3,854 research outputs found

    A Hubble Space Telescope Imaging Survey of Nearby Active Glactic Nuclei

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    We obtained 500-second F606W WFPC2 images of 256 of the nearest (z<0.035) Seyfert 1,Seyfert 2, and starburst galaxies. Less than 10% show tidal features or multiple nuclei. The incidence of inner starburst rings is about 10% in both classes of Sy galaxies. In contrast, galaxies with H II region emission line spectra appear substantially more irregular because of their much higher specific rates of star formation. An unresolved central continuum source in our HST images is a virtually perfect indicator of a Sy1 spectrum. 52% of these Sy1 point sources are saturated in our images; we use their wings to estimate their magnitudes. The converse is not however true, as over a third of Sy's with direct spectroscopic evidence for broad Balmer wings show no nuclear point source. Like the Sy2's, they have central surface brightnesses consistent with those expected for the bulges of normal galaxies. The frequency of bars in Sy1's and 2's and non-Sys are the same. The Sy2 galaxies are significantly more likely to show nuclear dust absorption, especially in lanes and patches which are irregular or reach close to the nucleus. The difference cannot be explained by different average redshifts or selection techniques. This is confirmed by our morphology classifications, which show that Sy1 nuclei reside in earlier type galaxies than Sy2 nuclei. This intrinsic difference in host galaxy properties may undermine the strong unification hypothesis for Sy galaxies that they appear different due to the orientation of their central engine. The excess galactic dust we see in Sy2's may cause substantial absorption which obscures their hypothesized broad emission-line regions and central nonstellar continua. This galactic dust could produce much of the absorption in Sy2 nuclei which had instead been attributed to a thick dusty accretion torus.Comment: The text of the paper is 23 pages (ms.tex), there are 8 tables, and 9 figures. Figures 1, 2, and 3 are the image gallery (45 pages) and are NOT included here. They can be ftp'ed from ftp.astro.ucla.edu. Log in as anonymous and give your e-mail address as the password. The images are in the /pub/submit/vg/AGNgallery . Figures 4-9 are in eps format and are included here and can be printed using the lpr command in unix system

    Likert Items: Should(n’t) We Really Care?

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    One of the controversial methodological topics in the social and behavioral sciences is the (ab)use of Likert Scale items, Likert-type items and ranked ordered response categories. The debate is whether parametric tests can be legitimately conducted on technically ordinal response categories that are represented with numbers. Participants answered survey questions on moral disengagement, where we changed the intervals of seven response categories and tested whether assigning numbers made any difference in two separate studies. The results showed that participants’ ratings were not significantly different with or without numbers. Participants tend to covertly superimpose numbers where none were provided. Also, there were no significant interactions between assignment of numbers and ‘intervalness’. However, ratings were significantly different between two key interval groups. Knowing the assumptions of respondents to these Likert items even without numbers could inform researchers especially if parametric tests are to be conducted

    Particle export from the upper ocean over the continental shelf of the west Antarctic Peninsula: A long-term record, 1992–2007

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    Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 55 (2008): 2118-2131, doi:10.1016/j.dsr2.2008.04.028.Includes supplemental materialsWe report on results of a long-term (1993-2007) time series sediment trap moored at 170 m to the west of the Antarctic Peninsula in the mid-continental shelf region (350 m depth; 64Âș30’ S, 66Âș00’ W). This is a region characterized by late spring-summer diatom blooms, moderately high seasonal primary productivity (50-150 mmol C m-2 d-1 in December-February) and high phytoplankton and krill biomass in the seasonal sea ice zone. The mass flux ranged from near 0 to over 1 g m-2 d-1 and was near 0 to >30% organic carbon (mean 8%). Sedimentation from the upper ocean as estimated by the trap collections at 170 m exhibited strong seasonality with high fluxes (1-10 mmol C m-2 d-1) in November-March following ice retreat and very low fluxes (<0.001 mmol C m-2 d-1) during the Austral winter and under sea ice cover. An average of 85% of the annual export of 212 mmol C m-2 occurred during the seasonal peak flux episodes. Over the trap record, the annual peak flux episode has tended to occur later in the Austral summer, advancing by about 40 days since 1993. The time-integrated sedimentation during the peak flux episode was <1 – 50% of the SeaWiFS-estimated primary production (mean 4%) at the trap site over the period 1998-2006. The elemental composition of material captured in the traps had an average C:N:P of 212:28:1, greater than the canonical Redfield values. High C:P ratios (400- 600) corresponded with the annual flux peak, indicating preferential loss of P from the sinking particles in the summer, ice-free period. The composition of the exported material more closely approximated the Redfield composition during the low-flux, winter period.This research was supported by NSF Grants OPP 9011927, 9632763 and 0217282 for the Palmer Long Term Ecological Research project

