Stability Of Sheath Research Articles

Axonal neurotransmitter release in the regulation of myelination.

Myelination of axons is a key determinant of fast action potential propagation, axonal health and circuit function. Previously considered a static structure, it is now clear that myelin is dynamically regulated in response to neuronal activity in the central nervous system (CNS). However, how activity-dependent signals are conveyed to oligodendrocytes remains unclear. Here, we review the potential mechanisms by which neurons could communicate changing activity levels to myelin, with a focus on the accumulating body of evidence to support activity-dependent vesicular signalling directly onto myelin sheaths. We discuss recent in vivo findings of activity-dependent fusion of neurotransmitter vesicles from non-synaptic axonal sites, and how modulation of this vesicular fusion regulates the stability and growth of myelin sheaths. We also consider the potential mechanisms by which myelin could sense and respond to axon-derived signals to initiate remodelling, and the relevance of these adaptations for circuit function. We propose that axonal vesicular signalling represents an important and underappreciated mode of communication by which neurons can transmit activity-regulated signals to myelinating oligodendrocytes and, potentially, more broadly to other cell types in the CNS.

Synergistic Effects of Magnesium Oxide and SBR Latex Additives on Cement Sheath Stability in Oil Well Operations.

Leaks through cement sheaths remain a complex and challenging issue in the oil industry, representing a persistent obstacle that has endured for decades. The drying shrinkage, an inherent characteristic of Portland cement, substantially exacerbates this problem, driving the formation of microcracks and heightened permeability under variable stress conditions. In this context, additives emerge as significant elements in addressing this issue, offering a pathway to mitigate the adverse effects of leaks. Among these additives, magnesium oxide (MgO) stands out for its ability to reduce drying shrinkage through structural modifications in the cement matrix. Simultaneously, SBR Latex, another important additive, acts to minimize gas migration due to its polymeric microstructure while also strengthening acid resistance and enhancing microstructural cohesion. This study aims to deepen the understanding of the interaction between MgO and SBR Latex additives in cement slurries, employing an experimental design to substantiate and expand upon the analyses conducted. The results reveal a synergistic integration of these additives, with MgO acting as an effective agent in reducing drying shrinkage and gel formation, thereby contributing to the strengthening of shear strength. Conversely, SBR Latex provides elasticity to the slurry, although with a slight compromise in compressive strength, with a relatively limited effect on shear strength. The strategic combination of these additives results in improvements in the mechanical integrity of cement slurries, a positive advancement in the context of petroleum well cementing operations. Thus, this study not only highlights the individual properties of MgO and SBR Latex but also offers valuable perspectives for the careful formulation of cements, with potential applications in challenging operational environments in the oil industry.

Secondary electron emission reduction from boron nitride composite ceramic surfaces by the artificial microstructures and functional coating

Boron nitride-silicon dioxide (BN–SiO2) composite ceramic is a typical Hall thruster wall material, and its secondary electron emission (SEE) property dominates the sheath characteristics inside the thrusters. Lowering the SEE yield (SEY) of the wall surface can remarkably improve the sheath stability of Hall thrusters. To accomplish the SEY reduction for BN–SiO2, artificial surface microstructure and surface coating technologies are employed. The morphology analysis demonstrated the shape and feature sizes of the microstructure could be largely controlled by adjusting the laser etching parameters. Then we realized an increasingly significant SEY reduction for BN–SiO2 as the average aspect ratio of the microhole increases. The microstructures showed a remarkable SEY reduction when the laser power was 10 W and the scanning cycle was 50. In this case, the SEY peak values (δ m) of the two BN–SiO2 samples with mass ratios of 7:3 and 6:4 decrease from 2.62 and 2.38 to 1.55 and 1.46 respectively. For a further SEY reduction, a sputtering process was employed to deposit TiN film on the microstructures. The results showed that the TiN coating of 246 nm thickness reduced the δ m values of the two samples from 1.55 and 1.46 to 0.82 and 0.76, which achieved a notable SEY reduction compared to the original surface. Via simulation work, the SEY reduction achieved by microstructures was theoretically interpreted. Besides, by considering the effect of surface charging, the results of SEY converged to 1 with the irradiation pulse increasing presented. The research demonstrated a remarkable SEY reduction for BN–SiO2 ceramic by constructing surface microstructure and depositing TiN coating, which has application sense for low SEY engineering in specific working scenarios.

Synaptic vesicle release regulates pre-myelinating oligodendrocyte-axon interactions in a neuron subtype-specific manner.

