Sudden Flow Research Articles

Capacitive voltage effect at a resistive sintering system container and its electrical model

Abstract The electric current activated/assisted sintering (ECAS) method enables various kinds of materials to be produced much faster and environmentally friendly compared to conventional sample production systems. The main handicap of this system is that the heating regime varies according to the material type even the chemical composition of the same type of material and causes partial melting due to the sudden current flow. Previously, the ECAS output equivalent circuit is modeled as a temperature-dependent resistor in the literature. This study shows that it is insufficient to model the ECAS output consisting of a container and two stiffs as a resistor considering experimental waveforms. We report the discovery of a capacitive effect at the output of the ECAS system that has not been reported before. We have given an equivalent electrical circuit for the ECAS system output and examined the effect’s temperature dependence. The circuit model, which consists of a parallel resistor-capacitor (R p-C) circuit in series with another resistor (R s), is suggested for the container and the stiffs. By using the experimental data, the equivalent circuit parameters are calculated by curve-fitting. The temperature dependence of the equivalent circuit parameters is also examined. Possible explanations for the capacitive effect are given. Such a model and further examining the effect may help design better ECAS systems.

Ventilatory Support, Extubation, and Cerebral Perfusion Changes in Pre-Term Neonates: A Near Infrared Spectroscopy Study.

Early extubation is considered to be beneficial for pre-term neonates. On the other hand, premature extubation can cause lung derecruitment, compromised gas exchange, and need for reintubation, which may be associated with severe brain injury caused by sudden cerebral blood flow changes. We used near infrared spectroscopy (NIRS) to investigate changes in cerebral oxygenation (rScO2) and fractional tissue oxygen extraction (+) after extubation in pre-term infants. This is a single-center retrospective study of NIRS data at extubation time of all consecutive pre-term neonates born at our institution over a 1-year period. Comparison between subgroups was performed. Nineteen patients were included; average gestational age (GA) was 29.4 weeks. No significant change was noted in rScO2 and cFTOE after extubation in the whole population. GA and germinal matrix hemorrhage (GMH)-intraventricular hemorrhage (IVH) showed a significant change in rScO2 and cFTOE after extubation. A significant increase in cFTOE was noted in patients with previous GMH-IVH (+0.040; p = 0.05). To conclude, extubation per se was not associated with significant change in cerebral oxygenation and perfusion. Patients with a diagnosed GMH-IVH showed an increase in cFTOE, suggesting perturbation in cerebral perfusion suggesting further understanding during this challenging phenomenon. Larger studies are required to corroborate our findings.

Simulation of expansion and contraction for sudden plastic flow of Bingham cement grout and Newtonian fluids in a rectangular duct, using the lattice Boltzmann method

Bingham-type fluids are crucial in many industries and in geology. This study examines their behavior in reinforcing fractured rocks. Rheological properties were derived from experimental data of a water-cement mixture. Computational simulations were conducted using Lattice Boltzmann Method, with a modification to the relaxation parameter. Behavior of these mixtures in narrow ducts that widen and narrow suddenly, common in fractured rocks, was analyzed. Comparing Bingham and Newtonian fluids in various duct shapes provided insight into pressure distribution. Findings demonstrate that both cement-water mixtures, with or without addition of cement, adhere to Forchheimer flow patterns. Furthermore, it is observed that Newtonian fluids generate more intense vortices in expansive and contractive areas, resulting in higher pressure drops compared to Bingham plastics. The ultimate goal is to propose a predictive model based on mortar reinforcement for fractured rocks, taking into account rheological properties and water-cement ratio, thus reducing the need for costly experiments.

Risk Zoning Method of Potential Sudden Debris Flow Based on Deep Neural Network

With the continuous increase in global climate change and human activities, the risk of sudden debris flow disasters is becoming increasingly severe. In order to effectively evaluate and zone the potential hazards of debris flows, this paper proposes a method for zoning the potential sudden hazards of debris flows based on deep neural networks. According to hazard identification, ten risk indicators of potential sudden debris flows are determined. The risk indicators of a potential sudden debris flow in each region were used as the input factors of a deep trust network (DBN) composed of a back propagation (BP) neural network and a restricted Boltzmann machine (RBM). The DBN is pre-trained using the contrast divergence method to obtain the optimal value of the parameter set of the DBN model, and a BP network is set at the last layer of the DBN for fine-tuning to make the network optimal. Using the DBN model with the best parameters, the risk probability of debris flows corresponding to each region is taken as an output. The risk grade is divided, the risk degree of potential sudden debris flow in each region is analyzed, and the potential sudden debris flow risk in each region is divided individually. The results show that this method can effectively complete the risk zoning of sudden debris flow. Moreover, the cumulative contribution of the indicators selected by this method is significant, and the correlation of indicators is not significant, which can play a role in the risk assessment of potential sudden debris flow. This study not only provides new ideas and methods for risk assessment of sudden debris flow disasters, but also fills a gap in the field of geological hazard susceptibility mapping.

