Flow Stagnation Research Articles

Dolichoectasia: a brain arterial disease with an elusive treatment

Dolichoectasia is a form of brain large artery disease associated with a high risk of mortality and morbidity. Progressive enlargement of arterial size is a predictor of mortality, but there are no specific treatments for arresting or slowing down dilatation. Additionally, dilated brain arteries can cause flow stagnation, which can trigger thrombosis and cause stroke. Pathology and genetic studies indicate a possible role for increased matrix metalloproteinase activation in arterial dilatation and thus in the pathophysiology of dolichoectasia. Therefore, therapeutic interventions aimed at slowing down arterial dilatation and preventing thrombosis could hypothetically play a role in treating patients with dolichoectasia. We present four patients with dolichoectasia that exemplify therapeutic challenges worth discussing in the context of the current literature. Two patients were treated off-label with doxycycline (based on its antiMMP properties) and with apixaban, one patient was put on warfarin and later switched to aspirin, and the fourth patient underwent endovascular treatment. We report four cases, all men 50years or older. Of the two patients treated with doxycycline, we noted a slowdown of the basilar artery (BA) growth, but the BA continued to grow in the other patient. Of the two patients who received apixaban, none had a subsequent stroke in 5 and 4years of follow-up, respectively. One patient was admitted with a fatal BA thrombosis and rupture, and pathological examination of the brain arteries demonstrated advanced arterial wall degeneration but no atherosclerosis. These cases exemplify the challenges of treating people with dolichoectasia and highlight the need for better evidence regarding the best possible treatment for this population.

Characterising Single and Two-Phase Homogeneous Isotropic Turbulence with Stagnation Points

It has been shown that, for dense, sub-Kolmogorov particles advected in a turbulent flow, carrier phase properties can be reconstructed from the particles’ velocity field. For that, the instantaneous particles’ velocity field can be used to detect the stagnation points of the carrier phase. The Rice theorem can therefore be used, implying that the Taylor length is proportional to the mean distance between such stagnation points. As this model has been only tested for one-dimensional time signals, this work discusses if it can be applied to two-phase, three-dimensional flows. We use direct numerical simulations with turbulent Reynolds numbers Reλ between 40 and 520 and study particle-laden flows with a Stokes number of St=0.5. We confirm that for the carrier phase, the Taylor length is proportional to the mean distance between stagnation points with a proportionality coefficient that depends weakly on Reλ. Then, we propose an interpolation scheme to reconstruct the stagnation points of the particles’ velocity field. The results indicate that the Rice theorem cannot be applied in practice to two-phase three-dimensional turbulent flows, as the clustering of stagnation points forms very dense structures that require a very large number of particles to accurately sample the flow stagnation points.

JMEMS Letters Fabrication of Self-Sealed Circular Microfluidic Channels in Glass by Thermal Blowing Method

We report fabrication of circular glass microchannels with radius less than 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> using the glass blowing technique. Silicon trenches filled with nitrogen are used for microchannel fabrication. We report an interesting reflow regime where the flowing glass fills the silicon trenches to form a completely circular microchannel. Circular microchannels have symmetric velocity profile and do not suffer from flow stagnation problems observed in rectangular channels. Besides circular shape, fabrication conditions of the semi-circular and elliptically shaped channels are also discussed. A mathematical model explaining the observation is also presented and is compared with the experimental results. [2021-0183]

Frequency of left ventricular thrombi after acute ST-Segment elevation myocardial infarction.

Objective: To determine the frequency of left ventricular thrombi after acute ST-Segment elevation myocardial infarction. Study Design: Case Series study. Setting: Cardiology Department, Lady Reading Hospital, Peshawar. Period: July 2018 to December 2018. Material &amp; Methods: Patients were included in study were of both gender having age 30-65 year admitted with acute STEMI (under the treatment of ST-Segment elevation myocardial infarction). Routine examination like ECG (cardiofax) and transthoracic echocardiography (Siemens’ Accuson CV-70) was done for all the patients who are already admitted and having treatment of acute ST-Segment elevation myocardial infarction. Left ventricular thrombus was measure on the basis of not contracting with systole, Wall motion near the structure is abnormal, color flow Doppler differentiates from stagnant flow after 2 weeks follow up. Any patients who lost to follow up were excluded from the study. Results: In this study a total of 120 patients were observed. The mean age was 48 years with standard deviation ± 11.45. Sixty two percent patients were male while 38% patients were female. More over 7% patients had Left ventricular thrombi while 93% patients didn’t had Left ventricular thrombi. Conclusion: Our study concludes that the frequency of left ventricular thrombi was 7% after acute ST-Segment elevation myocardial infarction.

