In-plane Flow Research Articles

A novel double-image-sequence correlation method for time-resolved particle image velocimetry

This work reports a novel method with a goal of improving the accuracy and robustness of time-resolved particle image velocimetry (TR-PIV) measurements. This method, named double-image-sequence correlation (DISC), accomplishes this goal by utilizing the temporal information stored in TR-PIV measurements. The key to such utilization is that the DISC method constructs two separate image sequences with well-selected sequence length and separation time. As a result, multiple cross-correlation maps from consecutive image pairs can be averaged to reduce the random measurement noises (e.g., due to laser shot-to-shot variation and out-of-plane flow motion), and also each individual cross-correlation map can be obtained using the image pair separated with optimal time to further reduce the uncertainties due to other factors such as non-optimal in-plane velocity gradients and flow accelerations. The DISC method was validated both numerically and experimentally. The results illustrated that this method was able to enhance the accuracy of velocity measurements by 20.4–47.2% in terms of velocity error and by 7.8–22.9% in terms of non-physical Eulerian acceleration, compared to past multi-frame PIV methods.

In situ tunable giant electrical anisotropy in a grating gated AlGaN/GaN two-dimensional electron gas

Materials with in-plane electrical anisotropy have great potential for designing artificial synaptic devices. However, natural materials with strong intrinsic in-plane electrical anisotropy are rare. We introduce a simple strategy to produce extremely large electrical anisotropy via grating gating of a semiconductor two-dimensional electron gas (2DEG) of AlGaN/GaN. We show that periodically modulated electric potential in the 2DEG induces in-plane electrical anisotropy, which is significantly enhanced in a magnetic field, leading to an ultra large electrical anisotropy. This is induced by a giant positive magnetoresistance and a giant negative magnetoresistance under two orthogonally oriented in-plane current flows, respectively. This giant electrical anisotropy is in situ tunable by tailoring both the grating gate voltage and the magnetic field. Our semiconductor device with controllable giant electrical anisotropy will stimulate new device applications, such as multi-terminal memtransistors and bionic synapses.

Machine learning for the automatic assessment of aortic rotational flow and wall shear stress from 4D flow cardiac magnetic resonance imaging.

Three-dimensional (3D) time-resolved phase-contrast cardiac magnetic resonance (4D flow CMR) allows for unparalleled quantification of blood velocity. Despite established potential in aortic diseases, the analysis is time-consuming and requires expert knowledge, hindering clinical application. The present research aimed to develop and test a fully automatic machine learning-based pipeline for aortic 4D flow CMR analysis. Four hundred and four subjects were prospectively included. Ground-truth to train the algorithms was generated by experts. The cohort was divided into training (323 patients) and testing (81) sets and used to train and test a 3D nnU-Net for segmentation and a Deep Q-Network algorithm for landmark detection. In-plane (IRF) and through-plane (SFRR) rotational flow descriptors and axial and circumferential wall shear stress (WSS) were computed at ten planes covering the ascending aorta and arch. Automatic aortic segmentation resulted in a median Dice score (DS) of 0.949 and average symmetric surface distance of 0.839 (0.632-1.071) mm, comparable with the state of the art. Aortic landmarks were located with a precision comparable with experts in the sinotubular junction and first and third supra-aortic vessels (p = 0.513, 0.592 and 0.905, respectively) but with lower precision in the pulmonary bifurcation (p = 0.028), resulting in precise localisation of analysis planes. Automatic flow assessment showed excellent (ICC > 0.9) agreement with manual quantification of SFRR and good-to-excellent agreement (ICC > 0.75) in the measurement of IRF and axial and circumferential WSS. Fully automatic analysis of complex aortic flow dynamics from 4D flow CMR is feasible. Its implementation could foster the clinical use of 4D flow CMR. • 4D flow CMR allows for unparalleled aortic blood flow analysis but requires aortic segmentation and anatomical landmark identification, which are time-consuming, limiting 4D flow CMR widespread use. • A fully automatic machine learning pipeline for aortic 4D flow CMR analysis was trained with data of 323 patients and tested in 81 patients, ensuring a balanced distribution of aneurysm aetiologies. • Automatic assessment of complex flow characteristics such as rotational flow and wall shear stress showed good-to-excellent agreement with manual quantification.

