Minimum Flow Resistance Research Articles

Role of nitric oxide in impaired coronary circulation and improvement by angiotensin II receptor antagonist in spontaneously hypertensive rats.

1. To determine whether coronary flow regulation by nitric oxide (NO) is impaired in the hypertensive heart (HTH), coronary perfusion was measured in isolated rat hearts using NO synthesis inhibitor L-NG-monomethyl arginine (L-NMMA) in Wistar-Kyoto (WKY) rat and spontaneously hypertensive rat (SHR) with and without chronic Nomega-nitro-L-arginine-methylester (L-NAME) treatment. Moreover, the effect of angiotensin II receptor antagonist (AT1 receptor antagonist) (TCV-116) on the impaired coronary circulation in HTH was examined. 2. Coronary flow (CF) was decreased in HTH accompanied with cardiac hypertrophy. The decreased response of CF to L-NMMA infusion was diminished in HTH. It is suggested that NO production was reduced in coronary vasculature in HTH. 3. In chronic L-NAME treated SHR, blood pressure and cardiac hypertrophy were accelerated. Although coronary flow resistance (CFR) was increased, the increased response of CFR to L-NMMA infusion was not altered. 4. The AT1 antagonist improved total minimal coronary flow resistance (MCFR) restoring CFR response in SHR, although it did not recover CFR response in chronic L-NAME treated SHR. 5. Taken together the findings suggest that NO production was exhausted in the coronary artery even in the developing stage of hypertension and this exhaustion could contribute to the impairment of coronary circulation of HTH.

The temperature window of minimum flow resistance in melt flow of polyethylene. Further studies on the effect of strain rate and branching

AbstractThe existence of a narrow temperature window (150–153°C) of smooth extrudability coupled with a minimum in flow resistance (extrusion pressure) in high‐molecular weight polyethylene (>4 × 105 g mol−1) was the subject of a previous article where it was associated with strain‐induced formation of the mobile hexagonal mesophase. The new findings of this note show that this minimum in flow resistance only sets in above a critical strain rate; this is interpreted in terms of the requirement of a critical strain rate in order to stretch molecules to their fully extended configuration. Furthermore, this critical strain rate is shown to be higher for lower molecular weight materials, in agreement with a priori considerations. Additionally, the temperature at which the pressure minimum occurs in a polyethylene containing methyl branches shifts to a significantly lower value than that for the linear material. This is interpreted in terms of the CH3 groups raising the crystal free energy, thereby lowering the temperature at which the transition to the hexagonal phase occurs.

Heuristics for dynamic selection and routing of parts in an FMS

Abstract As part of a hierarchical production control system, a policy is proposed for the admittance of new parts to a flexible manufacturing system (FMS) together with three different heuristics for dynamic routing of parts. The heuristics that consider the process plan's flexibility with respect to machines and operations are based upon fixed priorities, least reduction in entropy, and minimum flow resistance. The heuristics are simulated for different FMS characteristics and the results are analyzed.

Possible role of red cell deformability and microvasculature in microcirculation.

The roles of the deformability of red blood cells (RBC) and the microvasculature in the maintenance of blood flow were investigated in terms of the pressure (P)-flow rate (Q) relationships in human RBC suspension perfusions of bullfrog hind limb. Although isotonicity for the bullfrog is approximately 215 mOsm/kgH2O, perfusions in intact hind limbs showed no change in the P-Q relationship at test solution osmolalities ranging from approximately 150 to approximately 300 mOsm/kgH2O. The deformability of RBC was examined in glutaraldehyde-fixed hind limbs. Perfusion of fixed limbs with RBC suspension revealed minimum resistance to flow at osmolalities of approximately 250 to approximately 420 mOsm/kgH2O, whereas the same experiment in intact limbs revealed minimum flow resistance at osmolalities of approximately 200 to approximately 300 mOsm/kgH2O. It was noteworthy that the reduction of RBC deformability was not observed in intact limbs at osmolalities of approximately 250 to approximately 200 mOsm/kgH2O. Heinz body-forming RBC from a patient with unstable hemoglobin (Hb) disease (Hb Yokohama) exhibited a marked reduction in deformability as compared with normal RBC in fixed limbs, while there was no discernible difference between the two types of RBC in intact limbs, thereby suggesting that the microvascular bed can compensate, to an appreciable extent, for the impaired deformability of RBC, probably via its distensibility and/or a wall effect. The present study has considerable implications concerning the link between in vitro experiments and the in vivo situation, including the hemodynamic characteristics of RBC suspensions such as the effective viscosity.

