Goal-directed therapy in intraoperative fluid and hemodynamic management.

Intraoperative fluid management is pivotal to the outcome and success of surgery, especially in high-risk procedures. Empirical formula and invasive static monitoring have been traditionally used to guide intraoperative fluid management and assess volume status. With the awareness of the potential complications of invasive procedures and the poor reliability of these methods as indicators of volume status, we present a case scenario of a patient who underwent major abdominal surgery as an example to discuss how the use of minimally invasive dynamic monitoring may guide intraoperative fluid therapy

Mach 4 and Mach 8 axisymmetric nozzles for a shock tunnel

The performance of two axisymmetric nozzles which were designed to produce uniform, parallel flow with nominal Mach numbers of 4 and 8 is examined. A free-piston-driven shock tube was used to supply the nozzle with high-temperature, high-pressure test gas. The inviscid design procedure treated the nozzle expansion in two stages. Close to the nozzle throat, the nozzle wall was specified as conical and the gas flow was treated as a quasi-one-dimensional chemically-reacting flow. At the end of the conical expansion, the gas was assumed to be calorically perfect, and a contoured wall was designed (using method of characteristics) to convert the source flow into a uniform and parallel flow at the end of the nozzle. Performance was assessed by measuring Pitot pressures across the exit plane of the nozzles and, over the range of operating conditions examined, the nozzles produced satisfactory test flows. However, there were flow disturbances in the Mach 8 nozzle flow that persisted for significant times after flow initiation

Currents between tethered electrodes in a magnetized laboratory plasma

Laboratory experiments on important plasma physics issues of electrodynamic tethers were performed. These included current propagation, formation of wave wings, limits of current collection, nonlinear effects and instabilities, charging phenomena, and characteristics of transmission lines in plasmas. The experiments were conducted in a large afterglow plasma. The current system was established with a small electron-emitting hot cathode tethered to an electron-collecting anode, both movable across the magnetic field and energized by potential difference up to V approx.=100 T(sub e). The total current density in space and time was obtained from complete measurements of the perturbed magnetic field. The fast spacecraft motion was reproduced in the laboratory by moving the tethered electrodes in small increments, applying delayed current pulses, and reconstructing the net field by a linear superposition of locally emitted wavelets. With this technique, the small-amplitude dc current pattern is shown to form whistler wings at each electrode instead of the generally accepted Alfven wings. For the beam electrode, the whistler wing separates from the field-aligned beam which carries no net current. Large amplitude return currents to a stationary anode generate current-driven microinstabilities, parallel electric fields, ion depletions, current disruptions and time-varying electrode charging. At appropriately high potentials and neutral densities, excess neutrals are ionized near the anode. The anode sheath emits high-frequency electron transit-time oscillations at the sheath-plasma resonance. The beam generates Langmuir turbulence, ion sound turbulence, electron heating, space charge fields, and Hall currents. An insulated, perfectly conducting transmission line embedded in the plasma becomes lossy due to excitation of whistler waves and magnetic field diffusion effects. The implications of the laboratory observations on electrodynamic tethers in space are discussed

Computational estimation of haemodynamics and tissue stresses in abdominal aortic aneurysms

'o e Abdominal aortic aneurysm is a vascular disease involving a focal dilation of the aorta. The exact cause is unknown but possibilities include infection and weakening of the connective tissue. Risk factors include a history of atherosclerosis, current smoking and a close relative with the disease. Although abdominal aortic aneurysm can affect anyone, it is most often seen in older men, and may be present in up to 5.9 % of the population aged 80 years. Biomechanical factors such as tissue stresses and shear stresses have been shown to play a part in aneurysm progression, although the specific mechanisms are still to be determined. The growth rate of the abdominal aortic aneurysm has been found to correlate with the peak stress in the aneurysm wall and the blood flow is thought to influence disease development. In order to resolve the connections between biology and biomechanics, accurate estimations of the forces involved are required. The first part of this thesis assesses the use of computational fluid dynamics for modelling haemodynamics in abdominal aortic aneurysms. Boundary conditions from the literature o

Rotating Detonation Combustion: A Computational Study for Stationary Power Generation

