Conduit Flow Research Articles

Ultra and Very Long Period Seismic Signatures of Unsteady Eruptions Predicted From Conduit Flow Models

AbstractExplosive volcanic eruptions radiate seismic waves as a consequence of pressure and shear traction changes within the conduit/chamber system. Kinematic source inversions utilize these waves to determine equivalent seismic force and moment tensor sources, but relation to eruptive processes is often ambiguous and nonunique. In this work, we provide an alternative, forward modeling approach to calculate moment tensor and force equivalents of a model of eruptive conduit flow and chamber depressurization. We explain the equivalence of two seismic force descriptions, the first in terms of traction changes on conduit/chamber walls, and the second in terms of changes in magma momentum, weight, and momentum transfer to the atmosphere. Eruption onset is marked by a downward seismic force, associated with loss of restraining shear tractions from fragmentation. This is followed by a much larger upward seismic force from upward drag of ascending magma and reduction of magma weight remaining in the conduit/chamber system. The static force is upward, arising from weight reduction. We calculate synthetic seismograms to examine the expression of eruptive processes at different receiver distances. Filtering these synthetics to the frequency band typically resolved by broadband seismometers produces waveforms similar to very long period seismic events observed in strombolian and vulcanian eruptions. However, filtering heavily distorts waveforms, accentuating processes in early, unsteady parts of eruptions and eliminating information about longer (ultra long period time scale depressurization and weight changes that dominate unfiltered seismograms. Our workflow can be utilized to directly and quantitatively connect eruption models with seismic observations.

Disrupt the upper or the lower conduit? The dual role of gas exsolution in the conduits of persistently active volcanoes

Many volcanoes emit a significant portion of the gas they transport to the atmosphere during continual passive degassing rather than during eruptions. To maintain a high gas and thermal flux without erupting magma, the flow field in the volcanic conduit must be approximately balanced with gas-rich, buoyant magma ascending and degassed, heavy magma descending. In vertical conduits, this exchange flow takes the form of core–annular flow, where the gas-rich magma forms a core enclosed by an annulus of degassed magma. The flow dynamics of core–annular flow have been studied extensively in fluid dynamics, but mostly for constant material properties. Our study aims to advance our understanding of how core–annular flow responds to volatile exsolution – a simple, yet ubiquitous disruption in volcanic conduits, which alters both the density and the viscosity of the core fluid. By deriving an evolution equation for the core–annular interface based on a generalized exchange-flow condition using a lubrication approximation, we find that the response of the system to volatile exsolution depends on the conduit flow regime. The same nucleation event can lead to a flow adjustment only in the upper, only in the lower or in both portions of the volcanic conduit. Our results emphasize that the thermodynamic evolution of magma properties and volcanic conduit flow are intricately linked, which may help understand the observed variability of eruptive behaviour at persistently degassing volcanoes.

Competitive Flow in Vein Composite Grafts Based on the Left Internal Thoracic Artery: Early and 1-Year Angiographic Analyses

We assessed the incidence of competitive flow with early postoperative angiograms in patients who received a "no-touch" saphenous vein (NT SV) composite graft and reexamined the status of competitive flow at 1-year. Early postoperative angiograms were performed in 806 patients who underwent myocardial revascularization using a NT SV Y-composite graft based on the in situ left internal thoracic artery (LITA). Competitive conduit flow was observed in 102 distal anastomoses (102 of 3039 [3.4%] anastomoses) of 94 patients (94 of 806 [11.7%]; NT SV competitive flow in 74 and LITA competitive flow in 20). Of the 94 patients, 63 patients (50 with NT SV competition and 13 with LITA competition) were re-evaluated with 1-year postoperative angiograms. Fifty-six competitive NT SV conduits in 50 patients were reevaluated at 1-year postoperatively: 44 (78.6%) early competitive anastomoses had become patent and 12 (21.4%) were occluded. NT SV with pedicle tissue showed a higher tendency of being perfectly patent at 1-year postoperatively than NT SV without pedicle tissue (17 of 40 [42.5%] vs 2 of 16 [12.5%]; P = 0.007). Thirteen competitive LITA conduit anastomoses in 13 patients were reevaluated 1-year postoperatively: 9 (69.2%) early competitive anastomoses had become patent and 4 (30.8%) were occluded. Competitive flow was shown on early postoperative angiograms in 3.4% of distal anastomoses in patients who received NT SV Y-composite grafts. Approximately 80% of the competitive NT SV conduits were patent 1-year postoperatively, and perfect patency rates were higher in patients who had received NT SV with pedicle tissue than in patients who had received NT SV without pedicle tissue.

