455 research outputs found
Michaelis-Menten dynamics in protein subnetworks
To understand the behaviour of complex systems it is often necessary to use
models that describe the dynamics of subnetworks. It has previously been
established using projection methods that such subnetwork dynamics generically
involves memory of the past, and that the memory functions can be calculated
explicitly for biochemical reaction networks made up of unary and binary
reactions. However, many established network models involve also
Michaelis-Menten kinetics, to describe e.g. enzymatic reactions. We show that
the projection approach to subnetwork dynamics can be extended to such
networks, thus significantly broadening its range of applicability. To derive
the extension we construct a larger network that represents enzymes and enzyme
complexes explicitly, obtain the projected equations, and finally take the
limit of fast enzyme reactions that gives back Michaelis-Menten kinetics. The
crucial point is that this limit can be taken in closed form. The outcome is a
simple procedure that allows one to obtain a description of subnetwork
dynamics, including memory functions, starting directly from any given network
of unary, binary and Michaelis-Menten reactions. Numerical tests show that this
closed form enzyme elimination gives a much more accurate description of the
subnetwork dynamics than the simpler method that represents enzymes explicitly,
and is also more efficient computationally
Empirical Examination of the Role of Three Sets of Innovation Attributes for Determining Adoption of IRCTC Mobile Ticketing Service
The Indian Railway Catering and Tourism Corporation Limitedâs (IRCTC) mobile ticketing was recently introduced in India. In this study of its adoption, three competing attribute-sets are compared. This study aims to reveal the attribute-set best predicting its adoption. The research model was empirically tested and validated using SPSS. Four attributes from the Diffusion of Innovations (DOI) theory, four from the PCI theory, and four from Tornatzky and Kleinâs meta-analysis significantly affected behavioral intentions. Only complexity failed to influence use intentions, and behavioral intention and riskiness significantly impacted adoption
The State of Veteran Entrepreneurship Research: What We Know and Next Steps
This paper reviews the current state of research on veteran entrepreneurship, identifies critical gaps, and offers recommendations for future research. Helpful for awareness of the entrepreneurship industry
E-government adoption: A cultural comparison
This is the author's accepted manuscript. The final published article is available from the link below. Copyright @ Springer Science + Business Media, LLC 2008.E-government diffusion is an international phenomenon. This study compares e-government adoption in the U.K. to adoption in the U.S. In particular, this study seeks to determine if the same factors are salient in both countries. Several studies have explored citizen acceptance of e-government services in the U.S. However, few studies have explored this phenomenon in the U.K. To identify the similarities and differences between the U.K. and the U.S. a survey is conducted in the U.K. and the findings are compared to the literature that investigates diffusion in the U.S. This study proposes a model of e-government adoption in the U.K. based on salient factors in the U.S. A survey is administered to 260 citizens in London to assess the importance of relative advantage, trust and the digital divide on intention to use e-government. The results of binary logistic regression indicate that there are cultural differences in e-government adoption in the U.K. and the U.S. The results indicate that of the prevailing adoption constructs, relative advantage and trust are pertinent in both the U.S. and the U.K., while ICT adoption barriers such as access and skill may vary by culture. Implications for research and practice are discussed
Exact Product Formation Rates for Stochastic Enzyme Kinetics
The
rate of product formation is an important measure of the speed
of enzyme reactions. Classical studies of enzyme reactions have been
conducted in dilute solutions and under conditions that justified
the substrate abundance assumption. However, such assumption is well-known
to break down in the context of cellular biochemistry. Instead, the
concentration of available substrate can become rate limiting. Here
we use the chemical master equation to obtain expressions for the
instantaneous and time averaged rate of product formation without
invoking the conventional substrate abundance assumption. The expressions
are derived for a broad range of enzyme reaction mechanisms, including
those that involve one or many enzyme molecules, require multiple
substrates, and exhibit cooperativity and substrate inhibition. Novel
results include: (i) the relationship between the average rate of
product formation (calculated over the time it takes for the reaction
to finish) and the substrate concentration, for a MichaelisâMenten
(MM) reaction with one enzyme molecule, is approximately given by
a logarithmically corrected MM form; (ii) intrinsic noise decreases
the sharpness of cooperative switches but enhances the filtering response
of substrate inhibition; (iii) the relationship between the initial
average rate of product formation and the initial substrate concentration
for a MM reaction with no reversible reaction and with any number
of enzyme and substrate molecules is a sum of MichaelisâMenten
equations
CHARACTERISTICS OF THE INCREASED ADRENOCORTICAL FUNCTION OBSERVED IN MANY OBESE PATIENTS *
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75360/1/j.1749-6632.1965.tb34805.x.pd
The Early Days of Research on Carbonic Anhydrase
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73862/1/j.1749-6632.1984.tb12310.x.pd
Impact of environmental and genetic factors on the scale shape of zebrafish, Danio rerio (Hamilton 1822): A geometric morphometric study
Intraspecific morphological variability may reflect either genetic divergence among groups of individuals or response of individuals to environmental circumstances within the frame of phenotypic plasticity. Several studies were able to discriminate wild fish populations based on their scale shape. Here we examine whether the variations in the scale shape in fish populations could be related to genetic or environmental factors, or to both of them. In the first experiment, two inbred lines of zebrafish Danio rerio (Hamilton 1822) reared under identical environmental conditions were compared. Secondly, to find out what effect environmental factors might have, offsprings were divided into two groups and reared on different diets for 12 weeks. Potential recovery of scales from an environmental effect was also assessed. Experimental groups could successfully be distinguished according to the shape of scales in both experiments, and the results showed that both genetic and environmental factors may notably influence scale shape. It was concluded that scale shape analysis might be used as an explanatory tool to detect potential variability of environmental influences impacting genetically homogeneous groups of fish. However, due to its sensitivity to environmental heterogeneity, the applicability of this technique in identifying intraspecific stock membership of fish could be limited
Compulsive buying and branding phenomena
The purpose of this paper was to explore the impact of brand variables such as brand awareness, brand loyalty, brand attachment, and perceived brand quality on compulsive buying behavior. A self-administered questionnaire, containing demographic items and items related to compulsive buying, brand awareness, brand loyalty, brand attachment and perceived quality, was used to collect data. Participants were 269 US university students at a large mid-western university (138 men, 131 women; mean age = 21.96). Data were analyzed using descriptive statistics, t-test and MANOVA/ANOVA. Reliability of all scales was acceptable. In the current study, 18% of the participants were classified as compulsive buyers. Women showed higher compulsive buying tendency than men. Participants with greater compulsive buying tendency scored higher on brand attachment and brand loyalty and lower on brand awareness; there was no difference in scores on perceived brand quality. Results support that brand variables such as brand awareness, brand loyalty, and brand attachment are related to compulsive buying behavior. New perceptions and implications for both academicians and practitioners are provided
Exciton/Charge-transfer Electronic Couplings in Organic Semiconductors
Charge transfer (CT) states and excitons are important in energy conversion processes that occur in organic light emitting devices (OLEDS) and organic solar cells. An ab initio density functional theory (DFT) method for obtaining CTâexciton electronic couplings between CT states and excitons is presented. This method is applied to two organic heterodimers to obtain their CTâexciton coupling and adiabatic energy surfaces near their CTâexciton diabatic surface crossings. The results show that the new method provides a new window into the role of CT states in excitonâexciton transitions within organic semiconductors.United States. Dept. of Energy (DEFG02- 07ER46474)David & Lucile Packard Foundation (Fellowship
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