Laboratory Experiments on Performance Evaluation of Geocomposite Drainage Materials

Method of geocomposite drainage systems (GCDs) is relatively new and has been used as an alternative drainage system for geotechnical applications. The advantages of this system are cost- and time efficiency, environmentally sustainable, and at the same time, having comparable or higher drainage capability compared to current practices. However, the geocomposite materials, which is the main products of the GCD systems, need to meet certain criteria that are required for the sufficient drainage systems. These criteria are mainly related to their hydraulic and mechanical parameters that control the systems’ drainage capacity and durability during/after the construction. In this study, laboratory testing and evaluation of five different commercially available geocomposite products are conducted to improve the understanding of their physical, hydraulic and mechanical properties. Physical properties are defined by measuring their thicknesses and apparent opening sizes. Hydraulic parameters; permittivity (volumetric flow rate of water in normal direction) under various hydraulic head was measured using a constant-head equipment. Additional transmissivity and flow rate are defined under various hydraulic gradient and normal compressive stresses using in-plane flow rate testing apparatus. A number of strength testing; compressive strength, grab tensile strength, elongations, trapezoidal and puncture strength are conducted to evaluate the mechanical behavior of the geocomposite products. Results show that the parameters defined for each product are in the same order of magnitude in corresponding testing program, yet some differences are observed when compared with the manufacturer values. The reason of differences and recommendations on the selection of standard testing methods are discussed. Use of a factor of safety (FS) was suggested in the design of geocomposite drainage system when selecting the geocomposite materials.

Capillary Effects in Fiber Reinforced Polymer Composite Processing: A Review

Capillarity plays a crucial role in many natural and engineered systems, ranging from nutrient delivery in plants to functional textiles for wear comfort or thermal heat pipes for heat dissipation. Unlike nano- or microfluidic systems with well-defined pore network geometries and well-understood capillary flow, fiber textiles or preforms used in composite structures exhibit highly anisotropic pore networks that span from micron scale pores between fibers to millimeter scale pores between fiber yarns that are woven or stitched into a textile preform. Owing to the nature of the composite manufacturing processes, capillary action taking place in the complex network is usually coupled with hydrodynamics as well as the (chemo) rheology of the polymer matrices; these phenomena are known to play a crucial role in producing high quality composites. Despite its importance, the role of capillary effects in composite processing largely remained overlooked. Their magnitude is indeed rather low as compared to hydrodynamic effects, and it is difficult to characterize them due to a lack of adequate monitoring techniques to capture the time and spatial scale on which the capillary effects take place. There is a renewed interest in this topic, due to a combination of increasing demand for high performance composites and recent advances in experimental techniques as well as numerical modeling methods. The present review covers the developments in the identification, measurement and exploitation of capillary effects in composite manufacturing. A special focus is placed on Liquid Composite Molding processes, where a dry stack is impregnated with a low viscosity thermoset resin mainly via in-plane flow, thus exacerbating the capillary effects within the anisotropic pore network of the reinforcements. Experimental techniques to investigate the capillary effects and their evolution from post-mortem analyses to in-situ/rapid techniques compatible with both translucent and non-translucent reinforcements are reviewed. Approaches to control and enhance the capillary effects for improving composite quality are then introduced. This is complemented by a survey of numerical techniques to incorporate capillary effects in process simulation, material characterization and by the remaining challenges in the study of capillary effects in composite manufacturing.

Depth detection of spar cap defects in large-scale wind turbine blades based on a 3D heat conduction model using step heating infrared thermography

The defects dispersed in a spar cap often lead to the failure of large-scale wind turbine blades. To predict the residual service life of the blade and make the repair, it is necessary to detect the depth of spar cap defects. Step-heating thermography (SHT) is a common infrared technique in this domain. However, the existing methods of SHT on defect depth detection are generally based on 1D models, which are unable to accurately detect the depth of spar cap defects due to ignoring material anisotropy and in-plane heat flow. To improve the depth detection accuracy of spar cap defects, a 3D model based on the theory of heat transfer is established by using the equivalent source method (ESM), and a defect depth criterion is proposed based on the analytical solution of the heat conduction equation. The modeling process is as follows. The heat conduction model of SHT was established by ESM. Then, coordinate transformation, variables separation, and Laplace transformation were utilized to solve the 3D heat conduction equation. A defect depth criterion was proposed based on emerging contrast Cr. A glass fiber reinforced plastic composite plate containing 12 square flat-bottom holes with different sizes and depths was manufactured to represent a spar cap with large thermal resistance defects, such as delamination and cracks. The experimental results demonstrate the validity of the 3D model. Then, the model was applied to an on-site SHT test of a 1.5 MW wind turbine blade. The test results prove that the depth detection accuracy of spar cap defects can be significantly improved by using the 3D model. In addition, by using an improved principle component analysis (PCA) method containing a contrast enhancement factor, artifacts can be reduced and the recognition time of defects can be shortened. The 3D model provides a tool for detecting the depth of deep-lying defects in a thick composite structure, and the SHT technology is optimized by improved PCA.

