Maximum Wall Research Articles

Early esophageal carcinoma. Evaluation of the depth of invasion based on double-contrast esophagography.

The aim of this study was to assess the depth of invasion of early esophageal carcinoma (EEC) by means of double-contrast esophagography. The radiological findings of 46 EECs were retrospectively analyzed for the following factors that might be related to the depth of invasion: in depressed lesions (n = 30): maximum size, surface appearance, sharpness of contour, and wall rigidity; and in elevated lesions (n = 16): maximum size, height, shape, and wall rigidity. All lesions were surgically or endoscopically resected and the radiological findings were compared with the histological appearance. In depressed lesions, the size of the surface granules correlated very strongly with the depth of invasion (rs = 0.8147). In both depressed and elevated lesions, wall rigidity correlated strongly with the depth of invasion (rs = 0.7540 and rs = 0.6702 respectively). In depressed lesions, sharpness of contour also correlated strongly with the depth of invasion (rs = 0.6731). The other factors did not correlate with the depth of invasion. Double-contrast esophagography could provide useful information for assessing the depth of invasion of EECs.

Coronary arterial hyperreactivity and mesenteric arterial hyporeactivity after myocardial infarction in the rat.

After myocardial infarction, several neurohumoral systems become activated to maintain systemic perfusion pressure. We evaluated whether this leads to alterations of wall structure and contractile reactivity in the thoracic aorta, coronary septal artery, and mesenteric resistance arteries. In male Wistar rats, myocardial infarction (MI) was induced by permanent ligation of the left coronary artery. At 5 weeks after MI or sham operation, vessel segments were isolated, chemically sympathectomized, and mounted in a myograph for recording of isometric force development. Contractile reactivity to high potassium, norepinephrine, phenylephrine, serotonin, and Arg-vasopressin was determined. At the end of the experiments, vessels were fixed for morphometric analysis (cross-sectional area, media thickness, radius, and wall-to-lumen ratio). At 5 weeks after myocardial infarction, no alterations of contractile reactivity or wall structure were observed in the thoracic aorta of MI rats. In mesenteric resistance arteries, a nonselective reduction of maximal active wall tension and of active wall stress in response to vasoconstrictors was observed, whereas vessel wall structure and sensitivity to stimuli were not modified. On the other hand, coronary septal arteries displayed hyperreactivity to all strong contractile stimuli. These observations demonstrate a heterogeneity of arterial reactivity changes at 5 weeks after MI in the rat: (a) no alterations in thoracic aorta, (b) hyporeactivity of mesenteric resistance arteries despite maintenance of media mass, and (c) hyperreactivity of coronary vessels obtained from the hypertrophic remnant myocardium. This could result from the complex regional hemodynamic and neurohumoral changes associated with heart failure and may contribute to the further deterioration of cardiovascular function in this setting.

A Computational Model for an Open-Cycle Gas Core Nuclear Rocket

A computational model of an open-cycle gas core nuclear rocket (GCR) is developed. The solution is divided into two distinct areas--thermal hydraulics and neutronics. To obtain the thermal-hydraulic solution, a computer code is written that solves the Navier-Stokes, energy, and species diffusion equations. The two-dimensional transport code TWODANT is used to obtain the neutronics solution. The thermal-hydraulic and neutronic models are coupled, and the solution proceeds in an iterative manner until a consistent power density profile is obtained. Various open-cycle GCR designs are evaluated. First, it is assumed that the fuel and propellant do not mix. In this ideal case, it is found that the limiting factor in determining thrust and specific impulse is the maximum allowable wall heat flux. Following this simplified study, the results from a complete thermal-hydraulic/neutronic solution are presented, and the use of alternate fuels and propellants is considered. Next, a parametric design study is conducted that examine the rocket performance of the open-cycle GCR as a function of various design and operational parameters. It is found that fuel containment is very adversely affected by high reactor power or rocket acceleration. Finally, some concepts are discussed that could help improve fuel containment.

Contractile responses to various stimuli in isolated resistance vessels from simultaneously hypertensive and streptozotocin-diabetic rats.

