Propagating discontinuities in ionized porous media

Ionized porous media swell or shrink under changing osmotic conditions. Examples of such materials are shales, clays, hydrogels and tissues. The materials are represented as a multi-phase material consisting of a solid part and a fluid part with fixed charges embedded in the solid matrix and counter charges in the fluid. The presence of the so-called fixed charges causes an osmotic pressure difference between the material and surrounding fluid and with that prestressing of the material. The response of the material to load is dependent on the presence of the fluid, charges and cracks. Understanding the mechanisms for fracture and failure of these materials are important for the oil industry (such as hydraulic fracturing and borehole instability), material development (diapers, orthopaedic prosthesis and seals) and in medicine (intervertebral disc herniation and tissue engineering). The relation between presence of cracks and fluid flow has had little attention, but the relation between failure and osmotic conditions has had even less attention. The aim has therefore been to study with the Finite Element Method the effect of osmotic conditions on propagating discontinuities under different types of loads for osmoelastic saturated porous media. The work covers three parts. The first part is an analytical solution of a dislocation in a swelling medium, the second is the partition of unity modeling of a mode-II crack in a swelling medium and the third is the partition of unity modeling of a mode-I crack in a swelling medium. The analytical solution for a dislocation is used as a benchmark to verify the partition of unity modeling in the simplified situation of a non-propagating dislocation. The method through which fluid flow around the crack is modeled is essentially different for mode-I compared to mode-II. In mode-I, the pressure is assumed continuous in the crack area, while in mode-II the pressure is assumed discontinuous across the crack. The numerical results show that in mode-II, the crack propagation is reasonably mesh-independent. In mode-I the crack path is mesh independent, but the induced fluid flow and speed of propagation is not mesh-independent for low stiffness, low permeability cases. The reason for the mesh dependence is probably the insufficient capture of high gradients in the crack area, which require a very fine mesh around the crack. Step-wise crack propagation through the medium is seen. This is because the propagation of the crack alternates with pauses in which the crack-tip area consolidates. The consolidation results in a progressive transfer of the load from the fluid to the solid. As the load on the solid increases, the failure load is reached and the crack propagates again. This step-wise propagation is observed both for mode-II as for mode-I. Furthermore, propagation is shown to depend on the osmotic prestressing of the medium. The dependence is present for mode-II and mode-I. In mode-II the prestressing has an influence on the angle of growth. In mode-I, the prestressing is found to enhance crack propagation or protect against failure depending on the load and material properties. It is also found that osmotic prestressing in itself can propagate fractures without external mechanical load. This mechanism may be an explanation for the tears observed in intervertebral discs as degeneration progresses

Two-dimensional mode I crack propagation in saturated ionized porous media using partition of unity finite elements

Shales, clays, hydrogels, and tissues swell and shrink under changing osmotic conditions, which may lead to failure. The relationship between the presence of cracks and fluid flow has had little attention. The relationship between failure and osmotic conditions has had even less attention. The aim of this research is to study the effect of osmotic conditions on propagating discontinuities under different types of loads for saturated ionized porous media using the finite element method (FEM). Discontinuous functions are introduced in the shape functions of the FEM by partition of unity method, independently of the underlying mesh. Damage ahead of the crack-tip is introduced by a cohesive zone model. Tensile loading of a crack in an osmoelastic medium results in opening of the crack and high pressure gradients between the crack and the formation. The fluid flow in the crack is approximated by Couette flow. Results show that failure behavior depends highly on the load, permeability, (osmotic) prestress and the stiffness of the material. In some cases it is seen that when the crack propagation initiates, fluid is attracted to the crack-tip from the crack rather than from the surrounding medium causing the crack to close. The results show reasonable mesh-independent crack propagation for materials with a high stiffness. Stepwise crack propagation through the medium is seen due to consolidation, i.e., crack propagation alternates with pauses in which the fluid redistributes. This physical phenomenon challenges the numerical scheme. Furthermore, propagation is shown to depend on the osmotic prestressing of the medium. This mechanism may explain the tears observed in intervertebral disks as degeneration progresses

Implementation of the participatory approach for supervisors to prevent sick leave: a process evaluation