Modeling Monthly Nitrate Concentration in a Karst Spring with and without Discrete Conduit Flow

Understanding the coupled continuum pipe-flow framework for modeling contaminant transport in karst systems is critical for protecting water resources therein. This study simulated point and non-point source nitrate concentration in a karst spring and investigated the results generated from the flow and transport model with and without discrete conduit flow. CFPv2 and CMT3D models were integrated to address the changes in nitrate concentration at a monthly scale in a karst spring, and the results were compared with that from an equivalent porous media (EPM) model with high-hydraulic conductivity (K) zones set in the main karstified area to represent conduits. The results show that the CFPv2+CMT3D model is able to describe well the recession of nitrate concentration in spring discharge, and the relatively larger deviation (slower nitrate recession) from the observed trend for the EPM model is probably a result of the limitation of utilizing high hydraulic conductivity cells to represent conduit. Moreover, simulated hydraulic heads in poorly karstified areas from the two models both show slight differences from the observations (the head RMSE values of calibration/validation for CFPv2 and MODFLOW models are 0.16 m/0.25 m and 0.26 m/0.17 m, respectively), indicating the inclusion of conduits may not affect the simulation considerably, and the lower the proportion of karstic area, the slight effects brought from the inclusion of conduits in the model. For highly karstified areas, the CFPv2+CMT3D model could provide more accurate results (head RMSE of calibration/validation for CFPv2 and MODFLOW are 0.22 m/0.06 and 0.52 m/0.47 m, respectively), showing the coupled continuum pipe-flow framework may be more appropriate for applying to highly and maturely karstified areas where the variations in the behavior of flow and contaminant transport are more affected by turbulent flow regime.

Along the hidden Timavo. 90° Congresso della Società Geologica Italiana - Trieste, 14-16 settembre 2021. Pre congress Field Trip T2

Almost 200 years after the first studies on the Timavo River, researchers are still carrying out their investigations, thanks in part to European projects, aiming to improve the knowledge on the Reka/Timavo cross-border aquifer in order to protect the groundwater resource through quantitative and qualitative monitoring of the underground waters. The Classical Karst Region is, in fact, home to what is generically called the underground Timavo network, a set of underground drainage paths developed well below sea level. The waters flow both in large conduits and in small fractures characterizing the rock mass. Water is the engine that created all these hypogean features and the surface karst morphotypes thanks to the chemical (dissolution) and physical (erosion) processes. The topographical surface is studded with thousands of dolines. Throughout the territory, more than 5.000 caves have been explored, of which more than 150 have a development exceeding a hundred meters. Out of all of them, only less than a dozen reach the water base level (Timavo caves) and others are crossed by water during floods. In this framework is the field trip proposed in the guide book designed as an accompaniment for visitors and participants in the 90° SGI Congress. The excursion goes along the underground path of the Reka/Timavo River, starting from Slovenia, visiting the Škocjan caves in which the river disappears underground (UNESCO world heritage site since 1986). The excursion moves on to the Grotta Gigante cave with another stop at the surface dissolution laboratory and the museum, after which visitors will take part in the excellent sightseeing to be found at Doberdò Lake and at the Timavo Springs where freshwaters meet the salty Adriatic Sea.

A General Approach for Flow Optimization and Drag Reduction in Turbulent Pipe Flows

Flow optimization and drag reduction are of great importance in industrial applications. However, most of the structural optimization and drag reduction in pipe flows are based on industrial experience or a large number of experiments, and there is a lack of general theoretical guidance. In the present work, a general approach for flow optimization and drag reduction in turbulent pipe flows is developed based on the irreversibility of flow process and the principle of minimum mechanical energy dissipation. Considering that the effective viscosity coefficient is related to the space coordinates, the field synergy equation of turbulent flow is derived. The reliability and performance of the field synergy principle of turbulent flow as well as the general approach are then evaluated and validated in a turbulent parallel flow conduit, and finally applied to industrial pipe flows. It demonstrates that the present approach is able to optimize flow field for different purposes by adding speed splitter or deflector as an interface at proper locations to alter the interactions between fluid and wall. It is robust and easy to implement, which provides general theoretical guidance for flow optimization and drag reduction in turbulent pipe flows.

