533 research outputs found

    Compact Nuclei in Galaxies at Moderate Redshift:II. Their Nature and Implications for the AGN Luminosity Function

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    This study explores the space density and properties of active galaxies to z=0.8. We have investigated the frequency and nature of unresolved nuclei in galaxies at moderate redshift as indicators of nuclear activity such as Active Galactic Nuclei (AGN) or starbursts. Candidates are selected by fitting imaged galaxies with multi-component models using maximum likelihood estimate techniques to determine the best model fit. We select those galaxies requiring an unresolved point-source component in the galaxy nucleus, in addition to a disk and/or bulge component, to adequately model the galaxy light. We have searched 70 WFPC2 images primarily from the Medium Deep Survey for galaxies containing compact nuclei. In our survey of 1033 galaxies, the fraction containing an unresolved nuclear component greater than 5% of the total galaxy light is 9+/-1% corrected for incompleteness. In this second of two papers in this series, we discuss the nature of the compact nuclei and their hosts. We present the upper limit luminosity function (LF) for low-luminosity AGN (LLAGN) in two redshift bins to z=0.8. Mild number density evolution is detected for nuclei at -18 -16 and this flatness, combined with the increase in number density, is inconsistent with pure luminosity evolution. Based on the amount of density evolution observed for these objects, we find that almost all present-day spiral galaxies could have hosted a LLAGN at some point in their lives. We also comment on the likely contribution of these compact nuclei to the soft X-ray background.Comment: 50 pages, 14 figures, to appear in ApJ, April 199

    Luke's use of the expression "The Holy Spirit": its bearing upon the problem of his sources.

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    Typescript. Thesis (Ph.D.)--Boston University, Graduate School, 1928. Includes bibliographical references (leaves 253-258). Vita

    Address: The Impact of Separation of Powers on National Security

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    Federalists, I give you the former six-term congressman from Wyoming, the former Chief of Staff to President Ford, and the individual who, as much as anyone in Congress, made Gorbachev the man he is today-Secretary of Defense Dick Cheney

    Vice President Cheney\u27s Unused Resignation Letter

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    Resignation letter prepared by Vice President Dick Cheney for his chief of staff to deliver to President George W. Bush should Cheney become incapacitated. The letter was never delivered. It is accompanied by a memo written by Cheney\u27s chief of staff, David Addington, explaining the purpose of the resignation letter. Securing this document was a joint effort of Roy E. Brownell II and John Rogan.https://ir.lawnet.fordham.edu/twentyfifth_amendment_executive_materials/1015/thumbnail.jp

    The Vice President-More than an Afterthought?

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    A round-table discussion among former U.S. Vice President Richard B. Cheney, Caruso Family Professor of Law and retired U.S. Ambassador Douglas Kmiec, and former U.S. Attorney General Edwin Meese III considered the practical implications of conceiving the Vice President as a legislative officer, an executive officer, or both. It was noted that until the second half of the twentieth century, the Office of the Vice President was conceived as legislative. Funding for the Office appeared in budget lines relating to Congress and physically, the Vice President’s office was in the Capitol. Beginning with Walter Mondale’s service as Vice President, presidents have been delegating increasing executive authority, seeing the Vice President as a “deputy president.” Perhaps the most aggressive and influential of the modern “deputy presidents” was Vice President Cheney himself. Attorney General Meese concurred and saw this as positive. Ambassador Kmiec was less approving, encouraging Vice President Cheney and Attorney General Meese to contemplate the benefits that a dual-natured legislative–executive Vice President supplies to maintaining a workable government. The capacity of the Vice President to assert independence, as late Justice Scalia explained in an Office of Legal Counsel opinion, is unique. Unlike members of the Cabinet, the Vice President is not removable by the President, and thus, the Vice President can use his dual nature to advance executive–legislative compromise. Vice President Cheney’s reliance upon his significant, but personal, legislative experience prior to his vice presidency to facilitate executive–legislative bargaining suggests qualities that presidential nominees might consider more directly in vice presidential selection, and not just geographic complementarity and ideological compatibility. While it has been commonplace to think of the vice presidential office as “an afterthought” borrowed from state charters at the time of the founding, this dialogue suggests how a vice president with a foot in each of the Legislative and Executive Branches can assist in overcoming dysfunctional periods when partisan division is great

