Intraindividual comparison of human radial and internal thoracic arteries in vitro and the effect of preoperative calcium blocker therapy

The patency rate of radial artery (RA) conduits is considerably lower than that of internal thoracic artery (ITA) grafts and the evidence suggests that this is due to a clinically suspected higher incidence of vasospasm. The aim of this study was, therefore, to compare intraindividually the pharmacological reactivity of RA with that of ITA. Both RA and ITA were taken from the same patients and investigated in parallel. Changes in tone were monitored isometrically on ring preparations from both arteries in organ baths with modified Krebs-Henseleit solution containing 1.25 mm calcium chloride at 1 g passive preload. In intraindividual comparisons maximal receptor-mediated contractile responses to noradrenaline and endothelin-1 and endothelium-dependent acetylcholine-induced relaxant responses revealed no differences between both arteries. By contrast, depolarization-induced contractions to potassium chloride (KCl) appeared to be significantly higher in RA than in ITA. Further analysis, however, revealed that this difference was due to preoperative calcium entry blocker (Ca(2+)eB) therapy. Compared with control tissues, maximal responses to KCl were significantly attenuated in the ITA but unchanged in RA when arteries were obtained from patients with preoperative Ca(2+)eB therapy. The present results suggested that functional responses to pharmacological stimuli of both RA and ITA were quite similar. Preoperative Ca(2+)eB therapy, however, attenuated markedly responses to KCl of the ITA leaving those of RA unchanged. These results, demonstrating a lower sensitivity to Ca(2+)eB of RA, therefore suggested that in addition to Ca(2+)eB other classes of drug may be more effective at reducing the propensity of RA conduits to vasospasm.

Effect of mesh distortion on the accuracy of high order vorticity-velocity CFD approaches

The numerical solution of the incompressible Navier-Stokes equations offers an alternative to experimental analysis of fluid-structure interaction (FSI). We would save a lot of time and effort and help cut back on costs, if we are able to accurately model systems by these numerical solutions. These advantages are even more obvious when considering huge structures like bridges, high rise buildings or even wind turbine blades with diameters as large as 200 meters. The modeling of such processes, however, involves complex multiphysics problems along with complex geometries. This thesis focuses on a novel vorticity-velocity formulation called the Kinematic Laplacian Equation (KLE) to solve the incompressible Navier-stokes equations for such FSI problems. This scheme allows for the implementation of robust adaptive ordinary differential equations (ODE) time integration schemes, allowing us to tackle each problem as a separate module. The current algortihm for the KLE uses an unstructured quadrilateral mesh, formed by dividing each triangle of an unstructured triangular mesh into three quadrilaterals for spatial discretization. This research deals with determining a suitable measure of mesh quality based on the physics of the problems being tackled. This is followed by exploring methods to improve the quality of quadrilateral elements obtained from the triangles and thereby improving the overall mesh quality. A series of numerical experiments were designed and conducted for this purpose and the results obtained were tested on different geometries with varying degrees of mesh density.

Studying students' opinions : using surveys in writing program assessment

Administrators of writing programs are regularly faced with the problem of assessing the learning that students gain in their coursework. Many methods of assessment exist, but most have some problems associated with them related to the amount of time it takes to perform the study or the scope of the knowledge gained relative to number of participants or volume of information collected. This pilot study investigates the use of surveys of student opinion for their potential to assess composition instruction at Michigan Technological University. The primary goal of this pilot study is to test the effectiveness of using data collected in surveys to make recommendations for improvement of the composition program at Michigan Tech. The report concludes with recommendations for additional study and refinements to the instruments used.

Effect of high order interpolation in the stability and efficiency of the time-integration process in vorticity-velocity CFD algorithms