A temperature window of extrudability and reduced flow resistance in high‐molecular weight polyethylene; interpretation in terms of flow‐induced mobile hexagonal phase

AbstractAn unexpected feature of melt flow behavior has been identified in high‐molecular weight (≥ 4.105) polyethylenes such as are being considered unprocessable at conventional temperatures (> 160°C) and at practicable extrusion rates (> 1 cm/min). In addition to a lower temperature window of smooth extrudability, lying in the range of 138–155°C already observed in previous works, we now discovered within this window a narrow temperature interval (150–152°C) of minimum flow resistance (viscosity). The new effect has the attributes of being associated with a new phase of increased fluidity. This, in turn, we attribute to a transient mesophase arising through the chain‐orienting effect of the elongational flow within the extrusion orifice; from the experiments presented here, this mesophase depends critically on both molecular weight and strain rate. The hexagonal form of polyethylene, known to exist under other circumstances, is suggested as this mesophase. The relevance of the new findings for applications (extrusion, melt rheology) and for fundamentals (orientation‐induced phase transformations, liquid crystals from flexible chains in particular) should be obvious and are accordingly highlighted.

Thoracic duct lymph flow and its measurement in chronically catheterized sheep fetus.

A method was developed for chronic catheterization of the left thoracic lymph duct at the base of the neck in the sheep fetus, which did not disrupt the other major lymphatic vessels that join the venous circulation at the same location. The lymphatic catheter was connected to a catheter in a jugular vein when lymph flow was not being recorded, so that the lymph continuously returned to the fetal circulation. Special consideration of catheter size to minimize flow resistance and treatment to prevent clotting were required. Individual animals were maintained up to 17 days with lymph flow continuing. In 13 fetuses averaging 128 days gestation (term = 147 days) at the time of catheterization, lymph flow rate was measured for 1 h each day for the first 7 postsurgical days with an on-line computer technique that continuously calculated lymph flow rate. Lymph flow averaged 0.64 +/- 0.17 (SD) ml/min in fetuses weighing 2.3-4 kg and tended to undergo a nonsignificant increase with time. Lymph and plasma protein concentrations did not change with time. In individual fetuses, large spontaneous variations in lymph flow rate occurred over periods of several seconds to a few minutes. Analysis showed that these variations in flow rate were not associated with fetal breathing movements. Thus the present study describes a technique for studying the dynamics of lymph flow in the unanesthetized sheep fetus in utero over a time period limited primarily by the length of gestation. In addition, it appears that thoracic duct lymph flow rate in the fetus per unit body weight averages three to four times that in the adult.

