共查询到20条相似文献,搜索用时 15 毫秒
1.
This research involves the development and evaluation of a part flow control model for a type of flexible manufacturing system (FMS) called a dedicated flexible flow line (FFL). In the FFL, all part types flow along the same path between successive machine groups. The specific objective of the part flow control model for the FFL is to minimize makespan for a given set of parts produced in a FFL near-term schedule, given fixed available buffer constraints. The control model developed in this research involved the repeated, real-time execution of a mathematical programming algorithm. The algorithm attempts to release the right mix of parts at the tight time to keep the FFL operating smoothly. The focus of the approach is directed toward managing WIP buffers for each machine group queue. The algorithm specifically incorporates stochastic disturbance factors such as machine failures. Through a limited number of simulation experiments, performance of the control model is shown to be superior to other parts releasing and control methods reported in the literature. 相似文献
2.
3.
4.
Bone flow 总被引:1,自引:0,他引:1
L Krook L F Bélanger P A Henrikson L Lutwak B E Sheffy 《Revue canadienne de biologie / éditée par l'Université de Montréal》1970,29(2):157-167
5.
Cardot P Battu S Simon A Delage C 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2002,768(2):285-295
Interest in the development of field flow fractionation (FFF) systems for cell sorting recently increased with the possibility of collecting and characterizing viable cellular materials. There are various tools for the analysis of cell characteristics, but the reference is small- and large-angle light scattering often coupled with fluorimetric measurements. The well-known flow cytometry (FC) cell analysis techniques can be associated with FFF leading to the possibility of collecting information provided by a remarkable separation technique for micron-sized particles (cells) operating in the steric-hyperlayer elution mode with multiparametric detection provided by flow cytometry. Moreover FFF derived cell characteristics can be correlated with FC characteristics to describe in a unique way the nature of the eluted materials. Experimental demonstrations are described herein using nucleated cells (HL-60 cell lineage) and human red blood cells (HRBC). 相似文献
6.
7.
Claessens TE Van Herck PL Matthys KS Segers P Vrints CJ Verdonck PR 《Biomechanics and modeling in mechanobiology》2004,3(1):48-55
Fractional flow reserve (FFR) is a commonly used index to assess the functional severity of a coronary artery stenosis. It is conventionally calculated as the ratio of the pressure distal (Pd) and proximal (Pa) to the stenosis (FFR=Pd/Pa). We hypothesize that the presence of a zero flow pressure (P
zf), requires a modification of this equation. Using a dynamic hydraulic bench model of the coronary circulation, which allows one to incorporate an adjustable P
zf, we studied the relation between pressure-derived FFR=Pd/Pa, flow-derived true FFRQ=QS/QN (=ratio of flow through a stenosed vessel to flow through a normal vessel), and the corrected pressure-derived FFRC=(Pd–Pzf)/(Pa–Pzf) under physiological aortic pressures (70 mmHg, 90 mmHg, and 110 mmHg). Imposed Pzf values varied between 0 mmHg and 30 mmHg. FFRC was in good agreement with FFRQ, whereas FFR consistently overestimated FFRQ. This overestimation increased when Pzf increased, or when Pa decreased, and could be as high as 56% (Pzf=30 mmHg and Pa=70 mmHg). According to our experimental study, calculating the corrected FFRC instead of FFR, if Pzf is known, provides a physiologically more accurate evaluation of the functional severity of a coronary artery stenosis. 相似文献
8.
9.
Gharib M Pereira F Dabiri D Hove JR Modarress D 《Integrative and comparative biology》2002,42(5):964-970
Quantitative flow visualization has many roots and has takenseveral approaches. The advent of digital image processing hasmade it possible to practically extract useful information fromevery kind of flow image. In a direct approach, the image intensityor color (wavelength or frequency) can be used as an indicationof concentration, density and temperature fields or gradientsof these scalar fields in the flow (Merzkirch, 1987). For whole-fieldvelocity measurement, the method of choice by experimental fluidmechanicians has been the technique of Particle Image Velocimetry(DPIV). This paper presents a novel approach to extend the DPIVtechnique from a planar method to a full three-dimensional volumemapping technique useful in both engineering and biologicalapplications. 相似文献
10.
11.
12.
Numerical predictions of blood flow patterns and hemodynamic stresses in Abdominal Aortic Aneurysms (AAAs) are performed in a two-aneurysm, axisymmetric, rigid wall model using the spectral element method. Physiologically realistic aortic blood flow is simulated under pulsatile conditions for the range of time-averaged Reynolds numbers 50< or =Re(m)< or =300, corresponding to a range of peak Reynolds numbers 262.5< or =Re(peak) < or = 1575. The vortex dynamics induced by pulsatile flow in AAAs is characterized by a sequence of five different flow phases in one period of the flow cycle. Hemodynamic disturbance is evaluated for a modified set of indicator functions, which include wall pressure (p(w)), wall shear stress (tau(w)), and Wall Shear Stress Gradient (WSSG). At peak flow, the highest shear stress and WSSG levels are obtained downstream of both aneurysms, in a pattern similar to that of steady flow. Maximum values of wall shear stresses and wall shear stress gradients obtained at peak flow are evaluated as a function of the time-average Reynolds number resulting in a fourth order polynomial correlation. A comparison between predictions for steady and pulsatile flow is presented, illustrating the importance of considering time-dependent flow for the evaluation of hemodynamic indicators. 相似文献
13.