Water Management in PEM Fuel Cells

The Regulation of the amount of water in Proton Exchange Membrane Fas Cells (PEMFCs) is an issue addressed by many researchers to date. The challenges in water transport, handling excess water in the membrane, and water control techniques in a PEMFC are discussed in this article. Both an excessive or lagging of water in the Gas Diffusion Layer (GDL) can affect the overall performance of PEMFC. The effects of water content on the reduction reaction rate, oxidation reaction rate, gas diffusion rate, catalyst layer (CL), and flow conduit, are discussed. Application of an additional polymeric layer to improve the hydrophilic nature of the GDL to make it more apt for usage under normal conditions with a review of the performance of different kinds of material usable in the situation is explained in detail.

External Surface Water Influence on Explosive Eruption Dynamics, With Implications for Stratospheric Sulfur Delivery and Volcano-Climate Feedback

Explosive volcanic eruptions can inject sulfur dioxide (SO2) into the stratosphere to form aerosol particles that modify Earth’s radiation balance and drive surface cooling. Eruptions involving interactions with shallow layers (≤500 m) of surface water and ice modify the eruption dynamics that govern the delivery of SO2 to the stratosphere. External surface water controls the evolution of explosive eruptions in two ways that are poorly understood: 1) by modulating the hydrostatic pressure within the conduit and at the vent, and 2) through the ingestion and mixing of external water, which governs fine ash production and eruption column buoyancy flux. To make progress, we couple one-dimensional models of conduit flow and atmospheric column rise through a novel “magma-water interaction” model that simulates the occurrence, extent and consequences of water entrainment depending on the depth of a surface water layer. We explore the effects of hydrostatic pressure on magma ascent in the conduit and gas decompression at the vent, and the conditions for which water entrainment drives fine ash production by quench fragmentation, eruption column collapse, or outright failure of the jet to breach the water surface. We show that the efficiency of water entrainment into the jet is the predominant control on jet behavior. For an increase in water depth of 50–100 m, the critical magma mass eruption rate required for eruption columns to reach the tropopause increases by an order of magnitude. Finally, we estimate that enhanced emission of fine ash leads to up to a 2-fold increase in the mass flux of particles < 125 μm to spreading umbrella clouds, together with up to a 10-fold increase in water mass flux, conditions that can enhance the removal of SO2 via chemical scavenging and ash sedimentation. On average, compared to purely magmatic eruptions, we suggest that hydrovolcanic eruptions will be characterized by reduced climate forcing. Our results suggest one possible mechanism for volcano-climate feedback: temporal changes with climate in surface distributions of water and ice may modify the relative global frequency or dominance of hydrovolcanic eruption processes, modulating, in turn, global patterns in volcano-climate forcing.

Pipe Dreams: The Effects of Stream Bank Soil Pipes on Hyporheic Denitrification Caused by a Peak Flow Event

AbstractPeak flow events in gaining stream/river channels cause lung model hyporheic exchange with the banks (bank storage), which fosters beneficial reactions as polluted channel water cycles through riparian groundwater. Soil pipes are common along stream/riverbanks, and enhance exchange, yet their effect on reactions such as denitrification is unknown. We used MODFLOW with the Conduit Flow Package to simulate lung model exchange during a peak flow event in a section of stream bank/riparian soil with soil pipes, and MT3D‐USGS to estimate nitrate transport and denitrification. We varied soil matrix hydraulic conductivity (K) and first‐order reaction constant (k), as well as soil pipe density, length, and height above the initial channel water surface elevation (H). The addition of soil pipes enhanced stream bank (riparian) denitrification relative to banks without pipes, e.g., a 76% increase due to adding a single 1.5 m pipe. Denitrification increased linearly with pipe density but exhibited nonlinear trends with other parameters. Sensitivity analysis revealed length and density to be most influential. Soil pipe enhancement of denitrification was governed by hyporheic volume in most cases in our study. Exceptions included (a) coarse soil (K = 10−3 m/s) and (b) low k and H > 0. Scaling our results to the stream corridor scale estimated that five soil pipes per m cumulatively induced 3% nitrate removal along a 1 km reach. Overall, soil pipes enhanced advection of nitrate into the banks, and also increased residence times of that nitrate under certain conditions, which together enhanced denitrification. This enhancement has implications for excess nitrate management in watersheds.

