14,747 research outputs found
Frequency domain criteria for lp-robust stability of systems with fuzzy parameters
The paper deals with the problem of determining stability margin of linear continuous-time system with fuzzy parametric uncertainty. Non-symmetric multivariate membership functions with lp -constraints describing the uncertainty of characteristic polynomial parameters are considered. An elegant solution, graphical in nature, based on generation of Tsypkin-Polyak plot is presented
Evolutionary optimization of a fed-batch penicillin fermentation process
This paper presents a genetic algorithms
approach for the optimization of a fed-batch penicillin
fermentation process. A customized float-encoding
genetic algorithm is developed and implemented to a
benchmark fed-batch penicillin fermentation process.
Off-line optimization of the initial conditions and set
points are carried out in two stages for a single variable
and multiple variables. Further investigations with online
optimization have been carried out to demonstrate
that the yield can be significantly improved with an
optimal feed rate profile. The results have shown that the
proposed approaches can be successfully applied to
optimization problems of fed-batch fermentation to
improve the operation of such processes
Theory of wing rock
A theory is developed for predicting wing rock characteristics. From available data, it can be concluded that wing rock is triggered by flow asymmetries, developed by negative or weakly positive roll damping, and sustained by nonlinear aerodynamic roll damping. A new nonlinear aerodynamic model that includes all essential aerodynamic nonlinearities is developed. The Beecham-Titchener method is applied to obtain approximate analytic solutions for the amplitude and frequency of the limit cycle based on the three degree-of-freedom equations of motion. An iterative scheme is developed to calculate the average aerodynamic derivatives and dynamic characteristics at limit cycle conditions. Good agreement between theoretical and experimental results is obtained
A stochastic spectral analysis of transcriptional regulatory cascades
The past decade has seen great advances in our understanding of the role of
noise in gene regulation and the physical limits to signaling in biological
networks. Here we introduce the spectral method for computation of the joint
probability distribution over all species in a biological network. The spectral
method exploits the natural eigenfunctions of the master equation of
birth-death processes to solve for the joint distribution of modules within the
network, which then inform each other and facilitate calculation of the entire
joint distribution. We illustrate the method on a ubiquitous case in nature:
linear regulatory cascades. The efficiency of the method makes possible
numerical optimization of the input and regulatory parameters, revealing design
properties of, e.g., the most informative cascades. We find, for threshold
regulation, that a cascade of strong regulations converts a unimodal input to a
bimodal output, that multimodal inputs are no more informative than bimodal
inputs, and that a chain of up-regulations outperforms a chain of
down-regulations. We anticipate that this numerical approach may be useful for
modeling noise in a variety of small network topologies in biology
Do Consumers Trust the National Inspection Exemption Brands? Evidence from Infant Formula in China
Consumers are often uncertain about product quality and have to rely on different information, either given or pursued, to assess quality. Developing countries may lack institutional and technical resources to rigorously monitor and enforce product quality standards and/or to implement market-based instruments where market failures are common. The information-based instruments on product quality may work well in these countries as they reduce information asymmetry between firms and consumers. This study investigates one particular information-based instrument, the National Inspection Exemption (NIE) system in China. China launched the National Inspection Exemption (NIE) System in various industries in 2000 to award firms who are in compliance with the quality standards, to inform consumers of product quality, and to lessen the pressure on regulatory monitoring and enforcement of product quality standards. Once a firm is granted the NIE title by China's National Administration of Quality Supervision, Inspection and Quarantine (AQSIQ), its products are exempted from quality inspections by all governmental agencies at different levels for three years; but it is obligated to report the product quality condition to the local AQSIQ office annually. The NIE titled firms are also allowed to include the title in the product label and to use the status in the advertisement campaign. Based on the theoretical framework, we establish the hypothesis that consumers are more willing to buy the product with the NIE title and the NIE title is likely to increase sales revenue when consumers lack of means to assess quality. The empirical application of China dairy industry supports the theoretical hypothesis. In particular, using the firm-level panel data, we find that the NIE title boots sales revenue and the impact is both statistically and economically significant based on the difference-in-difference estimate and the random-fixed effect estimations. Furthermore, using the survey data collected right after the 2008 China milk scandal regarding the brand choice of infant formula among 1,228 mothers with infants and young children, we find that consumers’ preference for the NIE title still present even the NIE titled firms are involved in a food scare event. The positive NIE preference is particularly strong among highly educated consumers and those who buy domestic brands.brand choice, food safety, product quality, national inspection exemption, quality standards, Food Consumption/Nutrition/Food Safety, Institutional and Behavioral Economics,
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