Oligodendrocyte-lineage cells are central nervous system (CNS) glia that perform multiple functions including the selective myelination of some but not all axons. During myelination, synaptic vesicle release from axons promotes sheath stabilization and growth on a subset of neuron subtypes. In comparison, it is unknown if pre-myelinating oligodendrocyte process extensions selectively interact with specific neural circuits or axon subtypes, and whether the formation and stabilization of these neuron-glia interactions involves synaptic vesicle release. In this study, we used fluorescent reporters in the larval zebrafish model to track pre-myelinating oligodendrocyte process extensions interacting with spinal axons utilizing in vivo imaging. Monitoring motile oligodendrocyte processes and their interactions with individually labeled axons revealed that synaptic vesicle release regulates the behavior of subsets of process extensions. Specifically, blocking synaptic vesicle release decreased the longevity of oligodendrocyte process extensions interacting with reticulospinal axons. Furthermore, blocking synaptic vesicle release increased the frequency that new interactions formed and retracted. In contrast, tracking the movements of all process extensions of singly-labeled oligodendrocytes revealed that synaptic vesicle release does not regulate overall process motility or exploratory behavior. Blocking synaptic vesicle release influenced the density of oligodendrocyte process extensions interacting with reticulospinal and serotonergic axons, but not commissural interneuron or dopaminergic axons. Taken together, these data indicate that alterations to synaptic vesicle release cause changes to oligodendrocyte-axon interactions that are neuron subtype specific.

Анализ устойчивости крепи нефтедобывающих скважин при проведении кумулятивной перфорации на основе результатов геомеханического моделирования

Well cement sheath stability analysis for two oil-producing wells in the completion of productive formations by shaped charge perforating was performed. The data of direct measurements of pressures in the borehole at different distances from the cable head of the perforating tool at the moment of detonation, which exceeded 50 MPa, were used in the studies. The pressure values were approximated along the wellbore using a power law. To reliably predict the stress-strain state of the near-wellbore zone of the perforation interval, the ANSYS finite-element modeling software was used. To determine the stress field, an axisymmetric finite-element calculation scheme was built, the height of the model along the wellbore was 39 m. During modeling, it was taken into account that the geological and physical parameters of the simulated reservoirs differed in depth and reservoir pressure value were different. Elastic-strength properties of the cement stone formed were determined during the laboratory experiments for different recipes of cement slurries. According to the results of modeling, the areas of destruction and strength reserve of cement stone, as well as the values of radial displacement of the production casing in the perforation interval were determined. The developed model of the near-wellbore zone and methodical approaches can be used in future for choosing optimal elastic and strength properties of cement stone, perforation tools and technological parameters of perforating-explosive operations.

Early myelination involves the dynamic and repetitive ensheathment of axons which resolves through a low and consistent stabilization rate.

Oligodendrocytes in the central nervous system exhibit significant variability in the number of myelin sheaths that are supported by each cell, ranging from 1 to 50 (1-8). Myelin production during development is dynamic and involves both sheath formation and loss (3, 9-13). However, how these parameters are balanced to generate this heterogeneity in sheath number has not been thoroughly investigated. To explore this question, we combined extensive time-lapse and longitudinal imaging of oligodendrocytes in the developing zebrafish spinal cord to quantify sheath initiation and loss. Surprisingly, we found that oligodendrocytes repetitively ensheathed the same axons multiple times before any stable sheaths were formed. Importantly, this repetitive ensheathment was independent of neuronal activity. At the level of individual oligodendrocytes, each cell initiated a highly variable number of total ensheathments. However, ~80-90% of these ensheathments always disappeared, an unexpectedly high, but consistent rate of loss. The dynamics of this process indicated rapid membrane turnover as ensheathments were formed and lost repetitively on each axon. To better understand how these sheath initiation dynamics contribute to sheath accumulation and stabilization, we disrupted membrane recycling by expressing a dominant-negative mutant form of Rab5. Oligodendrocytes over-expressing this mutant did not show a change in early sheath initiation dynamics but did lose a higher percentage of ensheathments in the later stabilization phase. Overall, oligodendrocyte sheath number is heterogeneous because each cell repetitively initiates a variable number of total ensheathments that are resolved through a consistent stabilization rate.

