Specific Flow Patterns Research Articles

Flow characteristics of the rip current system adjacent to a coastal vertical structure for irregular waves

Rip currents are common hazards found on many beaches around the world. The present research examines the rip current flow features adjacent to a coastal vertical structure with total reflection function to the incident waves. The laboratory experiments were conducted over the planar beach for both regular and irregular waves to explore the specific phenomenon for the irregular waves, and a higher-order Boussinesq equation model was adopted in the simulations to analyze the formation mechanism of the flow features. The study results show that, the standing wave pattern for the irregular wave is much weaker than that for the regular wave with inducing only one apparent node rip at the first node line in the reflection wave area. Moreover, the specific “single-vortex” flow pattern was formed in the crossing wave field for the irregular wave tests. This specific flow pattern is found essentially induced by the larger wave reflection rate of the vertical structure, which leads to the strong lateral flow against the downstream longshore current. This specific flow pattern prefers to present for the smaller wave incident angles and larger wave heights and periods, and leads to the feeding flow volume rates discharged more in the form of lateral flow. The C-shaped lateral flow is found mainly induced by the longshore gradient of the wave set-up instead of the non-uniform wave radiation stress nearshore.

What can go wrong in a dividing wall column and how to detect it

Dividing wall columns are state of the art distillation arrangements performing three separation tasks within one unit. Compared to using two conventional columns in series this saves both capital costs and energy but on the other hand it brings a higher risk of malfunction. This simulation study analyses what can go wrong during the operation of dividing wall columns. The emphasis is on the operation of the prefractionator section, that is, on the choice on the liquid and vapor splits, which is crucial for the overall performance. The resulting two-way flows between the prefractionator and main column gives a broader feasible operating range than in a conventional column arrangement. This can lead to peculiar behavior, including circulation of components around the dividing wall. This paper identifies 15 non-optimal operating regions for the prefractionator with specific internal flow patterns, characteristic temperature and composition profiles for the separation of a fairly ideal mixture of benzene, toluene and p-xylene. From these results it is possible to identify and hopefully rectify wrong choices for the liquid and vapor splits in a dividing wall column.

Fully appreciating the impossibility of shock wave regular reflection from the axis of symmetry in axisymmetric internal flows

This study investigates the reflection of shock waves in internal axisymmetric flows and conclusively shows that regular reflection cannot occur over the axis of symmetry. The analysis employs the curved shock theory to examine flow gradients behind the axisymmetric shock. The curved shock equations are presented in explicit form using influence coefficients, which establish a direct relation between flow gradients in polar coordinates and shock curvatures. The gradient information reveals that the flow behind the incident shock around the reflection point is governed by the Taylor–Maccoll equation, indicating that the flow pattern is locally conical. By analyzing the singularity of internal conical flows, the only possible structure of conical shock reflection with a smooth singularity is constructed. After a thorough theoretical analysis of this conical shock reflection structure, the study concludes with definitive proof that this specific flow pattern cannot occur in practical applications because it requires the incident shock angle to be less than the freestream Mach angle. This suggests that regular reflection is impossible to occur over the axis of symmetry in internal axisymmetric flows.

Pore-scale insights into relative permeability in strongly and weakly wet natural fractures: A Lattice Boltzmann Method 2D simulation study

The simplified view of two-phase flow, such as oil and gas, in a fracture is often assumed to occur in a stratified behavior. However, recent studies and production practices have revealed that two-phase flow in fractures exhibits diverse flow patterns. This paper investigates the control of the fracture aperture, fluids viscosity, and wettability on two-phase flow in a 2D cross section of a 3D Berea fracture. Lattice Boltzmann Method (LBM) simulations are used to model the impact of these properties on relative permeability curves. Notably, in strongly wet fractures, two distinct permeability regimes emerge. High aperture values exhibit behavior resembling parallel planes, while low aperture values lead to a linear decrease in permeability due to fluid interactions between fracture surfaces. Conversely, anomalous behavior of the relative permeability curves is identified in weakly wet fractures within specific aperture ranges. This behavior is associated with the occurrence of specific flow patterns within the fracture. Results also emphasize that changes in viscosity ratio do not affect the presence or the saturation range of the anomalous behavior but do influence its intensity for each fluid. Comparisons with Poiseuille profile equations reveal the limited impact of the fracture roughness. These findings enhance our understanding of the interactions between aperture, viscosity, and wettability and how they control the shape of the relative permeability curves. These curves are pivotal parameters for the continuum scale modeling (reservoir models) in oil and gas application, for instance.