Effect of Interference Between Twin Tall Buildings with Recessed Corners on Wind-Induced Pressure

This paper investigates the results of wind tunnel model testing on pressure distribution and proximity effects between twin tall buildings with large recessed corners in an open circuit boundary layer wind tunnel. Experiments were carried out for isolated and for full, half and no blockage interference conditions. Three interference conditions were created by placing the building of identical shape and size at different locations on the windward side of the principal building under consideration. Based on the experimental results, mean and Root Mean Square (RMS) wind pressure coefficients and interference factors are presented and discussed for all cases. Mean wind pressure coefficients and interference factors at all faces of the building model are plotted in the form of contours and also plotted along the height of the building at all faces. Pressure coefficients and interference factors for three interference conditions are also compared with the results of isolated condition to bestow comprehensive evaluation of the effects of the interference on changing of wind loads. Results show that pressure coefficients variation greatly depends on the position of the interfering building. Oblique configuration produces more severe interference effects on windward surfaces. The re-entrant corners present in the model also affect the pressure distribution because of flow stagnation in these corners. The interference effects in no blockage condition are significant and unfavorable at windward faces near recessed corners towards the interfering building, where the mean interference factor of more than 13 is observed.

Morphing the left atrium geometry: A deeper insight into blood stasis within the left atrial appendage

Background: The left atrium appendage (LAA) is a protruding cavity located in the left atrium (LA), which is known to be associated with flow stagnation. This phenomenon, which occurs primarily during atrial fibrillation (AF) episodes, is highly suspected to cause thrombosis in the LAA and has been clinically associated with the incidence of systemic embolism and ischemic stroke. Although clinical studies have suggested a relationship between with the risk of stroke in AF patients due to blood stasis and atrial geometric parameters, such as the LAA volume, LAA ostium area or pulmonary vein (PV) orientations, the underlying mechanism is not yet fully understood. Reaching a consensus would be essential for updating clinical protocols and assessing risk quantification of AF patients. Aim: A novel method to physiologically parameterise the LA starting from a patient-specific atrial geometry, instead of working with a synthetic and idealized geometry. This method would make it possible to perform a parametric and extensive analysis of the different parameters that are known to affect left atrium appendage (LAA) stasis in the absence of atrial contraction, and to evaluate and compare their influence on the formation of a dead volume within the LAA. A new method to clearly quantify this dead volume and, thus, the blood stasis in the LAA is proposed, based on the fourth moment of the blood age probability distribution (M4). Methods: The atrial geometry of a cardiac patient has been segmented. The resulting geometry has been rigged and parameterised, providing it with an armature, which had been employed to apply plausible variations of geometrical and flow parameters, such as pulmonary vein (PV) orientation, LAA ostium area, LAA volume and cardiac output. Results: The findings of this study illustrate and quantify the influence of different geometric and flow parameters on the LAA stasis in the absence of atrial contraction due to fibrillation and thus could have future clinical implications for improving thrombosis risk medium and long-term prediction. Moreover, the herein proposed method to quantify the LAA dead volume employing the M4 index has proven to be an effective way of marking the volume in which stagnation occurs and detecting a fluid dynamic behaviour independent from the rest of the LAA.