False lumen rotational flow and aortic stiffness are associated with aortic growth rate in patients with chronic aortic dissection of the descending aorta: a 4D flow cardiovascular magnetic resonance study

BackgroundPatency of the false lumen in chronic aortic dissection (AD) is associated with aortic dilation and long-term aortic events. However, predictors of adverse outcomes in this population are limited. The aim of this study was to evaluate the relationship between aortic growth rate and false lumen flow dynamics and biomechanics in patients with chronic, patent AD.MethodsPatients with a chronic AD with patent false lumen in the descending aorta and no genetic connective tissue disorder underwent an imaging follow-up including a contrast-enhanced 4D flow cardiovascular magnetic resonance (CMR) protocol and two consecutive computed tomography angiograms (CTA) acquired at least 1 year apart. A comprehensive analysis of anatomical features (including thrombus quantification), and false lumen flow dynamics and biomechanics (pulse wave velocity) was performed.ResultsFifty-four consecutive patients with a chronic, patent false lumen in the descending aorta were included (35 surgically-treated type A AD with residual tear and 19 medically-treated type B AD). Median follow-up was 40 months. The in-plane rotational flow, pulse wave velocity and the percentage of thrombus in the false lumen were positively related to aortic growth rate (p = 0.006, 0.017, and 0.037, respectively), whereas wall shear stress showed a trend for a positive association (p = 0.060). These results were found irrespectively of the type of AD.ConclusionsIn patients with chronic AD and patent false lumen of the descending aorta, rotational flow, pulse wave velocity and wall shear stress are positively related to aortic growth rate, and should be implemented in the follow-up algorithm of these patients. Further prospective studies are needed to confirm if the assessment of these parameters helps to identify patients at higher risk of adverse clinical events.

Rheological response of compressible SMCs under various deformation kinematics: Experimental aspects and simple modelling approach

Flow conditions during compression moulding of Sheet Moulding Compounds (SMCs) govern the microstructure and the resulting mechanical properties of composite parts. Low-density and high-fibre content SMCs were subjected to simple compression, œdometric compression and through-thickness shear loadings, using dedicated rheometers. Simple compression and œdometric compression experiments revealed the compaction behaviour of both types of SMCs. During simple compression experiments, the compaction of low-density SMCs was accompanied by in-plane elongational flow phenomena, whereas the high-fibre content SMCs exhibited compaction below a characteristic axial strain and elongation and shear above. Shear tests showed that shear stress did not vary over a wide range of shear strain while being accompanied by axial compression stress. Both SMCs exhibited a shear-thinning behaviour with compression viscosities that depended on the fibre volume fraction. Finally, a transversely isotropic tensorial model for SMCs seen as compressible materials was proposed. Its predictions are consistent with the experiments.

Three-dimensional vortex-induced vibration analysis of catenary-type risers under flow with different incident angles

This paper proposes a three-dimensional (3D) numerical model for the analysis of vortex-induced vibration (VIV) on catenary-type risers (CTRs). Fully considering the geometrical nonlinearities and large deformation behavior of CTR, this model is established based on the vector form intrinsic finite element (VFIFE) theory and the independence principle (i.e., consider only the flow component perpendicular to the riser axis). The riser is discretized into a finite number of particles, the motion of these particles only has to satisfy Newton's second law and the structure is in perpetual dynamic equilibrium under the combined excitation of internal and external forces on the particles. Moreover, the unsteady hydrodynamic force associated with cross-flow (CF) vibration is modeled as distributed Van der Pol wake oscillators. The model is used to predict the VIV response of the CTRs under various flow conditions (i.e., in-plane uniform flow, shear flow, and diverse angled flow), and the results show well agreement with the corresponding experimental results. Then, the CTR's VIV characteristics under diverse angled flow are further analyzed. The obtained results highlight that the incident angle of the flow has a great influence on the mode transition, frequency locking position, energy transfer, and internal forces.

