摘要:

Cross-flow filtration with microporous membranes is increasingly used in the separation and concentration of particulate suspensions. Existing models for the filtrate flux are inadequate for correlating experimental observations and are based on contradictory physical mechanisms. We propose that the flux is limited by the formation of a dynamic concentration polarization boundary layer consisting of a high concentration of retained particles. A simple model is developed incorporating a shear-enhanced diffusivity of the large particles which arises from mutually induced velocity fields in the shear flow of the concentrated suspension. Predictions of the model agree well with experimental data for a variety of particulate suspensions. The model provides both a fundamental understanding of the physical phenomena governing flux and a rational basis for design of improved cross-flow filters.

ISSN:0098-6445    

DOI:10.1080/00986448608911751

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Pulsatile, in vitro flow visualization results are reported for aortic and mitral mechanical heart valve prostheses. Experiments were conducted in the Georgia Tech left heart pulse duplicator system. These studies give a clear picture of the complex flow phenomena caused by the prosthetic valves during various periods in the heart cycle. This overall picture helps to better interpret more detailed results obtained from LDA velocity and turbulence measurements, and pathologic studies. In addition, these clear pictures should help in interpreting the much less clear Color Doppler Row Mapping pictures.

ISSN:0098-6445    

DOI:10.1080/00986448608911752

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In clinical evaluations of patient-artificial kidney systems, residual kidney function and other physiological parameters impede accurate analysis of dialyzer performance. Characterization of solute transport in djalyzers is necessary to develop and maintain control of individual routines. CordisDow “D” series hollow fiber artificial kidneys (1.3, 1.8, and 2.5 square meters) were experimentally characterized in vitro at 25°C in a steady-state analysis of mass transfer of sodium chloride and disodium N-octadecylsulfosuccinate (A–18). Transmembrane pressure was maintained at 15O to 350 millimeters of mercury for ultrafiltration testing; dialysate flow rates were varied from 200 to 800 milliliters per minute, and bloodside flow rates ranged from 100 to 300 milliliters per minute.

ISSN:0098-6445    

DOI:10.1080/00986448608911753

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Multi-region simultaneous diffusion-reaction models are presented for describing oxygen tension profiles in human tumors. The models characterize the spherical tumor mass as either two regions, a central core of necrosis surrounded by a viable layer, or three regions where the viable layer is divided into a hypoxic region surrounded by a well-oxygenated rim. Estimates for the model parameters are based on steady-state clinical measurements obtainedin-vivoin humans via a microelectrode—CT scanning technique developed and performed at the Fox Chase Cancer Center. Models employing linear kinetic rate forms for oxygen consumption via cell respiration accurately reproduce the oxygen tension profiles in the ten different carcinoma and sarcoma investigated. Large tumors (7.0 cm in diameter or larger) which typically outgrow their blood supply have sharp profiles that are accurately represented by a two-region model. Conversely, small tumors (4.8 cm in diameter or less)which have a relatively high degree of vascularity require a three-region model to accurately reproduce their oxygen tension profiles.

ISSN:0098-6445    

DOI:10.1080/00986448608911754

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An experimental investigation was done on oxygen transfer into laminar flows of whole blood and saline downstream of an abrupt pipe expansion. This was used as the experimental model for regions of separated flow in the arterial system. The flow was fully-developed prior to the tube expansion with Reynolds numbers between 160 and 850. The results showed high transfer rates over most of the region downstream of the step, with maximum transfer occurring near the reattachment point. In addition, oscillations of the transfer rate were measured at the larger Reynolds numbers of 450 and 850.