Karst relief of the Mali me Gropa Massif, central Albania

The mid-altitude mountain massif of Mali me Gropa is located in the central part of Albania, rises to an altitude of 1500–1800 m a.s.l., is composed mostly of Mesozoic limestone, and is characterized by extensive surface karst development. The karst relief is dominated by “doline” morphology including “polygonal” karst. Detailed geomorphological analysis of the western part of the Mali me Gropa massif (so-called Western Massif) by means of GIS methods is used to determine and explain the morphometric and morphological diversity of the area’s topography. Based on a homogeneity criterion, a number of geomorphological units with specific kinds of karst relief have been distinguished within the massif. The differences in karst sculpture concern the size (diameter) of dolines and depressions, their depth, shape and symmetry, orientation, density of occurrence and spatial pattern, which provide the basis for distinguishing geomorphological units. The spatial differentiation of the karst relief is explained by the influence of factors which are evolutionary (geological and geomorphological evolution of the massif), hypsometric (altitude difference of terrains) and geomorphologic-structural (inclination of the slopes and layers). The relatively poor expression of open karst conduits (i.e. caves and vertical shafts) on the surface of the massif may result from the relative immaturity of the epikarst zone, the widespread occurrence of residual cover on the plateau, and the accumulation of large amounts of clay material in dolines and depressions. Detailed hydrogeological studies show, however, high karst permeability and dominance of conduit flow. Considering the high geomorphological landscape and ecological value of the area, it should be granted the status of a nature reserve or national park. Geomorphological and karstological research within the massif should be continued as it represents a type of karst found also in other parts of Albania. This type of karst area is of great economic (groundwater reserves) and natural protection (environmental) importance.

Applying a modified conduit flow process to understand conduit-matrix exchange of a karst aquifer

Due to the high heterogeneity and complexity of water flow movement for multiple karst water-bearing mediums, the evaluation, effective development, and utilization of karst water resources are significantly limited. Matrix flow is usually laminar, whereas conduit flow is usually turbulent. The driving mechanisms of water exchange that occur between the karst conduit and its adjacent matrix are not well understood. This paper investigates the hydrodynamic characteristics and the mechanism of flow exchange in dual water-bearing mediums (conduit and matrix) of karst aquifers through laboratory experimentation and numerical simulation. A karst aquifer consisting of a matrix network and a conduit was proposed, and the relationship between the water exchange flux and hydraulic head differences generated from the laboratory experiments was analyzed. Two modes of experimental tests were performed with different fixed water level boundaries in the laboratory karst aquifer. The results indicate that the water exchange capacity was proportional to the square root of hydraulic head differences. The linear exchange term in the conduit flow process (CFP) source program was modified according to experimental results. The modified CFP and the original CFP model experimental data results were compared, and it was found that the modified CFP model had better fitting effects. These results showed that the water exchange mechanism between conduit and matrix is very important for solid-liquid interface reaction, water resource evaluation, and understanding of karst hydrodynamic behavior.© 2022 China Geology Editorial Office.

