Axial Extension Research Articles

Incidence of Developmental Venous Anomalies in Patients With Multiple Sclerosis: A 3 Tesla MRI Study.

ObjectivesThere is evidence of involvement of the venous system in multiple sclerosis (MS). If this bears also an association with the frequency and extent of developmental venous anomalies (DVA) still has to be determined. We therefore investigated this in patients with different phenotypes of MS and in comparison, to a control population.MethodsWe analyzed the contrast-enhanced T1-weighted MR scans of 431 patients (clinically isolated syndrome—CIS, n = 108; MS, n = 323) and of 162 control individuals for the presence of a DVA. We also measured the size of the DVA and draining vein and compared the DVA frequency between MS phenotypes.ResultsA DVA was found in 38 (8.8 %) of patients with CIS or MS and in 11 (6.8%) controls (p = 0.4). DVA frequency was highest in CIS (14.8%) and lowest in progressive MS (4.0%). The mean cranio-caudal and axial extension of the DVA was significantly lower in MS patients than controls (p < 0.05).ConclusionsThe frequency of DVA in MS patients is comparable to that in controls. Whether DVA size and appearance may change over time will have to be investigated in a longitudinal manner and with larger sample size.

Inducing Tensile Failure of Claystone Through Thermal Pressurization in a Novel Triaxial Device

Complex coupled thermo-hydromechanical (THM) loading paths are expected to occur in clay rocks which serve as host formations for geological radioactive waste repositories. Exothermic waste packages heat the rock, causing thermal strains and temperature induced pore pressure build-up. The drifts are designed in such a way as to limit these effects. One has to anticipate failure and fracturing of the material, should pore pressures exceed the tensile resistance of the rock. To characterise the behaviour of the Callovo-Oxfordian claystone (COx) under effective tension and to quantify the tensile failure criterion, a laboratory program is carried out in this work. THM loading paths which correspond to the expected in situ conditions are recreated in the laboratory. To this end, a special triaxial system was developed, which allows the independent control of radial and axial stresses, as well as of pore pressure and temperature of rock specimens. More importantly, the device allows one to maintain axial effective tension on a specimen. Saturated cylindrical claystone specimens were tested in undrained conditions under constrained lateral deformation and under nearly constant axial stress. The specimens were heated until the induced pore pressures created effective tensile stresses and ultimately fractured the material. The failure happened at average axial effective tensile stresses around 3.0 MPa. Fracturing under different lateral total stresses allows one to describe the failure with a Hoek–Brown or Fairhurst’s generalized Griffith criterion. Measured axial extension strains are analysed based on a transversely isotropic thermo-poroelastic constitutive model, which is able to satisfactorily reproduce the observed behaviour.

A Comparative Biomechanical Analysis of the Impact of Different Configurations of Pedicle-Screw-Based Fixation in Thoracolumbar Compression Fracture.

The aim of this experimental study was to analyze the impact of applying different configurations of the transpedicular fixation system on selected mechanical parameters of the thoracolumbar spine under conditions of its instability (after simulated fracture). Five study groups were tested: physiological, with compression fracture of the vertebra, with two-segment fixation, with three-segment fixation, and with four-segment fixation. Each of the analyzed study groups was subjected to axial compression, flexion, and extension. Based on the conducted experimental tests, the mechanical parameters, i.e., stiffness coefficient and dissipation energy, were determined for all groups under consideration. The stiffness value of two-segment fixation is significantly lower than the physiological value (during flexion and extension). The use of long-segment fixation considered in two configurations (three- and four-segment fixation) may result in excessive stiffness of the system due to the high stiffness values achieved (approx. 25–30% higher than the physiological values in the case of compression and on average 60% higher in the case of flexion). The use of long-segment fixator design shows better results than short-segment fixation. Considering both biomechanical and clinical aspects, three-segment fixation seems to be a compromise solution as it saves the patient from more extensive stiffening of the spinal motion segments.

