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Engineering	50%

Selected Abstracts

Damage-based design with no repairs for multiple events and its sensitivity to seismicity model

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 3 2007
S. Das
Abstract Conventional design methodology for the earthquake-resistant structures is based on the concept of ensuring ,no collapse' during the most severe earthquake event. This methodology does not envisage the possibility of continuous damage accumulation during several not-so-severe earthquake events, as may be the case in the areas of moderate to high seismicity, particularly when it is economically infeasible to carry out repairs after damaging events. As a result, the structure may collapse or may necessitate large scale repairs much before the design life of the structure is over. This study considers the use of design force ratio (DFR) spectrum for taking an informed decision on the extent to which yield strength levels should be raised to avoid such a scenario. DFR spectrum gives the ratios by which the yield strength levels of single-degree-of-freedom oscillators of different initial periods should be increased in order to limit the total damage caused by all earthquake events during the lifetime to a specified level. The DFR spectra are compared for three different seismicity models in case of elasto-plastic oscillators: one corresponding to the exponential distribution for return periods of large events and the other two corresponding to the lognormal and Weibull distributions. It is shown through numerical study for a hypothetical seismic region that the use of simple exponential model may be acceptable only for small values of the seismic gap length. For moderately large to large seismic gap lengths, it may be conservative to use the lognormal model, while the Weibull model may be assumed for very large seismic gap lengths. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Matching a system behavior with a known set of models: A quadratic optimization-based adaptive solution

INTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 9 2009
Moisés Bonilla
Abstract The matching process between a time-domain external behavior of a lumped single-input single-output dynamical system and a known set of linear continuous time-invariant models is tackled in this paper. The proposed online solution is based on an adaptive structure detector, which in finite time locates in the known set of models the one corresponding to the observed external behavior; the detector results from the solution of a constrained quadratic optimization problem. The problem is expressed in terms of the time-domain activity of a family of discriminating filters and is solved via a normalized gradient algorithm, which avoids mismatching due to the presence of structural zeros in the filters and can take into account band-limited high-frequency measurement noise. A failure detection problem concerning a simulated servomechanism is included in order to illustrate the proposed solution. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Fate of clumps in damped Ly, systems

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
Ilian T. Iliev
ABSTRACT Recent observations have revealed that damped Ly, clouds (DLAs) host star formation activity. In order to examine if such star formation activity can be triggered by ionization fronts, we perform high-resolution hydrodynamics and radiative transfer simulations of the effect of radiative feedback from propagating ionization fronts on high-density clumps. We examine two sources of ultraviolet (UV) radiation field to which high-redshift (z, 3) galaxies could be exposed: one corresponding to the UV radiation originating from stars within the DLA, itself, and the other corresponding to the UV background radiation. We find that, for larger clouds, the propagating I-fronts created by local stellar sources can trigger cooling instability and collapse of significant part, up to 85 per cent, of the cloud, creating conditions for star formation in a time-scale of a few Myr. The passage of the I-front also triggers collapse of smaller clumps (with radii below ,4 pc), but in these cases the resulting cold and dense gas does not reach conditions conducive to star formation. Assuming that 85 per cent of the gas initially in the clump is converted into stars, we obtain a star formation rate of ,0.25 M, yr,1 kpc,2. This is somewhat higher than the value derived from recent observations. On the other hand, the background UV radiation which has harder spectrum fails to trigger cooling and collapse. Instead, the hard photons which have long mean free-path heat the dense clumps, which as a result expand and essentially dissolve in the ambient medium. Therefore, the star formation activity in DLAs is strongly regulated by the radiative feedback, both from the external UV background and internal stellar sources and we predict quiescent evolution of DLAs (not starburst-like evolution). [source]

Theoretical Studies of Damage to 3,-Uridine Monophosphate Induced by Electron Attachment

CHEMISTRY - A EUROPEAN JOURNAL, Issue 9 2008
bo Zhang Ass.
Abstract Low-energy electrons (LEE) are well known to induce nucleic acid damage. However, the damage mechanisms related to charge state and structural features remain to be explored in detail. In the present work, we have investigated the N1-glycosidic and C3,O(P) bond ruptures of 3,-UMP (UMP=uridine monophosphate) and the protonated form 3,-UMPH with ,1 and zero charge, respectively, based on hybrid density functional theory (DFT) B3,LYP together with the 6-31+G(d,p) basis set. The glycosidic bond breakage reactions of the 3,UMP and 3,UMPH electron adducts are exothermic in both cases, with barrier heights of 19,20,kcal,mol,1 upon inclusion of bulk solvation. The effects of the charge state on the phosphate group are marginal, but the C2,OH group destabilizes the transition structure of glycosidic bond rupture of 3,-UMPH in the gas phase by approximately 5.0,kcal,mol,1. This is in contrast with the C3,O(P) bond ruptures induced by LEE in which the charge state on the phosphate influences the barrier heights and reaction energies considerably. The barrier towards C3,O(P) bond dissociation in the 3,UMP electron adduct is higher in the gas phase than the one corresponding to glycosidic bond rupture and is dramatically influenced by the C2,OH group and bulk salvation, which decreases the barrier to 14.7,kcal,mol,1. For the C3,O(P) bond rupture of the 3,UMPH electron adduct, the reaction is exothermic and the barrier is even lower, 8.2,kcal,mol,1, which is in agreement with recent results for 3,-dTMPH and 5,-dTMPH (dTMPH=deoxythymidine monophosphate). Both the Mulliken atomic charges and unpaired-spin distribution play significant roles in the reactions. [source]