Giant paleo-seafloor craters and mass wasting associated with magma-induced uplift of the upper crust

Giant seafloor craters are known along many a continental margin with recurrent mass-wasting deposits. However, the impact of breakup-related magmatism on the evolution of such craters is barely understood. Using high-quality geophysical datasets, this work examines the genetic relationship among the location of magmatic sills, forced folds and the formation of giant paleo-seafloor craters underneath an ancient mass-transport complex in the Møre and Vøring basins, offshore Norway. The data reveal that forced folding of near-seafloor strata occurred because of the intrusion of several interconnected magmatic sills. Estimates of 1-dimensional uplift based on well data show that uplift occurred due to the intrusion of magma in Upper Cretaceous to Lower Eocene strata. Our findings also prove that subsurface fluid plumbing associated with the magmatic sills was prolonged in time and led to the development of several vertical fluid flow conduits, some of which triggered mass wasting in Neogene to Recent times. The repeated vertical expulsion of subsurface fluids weakened the strata on the continental slope, thereby promoting mass wasting, the selective cannibalization of the paleo-seafloor, and the formation of elongated craters at the basal shear zone of the mass-transport complex. Significantly, the model presented here proves a close link between subsurface magmatic plumbing systems and mass wasting on continental margins.

Impact of sedimentary fabrics on small-scale permeability variations within fine-grained sediments: Early Silurian Qusaiba Member, Northern Saudi Arabia

The main aim of this study is to constrain the range of reservoir properties observed in various depositional environments of the fine-grained sandstones of the early Silurian middle Qusaiba Member, Qalibah Formation, northwestern Saudi Arabia. Facies analysis, micro-X-ray fluorescence (μXRF), lamina-scale permeability measurements, automated helium porosity-permeability measurement, and pore system visualization were integrated to observe variations in these various environments. Seven main facies were recognized and interpreted to be deposited in an offshore “turbiditic-influenced” to lower shoreface paleoenvironments. These facies include current rippled siltstone (F1); Contorted silty sandstone (F2); current rippled fine-grained sandstone (F3); planar-laminated fine-grained sandstone (F4); Bioturbated to current-rippled argillaceous siltstone to silty sandstone (F5); Current rippled silty sandstone (F6); bioturbated sandstone (F7) facies. These facies were clustered into several fabric classes; 1) contorted fabrics associated with load casts flame structure that is characteristic of F2: These typically revealed slightly higher porosity and permeability values than the surrounding media with a spherical and relatively low anisotropy. 2) Planar-laminated fabrics in F4 that overlain by cryptic bioturbation: It comprises of clay mineral-rich laminae with higher porosity and permeability and the quartz-rich laminae with lower porosity and permeability probably due to abundant calcite cement associated with detrital quartz. Higher anisotropy, associated with this fabric, was observed. Cryptic bitourbated interval showed relatively low permeability. 3) In F7, three types of rock fabrics were observed, (1) Vertical sand-filled Piscichnus trace fossil: The burrow fill shows significantly higher porosity and permeability values than the laminated matrix; this fabric reveals an elliptical and highly anisotropic variance map. (2) Horizontal sand-filled Thalassinoides burrow (with iron oxide cement).: The internal core of this fabric was highly porous and permeable compared to the laminated fabric. Thalassinoides fabric had the most elliptical and highest anisotropic variance map in F7. (3) Entirely laminated fabric with bed-parallel gypsum veins: The permeability of the veins was slightly higher than that of the matrix, this resulted in a less anisotropic variance map. μCT scanning was used for F5 and F6; In the F5 facies, more significant porosity associated with quartz-rich lamina than iron oxide (e.g., siderite) and gypsum-rich lamina were observed probably due to higher chlorite alignment in the iron oxide-rich lamina. We found lower porosity and permeability within the vertical mud-filled burrows (Piscichnus) than the laminated fabric; this was also observed in the 3D pore system imaged by μCT scanning. These findings could have significant implications for different fabric types in fluid flow conduits in argillaceous sandstone and siltstone systems.

Natural fractures and their contribution to tight gas conglomerate reservoirs: A case study in the northwestern Sichuan Basin, China