Analysis of Postulated Accident Scenarios for the Transformational Challenge Reactor

The Transformational Challenge Reactor (TCR) is a helium-cooled, yttrium-hydride-moderated reactor that was designed for the U.S. Department of Energy Office of Nuclear Energy. A key objective of the TCR was to employ advanced manufacturing techniques in a nuclear system and demonstrate their potential for revolutionizing the nuclear reactor design process. One purpose of the present work is to demonstrate the safety of the TCR under postulated accidents. Based on RELAP5-3D and COMSOL analyses, the TCR remained below all current safety limits and far below the expected failure limits for the core materials. Another purpose of this work is to provide useful insights and recommendations regarding the application of RELAP5-3D to gas-cooled or other advanced reactors. A novel approach was implemented for simultaneously modeling conduction and radiation in RELAP5-3D, which was found to provide reasonable predictions of radial core, vessel, and ex-vessel heat transfer during postulated events. A multicode approach was also applied, in which high-fidelity COMSOL calculations were used to tune the radial heat transfer parameters in RELAP5-3D. The tuned RELAP5-3D model demonstrated comparable peak temperature predictions as COMSOL, despite a coarse treatment of the core in RELAP5-3D consisting of only two lumped heat structures. This high-fidelity tuning approach enabled enhanced accuracy as well as minimal complexity within the RELAP5-3D model, even for complex fuel geometric designs as in the TCR. Finally, investigations were made into the potential for flow reversal during a pressurized loss-of-forced-flow event in the TCR. The TCR is designed with downward helium flow through the core during normal operation. The RELAP5-3D model predicted that this downward flow would persist, without flow reversal, up to several days after the circulator trip. This was attributed to natural circulation hysteresis effects as have been noted in similar thermofluidic systems. Although flow stagnation and eventual reversal did not lead to unsafe TCR conditions, interesting spatial effects were observed which may have safety relevance for other reactor system designs and coolant types that are designed for downward core flow during normal operation, warranting closer investigation of the flow reversal phenomenon.

Joint Analysis of Morphological Parameters and In Silico Haemodynamics of the Left Atrial Appendage for Thrombogenic Risk Assessment

Background Atrial fibrillation (AF) is considered the most common human arrhythmia. In nonvalvular AF, around 99% of thrombi are formed in the left atrial appendage (LAA). Nevertheless, there is not a consensus in the community about the relevant factors to stratify the AF population according to thrombogenic risk. Objective To demonstrate the need for combining left atrial morphological and haemodynamics indices to improve the thrombogenic risk assessment in nonvalvular AF patients. Methods A cohort of 71 nonvalvular AF patients was analysed. Statistical analysis, regression models, and random forests were used to analyse the differences between morphological and haemodynamics parameters, extracted from computational simulations built on 3D rotational angiography images, between patients with and without transient ischemic attack (TIA) or cerebrovascular accident (CVA). Results The analysis showed that models composed of both morphological and haemodynamic factors were better predictors of TIA/CVA compared with models based on either morphological or haemodynamic factors separately. Maximum ostium diameter, length of the centreline, blood flow velocity within the LAA, oscillatory shear index, and time average wall shear stress parameters were found to be key risk factors for TIA/CVA prediction. In addition, TIA/CVA patients presented more flow stagnation within the LAA. Conclusion Thrombus formation in the LAA is the result of multiple factors. Analyses based only on morphological or haemodynamic parameters are not precise enough to predict such a phenomenon, as demonstrated in our results; a better patient stratification can be obtained by jointly analysing morphological and haemodynamic features.

Nonequilibrium shock layer in large-scale arc-heated wind tunnel

An arc-heated wind tunnel is one of the most important facilities to reproduce the high-temperature environment during atmospheric entry for plasma studies and spacecraft development. However, the properties of the plasma flow cannot be determined easily, because of the complex physical phenomena, such as arc discharge and supersonic expansion, occurring inside the tunnel. The shock-layer structure should be clarified to evaluate the aerodynamic characteristics, communication conditions, and thermal-protection performance in a high-temperature environment. In this study, shock-layer spectroscopic measurements of a plasma flow in a 1 MW-class arc-heated wind tunnel were performed. The γ-band system spectra of nitric oxide () molecules in the ultraviolet region were measured, and the rotational temperature was determined via spectral fitting through comparison with numerical spectra. The rotational temperature of the molecules in the shock layer was 6620 ± 350 K, whereas that in the free jet was much lower at 770 ± 60 K. This difference is attributed to the increase in translational temperature by flow stagnation across the shock wave, followed by the increase in rotational temperature owing to energy relaxation. A computational science approach revealed the detailed structure of the flow through comparisons with the spectroscopic measurement data. The wind tunnel flow became hypersonic with high temperature and low pressure due to the expansion and acceleration at the nozzle and test chamber. Although the temperature increased across the shock wave, the chemical reaction progressed slowly owing to the low-pressure environment. The rotational temperature in the shock layer increased with the translational temperature; this agrees with the trend of the measurement results. The arc-heated flow was found to be in strong thermochemical nonequilibrium in the shock layer. Through this study, a detailed structure of arc-heated flow was revealed and its methodology was also proposed.

