Probabilistic seismic demand modeling of local level response parameters of an RC frame

Probabilistic methods to evaluate the seismic vulnerability of reinforced concrete (RC) frames are largely used in the context of performance based design and assessment, often describing the structural response using global engineering demand parameters (EDPs) such as the maximum interstory drift. While such EDPs are able to synthetically describe the structural behavior, the use of local EDPs is necessary to provide a more realistic and thorough description of failure mechanisms of low-ductility frames lacking seismic details. The objective of this paper is to investigate viable probabilistic seismic demand models of local EDPs, which may be used in developing fragility curves for the assessment of the low-ductility RC frames. The present work explores adequate regression models, probability distributions and uncertainty variation of the demand models. In addition, the adequacy of several ground motion intensity measures (IMs) to be used for predictive modeling of local EDPs is investigated. A realistic benchmark three-story RC frame representative of non-ductile buildings is used as a case study to identify key considerations

The Glutaminase-dependent system confers extreme acid resistance to new species and atypical strains of Brucella

Neutralophilic bacteria have developed specific mechanisms to cope with the acid stress encountered in environments such as soil, fermented foods, and host compartments. In Escherichia coli, the glutamate decarboxylase (Gad)-dependent system is extremely efficient: it requires the concerted action of glutamate decarboxylase (GadA/GadB) and of the glutamate (Glu)/γ-aminobutyrate antiporter, GadC. Notably, this system is operative also in new strains/species of Brucella, among which Brucella microti, but not in the "classical" species, with the exception of marine mammals strains. Recently, the glutaminase-dependent system (named AR2_Q), relying on the deamination of glutamine (Gln) into Glu and on GadC activity, was described in E. coli. In Brucella genomes, a putative glutaminase (glsA)-coding gene is located downstream of the gadBC genes. We found that in B. microti these genes are expressed as a polycistronic transcript. Moreover, using a panel of Brucella genus-representative strains, we show that the AR2_Q system protects from extreme acid stress (pH =2.5), in the sole presence of Gln, only the Brucella species/strains predicted to have functional glsA and gadC. Indeed, mutagenesis approaches confirmed the involvement of glsA and gadC of B. microti in AR2_Q and that the acid-sensitive phenotype of B. abortus can be ascribed to a Ser248Leu substitution in GlsA, leading to loss of glutaminase activity. Furthermore, we found that the gene BMI_II339, of unknown function and downstream of the gadBC-glsA operon, positively affects Gad- and GlsA-dependent AR. Thus, we identified novel determinants that allow newly discovered and marine mammals Brucella strains to be better adapted to face hostile acidic environments. As for significance, this work may contribute to the understanding of the host preferences of Brucella species and opens the way to alternative diagnostic targets in epidemiological surveillance of brucellosis

Reliability Assessment of a Turbogenerator Coil Retaining Ring Based on Low Cycle Fatigue Data

Abstract Turbogenerator coil retaining rings are shrunk-fitted onto the rotor over the coils, in order to restrain them against the centrifugal force. They are typically subjected to low cycle fatigue, with a cycle being completed at every machine switch-on and switch-off. The subject of this paper consists in the determination of the failure probability of a coil retaining ring. The failure mode of the ring cracking, when it swells in tension, due to the centrifugal force is here considered. The reliability assessment is preceded by the study of the input variables affecting the low-cycle fatigue load and of their stochastic distributions. This question is tackled by the experimental determination of the static, cyclic and fatigue curves of the involved material and by the application of a statistical model to compute related parameters and their standard deviations. Upon the determination of variable distributions, the probability of failure is estimated in the form of a cumulative distribution function by a computationally efficient methodology, based on the Advanced Mean Value approach. The obtained results account for the material response and the local stressstrain states at the most loaded coil retaining ring region. The determined probability at the end of the machine life, in the order of 10-12, is compatible with reference values for structures under fatigue in the mechanical and aeronautical fields

Gene and protein expression in response to different growth temperatures and oxygen availability in Burkholderia thailandensis.

Published onlineJournal ArticleResearch Support, Non-U.S. Gov'tThis is the final version of the article. Available from Public Library of Science via the DOI in this record.Burkholderia thailandensis, although normally avirulent for mammals, can infect macrophages in vitro and has occasionally been reported to cause pneumonia in humans. It is therefore used as a model organism for the human pathogen B. pseudomallei, to which it is closely related phylogenetically. We characterized the B. thailandensis clinical isolate CDC2721121 (BtCDC272) at the genome level and studied its response to environmental cues associated with human host colonization, namely, temperature and oxygen limitation. Effects of the different growth conditions on BtCDC272 were studied through whole genome transcription studies and analysis of proteins associated with the bacterial cell surface. We found that growth at 37°C, compared to 28°C, negatively affected cell motility and flagella production through a mechanism involving regulation of the flagellin-encoding fliC gene at the mRNA stability level. Growth in oxygen-limiting conditions, in contrast, stimulated various processes linked to virulence, such as lipopolysaccharide production and expression of genes encoding protein secretion systems. Consistent with these observations, BtCDC272 grown in oxygen limitation was more resistant to phagocytosis and strongly induced the production of inflammatory cytokines from murine macrophages. Our results suggest that, while temperature sensing is important for regulation of B. thailandensis cell motility, oxygen limitation has a deeper impact on its physiology and constitutes a crucial environmental signal for the production of virulence factors.This work was supported by Fondazione CARIPLO (Progetto Vaccini, contract number 2009–3577) and by Ministero dell’Istruzione, dell’Università e della Ricerca (MIUR) (project FIRB RBLA039LSF). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript

FROM "MODELS" TO "REALITY", AND RETURN.SOME REFLECTIONS ON THE INTERACTION BETWEEN SURVEYAND INTERPRETATIVE METHODS FOR BUILT HERITAGE CONSERVATION

It's well known that more and more accurate methodologies and automatic tools are now available in the field of geometric survey and image processing and they constitute a fundamental instrument for cultural heritage knowledge and preservation; on the other side, very smart and precise numerical models are continuously improved and used in order to simulate the mechanical behaviour of masonry structures: both instruments and technologies are important part of a global process of knowledge which is at the base of any conservation project of cultural heritage. Despite the high accuracy and automation level reached by both technologies and programs, the transfer of data between them is not an easy task and defining the most reliable way to translate and exchange information without data loosing is still an open issue. The goal of the present paper is to analyse the complex process of translation from the very precise (and sometimes redundant) information obtainable by the modern survey methodologies for historic buildings (as laser scanner), into the very simplified (may be too much) schemes used to understand their real structural behaviour, with the final aim to contribute to the discussion on reliable methods for cultural heritage knowledge improvement, through empiricism

RSM applied to lattice patterns for stiffness optimization

Purpose - In this study, response surface methodology (RSM) is applied to a three-point bending stiffness analysis of low-cost material (PLA) specimens printed using FDM technology to analyze the performance of different internal lattice structures (Octet and IsoTruss principally). The purpose of this study is to extend the definition from a discrete (lattice) model to an analytical one for its use in subsequent design phases, capable of optimizing the type of cell to be used and its defining parameters to find the best stiffness-to-weight ratio. Design/methodology/approach - The representative function of their mechanical behavior is extrapolated through a two-variable polynomial model based on the cell size and the thickness of the beam elements characterizing it. The polynomial is obtained thanks to several tests performed according to the scheme of RSM. An analysis on the estimation errors due to discontinuities in the physical specimens is also conducted. Physical tests applied to the specimens showed some divergences from the virtual (ideal) behavior of the specimens. Findings - The study allowed to validate the RSM models proposed to predict the behavior of the system as the size, thickness and type of cells vary. Changes in stiffness and weight of specimens follow linear and quadratic models, respectively. This generally allows to find optimal design points where the stiffness-to-weight ratio is at its highest. Originality/value - Although the literature provides numerous references to studies characterizing and parameterizing lattice structures, the industrial/practical applications concerning lattice structures are often still detached from theoretical research and limited to achieving functioning models rather than optimal ones. The approach here described is also aimed at overcoming this limitation. The software used for the design is nTop. Subsequent three-point bending tests have validated the reliability of the model derived from the method's application

Disturbance Observer Based Control for a Remotely Operated Vehicle

This paper presents a Disturbance Observer Based Control scheme which deals with the full pose tracking control problem of a Remotely Operated Vehicle. The uncertainties are lumped, estimated by a Nonlinear Disturbance Observer and feed-forwarded in a tracking controller. The solutions only relies on known quantities, providing a dynamic disturbance compensation and ultimately bounded errors. The order of the disturbance observer is a design parameter, which is able to provide additional integral actions. Finally, numerical simulations test the proposed technique

Quasistatic delamination of sandwich-like Kirchhoff-Love plates

A quasistatic rate-independent adhesive delamination problem of laminated plates with a finite thickness is considered. By letting the thickness of the plates go to zero, a rate-independent delamination model for a laminated Kirchhoff-Love plate is obtained as limit of these quasistatic processes. The same dimension reduction procedure is eventually applied to processes which are sensitive to delamination modes, namely opening vs. shearing is distinguishe

Phase-field models for brittle and cohesive fracture

In this paper we first recapitulate some basic notions of brittle and cohesive fracture models, as well as the phase-field approximation to fracture. Next, a critical assessment is made of the sensitivity of the phase-field approach to brittle fracture, in particular the degradation function, and the use of monolithic versus partitioned solution schemes. The last part of the paper makes extensions to a recently developed phase-field model for cohesive fracture, in particular for propagating cracks. Using some simple examples the current state of the cohesive phase-field model is shown