Well-developed natural fractures in the tight gas conglomerate reservoirs of the northwestern Sichuan Basin, China, are proved to greatly contribute to the porosity and permeability of such reservoirs. Natural fractures can be storage space for hydrocarbons in the reservoir and also serve as fluid flow conduits. Outcrops, cores, and image logs were assessed in order to understand the natural gas production from the tight conglomerate reservoirs. Based on the type of interaction between fractures and clast grains, here we present three types of fractures in the conglomerate tight gas reservoirs: intergranular fractures, intragranular fractures, and grain-edge fractures. These fractures may be tectonic, diagenetic, or combined tectonic-diagenetic. Factors affecting natural fracture development in conglomerates include composition of grain and interstitial material, grain size, contact behavior of grains, and structural position. Well-developed open fractures make up over 70% of the porosity within the tight conglomerate reservoir, while the local permeability can be 3-5 orders higher than that of the matrix reservoir. Natural fractures can also significantly impact the natural gas productivity from individual wells. Production data suggests that higher natural fracture intensity correlate with higher natural gas productivity from wells. Compared with the intensity of intragranular fractures and grain-edge fractures, the high intensity of intergranular fractures shows a notably stronger correlation with high gas productivity. The impact of fractures on natural gas productivity varies greatly with fracture orientation. East-West fractures are predominant flow channels under the existing East-West stress field, contributing significantly to gas production. Northeast-Southwest-oriented fractures are of secondary importance.

Stylolites (re)activation: A factor in fluid flow and ore emplacement of Irankuh

Our research investigates the control of stylolites on fluid flow in dolostone host rocks in the Irankuh Zn-Pb world-class deposit located in Sanandaj-Sirjan Zone, Iran. Core samples from the north flank of this zone, originating from the Gushfil, Rowmarmar, and Tappehsorkh mines, were examined (macro- and microscopically) with respect to the different types of stylolites and their relationship to mineralization. The stylolites are mostly sutured with sharp peaks with simple wavy-like outlines. Tectonic stylolites are increasing in number toward ore intervals while burial stylolites usually occur in fine dolostones and clearly relate to the type of lithology. The stylolites in Irankuh often act as flow conduits which became enriched in residue solid hydrocarbon and in ore minerals (sphalerite and galena) toward intervals enriched in ores. The associated re-activation of stylolites resulted from tectonic forces and bulging. In conjunction, the injection of overpressured fluids formed intensely fractured and hydrothermal brecciated dolostone corridors. The abundance, typology, and re-activation of stylolites in Irankuh with respect to the tectonic regime support an epigenetic origin, which contrasts with the syn-sedimentary origin proposed in literature. The results presented in this study can aid in the prospection of similar ore deposits elsewhere.

Magma Mixing During Conduit Flow is Reflected in Melt‐Inclusion Data From Persistently Degassing Volcanoes

AbstractPersistent volcanic activity is thought to be linked to degassing, but volatile transport at depth cannot be observed directly. Instead, we rely on indirect constraints, such as CO2‐H2O concentrations in melt inclusions trapped at different depth, but this data is rarely straight‐forward to interpret. In this study, we integrate a multiscale conduit‐flow model for non‐eruptive conditions and a volatile‐concentration model to compute synthetic profiles of volatile concentrations for different flow conditions and CO2 fluxing. We find that actively segregating bubbles in the flow enhance the mixing of volatile‐poor and volatile‐rich magma in vertical conduit segments, even if the radius of these bubbles is several orders of magnitude smaller than the width of the conduit. This finding suggests that magma mixing is common in volcanic systems when magma viscosities are low enough to allow for bubble segregation as born out by our comparison with melt‐inclusion data: Our simulations show that even a small degree of mixing leads to volatile concentration profiles that are much more comparable to observations than either open‐ or closed‐system degassing trends for both Stromboli and Mount Erebus. Our results also show that two of the main processes affecting observed volatile concentrations, magma mixing and CO2 fluxing, leave distinct observational signatures, suggesting that tracking them jointly could help better constrain changes in conduit flow. We argue that disaggregating melt‐inclusion data based on the eruptive behavior at the time could advance our understanding of how conduit flow changes with eruptive regimes.

An essential function for autocrine hedgehog signaling in epithelial proliferation and differentiation in the trachea.