Diabetes mellitus and hypertension are common chronic diseases that frequently occur simultaneously. The induction of streptozotocin (STZ) diabetes mellitus in spontaneously hypertensive rats (SHR) offers the opportunity to investigate the influence of both entities in a reproducible manner. We investigated the effects of various vasoconstrictors on isolated small arteries from the mesenteric vascular bed of normotensive rats (Wistar-Kyoto rats, WKY) and SHR with chronic (8 weeks), STZ-induced diabetes mellitus. No consistent changes in hemodynamic parameters of the (STZ-) normotensive and (STZ-) hypertensive rats were noted. The K(+)-normalization procedure yields the individual optimal lumen diameter, which was the same for the arteries of the four groups of rats. The passive wall tension resulting from this normalization procedure was higher only in preparations from the control hypertensive group as compared with those from the control normotensive rats. Morphological investigations showed that small arteries from control SHR had an increased tunica media thickness as compared with those of control WKY; the STZ-WKY had an increased tunica media thickness as compared with preparations from control WKY. The vasoconstriction caused by alpha 1-adrenoceptor stimulation [norepinephrine (NE), methoxamine] and serotonin is unchanged in chronic experimental diabetes. The diabetic state reduced the sensitivity [-log EC50(M)] for the concentration-response curves (CRC) of calcium chloride. The CRC of potassium chloride indicated the same sensitivities, but maximal active wall tensions of vessels from STZ-SHR were reduced as compared with those from STZ-WKY. The well-known enhancement of the effects of various contractile stimuli caused by hypertension could not be demonstrated for the isolated small arteries used in the present study, although a nonsignificant tendency was observed. However, the STZ-diabetic state did not cause important additional pharmacodynamic changes, despite the morphological alterations in those vessels.

TRANSIENT THERMAL PERFORMANCE OF AXIALLY AND RADIALLY DILUTED NUCLEAR FUEL CELLS

A numerical investigation is presented of steady and unsteady heat transfer in axially and radially diluted nuclear fuel rods. The transient performance is assumed to follow a sudden and complete loss of coolant starting from steady state operation. Steady state conditions are obtained from solving numerically a conjugate conduction problem in the fuel rod and a turbulent forced convection problem in the coolant section. To model turbulence, the mixing length model is used. Dilution is accomplished by adding high thermal property materials, either axially or radially, to the original fuel rods with the intention of increasing the time delay before melting of the reactor in case of loss of coolant. The effects of the amount, distribution, and material of added diluent on steady and unsteady heat transfer are studied. Results indicate that axial dilution has negligible influence on the thermal performance of the reactor. Radial dilution, however, holds great promise and shows a reduction in the maximum wall...

Variation of Specific Gravity, Fibre Length and Cell Wall Thickness in Young Salix Clones

Abstract Specific gravity, fibre length and cell wall thickness of various hybrid Salix clones were compared. The densest clone was 1.47 times denser than the least dense clone. The highest specific gravity was 0.5, found in Salix viminalis L. whereas the lowest was 0.372, found in Salix dasyclados L. The clone with longest fibre was 1.34 times that of the clone with shortest fibre. Clones with long fibre also showed high specific gravity such as Salix viminalis L. The cell wall thickness in Salix clones varies from 0.0025 mm to 0.0037 mm or 1.48 times from minimum to maximum cell wall thickness. Since the above fibre properties indicate various paper strength characteristics such as flexibility coefficient and felting index, it is possible to select clones with superior characteristics for propagation as suitable source for pulp and paper industry.

Combined Air-Oil Cooling on a Supercharged TC & IC TAM Diesel Engine

In order to reduce the maximum cylinder wall temperatures of an air-cooled TC&IC diesel engine with large longitudinal and circumferential temperature gradients, a curved, squared cross-sectional channel supplied with engine lubrication oil was introduced into the upper part of the cylinder wall. Numerical analyses of the heat transfer within the baseline air-cooled cylinder and intensive experimental work helped to understand the temperature situation in the cylinder at diverse engine running conditions. The results of the combined cooling were greatly affected by the design, dimensions, position of the channel, and the distribution of the cooling oil flow, and are presented in the paper.

Length-tension relationship of vascular smooth muscle in single arterioles.

Longitudinal response gradients in the microcirculation may in part be explained in terms of the length-tension relationship of vascular smooth muscle at different points along the vascular tree. To test this hypothesis, four branching orders of arterial vessels (20-80 microns ID) were dissected from the hamster cheek pouch and cannulated with concentric micropipettes. Intraluminal pressure was monitored with a servo-null micropipette, and arteriolar dimensions were measured using a videomicrometer. All arterioles developed spontaneous tone in physiological saline solution. Pressure-diameter curves were recorded for maximally activated vessels and for passive vessels. Maximal active wall tension varied nearly threefold, but maximal active medial wall stress (approximately 4 x 10(6) dyn/cm2) varied only approximately 20% between the different vessel orders. These data support the concept that smooth muscle cells from vessels of different sizes are mechanically similar but do not completely explain the longitudinal response gradients reported in the cheek pouch microcirculation. An analysis of the effect of arteriolar wall buckling suggests that the luminal folds that develop at short vessel radii may broaden the peak of the active stress-length curve and extend the pressure range over which arterioles are most sensitive to physical and chemical stimuli.