The increased availability of gaseous fossil fuels in The US has led to the substantial growth of stationary Gas Turbine (GT) usage for electrical power generation. In fact, from 2013 to 2104, out of the 11 Tera Watts-hour per day produced from fossil fuels, approximately 27% was generated through the combustion of natural gas in stationary GT. The thermodynamic efficiency for simple-cycle GT has increased from 20% to 40% during the last six decades, mainly due to research and development in the fields of combustion science, material science and machine design. However, additional improvements have become more costly and more difficult to obtain as technology is further refined. An alternative to improve GT thermal efficiency is the implementation of a combustion regime leading to pressure-gain; rather than pressure loss across the combustor. One concept being considered for such purpose is Rotating Detonation Combustion (RDC). RDC refers to a combustion regime in which a detonation wave propagates continuously in the azimuthal direction of a cylindrical annular chamber. In RDC, the fuel and oxidizer, injected from separated streams, are mixed near the injection plane and are then consumed by the detonation front traveling inside the annular gap of the combustion chamber. The detonation products then expand in the azimuthal and axial direction away from the detonation front and exit through the combustion chamber outlet.;In the present study Computational Fluid Dynamics (CFD) is used to predict the performance of Rotating Detonation Combustion (RDC) at operating conditions relevant to GT applications. As part of this study, a modeling strategy for RDC simulations was developed. The validation of the model was performed using benchmark cases with different levels of complexity. First, 2D simulations of non-reactive shock tube and detonation tubes were performed. The numerical predictions that were obtained using different modeling parameters were compared with analytical solutions in order to quantify the numerical error in the simulations. Additionally, experimental data from laboratory scale combustors was used to validate 2D and 3D numerical simulations. The effects of different modeling parameters on RDC predictions was also studied. The validated simulation strategy was then used to assess the performance of RDC for different combustion chamber geometries and operating conditions relevant to GT applications. As a result, the limiting conditions for which continuous detonation and pressure gain combustion can be achieved were predicted and the effect of operating conditions on flow structures and RDC performance was assessed.;The modeling strategy and the results from this study could be further used to design more efficient and more stable RDC systems

Advanced life systems hardware development for future missions

An examination of the pulse formation in an externalized vessel suggests that the vessel does not behave as a simple visco-elastic tube. Pressure-pulse waveform transducers are sensitive either to the pressure present at the vessel wall or to the volume of blood filling a region of tissue. Results of comparisons between intra-and extra-vascular pressure recordings suggest that changes in vasomotor tone and transducer-vessel pressures may be the greatest contributors to the divergence of extra-vascular waveforms from intra-vascular waveforms

Development, Validation, and Clinical Application of a Numerical Model for Pulse Wave Velocity Propagation in a Cardiovascular System with Application to Noninvasive Blood Pressure Measurements

High blood pressure blood pressure is an important risk factor for cardiovascular disease and affects almost one-third of the U.S. adult population. Historical cuff-less non-invasive techniques used to monitor blood pressure are not accurate and highlight the need for first principal models. The first model is a one-dimensional model for pulse wave velocity (PWV) propagation in compliant arteries that accounts for nonlinear fluids in a linear elastic thin walled vessel. The results indicate an inverse quadratic relationship (R^2=.99) between ejection time and PWV, with ejection time dominating the PWV shifts (12%). The second model predicts the general relationship between PWV and blood pressure with a rigorous account of nonlinearities in the fluid dynamics, blood vessel elasticity, and finite dynamic deformation of a membrane type thin anisotropic wall. The nonlinear model achieves the best match with the experimental data. To retrieve individual vascular information of a patient, the inverse problem of hemodynamics is presented, calculating local orthotropic hyperelastic properties of the arterial wall. The final model examines the impact of the thick arterial wall with different material properties in the radial direction. For a hypertensive subject the thick wall model provides improved accuracy up to 8.4% in PWV prediction over its thin wall counterpart. This translates to nearly 20% improvement in blood pressure prediction based on a PWV measure. The models highlight flow velocity is additive to the classic pressure wave, suggesting flow velocity correction may be important for cuff-less, non-invasive blood pressure measures. Systolic flow correction of the measured PWV improves the R2 correlation to systolic blood pressure from 0.81 to 0.92 for the mongrel dog study, and 0.34 to 0.88 for the human subjects study. The algorithms and insight resulting from this work can enable the development of an integrated microsystem for cuff-less, non-invasive blood pressure monitoring

