Experimental study of cold-formed steel built-up columns

A comprehensive experimental programme was contrived with the aim of investigating the behaviour and the capacity of cold-formed steel built-up columns with particular emphasis on the effects of connector spacing and contact between individual components. A total of 24 built-up columns, including four different cross-sectional geometries, were tested between pin-ended boundary conditions, while applying the load with nominal eccentricities of L/1000 or L/1500. The columns were designed to fail by interaction of cross-sectional buckling of the components, possible global-type buckling of the components between connectors and global buckling of the whole column, and all these failure modes were successfully achieved. The built-up sections were fabricated from flat plates, plain channels and lipped channels and were assembled with either bolts or self-drilling screws. The connector spacing was varied between specimens of the same cross-sectional geometry. Tensile coupons were taken from the flat portions and the corners of the sections in order to determine their material properties, while detailed measurements of the geometric imperfections of each specimen were also carried out using a specially designed measuring rig. In addition, the isolated behaviour of both the bolts and the screws used in the specimens was investigated through single lap shear tests. It was observed that the buckling patterns in the built-up specimens were affected by contact between the various components and by the spacing between the connectors. However, in the cases where global buckling of the components in between connector points was not critical, the connector spacing had a minor influence on the ultimate capacity of the columns

Experimental investigation of cross-sectional bending capacity of cold-formed steel channels subject to local-distortional buckling interaction

This paper describes an experimental program carried out at the University of Sheffield to investigate the interaction of local and distortional buckling in cold-formed steel lipped channel beams. The channels were arranged in a back-to-back configuration and a total of six tests, including three different cross-sectional geometries, were completed. The specimens were tested in a four-point bending configuration with simply supported boundary conditions while being laterally braced at the loading points. The beams failed in the constant moment span by interaction of local and distortional buckling. The geometric imperfections of the channels were recorded before the test using a specially designed measuring rig employing laser sensors. Tensile coupons were also extracted from the flat portions and the corner regions of the cross sections in order to determine the material properties. Comparisons showed good agreement between the experimental results and the predictions of European design guidelines and current North American provisions, whereas other DSM formulations based on the NLD and NDL concepts resulted in rather conservative predictions

Oral Anticoagulation and Risk of Symptomatic Hemorrhagic Transformation in Stroke Patients Treated With Mechanical Thrombectomy: Data From the Nordictus Registry

Introduction: We aimed to evaluate if prior oral anticoagulation (OAC) and its type determines a greater risk of symptomatic hemorrhagic transformation in patients with acute ischemic stroke (AIS) subjected to mechanical thrombectomy. Materials and Methods: Consecutive patients with AIS included in the prospective reperfusion registry NORDICTUS, a network of tertiary stroke centers in Northern Spain, from January 2017 to December 2019 were included. Prior use of oral anticoagulants, baseline variables, and international normalized ratio (INR) on admission were recorded. Symptomatic intracranial hemorrhage (sICH) was the primary outcome measure. Secondary outcome was the relation between INR and sICH, and we evaluated mortality and functional outcome at 3 months by modified Rankin scale. We compared patients with and without previous OAC and also considered the type of oral anticoagulants. Results: About 1.455 AIS patients were included, of whom 274 (19%) were on OAC, 193 (70%) on vitamin K antagonists (VKA), and 81 (30%) on direct oral anticoagulants (DOACs). Anticoagulated patients were older and had more comorbidities. Eighty-one (5.6%) developed sICH, which was more frequent in the VKA group, but not in DOAC group. OAC with VKA emerged as a predictor of sICH in a multivariate regression model (OR, 1.89 [95% CI, 1.01–3.51], p = 0.04) and was not related to INR level on admission. Prior VKA use was not associated with worse outcome in the multivariate regression model nor with mortality at 3 months. Conclusions: OAC with VKA, but not with DOACs, was an independent predictor of sICH after mechanical thrombectomy. This excess risk was associated neither with INR value by the time thrombectomy was performed, nor with a worse functional outcome or mortality at 3 months

Population, Land Use and Deforestation in the Pan Amazon Basin: a Comparison of Brazil, Bolivia, Colombia, Ecuador, Perú and Venezuela

This paper discusses the linkages between population change, land use, and deforestation in the Amazon regions of Brazil, Bolivia, Colombia, Ecuador, Perú, and Venezuela. We begin with a brief discussion of theories of population–environment linkages, and then focus on the case of deforestation in the PanAmazon. The core of the paper reviews available data on deforestation, population growth, migration and land use in order to see how well land cover change reflects demographic and agricultural change. The data indicate that population dynamics and net migration exhibit to deforestation in some states of the basin but not others. We then discuss other explanatory factors for deforestation, and find a close correspondence between land use and deforestation, which suggests that land use is loosely tied to demographic dynamics and mediates the influence of population on deforestation. We also consider national political economic contexts of Amazon change in the six countries, and find contrasting contexts, which also helps to explain the limited demographic-deforestation correspondence. The paper closes by noting general conclusions based on the data, topics in need of further research and recent policy proposals.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42720/1/10668_2003_Article_6977.pd

Exploring the Fingerprints of Past Rain-on-Snow Events in a Central Andean Mountain Range Basin Using Satellite Imagery