ST-ExpertNet: A Deep Expert Framework for Traffic Prediction

Recently, forecasting the crowd flows has become an important research topic, and plentiful technologies have achieved good performances. As we all know, the flow at a citywide level is in a mixed state with several basic patterns (e.g., commuting, working, and commercial) caused by the city area functional distributions (e.g., developed commercial areas, educational areas and parks). However, existing technologies have been criticized for their lack of considering the differences in the flow patterns among regions since they want to build only one comprehensive model to learn the mixed flow tensors. Recognizing this limitation, we present a new perspective on flow prediction and propose an explainable framework named ST-ExpertNet, which can adopt every spatial-temporal model and train a set of functional experts devoted to specific flow patterns. Technically, we train a bunch of experts based on the Mixture of Experts (MoE), which guides each expert to specialize in different kinds of flow patterns in sample spaces by using the gating network. We define several criteria, including comprehensiveness, sparsity, and preciseness, to construct the experts for better interpretability and performances. We conduct experiments on a wide range of real-world taxi and bike datasets in Beijing and NYC. The visualizations of the expert's intermediate results demonstrate that our ST-ExpertNet successfully disentangles the city's mixed flow tensors along with the city layout, e.g., the urban ring road structure. Different network architectures, such as ST-ResNet, ConvLSTM, and CNN, have been adopted into our ST-ExpertNet framework for experiments and the results demonstrates the superiority of our framework in both interpretability and performances.

Rainstorms impacts on water, sediment, and trace elements loads in an urbanized catchment within Moscow city: case study of summer 2020 and 2021

In 2020 and 2021, the city of Moscow, Russia, has experienced two historical rainfall events that had caused major flooding of small rivers. Based on long-term observation datasets from the surrounding weather stations, regional mesoscale COSMO-CLM climate model results, and a detailed hydrological and water quality monitoring data, we performed a pioneer assessment of climate change and urbanization impact on flooding hazard and water quality of the urban Setun River as a case study. Statistically significant rise of some moderate ETCCDI climate change indices (R20mm and R95pTOT) was revealed for the 1966–2020 period, while no significant trends were observed for more extreme indices. The combined impact of climate change and increased urbanization is highly non-linear and results in as much as a fourfold increase in frequency of extreme floods and shift of water regime features which lead to formation of specific seasonal flow patterns. The rainstorm flood wave response time, involving infiltrated and hillslope-routed fraction of rainfall, is accounted as 6 to 11 h, which is more than twice as rapid as compared to the non-urbanized nearby catchments. Based on temporal trends before and after rainfall flood peak, four groups of dissolved chemicals were identified: soluble elements whose concentrations decrease with an increase in water discharge; mostly insoluble and well-sorted elements whose concentrations increase with discharge (Mn, Cs, Cd, Al); elements negatively related to water discharge during flood events (Li, B, Cr, As, Br and Sr); and a wide range of dissolved elements (Cu, Zn, Mo, Sn, Pb, Ba, La, Cs, U) which concentrations remain stable during rainfall floods. Our study identifies that lack of research focused on the combined impacts of climate change and urbanization on flooding and water quality in the Moscow urban area is a key problem in water management advances.

Hydrodynamic forces in a horizontal-horizontal elbow in a gas-liquid system

Understanding the force fluctuations in an elbow is critical for piping system design, especially in multiphase flow applications. A new experimental facility has been designed and built where flow parameters, structural forces, and pressure upstream and downstream of the elbow can be measured simultaneously. The new facility allowed the study of the impact of different flow patterns on the phenomenon, with a wide range of liquid and gas superficial velocities (vSL 0.1-2.5 m/s, vSG 1-10 m/s). Oil and air have been used to represent field conditions better. In-situ liquid holdup and structure or translational velocity instead of mixture velocity are characterized. The flow influence as the peak force magnitude was measured on a single elbow (90-degree) oriented in a horizontal-horizontal configuration to identify the flow parameters with the most effect on the force. The results show that the density and velocity of coherent flow structures are essential to describe the force fluctuation. Additionally, pressure fluctuations in the elbow are significant for estimating the force in specific flow patterns.

