All planetary materials sampled thus far vary in their relative abundance of the major isotope of oxygen, 16 O, such that it has not been possible to define a primordial solar system composition. We ...measured the oxygen isotopic composition of solar wind captured and returned to Earth by NASA's Genesis mission. Our results demonstrate that the Sun is highly enriched in 16 O relative to the Earth, Moon, Mars, and bulk meteorites. Because the solar photosphere preserves the average isotopic composition of the solar system for elements heavier than lithium, we conclude that essentially all rocky materials in the inner solar system were enriched in 17 O and 18 O, relative to 16 O, by ∼7%, probably via non—mass-dependent chemistry before accretion of the first planetesimals.
The Genesis Discovery mission returned solar matter in the form of the solar wind with the goal of obtaining precise solar isotopic abundances (for the first time) and greatly improved elemental ...abundances. Measurements of the light noble gases in regime samples demonstrate that isotopes are fractionated in the solar wind relative to the solar photosphere. Theory is required for correction. Measurement of the solar wind O and N isotopes shows that these are very different from any inner solar system materials. The solar O isotopic composition is consistent with photochemical self‐shielding. For unknown reasons, the solar N isotopic composition is much lighter than essentially all other known solar system materials, except the atmosphere of Jupiter. Ne depth profiling on Genesis materials has demonstrated that Ne isotopic variations in lunar samples are due to isotopic fractionation during implantation without appealing to higher energy solar particles. Genesis provides a precise measurement of the isotopic differences of Ar between the solar wind and the terrestrial atmosphere. The Genesis isotopic compositions of Kr and Xe agree with data from lunar ilmenite separates, showing that lunar processes have not affected the ilmenite data and that solar wind composition has not changed on 100 Ma time scales. Relative to Genesis solar wind, ArKrXe in Q (the chondrite noble gas carrier) and the terrestrial atmosphere show relatively large light isotope depletions.
It remains unclear in adult acute myeloid leukaemia (AML) whether leukaemic expression of CD33, the target antigen for gemtuzumab ozogamicin (GO), adds prognostic information on GO effectiveness at ...different doses. CD33 expression quantified in 1583 patients recruited to UK-NCRI-AML17 (younger adults) and UK-NCRI-AML16 (older adults) trials was correlated with clinical outcomes and benefit from GO including a dose randomisation. CD33 expression associated with genetic subgroups, including lower levels in both adverse karyotype and core-binding factor (CBF)-AML, but was not independently prognostic. When comparing GO versus no GO (n=393, CBF-AMLs excluded) by stratified subgroup-adjusted analysis, patients with lowest quartile (Q1) %CD33-positivity had no benefit from GO (relapse risk, HR 2.41 (1.27-4.56), P=0.009 for trend; overall survival, HR 1.52 (0.92-2.52)). However, from the dose randomisation (NCRI-AML17, n=464, CBF-AMLs included), 6 mg/m
GO only had a relapse benefit without increased early mortality in CD33-low (Q1) patients (relapse risk HR 0.64 (0.36-1.12) versus 1.70 (0.99-2.92) for CD33-high, P=0.007 for trend). Thus CD33 expression is a predictive factor for GO effect in adult AML; although GO does not appear to benefit the non-CBF AML patients with lowest CD33 expression a higher GO dose may be more effective for CD33-low but not CD33-high younger adults.
Science results from the Genesis Mission illustrate the major advantages of sample return missions. (i) Important results not otherwise obtainable except by analysis in terrestrial laboratories: the ...isotopic compositions of O, N, and noble gases differ in the Sun from other inner solar system objects. The N isotopic composition is the same as that of Jupiter. Genesis has resolved discrepancies in the noble gas data from solar wind implanted in lunar soils. (ii) The most advanced analytical instruments have been applied to Genesis samples, including some developed specifically for the mission. (iii) The N isotope result has been replicated with four different instruments.
The future of Genesis science Burnett, D. S.; Jurewicz, A. J. G.; Woolum, D. S.
Meteoritics & planetary science,
20/May , Letnik:
54, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Solar abundances are important to planetary science since the prevalent model assumes that the composition of the solar photosphere is that of the solar nebula from which planetary materials formed. ...Thus, solar abundances are a baseline for planetary science. Previously, solar abundances have only been available through spectroscopy or by proxy (CI). The Genesis spacecraft collected and returned samples of the solar wind for laboratory analyses. Elemental and isotopic abundances in solar wind from Genesis samples have been successfully measured despite the crash of the re‐entry capsule. Here we present science rationales for a set of 12 important (and feasible postcrash) Science and Measurement Objectives as goals for the future (Table 1). We also review progress in Genesis sample analyses since the last major review (Burnett ). Considerable progress has been made toward understanding elemental fractionation during the extraction of the solar wind from the photosphere, a necessary step in determining true solar abundances from solar wind composition. The suitability of Genesis collectors for specific analyses is also assessed. Thus far, the prevalent model remains viable despite large isotopic variations in a number of volatile elements, but its validity and limitations can be further checked by several Objectives.
