skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Magnesium isotopes of the bulk solar wind from Genesis diamond‐like carbon films
Abstract NASA's Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material.SWanalyses control the precision of the derived solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due toSWformation. Mg isotopes are “ground truth” for these models since, except forCAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation ofSWMg is primarily that ofSWformation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulkSWdiamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in theDLC. The resultingSWMg fractionation relative to theDSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơSEof the data combined with a 2.5‰ (total) error in theIMFdetermination. Two of theSWfractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on theCAInebular composition of McKeegan et al. (2011).  more » « less
Award ID(s):
1819550
PAR ID:
10374698
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley-Blackwell
Date Published:
Journal Name:
Meteoritics & Planetary Science
Volume:
55
Issue:
2
ISSN:
1086-9379
Page Range / eLocation ID:
p. 352-375
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, Journal of Analytical Atomic Spectrometry)
    null (Ed.)
    Minor and trace elements in diamond-like carbon (DLC) are difficult to quantify using SIMS analysis because minor elemental and structural variations can result in major matrix effects even across individual, cm-sized samples. While this material is most commonly used for tribological coatings where minor element composition is not of critical importance, it is being increasingly used in electronic devices. However, it is a unique application that spurred this work: anhydrous, tetrahedrally-coordinated DLC (ta-C) was used as a solar wind (SW) collector material in the Genesis solar-wind sample return mission (NASA Discovery 5). So, for ∼15 years, we have been working on attaining accurate and precise measurement of minor and trace elements in the Genesis DLC using SIMS to achieve our mission goals. Specifically, we have learned to deal with relevant matrix effects in our samples, ion implants into ta-C. Our unknown element for quantification is SW Mg, a low-dose (1.67 × 10 12 at cm −2 ; ∼6 μg g −1 24 Mg), low-energy (∼24 keV average energy) implant; our standard is a high-dose (∼1 × 10 14 at cm −2 of both 25 Mg, 26 Mg) 75 keV laboratory implant for which the absolute 26 Mg/ 25 Mg ratio had been measured to account for variable instrumental mass fractionation. Analyses were performed using O 2 + primary ions having both a low impact energy and a current density of ∼2 × 10 14 ions per cm 2 . Although our unknown was solar wind, the method is applicable to many situations where minor elements in DLC need to be quantified. Recommendations are presented for modifying this data-reduction technique for other SIMS conditions. 
    more » « less
  2. ; ; (, Applications in Plant Sciences)
    PremiseHerbarium specimens have been used to detect climate‐induced shifts in flowering time by using the day of year of collection (DOY) as a proxy for first or peak flowering date. Variation among herbarium sheets in their phenological status, however, undermines the assumption thatDOYaccurately represents any particular phenophase. Ignoring this variation can reduce the explanatory power of pheno‐climatic models (PCMs) designed to predict the effects of climate on flowering date. MethodsHere we present a protocol for the phenological scoring of imaged herbarium specimens using an ImageJ plugin, and we introduce a quantitative metric of a specimen's phenological status, the phenological index (PI), which we use inPCMs to control for phenological variation among specimens ofStreptanthus tortuosus(Brassicaceeae) when testing for the effects of climate onDOY. We demonstrate that includingPIas an independent variable improves model fit. ResultsIncludingPIinPCMs increased the modelR2relative toPCMs that excludedPI; regression coefficients for climatic parameters, however, remained constant. DiscussionOur protocol provides a simple, quantitative phenological metric for any observed plant. IncludingPIinPCMs increasesR2and enables predictions of theDOYof any phenophase under any specified climatic conditions. 