Assessment of Blood Biophysical Properties Using Pressure Sensing with Micropump and Microfluidic Comparator.

To identify the biophysical properties of blood samples consistently, macroscopic pumps have been used to maintain constant flow rates in a microfluidic comparator. In this study, the bulk-sized and expensive pump is replaced with a cheap and portable micropump. A specific reference fluid (i.e., glycerin solution [40%]) with a small volume of red blood cell (RBC) (i.e., 1% volume fraction) as fluid tracers is supplied into the microfluidic comparator. An averaged velocity (<Ur>) obtained with micro-particle image velocimetry is converted into the flow rate of reference fluid (Qr) (i.e., Qr = CQ × Ac × <Ur>, Ac: cross-sectional area, CQ = 1.156). Two control variables of the micropump (i.e., frequency: 400 Hz and volt: 150 au) are selected to guarantee a consistent flow rate (i.e., COV < 1%). Simultaneously, the blood sample is supplied into the microfluidic channel under specific flow patterns (i.e., constant, sinusoidal, and periodic on-off fashion). By monitoring the interface in the comparator as well as Qr, three biophysical properties (i.e., viscosity, junction pressure, and pressure-induced work) are obtained using analytical expressions derived with a discrete fluidic circuit model. According to the quantitative comparison results between the present method (i.e., micropump) and the previous method (i.e., syringe pump), the micropump provides consistent results when compared with the syringe pump. Thereafter, representative biophysical properties, including the RBC aggregation, are consistently obtained for specific blood samples prepared with dextran solutions ranging from 0 to 40 mg/mL. In conclusion, the present method could be considered as an effective method for quantifying the physical properties of blood samples, where the reference fluid is supplied with a cheap and portable micropump.

New challenges in the study of coastal aquifers from numerical modeling. The case of the Motril-Salobreña aquifer

Coastal aquifers are frequently complex systems with highly heterogeneous geological characteristics, specific flow patterns, presence of fluids with different densities, high risk of contamination both by salinization and by other pollutants, and highly modified by anthropic activity. Given this situation, numerical modeling becomes the most appropriate tool to determine the potential impact of global change on marine intrusion in this kind of aquifers. The mathematical models traditionally used in coastal aquifers have been those of flow and mass transport with variable density, which allow obtaining a distribution of salinities in the aquifer and reproducing the flow pattern in the area of discharge to the sea. In addition to these models, another type of numerical modeling can be applied that could also provide information on specific aspects of this type of aquifers. The study of the Motril-Salobreña coastal aquifer shows, for example, how heat transport models allow quantifying the recharge that occurs from rivers that frequently interact with coastal aquifers; as well as the age transport models provide data on the preferential groundwater circulation paths and its residence time, very relevant information in these frequently heterogeneous and anisotropic aquifers. Future challenges are directed towards determining the effects of sea level rise on marine intrusion and establishing the degree of equilibrium of the freshwater-saltwater contact with the current situation.

Clinical characteristics of a novel “Type 3” vasa previa: case series at a single center