Material phase change under extreme domain confinement in laser material interaction

Laser has been widely applied in the science and industry fields because of the good spatial and temporal coherence and narrow spectrum. And the spatial confinement is common in the laser-assisted manufacturing field and it results in the change of the manufacturing process. However, due to the short time duration and high energy, the underlying physics is hard to be probed by experiment. Molecular dynamic (MD) simulation is employed to investigate the phenomenon related to the spatial confinement which includes the shock wave, wall confinement in cold sintering and laser induced breakdown spectroscopy (LIBS) enhancement and the tip confinement in surface nanostructuring. Existence of the shock wave affects the phase change and stress wave development and propagation significantly. It suppressed the bubble growth and shortened their lifetime. No effect from shock wave on the stress wave in solid was observed. The absorption depth and laser fluence played important roles in the stress wave formation and evolution. Secondary stress wave in the target occurred because of the ablated cluster re-deposition. The final cold-sintered structure was found to be nanocrystalline. Smaller nanoparticles were easy to reconstruct, but the final structure was more destructed, and structural defects were observed. For larger particles, the final cold-sintered structure was partially nanocrystalline. The orientation-radial distribution function (ODF) was developed to investigate the degree of orientation twisting. It was proved to be more comprehensive than radial distribution function (RDF) in structure analysis for the additional angle information it provides. Spatial confinement was found effective in improving the sensitivity of laser-induced breakdown spectroscopy (LIBS). The temperature, pressure and number density of the shock wave were observed to increase dramatically immediately after the reflection from the wall. The reflected shock wave and the forward-moving shock wave had a strong collision, and such an atomic collision/friction made the velocity of the shock wave decreases to almost zero after reflection. A temperature rise as high as 218 K was observed for the shock wave front after the wall reflection. More importantly, the temperature of the plume is enhanced dramatically from 89 K to 132 K. Also this high temperature was maintained for quite a long time. This explains the sensitivity enhancement in the spatial confinement of LIBS. Nanoscale-tip based laser surface nanostructuring is a promising technique for ultrahigh density data storage and nanoelectronics industries. The phase change (e.g. melting, phase explosion, and solidification/re-crystallization) within the tip-substrate region is extremely confined at the scale of a few nm. Such extreme domain constraint could significantly affect the structuring process and the tip apex profile. On the other hand, little is known about this extremely confined phase change by both computer modeling and experiment. In this work, systematic atomistic modeling is employed to explore the tip-confinement effect on the surface nanostructuring. Material ablation is trapped by the tip and the number of atoms flying out from the substrate decreases due to the tip-confinement. Although large atom-clusters are observed in tip-free scenario, no such clusters are observed in tip-based surface nanostructuring. This is favorable for making nanoscale surface structures. Tip apex oscillation occurs because of its interaction with the substrate. The effect of tip-substrate distance and laser fluence on the surface nanostructuring is investigated in detail. The profile of the cone-shape crater in the substrate is not affected much by the tip-substrate distance. Instead, the laser fluence plays a dominant role in the final crater shape. The protrusion around the crater is affected by both the tip-substrate distance and the laser fluence. For the case of tip-substrate distance d= 7 nm, the protrusion is flatter but wider than d= 1 nm and 2 nm. The tip-confinement also affects the recrystallization process after laser heating. The recrystallization time is longer for the case with tip confinement due to the interaction between the tip and the substrate. The tip apex is distorted during laser ablation. Both the tip-substrate distance and the laser fluence play import roles in the distortion. For the case of laser fluence E= 10 J/m2, the tip apex is reshaped to be blunt. The nanotip-laser interaction (near-field focusing) could change negatively due to the tip-apex reshaping, and this change will induce undesirable surface nanostructure change. Although the tip-substrate confinement significantly prolongs the solidification/recrystallization process in the substrate, it has little negative effect on the defects formed in the nanostructuring region