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Three-dimensional cometary dust coma modelling in the collisionless regime: strengths and weaknesses
Inverse coma and tail modelling of comets based on the method developed by Finson & Probstein is commonly used to analyse cometary coma images. Models of this type often contain a large number of assumptions that may not be constrained unless wide temporal or spectral coverage is available and the comets are bright and at relatively small geocentric distance. They are used to predict physical parameters, such as the mass distribution of the dust, but rarely give assessments of the accuracy of the estimate. A three-dimensional cometary dust coma model in the collisionless regime has been developed to allow the effectiveness of such models to constrain dust coma properties to be tested. The model is capable of simulating the coma morphology for the following input parameters: the comet nucleus shape, size, rotation, emission function (including active fraction and jets), grain velocity distribution (and dispersion), size distribution, dust production rate, grain material and light scattering from the cometary dust.
Characterization of the model demonstrates that the mass distribution cannot be well constrained as is often assumed; the cumulative mass distribution index ? can only be constrained to within ±0.15. The model is highly sensitive to the input grain terminal velocity distribution so model input can be tested with a large degree of confidence. Complex secondary parameters such as jets, rotation and grain composition all have an effect on the structure of the coma in similar ways, so unique solutions for these parameters cannot be derived from a single optical image alone. Multiple images at a variety of geometries close in time can help constrain these effects.
The model has been applied to photometric observations of comets 126P/IRAS and 46P/Wirtanen to constrain a number of physical properties including the dust production rate and mass distribution index. The derived dust production rate (Qdust) for 46P/Wirtanen was 3+7/1.5 kg s1 at a pre-perihelion heliocentric distance of 1.8 au, and for P/IRAS was 50+100/20 kg s1 at a pre-perihelion heliocentric distance of 1.7 au; both comets exhibited a mass distribution index ? = 0.8 ± 0.15
Semiclassical description of the kinematically complete experiments
Based on the semiclassical, impact parameter method a theoretical model is
constructed to calculate totally differential cross sections for single
ionization of helium by impact with fast C ions. Good agreement with the
experiment is achieved in the scattering plane, while in the perpendicular
plane a similar structure to that observed experimentally is obtained. The
contribution of different partial waves to the cross section is also
investigated.Comment: 9 pages, 6 figure
The curatorial consequences of being moved, moveable or portable: the case of carved stones
It matters whether a carved stone is moved, moveable or portable. This influences perceptions of significance and of form and nature – is it a monument or an artefact? This duality may in turn affect understanding and appreciation of the resource. It has implications for how and if carved stones can be legally protected, who owns them, where and how they are administered, and by whom. The complexities of the legislation mean that all too often this is also a grey area. This paper explores these curatorial issues and their impact
Properties of nonaqueous electrolytes Quarterly report, 20 Dec. 1966 - 19 Mar. 1967
Properties of nonaqueous electrolytes - preparation of electrolytes, nuclear magnetic resonance structural studies, and physical property determination
Properties of nonaqueous electrolytes Quarterly report, 20 Jun. - 19 Sep. 1967
Electrolyte preparation, and physical property and nuclear magnetic resonance structural studies of nonaqueous electrolyte
Analysis of the project fire re-entry package flow field final technical report
Theoretical prediction of state of gas in flow field surrounding Apollo type vehicle in reentry at hypersonic speed
Perceived stress and emotional social support among women who are denied or receive abortions in the United States: a prospective cohort study.
BackgroundExamining women's stress and social support following denial and receipt of abortion furthers understanding of the effects of unwanted childbearing and abortion on women's well-being. This study investigated perceived stress and emotional social support over time among women who were denied wanted abortions and who received abortions, and compared outcomes between the groups.MethodsThe Turnaway Study is a prospective cohort study of women who sought abortions at 30 abortion facilities across the United States, and follows women via semiannual phone interviews for five years. Participants include 956 English or Spanish speaking women aged 15 and over who sought abortions between 2008 and 2010 and whose gestation in pregnancy fit one of three groups: women who presented up to three weeks beyond a facility's gestational age limit and were denied an abortion; women presenting within two weeks below the limit who received an abortion; and women who received a first trimester abortion. The outcomes were modified versions of the Perceived Stress Scale and the Multidimensional Scale of Perceived Social Support. Longitudinal mixed effects models were used to assess differences in outcomes between study groups over 30 months.ResultsWomen denied abortions initially had higher perceived stress than women receiving abortions near gestational age limits (1.0 unit difference on 0-16 scale, P = 0.003). Women receiving first-trimester abortions initially had lower perceived stress than women receiving abortions near gestational age limits (0.6 difference, P = 0.045). By six months, all groups' levels of perceived stress were similar, and levels remained similar through 30 months. Emotional social support scores did not differ among women receiving abortions near gestational limits versus women denied abortions or women having first trimester abortions initially or over time.ConclusionsSoon after being denied abortions, women experienced higher perceived stress than women who received abortions. The study found no longer-term differences in perceived stress or emotional social support between women who received versus were denied abortions
Resistência do milho (Zea mays L.) transgênico (Bt) a lagarta-do-cartucho, Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae).
No Brasil, a utilização de milho transgênico (Bt) pode reduzir perdas causadas por vários lepidópteros-pragas, equivalentes a aproximadamente 500 milhões de dólares anuais. O objetivo deste trabalho foi avaliar os hÃbridos de milho Bt disponÃveis no mercado americano para resistência à lagarta-do-cartucho do milho (LCM), Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). Nove hÃbridos de milho Bt expressando as toxinas Cry 1F, Cry 1A(b), Cry 1 A(c) e Cry 9C, além de um hÃbrido (MP 704 X 707) expressando resistência natural para a LCM, foram comparados num experimento, em campo, em blocos ao acaso, com parcela subdividida e quatro repetições. Nas parcelas, foram comparados os dez hÃbridos e, nas subparcelas, as versões Bt versus não-Bt, ou hÃbrido com resistência natural versus susceptÃvel. A infestação artificial foi realizada 33 dias após a semeadura e as avaliações basearam-se no número de larvas sobreviventes, aos 10 e 15 dias após a infestação, peso das larvas sobreviventes e notas de danos nas plantas. Para todas as variáveis estudadas, os resultados demonstraram diferenças significativas (P=0,05) entre os hÃbridos avaliados. Também as testemunhas não-Bts diferiram significativamente dos respectivos hÃbridos Bts, exceto para aqueles expressando a toxina Cry 9C. O hÃbrido 2722 IMI, expressando a toxina Cry 1F, foi o mais resistente (imune) e os hÃbridos expressando a toxina Cry 1A(b) e a resistência natural foram moderadamente resistentes. Em geral, os hÃbridos transgênicos resistentes produziram cerca de 32% a mais de grãos que as testemunhas suscetÃveis
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