Do morphological, haemodynamic and biomechanical parameters relate to aortic growth rate in chronic type B aortic dissection? A 4D flow CMR study

Abstract Background Aortic dissection (AD) is the most devastating complication of thoracic aortic disease (1). In the chronic phase, yearly clinical and imaging follow-up of the maximum aortic diameter is recommended, since indication for thoracic endovascular aortic repair or surgery is suggested by guidelines in case of thoracic aortic enlargement or false lumen (FL) aneurysms (2). Most of the reported parameters related adverse events in chronic AD are focused on morphological variables (3) and not on the haemodynamics and biomechanics of the FL. Purpose To evaluate the relationship between aortic growth rate and anatomical variables, flow patterns and aortic stiffness in patients with chronic type B AD. Methods Forty-one patients with chronic type B aortic dissection, no connective tissue disorders and with an imaging follow-up including two computed tomography angiograms (CTA) acquired at least 3 years apart underwent contrast-enhanced 4D-flow CMR and MR angiography (MRA). The FL volume was segmented from MRA, and velocity data inside the 3D volume of the FL was extracted from 4D-flow CMR and used for parameter quantification. Retrograde systolic and diastolic flow, wall shear stress (WSS) and in-plane rotational flow (IRF) were calculated at 8 equidistant planes in the distal descending aorta (DAo), from the pulmonary bifurcation to the diaphragmatic level, and averaged values were used [4]. Aortic stiffness in the FL was assessed in terms of pulse wave velocity (PWV), which was calculated from the third supraortic trunk to the diaphragmatic level on 4D-flow CMR [5]. The percentage of thrombus in the FL was calculated as the ratio of thrombus and FL volumes on MRA. Dominant entry tear area was quantified on the baseline CTA (Figure 1). Aortic growth rate (GR) was defined as the difference between final and baseline aortic diameters as measured on CTA divided by follow-up duration. Results Anatomical, haemodynamic and biomechanical parameters are shown in Table. Twenty-five patients have repaired type A AD with residual entry tear and 16 have type B AD. Mean follow-up duration was of 4.9±2.7 years. In bivariate analysis, WSS, IRF and PWV were positively related to GR, whereas dominant entry tear area and percentage of thrombus in the FL showed a positive tendency with GR (Table) (Figure). In multivariate analysis IRF, PWV, dominant entry tear area and thrombus in the FL were positively and independently associated with GR (Table). Retrograde systolic and diastolic flow were not related to GR while WSS tended to statistical significance. Conclusions In-plane rotational flow, regional aortic stiffness, dominant entry tear area and percentage of thrombus in the false lumen are positively and independently related to aortic growth rate in patients with chronic type B aortic dissection. Further prospective studies are needed to confirm if the assessment of these parameters may help to identify patients at higher risk of adverse clinical events. Funding Acknowledgement Type of funding sources: None. Table 1Figure 1

In-plane thermal conductivity of multi-walled carbon nanotube yarns under mechanical loading

We present a computational and experimental study of the in-plane heat transfer behavior of a coiled multi-walled carbon nanotube (MWCNT) yarn. The surface temperature of the MWCNT yarn in contact with the high-temperature wire is measured to verify that the thermal conductivity in the radial direction (TCRD) of the coiled MWCNT yarn is high enough to be captured by a thermal imaging camera. A significant change in the TCRD is observed under mechanical strain in particular. Furthermore, the in-plane heat flow of MWCNTs is studied using molecular dynamics simulations. The results confirm that the structural deformation of interstitial spaces between MWCNTs during mechanical loading is a key factor in explaining the heat transfer paths generated by the thermal vibrations of carbon atoms. It is also confirmed that the change in TCRD is reduced owing to an increase in the radial buckling strength of the yarn comprising MWCNTs of a smaller diameter. The TCRD change is crucial in MWCNT-yarn applications such as twistron energy harvesters.