Many theories of human debugging rely on complex mental constructs that offer little practical advice to builders of software engineering tools. Although hypotheses are important in debugging, a ...theory of navigation adds more practical value to our understanding of how programmers debug. Therefore, in this paper, we reconsider how people go about debugging in large collections of source code using a modern programming environment. We present an information foraging theory of debugging that treats programmer navigation during debugging as being analogous to a predator following scent to find prey in the wild. The theory proposes that constructs of scent and topology provide enough information to describe and predict programmer navigation during debugging, without reference to mental states such as hypotheses. We investigate the scope of our theory through an empirical study of 10 professional programmers debugging a real-world open source program. We found that the programmers' verbalizations far more often concerned scent-following than hypotheses. To evaluate the predictiveness of our theory, we created an executable model that predicted programmer navigation behavior more accurately than comparable models that did not consider information scent. Finally, we discuss the implications of our results for enhancing software engineering tools.
We compare element and isotopic fractionations measured in bulk solar wind samples collected by NASA's Genesis mission with those predicted from models incorporating both the ponderomotive force in ...the chromosphere and conservation of the first adiabatic invariant in the low corona. Generally good agreement is found, suggesting that these factors are consistent with the process of solar wind fractionation. Based on bulk wind measurements, we also consider in more detail the isotopic and elemental abundances of O. We find mild support for an O abundance in the range 8.75-8.83, with a value as low as 8.69 disfavored. A stronger conclusion must await solar wind regime-specific measurements from the Genesis samples.
Our discovery that the major coat protein of bacteriophage PRD1 resembles that of human adenovirus raised the unexpected possibility that viruses infecting bacteria could be related by evolution to ...those infecting animal hosts. We first review the development of this idea. We then describe how we have used structure-based modeling to show that several other viruses with no detectable sequence similarity are likely to have coats constructed from similar proteins—the “double-barrel trimer.” There is evidence that the group includes a diversity of viruses infecting very different hosts in all three domains of life: Eukarya; Bacteria; and Archaea that diverged billions of years ago. The current classification of viruses obscures such similarities. We propose that the occurrence of a double-barrel trimer coat protein in an icosahedral dsDNA virus with large facets, irrespective of its host, is a very strong indicator of its membership in a lineage of viruses with a common ancestor.
In August 2015, an expert colloquium commissioned by the Sexual Medicine Society of North America (SMSNA) convened in Washington, DC, to discuss the common clinical scenario of men who present with ...low testosterone (T) and associated signs and symptoms accompanied by low or normal gonadotropin levels. This syndrome is not classical primary (testicular failure) or secondary (pituitary or hypothalamic failure) hypogonadism because it may have elements of both presentations. The panel designated this syndrome adult-onset hypogonadism (AOH) because it occurs commonly in middle-age and older men. The SMSNA is a not-for-profit society established in 1994 to promote, encourage, and support the highest standards of practice, research, education, and ethics in the study of human sexual function and dysfunction. The panel consisted of 17 experts in men's health, sexual medicine, urology, endocrinology, and methodology. Participants declared potential conflicts of interest and were SMSNA members and nonmembers. The panel deliberated regarding a diagnostic process to document signs and symptoms of AOH, the rationale for T therapy, and a monitoring protocol for T-treated patients. The evaluation and management of hypogonadal syndromes have been addressed in recent publications (ie, the Endocrine Society, the American Urological Association, and the International Society for Sexual Medicine). The primary purpose of this document was to support health care professionals in the development of a deeper understanding of AOH, particularly in how it differs from classical primary and secondary hypogonadism, and to provide a conceptual framework to guide its diagnosis, treatment, and follow-up.
Electron probe microanalyser measurements of trace elements with high accuracy are challenging. Accurate Al measurements in olivine are required to calibrate SIMS implant reference materials for ...measurement of Al in the solar wind. We adopt a combined EPMA/SIMS approach that is useful for producing SIMS reference materials as well as for EPMA at the ~ 100 µg g−1 level. Even for mounts not polished with alumina photoelectron spectroscopy shows high levels of Al surface contamination. In order to minimise electron beam current density, a rastered 50 × 100 µm electron beam was adequate and minimised sensitivity to small Al‐rich contaminants. Reproducible analyses of eleven SIMS‐cleaned spots on San Carlos olivine agreed at 69.3 ± 1.0 µg g−1. The known Al mass fraction was used to calibrate an Al implant into San Carlos. Accurate measurements of Al were made for olivines in the pallasites: Imilac, Eagle Station and Springwater. Our focus was on Al in olivine, but our technique could be refined to give accurate electron probe measurements for other contamination‐sensitive trace elements. For solar wind, it is projected that the Al/Mg abundance ratio can be determined to 6%, a factor of 2 more precise than the solar spectroscopic ratio.
Key Points
Determination of Al in the solar wind requires high‐accuracy calibration of SIMS implant reference materials.
Well‐cleaned, diamond‐polished olivine reference materials still showed high levels of surface Al contamination.
Our combined EPMA/SIMS approach is recommended for accurate quantification of SIMS reference materials and EPMA of trace elements.
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