To perform a process evaluation of a multifaceted strategy to implement the participatory approach for supervisors to prevent sick leave in three organisations. The implementation strategy incorporated a working group meeting with stakeholder representatives, supervisor training, and optional supervisor coaching. Context, recruitment, reach, dose delivered, dose received, fidelity, and satisfaction with the strategy were assessed at organisational and supervisor level using questionnaires and registration forms. At least 4 out of 6 stakeholders were represented in the working group meetings, and 11 % (n = 116) of supervisors could be reached. The working group meetings and supervisor training were delivered and received as planned and were well appreciated within all three organisations. Three supervisors made use of coaching. At 6-month follow-up, 11 out of 41 supervisors (27 %) indicated that they had applied the participatory approach at least one time. The implementation strategy was largely carried out as intended. However, reach of both supervisors and department managers should be improved. Future studies should consider targeting employees with the strategy

Subadventitial stenting around occluded stents: A bailout technique to recanalize in-stent chronic total occlusions

To evaluate the outcomes of subadventitial stenting (SS) around occluded stents for recanalizing in-stent chronic total occlusions (IS-CTOs).There is little evidence on the outcomes of SS for IS-CTO.We examined the outcomes of SS for IS-CTO PCI at 14 centers between July 2011 and June 2017, and compared them to historical controls recanalized using within-stent stenting (WSS). Target-vessel failure (TVF) on follow-up was the endpoint of this study, and was defined as a composite of cardiac death, target-vessel myocardial infarction, and target-vessel revascularization.During study period, 422 IS-CTO PCIs were performed, of which 32 (7.6%) were recanalized with SS, usually when conventional approaches failed. The most frequent CTO vessel was the right coronary artery (72%). Mean J-CTO score was 3.1 ± 0.9. SS was antegrade in 53%, and retrograde in 47%. Part of the occluded stent was crushed in 37%, while the whole stent was crushed in 63%. Intravascular imaging was used in 59%. One patient (3.1%) suffered tamponade. Angiographic follow-up was performed in 10/32 patients: stents were patent in six cases, one had mild neointimal hyperplasia, and three had severe restenosis at the SS site. Clinical follow-up was available for 29/32 patients for a mean of 388 ± 303 days. The 24-month incidence of TVF was 13.8%, which was similar to historical controls treated with WSS (19.5%, P = 0.49).SS is rarely performed, usually as last resort, to recanalize complex IS-CTOs. It is associated with favorable acute and mid-term outcomes, but given the small sample size of our study additional research is warranted

Comparison of the Sapien 3 versus the ACURATE neo valve system: A propensity score analysis

Objectives: To compare the outcomes of transfemoral ACURATE neo (NEO) and Sapien 3 (S3) patients in terms of device success and clinical safety outcomes using a propensity score analysis. Background: Differences in clinical outcomes between the latest-generation balloon-expandable S3 and self-expanding NEO in a “real-world transfemoral TAVI population” are still unclear. Methods: We compared up to 6 months clinical outcomes using a propensity s

Absence of single-locus complementary sex determination in the braconid wasps Asobara tabida and Alysia manducator

In species with single-locus complementary sex determination (sl-CSD), sex is determined by multiple alleles at a single locus. In the haplodiploid Hymenoptera, sl-CSD results in females, if individuals are heterozygous at the sex locus, and in males, if individuals are hemizygous (haploid males) or homozygous (diploid males). Several hymenopteran species have been shown to have sl-CSD, but in several others sl-CSD is absent and the phylogenetic distribution remains unclear. In the family Braconidae, all four species tested so far were shown to possess sl-CSD. In this study, inbreeding experiments were used to test for the presence of sl-CSD in two species belonging to a subfamily of the Braconidae, Asobara tabida and Alysia manducator (Alysiinae). In both species inbreeding experiments showed no difference in brood size or sex ratio compared to the (outbred) control group. Furthermore, the sex ratios found in the inbreeding treatment differed significantly from the sex ratios expected under sl-CSD. Therefore, we conclude that sl-CSD is absent in these species. This study is the first to show the lack of sl-CSD in species of the Braconidae family and that hymenopteran sex-determining mechanisms can vary, even within a family.