Contribution of salt to arterial wall changes in DOCA hypertension in the rat.

The contribution of drinking fluid salt to the development of deoxycorticosterone (DOCA) hypertension and arterial wall changes was assessed in unilaterally nephrectomized rats. Half of the DOCA-treated animals received saline supplemented with 0.2% KCl and the other half received deionized water as drinking fluid. All animals were fed standard rat chow (Na content = 0.36%). After 8 weeks, arterial pressures were significantly elevated in both DOCA groups to values which were not significantly different. The heart weight to body weight ratio was also elevated in both DOCA groups with a larger response in the saline-treated ones. Body weight of saline-treated DOCA rats was significantly lower than untreated controls and water-treated DOCA rats. Arteries from both DOCA groups exhibited increased passive stiffness, larger maximum active stress, wall thickening, decreased collagen and elastin concentration, greater relative cell volume, and greater water and cation concentrations. Larger changes were generally found in the saline- than the water-treated group. These results show that saline administration is not necessary for the development of hypertension or hypertension-induced arterial wall changes in DOCA-treated, uninephrectomized rats. Hypertension developed more slowly and arterial wall changes were similar in magnitude in water-treated animals. These results suggest that the rate and/or time history of pressure elevation may be an important factor contributing to hypertension-related arterial changes.

A Model for First-Wall Thermal Response to Plasma Energy Deposition

A primarily analytical thermal analysis model is presented that allows for calculation of temperatures in fusion reactor first walls. The model utilizes input quantities based on plasma physics calculations and couples a 2 1/2-dimensional geometric analysis with a one-dimensional heat conduction analysis in determining temperature profiles over the surface of and within materials used to confine the plasma and vacuum. Given materials-related temperature limitations, methods are also provided for calculating maximum allowable wall power loadings. The results are primarily applicable to the steady-state operation of magnetic confinement devices such as tokamaks.

Structural and mechanical adaptations in rat aorta in response to sustained changes in arterial pressure.

Structural and mechanical adaptations in response to sustained changes in arterial pressure were studied on abdominal aorta of the male rat. Two models were used: 1. Aortic ligature (L), immediately below the renal arteries producing hypotension distal to the knot (duration before sacrifice 6 weeks or 3 months). 2. One-clip renal hypertensive rats (H) (duration 6 weeks). Normotensive sham-operated rats (C) served as controls. At sacrifice mean tail artery pressure was L: 58 +/- 1, C: 110 +/- 3, and H: 163 +/- 5 mmHg (SE, N=6). Segments of abdominal aorta were mounted in vitro for determination of their length-tension relations (activation: High-K+ solution with 2.5 mM Ca2+). At end of experiments the vessels were supramaximally stimulated at optimal circumference (1o) for active force (activation: High-K+ solution with 10 mM Ca2+, and 10(-5) M noradrenaline), and then fixated for light and electron microscopy. Passive and active length-tension relations were shifted towards lower and higher circumference values for hypo- and hypertensive vessels, respectively. The 1o values were L: 3.60 +/- 0.13, C: 4.44 +/- 0.19, and H: 4.91 +/- 0.29 mm. The media thickness at 1o was reduced in L: 56.0 +/- 3.3, and increased in H: 81.3 +/- 2.4 compared to C: 73.4 +/- 1.8 micron. Maximal active wall stress was L: 46.6 +/- 9.8, C: 74.2 +/- 7.0, and H: 83.8 +/- 7.7 mN/mm2. Intracellular volume (ICV) in the media was L: 30 +/- 2, C: 45 +/- 3, and H: 44 +/- 1% (n=4 for each).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of size of a tubular mold on the density of a loosely poured powder mass

An analytical expression, verified by experiment, has been obtained for calculating the maximum density of a powder mass composed of single-fraction spherical particles loosely poured into a tubular mold. Curves of maximum density vs wall thickness of tubular parts have been constructed for the range of values of k=(Ro-Ri)/d which are usually employed in the manufacture of standard filter elements. It has been established that with increasing k the density at first grows up to a certain limit, but beyond this point no significant increase in density is observed. It has been demonstrated by experiment that, for a powder poured into a tubular mold at an optimum rate, the maximum density of the powder mass is independent of mold height.