    Rationale MarktĂŒbertreibungen im Zusammenhang der aktuellen Finanzmarktkrise

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    Der Untersuchungsgegenstand der Arbeit ist die Darstellung der wichtigsten Anlegermotive bei MarktĂŒbertreibungen. Es wird dabei auf Konzepte der verhaltensorientierten Kapitalmarktforschung zurĂŒckgegriffen. Basierend auf den gewonnenen Erkenntnissen werden LösungsansĂ€tze zur Vermeidung von MarktĂŒbertreibungen abgeleitet. Untersuchungen, beispielsweise durch Bikhchandani und Sharma (2000), haben gezeigt, dass Herdenverhalten eine wichtige Rolle bei der ErklĂ€rung von PreisĂŒbertreibungen spielt. Dabei kann es rational sein, sich konform zur Masse der Marktteilnehmer zu verhalten. Neben dem Konzept des Herdenverhaltens kann Konservatismus unter Marktteilnehmern zur BestĂ€tigung vorherrschender Trends beitragen. Heuristiken werden angewandt, um komplexe Sachverhalte zu vereinfachen. Insbesondere die ReprĂ€sentativitĂ€tsheuristik kann zu einer VerstĂ€rkung bestehender PreisĂŒbertreibungen fĂŒhren. Die Autoren sind der Ansicht, dass vor allem eine Verbesserung der Informationsbasis zur Reduzierung von FehleinschĂ€tzungen durch Marktteilnehmer beitragen kann. Sowohl die VerfĂŒgbarkeit als auch die QualitĂ€t der Informationen spielen dabei eine Rolle. Ein weiterer Lösungsansatz betrifft die Risikoeinstellung und Kreditvergabe der Banken. In Boomphasen sollte das Risiko eines Crashs berĂŒcksichtigt werden.The paper deals with the motives of people to invest in overvalued markets. We resort to the concepts of behavioural finance to describe the most important factors. Based on these findings we deduct measures to avoid misjudgement of markets participants. As Bikhchandani and Sharma (2000) show, the concept of herd behaviour plays a decisive role in explaining exuberance in markets. There are incentives for investors, money managers and analysts to imitate other's actions. Furthermore, conservatism as well as heuristics like representativeness may also lead to a confirmation of prevailing trends. Another driver of misjudgement is the usage of heuristics like representativeness. The authors consider that the provision of information may substantially contribute to the reduction of misjudgement and exuberance in markets. Both availability and quality of information are important. Another approach aims at the regulation of bank lending, which should be limited particularly during a booming economy

    Crystal structure and equation of state of Fe-Si alloys at super-Earth core conditions

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    The high-pressure behavior of Fe alloys governs the interior structure and dynamics of super-Earths, rocky extrasolar planets that could be as much as 10 times more massive than Earth. In experiments reaching up to 1300 GPa, we combine laser-driven dynamic ramp compression with in situ x-ray diffraction to study the effect of composition on the crystal structure and density of Fe-Si alloys, a potential constituent of super-Earth cores. We find that Fe-Si alloy with 7 weight % (wt %) Si adopts the hexagonal close-packed structure over the measured pressure range, whereas Fe-15wt%Si is observed in a body-centered cubic structure. This study represents the first experimental determination of the density and crystal structure of Fe-Si alloys at pressures corresponding to the center of a ~3–Earth mass terrestrial planet. Our results allow for direct determination of the effects of light elements on core radius, density, and pressures for these planets

    Identifying the neurodevelopmental and psychiatric signatures of genomic disorders associated with intellectual disability: a machine learning approach

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    Background: Genomic conditions can be associated with developmental delay, intellectual disability, autism spectrum disorder, and physical and mental health symptoms. They are individually rare and highly variable in presentation, which limits the use of standard clinical guidelines for diagnosis and treatment. A simple screening tool to identify young people with genomic conditions associated with neurodevelopmental disorders (ND-GCs) who could benefit from further support would be of considerable value. We used machine learning approaches to address this question. Method: A total of 493 individuals were included: 389 with a ND-GC, mean age = 9.01, 66% male) and 104 siblings without known genomic conditions (controls, mean age = 10.23, 53% male). Primary carers completed assessments of behavioural, neurodevelopmental and psychiatric symptoms and physical health and development. Machine learning techniques (penalised logistic regression, random forests, support vector machines and artificial neural networks) were used to develop classifiers of ND-GC status and identified limited sets of variables that gave the best classification performance. Exploratory graph analysis was used to understand associations within the final variable set. Results: All machine learning methods identified variable sets giving high classification accuracy (AUROC between 0.883 and 0.915). We identified a subset of 30 variables best discriminating between individuals with ND-GCs and controls which formed 5 dimensions: conduct, separation anxiety, situational anxiety, communication and motor development. Limitations: This study used cross-sectional data from a cohort study which was imbalanced with respect to ND-GC status. Our model requires validation in independent datasets and with longitudinal follow-up data for validation before clinical application. Conclusions: In this study, we developed models that identified a compact set of psychiatric and physical health measures that differentiate individuals with a ND-GC from controls and highlight higher-order structure within these measures. This work is a step towards developing a screening instrument to identify young people with ND-GCs who might benefit from further specialist assessment
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