A multi-order nonlinear meta-analysis of bifluidic fireball sheath fluctuations

The stability of steady plasma fireball sheath (PFS) fluctuations in a bifluidic plasma model approach is explored by applying the standard method of multi-order nonlinear normal mode meta-analysis in a spherical geometry. We consider the fourth-order nonlinear local fluctuations of the relevant plasma parameters evolving across the PFS region for the first time. It includes the Mach number, population density, electrostatic potential, electric field, and so forth. The order-by-order analysis of the basic governing equations results in a unique system of the third-order non-homogenous ordinary differential equations (ODEs) on the perturbed potential. The explicit solutions, obtained with the help of MATLAB programming, especially developed in judicious conditions, yield atypical nonlinear PFS eigenmode structures as a unique peakon family. It is demonstrated that the order of plasma nonlinearity acts as a fluctuation steepening agent (anti-dispersive factor). The investigated peakonic patterns are found to be in fair corroboration with the experimental findings reported elsewhere. The main implications and applications of our results in the context of the diversified PFS circumstances in the astrolabcosmic domains are finally indicated, such as commercial patterned nanodots, plasma medicines, thermonuclear fusion devices, gamma-ray bursts, and so forth.

Numerical analyses of coupled thermo-mechanical behaviors of cement sheath in geothermal wells

The stability of cement sheath under high temperature and high pressure is one of the most critical issues for the durability of geothermal well systems. In this study, a two-dimensional plane-strain finite element code was developed to investigate the coupled thermo-mechanical behaviors of the casing-cement-formation system. Different from previous linear elastic analyses, a thermoelasto-plastic constitutive model based on the thermodynamic theory was adopted for the cement sheath. It is shown that the finite element simulations using the proposed model provide a more accurate and realistic prediction of stress–strain responses of the cement sheath under high temperature. The results demonstrate that the radial stress concentration and the tensile strain concentration occur at both the cement–casing interface and the cement–formation interface, where the cement sheath is most likely to fail. High strength and low stiffness in the cement sheath and the formation are preferred for the integrity of the system. Both large thermal cycles and large differences between the internal fluid pressure and the external pressure should be avoided during operation. The new code is an alternative tool for guiding the geothermal well design. The finite element framework described herein is universal for other thermo-mechanical applications, such as energy foundations and energy tunnels.

Ermin deficiency leads to compromised myelin, inflammatory milieu, and susceptibility to demyelinating insult.

Ermin is an actin‐binding protein found almost exclusively in the central nervous system (CNS) as a component of myelin sheaths. Although Ermin has been predicted to play a role in the formation and stability of myelin sheaths, this has not been directly examined in vivo. Here, we show that Ermin is essential for myelin sheath integrity and normal saltatory conduction. Loss of Ermin in mice caused de‐compacted and fragmented myelin sheaths and led to slower conduction along with progressive neurological deficits. RNA sequencing of the corpus callosum, the largest white matter structure in the CNS, pointed to inflammatory activation in aged Ermin‐deficient mice, which was corroborated by increased levels of microgliosis and astrogliosis. The inflammatory milieu and myelin abnormalities were further associated with increased susceptibility to immune‐mediated demyelination insult in Ermin knockout mice. Supporting a possible role of Ermin deficiency in inflammatory white matter disorders, a rare inactivating mutation in the ERMN gene was identified in multiple sclerosis patients. Our findings demonstrate a critical role for Ermin in maintaining myelin integrity. Given its near‐exclusive expression in myelinating oligodendrocytes, Ermin deficiency represents a compelling “inside‐out” model of inflammatory dysmyelination and may offer a new paradigm for the development of myelin stability‐targeted therapies.

Total transfemoral access in a new off-the-shelf thoracoabdominal inner-branched endograft.

Branched endovascular aneurysm repair (BEVAR) is increasingly being performed with the off-the-shelf devices. We evaluated the use of the wire-assisted sheath stabilization technique for the new inner branch-based (iBEVAR), off-the-shelf E-nside endograft in 2 patients. The cannulation of the 8 reno-visceral target vessels and the BSG implantation were successfully performed using the total transfemoral approach. Complications were not observed during the 3-month follow-up. The wire-assisted sheath stabilization technique was shown feasible in an off-the-shelf iBEVAR.

The Akt-mTOR Pathway Drives Myelin Sheath Growth by Regulating Cap-Dependent Translation.

