1,399 research outputs found

    Linkage between Accretion Disks and Blazars

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    The magnetic field in an accretion disk is estimated assuming that all of the angular momentum within prescribed accretion disk radii is removed by a jet. The magnetic field estimated at the base of the jet is extrapolated to the blazar emission region using a model for a relativistic axisymmetric jet combined with some simplifying assumptions based on the relativistic nature of the flow. The extrapolated magnetic field is compared with estimates based upon the synchrotron and inverse Compton emission from three blazars, MKN 501, MKN 421 and PKS 2155-304. The magnetic fields evaluated from pure synchrotron self- Compton models are inconsistent with the magnetic fields extrapolated in this way. However, in two cases inverse Compton models in which a substantial part of the soft photon field is generated locally agree well, mainly because these models imply magnetic field strengths which are closer to being consistent with Poynting flux dominated jets. This comparison is based on estimating the mass accretion rate from the jet energy flux. Further comparisons along these lines will be facilitated by independent estimates of the mass accretion rate in blazars and by more detailed models for jet propagation near the black hole.Comment: Submiteed to the Astrophysics & Space Science special issue on the 5th Stromlo Symposiu

    Space station integrated propulsion and fluid systems study

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    This Databook addresses the integration of fluid systems of the Space Station program. It includes a catalog of components required for the Space Station elements fluid systems and information on potential hardware commonality. The components catalog is in four parts. The first part lists the components defined for all the fluid systems identified in EP 2.1, Space Station Program Fluid Systems Configuration Databook. The components are cross-referenced in three sections. Section 2.1 lists the components by the fluid system in which they are used. Section 2.2 lists the components by type. Section 2.3 lists by the type of fluid media handled by the component. The next part of the catalog provides a description of the individual component. This section (2.4) is made up of data retrieved from Martin Marietta Denver Aerospace component data base. The third part is an assessment of propulsion hardware technology requirements. Section 2.5 lists components identified during the study as requiring development prior to flight qualification. Finally, Section 2.6 presents the results of the evaluation of commonality between components. The specific requirements of each component have been reviewed and duplication eliminated

    Space station integrated propulsion and fluid system study: Fluid systems configuration databook

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    This databook contains fluid system requirements and system descriptions for Space Station program elements including the United States and International modules, integrated fluid systems, attached payloads, fluid servicers and vehicle accommodation facilities. Separate sections are devoted to each of the program elements and include a discussion of the overall system requirements, specific fluid systems requirements and systems descriptions. The systems descriptions contain configurations, fluid inventory data and component lists. In addition, a list of information sources is referenced at the end of each section

    The pulsed air gust generator Final report

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    Wind tunnel simulation of jet pulsing apparatus for controlled gust

    Radio-Excess IRAS Galaxies: IV. Optical Spectroscopy

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    This is the fourth in our series of papers investigating radio-excess galaxies, which have radio emission associated with an active nucleus but which do not fit into the traditional categories of either radio-loud or radio-quiet active galaxies. In this paper, we present optical spectra of our sample of FIR-luminous radio-excess galaxies. Optical emission line diagnostics are used to determine the dominant source of the ionizing radiation. We find that radio excess is an excellent indicator of the presence of an active nucleus: the radio-excess sample contains a much higher fraction of AGN than samples selected on FIR luminosity alone, or using other criteria such as warm FIR colors. Several objects have ambiguous classifications and are likely to be composite objects with mixed excitation. The type of optical spectrum appears to be associated with the radio-loudness: radio-loud objects may be more `pure' AGN than radio-intermediate objects. We find strong evidence for interaction between the radio plasma and the surrounding gas. The jet energy fluxes of the radio-excess objects, inferred from the [O III] luminosities, are lower than in powerful radio sources, consistent with our previous results. We conclude that the jets of radio-intermediate sources are intrinsically weaker than those in sources with more powerful radio emission. A significant fraction of the sample spectra show post-starburst stellar continuum, with A-star absorption lines, consistent with the large fraction of merging or disturbed host galaxies in the sample. The ages of the radio sources are significantly less than those of A stars indicating that, if the radio sources are associated with merging activity, there is a delay between the interaction and the initiation of the radio activity. (Abridged.)Comment: Accepted for publication in AJ; version with high resolution figures available from http://www.cis.rit.edu/~clbsps/papers/paper4.pd

