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Synthesis Model (synthesis + model)
Selected AbstractsIonized gas in E/S0 galaxies with dust lanesMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2010Ido Finkelman ABSTRACT We report the results of multicolour observations of 30 E/S0 galaxies with dust lanes. For each galaxy we obtained broad-band images and narrow-band images using interference filters isolating the H,+[N ii] emission lines to derive the amount and morphology of dust and ionized gas. To improve the wavelength coverage we retrieved data from the Sloan Digital Sky Survey and Two Micron All Sky Survey and combined these with our data. Ionized gas is detected in 25 galaxies and shows in most cases a smooth morphology, although knots and filamentary structure are also observed in some objects. The extended gas distribution closely follows the dust structure, with a clear correlation between the mass of both components. An extinction law by the extragalactic dust in the dark lanes is derived and is used to estimate the dust content of the galaxies. The derived extinction law is used to correct the measured colours for intrinsic dust extinction and the data are fitted with a stellar population synthesis model. We find that the H, emission and colours of most objects are consistent with the presence of an ,old' stellar population (,10 Gyr) and a small fraction of a ,young' population (, 10,100 Myr). To check this we closely examine NGC 5363, for which archival Spitzer/Infrared Array Camera and Galaxy Evolution Explorer data are available, as a representative dust-lane E/S0 galaxy of the sample. [source] Is AGN feedback necessary to form red elliptical galaxies?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008A. Khalatyan ABSTRACT We have used the smoothed particle hydrodynamics (SPH) code gadget-2 to simulate the formation of an elliptical galaxy in a group-size cosmological dark matter halo with mass Mhalo, 3 × 1012 h,1 M, at z= 0. The use of a stellar population synthesis model has allowed us to compute magnitudes, colours and surface brightness profiles. We have included a model to follow the growth of a central black hole and we have compared the results of simulations with and without feedback from active galactic nuclei (AGN). We have studied the interplay between cold gas accretion and merging in the development of galactic morphologies, the link between colour and morphology evolution, the effect of AGN feedback on the photometry of early-type galaxies, the redshift evolution in the properties of quasar hosts, and the impact of AGN winds on the chemical enrichment of the intergalactic medium (IGM). We have found that the early phases of galaxy formation are driven by the accretion of cold filamentary flows, which form a disc galaxy at the centre of the dark matter halo. Disc star formation rates in this mode of galaxy growth are about as high as the peak star formation rates attained at a later epoch in galaxy mergers. When the dark matter halo is sufficiently massive to support the propagation of a stable shock, the gas in the filaments is heated to the virial temperature, cold accretion is shut down, and the star formation rate begins to decline. Mergers transform the spiral galaxy into an elliptical one, but they also reactivate star formation by bringing gas into the galaxy. Without a mechanism that removes gas from the merger remnants, the galaxy ends up with blue colours, which are atypical for its elliptical morphology. We have demonstrated that AGN feedback can solve this problem even with a fairly low heating efficiency. Our simulations support a picture where AGN feedback is important for quenching star formation in the remnant of wet mergers and for moving them to the red sequence. This picture is consistent with recent observational results, which suggest that AGN hosts are galaxies in migration from the blue cloud to the red sequence on the colour,magnitude diagram. However, we have also seen a transition in the properties of AGN hosts from blue and star forming at z, 2 to mainly red and dead at z, 0. Ongoing merging is the primary but not the only triggering mechanism for luminous AGN activity. Quenching by AGN is only effective after the cold filaments have dried out, since otherwise the galaxy is constantly replenished with gas. AGN feedback also contributes to raising the entropy of the hot IGM by removing low-entropy tails vulnerable to developing cooling flows. We have also demonstrated that AGN winds are potentially important for the metal enrichment of the IGM a high redshift. [source] Revisiting DDGX/DDG-51 Concept ExplorationNAVAL ENGINEERS JOURNAL, Issue 3 2007JUSTIN STEPANCHICK This study revisits concept exploration for DDG-51 using reconstructed 1978,1979 DDX and 1979,1980 DDGX requirements and options, and 2005 tools. The goal of this study is to assess and highlight the benefits of current tools and processes for concept exploration by comparison with a well-known design that did not use these tools. This case study was completed in a summer and fall ship design project at Virginia Tech. In 1979, the acquisition and design process did not begin with a Mission Need Statement, Analysis of Alternatives or Integrated Capabilities Document as is required today. It began with studies, Tentative Operational Requirements, and Draft Top Level Requirements. In this study, we revisit the 1978,1980 DDG-51 (DDX/DDGX) concept exploration based on the guidance, goals, and constraints of the DDX and DDGX studies, using a notional mission statement, concept of operations, and list of required capabilities. The design space is defined to include many of the same design alternatives that were considered in the DDX and DDGX studies. A multiple-objective genetic optimization (MOGO) based on military effectiveness, cost, and risk is used to search the design space and perform trade-offs. A simple ship synthesis model is used to balance the designs, assess feasibility, and calculate cost, risk, and effectiveness. Alternative designs are ranked by cost, risk, and effectiveness, and presented in a series of non-dominated frontiers. Concepts for further study and development are chosen from this frontier and a comparison with DDG-51 is made based on these results. [source] T-AKE: Acquiring the Environmentally Sound Ship of the 21st CenturyNAVAL ENGINEERS JOURNAL, Issue 3 2006Cdr. Stephen P. Markle USN (Ret.) P.E. Department of Defense (DoD) program managers are increasingly challenged with the difficulties of balancing the risks associated with cost, schedule, and performance in an era of intense competition for increasingly scarce resources. Requirements associated with environmental, safety, and health (ESH), in the context of thirty to forty-year service lives, have not been consistently, or in some cases adequately, addressed in DoD programs. Environmental protection (EP) requirements generally do not fit the normal requirements generation and product synthesis model typically applied to weapon system development. As with all requirements, early identification is the key to integration into the total system. Recognition that EP requirements must be integrated at program conception led to development of the ESH Integration Model by the U.S. Navy Lewis and Clark (T-AKE) Auxiliary Cargo Ammunition Ship Program. Institutionalization of this model has enabled the T-AKE Program to establish EP performance requirements for the twelve-ship class that substantially reduce the environmental footprint of the Navy. Compared to the fifteen ships that it will be replacing, T-AKE will require fifty percent less manning and reduce waste streams by seventy percent enabling an annual life cycle cost savings of $5M in ashore waste disposal costs. The T-AKE Program has been the first to achieve the Chief of Naval Operations vision for the "Environmentally Sound Warship of the 21st Century" through design integration of EP requirements. [source] Fuzzy approach to dependability performance evaluationQUALITY AND RELIABILITY ENGINEERING INTERNATIONAL, Issue 7 2008Dejan Ivezi Abstract This paper presents a model for dependability performance evaluation by fuzzy sets utilization. Basic dependability indicators (reliability, maintainability and maintenance support) are used for the analysis of technical systems' conditions from the aspects of design, construction, maintenance and logistics. These indicators as well as associated dependability expressions itself are described by linguistic variables, which are characterized by a membership function to the defined classes. The proposed model is primarily appropriate for introduction, analysis and synthesis of information related to quality of systems in operation. Such data are often available only as experts' judgment and estimations. A practical engineering example (mechanical system at bucket wheel excavator) has been presented to demonstrate the proposed dependability analysis and synthesis model. Copyright © 2008 John Wiley & Sons, Ltd. [source] | ||||||||||