Neptune's Migration into a Stirred-Up Kuiper Belt: A Detailed Comparison of Simulations to Observations

Nbody simulations are used to examine the consequences of Neptune's outward migration into the Kuiper Belt, with the simulated endstates being compared rigorously and quantitatively to the observations. These simulations confirm the findings of Chiang et al. (2003), who showed that Neptune's migration into a previously stirred-up Kuiper Belt can account for the Kuiper Belt Objects (KBOs) known to librate at Neptune's 5:2 resonance. We also find that capture is possible at many other weak, high-order mean motion resonances, such as the 11:6, 13:7, 13:6, 9:4, 7:3, 12:5, 8:3, 3:1, 7:2, and the 4:1. The more distant of these resonances, such as the 9:4, 7:3, 5:2, and the 3:1, can also capture particles in stable, eccentric orbits beyond 50 AU, in the region of phase space conventionally known as the Scattered Disk. Indeed, 90% of the simulated particles that persist over the age of the Solar System in the so-called Scattered Disk zone never had a close encounter with Neptune, but instead were promoted into these eccentric orbits by Neptune's resonances during the migration epoch. This indicates that the observed Scattered Disk might not be so scattered. This model also produced only a handful of Centaurs, all of which originated at Neptune's mean motion resonances in the Kuiper Belt. We also report estimates of the abundances and masses of the Belt's various subpopulations (e.g., the resonant KBOs, the Main Belt, and the so-called Scattered Disk), and also provide upper limits on the abundance of Centaurs and Neptune's Trojans, as well as upper limits on the sizes and abundances of hypothetical KBOs that might inhabit the a>50 AU zone.Comment: 60 pages, 16 figures. Accepted for publication in the Astronomical Journa

Casting a wide net: use of diverse model organisms to advance toxicology

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Hahn, M. E., & Sadler, K. C. Casting a wide net: use of diverse model organisms to advance toxicology. Disease Models & Mechanisms, 13, (2020): dmm.043844, doi: 10.1242/dmm.043844.Toxicology – the study of how chemicals interact with biological systems – has clear relevance to human health and disease. Persistent exposure to natural and synthetic chemicals is an unavoidable part of living on our planet; yet, we understand very little about the effects of exposure to the vast majority of chemicals. While epidemiological studies can provide strong statistical inference linking chemical exposure to disease, research in model systems is essential to elucidate the mechanisms of action and to predict outcomes. Most research in toxicology utilizes a handful of mammalian models that represent a few distinct branches of the evolutionary tree. This narrow focus constrains the understanding of chemical-induced disease processes and systems that have evolved in response to exposures. We advocate for casting a wider net in environmental toxicology research to utilize diverse model systems, including zebrafish, and perform more mechanistic studies of cellular responses to chemical exposures to shift the perception of toxicology as an applied science to that of a basic science. This more-inclusive perspective will enrich the field and should remain central to research on chemical-induced disease.K.C.S. acknowledges support from the National Institutes of Health (NIH)(5R01AA018886). M.E.H. acknowledges support from the National Institute ofEnvironmental Health Sciences (NIEHS) through the Boston University SuperfundResearch Program (P42ES007381) and the Woods Hole Center for Oceans andHuman Health (NIEHS grant P01ES028938 and National Science Foundation grantOCE-1840381)

How closely do baryons follow dark matter on large scales?

We investigate the large-scale clustering and gravitational interaction of baryons and dark matter (DM) over cosmic time using a set of collisionless N-body simulations. Both components, baryons and DM, are evolved from distinct primordial density and velocity power spectra as predicted by early-universe physics. We first demonstrate that such two-component simulations require an unconventional match between force and mass resolution (i.e. force softening on at least the mean particle separation scale). Otherwise, the growth on any scale is not correctly recovered because of a spurious coupling between the two species at the smallest scales. With these simulations, we then demonstrate how the primordial differences in the clustering of baryons and DM are progressively diminished over time. In particular, we explicitly show how the BAO signature is damped in the spatial distribution of baryons and imprinted in that of DM. This is a rapid process, yet it is still not fully completed at low redshifts. On large scales, the overall shape of the correlation function of baryons and DM differs by 2% at z = 9 and by 0.2% at z = 0. The differences in the amplitude of the BAO peak are approximately a factor of 5 larger: 10% at z = 9 and 1% at z = 0. These discrepancies are, however, smaller than effects expected to be introduced by galaxy formation physics in both the shape of the power spectrum and in the BAO peak, and are thus unlikely to be detected given the precision of the next generation of galaxy surveys. Hence, our results validate the standard practice of modelling the observed galaxy distribution using predictions for the total mass clustering in the Universe.Comment: 9 pages, 6 figures. Replaced with version published in MNRA