In the vertebrate CNS, oligodendrocytes produce myelin, a specialized membrane, to insulate and support axons. Individual oligodendrocytes wrap multiple axons with myelin sheaths of variable lengths and thicknesses. Myelin grows at the distal ends of oligodendrocyte processes, and multiple lines of work have provided evidence that mRNAs and RNA binding proteins localize to myelin, together supporting a model where local translation controls myelin sheath growth. What signal transduction mechanisms could control this? One strong candidate is the Akt-mTOR pathway, a major cellular signaling hub that coordinates transcription, translation, metabolism, and cytoskeletal organization. Here, using zebrafish as a model system, we found that Akt-mTOR signaling promotes myelin sheath growth and stability during development. Through cell-specific manipulations to oligodendrocytes, we show that the Akt-mTOR pathway drives cap-dependent translation to promote myelination and that restoration of cap-dependent translation is sufficient to rescue myelin deficits in mTOR loss-of-function animals. Moreover, an mTOR-dependent translational regulator was phosphorylated and colocalized with mRNA encoding a canonically myelin-translated protein in vivo, and bioinformatic investigation revealed numerous putative translational targets in the myelin transcriptome. Together, these data raise the possibility that Akt-mTOR signaling in nascent myelin sheaths promotes sheath growth via translation of myelin-resident mRNAs during development.SIGNIFICANCE STATEMENT In the brain and spinal cord, oligodendrocytes extend processes that tightly wrap axons with myelin, a protein- and lipid-rich membrane that increases electrical impulses and provides trophic support. Myelin membrane grows dramatically following initial axon wrapping in a process that demands protein and lipid synthesis. How protein and lipid synthesis is coordinated with the need for myelin to be generated in certain locations remains unknown. Our study reveals that the Akt-mTOR signaling pathway promotes myelin sheath growth by regulating protein translation. Because we found translational regulators of the Akt-mTOR pathway in myelin, our data raise the possibility that Akt-mTOR activity regulates translation in myelin sheaths to deliver myelin on demand to the places it is needed.

Coupled effects of hydrophilic nano silica oxide and anatase nano titanium oxide on strengths of oilwell cement

The life of oil wells depends on the stability of cement sheath and bond strength with the formation and casing. Extreme subsurface conditions cause substantial stresses on the cement sheath resulting in a serious impact on well integrity. The recommended API cement for oilwell fails to provide the required durability of the cemented well due to such conditions. Supplementary cementitious materials such as nanoparticles are added to improve the cement for long-lasting zonal isolation. In this study, the compressive and shear bond strengths of oilwell cement containing nano-SiO2 and nano-TiO2 were studied at 80 °C for 3, 7, 14, and 28 days of hydration. The XRD, TG, and DSC were used for the analysis of cement hydration products. The results revealed that both nano-SiO2 and nano-TiO2 increased strength evolution. A ternary system made with 2% nano-SiO2 and 2% nano-TiO2 improved compressive strength by 22.6 and 48.4%, while the shear bond strength increased by 110.6 and 55% at age of 3 days and 28 days, respectively, compared to their corresponding binary systems. Therefore, these results remark the potential of replacing an appropriate proportion of oilwell cement with coupled nano-SiO2 and nano-TiO2 to ensure cement sheath structure durability in the annular and long-lasting zonal isolation.
 Keywords: Nano-silica, nano-titanium, compressive strength, shear bond strength, oilwell cement

Unveiling the role of dielectric trap states on capacitively coupled radio-frequency plasma discharge: dynamic charging behaviors

The influence of charge trap states in the dielectric boundary material on capacitively coupled radio-frequency (RF) plasma discharge is investigated with theory and particle-in-cell/Monte Carlo collision simulation. It is found that the trap states of the wall material manipulated discharge properties mainly through the varying ion-induced secondary electron emission (SEE) coefficient in response to dynamic surface charges accumulated within the solid boundary. A comprehensive SEE model considering surface charging is established first, which incorporates the valence band electron distribution, electron trap density, and charge trapping through Auger neutralization and de-excitation. Theoretical analysis is carried out to reveal the effects of trap states on sheath solution, stability, plasma density and temperature, particle and power balance, etc. The theoretical work is supported by simulation results, showing the reduction of the mean RF sheath potential as charging-dependent emission coefficient increases. As the gas pressure increases, a shift of the maximum ionization rate from the bulk plasma center to the plasma-sheath interface is observed, which is also influenced by the trap states of the electrode material where the shift happens at a lower pressure with traps considered. In addition, charge traps are proven to be helpful for creating asymmetric plasma discharges with geometrically symmetric structures; such an effect is more pronounced in γ-mode discharges.