Objective Vasa previa is a condition in which fetal blood vessels are located on fetal membranes within 2 cm of the internal cervical os. Vasa previa has been classified into two types: Type 1, in which vessels connect a velamentous umbilical cord to the placenta, and Type 2, in which vessels connect the lobes of a bilobed placenta or the placenta to a succenturiate lobe. However, there are also atypical cases that cannot be classified into these two types. These cases are manifested by a center or marginal cord insertion with a normal shaped placenta, and fetal vessels were also located on membranes around the internal cervical os. These cases were recently proposed as Type 3 vasa previa. The present study investigated the incidence of Type 3 vasa previa and elucidated differences in clinical and ultrasonographical characteristics between traditional types and Type 3. Methods This was a single-center observational study using a cohort of all vasa previa cases between January 2010 and April 2020. Results Among 8,723 deliveries, there were 14 cases (0.16%) of vasa previa, all of which were diagnosed prenatally by US, not after vaginal delivery or CS. There were 9 (64%), 0, and 5 (36%) cases of Types 1, 2, and 3, respectively. All 5 Type 3 cases had only one fetal aberrant vessel of vasa previa, while 6 out of 9 Type 1 cases (67%) had two or more aberrant vessels. Seven Type 1 cases (78%) possessed two or more known risk factors, such as velamentous cord insertion, whereas all Type 3 cases only had one. Difficulties were associated with diagnosing two out of the 14 cases of vasa previa using routine transvaginal ultrasonography (TVUS). In these cases, the aberrant fetal vessel of vasa previa was only one vein with a thin wall that was not clearly visualized by gray-scale TVUS as well as slow flow that was easily misread by color-Doppler. These cases were ultimately diagnosed as vasa previa based on non-pulsatile flow detected by color and pulsed Doppler. Conclusions The present results suggest that Type 3 may account for a large proportion of vasa previa cases. Most Type 3 cases may present with only one fetal aberrant vessel of vasa previa and fewer risk factors, suggesting that the diagnosis of vasa previa may be more challenging in Type 3 cases than in the other types. Vasa previa with a venous vasa previa needs to be considered because of the difficulties associated with an antenatal diagnosis due to unclear imaging of the vasculature or the lack of specific color Doppler flow patterns. Pulsed Doppler imaging may be helpful for the diagnosis of these cases.

Dual-VENC 4D Flow MRI Can Detect Abnormal Blood Flow in the Left Atrium That Potentially Causes Thrombosis Formation after Left Upper Lobectomy.

Purpose: The purpose of the current study was to clarify the blood flow pattern in the left atrium (LA), potentially causing the formation of thrombosis after left upper lobectomy (LUL). The blood flow in the LA was evaluated and compared between LUL patients with and without thrombosis. For the evaluation, we applied highly accelerated 4D flow MRI with dual-velocity encoding (VENC) scheme, which was expected to be able to capture slow flow components in the LA accurately.Methods: Eight volunteers and 18 patients subjected to LUL underwent dual-VENC 4D Flow MRI. Eight patients had a history of thrombosis. We measured the blood flow velocity and stasis ratio (proportion in the volume that did not exceed 10 cm/s in any cardiac phase) in the LA and left superior pulmonary vein (LSPV) stump. For visual assessment, the presence of each collision of the blood flow from pulmonary veins and vortex flow in the LA were evaluated. Each acquired value was compared between healthy participants and LUL patients, and in LUL patients with and without thrombosis.Results: In LUL patients, blood flow velocity near the inflow part of the left superior pulmonary vein (Lt Upp) and mean velocity in the LA were lower, and stasis ratio in the LA was higher compared with healthy volunteers (Lt Upp 9.10 ± 3.09 vs.13.23 ± 14.19 cm/s, mean velocity in the LA 9.81 ± 2.49 vs. 11.40 ± 1.15 cm/s, and stasis ratio 25.28 ± 18.64 vs. 4.71 ± 3.03%, P = 0.008, 0.037, and < 0.001). There was no significant difference in any quantification values between LUL patients with and without thrombosis. For visual assessment, the thrombus formation was associated with no collision pattern (62.5% vs. 10%, P = 0.019) and not with vortex flow pattern (50% vs. 30%, P = 0.751).Conclusion: The net blood flow velocity was not associated with the thrombus formation. In contrast, a specific blood flow pattern, the absence of blood flow collision from pulmonary veins, correlates to the thrombus formation in the LA.