Effects of Design Parameters on Cooling Air Requirement in a Gas Turbine Combustor

T purpose of this paper is to show the effects of design parameters on the cooling air requirement in a typical can-annular aircraft gas turbine combustor. Works in this field have been reported earlier, for instance by Whittaker, ] showing how wall temperatures in different combustion zones depend upon various parameters. The objective of this work is the opposite, i.e., to prescribe a maximum allowable wall temperature and to calculate the total amount of cooling air required in order not to exceed this temperature at any location.

Norepinephrine sensitivity, tension development and neuronal uptake in resistance arteries from spontaneously hypertensive and normotensive rats.

Intact segments of mesenteric resistance arteries (200 micron) from 5-month-old spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rats were tested for norepinephrine (NE) sensitivity. Dose-response curves were obtained both before and after adrenergic denervation produced by short-term, in vitro, 6-hydroxydopamine (6-OHDA) treatment. NE sensitivities of innervated vessels were the same in SHR and WKY rats, however, after 6-OHDA, not only did both ED50s show significant decreases (8.7- and 3.8-fold, respectively), but the ED50 of SHR vessels was half that of WKY (NE sensitivity increased twofold). In addition there was a 33% increase in wall tension generated in response to maximum NE stimulation, and a 44% increase in neuronal NE uptake in the SHR vessels. These results show that several important alterations have occurred in resistance vessels from SHR rats in the established phase of hypertension. The relationship of the increase in neuronal uptake to the increased total peripheral resistance and increased vascular reactivity commonly seen in SHR perfused beds and whole animals is unknown. However, the increase in NE sensitivity and in maximum NE wall tension could contribute to increase in both of these characteristics.

A Parametric Study of a Lithium-Cooled Tokamak Blanket

Two design models illustrate the methodology used to obtain the acceptable ranges for a set of design parameters for a lithium-cooled tokamak blanket. The methodology can also be used to identify the limiting constraints for a particular design. For typical tokamaks, header diameter is approx. 12 cm; coolant inlet velocity is found to be < 0.1 m/s to maintan a reasonable hoop stress in the header. For the constant Q' model, where tubes are distributed to match the volumetric heat generation, the limiting constraints are found to be the total number of tubes and the maximum size of the headers that can fit radially in the blanket. The maximum first wall neutron loading is 7 MW/m/sup 2/. For the constant T/sub max/ model, where cooling channels are placed so that the peak temperatures between the channels are equal, the limiting constraint is found to be the thermal stress in the channel wall. The first wall neutron loading is found to be 2.1 MW/m/sup 2/.

Instability of a periodic boundary layer in a stratified fluid

It has been found that the periodic boundary layer formed on a vertically oscil-lating vertical wall bounding a stratified fluid is liable to two distinct modes of wavelike instability. In the first, which arises when the oscillation frequency ω is lower than 0·7 times the buoyancy frequency N, the phase lines are aligned horizontally. The second mode, in which the phase lines are aligned at 45° or more to the horizontal, becomes dominant as ω is increased above 0·9 N.In distinction from the unstratified periodic Stokes layer, there appears to be, for ω in the vicinity of N, a definite low threshold to the boundary-layer Stokes-Reynolds number (defined as Wo/(2ων)½, where Wo is the maximum vertical wall velocity and v is the kinematic viscosity) above which the instability is sustained a t a detectable level.

Notch Ductility Properties of SM-1A Reactor Pressure Vessel Following the In-Place Annealing Operation

Abstract : The embrittlement condition of the Army SM-1A reactor pressure vessel, as modified by the recently completed in-place anneal, was assessed and an analysis was made of the reembrittlement behavior of the vessel steel with subsequent radiation service. Experimental results from the reactor surveillance program developed through one complete irradiation and annealing cycle are presented, together with a summary of experimental information on the annealing response of the vessel steel (A350-LF1, Mod.) from accelerated irradiation programs. These data indicate a 0 deg F maximum pressure vessel wall Charpy-V 30 ft-lb transition temperature after the in-place anneal versus a -80 deg F preservice transition temperature (based on the notch-ductility properties of a duplicate ring forging). The maximum Charpy-V 30 ft-lb transition temperature of the pressure vessel before the annealing operation was estimated at 190 deg F. A projection of postanneal pressure vessel lifetime in terms of neutron fluence >0.5 Mev was derived from spectra calculations and the experimentally predicted reirradiation response of the pressure vessel steel. The maximum permissible vessel wall fluence is estimated at 5.5x10 to the 19th power n/sq cm > 0.5 Mev. This is comparable to 124.7 Megawatt years of reactor operation. (Author)

