Enzyme kinetics for a two-step enzymic reaction with comparable initial enzyme-substrate ratios

We extend the validity of the quasi-steady state assumption for a model double intermediate enzyme-substrate reaction to include the case where the ratio of initial enzyme to substrate concentration is not necessarily small. Simple analytical solutions are obtained when the reaction rates and the initial substrate concentration satisfy a certain condition. These analytical solutions compare favourably with numerical solutions of the full system of differential equations describing the reaction. Experimental methods are suggested which might permit the application of the quasi-steady state assumption to reactions where it may not have been obviously applicable before

An updated estimate of the economic costs of human illness due to food borne Salmonella in the United States

The Economic Research Service (ERS) of the U.S Department of Agriculture updated earlier estimates of the medical costs and productivity losses due to foodbome Salmonella infections in the United States. The update is based on a new estimate of annual salmonellosis cases by the Foodbome Diseases Active Surveillance Network (FoodNet) and new data on medical care for salmonellosis from a medical claims database. Using this information, ERS estimated that the annual economic costs of human illness due to foodbome Salmonella infections are $2.3 billion (in 1998 dollars). Data on foodbome disease outbreaks suggest that 6-9 percent of food borne Salmonella infections are associated with pork and pork products, so the annual costs of human illness due to Salmonella-contaminated pork appear to be approximately$0.1-0.2 billion

The Dynamics of Viral Marketing

We present an analysis of a person-to-person recommendation network, consisting of 4 million people who made 16 million recommendations on half a million products. We observe the propagation of recommendations and the cascade sizes, which we explain by a simple stochastic model. We analyze how user behavior varies within user communities defined by a recommendation network. Product purchases follow a 'long tail' where a significant share of purchases belongs to rarely sold items. We establish how the recommendation network grows over time and how effective it is from the viewpoint of the sender and receiver of the recommendations. While on average recommendations are not very effective at inducing purchases and do not spread very far, we present a model that successfully identifies communities, product and pricing categories for which viral marketing seems to be very effective

Crystal structures and magnetic order of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba): Possible orbital glass ferromagnetic state

The crystallographic and magnetic properties of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba) were investigated by means of neutron powder diffraction. All studied samples show the orthorhombic perovskite crystal structure, space group Pnma, with regular (Mn,Ru)O{6} octahedra and no chemical ordering of the Mn3+ and Ru4+ ions. Ferromagnetic spin structures were observed below Tc ~ 200-250 K, with an average ordered moment of ~ 1.8-2.0 Bohr magnetons per (Mn,Ru). The observation of long-range ferromagnetism and the absence of orbital ordering are rationalized in terms a strong Mn-Ru hybridization, which may freeze the orbital degree of freedom and broaden the eg valence band, leading to an orbital-glass state with carrier-mediated ferromagnetism

Scalar flux profile relationships over the open ocean

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S09, doi:10.1029/2003JC001960.The most commonly used flux-profile relationships are based on Monin-Obukhov (MO) similarity theory. These flux-profile relationships are required in indirect methods such as the bulk aerodynamic, profile, and inertial dissipation methods to estimate the fluxes over the ocean. These relationships are almost exclusively derived from previous field experiments conducted over land. However, the use of overland measurements to infer surface fluxes over the ocean remains questionable, particularly close to the ocean surface where wave-induced forcing can affect the flow. This study investigates the flux profile relationships over the open ocean using measurements made during the 2000 Fluxes, Air-Sea Interaction, and Remote Sensing (FAIRS) and 2001 GasEx experiments. These experiments provide direct measurement of the atmospheric fluxes along with profiles of water vapor and temperature. The specific humidity data are used to determine parameterizations of the dimensionless gradients using functional forms of two commonly used relationships. The best fit to the Businger-Dyer relationship [ Businger, 1988 ] is found using an empirical constant of a q = 13.4 ± 1.7. The best fit to a formulation that has the correct form in the limit of local free convection [e.g., Wyngaard, 1973 ] is found using a q = 29.8 ± 4.6. These values are in good agreement with the consensus values from previous overland experiments and the Coupled Ocean-Atmosphere Response Experiment (COARE) 3.0 bulk algorithm [ Fairall et al., 2003 ]; e.g., the COARE algorithm uses empirical constants of 15 and 34.2 for the Businger-Dyer and convective forms, respectively. Although the flux measurements were made at a single elevation and local similarity scaling is applied, the good agreement implies that MO similarity is valid within the marine atmospheric surface layer above the wave boundary layer.The FAIRS work was supported by the Office of Naval Research grant N00014-00-1-0403 while the GasEx work was supported by the National Science Foundation grant OCE-9986724

The cultural side of value creation

The question of how organizations create value has become a central question for understanding inter-firm competition and performance differentials. Much of the work on the topic emphasizes the importance of technological innovation for improving operational efficiency and/or product functionality . Accordingly, much of the work in the area has focused on understanding the development of technological capabilities and the dynamics of competition among different technologies. Whereas this line of research has contributed greatly to our understanding of value creation through technology performance improvement, it has also left unexplored the strategies for differentiating products on the basis of their cultural significance. Yet, research in a wide variety of disciplines ranging from anthropology, to cultural sociology, and consumer behavior shows that consumers value products not only for their functional and technical performance, but also for their cultural meanings. The infusion of products with cultural meanings enables consumers to use these products to make statements about their personal and social identity and status. It is therefore well understood that consumers derive value not only from what products do (functional value), but also from what they signify in a given social group (symbolic value). While strategy scholars recognize that product meanings are a source of differentiation and generate price premia (Porter, 1980), they also tend to view the activities that generate them – e.g. branding – as a part of the marketing strategy of the firm. More generally, strategy research has been criticized for its reluctance to delve into the demand side of value-creation. Rooted in disciplinary assumptions about atomistic consumers with idiosyncratic preferences, strategy researchers view demand as largely exogenous and ignore its cultural embeddedness in social conventions that define the cultural meanings of objects and shape consumption choices. As a result, they have given limited attention to the question of how firms can strategically manage the symbolic value of their products. In this paper we propose a cultural perspective on value creation that can direct strategic organization research toward the systematic investigation of how producers engage with the cultural meaning systems that supply frameworks for interpretation and valuation of goods. To guide research in this direction we first discuss how products acquire cultural significance and then outline three core implications of these ideas for the strategy and organization of firms. First, we discuss how recognizing the cultural significance of products shifts attention from technological innovation that alters product functionality to cultural innovation that alters their cultural significance. Second, we explain the need to develop distinct cultural resources that enable firms to identify and exploit opportunities for cultural innovation. Third, we draw attention to the need for cultural intent defined as developing an explicit strategy for utilizing cultural resources to achieve specific cultural positioning for the firm’s products

Science Literacy: Using Research-Based Facts to Make Real-World Decisions

Science Literacy: Using Research-Based Facts to Make Real-World Decisions As the next generation of leaders is entering the educational pipeline, it’s important to have an emphasis on science, technology, engineering and mathematics (STEM) to solve the grand challenge of feeding 9 billion people by 2050

International Spread of Multidrug-resistant Salmonella Schwarzengrund in Food Products

This serovar was isolated from persons, food, and food animals in Thailand, Denmark, and the United States