On cavitation inception and cavitating flow patterns in a multi-orifice microfluidic device with a functional surface

During the last decade, hydrodynamic cavitation has been implemented in various applications such as energy harvesting and biomedical applications. Facile hydrodynamic cavitation methods are required for fulfilling the requirements in these applications. In this study, a new generation microfluidic device containing eight parallel micro-orifices with a new design was fabricated and tested with the purpose of intensifying the cavitating flows and early cavitation inception. The roughness elements in the micro-orifices facilitated cavitation inception. This study presents a general perspective of occurrence of different cavitating flow patterns in microscale and addresses the ambiguities about the conditions for the formation of a specific flow pattern. Cavitation inception occurred with the appearance of small bubbles emerging from roughness elements at a rather low upstream pressure in the open loop experimental setup. A reduction in the cavitation number resulted in the formation of different flow patterns such as cavitation clouds, twin cavities, sheet cavities, and bubbly flows. Having several flow patterns with different intensities all together within a single microfluidic device is the main advantage of the proposed device over the state of the art microfluidic devices. Generation of flow patterns with various released energy levels makes this proposed device a unique multi-functional platform, which can be implemented to a lab on a chip platform for applications such as nanoparticle synthesis and wound healing.

Hydrological significance of Himalayan surface water and its management considering anthropogenic and climate change aspects

Water plays a key role in maintaining different ecosystem services. The anthropogenic and climate change impacts studies on Himalayan water resources has been trending in recent years. The Indian Himalayan region cover several states like Jammu & Kashmir, Ladakh (Union territory), Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh and the hilly regions of Assam and West Bengal. Water resources in this region are the life support for humankind and rich biodiversity. Researchers has reported that the warming in the Himalayas is more than the global average, thereby climate change can affect significantly in the mountainous water resources so as the snow and glacial melt is the main lifeline of the perennial rivers’ flow. Almost every year, the heavy monsoon rainfall brings floods on the upstream highlands and then the downstream plains causing enormous human suffering, loss of property, loss of life, agricultural crops damage as well as increased economic losses. The main challenges being associated to the frequency and magnitude of extreme weather events like monsoon rainfall which leads to flash floods, landslides and debris flow; and then the drought during dry season also, has had huge impacts on regional water security. Human actions like economic development and population growth have also brought changes in land cover/use to Himalayan watersheds recently. As a result of farming, grazing, tree planting, urbanization, etc., the changes in land cover have altered the water balance and transformed the water-flow paths in the global hydrological cycle. In contrast to freshwater ecosystems, demand is high, but their supply is limited, also depend on the specific flow pattern of rivers. Although, with interference of various infrastructure development upstream results in changes in flow pattern downstream causing non-availability of water to support aquatic life and communities that depend on for livelihoods. Initiation of monitoring and observation system for water resources and use of appropriate hydrological model are preferable to better understand the hydrological processes of the Himalayas.

Flow investigation of cross-flow turbine using CFD method

Cross-flow turbine is one of prime mover type that is simple, capable to extract water power and easy to be manufactured. The runner is working at 2 stages. The need of high momentum has lead researchers to design water nozzle, blades, as well as the set-up between nozzle and runner. High momentum water nozzle and cross-flow runner has been designed individually with the same design criteria. Unfortunately, experimental testing may not gain specific flow pattern inside the nozzle and the runner. The purpose of this study is to investigate the flow pattern inside the nozzle, runner using CFD method, Ansys 2019 R3 academic version. The CFD simulation done 3-dimensionally with 5 nozzle inlet velocity variations: 2 m/s, 3 m/s, 4 m/s, 5 m/s and 6,487 m/s. The fluid is assumed to be 1 phase, using mesh with 17.750 nodes, inlet fluid pressure 1,05 Pa, and temperature 24,85°C. The results showed that the lowest velocity and pressure for variation 1 at 1st stage (v1) = 6,65 m/s and (p1) = -11931,5 Pa, and the highest velocity and pressure at 1st stage (v5) = 21,72 m/s and (p5) = -127521 Pa. At 2nd stage, variation 1 and 5 resulting velocity (v1) = 1,78 m/s and (p1) 593,264 Pa, (v5) = 5,83 m/s and (p5) = 6360,32 Pa respectively. The main different of the flow pattern between 5 inlet velocity variations is the final flow thickness inside the runner get thicker at higher velocity, which is assumed to gain more rotational velocity.