    Systematic review of the development and effectiveness of digital health information interventions, compared with usual care, in supporting patient preparation for paediatric hospital care, and the impact on their health outcomes

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    Background and aim: Elective surgery can be overwhelming for children, leading to pre-operative anxiety, which is associated with adverse clinical and behavioural outcomes. Evidence shows that paediatric preparation digital health interventions (DHIs) can contribute to reduced pre-operative anxiety and negative behavioural changes. However, this evidence does not consider their design and development in the context of behavioural science. This systematic review used the Theoretical Domains Framework (TDF) to evaluate the design and development of DHIs used to support children up to 14 years of age and their parents, prepare for hospital procedures, and determine any correlation to health outcomes. It also considered whether any behavioural frameworks and co-production were utilised in their design. Methods: A search of the MEDLINE, EMBASE, PsycINFO, and HMIC databases was carried out, looking for original, empirical research using digital paediatric preparation technologies to reduce pre-operative anxiety and behavioural changes. Limitations for the period (2000–2022), English language, and age applied. Results: Seventeen studies were included, sixteen randomised control trials and one before and after evaluation study. The results suggest that paediatric preparation DHIs that score highly against the TDF are (1) associated with improved health outcomes, (2) incorporate the use of co-production and behavioural science in their design, (3) are interactive, and (4) are used at home in advance of the planned procedure. Conclusion: Paediatric preparation DHIs that are co-produced and designed in the context of behavioural science are associated with reduced pre-operative anxiety and improved health outcomes and may be more cost-effective than other interventions. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/, identifier: CRD42022274182

    Spaceborne synthetic-aperture imaging radars: Applications, techniques, and technology

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    In the last four years, the first two Earth-orbiting, space-borne, synthetic-aperture imaging radars (SAR) were successfully developed and operated. This was a major achievement in the development of spaceborne radar sensors and ground processors. The data acquired with these sensors extended the capability of Earth resources and ocean-surface observation into a new region of the electromagnetic spectrum. This paper is a review of the different aspects of spaceborne imaging radars. It includes a review of: 1) the unique characteristics of space-borne SAR systems; 2) the state of the art in spaceborne SAR hardware and SAR optical and digital processors; 3) the different data-handling techniques; and 4) the different applications of spaceborne SAR data

    RhoJ/TCL Regulates Endothelial Motility and Tube Formation and Modulates Actomyosin Contractility and Focal Adhesion Numbers

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    Objective—RhoJ/TCL was identified by our group as an endothelial-expressed Rho GTPase. The aim of this study was to determine its tissue distribution, subcellular localization, and function in endothelial migration and tube formation. Methods and Results—Using in situ hybridization, RhoJ was localized to endothelial cells in a set of normal and cancerous tissues and in the vasculature of mouse embryos; endogenous RhoJ was localized to focal adhesions by immunofluorescence. The proangiogenic factor vascular endothelial growth factor activated RhoJ in endothelial cells. Using either small interfering (si)RNA-mediated knockdown of RhoJ expression or overexpression of constitutively active RhoJ (daRhoJ), RhoJ was found to positively regulate endothelial motility and tubule formation. Downregulating RhoJ expression increased focal adhesions and stress fibers in migrating cells, whereas daRhoJ overexpression resulted in the converse. RhoJ downregulation resulted in increased contraction of a collagen gel and increased phospho–myosin light chain, indicative of increased actomyosin contractility. Pharmacological inhibition of Rho-kinase (which phosphorylates myosin light chain) or nonmuscle myosin II reversed the defective tube formation and migration of RhoJ knockdown cells. Conclusion—RhoJ is endothelial-expressed in vivo, activated by vascular endothelial growth factor, localizes to focal adhesions, regulates endothelial cell migration and tube formation, and modulates actomyosin contractility and focal adhesion numbers
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