Rain-on-snow (ROS) events can alter nival regimes and increase snowmelt, peak river flow, and reduce water storage. However, detection of ROS events is challenging and only the most intense and obvious cases are identified. Rain is known to reduce snow cover and decrease near-infrared reflectance due to increased grain size. This study explored the fingerprints of ROS events on mountain snowpack with a simple typology that classifies changes in snow reflectance using fifteen years of MODIS imagery, reanalysis, and surface hydrometeorological data. The Maipo River Basin, with strong nival regime and a steep topography, in the western Andean mountain range was selected as a case study. Statistical analysis showed two distinct and opposite responses in the near infrared reflectance distribution of snow-covered pixels after precipitation, consistent with the typology for rain or snow events. For the probable ROS events, the daily maximum and minimum temperature increased in the days preceding the event and subsequently decreased, in some cases followed by a less consistent response in river flow. Although much remains to be studied, this approach can be used to expand historical records and improve modelling and detection schemes

Experimental study of cold-formed steel built-up beams

This paper describes a comprehensive experimental program on cold-formed steel built-up beams with two different cross-sectional geometries. The work aimed to experimentally investigate the interaction between the individual components under increasing loading and to quantify the effect of the connector spacing on the cross-sectional moment capacity and the behavior of the beams. In total, 12 specimens were tested in a four-point bending configuration, with lateral restraints provided at the loading points in order to avoid global instabilities. The built-up specimens were composed of three or four plain channels with nominal thicknesses of 1.2 and 1.5 mm, which were joined together using M6 bolts. Each built-up geometry was tested with three different connector spacings. The specimens were designed to fail by local buckling of their components. Additionally, strut buckling of the channel comprising the top flange in between connector points was observed. The local buckling deformations and the beam deflections were recorded during the tests. The material properties of the test specimens were determined by means of coupon tests and the geometric imperfections were measured prior to testing. The experimental results showed clear evidence of interaction between the local buckling patterns of the components, with the interaction being affected by the connector spacing and the type of geometry. However, the connector spacing showed a less significant effect on the ultimate capacity when failure was governed by local instabilities of the components

Climate change impacts on an alpine watershed in Chile: Do new model projections change the story?

Due to global warming the climate of central Chile is expected to experience dramatic changes in the 21st century including declining precipitation, earlier streamflow peaks, and a greater proportion of precipitation falling as rain. We used 12-member ensembles of General Circulation Models (GCMs) from the Coupled Model Intercomparison Project Phase 3 (CMIP3) and Phase 5 (CMIP5) to evaluate climate-attributed changes in the hydrology of the Mataquito river basin in central Chile, South America. Simulations using the Variable Infiltration Capacity (VIC) hydrology model indicate that a drier and warmer future will shift the location of snow line to higher elevations and reduce the number of days with precipitation falling as snow. Extreme precipitation and streamflow events are expected to become more frequent. Conversely, low flow conditions will intensify during the warm months. The changes in the mean of hydrologic states and fluxes by the end of the 21st century are statistically robust, whereas changes in the variance are not found to be statistically significant. Results of the ensembles for CMIP3 and CMIP5 are generally indistinguishable regarding projected impacts on hydrology

Hepatic fibrosis. Role of matrix metalloproteases and TGFβ [Fibrosis hepática. El papel de las metaloproteinasas y deTGF-β]

Liver fibrosis and cirrhosis involve multiple cellular and molecular events that lead to deposition of an excess of extracellular matrix proteins and increase the distortion of normal liver architecture. Etiologies include chronic viral hepatitis, alcohol abuse and drug toxicity. Degradation of these matrix proteins occurs predominantly as a result of a family of enzymes called metalloproteases (MMPs) that specifically degrade collagenous and non-collagenous substrates. Matrix degradation in the liver is due to the action of at least four of the se enzymes: MMP-1, MMP-2, MMP-3 and MMP-9. In the fibrinolytic system, MMPs can be activated through proteolytic cleavage by the action of urokinase plasminogen activator; a second mechanism includes the same metalloproteases. This activity is regulated at many levels in the fibrinolytic system. The main regulator is the PAI-1. This molecule blocks the conversion of plasminogen into plasmin, and the MMP cannot be activated. At a second level, the inhibition is possible by binding to inhibitors called TIMP that can inhibit the proteolitic activity even when the MMPs had been previously activated by plasmin. During abnormal conditions, overexpression of these inhibitors is directed by the transforming growth factor-β that in a fibrotic disease acts as an extremely important adverse factor

Hepatic fibrosis. Role of matrix metalloproteases and TGF? [Fibrosis hep�tica. El papel de las metaloproteinasas y deTGF-?]

Liver fibrosis and cirrhosis involve multiple cellular and molecular events that lead to deposition of an excess of extracellular matrix proteins and increase the distortion of normal liver architecture. Etiologies include chronic viral hepatitis, alcohol abuse and drug toxicity. Degradation of these matrix proteins occurs predominantly as a result of a family of enzymes called metalloproteases (MMPs) that specifically degrade collagenous and non-collagenous substrates. Matrix degradation in the liver is due to the action of at least four of the se enzymes: MMP-1, MMP-2, MMP-3 and MMP-9. In the fibrinolytic system, MMPs can be activated through proteolytic cleavage by the action of urokinase plasminogen activator; a second mechanism includes the same metalloproteases. This activity is regulated at many levels in the fibrinolytic system. The main regulator is the PAI-1. This molecule blocks the conversion of plasminogen into plasmin, and the MMP cannot be activated. At a second level, the inhibition is possible by binding to inhibitors called TIMP that can inhibit the proteolitic activity even when the MMPs had been previously activated by plasmin. During abnormal conditions, overexpression of these inhibitors is directed by the transforming growth factor-? that in a fibrotic disease acts as an extremely important adverse factor

Assessments CO2 assimilation on a per-leaf-area basis are related to total leaf area

Moreno, Yerko and Ortega-Farias, Samuel. Facultad de Ciencias Agrarias,University of Talca,Talca,Chile