FARM BUSINESS GOALS AND COMPETITIVE ADVANTAGE

This paper investigates empirically the relationship between both farm business goals and sources of competitive advantage, and various farm and producer characteristics using new primary data collected from a survey of Ohio farmers. Results show that most farmers do not recognize sources of competitive advantage and practice strategy implementation beyond reliance on longstanding paradigms for success within the context of government farm program support and the use of traditional risk management tools. However, several key insights emerge. Farmers who engage in cost leadership strategies are more profitable. Farmers who suggest that the goal of their farming operation is to enhance profitability/efficiency use more management tools, while lifestyle farmers use fewer. Larger farmers are more apt to engage in a cost leadership strategy, while those with higher debt-to-asset ratios and those that are more livestock oriented are more likely to engage in differentiation or focus strategies. Smaller farmers and those that produce specialty or value-added crops are more likely to focus on a particular niche market. Lastly, the use of the Internet as part of the farming operation does not influence the probability of engaging in any particular business strategy. It is apparent that the government farm program has contributed to a strategic where few producers have an explicit or implicit farm business strategy beyond "working the program" and acting as price takers. Or if a strategic choice is apparent, it rests primarily with cost leadership.Farm Management,

The Myth of Network Neutrality and What We Should Do About It

A quarter century ago, there was a very influential paper that shaped thinking on how best to design what we now call the Internet. The article offered a design principle called "end-to-end." The idea was to keep the inner part of a computer network as simple as possible and allow the "intelligence" to reside at the edges of the network closer to the end user. Proponents of this grand design have pushed for net neutrality legislation, which would discourage access providers from placing any intelligence in the inner part of the network. Their ideal of a "dumb network" would be achieved by preventing access providers from charging content providers for prioritized delivery and other quality enhancements made possible by placing intelligence at the center of the network. This essay examines the merits of the end-to-end argument as it relates to the net neutrality debate. First, we review the evidence on the current status of the Internet, concluding that all bits of information are not treated equally from an economic standpoint. Second, we demonstrate that because consumers and business place a premium on speed and reliability for certain kinds of Internet services, network owners and specialized service providers have responded with customized offerings. Third, we consider our findings in the context of the current legislative proposals involving net neutrality. Fourth, we consider some of the problems with regulating prices and quality of service, which is essentially what the net neutrality proponents propose. Our principle conclusions are that the end-to-end principle does not make sense from an economic perspective and that further regulation of the Internet is not warranted at this point in time.Technology and Industry

An Analysis of the Ninth Government Report on the Costs and Benefits of Federal Regulations

This paper critically reviews the draft of the Office of Management and Budget's ninth report on the benefits and costs of federal regulation. The draft report is similar to previous reports, and does not break new ground. We offer seven recommendations, six for OMB and one for Congress, that would help hold lawmakers and regulators more accountable for the regulations they produce. Our recommendations focus on getting the regulatory agencies to produce better analysis, making that analysis more transparent and readily available, and making the regulatory process itself more transparent. We recommend that OMB: examine the extent to which regulations maximize net benefits; include a scorecard showing the number and percentage of final regulations that pass a benefit-cost test based on factors that can be quantified and monetized; request that all agencies report on the extent to which they comply with OMB's guidelines for conducting regulatory analysis; provide guidelines for assessing the effectiveness of antiterrorism regulations; include a discussion of the costs and benefits of antitrust activities in its annual report; and facilitate the use of information markets to increase overall economic efficiency and to inform regulatory decision making. We also recommend that Congress require all agencies to comply with OMB's guidelines for conducting regulatory analysis.