrainment, music training, nor ADHD symptoms impacted beat-keeping performance in general, ADHD symptoms predicted better beat-keeping during stimulus gap periods. Results in general paint a complicated picture of acute entrainment effects and individual differences.

Clouds are one of the major uncertainties in climate change predictions caused by their complex structure and dynamics. Numerous cloud processes are acting from cloud-scale down to mm-scale and interplay with each other as well as with atmospheric processes. This complexity on the one hand and the high spatial resolution required to analyse the small scale processes on the other hand cause difficulties in cloud research. One important and until now insufficiently understood process in cloud microphysics is the entrainment process. It defines the turbulent transport of sub-saturated environmental air into the cloud region. Subsequent mixing leads to the evaporation of cloud droplets resulting in negatively buoyant air at cloud edge. One distinguishes between two types of entrainment processes: cloud top and lateral entrainment. While the first type is mostly detected at the top of stratiform clouds, lateral entrainment plays an important role for the dynamics of cumulus clouds. Within in this thesis, highly-resolved measurements with a resolution down to the centimeter scale performed with the helicopter-borne measurement payload ACTOS (Airborne Cloud Turbulence Observation System) are used to study both types of entrainment processes. Shear-induced cloud top entrainment leads to a turbulent inversion layer (TIL) atop of a stratocumulus layer consisting of clear air. The TIL seems to be coupled with the underlying cloud layer due to the turbulence intensity. With increasing thickness of the TIL the turbulence inside is damped monotonically leading to a maximum layer thickness and inhibiting direct mixing between cloud top and free troposphere. At the edges of shallow trade wind cumuli, shear-induced lateral entrainment generates a subsiding shell. Its evolution is analysed based on detailed measurements in continuously developing shallow cumuli. With the cloud evolution, the subsiding shell grows at the expense of the cloud core region and an increasing downdraft velocity is observed within this region. These observations are confirmed with the simulation of an idealised subsiding shell. The results present unique observations at the edges of clouds and are an appreciable progress in cloud research which decisively influence future research.

The design of smoke management systems for buildings such as atria, covered shopping malls and sports arenas require appropriate calculation methods to predict the volume of smoky gases produced in the event of a fire. The volume of smoke must be calculated in order to determine the required fan capacity or ventilator area for a smoke management system. In design, consideration is often given to entrainment of air into a smoke flow from a compartment opening that subsequently spills and rises into an adjacent atrium void. This type of plume is commonly known as a thermal spill plume. There has been much controversy over the validity of various entrainment calculation methods for the spill plume and there are considerable differences in the calculated smoke production rates using these methods. There are also scenarios involving the spill plume where design guidance is very limited. Whilst over-sizing of the required smoke exhaust can be uneconomical, under-sizing can compromise the design objectives. This work attempts to rigorously characterises thermal spill plume entrainment using new data obtained from an extensive series of 1/10th physical scale modelling experiments, supported by numerical modelling using Computational Fluid Dynamics. Spill plume behaviour and subsequent entrainment appears to be specifically dependent on the characteristics of the layer flow below spill edge, particularly in terms of the width and the depth of the flow. Plumes generated from narrow, deep layer flows entrain air at a greater rate with respect to height compared to plumes generated from wide, shallow layers. The findings of this work go some way to explain and reconcile differences in entrainment reported between previous studies. New guidance has been developed for the thermal spill plume in smoke management design, in the form of a range of new simplified design formulae,improvements to analytical calculation methods and an initial assessment of the use of numerical modelling using Computational Fluid Dynamics.

Oscillations and rhythms are measured in the brain through large-scale measures like EEG (electroencephalogram) and LFP (Local Field Potential). Particularly, cortical gamma rhythms (30-90 Hz) found in different brain regions are correlated with different cognitive states. Despite vast differences in the range frequencies in gamma rhythms, the regions communicate to complete high-level tasks. One way in which this takes place is entrainment, where the postsynaptic group phase-lock to the rhythmic input from the presynaptic group (constant phase-shift). Mathematical models of the neurons and the neural networks are proposed to uncover the mechanisms behind experimentally observed phenomena. Most works have used homogeneous models of spiking networks. These simplified models provide a valuable understanding of neural dynamics. However, neural heterogeneity (variation in the neural or network parameters) has been experimentally observed and shown to have a non-trivial effect on many neural processes. Few studies have dealt with the role of different types of neural heterogeneity in the entrainment of a large network, and how it affects the frequency range the neural network entrains to. In this project, we aimed to show how different types of network heterogeneity affect the ability of the networks to entrain to gamma frequencies. We used the Pyramidal-Interneuronal Network Gamma (PING) model, a model consisting of excitatory pyramidal cells (E-cells) and inhibitory interneurons (I-cells) that are synaptically connected and generate gamma oscillations. We show that heterogeneity in the synaptic conductance from excitatory neurons to inhibitory neurons greatly increases the frequency range over which the network can entrain. The mechanism that allows this to happen requires the heterogeneity to 1. Create an I-cell excitability gradient; 2. Introduce input synchrony difference among the I-cells. The entrained I-cell subsets formed under these two conditions are necessary for well-enhanced entrainment as they support the entrainment of the whole network through feedback inhibition. This improvement is shown to be robust in large parameter space.