No description available.

No description available.

No description available.

A digital-electronic video-rate reconstruction system for Magnetic Resonance Imaging (MRI) has been designed to first order. The maturation of ultra-fast acquisition techniques in MRI has produced the need for a reconstruction system that will enable dynamic processes to be viewed on-line. Conventional reconstruction hardware is not configured for real-time reconstruction and previous developments are limited in accuracy and flexibility. The real-time reconstruction system presented here consists of three main subsystems. A digitizer interfaces with an MR scanner to digitize data matrices of resolutions up to 256 x 256 at arbitrary rates up to video rates. A Fourier processor performs either 2D Fourier transformation or projection filtering on the digitized data at video-rates. A backprojector performs the backprojection operation on filtered-projection data at video-rates. The complete system would be able to reconstruct data acquired from nearly any acquisition technique. True real-time MRI is then possible.

Source: Dissertation Abstracts International, Volume: 35-02, Section: B, page: 0670. / Thesis (Ph.D.)--The Florida State University, 1973.

Pulmonary airway closure occurs in the elderly, emphysemics, and premature neonates, resulting in impaired gas exchange. The impetus of this study was to investigate the mechanisms relevant to the reopening of a collapsed pulmonary airway, where the walls and surrounding parenchyma collapse and are held in apposition by the cohesive properties of the lining fluid. The airway can reopen by either a positive pressure that pushes a bubble of air through the collapsed region, or a negative suction pressure in the collapsed region that pulls the bubble through the collapsed region. Three benchtop models were designed to study the untethered and tethered behavior of the system. The objective of this investigation was to examine how the fluid properties (viscosity, $\mu$, and surface tension, $\gamma$) and the structural characteristics of the models (effective diameter, D, longitudinal tension, T, fluid film thickness, H, and foam stiffness, K) affected the reopening of the airway. The pressure (P$\sb{\rm AW}$) required to move the meniscus down the tube at a constant velocity (U) was measured. In the untethered model, D was the dominant structural characteristic, causing P$\sb{\rm AW}$ to increase with a decrease in D. The relevant dimensionless parameters were also investigated. The dimensionless post-startup pressure (P$\sb{\rm AW}/(\gamma$/D)) increased monotonically with the Capillary Number (Ca = $\mu$U/$\gamma$). A 'yield pressure' of 3.69 $\gamma$/D, must be exceeded to initiate reopening. From these results, the reopening times and pressures were predicted for collapsed pulmonary airways under normal and disease conditions Two tethered models were designed to evaluate the coupling between the internal forces created by the airway lining fluid and the external forces produced by the surrounding parenchyma. In these studies, open-cell foam was used to mimic parenchyma. P$\sb{\rm AW}$ still scaled with $\gamma$/D, even though D was a dependent variable. Reducing the downstream suction (P$\sb{\rm DN}$), through tethering, caused an equivalent reduction in P$\sb{\rm AW}$ required to reopen the airway. A physiological dimensionless parameter $\lambda$ was derived from the transmeniscus pressure $(\rm P\sb{TRANS} = P\sb{AW} - P\sb{\rm DN}$) that represented the ratio of fluid and tethering forces in a collapsed airway. $\lambda$ was used to investigate whether parenchymal tethering would reopen collapsed airways in various disease states / acase@tulane.edu

In the present study, distinctive interactions of divalent cations and specific blockers with calcium channels were exploited to probe several functional features related to permeation through calcium channels in frog sympathetic neurons In the first study, our experiments have focused on resolving a paradox why the whole-cell current has not been observed under typical recording conditions for one type of calcium channel that is highly expressed in frog sympathetic neurons. These channels are referred to as Ef-channels, and they are present in the membrane at a density greater than the channels that carry ∼90% of whole-cell current in low Ba2+, but Ef-current has not been detected in low Ba2+. Using Ca2+, instead of Ba2+ as the charge carrier, we recorded a possible E-type current in frog sympathetic neurons. The current contributed about 12% of total current at peak voltage in 3 mM Ca2+ , and increased at voltages more hyperpolarized to the peak, reaching ∼40% at -30 mV. The presence of Ef-current in 3 mM Ca2+ , suggests a potential role of Ef-channels in regulating calcium influx into sympathetic neurons In the second study, the effect of Ba2+ on the block of N-channels by o-conotoxin GVIA (oCGVIA) was investigated. oCGVIA has been reported to be an irreversible blocker of N-type calcium channels (Cav 2.2). Surprisingly, oCGVIA block was rapidly reversed in 0 Ba2+. The off-rate of oCGVIA from N-channels was dependent on [Ba2+]o, since at an intermediate concentration (3 muM Ba2+), current recovered with a tau of 64 +/- 16 s (n = 6), significantly slower than in 0 Ba2+ but faster than in 3 mM Ba2+ In the final study, we examined Ca2+ permeation through N-channels. Models of permeation through voltage-gated Ca2+ channels have been constructed based on L-channel data. Specifically, our goal was to determine if an apparent high affinity binding site underlies channel selectivity for Ca2+, and an apparent low affinity binding site supports Ca2+ conductance in N-channels. Our data confirmed that Ca2+ binding inside N-channels is involved in both Ca2+ selectivity and conductance. (Abstract shortened by UMI.) / acase@tulane.edu

Using a modified form of Fogelson's continuum model of platelet aggregation, this work investigated relationships between platelet aggregation and the Reynolds number of the flow, the ratio of the formation of interplatelet links to the destruction of interplatelet links, and the platelet activation rate. Numerical simulations were performed via the finite element method using the FreeFem+ programming environment, and the flow domain was a straight vessel with a portion of the wall transiently releasing ADP into the flow to stimulate aggregation. The growth of an aggregate was found to be inversely related to the inlet Reynolds number. As the inlet Reynolds number increased, the overall profile of the aggregate decreased along with the concentration of platelets within the aggregate. For a given inlet Reynolds number, an upper limit was found for the ratio of link formation to link destruction, beyond which a stable aggregate could not be formed. A similar trend was observed for the rate of platelet activation, with a maximum rate of platelet activation for each inlet Reynolds number. Collectively, a region of stability was determined for the parameter values of the model, and the results compared well with experimental data / acase@tulane.edu

In this thesis, we provide a starting point for the development of computational models of both uterine and oviductal fluid mechanics. The method of regularized Stokeslets provides a framework that is easily implemented and may be adapted to include the full fluid-structure interactions that are observed physiologically We compare our computational results to analytic results in settings where the geometry of the channel (in 213) or tube (in 3D) undergoes small amplitude, symmetric contractions. These comparisons allow us to validate our numerics, and give us insight into the choice of our numerical parameters We demonstrate that our results for tapered channels and non-symmetric channels in two dimensions match the lubrication theory of Elad et al. [6]. We extend these simulations to three dimensions. In addition, we include an inserted catheter in our two-dimensional model, as in the finite element calculations presented by [25]. Finally, we present preliminary results of a full, three-dimensional model of a peristaltic tube with an inserted catheter / acase@tulane.edu

No description available.