Auxetic Meta‐Display: Stretchable Display without Image Distortion

AbstractMechanical metamaterials possess unusual mechanical properties that cannot be found in nature. Auxetic metamaterials have negative Poisson's ratios and tend to expand in a direction perpendicular to the axial extension direction. When the Poisson's ratio of a display circuit board is forced to be −1 by adopting an auxetic metamaterial, a display can be stretchable without image distortion, and this display is called a meta‐display in this study. The critical obstacles to implementing a stretchable display are large stretchability, high deformation uniformity, and low image distortion. The meta‐display overcomes these obstacles by incorporating micro‐LEDs and a kirigami‐based auxetic circuit board. An auxetic meta‐display with a stretchability of 24.5%, Poisson's ratio of −1, and no image distortion under uniaxial stretching is demonstrated. Finally, the roll transfer process enabled the scaling‐up of a 3‐inch meta‐display attachable to surfaces with non‐zero Gaussian curvatures. This conformity to the non‐zero Gaussian curvature helps realize biomedical applications such as wearable display, phototherapy, and skincare.

Spatially modulated illumination microscopy: application perspectives in nuclear nanostructure analysis

Thousands of genes and the complex biochemical networks for their transcription are packed in the micrometer sized cell nucleus. To control biochemical processes, spatial organization plays a key role. Hence the structure of the cell nucleus of higher organisms has emerged as a main topic of advanced light microscopy. So far, a variety of methods have been applied for this, including confocal laser scanning fluorescence microscopy, 4Pi-, STED- and localization microscopy approaches, as well as (laterally) structured illumination microscopy (SIM). Here, we summarize the state of the art and discuss application perspectives for nuclear nanostructure analysis of spatially modulated illumination (SMI). SMI is a widefield-based approach to using axially structured illumination patterns to determine the axial extension (size) of small, optically isolated fluorescent objects between less than or equal to 200 nm and greater than or equal to 40 nm diameter with a precision down to the few nm range; in addition, it allows the axial positioning of such structures down to the 1 nm scale. Combined with SIM, a three-dimensional localization precision of less than or equal to 1 nm is expected to become feasible using fluorescence yields typical for single molecule localization microscopy applications. Together with its nanosizing capability, this may eventually be used to analyse macromolecular complexes and other nanostructures with a topological resolution, further narrowing the gap to Cryoelectron microscopy. This article is part of the Theo Murphy meeting issue ‘Super-resolution structured illumination microscopy (part 2)’.

Molecular Engineering Enables TADF Emitters Well Suitable for Non‐Doped OLEDs with External Quantum Efficiency of Nearly 30%

AbstractNon‐doped organic light‐emitting diodes (OLEDs) are particularly appealing due to the merit of the extremely simple device structure. However, the performance of non‐doped OLEDs is usually far inferior than that of doped devices, mainly due to the lack of desirable emitters. An ideal emitter for non‐doped OLEDs should not merely be highly emissive in the host matrix but also be capable of delivering excellent properties in its condensed state. Herein, through molecular engineering, an “axial and equatorial carbazolyl extension” approach to manipulate the molecular packing behavior is developed, and thus, the emitter is awarded with superior properties in its neat film. Based on this approach, through simply modifying the conventional acridine donor in a thermally activated delayed fluorescence (TADF) emitter with carbazole moieties in the way of hyper‐conjugation, two new TADF emitters with the molecular skeleton being extended both horizontally and vertically by carbazole moieties are constructed. The resulted TADF emitters reveal superb properties with simultaneous excellent thermal and morphological stabilities, photophysical behaviors, and charge transporting ability in their neat film. Owing to the merits of these synergistic superior properties, highly efficient non‐doped green emissive OLED with the state‐of‐the‐art external quantum efficiency of nearly 30% is realized.

Hyperelastic Membrane Actuators: Analysis of Toroidal and Helical Multifunctional Configurations.

Technologies that provide mechanical assistance are required in the medical field, such as implants that regenerate tissue through elongation and stimulation. One of the challenges is to develop actuators that combine the benefits of high axial extension at low pressures, modularity, multifunction, and load-bearing capabilities into one design while maintaining their shape and softness. Overcoming such a challenge will provide implants with enhanced capacity for mechanical assistance to induce tissue regeneration. We introduce two novel actuators (M2H) built of stacked Hyperelastic Ballooning Membrane Actuators (HBMAs) that can be realized using helical and toroidal configurations. By restraining the HBMA expansion deterministically using a semisoft exoskeleton, the actuators are endowed with axial extension and radial expansion capabilities. These actuators are thus built of modules that can be configured to different therapeutical needs and multifunctionality, to provide anatomically congruent stimulation. We present the design, fabrication, testing, and numerical and experimental validation of the M2H-HBMAs. They can axially extend up to 41% and 32% in their helical and toroidal configurations at input pressures as low as 26 and 24 kPa, respectively. If the axial extension module is used separately, its extension capacity reaches >170%. The M2H-HBMAs can perform independent and simultaneous expansion and extension motions with negligible intraluminal deformation as well as stand at least 1 kg of axial force without collapsing. The M2H-HBMAs overcome the limitations of hyperexpanding machines that show low resistance to load. We envisage M2H-HBMAs as promising tools to perform tissue regeneration procedures.