Measurement and determination of local film cooling performance along a transonic turbine blade tip with viscous dissipation

Presented are experimental and analytic procedures for the measurement and determination of film cooling performance parameters for a transonic flow environment along a turbine blade tip, which account for the influences of viscous dissipation. Such viscous dissipation magnitudes are vital to ascertain appropriate driving temperatures for convective heat transfer within high velocity, compressible environments. A key step in this procedure is the separation of adiabatic surface temperature magnitudes due to the thermal field from adiabatic surface temperature values associated with flow effects related to viscous dissipation. These latter adiabatic surface temperature magnitudes, from flow effects only, are determined with no film cooling, which, when considered relative to flow stagnation temperature, are directly related to local Mach number values within the tip gap flow along the blade tip surface. After the separation is implemented, adiabatic surface temperature variations from film cooling thermal effects only are provided relative to local baseline values with no film cooling. Resulting local adiabatic film cooling effectiveness and local heat transfer coefficients are subsequently determined which are based entirely upon locally measured temperatures (without the use of global temperature parameters), which is the most appropriate perspective for presentation of spatially-resolved surface heat transfer characteristics. Associated data are provided for the surface of a blade tip with a squealer rim and recess, with and without film cooling. An array of five film cooling holes, located along the upper pressure side of a two-dimensional turbine blade, are employed to provide the film coolant, with a local blowing ratio BR of 3.02. Ratios of tip gap to true blade span are 0.66%, and 1.16%. Experimental procedures employed to obtain the spatially-resolved surface data include infrared thermography, transient testing techniques, and the impulse response method for transient data analysis.

Contrast Agent-Free Assessment of Blood Flow and Wall Shear Stress in the Rabbit Aorta using Ultrasound Image Velocimetry.

Blood flow velocity and wall shear stress (WSS) influence and are influenced by vascular disease. Their measurement is consequently useful in the laboratory and clinic. Contrast-enhanced ultrasound image velocimetry (UIV) can estimate them accurately but the need to inject contrast agents limits utility. Singular value decomposition and high-frame-rate imaging may render contrast agents dispensable. Here we determined whether contrast agent-free UIV can measure flow and WSS. In simulation, accurate measurements were achieved with a signal-to-noise ratio of 13.5 dB or higher. Signal intensity in the rabbit aorta increased monotonically with mechanical index; it was lowest during stagnant flow and uneven across the vessel. In vivo measurements with contrast-free and contrast-enhanced UIV differed by 4.4% and 1.9% for velocity magnitude and angle and by 9.47% for WSS. Bland–Altman analysis of waveforms revealed good agreement between contrast-free and contrast-enhanced UIV. In five rabbits, the root-mean-square errors were as low as 0.022 m/s (0.81%) and 0.11 Pa (1.7%). This study indicates that with an optimised protocol, UIV can assess flow and WSS without contrast agents. Unlike contrast-enhanced UIV, contrast-free UIV could be routinely employed.

Experimental and computational study of pulsatile flow characteristics in Romanesque and gothic aortic arch models