Investigation of drainage function of geosynthetics for basal-reinforced embankments

This study investigates the behaviour of basal-reinforced embankments under seepage flow. For this purpose, physical embankment models with dimensions of 195 cm long, 100 cm wide and 110 cm high were constructed in the laboratory. The seepage gradient within the embankment was generated by applying a constant water head of 100 cm at the water compartment located behind the models. The unreinforced embankment experienced seepage erosion at the toe section which triggered deep-seated global failure. Due to the limited transmissivity of the non-woven geotextile, the geotextile-reinforced embankment exhibited similar pore-water pressure distribution to that of the unreinforced embankment, which resulted in lateral spreading failure between the base of the embankment and the non-woven geotextile. In contrast, the geocomposite drain, which has a higher in-plane flow capacity compared to that of the geotextile, significantly alleviated the pore-water pressures within the embankment. The behaviour of the physical models was verified numerically by variably saturated flow modelling conducted for a wide range of in-plane permeabilities for the basal reinforcement. The effect of increasing in-plane permeability of the basal reinforcement layer on pore-water pressure reduction was quantified irrespective of the geosynthetic type.

Quantitative time-of-flight MR angiography for simultaneous luminal and hemodynamic evaluation of the intracranial arteries.

To report a quantitative time-of-flight (qTOF) MRA technique for simultaneous luminal and hemodynamic evaluation of the intracranial arteries. Implemented using a thin overlapping slab 3D stack-of-stars based 3-echo FLASH readout, qTOF was tested in a flow phantom and for imaging the intracranial arteries of 10 human subjects at 3 Tesla. Display of the intracranial arteries with qTOF was compared to resolution-matched and scan time-matched standard Cartesian 3D time-of-flight (TOF) MRA, whereas quantification of mean blood flow velocity with qTOF, done using a computer vision-based inter-echo image analysis procedure, was compared to 3D phase contrast MRA. Arterial-to-background contrast-to-noise ratio was measured, and intraclass correlation coefficient was used to evaluate agreement of flow velocities. For resolution-matched protocols of similar scan time, qTOF portrayed the intracranial arteries with good morphological correlation with standard Cartesian TOF, and both techniques provided superior contrast-to-noise ratio and arterial delineation compared to phase contrast (20.6 ± 3.0 and 37.8 ± 8.7 vs. 11.5 ± 2.2, P < .001, both comparisons). With respect to phase contrast, qTOF showed excellent agreement for measuring mean flow velocity in the flow phantom (intraclass correlation coefficient = 0.981, P < .001) and good agreement in the intracranial arteries (intraclass correlation coefficient = 0.700, P < .001). Stack-of-stars data sampling used with qTOF eliminated oblique in-plane flow misregistration artifacts that were seen with standard Cartesian TOF. qTOF is a new 3D MRA technique for simultaneous luminal and hemodynamic evaluation of the intracranial arteries that provides significantly greater contrast-to-noise ratio efficiency than phase contrast and eliminates misregistration artifacts from oblique in-plane blood flow that occur with standard 3D TOF.

Thin-film smoothed particle hydrodynamics fluid

We propose a particle-based method to simulate thin-film fluid that jointly facilitates aggressive surface deformation and vigorous tangential flows. We build our dynamics model from the surface tension driven Navier-Stokes equation with the dimensionality reduced using the asymptotic lubrication theory and customize a set of differential operators based on the weakly compressible Smoothed Particle Hydrodynamics (SPH) for evolving pointset surfaces. The key insight is that the compressible nature of SPH, which is unfavorable in its typical usage, is helpful in our application to co-evolve the thickness, calculate the surface tension, and enforce the fluid incompressibility on a thin film. In this way, we are able to two-way couple the surface deformation with the in-plane flows in a physically based manner. We can simulate complex vortical swirls, fingering effects due to Rayleigh-Taylor instability, capillary waves, Newton's interference fringes, and the Marangoni effect on liberally deforming surfaces by presenting both realistic visual results and numerical validations. The particle-based nature of our system also enables it to conveniently handle topology changes and codimension transitions, allowing us to marry the thin-film simulation with a wide gamut of 3D phenomena, such as pinch-off of unstable catenoids, dripping under gravity, merging of droplets, as well as bubble rupture.

