Numerical framework for seismic collapse assessment of rigid wall-flexible diaphragm structures

This study focuses on the development of a two dimensional (2D) simplified numerical framework of rigid wall-flexible diaphragm (RWFD) structures that can be used to validate seismic design approaches. This type of low-rise industrial buildings, which is widely used in North America, incorporates rigid in-plane concrete or masonry walls and flexible in-plane wood, steel or “hybrid” roof diaphragms. The numerical modeling is detailed enough to capture the nonlinear seismic response of RWFD buildings, but simplified enough to efficiently conduct a large number of nonlinear time-history dynamic analyses. The 2D numerical modeling framework is based on a three step sub-structuring approach including: (1) a hysteretic response database for diaphragm connectors, (2) a 2D inelastic roof diaphragm model incorporating hysteretic connector response and (3) a simplified 2D building model incorporating hysteretic diaphragm model response. The diaphragm connector database (step 1) was developed for both wood and steel deck connectors using cyclic test data available in the literature. Two well-known hysteretic models (Wayne-Stewart and CUREE-SAWS) were used for estimating/fitting hysteretic parameters of each connector type. The analytical model of the inelastic roof diaphragm (step 2) was generated to account for the elastic shear deformation of deck panels, elastic flexural deformations of chord members as well as inelastic deformations of deck-to-frame connectors (from the connector database-step 1). This model includes monotonic and cyclic analysis capabilities. The last step of the proposed analytical framework is a simplified two dimensional model of a RWFD building developed in RUAUMOKO2D to account for the inelastic response of roof diaphragms (based on the analytical roof diaphragm model-step 2) and the out-of-plane walls as well as second order (P-Δ) effects. Both the proposed analytical model of the roof diaphragm and the proposed simplified building model were validated with experimental and analytical studies available in the literature. Furthermore, a sensitivity study was conducted to examine the effect of: (i) analysis time step, (ii) different base fixity of the out-of-plane walls, (iii) P-Δ effects, (iv) inherent viscous damping and (v) direction of shaking on the collapse assessment of RWFD structures

Global transcriptional responses of Pseudomonas syringae DC3000 to changes in iron bioavailability in vitro

BACKGROUND: Pseudomonas syringae pv tomato DC3000 (DC3000) is a Gram-negative model plant pathogen that is found in a wide variety of environments. To survive in these diverse conditions it must sense and respond to various environmental cues. One micronutrient required for most forms of life is iron. Bioavailable iron has been shown to be an important global regulator for many bacteria where it not only regulates a wide variety of genes involved in general cell physiology but also virulence determinants. In this study we used microarrays to study differential gene regulation in DC3000 in response to changes in levels of cell-associated iron. RESULTS: DC3000 cultures were grown under highly controlled conditions and analyzed after the addition of iron citrate or sodium citrate to the media. In the cultures supplemented with iron, we found that cell-associated iron increased rapidly while culture densities were not significantly different over 4 hours when compared to cultures with sodium citrate added. Microarray analysis of samples taken from before and after the addition of either sodium citrate or iron citrate identified 386 differentially regulated genes with high statistical confidence. Differentially regulated genes were clustered based on expression patterns observed between comparison of samples taken at different time points and with different supplements. This analysis grouped genes associated with the same regulatory motifs and/or had similar putative or known function. CONCLUSION: This study shows iron is rapidly taken up from the medium by iron-depleted DC3000 cultures and that bioavailable iron is a global cue for the expression of iron transport, storage, and known virulence factors in DC3000. Furthermore approximately 34% of the differentially regulated genes are associated with one of four regulatory motifs for Fur, PvdS, HrpL, or RpoD

Influence of the molybdenum cofactor biosynthesis on anaerobic respiration, biofilm formation and motility in Burkholderia thailandensis

types: Journal Article; Research Support, Non-U.S. Gov'tCopyright © 2013 Institut Pasteur. Published by Elsevier Masson SAS.Elsevier. NOTICE: This is the author’s version of a work accepted for publication by Elsevier. Changes resulting from the publishing process, including peer review, editing, corrections, structural formatting and other quality control mechanisms, may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Research in Microbiology, 2014, Vol. 165, Issue 1, pp. 41 – 49 DOI: 10.1016/j.resmic.2013.10.009Burkholderia thailandensis is closely related to Burkholderia pseudomallei, a bacterial pathogen and the causative agent of melioidosis. B. pseudomallei can survive and persist within a hypoxic environment for up to one year and has been shown to grow anaerobically in the presence of nitrate. Currently, little is known about the role of anaerobic respiration in pathogenesis of melioidosis. Using B. thailandensis as a model, a library of 1344 transposon mutants was created to identify genes required for anaerobic nitrate respiration. One transposon mutant (CA01) was identified with an insertion in BTH_I1704 (moeA), a gene required for the molybdopterin biosynthetic pathway. This pathway is involved in the synthesis of a molybdopterin cofactor required for a variety of molybdoenzymes, including nitrate reductase. Disruption of molybdopterin biosynthesis prevented growth under anaerobic conditions, when using nitrate as the sole terminal electron acceptor. Defects in anaerobic respiration, nitrate reduction, motility and biofilm formation were observed for CA01. Mutant complementation with pDA-17:BTH_I1704 was able to restore anaerobic growth on nitrate, nitrate reductase activity and biofilm formation, but did not restore motility. This study highlights the potential importance of molybdoenzyme-dependent anaerobic respiration in the survival and virulence of B. thailandensis.BBSRC studentship (C. A. Andreae

