Globally smooth expressions for shock pressure decay in impacts

Hypervelocity meteorite impacts on planets subject the target to very high shock pressures. The isobars in the affected region are approximately spherical and centered on a point at a certain depth below the point of impact. The decay of the shock pressure with increasing distance from that center is usually represented in the form lg p=a+n lg(r/R), where p is the shock pressure, r is the distance from the center of the sphere, R is the radius of the impactor, and a and n are fitting constants; a similar relation is also used for the particle velocity. Although its simplicity seems to speak in its favor, this form has some problems: it is not bounded from above, thus necessitating an imposed maximum value that depends on additional assumptions; the slope of the decay is not accurately described by a single n for all r; the transition between domains with different decay parameters introduces kinks into p(r) at poorly defined points. It is therefore proposed to replace the decay law with other functional forms that are bounded and smooth and can be fully derived from data from numerical experiments. The proposed functions are applied to data of dunite-on-dunite impacts from the literature

Globally smooth approximations for shock pressure decay in impacts

New forms of empirical formulae that provide an approximate description of the decay of shock pressure with distance in hypervelocity impacts are proposed. These forms, which are intended for use in applications such as large-scale mantle convection models, are continuous and smooth from the point of impact to arbitrarily large distances, thereby avoiding the need to divide the domain into different decay regimes and yielding the maximum pressure in a self-consistent way without resorting to the impedance-match solution. Individual fits for different impact velocities as well as a tentative general fitting formula are given, especially for the case of dunite-on-dunite impacts. The temperature effects resulting from the shock are estimated for different decay models, and the differences between them are found to be substantial in some cases, potentially leading to over- or underestimates of impact heating and melt production in modeling contexts like mantle convection, where such parameterizations are commonly used to represent giant impacts

The habitability of a stagnant-lid Earth

Plate tectonics is a fundamental component for the habitability of the Earth. Yet whether it is a recurrent feature of terrestrial bodies orbiting other stars or unique to the Earth is unknown. The stagnant lid may rather be the most common tectonic expression on such bodies. To understand whether a stagnant-lid planet can be habitable, i.e. host liquid water at its surface, we model the thermal evolution of the mantle, volcanic outgassing of H$_2$O and CO$_2$, and resulting climate of an Earth-like planet lacking plate tectonics. We used a 1D model of parameterized convection to simulate the evolution of melt generation and the build-up of an atmosphere of H$_2$O and CO$_2$ over 4.5 Gyr. We then employed a 1D radiative-convective atmosphere model to calculate the global mean atmospheric temperature and the boundaries of the habitable zone (HZ). The evolution of the interior is characterized by the initial production of a large amount of partial melt accompanied by a rapid outgassing of H$_2$O and CO$_2$. At 1 au, the obtained temperatures generally allow for liquid water on the surface nearly over the entire evolution. While the outer edge of the HZ is mostly influenced by the amount of outgassed CO$_2$, the inner edge presents a more complex behaviour that is dependent on the partial pressures of both gases. At 1 au, the stagnant-lid planet considered would be regarded as habitable. The width of the HZ at the end of the evolution, albeit influenced by the amount of outgassed CO$_2$, can vary in a non-monotonic way depending on the extent of the outgassed H$_2$O reservoir. Our results suggest that stagnant-lid planets can be habitable over geological timescales and that joint modelling of interior evolution, volcanic outgassing, and accompanying climate is necessary to robustly characterize planetary habitability

Synthetic geophysical observables from martian mantle convection models, with application to InSight

Fully dynamical convection models of the martian mantle coupled with a mineralogical model and a parameterized representation of a large meteorite impact are used to derive geophysical observables, in particular synthetic density/gravity, seismic velocities, electrical conductivity, and heat flow, which are of interest with respect to the ongoing InSight mission

