Dynamic thermophysical measurements in space

The objective is to develop an accurate dynamic technique which, in a microgravity environment, would enable performance of thermophysical measurements on high-melting-point electrically conducting substances in their liquid state. In spite of the critical need in high temperature technologies related to spacecraft, nuclear reactors, effects of power laser radiation, and in validating theoretical models in related areas, no accurate data on thermophysical properties exist. This is primarily due to the limitation of the reliable steady-state techniques to temperatures below about 2000 K, and the accurate millisecond-resolution pulse heating techniques to the solid state of the specimen. The limitation of the millisecond-resolution techniques to temperatures below the melting point stems from the fact that the specimen collapses due to the gravitational force once it starts to melt. The rationale for the use of the microgravity is that by performing the dynamic experiments in a microgravity environment the specimen will retain its geometry, and thus it will be possible to extend the accurate thermophysical measurements to temperatures above the melting point of high-melting-point substances

Planting the Union Flag in Texas: The Campaigns of Major General Nathaniel P. Banks in the West

Nathaniel Banks in Texas Over the years Gary Joiner and others have offered examinations of various parts of General Nathaniel P. Banks’s Western command in the latter years of the Civil War; comes now a full review of Banks’s activities by Stephen A. Dupree. The author\u27s efforts remin...

Carotid endarterectomy outcome with vein or Dacron graft patch angioplasty and internal carotid artery shortening

AbstractObjective: This analysis of the outcome of carotid endarterectomy (CEA) was performed during a period of transition from the frequent use of autologous greater saphenous vein grafting to the frequent use of Dacron graft patch reconstruction and from the infrequent use to the moderate use of eversion plication shortening of the endarterectomized internal carotid artery segment. Methods: From 1990 to 1997, 697 consecutive primary CEAs were performed on 326 men (61 bilateral CEAs) and 272 women (38 bilateral CEAs) with a mean age (± SD) of 68 ± 9 years. The indications were transient ischemic attack in 31% of the patients, stroke or reversible ischemic neurologic deficit in 18%, global ischemia in 12%, and asymptomatic stenosis ≥70% in 39%. Patch reconstruction was performed in the 678 CEAs in which the arteriotomy extended distal to the internal carotid artery bulb (97%; 370 saphenous vein grafts, 308 Dacron grafts). Primary closure was used in the other 19 CEAs. Early in this series, saphenous vein patching frequently was performed, with a gradual transition to the frequent use of knitted Dacron grafts. Concurrent with this, the frequency of the shortening of the internal carotid artery increased from 7% to 40%. Postoperative duplex scans were obtained on 619 CEAs (91%). Results: There were four deaths (0.6%) in 30 days—three from myocardial infarction and one from hyperperfusion stroke. Thirteen strokes (1.9%), nine ipsilateral and four contralateral, occurred in 30 days. Four nonfatal strokes and one death occurred in the saphenous vein group (3.2%), and eight strokes and two deaths occurred in the Dacron graft group (1.4%; P = .16). The combined 30-day stroke or death rate was 2.3% (16/697), and the hospital rate was 1.7% (12/697). Of the three internal carotid artery occlusions, two were identified at 2 months (one Dacron graft, one saphenous vein) and one was identified at 1 year (Dacron graft). Nonocclusive (≥50%) restenosis was identified in 16 CEAs. Fifteen of these were in the internal carotid artery. The cumulative Kaplan-Meier method of life-table analysis for the ≥50% restenosis rate at 2 months, 6 months, 1 year, and 3 years for Dacron graft patched CEA was 1.7%, 2.3%, 8.8%, and 12.3% and for saphenous vein patched CEA was 0.3%, 0.3%, 0.3%, and 1.1% ( P < .0001). At the same time intervals, the ≥50% restenosis rate for internal carotid artery shortening was 1.0%, 2.5%, 13.7%, and 19.5%, and, when shortening was not done, the rate was 0.8%, 0.8%, 1.1%, and 3.1% (P < .0001). The ≥50% restenosis rate at the same intervals for women was 0.8%, 1.3%, 5.2%, and 8.9%, and, for men, the rate was 0.9%, 0.9%, 1.8%, and 2.5% (P = .11). Univariate analysis of the rate of ≥50% restenosis in 3 years for the 346 vein patched (2; 0.6%) and 186 Dacron graft patched (7; 3.8%) CEAs that did not have internal carotid artery shortening gave a P value of .015. Similarly, Kaplan-Meier method analysis of this subset of nonshortened CEAs gave a higher restenosis rate with Dacron graft patching (P = .012). With multiple logistic regression, the ≥50% restenosis rate was significantly associated with Dacron graft patching (P = .023; odds ratio, 4.5) and internal carotid artery shortening (P = .025; odds ratio, 3.1) and was weakly associated with female gender (P = .15; odds ratio, 2.0). Cox proportional hazards model analysis for ≥50% restenosis gave relative risk ratios of 3.0 (1.6 to 6.8; 95% confidence interval [CI]) for Dacron graft versus vein patching, 2.0 (1.2 to 3.3; 95% CI) for shortening versus not shortening, and 1.5 (0.9 to 2.4; 95% CI) for female versus male gender. Conclusion: CEA patching with Dacron grafts and saphenous vein grafts have similar low perioperative thrombosis, stroke, and death rates, although the stroke and death rates were slightly higher but not statistically different when Dacron grafts were used. Dacron graft patched CEAs are more likely to develop ≥50% restenosis than are those that are patched with saphenous vein grafts. Eversion plication shortening of the internal carotid artery predisposes the graft to restenosis. (J Vasc Surg 1999;29:654-64.