Edge Race-Tracking during Film-Sealed Compression Resin Transfer Molding

Edge race-tracking is a frequently reported issue during resin transfer molding. It is caused by highly permeable channels and areas between the preform edge and cavity, which can significantly change the preform impregnation pattern. To date, information is scarce on the effect of edge race-tracking in compression resin transfer molding (CRTM). To close this gap, laboratory equipment was developed to study the CRTM preform impregnation via flow visualization experiments. The preform was thereby encapsulated in thin thermoplastic films sealing its impregnation. Film-sealed compression resin transfer molding (FS-CRTM) experiments of preforms with a small geometrical aspect ratio showed fast filling of the injection gap and a subsequent through-thickness preform impregnation. Creating an edge race-tracking channel, an additional lateral in-plane flow from the channel towards the preform center was observed, initiating soon after the injection started and caused by the spatial connection between the injection gap and the race-tracking channel. To diminish edge race-tracking, a passive flow control strategy was implemented via a split design of the upper tool to spatially isolate the injection gap from the channel and to pre-compact the preform edge. A delayed and reduced lateral race-tracking flow was observed, showing that the passive flow control strategy increases the process robustness of FS-CRTM regarding edge race-tracking effects.

Thin-film smoothed particle hydrodynamics fluid

We propose a particle-based method to simulate thin-film fluid that jointly facilitates aggressive surface deformation and vigorous tangential flows. We build our dynamics model from the surface tension driven Navier-Stokes equation with the dimensionality reduced using the asymptotic lubrication theory and customize a set of differential operators based on the weakly compressible Smoothed Particle Hydrodynamics (SPH) for evolving pointset surfaces. The key insight is that the compressible nature of SPH, which is unfavorable in its typical usage, is helpful in our application to co-evolve the thickness, calculate the surface tension, and enforce the fluid incompressibility on a thin film. In this way, we are able to two-way couple the surface deformation with the in-plane flows in a physically based manner. We can simulate complex vortical swirls, fingering effects due to Rayleigh-Taylor instability, capillary waves, Newton's interference fringes, and the Marangoni effect on liberally deforming surfaces by presenting both realistic visual results and numerical validations. The particle-based nature of our system also enables it to conveniently handle topology changes and codimension transitions, allowing us to marry the thin-film simulation with a wide gamut of 3D phenomena, such as pinch-off of unstable catenoids, dripping under gravity, merging of droplets, as well as bubble rupture.

Aortic rotational flow patterns and stiffness by 4D flow CMR in patients with Loeys-Dietz syndrome compared to healthy volunteers and patients with Marfan syndrome

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): La Marató de TV3, Instituto de Salud Carlos III through the project and Spanish Ministry of Science, Innovation and Universities. BACKGROUND Loeys-Dietz (LDS) and Marfan (MFS) syndromes are rare genetic connective tissue disorders associated with progressive aortic dilation, however, aortic dissections have been observed at lower aortic root diameters in LDS than in MFS. Recent CMR studies in MFS patients reported increased aortic stiffness (1–3) and altered rotational flow (4), but research on aortic flow dynamics and biomechanics in LDS is lacking. PURPOSE The aim of this study was to assess rotational aortic flow and aortic stiffness in LDS compared to healthy volunteers (HV) and MFS patients, using 4Dflow CMR. METHODS Twenty-one LDS and 44 MFS patients, without previous aortic dissection or surgery, and 43 HV underwent a non-contrast-enhanced 4D flow CMR. Aortic stiffness was quantified at the AAo and DAo using pulse wave velocity (PWV). In-plane rotational flow (IRF), systolic flow reversal ratio (SFRR) (5) and local aortic diameters were obtained at 20 equidistant planes from the ascending (AAo) to the proximal descending aorta (DAo). RESULTS LDS patients had lower IRF at the distal AAo and proximal DAo compared to HV (p = 0.053 and 0.004, respectively), once adjusted for age, stroke volume and local aortic diameter; but no differences were found with respect to MFS (Figure). Although SFRR at the proximal DAo was increased in LDS patients compared to both HV (p = 0.037) and MFS populations (p = 0.015), once adjusted for age and aortic diameter, the difference in magnitude was small (Figure). On the other hand, AAo and DAo PWV revealed stiffer aortas in LDS patients compared to HV but no differences versus MFS patients (Table). CONCLUSIONS Patients with Loeys-Dietz syndrome showed decreased in-plane rotational flow and abnormally-high regional aortic stiffness compared to healthy controls, and similar hemodynamics and aortic stiffness with respect to patients with Marfan syndrome.

