We report new K-Ar isochron data for two approximately 380 million-years-old basaltic rocks, using an updated version of the Potassium-Argon Laser Experiment (KArLE), which is being developed for ...future in situ dating of planetary materials. These basalts have K contents comparable with those of lunar KREEP basalts or igneous lithologies found by Mars rovers, whereas previous proof-of-concept studies focused primarily on more K-rich rocks. We aim to measure these analogous samples to show the advancing capability of in situ K-Ar geochronology.
Several laboratories have been investigating the feasibility of in situ K-Ar dating for use in future landing planetary missions. One drawback of these laboratory demonstrations is the insufficient ...analogy of the analyzed analog samples with expected future targets. We present the results obtained using the K-Ar laser experiment (KArLE) on two old and K-poor chondritic samples, Pułtusk and Hvittis, as better lunar analogs. The KArLE instrument uses laser ablation to vaporize rock samples and quantifies K content by laser-induced breakdown spectroscopy (LIBS), Ar by quadrupole mass spectrometry (QMS), and ablated mass by laser profilometry. We performed 64 laser ablations on the chondrites to measure spots with a range of K2O and Ar content and used the data to construct isochrons to determine the chondrite formation age. The KArLE isochron ages on Pułtusk and Hvittis are 5059 ± 892 Ma and 4721 ± 793 Ma, respectively, which is within the uncertainty of published reference ages, and interpreted as the age of their formation. The uncertainty (2σ) on the KArLE ages obtained in this study is better than 20% (18% for Pułtusk and 17% for Hvittis). The precision, which compares our obtained ages to the reference ages, is also better than 20% (11% for Pułtusk and 4% for Hvittis). These results are encouraging for understanding the limits of this technique to measure ancient planetary samples and for guiding future improvements to the instrument.
Crystalline impact‐melt samples were created in high‐temperature environments by relatively large craters and, as such, give additional constraints on the nature of the impacts that created them. ...This article provides new 40Ar‐39Ar ages of impact‐melt clasts in howardites and shows that these clasts formed on the HED parent body, 4 Vesta, within the time period 3.3–3.8 Ga. Rather than resulting from an increased number of impacts, however, impact‐melted material in howardites may result from unusually high‐velocity impacts occurring in the asteroid belt during this period. This scenario is similar to the late heavy bombardment of the Moon, pointing to an unusual dynamical event at this time across the inner solar system. Therefore, impact‐melt rocks in howardites uniquely record a Vestan cataclysm.
10.1111/maps.12188
This article recounts the FDA testing performed to create a drug facts label for the use of naloxone obtained through over-the-counter sales. The study involved structured interviews with 710 adults ...and adolescents, including many who use opioids and their family and friends.
Women tend to supplement their diets with multivitamin/mineral (MVM) supplements more often than men, and reports indicate that more than 90% of pregnant women in the United States supplement their ...diets with prenatal MVMs. Given the widespread use of MVMs among women and given the increasing efforts to unveil the importance of phenotype-specific health determinants, it seems imperative to review what is known about variations in nutrient physiology among women from different ethnic and racial groups and at different reproductive stages of life. In this study, we embark on an assessment of the scientific evidence and knowledge gaps that impact the precise determination of nutrient levels (specifically calcium, iron, and folic acid) that confer benefits to various subpopulations of women in the United States.
Geochronological evidence for and against a late heavy bombardment (LHB) spike in impact rates on the Moon and meteorite parent bodies is re-examined. In particular, we find that the sampling of ...impact melts on the Moon is strongly biased against older examples, possibly due to preferential surface deposition of such melts and/or blanketing and burial by basin ejecta (arguments that the bias might be due to pulverization of old impact melts at depth are incorrect). The apparent absence of melts older than 4 Ga thus provides much weaker evidence for a pre-nectarian lull in bombardment (which would define a post-nectarian cataclysm) than has been argued, although their absence compared with other rocks from depth may remain a weak constraint. Differences in rock-age histograms between meteorite parent bodies and the Moon may imply that different sampling biases exist for bodies in the asteroid belt; otherwise, the more straightforward interpretation is that the bombardment that affected the asteroids was more long-lasting than the lunar LHB. Since the strongest constraint on the dynamics of source populations for the LHB remains the very rapid decline in rate of basin formation from 3.90 to 3.85 Ga, we must re-establish that the associations of dated samples with particular basins are robust. Further studies of processes that can bias sampling are warranted, in particular more quantitative modeling of regolith and megaregolith evolution. In summary, we find that constraints either for or against the lunar cataclysm as a spike in the bombardment rate that commenced shortly before the formation of Nectaris are very weak. There may or may not have been a lull in bombardment before 3.9 Ga. Only the rapid decline in bombardment rate after Imbrium is fairly secure and can be adopted as a constraint to be matched by various dynamical scenarios for the impact history of the Moon.
Making sense of rapidly evolving evidence on genetic associations is crucial to making genuine advances in human genomics and the eventual integration of this information in the practice of medicine ...and public health. Assessment of the strengths and weaknesses of this evidence, and hence the ability to synthesize it, has been limited by inadequate reporting of results. The STrengthening the REporting of Genetic Association studies (STREGA) initiative builds on the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) Statement and provides additions to 12 of the 22 items on the STROBE checklist. The additions concern population stratification, genotyping errors, modelling haplotype variation, Hardy-Weinberg equilibrium, replication, selection of participants, rationale for choice of genes and variants, treatment effects in studying quantitative traits, statistical methods, relatedness, reporting of descriptive and outcome data, and the volume of data issues that are important to consider in genetic association studies. The STREGA recommendations do not prescribe or dictate how a genetic association study should be designed but seek to enhance the transparency of its reporting, regardless of choices made during design, conduct, or analysis.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Cohen et al. 2000 recently confirmed the hypothesis that the Moon was resurfaced by an intense period of impact cratering ∼3.9 Ga ago and, by inference, that the Earth also sustained bombardment. ...Analyses of lunar impact melts indicate that at least one of the projectiles that hit the Moon was a differentiated iron‐rich core, implying the bombardment was caused by asteroids. Meteorite analyses indicate asteroids in the asteroid belt were also heavily cratered ∼3.9 Ga and that the ancient cratered highlands of Mars suffered impacts at this time. Collectively, these data suggest there was an impact cataclysm that affected the entire inner solar system, resurfacing the terrestrial planets, and that the source of the impacting debris was the asteroid belt. Comets do not appear to have been important.
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