DroidClone: Attack of the android malware clones - a step towards stopping them

Code clones are frequent in use because they can be created fast with little effort and expense. Especially for malware writers, it is easier to create a clone of the original than writing a new malware. According to the recent Symantec threat reports, Android continues to be the most targeted mobile platform, and the number of new mobile malware clones grew by 54%. There is a need to develop techniques and tools to stop this attack of Android malware clones. To stop this attack, we propose DroidClone that exposes code clones (segments of code that are similar) in Android applications to help detect malware. DroidClone is the first such effort uses specific control flow patterns for reducing the effect of obfuscations and detect clones that are syntactically different but semantically similar up to a threshold. DroidClone is independent of the programming language of the code clones. When evaluated with real malware and benign Android applications, DroidClone obtained a detection rate of 94.2% and false positive rate of 5.6%. DroidClone, when tested against various obfuscations, was able to successfully provide resistance against all the trivial (Renaming methods, parameters, and nop insertion, etc) and some non-trivial (Call graph manipulation and function indirection, etc.) obfuscations.

An integrated model of predicting sand erosion in elbows for multiphase flows

Sand erosion is a serious problem to be solved in the oil and gas industry. During the transportation of oil and gas, different multiphase flow patterns may occur due to variations of factors, such as the conveying speed, fluid property and pipe geometry. The present work aims at developing a novel framework to predict sand erosion in elbows for multiphase flows. Firstly, the effects of flow patterns on sand erosion are analyzed. Based on these analyses, the erosion model for each specific flow pattern is established. Combining with the basic penetration ratio in gas flow and erosion coefficients, the erosion models of different flow patterns can be unified as an integrated model. Then, the accuracy of the integrated model is examined by 108 experimental cases. After the experimental validation, an optimal coefficient is proposed to further optimize the integrated model. A comparison between the optimized integrated model and the non-optimized integrated model is performed. The results demonstrate that the optimized integrated model performs well in improving the accuracy. Finally, the integrated model is compared with other existing erosion models. According to the comparative study, the non-optimized integrated model already owns the similar accuracy compared with existing erosion models, while the optimized integrated model performs best in accuracy and efficiency.

A simple and general macroscopic model for local-deformation effects in fluid-saturated porous rock

SUMMARYWave-induced fluid flows (WIFF) can be viewed as cases of broader local-deformation (LD) phenomena and represent the principal causes of seismic-wave attenuation in fluid-saturated porous rock. Most existing WIFF models refer to greatly simplified microstructures and specific flow patterns, such as planar divergent flows within thin cracks (squirt flows, SF) or flows within patchy-saturation zones. However, such microstructures represent only idealized mathematical models that may be impossible to consistently identify within a given rock. At the same time, most details of such microstructures are insignificant for seismic waves, which are only sensitive to averaged properties of the medium. To perform microstructure-independent modelling of LD effects, we develop a simple yet general approach based entirely on a macroscopic local-deformation variable. This variable is broadly analogous to Biot's fluid content and is illustrated for two specific microstructural models. The macroscopic model is Biot-consistent and uses only time- and frequency-independent material properties. Both local and global (Biot's) pore flows and all types of waves and deformations are explained in a rigorous and consistent manner. The model allows constraining a minimal set of material properties responsible for all observed elastic and anelastic effects in porous rock. Because of making no assumptions about the microstructures and their spatial scales, this approach should comprise at least some of the existing WIFF models. In particular, this model accurately reproduces all attenuation and velocity dispersion spectra predicted by a broadly used SF model. The model also contains effects not considered previously, such as bulk viscosity of pore fluid and viscous coupling between the rock frame and fluid-filled pores. The model offers straightforward extensions to multiple porosities and cases of viscous fluids in primary pores. Based on the resulting differential equations, physically consistent schemes for numerical modelling of seismic wavefields can be developed for porous rock with arbitrary LD effects.

Experimental and Computational Analysis of the Unstable Flow Structure in a Centrifugal Compressor with a Vaneless Diffuser

The unstable flow phenomena in compressors, such as stall and surge, are closely related to the efficiency and the operating region. It is indispensable to capture the unstable flow structure in compressors and understand the mechanism of flow instability at low flow rates. Cooperated with the manufacturer, an industrial centrifugal compressor with a vaneless diffuser is tested by its performance test rig and our multi-phase dynamic measurement system. Many dynamic pressure transducers are circumferentially mounted on the casing surface at seven radial locations, spanning the impeller region and the diffuser inlet region. The pressure fields from the design condition to surge are measured in details. Based on the multi-phase dynamic signals, the original location of stall occurring can be determined. Meanwhile, the information of the unstable flow structure is obtained, such as the circumferential mode and the propagating speed of stall cells. To get more details of the vortex structure, an unsteady simulation of this tested compressor is carried out. The computational result is well matched with the experimental result and further illustrates how the unstable flow structure in the impeller region gradually affects the stability of the total machine at low flow rates. The dynamic mode decomposition (DMD) method is applied to get the specific flow pattern corresponding to the stall frequency. Both experimental and computational analysis show that the flow structure at a particular radial location in the impeller region has a great impact on the stall and surge. Some differences between the computational and experimental result are also discussed. Through these two main analytical methods, an insight into the unstable flow structure in an industrial compressor is gained. The result also plays a crucial role in the guidance of the compressor stabilization techniques.

Tracing patterns and shapes in remittance and migration networks via persistent homology

Pattern detection in network models provides insights to both global structure and local node interactions. In particular, studying patterns embedded within remittance and migration flow networks can be useful in understanding economic and sociologic trends and phenomena and their implications both in regional and global settings. We illustrate how topo-algebraic methods can be used to detect both local and global patterns that highlight simultaneous interactions among multiple nodes, giving a more holistic perspective on the network fabric and a higher order description of the overall flow structure of directed networks. Using the 2015 Asian net migration and remittance networks, we build and study the associated directed clique complexes whose topological features correspond to specific flow patterns in the networks. We generate diagrams recording the presence, persistence, and perpetuity of patterns and show how these diagrams can be used to make inferences about the characteristics of migrant movement patterns and remittance flows.

Necrotising enterocolitis and point of care neonatal abdominal USS

Neonatal intensive care has seen dramatic improvements over last four decades in rates of survival for most preterm newborns. Limits of survival were generally regarded 27 weeks gestation in the 80’s, are now 23 weeks gestation. These micro-premies are much smaller (500 to 800 grams birth weight) and are now increasingly managed with nasal continuous positive airway pressure as respiratory support. Acute abdominal emergencies are common in these infants and can be difficult to distinguish from dysmotile intestinal function in early stages. Preterm infants treated with nasal continuous positive airway pressure often have distended abdomens with feed intolerance requiring evaluation for potentially life-threatening conditions such as necrotising enterocolitis. Plain abdominal radiography is the gold standard modality for diagnosis, monitoring and guiding management in clinically suspected diseased neonatal bowel states. Timely access of expert surgical opinion poses frequent dilemmas of transporting a critically ill preterm infant to a surgical facility. There is compelling evidence demonstrating diagnostic bowel ultrasound findings in necrotising enterocolitis by trained medical ultrasonographers. There is a growing interest in utility of performing bowel ultrasound amongst point-of-care neonatal clinicians. Despite technical challenges, point-of-care bowel ultrasound has the added ability to measure bowel wall thickness, provide real-time evaluation of bowel peristalsis, perfusion, detection of free abdominal fluid; in addition to detection of pneumatosis intestinalis, portal venous gas and pneumoperitoneum like plain abdominal radiographs. This provides a more complete understanding of bowel state. Specific color doppler bowel wall arterial flow patterns have been described in necrotising enterocolitis, as “zebra”, “Y” and the “ring” patterns corresponding to inflamed viable bowel. Bowel ultrasound is more sensitive than abdominal radiography in the detection of pneumotosis intestinalis in early stages of necrotising enterocolitis. As the disease progresses, the visualization of thinned bowel wall with lack of bowel wall perfusion on ultrasound implies nonviable bowel with impending perforation. Detection of this bowel state early is valuable in the clinical management as pneumoperitoneum suggesting bowel perforation on plain abdominal radiograph is a late sign. Rarer diagnoses with acute neonatal surgical conditions can also be assessed with the use of bowel ultrasound such as malrotation. With widening of knowledge and appropriate training in ultrasound techniques, neonatologists will be able to enhance their diagnostic acumen by performing point-of-care bowel ultrasound in addition to plain radiography for a broad array of diseased bowel states in neonates.