Strong Collapse Research Articles

The effects of dynamic factors inside the bubble on sono-hydrogen yield: A numerical study

The formation of H2 by introducing ultrasonic waves to liquid has been widely recognized as a way to provide a clean, efficient, and reliable source of H2, known as Sono-Hydro-Gen. H2 comes from the chemical effects of ultrasonic waves (sonochemistry) caused by the growth and collapse of acoustic cavitation bubbles. In this work, the effects of dynamic parameters (i.e., bubble temperature, the amount of water vapor trapped inside the bubble, and collapse time) in the evolution of cavitation bubbles on H2 production are studied numerically. For an oxygen bubble, computational simulations are performed for the wide range of acoustic amplitudes (1.5–3 atm), ultrasonic frequencies (140–515 kHz), and ambient radii (0.25–20 μm), considering 22 reversible chemical reactions and 10 chemical species inside the bubble. The numerical results show that the amount of water vapor has a significant effect on the bubble collapse temperature. At low excitation amplitudes, the amount of water vapor is not enough to cause the bubble to form a strong collapse. Nevertheless, at high excitation amplitudes, the amount of water vapor is too much to reduce the bubble temperature. There exist optimal values of bubble temperature and amount of water vapor for H2 production. The optimal bubble temperatures are 5267, 4813, 4626, and 3856 K, corresponding to H2 productions of 4.21 × 10−18, 1.29 × 10−18, 2.61 × 10−19, and 8.48 × 10−20 mol, respectively, at ultrasonic frequencies of 140, 213, 355, and 515 kHz. No matter what the excitation parameters are, the optimal water vapor fraction is 0.78 ± 0.04 for H2 production. The obtained results of the present work can provide guidelines for H2 production in acoustic cavitation.

Investigation of engineering characteristics of red sand in Luanda, Angola

Red sand is widely distributed on the west coast of Africa, south of the Sahara, and is an essential material for local engineering construction. Red sand possesses orthostasis and high sensitivity to water, exhibiting characteristics that are different from ordinary sandy soil. Laboratory and in-situ tests were conducted to assess its engineering characteristics, including collapsibility, shear characteristics, and bearing capacity. The water sensitivity of red sand was analyzed along with the images from a scanning electron microscope. The findings indicate that red sand can be classified as silty sand. It demonstrates strong collapsibility, with the collapsibility coefficient decreasing as water content increases. The critical water content for red sand to avoid collapsibility is 13%. The shear strength, internal friction angle, and cohesion of undisturbed and remolded red sand decrease with increasing water content. The critical water content for red sand to lose cohesion is 13%. The bearing capacity and deformation modulus of red sand decrease with increasing water content. Red sand exhibits a softening property, with a softening coefficient of 0.4. The water sensitivity of red sand can be attributed to the cementing effects of fine-grained clay minerals adhering to the surface of large particles or aggregating at particle contacts.

EPIDEMIOLOGICAL PROFILE OF CONFIRMED CASES OF COVID-19 IN THE PERIOD FROM APRIL TO MAY 2020 IN THE STATE OF MARANHÃO

Brazil was the first South American country to report a confirmed case of Coronavirus Disease 2019 (COVID-19), on February 26, 2020, in the state of São Paulo. Maranhão was one of the states in Brazil where the pandemic picked up speed early. Thus, the objective of this study is to report the initial experience regarding the epidemiological and clinical aspects of COVID-19 in the State of Maranhão. This is a cross-sectional study and the data used come from a database provided by the Central Laboratory of the State of Maranhão – LACEN, with the approval of the Research Ethics Committee of the State University of Maranhão according to CAAE: 32171220.0.0000.5087. The initial sample included data from 2,336 individuals, but 646 patients were excluded because they did not contain information about epidemiological data, thus totaling a final sample of 1,690 individuals. For data archiving and statistical analysis, SPSS ® version 25.0 software was used. The final sample consisted of 1690 individuals, of whom 64.9% (n=1098) tested positive for COVID-19, 52.2% (n=882) were women, 82.8% (n=1374) came from the public health sector and 82.3% (n=1400) from the metropolitan region of the state. The highest prevalence of positive cases for COVID-19 was in the state capital, with 86.5% (n=950). It was found that most patients depended directly on the unified health system as a form of priority care, which led to a strong collapse since they were not prepared for the demand arising from the pandemic. Emphasizing the importance of investments in the Unified Health System, as well as the supervision of these resources.