ABSTRACTThe tracheal epithelium is a primary target for pulmonary diseases as it provides a conduit for air flow between the environment and the lung lobes. The cellular and molecular mechanisms underlying airway epithelial cell proliferation and differentiation remain poorly understood. Hedgehog (HH) signaling orchestrates communication between epithelial and mesenchymal cells in the lung, where it modulates stromal cell proliferation, differentiation and signaling back to the epithelium. Here, we reveal a previously unreported autocrine function of HH signaling in airway epithelial cells. Epithelial cell depletion of the ligand sonic hedgehog (SHH) or its effector smoothened (SMO) causes defects in both epithelial cell proliferation and differentiation. In cultured primary human airway epithelial cells, HH signaling inhibition also hampers cell proliferation and differentiation. Epithelial HH function is mediated, at least in part, through transcriptional activation, as HH signaling inhibition leads to downregulation of cell type-specific transcription factor genes in both the mouse trachea and human airway epithelial cells. These results provide new insights into the role of HH signaling in epithelial cell proliferation and differentiation during airway development.

Bubbles rising through a layer of Carbopol capped with water

Air bubbles are injected into a Carbopol column capped with water to mimic ebullition from lake sediments. The first bubble sets an invisible path as it rises through the Carbopol. Subsequent bubbles rise along this path and, unlike the first bubble, break up into two separate bubbles. The leading bubble rises through the water column, while the smaller breakup bubble separates and remains trapped within the Carbopol. A conduit that forms above this breakup bubble gradually fills with water from the upper layer. After a period of growth this conduit reaches an equilibrium depth, and then starts to shrink. Inside the conduit, the rising bubbles resemble Taylor bubbles, but have velocities approximately 5–7 times the maximum velocity of standard Taylor bubbles. The variation in rise velocity depends on the interaction of the rising bubble with previous breakup bubbles. In addition, rising bubbles expel water from the conduit and water flows back after bubbles escape. This process can enhance the transport of heat and contaminants to and from aquatic sediments during ebullition events. • A damaged pathway forms inside Carbopol due to the passage of bubbles. • Bubbles break up as they cross the Carbopol–water interface. • Upper portion of the damaged pathway evolves into a water-filled conduit. • Bubbles rise much faster inside the conduit than standard Taylor bubbles. • Water flows in and out of the conduit, enhancing mixing in aquatic sediments.

Analysis of flow loss characteristics of slanted axial-flow pump device based on entropy production theory.

Slanted axial-flow pump devices are widely applied in urban water supply, irrigation and drainage engineering fields. The second law of thermodynamics is applied to investigate the flow loss characteristics of the 30° slanted axial-flow pump model according to the flow loss analysis method of entropy production theory, so that the hydraulic loss characteristics can be revealed in internal flow process of the slanted axial-flow pump. The three-dimensional numerical simulation of the whole flow conduit in slanted axial-flow pump was conducted and the entropy production increased in the flow process was calculated. The location and distribution characteristics of the flow loss of the pump were qualitatively analysed. The results show that the entropy production in impeller is the highest among the pump components. With the increase of flow rate, the proportion of the entropy production in impeller in total value of the pump device increases continuously. The wall entropy production of impeller, guide vane and outlet conduit are lower than the mainstream entropy production, and the mainstream entropy production occupies the dominant position. As the flow rate grows, the proportion of turbulent dissipation entropy production decreases, and the proportion of wall dissipation entropy production increases. At 0.8Qbep, the proportion of turbulent dissipation entropy production is close to 74%, which is about 2.8 times that of wall entropy production. Under 1.2Qbep condition, the proportion of turbulent dissipation entropy production is just 5.5% higher than that of wall dissipation entropy production.

Analyzing Vessel Regression and Endothelial Apoptosis as a Component of Angiogenic Vessel Remodeling.

Angiogenic vessel remodeling is a critical step in establishing a hierarchical vessel network. Vessel networks rapidly expand through angiogenesis in response to pro-angiogenic factors. This leads to an initially dense vessel network that requires selective regression of vessel branches to establish a hierarchical conduit for blood flow, a process known as pruning. This involves migration of endothelial cells from low-flow vessels to adjacent high-flow vessels and generally occurs independently of cell death. Vessels may also regress in response to other stimuli, including reduced metabolic demand, redundancy, and pathological stimuli. In these contexts, widespread vessel regression typically occurs and involves loss of endothelial cells by apoptotic cell death. Thus, vessel remodeling occurs via both apoptosis independent and dependent vessel regression. In this chapter, we outline a semi-automated method for quantifying vessel regression using the neonatal model of angiogenesis. We further provide instruction on analyzing endothelial apoptosis in this model.