    Magnetic interactions in iron superconductors: A review

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    High temperature superconductivity in iron pnictides and chalcogenides emerges when a magnetic phase is suppressed. The multi-orbital character and the strength of correlations underlie this complex phenomenology, involving magnetic softness and anisotropies, with Hund's coupling playing an important role. We review here the different theoretical approaches used to describe the magnetic interactions in these systems. We show that taking into account the orbital degree of freedom allows us to unify in a single phase diagram the main mechanisms proposed to explain the (\pi,0) order in iron pnictides: the nesting-driven, the exchange between localized spins, and the Hund induced magnetic state with orbital differentiation. Comparison of theoretical estimates and experimental results helps locate the Fe superconductors in the phase diagram. In addition, orbital physics is crucial to address the magnetic softness, the doping dependent properties, and the anisotropies.Comment: Invited review article for a focus issue of Comptes Rendus Physique: 26 pages, 10 figures. Revised version, as accepted. Small changes throughout the text plus new subsection (Sec. IIIE

    Myosin-X and disease

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    Myosin-X (Myo10) is a motor protein well known for its role in filopodia formation. New research implicates Myo10 in a number of disease states including cancer metastasis and pathogen infection. This review focuses on these developments with emphasis on the emerging roles of Myo10 in formation of cancer cell protrusions and metastasis. A number of aggressive cancers show high levels of Myo10 expression and knockdown of Myo10 has been shown to dramatically limit cancer cell motility in 2D and 3D systems. Myo10 knockdown also limits spread of intracellular pathogens marburgvirus and Shigella flexneri. Consideration is given to how these properties might arise and potential paths of future research

    Myosin-X: a MyTH-FERM myosin at the tips of filopodia

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    Myosin-X (Myo10) is an unconventional myosin with MyTH4-FERM domains that is best known for its striking localization to the tips of filopodia and its ability to induce filopodia. Although the head domain of Myo10 enables it to function as an actin-based motor, its tail contains binding sites for several molecules with central roles in cell biology, including phosphatidylinositol (3,4,5)-trisphosphate, microtubules and integrins. Myo10 also undergoes fascinating long-range movements within filopodia, which appear to represent a newly recognized system of transport. Myo10 is also unusual in that it is a myosin with important roles in the spindle, a microtubule-based structure. Exciting new studies have begun to reveal the structure and single-molecule properties of this intriguing myosin, as well as its mechanisms of regulation and induction of filopodia. At the cellular and organismal level, growing evidence demonstrates that Myo10 has crucial functions in numerous processes ranging from invadopodia formation to cell migration

    Dynamics of hinged wings in strong upward gusts

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    A bird's wings are articulated to its body via highly mobile shoulder joints. The joints confer an impressive range of motion, enabling the wings to make broad, sweeping movements that can modulate quite dramatically the production of aerodynamic load. This is enormously useful in challenging flight environments, especially the gusty, turbulent layers of the lower atmosphere. In this study, we develop a dynamics model to examine how a bird-scale gliding aircraft can use wing-root hinges (analogous to avian shoulder joints) to reject the initial impact of a strong upward gust. The idea requires that the spanwise centre of pressure and the centre of percussion of the hinged wing start, and stay, in good initial alignment (the centre of percussion here is related to the idea of a ‘sweet spot’ on a bat, as in cricket or baseball). We propose a method for achieving this rejection passively, for which the essential ingredients are (i) appropriate lift and mass distributions; (ii) hinges under constant initial torque; and (iii) a wing whose sections stall softly. When configured correctly, the gusted wings will first pivot on their hinges without disturbing the fuselage of the aircraft, affording time for other corrective actions to engage. We expect this system to enhance the control of aircraft that fly in gusty conditions
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