Effect of in-plane shear flow on the magnetic island coalescence instability

Using a 2D Viscoresistive Reduced MagnetoHydroDynamic model, the magnetic island coalescence problem is studied in the presence of in-plane, parallel shear flows. Extending the analytical work of Waelbroeck et al. [Phys. Plasmas 14, 022302 (2007)] and Throumoulopoulos et al., [J. Phys. A 42, 335501 (2009)] in the sub-Alfvénic flow shear regime for Fadeev equilibrium, the super-Alfvénic regime is studied for the first time numerically. A wide range of values of shear flow amplitudes and shear scale lengths have been considered to understand the effect of sub-Alfvénic and super-Alfvénic flows on the coalescence instability and its nonlinear fate. We find that for flow shear length scales greater than the magnetic island size, the maximum reconnection rate decreases monotonically from sub-Alfvénic to super-Alfvénic flow speeds. For scale lengths smaller than the island size, the reconnection rate decreases up to a critical value v0c, beyond which the shear flow is found to destabilize the islands. The value of v0c decreases with a decrease in the value of shear flow length scale. Interestingly, for our range of parameters, we find suppression of the Kelvin–Helmholtz instability in super-Alfvénic flows even when the shear scale length is smaller than the island width. Observation of velocity streamlines shows that the plasma circulation inside the islands has a stabilizing influence in strong shear flow cases. Plasma circulation is also found to be responsible for the decrease in upstream velocity, causing less pileup of magnetic flux on both sides of the reconnection sheet.

Aortic flow dynamics and stiffness in Loeys-Dietz syndrome patients: a comparison with healthy volunteers and Marfan syndrome patients.

To assess aortic flow and stiffness in patients with Loeys-Dietz syndrome (LDS) by 4D flow and cine cardiovascular magnetic resonance (CMR) and compare the results with those of healthy volunteers (HV) and Marfan syndrome (MFS) patients. Twenty-one LDS and 44 MFS patients with no previous aortic dissection or surgery and 35 HV underwent non-contrast-enhanced 4D flow CMR. In-plane rotational flow (IRF), systolic flow reversal ratio (SFRR), and aortic diameters were obtained at 20 planes from the ascending (AAo) to the proximal descending aorta (DAo). IRF and SFRR were also quantified for aortic regions (proximal and distal AAo, arch and proximal DAo). Peak-systolic wall shear stress (WSS) maps were also estimated. Aortic stiffness was quantified using pulse wave velocity (PWV) and proximal AAo longitudinal strain. Compared to HV, LDS patients had lower rotational flow at the distal AAo (P = 0.002), arch (P = 0.002), and proximal DAo (P < 0.001) even after adjustment for age, stroke volume, and local diameter. LDS patients had higher SFRR in the proximal DAo compared to both HV (P = 0.024) and MFS patients (P = 0.015), even after adjustment for age and local diameter. Axial and circumferential WSS in LDS patients were lower than in HV. AAo circumferential WSS was lower in LDS compared to MFS patients. AAo and DAo PWV and proximal AAo longitudinal strain revealed stiffer aortas in LDS patients compared to HV (P = 0.007, 0.005, and 0.029, respectively) but no differences vs. MFS patients. Greater aortic stiffness as well as impaired IRF and WSS were present in LDS patients compared to HV. Conversely, similar aortic stiffness and overlapping aortic flow features were found in Loeys-Dietz and Marfan patients.

Ultrasonic Removal of Clogging and Evaluation of Flow Capacity of Geotextile Drain

Clogging of geotextile drains is very common when used in fine-grained soil geo-structure such as reinforced earth retaining wall, slopes, embankments. As on date the index properties of the embedded drains are usually standardized with respect to factory-defined parameters. This paper explains the application of ultrasonic excitation for the removal of clogging of geotextiles drains extracted from two fine-grained soils, Kanto Loam, a naturally occurring soil in Japan and a commercially available clayey silt, whose drainage capacity was tested with consolidation from slurry stage. The mechanism of ultrasound for the cleaning of clogging as well as various other similar industrial applications has been explained. The amounts fine-grained soil entrapped within geotextile pores, before and after cleansing in an ultrasonic water tub was evaluated. Several terms, such as clogging index, clogging potential, cleansing efficiency, have been explained and evaluated based on the experimental data. The in-plane and cross-plane flows of clogged geotextile drains, both before and after ultrasonic cleaning, showed that cleansing efficiency was greater than 80%, which were irrespective of the type of geotextile selected and the nature of clogging by both fine-grained soils. Compared to the clogged geotextile specimens’ transmissivity and permittivity recovered nearly to 75% and above after ultrasonic cleaning. The importance of geotextile drains under confinement and in situ removal of its clogging by ultrasonics is elaborated.