Structural Optimization-Past, Present, and Future

' Introduction T concept of optimization is intrinsically tied to natural phenomena as well as to the human desire to excel. Sir George Cayley (1773-1857) measured the shape of a trout and noted, without mathematical proof, that the trout was ideally proportioned to minimize flow resistance. Theodore von Kdrmdn observed that this is precisely the shape of a lowdrag airfoil. Oliver Wendell Holmes (1809-1894), in his classic verse, Deacon's Masterpiece; or, The Wonderful OneHoss Shay, recorded man's desire to produce a uniformly strong, durable product. In this case it was the structural design of a shay to last a hundred years. Perhaps the first analytical work in structural optimization was by Maxwell in 1869, followed by the better-known work of Michell in 1904. These works provided theoretical lower bounds on the weight of trusses, and, although highly idealized, offer considerable insight into the structural optimization problem and the design process. The 1940s and early 1950s saw development of component optimization in such works as Shanley's Weight-Strength Analysis of Aircraft Structures. Also during this period, availability of the digital computer led to application of linear programming techniques to plastic design of frames, for example, the work of Heyman. This early numerical work is particularly significant in that it used mathematical programming techniques developed in the operations research community to solve structural design problems. Schmit in 1960 was the first to offer a comprehensive statement of the use of mathematical programming techniques to solve the nonlinear-inequality-constrained problem of designing elastic structures under a multiplicity of loading conditions. This work is significant, not only in that it ushered in an era of structural optimization, but also because it offered a new philosophy of engineering design which is only now beginning to be broadly applied. In Ref. 9 Schmit provides an excellent historical review of the development of this concept. Although this discussion will emphasize numerical design techniques, it is important to note that there has been an extensive amount of research in analytical methods of design. That work, although sometimes lacking the practicality of being applied to realistic structures, is nonetheless of fundamental importance because it provides insight into the design problem and because it often provides theoretical lower bounds against which more practical designs may be judged. References 10 and 11 provide an extensive review of the state-of-the-art in analytical design techniques. It is the use of numerical techniques in structural optimization that is emphasized here. The purpose is not to offer a tutorial on optimization or a comprehensive literature survey, although such works are referenced. Rather, it is to look briefly at the short history of modern structural optimization and assess the state-of-the-art from a somewhat more philosophical viewpoint. In this way we may begin to understand the ramifications of this fascinating approach to design. By learning what is now possible and what is not now possible, we may encourage the use of these techniques by practicing designers as well as identify research and development needs of the future.

Electrolytic removal of heavy metals from wastewaters. Elimination of end‐of‐the‐line treatment is the key to important savings of capital and operating costs

An electrolytic reactor with a cathode made of carbon fibers and an anode made of carbon fibers or metal oxide is described which effectively removes toxic metals from wastewater. The carbon-fiber pad provides a large surface area and large void volume, allowing a high removal rate with minimum flow resistance. Electrolytic reactors designed for high flow rate with short flow path are effective for metal cleanup in a recirculating flow mode. One specific application of such reactors is the cleanup of a dragout tank in an electroplating line. By continuously removing the metals at the same rate as they are introduced by dragout from the plating bath, it is possible to eliminate the end-of-the-line treatment. This source treatment by an electrolytic process greatly simplifies the wastewater-treatment process and results in savings of capital and operating costs. 5 references, 8 figures, 2 tables.

On-line diluter for atomic-absorption spectrophotometry

The short calibration range of atomic-absorption spectrophotometers and the widely varying sensitivities available for various elements tend to complicate the analysis of environmental materials. The complication stems from (a) the wide range of analyte concentrations found, which requires extra dilution for sporadic samples, and (b) the systematic dilution of every sample solution needed when combinations of certain elements are determined. For example, in the analysis of soils for cadmium and zinc, different dilutions are required for the two elements because of their very different abundances, and the absence of medium-sensitivity lines for zinc. These complications do not constitute a problem for small analytical loads. However, in long runs, and especially when automatic systems are employed, the retrospective replacement of out-of-range measurements and the use of two separate dilutions for difierent elements add substantially to the workload. There are a number of discrete dilution systems available commercially,l although we are aware of no previous examples of an on-line continuous dilution system for atomic absorption. Here we describe an on-line diluter that can obviate manual intervention. If a test solution is found to have a concentration above the useful range the flow can be immediately diverted through the diluter to supply a fixed-ratio dilution to the nebuliser. The device described here is hand operated, but could readily be adapted to automatic control. The mixing chamber produces turbulent mixing with minimum flow resistance, which are the conditions required for this application.

Installation and Maintenance of Gate Valves

THE primary function of gate valves is to start or stop the flow of gas or liquid in the pipeline. They do not take the place of check valves, altitude valves, regulators and other special types of valves, nor, except to a limited degree, are they used for throttling the flow of water. Gate valves should be designed to produce a minimum flow resistance in a wide-open position and to be operated with a minimum of effort even though such operation might very seldom be neces-