    more » « less
  3. ; ; ; (, The Plant Journal)
    Summary Like metazoans, plants use small regulatoryRNAs (sRNAs) to direct gene expression. Several classes ofsRNAs, which are distinguished by their origin and biogenesis, exist in plants. Among them, microRNAs (miRNAs) andtrans‐acting small interferingRNAs (ta‐siRNAs) mainly inhibit gene expression at post‐transcriptional levels. In the past decades, plant miRNAs and ta‐siRNAs have been shown to be essential for numerous developmental processes, including growth and development of shoots, leaves, flowers, roots and seeds, among others. In addition, miRNAs and ta‐siRNAs are also involved in the plant responses to abiotic and biotic stresses, such as drought, temperature, salinity, nutrient deprivation, bacteria, virus and others. This review summarizes the roles of miRNAs and ta‐siRNAs in plant physiology and development. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, Global Change Biology)
    Abstract Anthropogenic climate change compromises reef growth as a result of increasing temperatures and ocean acidification. Scleractinian corals vary in their sensitivity to these variables, suggesting species composition will influence how reef communities respond to future climate change. Because data are lacking for many species, most studies that model future reef growth rely on uniform scleractinian calcification sensitivities to temperature and ocean acidification. To address this knowledge gap, calcification of twelve common and understudied Caribbean coral species was measured for two months under crossed temperatures (27, 30.3 °C) andCO2partial pressures (pCO2) (400, 900, 1300 μatm). Mixed‐effects models of calcification for each species were then used to project community‐level scleractinian calcification using Florida Keys reef composition data andIPCC AR5 ensemble climate model data. Three of the four most abundant species,Orbicella faveolata, Montastraea cavernosa,andPorites astreoides, had negative calcification responses to both elevated temperature andpCO2. In the business‐as‐usualCO2emissions scenario, reefs with high abundances of these species had projected end‐of‐century declines in scleractinian calcification of >50% relative to present‐day rates.Siderastrea siderea, the other most common species, was insensitive to both temperature andpCO2within the levels tested here. Reefs dominated by this species had the most stable end‐of‐century growth. Under more optimistic scenarios of reducedCO2emissions, calcification rates throughout the Florida Keys declined <20% by 2100. Under the most extreme emissions scenario, projected declines were highly variable among reefs, ranging 10–100%. Without considering bleaching, reef growth will likely decline on most reefs, especially where resistant species likeS. sidereaare not already dominant. This study demonstrates how species composition influences reef community responses to climate change and how reducedCO2emissions can limit future declines in reef calcification. 
    more » « less
  5. ; ; ; ; ; ; ; ; (, The Plant Journal)
    Summary In seed plants, cellulose is synthesized by rosette‐shaped cellulose synthesis complexes (CSCs) that are obligate hetero‐oligomeric, comprising three non‐interchangeable cellulose synthase (CESA) isoforms. The mossPhyscomitrella patenshas rosetteCSCs and sevenCESAs, but its common ancestor with seed plants had rosetteCSCs and a singleCESAgene. Therefore, ifP. patensCSCs are hetero‐oligomeric, thenCSCs of this type evolved convergently in mosses and seed plants. Previous gene knockout and promoter swap experiments showed that PpCESAs from class A (PpCESA3 and PpCESA8) and class B (PpCESA6 and PpCESA7) have non‐redundant functions in secondary cell wall cellulose deposition in leaf midribs, whereas the two members of each class are redundant. Based on these observations, we proposed the hypothesis that the secondary class A and class B PpCESAs associate to form hetero‐oligomericCSCs. Here we show that transcription of secondary class APpCESAs is reduced when secondary class BPpCESAs are knocked out and vice versa, as expected for genes encoding isoforms that occupy distinct positions within the sameCSC. The class A and class B isoforms co‐accumulate in developing gametophores and co‐immunoprecipitate, suggesting that they interact to form a complexin planta. Finally, secondary PpCESAs interact with each other, whereas three of four fail to self‐interact when expressed in two different heterologous systems. These results are consistent with the hypothesis that obligate hetero‐oligomericCSCs evolved independently in mosses and seed plants and we propose the constructive neutral evolution hypothesis as a plausible explanation for convergent evolution of hetero‐oligomericCSCs. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email