Romanesque and Gothic are two types of deformed aortic arch geometries after surgical repair of coarctation of the aorta. The abnormal arch geometry and hemodynamics are associated with late systemic hypertension, aortic aneurysms, and other cardiovascular complications. To understand the fluid dynamic signatures of such flow, a combined experimental and computational fluid dynamic (CFD) study has been conducted to quantitatively compare the main (axial) and secondary flow characteristics. In the experiments, a pulsatile flow simulator was used to generate the pulsatile flow conditions. Phase-locked planar and tomographic particle image velocimetry techniques were employed to quantitatively study the flow fields. Three-dimensional CFD simulations were also performed and compared with the experimental data. The results show that in the Romanesque arch, the flow first accelerates along the inner wall and then becomes more uniform in the cross-section after the peak systole. A pair of wall vortices and Dean-type vortices develop during the systolic phase. The coherent structures are continuously extended into the descending aorta and persist throughout the cycle. In comparison, the Gothic arch exhibits a highly skewed velocity distribution with high velocity around the arch apex. The sharp curvature causes flow separation, jet impingement, and stagnant flow near the top. The coherent structures in the Gothic arch are less continuous in the descending aorta, which also differ from those observed in the Romanesque model. The distinct flow characteristics of the Gothic arch lead to more temporal and spatial variations of wall shear stress in the descending aorta, implying hemodynamic risks for aortic complications.

Impact of Postthrombotic Vein Wall Biomechanics on Luminal Flow during Venous Angioplasty and Stent Placement: Computational Modeling Results

This study characterized the impact of vein wall biomechanics on inflow diameter and luminal flow during venous angioplasty and stent placement, using postthrombotic and healthy biomechanical properties from an ovine venous stenosis and thrombosis model. Finite element analysis demonstrated more pronounced inflow channel narrowing in the postthrombotic vein compared with the healthy control vein during angioplasty and stent placement (relative inflow diameter reduction of 42% versus 13%, P < .0001). Computational fluid dynamics modeling showed increased relative areas of low wall shear rate in the postthrombotic vein compared with the normal vein (0.46 vs 0.24 for shear rate < 50 s−1; 0.13 vs 0.07 for shear rate < 15 s−1; P < .05), with flow stagnation and recirculation. Since inflow narrowing and low wall shear rate are associated with in-stent restenosis and reintervention, these computational results based on experimentally obtained biomechanical values highlight the significance of postthrombotic venous properties in optimizing venous intervention outcomes.

Second law analysis of aerodynamic characteristics with flow temperature variations of simple angle and compound angle full coverage film cooling

The present investigation employs entropy generation to quantify aerodynamic characteristics with flow temperature variations, and the associated second law losses, which are present within a film cooled boundary layer produced by a unique full-coverage compound angle hole configuration. With this arrangement, an alternating sign for the compound angle β is employed from one streamwise row of holes to another, such that compound angle β is +30° in one row of holes, followed by −30° in the next row of holes. Entropy change distributions, entropy generation distributions, and mass-averaged overall exergy destruction from this compound angle arrangement are compared to results from a simple angle arrangement with β = 0°. These quantities are determined from flow field measurements of local flow temperature variations, and local stagnation pressure variations with film cooling. Within the investigation, full-coverage film cooling blowing ratio values range from 2.9 to 6.0, mainstream Reynolds numbers Rems range from 127,000 to 142,000, and effusion flow Reynolds numbers range from about 7000 to approximately 13,000. Distributions of local entropy generation and mass-averaged overall exergy destruction (both relative to freestream flow) are determined using three analysis approaches, which account for local flow temperature variations only, local flow stagnation pressure variations only, and variations of stagnation pressure and local flow temperature together. Similar qualitative trends of local entropy generation for the three different types of data are observed, which mean that temperature and stagnation pressure within the flow experience similar rearrangements by secondary advection and diffusion phenomena for the two film cooling arrangements. From a quantitative perspective, values associated with flow temperature variations only, are consistently larger than values associated with stagnation pressure variations only. Important local variations of local entropy generation are observed for the compound angle arrangement, which are due to skewed and non-symmetric film distributions, along with the associated tilted horseshoe-shaped vortex, which forms around each film coolant concentration.

