Based on computational approximations, product designers routinely simplify algebraic expressions of complex transfer functions, which, in turn, simplify post-design analysis. This practice is justified because both the simplified and actual transfer functions yield approximately equal average performance values. However, utilizing the design of a switching regulator circuit, it is shown that such simplified expressions underestimate output variation. The discrepancy between the actual and underestimated output variation spans an analytically unobservable failure event. Since the observable portion constitutes a partial characterization of product unreliability and quality problems, only a partial solution is possible at the design stage. This severely limits the effectiveness of concurrent product design, reliability, and quality assurance methodologies that are based on variation modeling and analysis. 相似文献
Abstract: The chemical stability of citral, a flavor component widely used in beverage, food, and fragrance products, in oil-in-water emulsions stabilized by surfactants with different charge characteristics was investigated. Emulsions were prepared using cationic (lauryl alginate, LAE), non-ionic (polyoxyethylene (23) lauryl ether, Brij 35), and anionic (sodium dodecyl sulfate, SDS) surfactants at pH 3.5. The citral concentration decreased over time in all the emulsions, but the rate of decrease depended on surfactant type. After 7 d storage, the citral concentrations remaining in the emulsions were around 60% for LAE- or Brij 35-stabilized emulsions and 10% for SDS-stabilized emulsions. An increase in the local proton (H+) concentration around negatively charged droplet surfaces may account for the more rapid citral degradation observed in SDS-stabilized emulsions. A strong metal ion chelator (EDTA), which has previously been shown to be effective at increasing the oxidative stability of labile components, had no effect on citral stability in LAE- or Brij 35-stabilized emulsions, but it slightly decreased the initial rate of citral degradation in SDS-stabilized emulsions. These results suggest the surfactant type used to prepare emulsions should be controlled to improve the chemical stability of citral in emulsion systems. 相似文献
PPARγ agonist DIM‐Ph‐4‐CF 3 , a template for RXRα agonist (E)‐3‐[5‐di(1‐methyl‐1H‐indol‐3‐yl)methyl‐2‐thienyl] acrylic acid: DIM‐Ph‐CF3 is reported to inhibit cancer growth independent of PPARγ and to interact with NR4A1. As both receptors dimerize with RXR, and natural PPARγ ligands activate RXR, DIM‐Ph‐4‐CF3 was investigated as an RXR ligand. It displaces 9‐cis‐retinoic acid from RXRα but does not activate RXRα. Structure‐based direct design led to an RXRα agonist.