1,721,143 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Influence of model parameter uncertainties on the seismic vulnerability analysis of continuous steel-concrete composite bridges exhibiting dual-load paths
No full textThe performance of multi-span steel-concrete composite bridges in recent seismic events has shown that these structures are very sensitive to earthquake loading. Following the Performance-Based Earthquake Engineering (PBEE) framework, the vulnerability assessment of these systems must take rigorously into account all pertinent sources of uncertainty, including uncertainties in the loading and in the structural/mechanical/geometrical properties (model parameter uncertainty). The model parameter uncertainty
affects not only the structural capacity, but also the Engineering Demand Parameters (EDPs). However, most of the procedures for fragility calculation focus on the variability of EDPs due to input ground motion uncertainty (record-to-record variability) and neglect model parameter uncertainty effects, or incorporate these effects only in a simplified way. This paper aims at studying the effects of model parameter uncertainty on the seismic response and on the seismic vulnerability of steel-concrete composite bridges with abutment transverse restraints. In this paper, the Extended Incremental Dynamic Analysis (EIDA) method is used to account for all sources of aleatoric uncertainty. EIDA is applied to a benchmark SCC bridge system with dual load path to estimate the first- and second-order statistics of the EDPs of interest, to assess the sensitivity of the structural response to the model parameter uncertainty, and to evaluate the seismic vulnerability accounting for all pertinent sources of uncertainty
POLLUTED MARINE ECOSYSTEMS: RESERVOIR OF MICROBIAL RESOURCES FOR HYDROCARBON BIOREMEDIATION
Full text linkHydrocarbon (HC) pollution is a worldwide threat to marine natural ecosystems due to the increasing exploitation of underground marine petroleum deposits in several areas and to the high traffic of oil tankers and the presence of submarine pipes that are main transport routes for crude oil and refined products. HCs spread in the marine environment is mainly due to accidental oil spills or inadequate practices and their release affects marine ecosystems causing severe ecological and economical damages. The Mediterranean Sea is particularly endangered by hydrocarbon pollution because of its physical nature – it is an enclosed basin with a slow water exchange – and because it hosts about 20% of the global oil tanker traffic in its waters and tens of oil-related sites along its coastline. The conventional remediation strategies, comprising chemical and physical methods, are extremely expensive and invasive, therefore the development of cheaper and eco-friendly approaches is crucial to preserve human and ecosystem health. In this perspective, bioremediation (i.e. the use of living organisms to remove pollutants from a contaminated area) is a promising technology which, taking advantage of microbes’ metabolic potential to degrade a wide range of pollutants, can both reduce the costs and may represent a permanent solution. Nevertheless, there is still a scarce knowledge of the processes and the microorganisms involved in the clean-up of hydrocarbons from marine environments, hence some problems still exist concerning the in-field application of bioremediation.
The aim of the present PhD thesis was to: i) investigate the overall prokaryotic diversity of pristine and oil polluted sites across the whole Mediterranean Sea; ii) depict the phylogenetic and functional diversity of hydrocarbonoclastic bacteria inhabiting pristine and polluted sites; iii) establish a large collection of bacteria showing degrading activities toward hydrocarbon compounds; iv) set up microcosm experiments to investigate the potential of bacterial bioaugmentation in bioremediation processes under laboratory scale conditions, v) test the degrading potential of selected bacterial strains and consortia under different pressure values, simulating different depths along the water column.
The diversity of planktonic bacterial communities in the Mediterranean Sea was firstly evaluated on open seawater samples collected at different depths in a transect covering the main oil tanker route across the whole basin, from the Levantine Sea to the Gibraltar strait. Automated Ribosomal Intergenic Spacer Analysis (ARISA) showed that the microbiome inhabiting deep and surface water samples were sharply separated. Furthermore, the composition of the bacterial communities described in the surface layers of the water columns at different sampling stations has been significantly correlated, beside to their geographical position and depth, to the temperature and salinity values recorded for each sample.
Denaturing Gradient Gel Electrophoresis (DGGE) and ARISA fingerprinting were also applied to depict the bacterial composition of highly polluted sediments collected at the Ancona harbor (Italy) and El-Max district (Egypt), showing the significant influence of the different pollutants’ concentration (i.e. hydrocarbons, heavy metals) in the selection of peculiar bacterial assemblages . This molecular approach led to the identification of bacterial species potentially useful for site-tailored bioremediation purposes. A large collection of hydrocarbon degrading bacterial strains was hence established from enrichments using contaminated sediments as inoculum and diesel, crude oil and naphthalene as unique carbon sources. The cultivation approaches adopted to enrich and isolate hydrocarbonoclastic bacteria from chronically polluted area, like the Ancona harbor, permitted to evaluate the influence of different hydrocarbon pollutants used as single carbon source in the selection of specific marine bacteria populations. The results obtained taking advantage of DGGE fingerprinting and 16S rRNA pyrosequencing applied on the enrichments showed that, under laboratory conditions, the supply of different hydrocarbon compounds led to the selection of different, and specialized, bacterial communities.