A novel stabilization mechanism for the type VI secretion system sheath

The type VI secretion system (T6SS) is a phage-derived contractile nanomachine primarily involved in interbacterial competition. Its pivotal component, TssA, is indispensable for the assembly of the T6SS sheath structure, the contraction of which propels a payload of effector proteins into neighboring cells. Despite their key function, TssA proteins exhibit unexpected diversity and exist in two major forms, a short form (TssAS) and a long form (TssAL). While TssAL proteins interact with a partner, called TagA, to anchor the distal end of the extended sheath, the mechanism for the stabilization of TssAS-containing T6SSs remains unknown. Here we discover a class of structural components that interact with short TssA proteins and contribute to T6SS assembly by stabilizing the polymerizing sheath from the baseplate. We demonstrate that the presence of these components is important for full sheath extension and optimal firing. Moreover, we show that the pairing of each form of TssA with a different class of sheath stabilization proteins results in T6SS apparatuses that either reside in the cell for some time or fire immediately after sheath extension. We propose that this diversity in firing dynamics could contribute to the specialization of the T6SS to suit bacterial lifestyles in diverse environmental niches.

Sphingolipids and physical function in the Atherosclerosis Risk in Communities (ARIC) study

Long-chain sphingomyelins (SMs) may play an important role in the stability of myelin sheath underlying physical function. The objective of this study was to examine the cross-sectional and longitudinal associations of long-chain SMs [SM (41:1), SM (41:2), SM (43:1)] and ceramides [Cer (41:1) and Cer (43:1)] with physical function in the Atherosclerosis Risk in Communities (ARIC) study. Plasma concentrations of SM (41:1), SM (41:2), SM (43:1), Cer (41:1) and Cer (43:1) were measured in 389 ARIC participants in 2011–13. Physical function was assessed by grip strength, Short Physical Performance Battery (SPPB), 4-m walking speed at both 2011–13 and 2016–17, and the modified Rosow-Breslau questionnaire in 2016–2017. Multivariable linear and logistic regression analyses were performed, controlling for demographic and clinical confounders. In cross-sectional analyses, plasma concentrations of SM 41:1 were positively associated with SPPB score (β-coefficients [95% confidence internal]: 0.33 [0.02, 0.63] per 1 standard deviation [SD] increase in log-transformed concentration, p value 0.04), 4-m walking speed (0.042 m/s [0.01, 0.07], p value 0.003), and negatively with self-reported disability (odds ratio = 0.73 [0.65, 0.82], p value < 0.0001). Plasma concentrations of the five metabolites examined were not significantly associated with longitudinal changes in physical function or incidence of poor mobility. In older adults, plasma concentrations of long-chain SM 41:1 were cross-sectionally positively associated with physical function.

Individual neuronal subtypes control initial myelin sheath growth and stabilization

BackgroundIn the developing central nervous system, pre-myelinating oligodendrocytes sample candidate nerve axons by extending and retracting process extensions. Some contacts stabilize, leading to the initiation of axon wrapping, nascent myelin sheath formation, concentric wrapping and sheath elongation, and sheath stabilization or pruning by oligodendrocytes. Although axonal signals influence the overall process of myelination, the precise oligodendrocyte behaviors that require signaling from axons are not completely understood. In this study, we investigated whether oligodendrocyte behaviors during the early events of myelination are mediated by an oligodendrocyte-intrinsic myelination program or are over-ridden by axonal factors.MethodsTo address this, we utilized in vivo time-lapse imaging in embryonic and larval zebrafish spinal cord during the initial hours and days of axon wrapping and myelination. Transgenic reporter lines marked individual axon subtypes or oligodendrocyte membranes.ResultsIn the larval zebrafish spinal cord, individual axon subtypes supported distinct nascent sheath growth rates and stabilization frequencies. Oligodendrocytes ensheathed individual axon subtypes at different rates during a two-day period after initial axon wrapping. When descending reticulospinal axons were ablated, local spinal axons supported a constant ensheathment rate despite the increased ratio of oligodendrocytes to target axons.ConclusionWe conclude that properties of individual axon subtypes instruct oligodendrocyte behaviors during initial stages of myelination by differentially controlling nascent sheath growth and stabilization.