The numerical solution of the incompressible Navier-Stokes Equations offers an effective alternative to the experimental analysis of Fluid-Structure interaction i.e. dynamical coupling between a fluid and a solid which otherwise is very complex, time consuming and very expensive. To have a method which can accurately model these types of mechanical systems by numerical solutions becomes a great option, since these advantages are even more obvious when considering huge structures like bridges, high rise buildings, or even wind turbine blades with diameters as large as 200 meters. The modeling of such processes, however, involves complex multiphysics problems along with complex geometries. This thesis focuses on a novel vorticity-velocity formulation called the KLE to solve the incompressible Navier-stokes equations for such FSI problems. This scheme allows for the implementation of robust adaptive ODE time integration schemes and thus allows us to tackle the various multiphysics problems as separate modules. The current algorithm for KLE employs a structured or unstructured mesh for spatial discretization and it allows the use of a self-adaptive or fixed time step ODE solver while dealing with unsteady problems. This research deals with the analysis of the effects of the Courant-Friedrichs-Lewy (CFL) condition for KLE when applied to unsteady Stoke’s problem. The objective is to conduct a numerical analysis for stability and, hence, for convergence. Our results confirmthat the time step ∆t is constrained by the CFL-like condition ∆t ≤ const. hα, where h denotes the variable that represents spatial discretization.

Studies of spatial clustering of inertial particles in turbulence

We present studies of the spatial clustering of inertial particles embedded in turbulent flow. A major part of the thesis is experimental, involving the technique of Phase Doppler Interferometry (PDI). The thesis also includes significant amount of simulation studies and some theoretical considerations. We describe the details of PDI and explain why it is suitable for study of particle clustering in turbulent flow with a strong mean velocity. We introduce the concept of the radial distribution function (RDF) as our chosen way of quantifying inertial particle clustering and present some original works on foundational and practical considerations related to it. These include methods of treating finite sampling size, interpretation of the magnitude of RDF and the possibility of isolating RDF signature of inertial clustering from that of large scale mixing. In experimental work, we used the PDI to observe clustering of water droplets in a turbulent wind tunnel. From that we present, in the form of a published paper, evidence of dynamical similarity (Stokes number similarity) of inertial particle clustering together with other results in qualitative agreement with available theoretical prediction and simulation results. We next show detailed quantitative comparisons of results from our experiments, direct-numerical-simulation (DNS) and theory. Very promising agreement was found for like-sized particles (mono-disperse). Theory is found to be incorrect regarding clustering of different-sized particles and we propose a empirical correction based on the DNS and experimental results. Besides this, we also discovered a few interesting characteristics of inertial clustering. Firstly, through observations, we found an intriguing possibility for modeling the RDF arising from inertial clustering that has only one (sensitive) parameter. We also found that clustering becomes saturated at high Reynolds number.

Dynamic properties of wood using the Split-Hopkinson Pressure Bar

Strain rate significantly affects the strength of a material. The Split-Hopkinson Pressure Bar (SHPB) was initially used to study the effects of high strain rate (~103 1/s) testing of metals. Later modifications to the original technique allowed for the study of brittle materials such as ceramics, concrete, and rock. While material properties of wood for static and creep strain rates are readily available, data on the dynamic properties of wood are sparse. Previous work using the SHPB technique with wood has been limited in scope to variability of only a few conditions and tests of the applicability of the SHPB theory on wood have not been performed. Tests were conducted using a large diameter (3.0 inch (75 mm)) SHPB. The strain rate and total strain applied to a specimen are dependent on the striker bar length and velocity at impact. Pulse shapers are used to further modify the strain rate and change the shape of the strain pulse. A series of tests were used to determine test conditions necessary to produce a strain rate, total strain, and pulse shape appropriate for testing wood specimens. Hard maple, consisting of sugar maple (Acer saccharum) and black maple (Acer nigrum), and eastern white pine (Pinus strobus) specimens were used to represent a dense hardwood and a low-density soft wood. Specimens were machined to diameters of 2.5 and 3.0 inches and an assortment of lengths were tested to determine the appropriate specimen dimensions. Longitudinal specimens of 1.5 inch length and radial and tangential specimens of 0.5 inch length were found to be most applicable to SHPB testing. Stress/strain curves were generated from the SHPB data and validated with 6061-T6 aluminum and wood specimens. Stress was indirectly corroborated with gaged aluminum specimens. Specimen strain was assessed with strain gages, digital image analysis, and measurement of residual strain to confirm the strain calculated from SHPB data. The SHPB was found to be a useful tool in accurately assessing the material properties of wood under high strain rates (70 to 340 1/s) and short load durations (70 to 150 μs to compressive failure).