The Thermosludge Water Treating and Steam Generation Process

Abstract The Thermosludge process internally softens and makes high-pressure steam directly from hard and saline oilfield or other water. Pilot plant and early full-scale plant work established several physical and chemical principles found necessary or desirable for good operation, and for control and practical elimination of scale on the process heating surfaces. These principles are use of a secondary liquid heat transfer medium, provision of time and space for water chemical reactions ahead of the boiling zone, and presence of sludged reaction products throughout the boiling zone. Other pertinent factors are discussed such as dissolved and suspended solids limits, foaming, corrosion, and heat transfer. Introduction In 1964 considerable use of steam in California oil fields was beginning to cause shortages of good steam generator feedwater in some areas. It seemed evident that in some situations oilfield brine or other low-quality water would have to be used to generate high-pressure steam directly. The Thermosludge process was developed to meet this need, and early results of its field use have been reported previously. This article discusses both pilot plant and full-scale plant design and operation particularly relative to the high-temperature reactions and scaling characteristics of some of the chemicals present in the waters. Present understanding of the process should allow broader use in its original field, and in other processing areas dealing with difficult waters. Pilot Plant Design and Operation After considerable study of chemical and engineering factors involved, a pilot plant program was set up. Three main theories or principles believed to lead to successful operation were followed in the pilot plant design and the same principles were carried into the full-scale plant design. First, heat should be applied via a secondary fluid heat transfer medium rather than directly in a combustion space. Relative to direct-fired beating, the secondary fluid heating guarantees that maximum tube wall temperature will be well within the allowable metal temperature limit regardless of local scaling or salting up. Many situations call for soluble salt in the steam generator in concentrations of as much as 15 percent by weight perhaps half of the limiting solubility. Even if conventional tube scaling were somehow entirely prevented, such situations would require the inherent heat flux control of a secondary heat medium to prevent gross fouling and plugging by salt deposits. Second, means should be provided in terms of high-temperature time and volume to preheat and chemically react the feedwater before it enters the boiling zone. The practicality of this is based on the expectation that thermally induced mineral sludging reactions will proceed much faster and more completely in the 350 to 600F environment than, for example, in the conventional lime-soda process. Thus, the feedwater should be entirely softened by the time it arrives at the boiling zone.

Laboratory Investigation of Reduction of Fracture Pressures of Rocks by Intensive Borehole Heating

Abstract The feasibility of reducing pressures needed to fracture formations by heating the borehole intensively has been investigated on a laboratory scale. Reductions in fracture pressures of heated Bandera, Berea and Boise sandstone cores were observed at various confining pressures, simulating reservoir stress conditions to a depth of 5,000 ft. Both permeable and impermeable borehole boundary conditions were tested. Three heating conditions were used in the tests. One group of samples was heated in a furnace to a temperature of 600C, cooled to room temperature, and then tested for fracture pressures. Two other groups of samples were heated with a borehole heater to maximum borehole wall temperatures of 625 and 792C, then cooled and tested. In all cases, heated samples showed substantial reductions in fracture pressures compared to unheated samples. The higher temperature borehole heated samples showed the greatest reduction, amounting to 70 per cent in the extreme case. In actual application to wells, it was concluded that fracture pressures may be reduced by 20 to 50 percent by intensive borehole heating before fracturing. INTRODUCTION Hydraulic fracturing of oil and gas wells is an accepted and effective technique for increasing well productivity in many areas, but is notoriously unsuccessful in other areas. The technique becomes less interesting for production stimulation purposes when excessive fracture pressures are necessary. Formations which do fracture but require high pressures, probably form horizontal fractures. There is good evidence to indicate that some formations do not fracture at all, but yield plastically under high pressure. Thus, any technique which will make formations easier to fracture or will reduce fracture pressures is potentially interesting to petroleum producers. Horizontal fractures generally occur in planes of weakness, such as bedding planes, and at pressures equaling or exceeding the effective overburden stress. In the unusual case where planes of weakness do not exist, a slightly higher pressure must be applied to overcome the tensile strength of the rock. In general, high fluid-loss fracturing fluids are conducive to the formation of horizontal fractures.1 Vertical fractures, when they do occur, are initiated at pressures generally lower than overburden pressure and are favored by low fluid-loss fracturing fluids or impermeable boreholes. The pressure necessary to create a vertical fracture in an impermeable, elastic medium can be predicted from the so-called "thick-walled cylinder" equation:Equation 1 where pf = fracture pressure sr=radial stress st=tensile strength of medium. This equation indicates that to fracture it is necessary to overcome a tangential compressive stress, induced by and equal to two times the radial confining stress, plus the tensile strength of the medium.