Role of Three-Dimensional Swirl in Forced Convection Heat Transfer Enhancement in Wavy-Plate-Fin Channels

Abstract The influence of wall-corrugation-induced swirl flow on enhanced forced convection in wavy-plate-fin cores has been investigated. Three-dimensional computational simulations were carried out for steady-state periodically developed air flow (Pr ∼ 0.71; 50 ≤ Re ≤ 4000) with channel walls subject to constant-uniform temperature conditions. The recirculation that develops in the wall troughs and grows to have an axially helical character is scaled by the Swirl number Sw. As Sw increases with higher flowrate and/or corrugation severity, tornado-shaped vortices appear in the wave trough region midway of the interfin channel height, then extend longitudinally to encompass majority of the flow channel. The local wall-shear and heat transfer coefficient variations indicate that boundary-layer thinning upstream of the wave peak aids in intensifying momentum and heat transfer. However, the flow recirculation in wall trough impedes heat transfer at low Sw due to flow stagnation but promotes it at high Sw because of the vortices-induced augmented fluid mixing. The effects of this secondary flow are quantified by Φf(or j), which is seen to increase log-linearly as fin corrugation aspect ratio γ and/or fin spacing ratio ζ increases; the influence of cross section aspect ratio α is marginal. Moreover, the pressure drag penalty due to swirl critically affects overall pressure loss, and its proportion remains nearly constant when α varies, but grows as Sw, γ, and/or ζ increases and can be as much as 80% of the total pressure drop.

Measurement and determination of local film cooling performance along a transonic turbine blade tip with viscous dissipation

Abstract Presented are experimental and analytic procedures for the measurement and determination of film cooling performance parameters for a transonic flow environment along a turbine blade tip, which account for the influences of viscous dissipation. Such viscous dissipation magnitudes are vital to ascertain appropriate driving temperatures for convective heat transfer within high velocity, compressible environments. A key step in this procedure is the separation of adiabatic surface temperature magnitudes due to the thermal field from adiabatic surface temperature values associated with flow effects related to viscous dissipation. These latter adiabatic surface temperature magnitudes, from flow effects only, are determined with no film cooling, which, when considered relative to flow stagnation temperature, are directly related to local Mach number values within the tip gap flow along the blade tip surface. After the separation is implemented, adiabatic surface temperature variations from film cooling thermal effects only are provided relative to local baseline values with no film cooling. Resulting local adiabatic film cooling effectiveness and local heat transfer coefficients are subsequently determined which are based entirely upon locally measured temperatures (without the use of global temperature parameters), which is the most appropriate perspective for presentation of spatially-resolved surface heat transfer characteristics. Associated data are provided for the surface of a blade tip with a squealer rim and recess, with and without film cooling. An array of five film cooling holes, located along the upper pressure side of a two-dimensional turbine blade, are employed to provide the film coolant, with a local blowing ratio BR of 3.02. Ratios of tip gap to true blade span are 0.66 percent, and 1.16 percent. Experimental procedures employed to obtain the spatially-resolved surface data include infrared thermography, transient testing techniques, and the impulse response method for transient data analysis.

Feasibility of blood speckle imaging parameters as predictors of intracavitary thrombus in apical aneurysm

Abstract Funding Acknowledgements Type of funding sources: None. Introduction In patients with apical aneurysm, left ventricular thrombus (LVT) is a major complication associated with systemic embolism. Likely, abnormalities in apical wall contraction produce stagnant flow which leads to the thrombus formation. Currently, there is a lack of knowledge about predictors of thrombus in such patients. However, new imaging techniques might be able to identify flow properties useful for risk stratification. Specifically, blood speckle imaging (BSI), a technology based on high-frame rate ultrasound, is a promising pattern-matching technique that could allow a comprehensive assessment of blood flow in patients with apical aneurysms (1,2). Purpose The aim of the study was to demonstrate the feasibility of obtaining quantitative and qualitative measurements with BSI in patients with apical aneurysms and to explore which parameters may be associated with LVT. Methods We examined cases of patients with apical aneurysm and LVT studied in our tertiary center. In order to exclude from our analysis the pro-inflammatory effects of the acute event, patients with thrombus formation within the first month after the ischemic event were excluded. Patients with current presence of thrombus were also discarded. A control group of patients with apical aneurysm but without history of LVT was included. A basic 2-dimensional echocardiography study was obtained, along with BSI images. BSI acquisitions were performed with a 29 cm/s (2.5 mHz) scale. Data regarding vortex flow were collected, including its presence, area, length, besides area without BSI vectors (Image 1). All measures were indexed by telediastolic left ventricular volume. Results Eight patients with apical aneurysms were enrolled in the study, four of them with history of LVT. Although in patients with history of thrombus a larger vortex area was found (Table 1), none of the differences in the BSI parameters was statistically significant. Conclusion This study shows for the first time the feasibility of BSI for characterizing complex flow patterns such as vortex in patients with apical aneurysms. Explorations in larger cohorts of patients are needed to prove significant findings with this technology in the future. Abstract Figure. Image 1 Abstract TABLE 1

