1,721,985 research outputs found
Lagrangian dynamics and the mass function
No full textThe problem of the analytical determination of the mass function is set up in terms of Lagrangian dynamics. The use of the perturbative Lagrangian approach, the definition of collapse and the role of smoothing are discussed. Then first-order calculations, corresponding to the use of the Zel'dovich approximation, are reviewed. The homogeneous ellipsoidal collapse model is carefully introduced. The result of such calculation is an increase of the number of large-mass objects; the resulting mass function is similar, at large masses, to a Press & Schechter function with a parameter δc of about 1.5. © 1997 OPA (Overseas Publishers Association) Amsterdam B.V. Published under license under the Gordon and Breach Science Publishers imprint
Feedback in galaxy formation with two-phase ISM
No full textI present a model for galaxy formation based on the physics of two-phase ISM in pressure equilibrium. In this model gas cools or infalls from an external halo, fragmenting into small clouds. These coagulate to form giant molecular complexes, which collapse and form stars. Supernovae drive superbubbles into the hot phase. The effect of feedback depends on whether superbubbles are confined or blow out of the system before cooling. Depending on the density and geometry of the system, I obtain self-regulated systems, rapid starbursts or critical systems where the hot phase suddenly collapses
Non-spherical collapse and the analytical mass function
No full textNon-spherical dynamical approximations and models for gravitational collapse are used to extend the well-known Press & Schechter (PS) approach, in order to determine analytical expressions for the mass function of cosmic structures. The problem is rigorously set up by considering the intrinsic Lagrangian nature of the mass function. The Zel'dovich approximation (ZEL), a ZEL-based model and the homogeneous ellipsodail collapse model are used to predict the collapse time of a mass element. It results that more large-mass objects are expected to form than the usual PS relation. In particular, it can be dynamically explained why lower δc values are found to fit the results of several N-body simulations. © 1996 OPA (Overseas Publishers Association) Amsterdam B.V. Published in The Netherlands under license by Gordon and Breach Science
Environmental effects in the local supercluster
No full textA number of recent works on the relation between galactic environment and the properties of nearby galaxies is reviewed. The 3D nature of the quantities used is stressed, together with the importance of considering the environment at different scales. The results obtained are reported, with a special attention to the small-and large-scale segregation of low-luminosity AGNs hosted in early-type spirals. Finally, an outline of future projects on this subject is presented. © 1996 OPA (Overseas Publishers Association) Amsterdam B.V. Published in The Netherlands under license by Gordon and Breach Science
Performance capability testing of a slab track system
No full textThe permanent way being laid for the urban rail project "Metropolitana Bari Centrale - Quartiere San Paolo" in Bari, Italy, is of the Margaritelli slab track type, whereby prefabricated unstressed reinforced concrete slabs are laid unconnected on elastic matting over a cement layer. To analyse the performance capability of this permanent way type, extended-time threshold testing was carried out in the laboratory. The article describes the tests carried out and the results obtained
Site Effects from the Building Scale to the Seismic Microzonation Scale: Examples from the Experience of L'Aquila
No full textThis paper illustrates the site characterization for evaluating local ground motion amplifications at two sites in the urban area of L'Aquila, performed for the reconstruction of buildings damaged by the April 6, 2009 earthquake. The paper is focused on the comparison between results obtained from site investigations carried out at the building scale and from information contained in the seismic microzonation study. Local amplifications inferred from microzonation may be considerably different from those provided by ground response analyses based on punctual soil data, due to the complex geological setting and the marked variability in geotechnical properties of the foundation soils. The practice of using seismic microzonation data for deriving the seismic action on buildings, not infrequent in structural engineering design, should be avoided or considered with caution
Recent Improvements in the Use, Interpretation, and Applications of DMT and SDMT in Practice
No full textThis article presents an overview of the current trends and ongoing developments in the use, interpretation, and application of the flat dilatometer (DMT) and the seismic dilatometer (SDMT) to site characterization and geotechnical design. In particular, the following issues are specifically addressed: the sensitivity of DMT to stress history, combined use of DMT and the cone/piezocone penetration test (in-situ multi-parameter/multi-test approach), estimating overconsolidation ratio and K0 in sand, DMT interpretation in partially draining niche silts and in non-textbook soils, interrelationship small/operative strain stiffness and in situ stiffness decay curves using SDMT, and liquefaction assessment
Experimental enquire on reinforced concrete precast formations for "50 UNI" rails
No full textAn experimental test campaign has been carried out on the track equipment system for "50 UNI" rails with reinforced concrete precast formation laid down on elastomeric mattress. This system will be utilised for the preparation of the Bari-S. Paolo underground railway superstructure. Some experimental test have been carried out on prototypes in order to verify the performances of the proposed system. The paper illustrates the results of the tests and gives some design directives deriving from the analysis of the experimental tests
DMT-based liquefaction triggering procedure accounting for the fines content effect
No full textThe application of semi-empirical charts based on in-situ testing results represents the first step in the earthquake-induced soil liquefaction assessment. Among them, the CPT-based charts have been largely developed in the last decades, especially after the 2010–2011 Canterbury earthquakes in New Zealand, while the main drawback of the existing approach based on DMT is related to the lack of a correction factor for the fines content. In this regard, this study proposes a new empirical relationship between the cyclic resistance ratio and the horizontal stress index where the effects of the fines content are incorporated. The new method is calibrated on specific sites located in the Emilia-Romagna plain (Italy), where an extensive soil characterization from in-situ and laboratory tests was available for the silty sand and sandy silt deposits affected by liquefaction after the 2012 Emilia earthquake. The performance of the new curve accounting for the fines content effect is compared with that obtained by adopting the “clean sand” curves proposed in the past, as well as with that obtained by using the most recent CPT-based method. Even though verified only for specific Italian soils and requiring further field validation, the proposed approach appears as promising to improve the DMT-based liquefaction assessment in silty sands
Dynamic Control of Bridges with Slender Piers
No full textIn this paper a vibrational method for in situ investigations is described. The method has been applied to a bridge viaduct of about 800 m in length, with slender piers, a continuous deck and supports with a viscoelastic behavior. Three techniques of excitation of the structure have been utilized. The modes of vibration of the deck and the piers have been found with two techniques of excitation. The dynamic inputs for in situ tests have been produced by an artificial generator of vibrations (REM). The structural response has been measured with accelerometers. The spectral analysis of the environmental noise (wind) has been applied and the vibrational modes of the taller piers in the low frequency range have been determined. In this paper the bridge has been modeled with a finite element program and the dynamic behavior of the structure has been numerically determined. Then its vibrational modes have been compared with the ones experimentally obtained. The plots of the Power Spectral Densities (PSD) induced by the wind furnished more information on the vibration modes of the structure in the field of low frequencies. These information filled the lacks determined in this range performing the dynamic tests with the artificial generator of vibrations
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