Numerical analysis of thermo-mechanical behavior in flow forming

Flow forming is a metal forming process for cylindrical workpieces where high velocity deformation leads to radial thinning and axial extension. In the current study, a thermomechanical, dynamic and explicit finite element model of a flow forming process is developed on ABAQUS software. The model is validated through the comparison of reaction forces and geometry obtained from the experiments. Coolant convection effect is analyzed in conjunction with roller and mandrel conduction cooling to study the thermal variations in the deformation zone during the process. The methodology detailed in this study facilitates a deeper understanding of the evolution of heat during the flow forming process and lays the groundwork for further exploration into the possible role of a material’s thermal properties in the definition of flow formability.

Optimal design of drag reduction oscillators by considering drillstring fatigue and hydraulic loss in sliding drilling

Practice has proved that drag reduction oscillators can be used to decrease the axial friction and increase wellbore extension effectively in sliding drilling. However, the complicated mechanical behaviors of drillstring with drag reduction oscillators have not been revealed sufficiently, and there has no theoretical method to optimize drag reduction parameters. In this paper, an optimization design model of drag reduction oscillators is built with drag reduction efficiency as the target, and the mechanical model of drillstring with drag reduction oscillators is established by considering the friction nonlinearity. Further introducing the initial conditions, boundary conditions, and continuity conditions, the finite differential equation of drillstring vibration is obtained and solved. Next, combined with the oscillation propagation length and the installation position optimization models, the orthogonal experimental design method is applied to optimize the relevant parameters. In the optimization process, the constraint factors, including drillstring failure and hydraulic loss, are considered. Finally, the new model is applied to a field case study, in which the drag reduction effects of drillstring with and without oscillators are compared, and the impact of relevant factors on drag reduction are analyzed. The results show that the equivalent friction coefficient near the oscillator installation position is significantly reduced, whereas the hook load and weight on bit (WOB) are increased significantly with drag reduction oscillators. With the increase of amplitude or frequency, the propagation distance of the oscillator increases. The amplitude of vibration force and the number of oscillators are the two main factors affecting drag reduction efficiency. Three hydraulic oscillators with vibration amplitudes of 40 KN are recommended, and the drag reduction efficiency is 51.78%. However, excessively large oscillation amplitude may lead to drillstring failure and too many oscillators will increase the hydraulic loss a lot. Therefore, there are optimal values of oscillation amplitude and the number of oscillators. The research results are of significant guiding significance for optimal design and safety control of drag reduction oscillators in sliding drilling.

Vangl2-environment interaction causes severe neural tube defects, without abnormal neuroepithelial convergent extension.

ABSTRACTPlanar cell polarity (PCP) signalling is vital for initiation of mouse neurulation, with diminished convergent extension (CE) cell movements leading to craniorachischisis, a severe neural tube defect (NTD). Some humans with NTDs also have PCP gene mutations but these are heterozygous, not homozygous as in mice. Other genetic or environmental factors may interact with partial loss of PCP function in human NTDs. We found that reduced sulfation of glycosaminoglycans interacts with heterozygosity for the Lp allele of Vangl2 (a core PCP gene), to cause craniorachischisis in cultured mouse embryos, with rescue by exogenous sulphate. We hypothesized that this glycosaminoglycan–PCP interaction may regulate CE, but, surprisingly, DiO labelling of the embryonic node demonstrates no abnormality of midline axial extension in sulfation-depleted Lp/+ embryos. Positive-control Lp/Lp embryos show severe CE defects. Abnormalities were detected in the size and shape of somites that flank the closing neural tube in sulfation-depleted Lp/+ embryos. We conclude that failure of closure initiation can arise by a mechanism other than faulty neuroepithelial CE, with possible involvement of matrix-mediated somite expansion, adjacent to the closing neural tube.

