The effect of surface roughness on tlie performance of hydrodynanric slider bearings is studied. A generalized form of surface rorrghness characterized by a stochastic random variable with tron-zero mean, variance and skewness is assrtnred to define the bearing srtrface topograplry. Various film shapes srtch as: plane slider; esponential, secant and hyperbolic are considered. The results are obtoitred for the general lubricant film shape in inregral form which are nrmlerically computed for the shapes under consideration. The results are presented both graphically as well as in tabular form. The performance of a rorrgh bearing can be considered in terms of an identical snzootl~ bearing with an equivaletrt film thickness. It is observed, for the lubricant filnr shapes rmder consirleration, that the increasing positive values of a, a and E decrease the load carrying capacity, frictional force and Final manuscript approved January 12, 1999 Review led by Marc Carpino temperature rise while it increases tlie coeflcient of friction. Increasing positive values of a and E sliifr the center of press~tre towards the outlet edge. For negative valrres of a, the increasing value reverses tire trend of the effect on petfortnrrnce choructeristics which is in conformity with the physical aspects of the problem. A sinrilar trend is observed in case of the effect of negative valrtes of E. Thus, a negatively skewed surface rortghness nrodijies the performance of the slider bearings whereas the petfornlance of a bearing suffers on account of positively skewed srrrface ro~rghness. Moreover, it is noticed that in the case of e.vpotienria1 and hyperbolic slider bearings the effect of increasing vairres of a is more pronoutrced ~jher-eas in case of platre slider and secant shaped slider this effect is marginal. KEY WORDS Hydrodynamic Slider Bearings; Surface Roughness NOMENCLATURE d = variance E = expected value h(s)= film thickness P = viscosity of the lubricant h(x) = film thickness measured between the nominal mean levels /'I = inlet film thickness of the bearing surfaces h0 = outlet film thickness /IS = stochastic film thickness measured from the nominal mean = h, -h, level of the bearing surface F = dimensionless frictional force P = lubricant pressure f = dimensionless friction co-efficient P = expected value of the lubricant pressure x = dimensionless center of pressure P = dimensionless pressure AT = dimensionless temperature rise W = load carrying capacity = gravitational acceleration W = dimensionless load carrying capacity J =Joule's mechanical equivalent of heat a = mean of the stochastic film thickness c = specific heat of the lubricant o = standard deviation of the stochastic film thickness P = density of the lubricant E = measure of symmetry of the stochastic random variable h 29 1
Recombinant protein production (RPP) in Escherichia coli (E. coli) often induces metabolic burden to the cells that compromise their overall growth and productivity. Amino acid starvation due to RPP is a major contributor of the metabolic burden on the cells and induces global stress response known as a stringent‐like response. In this study, the effect of amino acid supplementation in a chemically defined medium on cellular growth and recombinant pramlintide production was investigated. Based on the consumption profile, few amino acids were categorized as growth‐promoting (GP1) and protein production promoting (GP2). Feeding strategies of GP1 and GP2 were tested in shake flasks followed by scale up into the bioreactor. A 40% increase in the recombinant pramlintide (rPramlintide) production (protein concentration of 3.09 ± 0.12 g/L and yield of 227.69 ± 19.72 mg pramlintide per gram dry cell weight) was realized. Furthermore, transcriptomics data indicated the downregulation of several genes associated with global stress response and genes involved in amino acid biosynthesis in test culture, supported by proteomics analysis. These results signify that the external supply of critical amino acids decreases cellular stress during RPP and improves process productivity.
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