Network Evolution of Body Plans

Segmentation in arthropod embryogenesis represents a well-known example of body plan diversity. Striped patterns of gene expression that lead to the future body segments appear simultaneously or sequentially in long and short germ-band development, respectively. Regulatory genes relevant for stripe formation are evolutionarily conserved among arthropods, therefore the differences in the observed traits are thought to have originated from how the genes are wired. To reveal the basic differences in the network structure, we have numerically evolved hundreds of gene regulatory networks that produce striped patterns of gene expression. By analyzing the topologies of the generated networks, we show that the characteristics of stripe formation in long and short germ-band development are determined by Feed-Forward Loops (FFLs) and negative Feed-Back Loops (FBLs) respectively. Network architectures, gene expression patterns and knockout responses exhibited by the artificially evolved networks agree with those reported in the fly Drosophila melanogaster and the beetle Tribolium castaneum. For other arthropod species, principal network architectures that remain largely unknown are predicted.Comment: 35 pages, 4 figures and 1 tabl

Do High Technology Policies Work? An Analysis of High Technology Industry Employment Growth in U.S. Metropolitan Areas, 1988-1998

In the past three decades, federal, state and local governments have launched an array of new high technology development programs. Researchers and policy-makers disagree about the relative merits of these policies as economic development tools. We address two questions: (1) Do these policies affect high technology industry employment net of location and agglomeration factors? (2) Do these policies interact with existing agglomeration advantages to boost high technology industry employment? Using a conditional change score design to examine the effects of seven major high technology policies on the change in high technology industry employment in metropolitan statistical areas (MSAs) between 1988 and 1998, we find that two programs--technology grant and loan programs, and technology research parks--have direct effects net of controls for location and agglomeration factors. All of these programs, except for SBIRs and technology development programs, positively interact with existing agglomeration advantages to create high technology industry employment growth. Technology development programs compensate for deficits in agglomeration resources. High technology growth is an organic, path-dependent process that depends primarily on location and agglomeration advantages but also can be planned by adapting high technology programs to magnify these local growth advantages.Urban Affairs Program (Project #739365) and the John Glenn Institute for Public Service and Public Policy, The Ohio State Universit

Creating High-Technology Growth: High-Tech Employment Growth in U.S. Metropolitan Areas, 1988-1998

Growth in the share of high-technology employment is critical to discussions of the postindustrial transition. Do new state and local technology policies create growth in the share of high-technology employment? This article examines this question along with the effects of location and agglomeration advantages, identifying sources of qualitative growth in the U.S. economy. Copyright (c) 2008 by the Southwestern Social Science Association.

Review: Denitrifying bioreactors—An approach for reducing nitrate loads to receiving waters

Low-cost and simple technologies are needed to reduce watershed export of excess nitrogen to sensitive aquatic ecosystems. Denitrifying bioreactors are an approach where solid carbon substrates are added into the flow path of contaminated water. These carbon (C) substrates (often fragmented wood-products) act as a C and energy source to support denitrification; the conversion of nitrate (NO³⁻) to nitrogen gases. Here, we summarize the different designs of denitrifying bioreactors that use a solid C substrate, their hydrological connections, effectiveness, and factors that limit their performance. The main denitrifying bioreactors are: denitrification walls (intercepting shallow groundwater), denitrifying beds (intercepting concentrated discharges) and denitrifying layers (intercepting soil leachate). Both denitrifcation walls and beds have proven successful in appropriate field settings with NO³⁻ removal rates generally ranging from 0.01 to 3.6 g N m⁻³ day⁻¹ for walls and 2–22 g N m⁻³ day⁻¹ for beds, with the lower rates often associated with nitrate-limitations. Nitrate removal is also limited by the rate of C supply from degrading substrate and removal is operationally zero-order with respect to NO³⁻ concentration primarily because the inputs of NO³⁻ into studied bioreactors have been generally high. In bioreactors where NO³⁻ is not fully depleted, removal rates generally increase with increasing temperature. Nitrate removal has been supported for up to 15 years without further maintenance or C supplementation because wood chips degrade sufficiently slowly under anoxic conditions. There have been few field-based comparisons of alternative C substrates to increase NO³⁻ removal rates but laboratory trials suggest that some alternatives could support greater rates of NO³⁻ removal (e.g., corn cobs and wheat straw). Denitrifying bioreactors may have a number of adverse effects, such as production of nitrous oxide and leaching of dissolved organic matter (usually only for the first few months after construction and start-up). The relatively small amount of field data suggests that these problems can be adequately managed or minimized. An initial cost/benefit analysis demonstrates that denitrifying bioreactors are cost effective and complementary to other agricultural management practices aimed at decreasing nitrogen loads to surface waters. We conclude with recommendations for further research to enhance performance of denitrifying bioreactors

Hypothesis testing: discussion

Discussion on the papers by Zellner, Arnold and Siow, Aloysius, Posterior odds ratios for selected regression hypotheses and by Bernardo, José M., A Bayesian analysis of classical hypotheses testing, both of them part of a round table on Hypothesis testing held in the First International Congress on Bayesian Methods (Valencia, Spain, 28 May - 2 June 1979