Mechanical behavior of drillstring with drag reduction oscillators and its effects on sliding drilling limits

Practice has proved that drag reduction oscillators can decrease the axial friction and increase wellbore extension effectively in sliding drilling operations. However, the complicated mechanical behavior of drillstring with drag reduction oscillators has not been revealed sufficiently. In this paper, the mechanical model of drillstring with drag reduction oscillators is established by considering the friction nonlinearity. Further introducing the initial conditions, boundary conditions and continuity conditions, the finite differential equation of drillstring vibration is obtained and solved. The new model has been applied to a case study, in which the drag reduction effects of drillstring with and without oscillators are compared and the effects of relevant factors on drag reduction are analyzed. The results show that the hook loads increase obviously by reducing downhole average friction coefficient for drillstring with oscillators. Increasing vibration amplitude of the drag reduction oscillator can decrease axial friction, but the vibration frequency is nearly irrelevant to drag reduction. Increasing number of drag reduction oscillators can decrease axial friction, but may lead to large hydraulic power loss and high risk of drillstring fatigue. Therefore, there is an optimal number of drag reduction oscillators. The research results are of significant guiding significance for optimal design and safety control in sliding drilling operations.

A general sandwich‐type model for delamination failure in angle‐ply laminates under thermo‐mechanical loading

AbstractWe propose a highly efficient analytical closed‐form approach to assess the interlaminar stresses at the free edge in symmetric angle‐ply laminates under uniform axial extension and homogeneous thermal loading. The model is based on a two‐dimensional generalized plane strain representation of the structural situation – a so‐called general sandwich‐type model. Using the results of this approach we predict the delamination onset by means of a coupled stress and energy criterion within the framework of finite fracture mechanics. For comparative purposes we use numerical results from a cohesive zone model as well as experimental findings from the literature.

Primary stability of the Activ L® intervertebral disc prosthesis in cadaver bone and comparison of the keel and spike anchoring concept

BackgroundHigh primary stability is the key prerequisite for safe osseointegration of cementless intervertebral disc prostheses. The aim of our study was to determine the primary stability of intervertebral disc prostheses with two different anchoring concepts – keel and spike anchoring.MethodsTen ActivL intervertebral disc prostheses (5 x keel anchoring, 5 x spike anchoring) implanted in human cadaver lumbar spine specimens were tested in a spine movement simulator. Axial load flexion, extension, left and right bending and axial rotation motions were applied on the lumbar spine specimens through a defined three-dimensional movement program following ISO 2631 and ISO/CD 18192-1.3 standards. Tri-dimensional micromotions of the implants were measured for both anchor types and compared using Student’s T-test for significance after calculating 95 % confidence intervals.ResultsIn the transverse axis, the keel anchoring concept showed statistically significant (p < 0.05) lower mean values of micromotions compared to the spike anchoring concept. The highest micromotion values for both types were observed in the longitudinal axis. In no case the threshold of 200 micrometers was exceeded.ConclusionsBoth fixation systems fulfill the required criteria of primary stability. Independent of the selected anchorage type an immediate postoperative active mobilization doesn’t compromise the stability of the prostheses.

The deformation behaviour of an anisotropically consolidated kaolin clay under lateral cyclic loading

The soil behind wharfs or around pile foundations for wind turbines may be subjected to lateral cyclic loading. A series of cyclic triaxial tests were performed on a kaolin clay to study the response of the soil to lateral cyclic loading. Cyclic cell pressure was applied under a constant total vertical stress condition. The deformation behaviour of the clay under undrained condition is presented and discussed under different cyclic stress amplitudes, initial static deviatoric stresses and effective consolidation stresses. The results indicate that, the samples prepared under isotropic consolidation condition experienced axial extension, while those prepared under anisotropic consolidation condition exhibited axial compression under cyclic loading. There exists a static deviatoric stress ratio (between zero and 0.15) at which pure excess pore water pressure accumulates without axial strain development. Under anisotropic consolidation condition, with the increase of static deviatoric stress ratio, the deviatoric component of direction of strain accumulation increases in comparison to volumetric (excess pore water pressure) portion. The flow rule of Modified Cam Clay model (MCC) is revised to describe the direction of strain accumulation with the consideration of anisotropy of the clay. The predicted direction of strain accumulation is comparable with the observed values. Highlights The deformation behaviour of a kaolin clay under lateral cyclic loading is analysed. Zero axial strain accumulated at the static deviatoric stress ratio of about 0.1 (rigorously between 0 and 0.15). The flow rule of MCC is modified to describe the direction of strain accumulation considering the anisotropy of the clay.