Dynamics of settling charged particles in turbulence : theory and experiments

It has been proposed that inertial clustering may lead to an increased collision rate of water droplets in clouds. Atmospheric clouds and electrosprays contain electrically charged particles embedded in turbulent flows, often under the influence of an externally imposed, approximately uniform gravitational or electric force. In this thesis, we present the investigation of charged inertial particles embedded in turbulence. We have developed a theoretical description for the dynamics of such systems of charged, sedimenting particles in turbulence, allowing radial distribution functions to be predicted for both monodisperse and bidisperse particle size distributions. The governing parameters are the particle Stokes number (particle inertial time scale relative to turbulence dissipation time scale), the Coulomb-turbulence parameter (ratio of Coulomb ’terminalar speed to turbulence dissipation velocity scale), and the settling parameter (the ratio of the gravitational terminal speed to turbulence dissipation velocity scale). For the monodispersion particles, The peak in the radial distribution function is well predicted by the balance between the particle terminal velocity under Coulomb repulsion and a time-averaged ’drift’ velocity obtained from the nonuniform sampling of fluid strain and rotation due to finite particle inertia. The theory is compared to measured radial distribution functions for water particles in homogeneous, isotropic air turbulence. The radial distribution functions are obtained from particle positions measured in three dimensions using digital holography. The measurements support the general theoretical expression, consisting of a power law increase in particle clustering due to particle response to dissipative turbulent eddies, modulated by an exponential electrostatic interaction term. Both terms are modified as a result of the gravitational diffusion-like term, and the role of ’gravity’ is explored by imposing a macroscopic uniform electric field to create an enhanced, effective gravity. The relation between the radial distribution functions and inward mean radial relative velocity is established for charged particles.

Changes in blood flow velocity in the middle and anterior cerebral arteries evoked by walking

PURPOSE: Transcranial Doppler sonography (TCD) is an established method for assessing changes in blood flow velocity (BFV) coupled to brain activity. Our objective was to investigate whether walking induces measurable changes in BFV in healthy subjects. METHODS: Changes in BFV in both middle cerebral arteries (MCAs) of 40 healthy adult subjects during walking on a treadmill were measured using bilateral TCD. In 8 of the 40 subjects, 1 anterior cerebral artery (ACA) was monitored simultaneously with the contralateral MCA. The percentage increase in BFV (BFVI%) compared with the baseline velocity (V(0)), the percentage decrease in BFV (BFVD%) compared with the V(0), and the normalized ACA-MCA ratio were analyzed. RESULTS: The overall mean (+/- standard deviation [SD]) V(0) was 59.9 +/- 11.6 cm/second in the left MCA and 60.1 +/- 12.9 cm/second in the right MCA. Women had higher V(0) values than men had. Walking evoked an initial mean overall BFVI% in both left (8.4 +/- 5.1%) and right MCAs (9.1 +/- 5.1%), followed by a decrease to below baseline values in 38 of 40 subjects. A statistically significant increase of the normalized ACA-MCA ratio was measured, indicating that changes in BFV in the ACA territory were coupled to brain activation during walking. CONCLUSIONS: The use of functional TCD showed different changes in BFV in the ACAs and MCAs during walking. This method may be an interesting tool for monitoring progress in patients with motor deficits of the legs, such as paresis.

Velocity recovery cycles of human muscle action potentials and their sensitivity to ischemia

This study was undertaken to test whether recovery cycle measurements can provide useful information about the membrane potential of human muscle fibers. Multifiber responses to direct muscle stimulation through needle electrodes were recorded from the brachioradialis of healthy volunteers, and the latency changes measured as conditioning stimuli were applied at interstimulus intervals of 2-1000 ms. In all subjects, the relative refractory period (RRP), which lasted 3.27 +/- 0.45 ms (mean +/- SD, n = 12), was followed by a phase of supernormality, in which the velocity increased by 9.3 +/- 3.4% at 6.1 +/- 1.3 ms, and recovered over 1 s. A broad hump of additional supernormality was seen at around 100 ms. Extra conditioning stimuli had little effect on the early supernormality but increased the later component. The two phases of supernormality resembled early and late afterpotentials, attributable respectively to the passive decay of membrane charge and potassium accumulation in the t-tubules. Five minutes of ischemia progressively prolonged the RRP and reduced supernormality, confirming that these parameters are sensitive to membrane depolarization. Velocity recovery cycles may provide useful information about altered muscle membrane potential and t-tubule function in muscle disease. Muscle Nerve, 2008.