ISSN:0098-6445    

DOI:10.1080/00986448608911755

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

We have modified a model for the oxyhemoglobin equilibrium curve (OHEC) and developed an algorithm for which the nonstandard OHEC can be computed. The model requires 2 parameters and a scaling factor (Sm.) The model parameters are: P*, the oxygen partial pressure where the slope of the OHEC is at its maximum, and a rate parameter K. We estimated P* = 2.76 ± 0.04 SE kPa and K = 0.544 ±0.044 (SE) kPa−1from ten previous literature reports for the human OHEC at standard conditions (T = 37°C, pH = 7.4, PCO2= 5.33kPa and the molar concentration ratio [DPG7sol;Hb] = 0.9). We also determined how P* and K vary under nonstandard conditions by comparing the modified model with two previous nonstandard OHEC algorithms in the literature. These variations can be characterized by an additional 4 parameters. The dimensionless parameter product KP* was found to be relatively insensitive to deviations from standard conditions. We propose a new algorithm for the nonstandard OHEC which requires a total of 7 parameters, is simpler to implement and is computationally more efficient than other algorithms we investigated.

ISSN:0098-6445    

DOI:10.1080/00986448608911756

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Whole blood pH values measured in response to changes in gas phase carbon dioxide concentration are compared with predictions derived from the analysis of Part I of this series. Comparison is also made of experimental oxyhemoglobin saturation with algorithmic predictions. The role of 2,3-diphosphoglycerate is examined in each case. Furthermore, means of inferring DPG concentration from saturation measurements are demonstrated.

ISSN:0098-6445    

DOI:10.1080/00986448608911757

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

ISSN:0098-6445    

DOI:10.1080/00986448608911758

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An intravital microscopic system (equipped with computer-assisted analytical and graphic capabilities) has been designed and built for in vivo leukoemboli investigations. Sprague-Dawley rates were set up for intravital manipulation and microvascular documentation. Fluorescein-tagged leukocytes, prepared before experimentation, were injected intravenously into the rats. With epi-violet irradiation, the fluorescein-tagged leukocytes were activated to fluoresce and their in vivo movement characteristics were videotaped by intravital microscopy with a S.I.T, videocamera. Endotoxin-activated plasma (or zymosan-activated plasma) was then administered intravenously into the rats and the resulting leukoembolization (leukoemboli formation) and later deembolization were videotaped. Analysis and quantification were carried out by computer-assisted micro-image-processing. Video signals were digitized at a resolution of 240 × 320 pixels and at 256 gray levels with a Datacube analog/digital converter which was put on line with a DEC LSI 11/73 computer operating under RT-11/TSX+. The digitized data were then used for computation of leukocyte and leukoembolus sizes, speed of embolization/deembolization, movement and aggregation characteristics, with the utilization of computer programs written in Fortran and Macro Assembly languages. This methodology can yield a quantitative and in-depth characterization of complement-leukocyte interaction, leukoembolization, leukostasis and deembolization.

ISSN:0098-6445    

DOI:10.1080/00986448608911759

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

A cone and plate viscometer, Coulter counter, and spectrophotometer were used to study platelet modulation of polymorphonuclear leukocyte (PMNL) function caused by controlled shear stress. Aggregation and release of the enzymes β-glucuronidase and lactate dehydrogenase (LDH) were observed. PMNL suspensions in buffer (1.0 × 107cells/ml, final concentration) did not show any aggregate formation or enzyme release at shear stresses below 150 dynes/cm2for an exposure time of 1 minute. However, supernatant plasma from sheared platelets initiated PMNL aggregation and β-glucuronidase release at moderate shear stresses (150 dynes/cm2for 1 minute). These stress-induced alterations were compared with chemotactic factor and calcium ionophore A23187 induced functional changes. LDH release was less than 3% in all the experiments indicating little overt lysis. The shear-induced enzyme release was enhanced by cytochalasin B and heparinized samples showed greater effects than citrated samples. The use of a cyclooxygenase inhibitor (acetylsalicyclic acid, 50 μM) did not suppress the aggregation of PMNLs after shear. However, preincubation with lipoxygenase inhibitors (nordihydroguaiaretic acid, 10 μM, and U-60257, 10 μM) suppressed aggregation and enzyme release. The formation of arachidonic acid metabolites activated by shear stress was documented by reversed phase-high pressure liquid chromatography. Thus, an interaction between C-12 and C-5 lipoxygenase enzymes can promote the formation of leukotriene B4and these data strongly support the possibility of a cooperation between platelet and PMNL arachidonic acid metabolites in shear-induced PMNL functional changes.

ISSN:0098-6445    

DOI:10.1080/00986448608911760

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor