Determination of the critical state of granular materials with triaxial tests

Abstract While the Critical State Locus (CSL) determined from triaxial compression tests is commonly adopted for the constitutive modelling of soil, the validity of the locus for other stress paths needs to be proved. Several authors have tried to experimentally verify whether the classical CSL representation in the stress invariants – void ratio space could be considered as unique or should depend on the loading direction, but the question is still being debated and a unique conclusion has not been convincingly drawn. In order to clarify this issue, compression and extension triaxial tests are performed on granular materials with different characteristics, namely, two homogeneously distributed sands and an assembly of steel spheres prepared under different initial conditions. The procedure for identifying the CSL is reviewed and indicates the limitations arising from strain localization (shear bands and necking). All the tests show that the materials head to systematically different traces in the e-p′ and p′-q planes when sheared under triaxial compression and extension. Searching for the reasons for this phenomenon, small samples of sand are subjected to the same tests quantifying the whole strain field with X-ray tomography and a digital image correlation. This analysis reveals an inhomogeneous pattern of deformation that is strongly affected by the presence of the two rigid frictional bases and the flexible side membrane, even for the samples deforming in an apparently uniform manner. The different localization observed for the compression and extension tests justifies the dependence of the CSL on the stress path seen on the global scale. On the other hand, a unique trace of the CSL is obtained in the volumetric e-p′ plane when the void ratio is measured limitedly to the zones affected by the largest distortion

A micro finite element model for soil behaviour: experimental evaluation for sand under triaxial compression

This paper evaluates the ability of a combined discrete-finite element approach to replicate the experimental response of a dry sand under triaxial compression. The numerical sample was created by virtualising the fabric of a Martian regolith-like sand sample obtained from an in-situ test using X-ray micro Computed Tomography and physical properties of the grains obtained from laboratory data were used as input. The boundary and contact conditions were defined according to the experimental test. A key feature of the model is the use of deformable thin-shell elements to represent the numerical membrane, which allows for a realistic failure mode and volumetric deformation. The macroscopic response of the numerical simulation is shown to compare well with the experiment. The contact regions are identified based on their ability to transmit stress and the evolution of the contact normals is shown to correlate well with the macro stress evolution. The computed stress fields within each grain are used to identify the load bearing grains in the assembly, contributing new insights beyond the commonly reported force chains

A Nonlinear Energy Harvester by Direct Printing Technology

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Zircon as a provenance tracer: Coupling Raman spectroscopy and Usingle bondPb geochronology in source-to-sink studies

Usingle bondPb zircon geochronology is one of the most widely used techniques in sedimentary provenance analysis. Unfortunately, the ability of this method to identify sediment sources is often degraded by sediment recycling and mixing of detritus from different source rocks sharing similar age signatures. These processes create non-unique zircon Usingle bondPb age signatures and thereby obscure the provenance signal. We here address this problem by combining detrital zircon Usingle bondPb geochronology with Raman spectroscopy. The position and width of the Raman signal in zircon scales with its degree of metamictization, which in turn is sensitive to temperature. Thus, combined U-Pb + Raman datasets encode information about the crystallization history of detrital zircons as well as their thermal history. Using three borehole samples from Mozambique as part of a source-to-sink study of interest for hydrocarbon exploration, we show that zircon populations with similar Usingle bondPb age distributions can exhibit different Raman signatures. The joint U-Pb + Raman analysis allowed us to identify three different annealing trends, which were linked to specific thermal events. Thus we were able to differentiate a dominant Pan-African Usingle bondPb age peak into several sub-populations and highlight the major effect of Karoo tectono-magmatic events. In our case study, we used Raman also as a means to systematically identify all zircon grains in heavy-mineral mounts, resulting in considerable time savings. Raman spectroscopy is a non-destructive and cost-effective method that is easily integrated in the zircon Usingle bondPb dating workflow to augment the resolution power of detrital zircon Usingle bondPb geochronology

Alcohol Septal Ablation for Hypertrophic Obstructive Cardiomyopathy: A Contemporary Reappraisal

Percutaneous alcohol septal ablation (ASA) is an effective and minimally invasive therapeutic strategy to resolve left ventricular outflow tract obstruction (LVOTO) in patients with hypertrophic cardiomyopathy who remain symptomatic on maximally tolerated medical therapy. First performed by Sigwart in 1994, the procedure consists in determining an iatrogenic infarction of the basal interventricular septum to reduce LVOTO and alleviate symptoms. Since its first description, numerous studies have demonstrated its efficacy and safety, proposing ASA as a valid and attractive alternative to surgical septal myectomy. The success rate of the intervention is profoundly affected by patient selection and centre experience. In this review, we sought to summarise current evidence on ASA, describing the procedure and proposing a cardiomyopathy team-based approach to resolve clinical disputes in clinical practice

Evolution of deformation and breakage in sand studied using X-ray tomography

International audienceParticle breakage of a granular material can cause significant changes in its microstructure, which will govern its macroscopic behaviour; this explains why the mechanisms leading to particle breakage have been a common subject within several fields, including geomechanics. In this paper, X-ray computed micro-tomography is used, to obtain three-dimensional images of entire specimens of sand, during high-confinement triaxial compression tests. The acquired images are processed and measurements are made on breakage, local variations of porosity, volumetric strain, maximum shear strain and grading. The evolution and spatial distribution of quantified breakage and the resulting particle size distribution for the whole specimen and for specific areas are presented here for the first time and are further related to the localised shear and volumetric strains. Before peak stress is reached, compaction is the governing mechanism leading to breakage; neither compressive strains nor breakage are significantly localised and the total amount of breakage is rather low. Post peak, in areas where strains localise and breakage is present, a dilative volumetric behaviour is observed locally, as opposed to the overall compaction of the specimen. Some specimens exhibited a compaction around the shear band at the end of the test, but there was no additional breakage at that point. From the grading analysis, it is found that mainly the grains with diameter close to the mean diameter of the specimen are the ones that break, whereas the biggest grains that are present in the specimen remain intact

Dynamic uplift, recycling, and climate control on the petrology of passive-margin sand (Angola)

The subequatorial Angolan continental margin offers excellent conditions to test textbook theories on the composition of passive-margin sediments generated in different climatic and tectonic regimes. We use here comprehensive petrographic, heavy-mineral, geochemical and zircon-geochronology datasets on modern fluvial, beach, shelfal, and deep-marine sands and muds collected from hyperarid northern Namibia to hyperhumid Congo to investigate and assess: a) how faithfully sand mineralogy reflects the lithological and time structures of source rocks in a tectonically active rifted margin; b) in what climatic and geomorphological conditions the mark of chemical weathering becomes strong and next overwhelming; and, c) to what extent the effect of weathering can be isolated from quartz dilution by recycling of older siliciclastic strata and other physical controls including hydraulic sorting and mechanical wear. A new refined classification of feldspatho-quartzose and quartzose sands and sandstones is proposed.First-cycle quartzo-feldspathic to feldspar-rich feldspatho-quartzose sand eroded from mid-crustal granitoid gneisses of the Angola Block exposed in the dynamically uplifted Bié-Huila dome is deposited in arid southern Angola, whereas quartz-rich feldspatho-quartzose to quartzose sand characterizes the lower-relief, less deeply dissected, and more intensely weathered rifted margin of humid northern Angola. Pure quartzose, largely recycled sand is generated in the vast, low-lying hyperhumid continental interiors drained by the Congo River. The progressive relative increase of durable minerals toward the Equator results from three distinct processes acting in accord: active tectonic uplift in the arid south, and progressively stronger weathering coupled with more extensive recycling in the humid north. The quartz/feldspar ratio increases and the plagioclase/feldspar ratio decreases rapidly in first-cycle sand generated farther inland in the Catumbela catchment, reflecting stronger weathering in wet interior highlands. Discriminating weathering from recycling control is difficult in northern Angola. Although textural features including deep etch pits even on relatively resistant minerals such as quartz and microcline or rounded outline and abraded overgrowths provide valuable independent information, recycling remains as a most elusive problem in provenance analysis of terrigenous sediments

Radial versus femoral access in patients with acute coronary syndromes undergoing invasive management: a randomised multicentre trial.

Summary Background It is unclear whether radial compared with femoral access improves outcomes in unselected patients with acute coronary syndromes undergoing invasive management. Methods We did a randomised, multicentre, superiority trial comparing transradial against transfemoral access in patients with acute coronary syndrome with or without ST-segment elevation myocardial infarction who were about to undergo coronary angiography and percutaneous coronary intervention. Patients were randomly allocated (1:1) to radial or femoral access with a web-based system. The randomisation sequence was computer generated, blocked, and stratified by use of ticagrelor or prasugrel, type of acute coronary syndrome (ST-segment elevation myocardial infarction, troponin positive or negative, non-ST-segment elevation acute coronary syndrome), and anticipated use of immediate percutaneous coronary intervention. Outcome assessors were masked to treatment allocation. The 30-day coprimary outcomes were major adverse cardiovascular events, defined as death, myocardial infarction, or stroke, and net adverse clinical events, defined as major adverse cardiovascular events or Bleeding Academic Research Consortium (BARC) major bleeding unrelated to coronary artery bypass graft surgery. The analysis was by intention to treat. The two-sided α was prespecified at 0·025. The trial is registered at ClinicalTrials.gov, number NCT01433627. Findings We randomly assigned 8404 patients with acute coronary syndrome, with or without ST-segment elevation, to radial (4197) or femoral (4207) access for coronary angiography and percutaneous coronary intervention. 369 (8·8%) patients with radial access had major adverse cardiovascular events, compared with 429 (10·3%) patients with femoral access (rate ratio [RR] 0·85, 95% CI 0·74-0·99; p=0·0307), non-significant at α of 0·025. 410 (9·8%) patients with radial access had net adverse clinical events compared with 486 (11·7%) patients with femoral access (0·83, 95% CI 0·73-0·96; p=0·0092). The difference was driven by BARC major bleeding unrelated to coronary artery bypass graft surgery (1·6% vs 2·3%, RR 0·67, 95% CI 0·49-0·92; p=0·013) and all-cause mortality (1·6% vs 2·2%, RR 0·72, 95% CI 0·53-0·99; p=0·045). Interpretation In patients with acute coronary syndrome undergoing invasive management, radial as compared with femoral access reduces net adverse clinical events, through a reduction in major bleeding and all-cause mortality. Funding The Medicines Company and Terumo. © 2015 Elsevier Ltd

MEMS Technologies for Energy Harvesting

The objective of this chapter is to introduce the technology of Microelectromechanical Systems, MEMS, and their application to emerging energy harvesting devices. The chapter begins with a general introduction to the most common MEMS fabrication processes. This is followed with a survey of design mechanisms implemented in MEMS energy harvesters to provide nonlinear mechanical actuations. Mechanisms to produce bistable potential will be studied, such as introducing fixed magnets, buckling of beams or using slightly slanted clamped-clamped beams. Other nonlinear mechanisms are studied such as impact energy transfer, or the design of nonlinear springs. Finally, due to their importance in the field of MEMS and their application to energy harvesters, an introduction to actuation using piezoelectric materials is given. Examples of energy harvesters found in the literature using this actuation principle are also presented

Cancer incidence and mortality in patients with insulin-treated diabetes: a UK cohort study

Raised risks of several cancers have been found in patients with type II diabetes, but there are few data on cancer risk in type I diabetes. We conducted a cohort study of 28 900 UK patients with insulin-treated diabetes followed for 520 517 person-years, and compared their cancer incidence and mortality with national expectations. To analyse by diabetes type, we examined risks separately in 23 834 patients diagnosed with diabetes under the age of 30 years, who will almost all have had type I diabetes, and 5066 patients diagnosed at ages 30–49 years, who probably mainly had type II. Relative risks of cancer overall were close to unity, but ovarian cancer risk was highly significantly raised in patients with diabetes diagnosed under age 30 years (standardised incidence ratio (SIR)=2.14; 95% confidence interval (CI) 1.22–3.48; standardised mortality ratio (SMR)=2.90; 95% CI 1.45–5.19), with greatest risks for those with diabetes diagnosed at ages 10–19 years. Risks of cancer at other major sites were not substantially raised for type I patients. The excesses of obesity- and alcohol-related cancers in type II diabetes may be due to confounding rather than diabetes per se