A total of 248 bacterial strains have been isolated from open sea surface water collected along oil tanker routes and the chronically polluted sediments, and have been identified by 16S rRNA gene sequencing. Alcanivorax and Marinobacter, two ubiquitous marine hydrocarbonoclastic genera, were the most abundant within the established collection, representing respectively 67% and 23% of the isolates. Due to the great importance of the Alcanivorax genus for hydrocarbon remediation of marine polluted sites, all the isolates belonging to this genus were investigated at a finer level in terms of phylogenetic and functional diversity. This sub-collection, comprising 179 isolates belonging to the 4 species A. borkumensis, A. jadensis, A. venustensis and A. dieselolei, were genotyped using two different fingerprinting techniques: Internal Transcribed Spacer (ITS)-PCR and BOX-PCR. The combination of the applied techniques allowed the identification of 85 genotypes, distributed among the different sites investigated, showing clear evidence of geographic divergence. The functional diversity of these strains was furthermore investigated through the PCR amplification of the alkB gene, encoding for an alkane monooxigenase involved in the first step of hydrocarbons degradation, and subsequent Restriction Fragment Length Polymorphism (RFLP) analysis of the amplicons, allowing the identification of 16 different polymorphisms. The results demostrated the existence of a high degree of geographical divergence within the Alcanivorax genus, suggesting a potentially high metabolic diversity that could be exploited for site-tailored bioremediation interventions.
Recently, the Deepwater Horizon break in the Gulf of Mexico (2010) and the subsequent huge oil spill occurred at a depth of 1500 meters, highlighted the need to get more insight on bioremediation processes occurring at high depth. This accident represents a milestone and shed a light on the importance to investigate the effect of pressure, an environmental parameter that might hamper the activity of oil-degrading strains, on growth and degradation capabilities. The capability of selected hydrocarbonoclastic strains, belonging to the species A. jadensis, A. dieselolei and M. hydrocarbonoclasticus, to adapt and degrade a model alkane molecule (dodecane) at high pressure was therefore tested. The growth of the strains at increasing hydrostatic pressure and their physiologic activities were evaluated, comparing the results with the type strain A. borkumensis SK2. Overall, the results showed a detrimental effect of pressure for all the strains in terms of growth rates, O2 consumption and CO2 production. The potential adaptation of A. borkumensis and A.dieselolei was evaluated also with less recalcitrant carbon source than alkanes (pyruvate), without showing substantial differences, except for the higher consumption of pyruvate by A. borkumensis SK2. This investigation pinpointed that the tested bacteria can survive at high hydrostatic pressures, even though both their growth and degradation capability were mostly inhibited with the increase in hydrostatic pressure. Moreover, aiming to create a baseline for future transcriptomic analyses, the complete genome of this 4 strains was sequenced and annotated: all the strains owned multiple copies of the genes involved in the degradation of hydrocarbons (alkane monoossigenase, alk and cytochrome p450, cyp450), apparently belonging to different families, highlighting the great functional potential of these strains.
A second sub-collection of hydrocarbonoclastic bacteria, isolated from chronically polluted sediments, was screened for the presence of functional genes involved in the degradation/detoxification of specific pollutants (alkanes and heavy metals), the ability to grow on different HCs and the ability to produce biosurfactant and from biofilm. The results showed that several isolates, mainly belonging to the Marinobacter genus, were positive for the investigated traits, hence they could be potentially exploited for autochthonous bioaugmentation (ABA) purposes in the sites of provenience.
Finally, the bacterial community response in a biodegradation process based on an ex-situ landfarming set-up was evaluated. Landfarming was performed, using a combination of biostimulation and bioaugmentation, to remediate oil-polluted sediment collected at Elefsina bay (Greece). This work was realized to determine the effect of bioaugmentation by four allochthonous oil-degrading bacterial consortia, previously isolated from 4 polluted areas located in the Southern Mediterranean, in relation to the degradation efficiency of the indigenous community. DGGE fingerprinting analysis allowed the characterization of the bacterial community dynamics, evaluating the dominant taxa through time and at each treatment. The results showed that the added allochthonous bacteria quickly perished and were rarely detected, furthermore their addition induced minimal shifts in the community structure. These data, together with the measurement of HC degradation over the experimental time, suggested that, during the landfarming, biodegradation was mostly performed by the autochthonous populations rather than by the allochthonous ones. Furthermore, biostimulation, in contrast to bioaugmentation, was proved to enhance the HCs degradation when compared to the control treatment.