Particle hemodynamics analysis of Miller cuff arterial anastomosis

AbstractObjectiveStudies of animal and human below-knee anastomoses with Miller cuffs indicate that improved graft patency results from redistribution of intimal hyperplasia away from areas critical to flow delivery, such as the arterial toe. We hypothesize that particle hemodynamic conditions are a biophysical mechanism potentially responsible for the clinically observed shift in intimal hyperplasia localization associated with better patency of the Miller configuration.MethodsComputational fluid dynamics analysis of vortical flow patterns, wall shear stress fields, and potential for platelet interaction with the vascular surface was performed for realistic three-dimensional conventional and Miller cuff distal end-to-side anastomoses. Sites of significant platelet-wall interaction, including elevated near-wall particle concentrations and stasis, were identified with a validated near-wall residence time model, which includes shear stress–based factors for particle activation and surface reactivity.ResultsParticle hemodynamics largely coincide with the observed redistribution of intimal hyperplasia away from the critical arterial toe region. Detrimental changes in wall shear stress vector magnitude and direction are significantly reduced along the arterial suture line of the Miller cuff, largely as a result of increased anastomotic area available for flow redirection. However, because of strong particle-wall interaction, resulting high near-wall residence time contours indicate significant intimal hyperplasia along the graft-vein suture line and in the vicinity of the arterial heel.ConclusionsWhile a number of interacting mechanical, biophysical, and technical factors may be responsible for improved Miller cuff patency, our results imply that particle hemodynamics conditions engendered by Miller cuff geometry provide a mechanism that may account for redistribution of intimal hyperplasia. In particular, it appears that a focal region of significant particle-wall interaction at the arterial toe is substantially reduced with the Miller cuff configuration

Geometric dimension changes with carotid endarterectomy reconstruction

Abstract Purpose: The geometry of carotid endarterectomy (CEA) reconstruction is a major determinant of carotid bifurcation hemodynamics that, in turn, may play a significant role in the likelihood of early postoperative thrombosis and early and late restenosis. The purpose of this study was to measure the geometry of various types of CEA reconstructions. Methods: Six carotid artery diameters and lengths were measured during surgery, before and after CEA. Three reconstruction methods were used in 562 CEA procedures: a greater saphenous vein patch in 389, a synthetic patch in 157, and primary closure in 16. Veins 6 mm or more in distended diameter were trimmed before use as a patch. Synthetic patches were 8 to 11 mm in width. Patch reconstruction was used when the length of the arteriotomy required to obtain a complete distal endarterectomy end point extended beyond the internal carotid artery bulb. Saphenous vein patches were used when it was available and adequate. Neither gender nor internal carotid artery diameter was used as a criteria for the selection of the reconstruction method. Results: Before endarterectomy, the 302 male carotid arteries had 7% to 15% greater linear dimensions than the 260 female arteries (p < 0.001). Both vein and synthetic patch reconstruction produced up to 16% changes in linear dimensions except for almost doubling of the length of the internal carotid bulb. Patching made the elliptical common carotid bulb significantly more round, but the maximum diameter of curvature of the carotid bulb remained unchanged. Primary closure slightly decreased the diameter of the internal carotid bulb.Conclusions: CEA patch reconstruction has two major effects on carotid geometry: an increase in internal carotid bulb length and a more round common carotid bulb. The former allows for a gradual transition from the terminal common carotid bulb to the uniform diameter more distal internal carotid artery. It also separates the two major causes of disturbed flow: the bifurcation and the step-down in internal carotid artery diameter. Primary closure has minimal effect on preoperative geometry. (J Vasc Surg 1997;25:488-98.