An Actuator Concept for Adaptive Concrete Columns

The building industry accounts for half of the global resource consumption and roughly one third of global CO2 emissions. Global population growth and increasing resource scarcities require engineers and architects to build for more people with less material and emissions. One promising solution are adaptive load-bearing structures. Here, the load-bearing structure is equipped with actuators, sensors, and a control unit which allows the structure to adapt to different load cases, resulting in substantial material savings. While the first prototypes use industry standard actuators to manipulate deformations and stress states, it is essential to develop actuator concepts which fit the specific requirements of civil engineering structures. This paper introduces new concepts for linear actuators, developed within the Collaborative Research Centre (SFB) 1244 Adaptive Skins and Structures for the Built Environment of Tomorrow, which can be used as adaptive concrete columns. The concept of an actuator which actuates a concrete column by external compression through hydraulic pressure is discussed in further detail. This concept allows for controlled axial extension while also increasing the compressive strength of the concrete column.

Numerical study on the production and transport of O and OH in a helium–humid air atmospheric pressure plasma jet interacting with a substrate

In this paper, the spatiotemporal developments of OH and O density in an atmospheric pressure helium–humid air plasma jet, both along the effluent and in particular close to the substrate surface, are evaluated under different governing parameters by performing two-dimensional numerical simulation. The results show that reducing the gas flow velocity can increase its density and shorten delivery time to the substrate surface. However, in different jet propagation stages, the dependences of the density distributions of two species on the gas flow speed are different. Before the plasma jet impinges the substrate surface, the O atom has a relatively higher density throughout the jet channel at low gas flow velocity; the increase in the flow velocity makes the peak O density shift to the jet head, whereas the OH radical is mainly distributed near the tube nozzle area and is almost unaffected by gas flow velocity. When the plasma jet moves along the substrate surface, increasing flow speed has little influence on the O density distribution but results in a longer spread length of OH along the substrate surface. By changing the relative permittivity of the substrate, it is found that both the densities and the axial extension lengths of O and OH increase with the relative permittivity, while the radial spread length over the substrate surface decreases. An earlier delivery of reactive species to the surface can be observed for the larger permittivity. The causes for these behaviors are also analyzed and discussed.

Strain maps characterize the symmetry of convergence and extension patterns during zebrafish gastrulation

During gastrulation of the zebrafish embryo, the cap of blastoderm cells organizes into the axial body plan of the embryo with left–right symmetry and head–tail, dorsal–ventral polarities. Our labs have been interested in the mechanics of early development and have investigated whether these large-scale cell movements can be described as tissue-level mechanical strain by a tectonics-based approach. The first step is to image the positions of all nuclei from mid-epiboly to early segmentation by digital sheet light microscopy, organize the surface of the embryo into multi-cell spherical domains, construct velocity fields from the movements of these domains and extract strain rate maps from the change in density of the domains. During gastrulation, tensile/expansive and compressive strains in the axial and equatorial directions are detected as anterior and posterior expansion along the anterior–posterior axis and medial–lateral compression across the dorsal–ventral axis and corresponds to the well characterized morphological movements of convergence and extension. Following gastrulation strain is represented by localized medial expansion at the onset of segmentation and anterior expansion at the onset of neurulation. In addition to linear strain, symmetric patterns of rotation/curl are first detected in the animal hemispheres at mid-epiboly and then the vegetal hemispheres by the end of gastrulation. In embryos treated with C59, a Wnt inhibitor that inhibits head and tail extension, the axial extension and vegetal curl are absent. By analysing the temporal sequence of large-scale movements, deformations across the embryo can be attributed to a combination of epiboly and dorsal convergence-extension.