Loading protocols for European regions of low to moderate seismicity

Existing loading protocols for quasi-static cyclic testing of structures are based on recordings from regions of high seismicity. For regions of low to moderate seismicity they overestimate imposed cumulative damage demands. Since structural capacities are a function of demand, existing loading protocols applied to specimens representative of structures in low to moderate seismicity regions might underestimate structural strength and deformation capacity. To overcome this problem, this paper deals with the development of cyclic loading protocols for European regions of low to moderate seismicity. Cumulative damage demands imposed by a set of 60 ground motion records are evaluated for a wide variety of SDOF systems that reflect the fundamental properties of a large portion of the existing building stock. The ground motions are representative of the seismic hazard level corresponding to a 2% probability of exceedance in 50 years in a European moderate seismicity region. To meet the calculated cumulative damage demands, loading protocols for different structural types and vibration periods are developed. For comparison, cumulative seismic demands are also calculated for existing protocols and a set of records that was used in a previous study on loading protocols for regions of high seismicity. The median cumulative demands for regions of low to moderate seismicity are significantly less than those of existing protocols and records of high seismicity regions. For regions of low to moderate seismicity the new protocols might therefore result in larger strength and deformation capacities and hence in more cost-effective structural configurations or less expensive retrofit measures

Fail-safe optimization of viscous dampers for seismic retrofitting

This paper presents a new optimization approach for designing minimum-cost fail-safe distributions of fluid viscous dampers for seismic retrofitting. Failure is modeled as either complete damage of the dampers or partial degradation of the dampers' properties. In general, this leads to optimization problems with large number of constraints. Thus, the use of a working-set optimization algorithm is proposed. The main idea is to solve a sequence of relaxed optimization sub-problems with a small sub-set of all constraints. The algorithm terminates once a solution of a sub-problem is found that satisfies all the constraints of the problem. The retrofitting cost is minimized with constraints on the inter-story drifts at the peripheries of frame structures. The structures considered are subjected to a realistic ensemble of ground motions, and their response is evaluated with time-history analyses. The transient optimization problem is efficiently solved with a gradient-based sequential linear programming algorithm. The gradients of the response functions are calculated with a consistent adjoint sensitivity analysis procedure. Promising results attained for 3-D irregular frames are presented and discussed. The numerical results highlight the fact that the optimized layout and size of the dampers can change significantly even for moderate levels of damage

Ambient fabrication of flexible and large-area organic light-emitting devices using slot-die coating

The grand vision of manufacturing large-area emissive devices with low-cost roll-to-roll coating methods, akin to how newspapers are produced, appeared with the emergence of the organic light-emitting diode about 20 years ago. Today, small organic light-emitting diode displays are commercially available in smartphones, but the promise of a continuous ambient fabrication has unfortunately not materialized yet, as organic light-emitting diodes invariably depend on the use of one or more time- and energy-consuming process steps under vacuum. Here we report an all-solution-based fabrication of an alternative emissive device, a light-emitting electrochemical cell, using a slot-die roll-coating apparatus. The fabricated flexible sheets exhibit bidirectional and uniform light emission, and feature a fault-tolerant >1-μm-thick active material that is doped in situ during operation. It is notable that the initial preparation of inks, the subsequent coating of the constituent layers and the final device operation all could be executed under ambient air

Genome-Wide Identification of Transcriptional Start Sites in the Plant Pathogen Pseudomonas syringae pv. tomato str. DC3000

RNA-Seq has provided valuable insights into global gene expression in a wide variety of organisms. Using a modified RNA-Seq approach and Illumina's high-throughput sequencing technology, we globally identified 5′-ends of transcripts for the plant pathogen Pseudomonas syringae pv. tomato str. DC3000. A substantial fraction of 5′-ends obtained by this method were consistent with results obtained using global RNA-Seq and 5′RACE. As expected, many 5′-ends were positioned a short distance upstream of annotated genes. We also captured 5′-ends within intergenic regions, providing evidence for the expression of un-annotated genes and non-coding RNAs, and detected numerous examples of antisense transcription, suggesting additional levels of complexity in gene regulation in DC3000. Importantly, targeted searches for sequence patterns in the vicinity of 5′-ends revealed over 1200 putative promoters and other regulatory motifs, establishing a broad foundation for future investigations of regulation at the genomic and single gene levels

RNA-seq Analysis Reveals That an ECF σ Factor, AcsS, Regulates Achromobactin Biosynthesis in Pseudomonas syringae pv. syringae B728a

Iron is an essential micronutrient for Pseudomonas syringae pv. syringae strain B728a and many other microorganisms; therefore, B728a has evolved methods of iron acquirement including the use of iron-chelating siderophores. In this study an extracytoplasmic function (ECF) sigma factor, AcsS, encoded within the achromobactin gene cluster is shown to be a major regulator of genes involved in the biosynthesis and secretion of this siderophore. However, production of achromobactin was not completely abrogated in the deletion mutant, implying that other regulators may be involved such as PvdS, the sigma factor that regulates pyoverdine biosynthesis. RNA-seq analysis identified 287 genes that are differentially expressed between the AcsS deletion mutant and the wild type strain. These genes are involved in iron response, secretion, extracellular polysaccharide production, and cell motility. Thus, the transcriptome analysis supports a role for AcsS in the regulation of achromobactin production and the potential activity of both AcsS and achromobactin in the plant-associated lifestyle of strain B728a