Taxonomy Based on Science is Necessary for Global Conservation

Taxonomy is a scientific discipline that has provided the universal naming and classification system of biodiversity for centuries and continues effectively to accommodate new knowledge. A recent publication by Garnett and Christidis (Garnett ST, Christidis L. Taxonomy anarchy hampers conservation. Nature. 2017; 546(7656):25±27. https://doi.org/10.1038/546025a) expressed concerns regarding the difficulty that taxonomic changes represent for conservation efforts and proposed the establishment of a system to govern taxonomic changes. Their proposal to restrict the freedom of taxonomic action through governing subcommittees that would review taxonomic papers for compliance and their assertion that the scientific community\u27s failure to govern taxonomy threatens the effectiveness of global efforts to halt biodiversity loss, damages the credibility of science, and is expensive to society are flawed in many respects. They also assert that the lack of governance of taxonomy damages conservation efforts, harms the credibility of science, and is costly to society. Despite its fairly recent release, Garnett and Christidis\u27 proposition has already been rejected by a number of colleagues. Herein, we contribute to the conversation between taxonomists and conservation biologists aiming to clarify some misunderstandings and issues in the proposition by Garnett and Christidis. Placing governance over the science of taxonomy blurs the distinction between taxonomy and nomenclature. Garnett and Christidis’s proposal is far-reaching but represents a narrow perspective of taxonomy, as utilized by conservation, and reflects an increasingly broad misunderstanding throughout biology of the scientific basis of taxonomy, formalized nomenclature, and the relationship between them. This trend may have resulted from the attenuation of instruction in taxonomic principles and, in particular, nomenclature at many universities, in part because of a shift in research priorities away from taxonomy. Garnett and Christidis assert that an “assumption that species are fixed entities underpins every international agreement on biodiversity conservation.” This assumption demonstrates a fundamental misunderstanding of taxonomy and the evolving view of what species represent. The essential features of science include documenting natural patterns and processes, developing and testing hypotheses, and refining existing ideas and descriptions of nature based on new data and insights. Taxonomy, the science of recognizing and delimiting species, adheres to these fundamental principles. Discoveries of new organisms together with advances in methodology continue unabated, leading to a constant reevaluation of the boundaries between taxonomic entities. Species (and higher taxa) comprise related organisms that may be clustered together differently depending on which sets of criteria are emphasized. Hey et al. acknowledge “the inherent ambiguity of species in nature” but point out that “species-related research and conservation efforts can proceed without suffering from, and without fear of, the ambiguity of species.” Through taxonomic research, our understanding of biodiversity and classifications of living organisms will continue to progress. Any system that restricts such progress runs counter to basic scientific principles, which rely on peer review and subsequent acceptance or rejection by the community, rather than third-party regulation. Thiele and Yeates cautioned that such a system “could lead to authoritarianism and a stifling of innovative taxonomic viewpoints. No other hypothesis-driven field of science would accept such a straitjacket”. Taxonomy and associated nomenclature are not without problems. Even with a common set of facts, alternative interpretations of how to classify organisms can lead to differing classifications. However, the science of taxonomy is increasingly rigorous, which can improve the foundation for targeted legislative action regarding species. Taxonomic instability does not affect all taxonomic groups equally. Garnett and Christidis provide examples from mammals and birds, which collectively represent a small fraction

Comment Re: Non-Compete Clause Rulemaking, Matter No. P201200

Within signed law professors and law students submitted this letter to the Federal Trade Commission, writing in their individual capacities, not as agents of their affiliated institutions, in support of the Federal Trade Commission’s proposed rule to ban most non-compete clauses (the “Proposal”) as an unfair method of competition. This letter offers comments in response to areas where the FTC has requested public comment. To make our views clear, this letter contains the following sections: I. Summary of the Proposal; II. The Commission Should Consider Expanding Its Definition of Non-Compete Clauses to Prevent Employers from Requiring Workers to Quit Before Seeking Alternative Employment; III. Non-Compete Clauses Are Unfair Methods of Competition; IV. Non-Compete Clauses Negatively Impact Workers and Their Families; V. The Proposed Rule Protects Small Businesses and Entrepreneurs; and VI. The Commission Should Consider a Factor Test for Its Unfairness Analysis for Senior Executive

Experimental Evidence for Reduced Rodent Diversity Causing Increased Hantavirus Prevalence