Modified discrete element method (MDEM) as a numerical tool for cement sheath integrity in wells

Cement sheaths undergo extreme loading conditions in wells during subsurface operations. A damaged cement sheath may lead to fluid communication between different formation layers and fluid migration up to the surface, which can cause environmental, technical, and economic problems. In this study, we numerically analyze cement sheath stability using the modified discrete element method (MDEM). MDEM considers the cement sheath and rock formation as porous media and can model discontinuous fracturing of the materials. Analyses are performed based on a small-scale cement sheath integrity test and field cement pressure data measured by Cooke et al. (1983). Oil well class H cement was used, and its poroelastic properties were estimated using a micromechanics model and a multi-scale homogenization technique. First, the evolution of the stress state was approximated in the cement sheath and rock formation. Then, radial fracturing, shear failure, and interface debonding formation were studied under pressure increase/decrease operations. The effects of several parameters, such as the casing size, rock elastic parameters, and loading time, were also investigated. During the hydration of cement, the compressive and shear stresses evolved in the cement sheath, and the stresses in the surrounding formation also changed. The simulation results showed that a decrease in the casing pressure can lead to debonding of the casing-cement interface, and the calculated interface opening was within 1–50 μm. A pressure increase in the casing can lead to progressive shear and tensile failures in the cement sheath. A further pressure increase did not extend those failures into the rock formation; rather, it increased the number of radial fractures in the cement sheath. The analyses showed that a lower decrease and increase in the casing pressure is required to generate debonding and radial fracture in the cement sheath, respectively, in the early stages of hydration after the cement is set. This is also the case when the casing has a larger diameter and smaller thickness. When the cement sheath is bonded to a softer rock formation, the pressure increase required to create a fracture in the cement is lower compared with the case in which the sheath is bonded to a stiffer formation. However, in the case of softer formation, debonding was not observed.

‘Fire Tube’ Formation in Expanding RF Plasma

Multiple double layers develop during expanding capacitive mode of RF discharge in a linear vacuum vessel in the absence of external magnetic field. Dynamics of multiple double layers have been studied through electric probe diagnostics in nitrogen RF plasma operated at 13.56 MHz frequency. The burst oscillations of the potential, fire tube formations and space charge formations suggest formations of complex structures during the discharge. Our first experimental results provide interesting information about the stability of plasma sheath and space charge effect on it. The visibly bright discharge transforms into multiple intensely coaxial luminous “Fire Tube” structures on increasing the input RF power in plasma.

Dual-balloon assisted super-selective embolisation of high flow arterial venous fistula within a transplant kidney

BackgroundIn this case report, we describe a novel application of the technique of ‘dual-balloon assisted’ cannulation and embolisation of a high flow arterial venous fistula (AVF) in transplant kidney, where attempts at standard and previously described embolisation techniques were proving difficult to achieve.Case presentationSeventy year old gentleman with renal transplant presenting with high output cardiac failure and deteriorating renal function. Angiography demonstrated high flow traumatic AV fistula within transplanted kidney, secondary to multiple biopsies. Attempts at guidewire and guiding sheath placement and stability for occlusion plug deployment were failing due to combination of very high back-flow pressures within the AVF and challenging vascular anatomy; with an aneurysmal, tortuous iliac artery as well as intra renal transplanted vessels. A combination of angioplasty and remodeling aortic balloons in the transplant artery and the host external iliac vein respectively, facilitated stabilization of guiding sheath and hence controlled delivery of an occlusion plug from the venous side of the fistula. The fistula was successfully embolised, leading to complete resolution of patient symptoms and improvement of renal function beyond his previous baseline.ConclusionsPercutaneous embolisation is an established technique to treat iatrogenic AVF in transplant kidneys. High flow pressure through an AVF, as demonstrated in this case, can cause difficulty and raise safety issues in accessing and embolising the AVF using previously described techniques. This case report describes an effective and novel application of the technique of using a second balloon in the host common iliac vein to; lower flow pressure, stabilise the guidewires during plug deployment and prevent displacement of wires and/or plug into the common iliac vein.

The impact of circularity defects on bridge stay cable dry galloping stability

The present work studies the influence of circularity defects, on the aerodynamic behaviour of stay cables of cable-stayed bridges. It focuses on wind tunnel tests on High-Density Polyethylene cable covers with and without helical fillets, in a range of Reynolds numbers from the sub-critical to the critical regime. The paper considers the impact of circularity defects on the aerodynamic stability of cable sheaths by testing various amplitudes of imposed ovalization. The defects are artificially applied on real sheaths whose original cross-sections are close to circular. The experiment consists in measuring surface pressures to investigate how the amplitude of ovalization influences the flow around the sheaths, especially in the critical Reynolds number regime when transition in the boundary layer occurs. The analysis is based on bifurcation diagrams and Proper Orthogonal Decomposition. The investigation demonstrates that important circularity defects can significantly increase the bi-stable nature of the flow around a sheath at the critical regime. Nevertheless, the introduction of a helical fillet de-correlates the flow around the sheath, causing jumps in lift that have different sign along its length.