To conclude, the results obtained this Ph.D. project emphasized the high bacterial diversity of the Mediterranean Sea in both pristine and polluted sites and the occurrence of distribution patterns which were significantly related to several environmental parameters, including the concentration of hydrocarbons and heavy metals. Moreover, this study confirmed the great potential of the Mediterranean Sea as a source of bacterial strains harbouring degradation capabilities toward different hydrocarbon molecules and, through the ex-situ application of different bioremediation strategies (bioaugmentation and biostimulation), it demonstrated the great importance of autochthonous microbial community in remediating polluted environments
Transverse seismic response of continuous steel-concrete composite bridges exhibiting dual load path
No full textMulti-span steel-concrete composite (SCC) bridges are very sensitive to earthquake loading. Extensive damage may occur not only in the substructures (piers), which are expected to yield, but also in the other components (e.g., deck, abutments) involved in carrying the seismic loads. Current seismic codes allow the design of regular bridges by means of linear elastic analysis based on inelastic design spectra. In bridges with superstructure transverse motion restrained at the abutments, a dual load path behavior is observed. The sequential yielding of the piers can lead to a substantial change in the stiffness distribution. Thus, force distributions and displacement demand can significantly differ from linear elastic analysis predictions. The objectives of this study are assessing the influence of piers-deck stiffness ratio and of soilstructure interaction effects on the seismic behavior of continuous SCC bridges with dual load path, and evaluating the suitability of linear elastic analysis in predicting the actual seismic behavior of these bridges. Parametric analysis results are presented and discussed for a common bridge typology. The response dependence on the parameters is studied by nonlinear multi-record incremental dynamic analysis (IDA). Comparisons are made with linear time history analysis results. The results presented suggest that simplified linear elastic analysis based on inelastic design spectra could produce very inaccurate estimates of the structural behavior of SCC bridges with dual load path
Performance-Based Hurricane Engineering Methodology for Mid-rise Buildings
No full textPerformance-Based Engineering (PBE) is a general methodology that states the performances required for a structure, and provides criteria and methods for verifying the achievement of these performances and for improving the structural design. PBE has already been vastly developed for seismic engineering [1]. At the present time, the research in hurricane engineering appears to be sufficiently mature to develop a sound Performance-Based Hurricane Engineering (PBHE) methodology for risk assessment and design of structures, following the results already obtained in other engineering fields [2].
Post-hurricane surveys indicate that the major economic losses to buildings stem mainly from the breach of the building envelope. Once the envelope is breached, the building and its contents are increasingly likely to suffer severe damage from water or wind effect [3]. A typical example for this type of scenario is that of mid-rise engineered buildings. These buildings generally suffer little damage to the load bearing structural system when the integrity of the building envelope is preserved. However, when the building envelope is breached, the same buildings can suffer extensive cladding and interior damage, and even structural damage due to pressurization of the interior of the building [4].
Guidelines for performance-based engineering of structures subjected to extreme winds and hurricanes are not yet available. The objective of this paper is to propose a list of performance expectations and damage descriptors that can be used for both the performance-based assessment and design of mid-rise steel building. In this paper, a recently proposed multi hazard PBHE framework [5] is applied to a typical mid-rise steel building with glass cladding located in an urban area. The mean annual frequency of exceedance is calculated for structural response parameters that are needed in the definition of the performance expectations and damage descriptors proposed in this paper
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Nonlinear finite element response sensitivity analysis of steel-concrete composite beams
No full textThe behavior of steel-concrete composite beams is strongly influenced by the type of connection between the steel beam and the concrete slab. For accurate analysis, the structural model must account properly for the interlayer slip between the components. This paper focuses on nonlinear finite element response sensitivity analysis using a displacement-based formulation for composite beams with deformable shear connection. Realistic uniaxial constitutive laws are adopted for the concrete and steel materials as well as for the
shear connectors. A non-symmetrical two-span composite beam structure for which experimental results are available is used as application example. The finite element response is validated through the experimental results available for monotonic loading condition. Then, the finite element response sensitivity analysis is
performed according to the Direct Differentiation Method (DDM) and validated through Forward Finite Difference (FFD) analysis. Selected results of the sensitivity analysis are presented in order to show the relative importance of concrete, steel, and shear connection material parameters
Material-dependent catalytic recombination modeling for hypersonic flows
No full textA new model to predict catalytic recombination rates of O and N atoms over silica re-entry thermal protection system is reported. The model follows the general approach of Halpern and Rosner, but adds estimates of some key physical mechanism parameters based on realistic surface potentials. This novel feature can therefore produce rate expressions for any surface for which structure is known, Testing the model for N over W, and N and O over SiO2 produces recombination probabilities in good agreement with published measurements at high surface temperature, In the case of N and O over SiO2, the model accounts for surface NO production due to O and N cross recombination
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