Magnetic Force Calculation of Movable YBCO Superconducting Helical Coils Applicable to Electric Vehicles Wireless Power Transfer

Background and Objectives: Today, replacing gasoline-powered vehicles with electric vehicles (EVs) and connecting them to an electric power source have made the optimal usage of energy-saving resources. Therefore, wireless Power Transfer (WPT) outstands as an alternative technology to improve the user perception about the charging process of the EVs. Superconducting coils (SCs) with high-temperature have an applied feature in decreasing losses of wireless power transmission (WPT). The Magnetic force has effects of overall deformation modes between two current carrier superconducting coils, i.e. axial extension, torsion, and bending. Coil misalignment is a fundamental problem and its impact on wireless power transmission efficiency is very complex. The analysis of a magnetic force which is presented in this paper are beneficially for the design and application of the WPT systems. Here, a fast analytical solution is presented to obtain the magnetic force between the transmitter and receiver helical superconducting coils in different positions.Methods: In this paper, a new method applied to solve the numerically magnetic force solutions in different superconducting coils mismatch states for WPT. Finally, for improvement of efficiency, the WPT system has been designed on the basis of mutual inductance changes which receiving helical coil was moved inside the transmitting helical coil. Hence, the magnetic force calculation of movable YBCO superconducting helical coils inside each other is presented. These models have been compared with the FEM.Results: Results show that the presented equations are reliable as well. According to the comparing the analysis and FEM data, the obtained results indicated the errors with less than 0.0064%. Also, results show an excellent agreement with respect to the finite element method.Conclusion: In this paper, the numerical solutions of magnetic force in different superconducting coils mismatch states were solved by a new method. The magnetic force analysis basics introduced in this paper are useful to develop and apply for wireless power transmission system. The simulation results show that only by applying some constraints, the efficiency of the transmitted wireless power will be optimized. Then, analytical models have been presented which make it possible to calculate the axial force which was exerted between two axially Helical magnetized and two thin coils in air. Also, the analytical stiffness calculation applied between these distributions of magnetic source has been presented. These models have been compared with the FEM to show an appropriate consistency.

Pneumatic Soft Actuators With Kirigami Skins.

Soft pneumatic actuators have become indispensable for many robotic applications due to their reliability, safety, and design flexibility. However, the currently available actuator designs can be challenging to fabricate, requiring labor-intensive and time-consuming processes like reinforcing fiber wrapping and elastomer curing. To address this issue, we propose to use simple-to-fabricate kirigami skins—plastic sleeves with carefully arranged slit cuts—to construct pneumatic actuators with pre-programmable motion capabilities. Such kirigami skin, wrapped outside a cylindrical balloon, can transform the volumetric expansion from pneumatic pressure into anisotropic stretching and shearing, creating a combination of axial extension and twisting in the actuator. Moreover, the kirigami skin exhibits out-of-plane buckling near the slit cut, which enables high stretchability. To capture such complex deformations, we formulate and experimentally validates a new kinematics model to uncover the linkage between the kirigami cutting pattern design and the actuator’s motion characteristics. This model uses a virtual fold and rigid-facet assumption to simplify the motion analysis without sacrificing accuracy. Moreover, we tested the pressure-stroke performance and elastoplastic behaviors of the kirigami-skinned actuator to establish an operation protocol for repeatable performance. Analytical and experimental parametric analysis shows that one can effectively pre-program the actuator’s motion performance, with considerable freedom, simply by adjusting the angle and length of the slit cuts. The results of this study can establish the design and analysis framework for a new family of kirigami-skinned pneumatic actuators for many robotic applications.

Response of a polymer liner passing across a pressure pipeline joint opening under axial ground movements

A closed form solution is developed to quantify the stresses that develop in polymer liners installed within pressure pipes, where the liner spans across a joint or ring fracture in the ‘host’ pipeline that is subjected to axial extension as a result of ground movements. The solution considers the zones of slip between liner and host pipe on either side of the joint that is opening. The expression derived indicates that maximum axial liner stress is proportional to the square root of the product of the gap that opens across the joint, liner modulus, internal fluid pressure, coefficient of friction between liner and host pipe, and inverse of liner thickness. Calculations are presented for a typical liner installed within a cast iron water pipe, though research is needed to quantify liner-host pipe friction. Comparisons to finite element calculations demonstrated that the new solution characterises the liner as having higher stiffness than numerical analysis using thick shell elements. Initially the two solutions match, but the new closed form solution becomes more conservative with increasing gap size. FEA was then used to show that temporary reductions in water pressure decrease axial liner stresses significantly.