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Alan S. Michaels

Bio: Alan S. Michaels is an academic researcher from Stanford University. The author has contributed to research in topics: Membrane & Hollow fiber membrane. The author has an hindex of 16, co-authored 21 publications receiving 1367 citations.

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TL;DR: It is concluded that not only is the log-probability correlation a reasonable and convenient means for interpreting and predicting membrane sieving data, but that most membranes examined conform surprisingly closely to a log-normal-probs relationship between θ and α.
Abstract: Sieving curves [variations in sieving coefficient (θ) with Einstein-Stokes radius (α) of the permeating macromolecule] of a number of synthetic ultrafiltration membranes, and of a variety of mammalian glomerular membranes studied in vivo, conform surprisingly closely to a log-normal-probability relationship between θ and α which allows determination of the complete sieving curve from experimental measurement of only two sieving coefficients for two macrosolutes of differing ESR. Even more striking is the finding that, for all membranes examined, the value of α corresponding to θ = 0.5 (the inflection point in the sieving curve) varies only between 17 and 34 A, and geometric standard deviation about the mean macrosolute radius ([sgrave]α), which is inversely related to the “sharpness” of the sieving curve, lies between 1.2 and 1.7. It is concluded that not only is the log-probability correlation a reasonable and convenient means for interpreting and predicting membrane sieving data, but that most ...

179 citations

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TL;DR: It is concluded that the development of large pores (or defects) within the glomerular membrane in advanced diabetic nephropathy permits the unrestricted passage of large plasma proteins into the urine.

146 citations

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TL;DR: It is suggested that uncharged polysaccharides with ESR creatinine , thus accounting for the increase of CCreatinine above C inulin in patients with the nephrotic syndrome, is accounted for.

141 citations

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TL;DR: In this article, a simple particle filtration model, based on the build-up of a BSA filter cake of constant hydraulic permeability, adequately correlates the observed results of the solute polarization process.

131 citations

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TL;DR: The inhibition of ethanol production and the reduction in fermentation efficiency arose primarily from the accumulation of CO(2) gas within the sealed reactor shell space.
Abstract: Saccharomyces cerevisiae ATCC 4126 was grown within the macroporous matrix of asymmetric-walled polysulfone hollow-fiber membranes and on the exterior surfaces of isotropic-walled polypropylene hollow-fiber membranes. Nutrients were supplied and products were removed by single-pass perfusion of the fiber lumens. Growth of yeast cells within the macrovoids of the asymmetric-walled membranes attained densities of greater than 10 cells per ml and in some regions accounted for nearly 100% of the available macrovoid volume, forming a tissue-like mass. A radial distribution of cell packing existed across the fiber wall, indicating an inadequate glucose supply to cells located beyond 100 mum from the lumen surface. By comparison, yeast cell growth on the exterior surfaces of the isotropic-walled membranes resulted in an average density of 3.5 x 10 viable cells per ml. Ethanol production by reactors containing isotropic polypropylene fibers reached a maximum value of 26 g/liter-h based on the total reactor volume. Reactor performance depended on the fiber packing density and on the glucose medium flow rate and was limited by low nutrient and product transport rates. The inhibition of ethanol production and the reduction in fermentation efficiency arose primarily from the accumulation of CO(2) gas within the sealed reactor shell space.

126 citations


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TL;DR: The fundamental principles of physiology, metabolism, and analytical chemistry that are necessary to correctly interpret the serum creatinine concentration are reviewed and applied to important clinical circumstances, including aging, pregnancy, diabetes mellitus, drug administration, and acute and chronic renal failure.
Abstract: The serum creatinine concentration is widely interpreted as a measure of the glomerular filtration rate (GFR) and is used as an index of renal function in clinical practice. Glomerular filtration of creatinine, however, is only one of the variables that determines its concentration in serum. Alterations in renal handling and metabolism of creatinine and methodological interferences in its measurement may have a profound impact on the serum concentration of creatinine. We review the fundamental principles of physiology, metabolism, and analytical chemistry that are necessary to correctly interpret the serum creatinine concentration. These principles are then applied to important clinical circumstances, including aging, pregnancy, diabetes mellitus, drug administration, and acute and chronic renal failure. Despite numerous limitations, serum creatinine remains a useful clinical tool, but more accurate measures of renal function are frequently necessary.

1,550 citations

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TL;DR: In this article, the effect of various detoxification methods on the fermentability and chemical composition of lignocellulosic hydrolysates is discussed. But, the main focus of this paper is on the effects of different batch, fed-batch, and continuous fermentation strategies in relation to inhibition of fermentation.

1,320 citations

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TL;DR: It is concluded that true filtration markers with rs less than 20 A, including inulin, are unrestricted in glomerular disease, and that creatinine is hypersecreted progressively by remnant renal tubules as the disease worsens.

1,182 citations

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01 Jun 1983-Diabetes
TL;DR: A series of stages in the development of renal changes in diabetes, characterized by early hyperfunction and hypertrophy, are defined, which may be useful both in clinical work and in research activities.
Abstract: Alterations in renal function and structure are found even at the onset of diabetes mellitus. Studies performed over the last decade now allow definition of a series of stages in the development of renal changes in diabetes. Such a classification may be useful both in clinical work and in research activities. Stage 1 is characterized by early hyperfunction and hypertrophy. These changes are found at diagnosis, before insulin treatment. Increased urinary albumin excretion, aggravated during physical exercise, is also a characteristic finding. Changes are at least partly reversible by insulin treatment. Stage 2 develops silently over many years and is characterized by morphologic lesions without signs of clinical disease. However, kidney function tests and morphometry on biopsy specimens reveal changes. The function is characterized by increased GFR. During good diabetes control, albumin excretion is normal; however, physical exercise unmasks changes in albuminuria not demonstrable in the resting situation. During poor diabetes control albumin excretion goes up both at rest and during exercise. A number of patients continue in stage 2 throughout their lives. Stage 3, incipient diabetic nephropathy, is the forerunner of overt diabetic nephropathy. Its main manifestation is abnormally elevated urinary albumin excretion, as measured by radioimmunoassay. A level higher than the values found in normal subjects but lower than in clinical disease is the main characteristic of this stage, which appeared to be between 15 and 300 micrograms/min in the baseline situation. A slow, gradual increase over the years is a prominent feature in this very decisive phase of renal disease in diabetes when blood pressure is rising. The increased rate in albumin excretion is higher in patients with increased blood pressure. GFR is still supranormal and antihypertensive treatment in this phase is under investigation, using the physical exercise test. Stage 4 is overt diabetic nephropathy, the classic entity characterized by persistent proteinuria (greater than 0.5 g/24 h). When the associated high blood pressure is left untreated, renal function (GFR) declines, the mean fall rate being around 1 ml/min/mo. Long-term antihypertensive treatment reduces the fall rate by about 60% and thus postpones uremia considerably. Stage 5 is end-stage renal failure with uremia due to diabetic nephropathy. As many as 25% of the population presently entering the end-stage renal failure programs in the United States are diabetic. Diabetic nephropathy and diabetic vasculopathy constitute a major medical problem in society today.

870 citations

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TL;DR: A number of clinical studies have been performed in an attempt to dissect the particular component or components of the diabetic state responsible for these early elevations in glomerular filtration rate, and no single factor appears to account fully for this phenomenon.

819 citations