Adenoviral vector-based COVID-19 vaccines-associated cerebral venous sinus thromboses: Are those adverse events related to the formation of neutrophil extracellular traps?

In March and April 2021 several countries temporarily suspended vaccinations with adenoviral vector-based COVID-19 vaccines. Concerns of national regulators particularly regarded very rare cases of cerebral venous sinus thrombosis after immunization with this type of vaccine. Until now, these adverse events were interpreted as standard hypercoagulable events, but their clinical characteristics suggest that they may actually represent unique thrombotic disorders referred to as immunothrombosis. In this paper it is speculated that it is possible that immunothrombosis after this type of vaccine results from formation of neutrophil extracellular traps (NETs) in veins affected by stagnant blood flow. Such a stasis occurs in individuals with anatomical variants of cerebral venous outflow, which may explain why these events are primarily seen in the cerebral veins. It has already been found that SARS-CoV-2 spike protein can evoke release of NETs. There is also a question if thrombotic events after adenoviral vector-based COVID-19 vaccines could be avoided. These vaccines will still be needed to curb COVID-19 worldwide, since they do not require transportation and storage at very low temperatures. Perhaps, vaccinations with these vaccines should be performed in combination with prophylactic administration of dipyridamole, which is an inexpensive pharmaceutical agent reducing the release of NETs.

Fog Harvesting with Highly Wetting and Nonwetting Vertical Strips.

Highly wetting and nonwetting substrates have been widely used in fogwater collection systems for enhanced water harvesting. In this work, fog harvesting substrates comprising PVC strips of different wetting properties and widths ranging from 1-5 mm were vertically aligned and spaced apart at regular intervals to give the same solid area fraction of 0.8. Evaluation of the water collection efficiencies of the tested configurations revealed that 1 mm wide superhydrophilic strips was the most efficient, achieving double the amount of water harvested compared with 2.8 mm wide strips. This finding was attributed to the low Stokes numbers of the aerosol particle distribution of the fog which tended to result in them being brought by the flow streamlines toward the air gaps between the strips. Stagnant flow regions at the edges of each strip, revealed through potential flow calculations, then caused higher liquid imbibition and impaction there for water harvesting. It was also found that the Cassie nonwetting substrates that originally exhibited contact angles of 161° transformed to Wenzel wetting with zero contact angle within 60 min of fog interception. Optical profilometry revealed no obvious difference in surface roughness between the central region and edges of the strips, indicating that surface morphology was unlikely to be a contributing factor for enhanced water collection at the edges. The findings here indicated that highly wetting vertical strip architectures with narrow widths (1 mm) were favorable over wider strips for water harvesting provided that clogging and re-entrainment were not significant factors.

Depinning of Multiphase Fluid Using Light and Photo-Responsive Surfactants.

The development of noninvasive and robust strategies for manipulation of droplets and bubbles is crucial in applications such as boiling and condensation, electrocatalysis, and microfluidics. In this work, we realize the swift departure of droplets and bubbles from solid substrates by introducing photoresponsive surfactants and applying asymmetric illumination, thereby inducing a “photo-Marangoni” lift force. Experiments show that a pinned toluene droplet can depart the substrate in only 0.38 s upon illumination, and the volume of an air bubble at departure is reduced by 20%, indicating significantly faster departure. These benefits can be achieved with moderate light intensities and dilute surfactant concentrations, without specially fabricated substrates, which greatly facilitates practical applications. Simulations suggest that the net departure force includes contributions from viscous stresses directly caused by the Marangoni flow, as well as from pressure buildup due to flow stagnation at the contact line. The manipulation scheme proposed here shows potential for applications requiring droplet and bubble removal from working surfaces.