Emerging and re-emerging infectious diseases have become a major global environmental problem with important public health, economic, and political consequences. The etiologic agents of most emerging infectious diseases are zoonotic, and anthropogenic environmental changes that affect wildlife communities are increasingly implicated in disease emergence and spread. Although increased disease incidence has been correlated with biodiversity loss for several zoonoses, experimental tests in these systems are lacking. We manipulated small-mammal biodiversity by removing non-reservoir species in replicated field plots in Panama, where zoonotic hantaviruses are endemic. Both infection prevalence of hantaviruses in wild reservoir (rodent) populations and reservoir population density increased where small-mammal species diversity was reduced. Regardless of other variables that affect the prevalence of directly transmitted infections in natural communities, high biodiversity is important in reducing transmission of zoonotic pathogens among wildlife hosts. Our results have wide applications in both conservation biology and infectious disease management

Sin Nombre Virus and Rodent Species Diversity: A Test of the Dilution and Amplification Hypotheses

BACKGROUND:Species diversity is proposed to greatly impact the prevalence of pathogens. Two predominant hypotheses, the "Dilution Effect" and the "Amplification Effect", predict divergent outcomes with respect to the impact of species diversity. The Dilution Effect predicts that pathogen prevalence will be negatively correlated with increased species diversity, while the Amplification Effect predicts that pathogen prevalence will be positively correlated with diversity. For many host-pathogen systems, the relationship between diversity and pathogen prevalence has not be empirically examined. METHODOLOGY/PRINCIPAL FINDINGS:We tested the Dilution and Amplification Effect hypotheses by examining the prevalence of Sin Nombre virus (SNV) with respect to diversity of the nocturnal rodent community. SNV is directly transmitted primarily between deer mice (Peromyscus maniculatus). Using mark-recapture sampling in the Spring and Fall of 2003-2005, we measured SNV prevalence in deer mice at 16 landscape level sites (3.1 hectares each) that varied in rodent species diversity. We explored several mechanisms by which species diversity may affect SNV prevalence, including reduced host density, reduced host persistence, the presence of secondary reservoirs and community composition. We found a negative relationship between species diversity and SNV prevalence in deer mice, thereby supporting the Dilution Effect hypothesis. Deer mouse density and persistence were lower at sites with greater species diversity; however, only deer mouse persistence was positively correlated with SNV prevalence. Pinyon mice (P. truei) may serve as dilution agents, having a negative effect on prevalence, while kangaroo rats (Dipodomys ordii), may have a positive effect on the prevalence of SNV, perhaps through effects on deer mouse behavior. CONCLUSIONS/SIGNIFICANCE:While previous studies on host-pathogen systems have found patterns of diversity consistent with either the Dilution or Amplification Effects, the mechanisms by which species diversity influences prevalence have not been investigated. Our study indicates that changes in host persistence, coupled with interspecific interactions, are important mechanisms through which diversity may influence patterns of pathogens. Our results reveal the complexity of rodent community interactions with respect to SNV dynamics

Molecular Approach to the Identification of Fish in the South China Sea

BACKGROUND: DNA barcoding is one means of establishing a rapid, accurate, and cost-effective system for the identification of species. It involves the use of short, standard gene targets to create sequence profiles of known species against sequences of unknowns that can be matched and subsequently identified. The Fish Barcode of Life (FISH-BOL) campaign has the primary goal of gathering DNA barcode records for all the world's fish species. As a contribution to FISH-BOL, we examined the degree to which DNA barcoding can discriminate marine fishes from the South China Sea. METHODOLOGY/PRINCIPAL FINDINGS: DNA barcodes of cytochrome oxidase subunit I (COI) were characterized using 1336 specimens that belong to 242 species fishes from the South China Sea. All specimen provenance data (including digital specimen images and geospatial coordinates of collection localities) and collateral sequence information were assembled using Barcode of Life Data System (BOLD; www.barcodinglife.org). Small intraspecific and large interspecific differences create distinct genetic boundaries among most species. In addition, the efficiency of two mitochondrial genes, 16S rRNA (16S) and cytochrome b (cytb), and one nuclear ribosomal gene, 18S rRNA (18S), was also evaluated for a few select groups of species. CONCLUSIONS/SIGNIFICANCE: The present study provides evidence for the effectiveness of DNA barcoding as a tool for monitoring marine biodiversity. Open access data of fishes from the South China Sea can benefit relative applications in ecology and taxonomy