Nitrogen Oxide Concentrations in Natural Waters on Early Earth

A key challenge in origins-of-life studies is estimating the abundances of species relevant to the chemical pathways proposed to have contributed to the emergence of life on early Earth. Dissolved nitrogen oxide anions (NO$_{X}^{-}$), in particular nitrate (NO$_{3}^{-}$) and nitrite (NO$_{2}^{-}$), have been invoked in diverse origins-of-life chemistry, from the oligomerization of RNA to the emergence of protometabolism. Recent work has calculated the supply of NO$_{X}^{-}$ from the prebiotic atmosphere to the ocean, and reported steady-state [NO$_{X}^{-}$] to be high across all plausible parameter space. These findings rest on the assumption that NO$_{X}^{-}$ is stable in natural waters unless processed at a hydrothermal vent. Here, we show that NO$_{X}^{-}$ is unstable in the reducing environment of early Earth. Sinks due to UV photolysis and reactions with reduced iron (Fe$^{2+}$) suppress [NO$_{X}^{-}$] by several orders of magnitude relative to past predictions. For pH$=6.5-8$ and $T=0-50^\circ$C, we find that it is most probable that NO$_{X}^{-}$]$<1~\mu$M in the prebiotic ocean. On the other hand, prebiotic ponds with favorable drainage characteristics may have sustained [NO$_{X}^{-}$]$\geq 1~\mu$M. As on modern Earth, most NO$_{X}^{-}$ on prebiotic Earth should have been present as NO$_{3}^{-}$, due to its much greater stability. These findings inform the kind of prebiotic chemistries that would have been possible on early Earth. We discuss the implications for proposed prebiotic chemistries, and highlight the need for further studies of NO$_{X}^{-}$ kinetics to reduce the considerable uncertainties in predicting [NO$_{X}^{-}$] on early Earth.Comment: In review for publication at Geochemistry, Geophysics, and Geosystems (G-cubed). Comments, questions, and criticism solicited; please contact corresponding author at [email protected]. SI at: https://web-cert.mit.edu/sukrit/Public/nox_si.pdf. GitHub at: https://github.com/sukritranjan/no

Synthesis of neutral nickel catalysts for ethylene polymerization – the influence of ligand size on catalyst stability

A facile synthesis of nickel salicylaldimine complexes with labile dissociating ligands is described. In addition to producing highly active ethylene polymerization catalysts, important insights into the effect of ligand size on catalyst stability and information on the mechanism of polymerization are provided

Physicians\u27 use of the personal digital assistant (PDA) in clinical decision making

Purpose: This study examined how frequently attending physicians and physicians in training used personal digital assistants (PDAs) for patient care and explored physicians\u27 perceptions of the impact of PDA use on several areas of clinical decision making. Setting/Subjects: The 108 participants included 59 attending physicians and 49 physicians in training from teaching hospitals in Tennessee, Florida, Alabama, Kentucky, and Pennsylvania. Methodology: Respondents completed a questionnaire designed to explore PDA use in a clinical setting. Results: Eighty-seven percent of the respondents reported PDA use for patient encounters. Fifty-five percent of respondents reported frequent use, and 32% reported occasional use of a PDA for patient care. Of the frequent PDA users, 85% said PDA use had influenced their overall clinical decision making and 73% mentioned treatment alterations specifically. Approximately 60% of the participants reporting occasional PDA use indicated that the PDA had influenced their overall clinical decision making, while 54% specifically mentioned a change to their patient\u27s treatment plan. Discussion/Conclusion: Attending physicians and physicians in training who used a PDA during patient encounters perceived that even occasional PDA use had an impact on their clinical decision making and treatment choices. Health sciences librarians are perfectly positioned to provide PDA training and assistance not only to physicians who are frequent PDA users, but also to those who are occasional users

Insights into the Deactivation of Neutral Nickel Ethylene Polymerization Catalysts in the Presence of Functionalized Olefins

A study on the products of reaction between a neutral nickel(II) olefin polymerization catalyst and methyl acrylate is presented. A deactivation mechanism involving hydrogen transfer from substrate to catalyst is suggested

Monitoring Inventory Accuracy With Statistical Process Control

Inventory accuracy is critical in most industrial environments such as distribution, warehousing, and retail. Many companies use a technique called cycle counting and have realized outstanding results in monitoring and improving inventory accuracy. The time and resources to complete cycle counting are sometimes limited or not available. In this work, we promote statistical process control (SPC) to monitor inventory accuracy. Specifically, we model the complex underlying environments with mixture distributions to demonstrate sampling from a mixed but stationary process. For our particular application, we concern ourselves with data that result from inventory adjustments at the stock keeping unit (SKU) level when a given SKU is found to be inaccurate. We provide estimates of both the Type I and Type II errors when a classic C chart is used. In these estimations, we use both analytical as well as simulation results, and the findings demonstrate the environments that might be conducive for SPC approach

‘Flex Your Power’: Energy crises and the shifting rhetoric of the grid

In response to widespread power outages, rolling blackouts, and ubiquitous energy debates, this essay considers our relation to energy and the grid that produces it. First, we investigate California\u27s multimedia Flex Your Power campaign, which defines consumers as nodes of the grid to emphasize their responsibility to maintain a stable energy supply. Second, we examine state and national responses to the 2003 blackout in the Northeastern United States, attending to three strategies through which grid administrators sought to impose order, enact hierarchy, and deindividuate power. We propose that the grid invokes personalization at the local level and abstraction at the national level. These contradictory (but overlapping) narratives show a complex, nuanced set of relations between human society and mechanized processes of power distribution