Experimental investigations on the physico-mechanical and microstructural properties of loess reinforced with anionic polyacrylamide

The typical characteristics of loess, such as macropores, weak cementation, and strong collapsibility, can adversely affect the stability of building foundations, transportation infrastructure, and other geotechnical systems. To address this problem, a water-soluble anionic polyacrylamide (APAM) was used to improve the characteristics of loess. A series of multi-scale geotechnical engineering tests, such as sedimentation column, zeta potential, Atterberg limits, standard compaction, permeability, triaxial compression strength, scanning electron microscope (SEM), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) tests were conducted on the loess samples. The results showed that the APAM polymer could flocculate fine loess particles into stable agglomerates via a series of physical actions, including charge neutralization, adsorption and bridging, and hydrophobic interactions. The contact form among the loess particles changed from loose point contact to strong mosaic contact with the addition of the APAM polymer, the surface porosity, fractal dimension, and interplanar spacing of the treatment material decreased significantly. The considerable improvement of loess microstructure affected its macroscopic physical and mechanical properties. The optimum moisture content and permeability coefficient of the treated loess decreased with the increases of the APAM content, whereas the plasticity index and maximum dry density increased. Additionally, the failure strength of the loess samples first increased then decreased as the APAM content increased, which showed the maximum value at an addition amount of 0.30% content, beyond which its strength value decreased. The test results demonstrated that the APAM polymer treatment could provide significant improvement in the macroscopic physico-mechanical and microstructural properties of loess. This study will serve as a crucial resource for loess foundation stabilization using the environmentally friendly and cost-effective polymer.

The impacts of material acoustic impedance and thickness on single laser-induced bubble dynamics and determining factors in resulting pressure

The objective of this paper is to experimentally identify the primary sources of pressure when a laser-induced cavitation bubble is collapsing to a wall with specific emphases on the material acoustic impedance and thickness. Both high-speed videos and local wall pressure measurements were performed for various standoff ratios γ, bubble diameters, and wall materials. In the case of a rigid wall, in addition to the known high pressure for γ<0.6 where the bubble attaches and collapses on the wall (ring collapse), at γ≈1.12 where the jet is dominant, and low pressure obtained at γ≈0.913, where neither effect is significant, we further captured similar pressure profiles during the collapse after the first rebound at γ≈1.16 for the ring collapse, γ≈1.79 for the jet, and γ≈1.41 for the minimal, respectively. This indicates a strong jet is typically followed by a strong ring collapse. Generally, the pressure from the second collapse increases faster with the bubble size than that of the first collapse. For walls featuring smaller acoustic impedance or thickness, which cannot be approximated as rigid bodies or accessed by pressure sensor, our unique bubble edge analyzing tool shows that the ring collapse and jet effects are moved to smaller values of γ. The maximum pressure exerted on the wall in these cases is smaller than that on the rigid wall. Finally, we summarized the asymptotic evolution curves of each edge which bound the bubble dynamics at different standoff ratios.

Evaluation of GDI spray structures under flash boiling and strong collapse conditions with diverse fuels

GDI (Gasoline Direct Injection) sprays are a matter of continuous research due to their potential for higher thermal efficiency and power output. Injections in GDI engines tend to happen at relatively high temperatures, which, combined with volatile fuels, are a perfect environment for flashing sprays, which are present in recently developed GDI engine passenger cars. Phenomena like flash boiling and especially spray collapse are still being investigated due to their complexity and impact on the engine performance. In the present research, the impact of different levels of flash boiling in the sprays is analyzed. Four surrogate mono-component fuels were tested with different volatile properties. Two optical techniques were carried out simultaneously: light extinction images (DBI) and frontal MIE scattering. The spray width was used to represent the radial expansion and study its relation with the spray collapse due to flash boiling. The degree of collapse was quantified by means of the instantaneous spray width variation for which three levels of collapse were identified. A novel MIE frontal approach was employed to study the spray surface evolution and the collapsing time by monitoring the nozzle tip clouding (opaquing) by the fuel. Results showed an increment of the width with the ratio of saturation to ambient pressure (Rp), as well as a strong correlation between the spray surface and the Rp at each fuel temperature when the spray is stabilized. Based on the MIE technique, three collapse instants were identified throughout the injection time depending on the Rp.

Accelerated Structural Evolution of Galaxies in a Starbursting Cluster at z = 2.51

Structural properties of cluster galaxies during their peak formation epoch, z ∼ 2–4 provide key information on whether and how the environment affects galaxy formation and evolution. Based on deep Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) imaging toward the z = 2.51 cluster, J1001, we explore environmental effects on the structure, color gradients, and stellar populations of a statistical sample of cluster star-forming galaxies (SFGs). We find that the cluster SFGs are on average smaller than their field counterparts. This difference is most pronounced at the high-mass end (M ⋆ > 1010.5 M ⊙), with nearly all of them lying below the mass–size relation of field galaxies. The high-mass cluster SFGs are also generally old, with a steep negative color gradient, indicating an early formation time likely associated with strong dissipative collapse. For low-mass cluster SFGs, we unveil a population of compact galaxies with steep positive color gradients that are not seen in the field. This suggests that the low-mass compact cluster SFGs may have already experienced strong environmental effects, e.g., tidal/ram pressure stripping, in this young cluster. These results provide evidence on the environmental effects at work in the earliest formed clusters with different roles in the formation of low- and high-mass galaxies.

A Mathematical Model for Non-Linear Structural Analysis Reinforced Beams of Composite Materials

The beams are frequently utilized in construction as well as in the fabrication of vehicles like as trains, ships, and airplanes. Depending on the necessary working circumstances, several materials may have been utilized in the production of these beams, from high fatigue resistance, high corrosion resistance, strong earthquake resistance, and other aspects. As a result, composite beams made of glass or carbon fibers are increasingly commonly employed. This is a result of its strong collapse resistance, light weight, and strong fatigue stress resistance. In order to compare the models' resistance to deformations, stresses, and strains that they are exposed to during loading, this article focuses on constructing a variety of models using a variety of composite materials and shapes. The outcomes demonstrate a rise in the rate of deformation. against beams with linear shapes in those with non-linear shapes. Additionally, the findings demonstrate an increase in stresses and strains in regions with curves (i.e., areas that are nonlinear).

Modeling acoustic emissions and shock formation of cavitation bubbles

Despite significant progress in understanding and foretelling pressure-driven bubble dynamics, models that faithfully predict the emitted acoustic waves and the associated shock formation of oscillating or collapsing bubbles have received comparably little attention. We propose a numerical framework using a Lagrangian wave tracking approach to model the acoustic emissions of pressure-driven bubbles based on the Kirkwood–Bethe hypothesis and under the assumption of spherical symmetry. This modeling approach is agnostic to the equation of the state of the liquid and enables the accurate prediction of pressure and velocity in the vicinity of pressure-driven bubbles, including the formation and attenuation of shock fronts. We validate and test this new numerical framework by comparison with solutions of the full Navier–Stokes equations and by considering a laser-induced cavitation bubble as well as pressure-driven microbubbles in excitation regimes relevant to sonoluminescence and medical ultrasound, including different equations of state for the liquid. A detailed analysis of the bubble-induced flow field as a function of the radial coordinate r demonstrates that the flow velocity u is dominated by acoustic contributions during a strong bubble collapse and, hence, decays predominantly with u∝r−1, contrary to the frequently postulated decay with u∝r−2 in an incompressible fluid.

Contiguity distance between simplicial maps

For simplicial complexes and simplicial maps, the notion of being in the same contiguity class is defined as the discrete version of homotopy. In this paper, we study the contiguity distance, $SD$, between two simplicial maps adapted from the homotopic distance. In particular, we show that simplicial versions of $LS$-category and topological complexity are particular cases of this more general notion. Moreover, we present the behaviour of $SD$ under the barycentric subdivision, and its relation with strong collapsibility of a simplicial complex.

Gas bubbling exfoliation strategy towards 3D g-C3N4 hierarchical architecture for superior photocatalytic H2 evolution

Graphitic carbon nitride (g-C 3 N 4 ) shows a graphite-like layered structure, which provides a high theoretical value for solar-to-hydrogen evolution especially for a 2D nanostructure. However, conventional polycondensation induces a strong agglomeration and collapse of nanostructure, resulting in a relatively poor photocatalytic performance. To overcome this problem, we develop a gas bubbling exfoliation strategy with NH 4 Cl assistant to make ultrathin 2D g-C 3 N 4 nanosheets self-assembled into a 3D macroporous network on a large scale. The hierarchical structure significantly improves the specific surface area to 176.4 m 2 g −1 (11.6 times higher than the reference g-C 3 N 4 ), which allows a large water/g-C 3 N 4 interface for photocatalytic water reduction reaction. The ultrathin 2D g-C 3 N 4 nanosheets show a thickness of about 1.4 nm, which greatly suppress photoinduced carriers recombination and enhance charge transfer at the interface. Furthermore, the doping of N and Cl is achieved during synthesis. As a result, the resulting g-C 3 N 4 demonstrates a remarkable improvement in H 2 production of 12.89 mmol g -1 h −1 , which is 21 times higher than the g-C 3 N 4 obtained from the conventional condensation method. These explorations provide a facile guidance for the quasi 3D g-C 3 N 4 hierarchical architecture engineering even for various energy-related applications. • Ultrathin 2D g-C 3 N 4 nanosheets self-assembled into a 3D macroporous network. • Enhanced H 2 production of 12.89 mmol g -1 h −1 is achieved, which is 21 times higher. • The hierarchical structure improves the specific surface area to 176.4 m 2 g −1 . • The ultrathin 2D g-C 3 N 4 nanosheets show a thickness of about 1.4 nm.

초음파 압력 펄스에 의한 미세기포와 세포 간의 상호작용에 대한 수치적 연구

The collapse of microbubbles using ultrasonic pressure pulses is accompanied by strong shock waves and jets. This phenomenon is an important topic applied to various environmental and medical fields such as surface cleaning, algae removal, cell poration, and drug delivery. However, a numerical model that can capture the strong bubble collapse, liquid jet, and associated deformation of a cell is lacking in the literature. In this work, numerical simulations are performed for the interaction between the spherical bubble and cell under an ultrasonic pulse condition including the effects of bubble collapsing jet and cell deformation. The cell is treated as a compressible liquid and two distance level-set functions are used for the bubble and cell interfaces. The conservation equations of mass and momentum are solved for compressible two-phase flows. The effects of acoustic amplitude and frequency and initial bubble-cell distance are investigated. The results show that cell deformation increases with increasing acoustic amplitude or decreasing frequency, and the distance between the bubble and cell is observed as an important parameter for cell deformation under the same ultrasound conditions. The present work can contribute to a safer and more efficient use of ultrasound in environmental and medical applications.

Experimental study on shear strength of saturated remolded loess.

Loess has the characteristics of large porosity, loose structure, uniform composition and strong collapsibility. When encountering heavy rainfall and irrigation prone to saturation, resulting in loess landslides, roadbed subsidence and dam instability. In order to study the effect of dry density and shear rate on the shear strength of saturated remolded loess, the consolidated undrained (CU) test was carried out in Yan’an City by using SLB-6A stress-strain controlled triaxial shear permeability test instrument. The shear rate, confining pressure and dry density were controlled during the test. The dry densities of the samples were 1.5 g / cm3, 1.6 g / cm3 and 1.7 g / cm3, respectively. CU tests of saturated remolded loess were carried out at different shear rates under the confining pressures of 100 kPa, 150 kPa and 200 kPa, respectively. It is found that the stress-strain curve of saturated remolded loess gradually moves upward with the increase of dry density. With the increase of dry density, the cohesion and internal friction angle of remolded saturated loess samples increase. At the same shear rate, with the increase of dry density, the deviatoric stress of the specimen increases significantly.

Study on Improving Loess Properties with Permeable Polymer Materials.

Loess has strong water sensitivity, strong collapsibility, and low strength resulting in failures such as landslides, due to its loose structure. In order to improve the loess characteristics and to better meet the needs of engineering, a colorless, transparent, and permeable composite material is proposed in this paper. Water stability, erosion, unconfined compression, and triaxial tests were conducted to investigate the change of the strength properties and soil erosion resistance. The water sensitivity and strength properties of the loess are significantly improved as the stabilizer concentration increases. When scoured for 20 min, the erosion rates of the reinforced and the unreinforced soil were 95% and 6.25%, respectively, and demonstrated a 15.12 times reduction in erosion rates. The optimal concentration of the mixed solution is 0.6%. The triaxial test, CT, and SEM scanning tests were used to reveal the intrinsic mechanisms. The results demonstrated that the internal friction angle of the reinforced soil increases from 28.09° to 30.57°, and the cohesion changes from 25 kPa to 37.4 kPa. A large number of pores with a diameter of 900–1000 μm are reduced to 0–200 μm, and some pores with a length greater than 600 μm reduce to a length of less than 200 μm; The agglomeration and cementation, the filling of pores, and the formation of membrane structures have contributed greatly to the improvement of loess properties. Furthermore, the newly composite material has significant application potential needed to stabilize soil.

P-213 Assisted Hatching as new indication to improve diminished implantation potential after spontaneous collapsed blastocyst

Abstract Study question To demonstrate whether assisted hatching (AH) could improve reproductive outcome of collapsed blastocysts (CB). Pregnancy rate (PR) and the implantation rate (IR) were studied. Summary answer Our results demonstrate an indication of AH for collapsed blastocyst. The AH could reverse or minimize the negative impact of the collapse on implantation. What is known already With the introduction of the time-lapse thecnology, different aspects of the embryonic development are analyzed in detail. According to Marcos et al., 2015, the incidence of spontaneous blastocyst collapse is 19% and decreases the implantation potential from 48.5% to 35.1%. Recently, Sciorio et al., 2020 described significantly higher IR of 61.2% and OPR of 53.7% when blastocysts which had not collapsed were replaced compared to cycles in which collapsed blastocysts were transferred (IR rate 22.6% and OPR 17.7%). This study suggests that human collapsed blastocysts are less likely to implant and generate a pregnancy compared with embryos that do not. Study design, size, duration Retrospective study performing AH routinely in warmed embryos for 5 years in 4 groups: study groups CB (No-AH /CB- AH) and control groups NCB (No-AH / NCB-AH). To find out if the differences between the study groups were due solely to the effect of AH, we introduced two additional contemporary control groups NCB with and without HA. SET (single embryo transfer) was performed. IR and PR were analyzed and compared using the Chi-square test. Participants/materials, setting, methods A total of 754 blastocysts distributed in 4 groups were analyzed: 188 CB without AH (No-AH), 161 CB with AH, 199 NCB No-AH and 206 NCB with AH. All blastocysts were warmed embryos and the collapse was identified retrospectively in a time-lapse system before warming. The AH was performed by laser (removing 1/4 part of the ZP) after warming the embryos. Main results and the role of chance Comparing the clinical PR between embryos with or without collapse a significant adverse effect was confirmed by the collapse (CB 47.6% 166/349 vs NCB 60.5% 245/405) p < 0.001. The same trend was observed in the ongoing PR (OPR),(CB 30.7% 107/349 vs NCB 40.2% 163/405, p = 0.006). Regarding the AH effect, and considering all warmed embryos (regardless if they were affected by collapse or not) we did not find any improvement in the PR and IR when we performed AH on the blastocysts. For PR: No-AH: 53.2% 206/387 vs AH: 55.9% 205/367, p = 0.469 and for IR: No-AH: 42.6% 165/387 vs AH: 47.7% 175/367, p = 0.164. Focussing solely on warmed blastocyst which collapsed, and performing AH, we encountered significant differences regarding OPR (No-AH 25.5% 48/188 vs AH 36.6% 59/161, p = 0.025). When selecting only day 5 embryos the same effect was observed (No-AH 25.8% 40/155 vs 37.9% 47/124, p = 0.03). Limitations, reasons for caution The collapse was described as ≥ 50% of the surface of the trophectoderm being separated from the ZP regardless how far the trophectoderm cells are apart from the ZP. Some blastocysts suffer a strong collapse reducing considerably the size of the embryo, but in others the collapse is quite subtle. Wider implications of the findings Our results demonstrate a real indication for AH in CB. It would be interesting to incorporate continuous embryo monitoring in laboratories to identify collapse to ensure AH and improving results. Maybe these events of collapse would imply an additional metabolic stress which may affect viability or displacing the implantation window. Trial registration number not applicable

Analysis of the Mechanism of Ground Fissures in the Nairobi–Malaba Railway Rift Valley Area in Kenya

During the rainy season from March to May 2018, four ground fissures were generated in the rift valley area along the first phase of the Nairobi–Malaba Railway in Kenya, among which the ground fissures B3 highway, DK76, and DK77 were larger in scale, which seriously endangered the safety of the railway. According to the author’s previous study, the ground fissure B3 highway belongs to a typical fault-type fissure, and the ground fissures DK76 and DK77 are qualitatively concluded to be generated under the groundwater erosion of collapsible soils. To quantitatively summarize the mechanism of ground fissures, DK76 and DK77, physical model tests on the overlying soil properties, compactness, the intersection angle between hidden cracks and the water flow direction, the height of confined water level, and the groundwater flow rate are conducted to analyze the effect of these factors on the formation and expansion of ground fissures. The test results show that the soil with strong collapsibility under the action of underground erosion produces fissures, collapses, and holes similar to those in the rift valley area along the first phase of the Nairobi–Malaba Railway in Kenya; the loose overburden is conducive to the occurrence of surface collapse; the collapse of the soil surface is the most severe when the underlaid cracks are parallel to the water flow direction; the higher confined water level and faster inflow rate will aggravate the collapse of the overlying soil layer.

Influence of temperature on bulk nanobubble generation by ultrasonication

The effects of liquid temperature on bulk nanobubbles (BNBs) generation using ultrasound was investigated. When liquid at different temperatures and relatively similar dissolved oxygen concentration (25 °C: 8.29 ppm; 50 °C: 8.11 ppm; and 75 °C: 7.78 ppm) were sonicated, a high number of negatively charged (−13 to −21 mV) BNBs were consistently generated within a few minutes. As the temperature of the liquid increased, it is expected that the concentration of BNBs considerably increased due to a lot of nucleation site and strong collapse of tiny bubbles. On the other hand, in a liquid with relatively low temperature, a high number of large bubbles were formed and the BNBs concentration considerably decreased. It is suggested that it has less nucleation sites compared to a liquid with higher temperature; thus, the bubble growth was accelerated by rectified diffusion and coalescence, owing to less nucleation sites versus dissolved gas concentration.

Prediction of thrombosis in atrial fibrillation with compact atrial shape representation

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – EU funding. Main funding source(s): IHU LIRYC ANR-10-IAHU-04 ERACoSysMed PARIS Project Background The impact of LA shape on clot formation in AF is yet to be understood Purpose To analyze the impact of LA, PVs and LAA orientations on clot formation Methods Pts with history of AF and an indication for LAA closure underwent pre-operative cardiac CT. Those with either a prior history of embolism or a clot detected on arterial and venous-enhanced CT images were categorized as clot positive. On CT images, the LA was segmented and meshed. Automated labelling of PVs and LAA was employed to build a compact skeleton representation of the LA (by registering labels from a template to all cases, and by connecting the center of mass of each labels). LA skeletons were used to train a novel Neural Network model for joint classification of heterogeneous data, such as images taken at different phases of the cardiac cycle. Such model consists of one encoder per dataset followed by a common classifier, enforcing a joint representation of all datasets in the same latent space. This is made possible by writing the task as a variational problem to optimise, we call this model a multi-channel variational classifier. The model was trained to predict clot positive patients and its generalizability was assessed on a test population. Results 237 pts were included (age 74±8, 70% males, CHADS-VASc 4.3±1.2). CTs were acquired during systole in 117 and diastole in 120. 100 (42%) patients were considered clot positive. Segmentation, labeling and skeletization was successfully achieved in all pts. The model was trained using a 10-Fold cross validation. We compared the results after training on diastole and systole cases independently and by jointly training on both datasets. At testing, our model reached a 0.72 overall accuracy for the prediction of LAA clots (0.83 for systole and 0.61 for diastole), while training separately on systole and diastole was prone to strong overfitting and mode collapse with 0.52 and 0.48 accuracy, respectively. Conclusion While LA shape, LA size, PV and LAA orientations alone may not be sufficient for robust clot prediction, we introduce a compressed representation of the global anatomy that closely relates to LAA thrombosis, possibly identifying global features related to adverse hemodynamics. The method is reproducible and introduces a novel approach to accommodate heterogeneous diastole and systole datasets.

PO-706-04 COMPACT REPRESENTATION OF ATRIAL SHAPE FOR THROMBOSIS RISK PREDICTION IN AF

The impact of LA shape on clot formation in AF is yet to be understood To analyze the impact of LA, PVs and LAA orientations on clot formation Pts with history of AF and an indication for LAA closure underwent pre-operative cardiac CT. Those with either a prior history of embolism or a clot detected on arterial and venous-enhanced CT images were categorized as clot positive. On CT images, the LA was segmented and meshed. Automated labelling of PVs and LAA was employed to build a compact skeleton representation of the LA (by registering labels from a template to all cases, and by connecting the center of mass of each labels). LA skeletons were used to train a novel Neural Network model for joint classification of heterogeneous data, such as images taken at different phases of the cardiac cycle. Such model consists of one encoder per dataset followed by a common classifier, enforcing a joint representation of all datasets in the same latent space. This is made possible by writing the task as a variational problem to optimise, we call this model a multi-channel variational classifier. The model was trained to predict clot positive patients and its generalizability was assessed on a test population. 237 pts were included (age 74±8, 70% males, CHA₂DS₂-VASc 4.3±1.2). CTs were acquired during systole in 117 and diastole in 120. 100 (42%) patients were considered clot positive. Segmentation, labeling and skeletization was successfully achieved in all pts. The model was trained using a 10-Fold cross validation. We compared the results after training on diastole and systole cases independently andby jointly training on both datasets. At testing, our model reached a 0.72 overall accuracy for the prediction of LAA clots (0.83 for systole and 0.61 for diastole), while training separately on systole anddiastole was prone to strong overfitting and mode collapse with 0.52 and 0.48 accuracy, respectively. While LA shape, LA size, PV and LAA orientations alone may not be sufficient for robust clot prediction, we introduce a compressed representation of the global anatomy that closely relates to LAA thrombosis, possibly identifying global features related to adverse hemodynamics. The method is reproducible andintroduces a novel approach to accommodate heterogeneous diastole and systole datasets.

Understanding the collapse of flash-boiling sprays formed by multi-hole injectors operating at low injection pressures

Sprays consisting of initially separated plumes, which are generated by multi-hole injectors in strong flash-boiling conditions, may collapse and form a single spray cloud. It has been shown that for high-pressure injection systems (≥5 MPa), such behaviour is dependent on both the superheat and the geometrical configuration of the injector; while the spray collapse in low-pressure systems (≤1 MPa) is not yet understood. To the best of the author's knowledge, this is the first study aimed at filling this information gap. The principal novelty of this work is related to understanding the collapse in low-pressure systems, in terms of the different numbers of nozzles and the difference in the effects from flash boiling between low- and high-pressure sprays.The results showed that the flash-boiling sprays formed by the two- and six-hole injectors were substantially different, which is similar behaviour as for high-pressure sprays. The major difference from the sprays formed at high pressure is that the flash boiling does not result in an increased penetration (in relation to the subcooled conditions). This distinct behaviour was linked with a different jet break-up regime, and different droplet size reduction due to flash boiling, both depending on the injection pressure. This work discusses that the importance of the aerodynamic drag force due to a stronger droplet size reduction in the case of low-pressure sprays can be increased more than twofold compared to the high-pressure sprays.The lack of increased penetration leads to an important finding in terms of practical applications. In contrast to high-pressure systems, flash boiling will not lead to enhanced wall wetting regardless of the number of nozzles.This study has revealed that the interaction of the spray plumes is not sufficient to cause a strong spray collapse and the formation of the single jet-like spray structure. The necessary additional factor is the flow acceleration in the axis of the injector. The results highlighted the crucial role of the circular pattern, which already in subcooled cases led to the creation of flow conditions promoting axial propagation of a gaseous medium; while in the event of flash boiling, it prevented the surrounding air from entering the centre region of the spray cloud.