Roy AS Banerjee RK Back LH Back MR Khoury S Millard RW 《American journal of physiology. Heart and circulatory physiology》2005,289(1):H392-H397
Hemodynamic analysis was conducted to determine uncertainty in clinical measurements of coronary flow reserve (CFR) and fractional flow reserve (FFR) over pathophysiological conditions in a patient group with coronary artery disease during angioplasty. The vasodilation-distal perfusion pressure (CFR-p(rh)) curve was obtained for 0.35- and 0.46-mm guide wires. Our hypothesis is that a guide wire spanning the lesions elevates the pressure gradient and reduces the flow during hyperemic measurements. Maximal CFR-p(rh) was uniquely determined by the intersection of measured CFR and calculated p(rh) of native and residual epicardial lesions in patients without microvascular disease, during angioplasty. Extrapolation of the linear curve gave a zero-coronary flow mean pressure (p(zf)) of approximately 20 mmHg and a corresponding p(rh) of 55 mmHg in the native lesions, which coincided with the level that causes ischemia in human hearts. On this linear curve, values of CFR and FFRmyo (pathophysiological condition) and CFRg and FFRmyog (in the presence of the guide wire) were obtained in native and residual lesions. A strong linear correlation was found between CFR and CFRg [CFR = CFRg x 0.689 + 1.271 (R2= 0.99) for 0.46 mm and CFR = CFRg x 0.757 + 1.004 (R2= 0.99) for 0.35 mm] and between FFRmyo and FFRmyog [FFRmyo = FFRmyog x 0.737 + 0.263 (R2= 0.99) for 0.46 mm and FFRmyo = FFRmyog x 0.790 + 0.210 (R2= 0.99) for 0.35 mm]. This study establishes a strong correlation between CFR and CFRg and between FFRmyo and FFRmyog, which could be used to obtain the true state of occlusion in the coronary artery during angioplasty. 相似文献
14.
15.
Blood damage and platelet activation are inherent problems with present day mechanical heart valve designs. We investigate the approach of passive flow control applied to bileaflet mechanical heart valve (BMHV) flows as a means of optimizing leakage flow hemodynamics at length scales relevant to blood damage and platelet activation. Rectangular and hemispherical vortex generator (VG) arrays were mounted on the downstream surfaces of a 25 mm St. Jude Medical valve adjacent to the b-datum leaflet edge (central line where the two leaflets touch in closed position). The effect of VGs on the flow structure emanating from the b-datum line under both pulsatile and steady flow conditions was measured using high resolution particle image velocimetry technique. The VGs were seen to spatially disperse and dissipate the coherent leakage jet structure emanating from the b-datum line. This resulted in a significant diminution of turbulence stresses, particularly with the rectangular VG configuration. This study shows that passive flow control techniques deployed on BHMVs is potentially beneficial as significant control of flow at small length scales may be achieved without altering large scale designs of the valve. 相似文献
16.
17.
Melvin Praissman Irving F. Miller Harry P. Gregor Jesse M. Berkowitz 《The Journal of membrane biology》1973,11(1):139-151
Summary The electroosmotic flows of solution produced by the chloride salts of H, Na, K, tetramethylammonium (TMA) and tetraethylammonium (TEA) through three membranes of net negative charge and high water content (40 to 60%) have been obtained. The amount of solution transported, (EO
s), increased in the order: HCl, KCl, NaCl, TMACl and TEACl in a membrane of 43% hydration. In membranes 60% hydrated the order became HCl, KCl, NaCl, TEACl and TMACl. (EO
s) for a salt increased as membrane hydration became larger. The permselectivity of the three membranes for cations declined in the order: HCl, KCl=NaCl, TMACl and TEACl. Cation permselectivity also declined with increases in membrane hydration. The (EO
s) is a net solution flow and is the difference between the cation-induced water flow and the chloride-induced water flow in the opposite direction. In membranes of moderate to high H2O content, co-ion transport is significant and the water-flow associated with co-ion movement must be determined if the contribution of the counter-ion ([EO]cation) to the (EO
s) is to be found. Cl-ion induced water flow was determined by assuming an identity of K and Cl ions. [EO]cation increased as the hydrated radii of the cations increased and for any particular cation [EO]cation was at least 100% greater in the 60% hydrated membrane than in the 43% hydrated membrane. The current-induced water flow was found to be composed of both an electroosmotic and an osmotic component. The latter represented between 10 and 40% of the total water flow.Presented in part before the American Physiological Society at the 54th meeting of the F.A.S.E.B., Atlantic City, N.J., April, 1970. 相似文献
19.
20.