Assessing water quality in a distribution network based on hydraulic conditions

Abnormalities in hydraulic conditions inside a water distribution network are strongly related to the deterioration of drinking water quality. Leaking pipes and valves cause changes to the hydraulic conditions and allow the entry of impurities into the distribution system. Sudden flow and pressure shocks can detach soft deposits and biofilms from the pipe surface, resulting in deterioration of water quality. Online water quality measurements in a distribution network are scarce, but more common online flow and pressure measurements reveal the changes in hydraulic conditions in a distribution network and can be utilized to assess the water quality continuously and near real-time via modelling. Here, a data-driven model based solely on the online flow and pressure measurements in a distribution network for assessing the water quality at the end of an urban district metered area is presented. With the accuracy of R2 0.77, the developed data-driven model is able to assess the level of and the changes in potable water quality in a non-laborious and cost-effective way, also enabling proactive operations to ensure the distribution of high-quality drinking water to the consumers.

Influence of Hematocrit Level and Integrin αIIbβIII Function on vWF-Mediated Platelet Adhesion and Shear-Induced Platelet Aggregation in a Sudden Expansion.

Shear-mediated thrombosis is a clinically relevant phenomenon that underlies excessive arterial thrombosis and device-induced thrombosis. Red blood cells are known to mechanically contribute to physiological hemostasis through margination of platelets and vWF, facilitating the unfurling of vWF multimers, and increasing the fraction of thrombus-contacting platelets. Shear also plays a role in this phenomenon, increasing both the degree of margination and the near-wall forces experienced by vWF and platelets leading to unfurling and activation. Despite this, the contribution of red blood cells in shear-induced platelet aggregation has not been fully investigated-specifically the effect of elevated hematocrit has not yet been demonstrated. Here, a microfluidic model of a sudden expansion is presented as a platform for investigating platelet adhesion at hematocrits ranging from 0 to 60% and shear rates ranging from 1000 to 10,000 s-1. The sudden expansion geometry models nonphysiological flow separation characteristic to mechanical circulatory support devices, and the validatory framework of the FDA benchmark nozzle. PDMS microchannels were fabricated and coated with human collagen. Platelets were fluorescently tagged, and blood was reconstituted at variable hematocrit prior to perfusion experiments. Integrin function of selected blood samples was inhibited by a blocking antibody, and platelet adhesion and aggregation over the course of perfusion was monitored. Increasing shear rates at physiological and elevated hematocrit levels facilitate robust platelet adhesion and formation of large aggregates. Shear-induced platelet aggregation is demonstrated to be dependent on both αIIbβIII function and the presence of red blood cells. Inhibition of αIIbβIII results in an 86.4% reduction in overall platelet adhesion and an 85.7% reduction in thrombus size at 20-60% hematocrit. Hematocrit levels of 20% are inadequate for effective platelet margination and subsequent vWF tethering, resulting in notable decreases in platelet adhesion at 5000 and 10,000 s-1 compared to 40% and 60%. Inhibition of αIIbβIII triggered dramatic reductions in overall thrombus coverage and large aggregate formation. Stability of platelets tethered by vWF are demonstrated to be αIIbβIII-dependent, as adhesion of single platelets treated with A2A9, an anti-αIIbβIII blocking antibody, is transient and did not lead to sustained thrombus formation. This study highlights driving factors in vWF-mediated platelet adhesion that are relevant to clinical suppression of shear-induced thrombosis and in vitro assays of platelet adhesion. Primarily, increasing hematocrit promotes platelet margination, permitting shear-induced platelet aggregation through αIIbβIII-mediated adhesion at supraphysiological shear rates. The online version contains supplementary material available at 10.1007/s12195-024-00796-0.

PSO‐SMADRC for altitude test facility intake pressure environmental simulation system

AbstractTo address significant disturbances, including sudden air flow variation, model uncertainty, and unavoidable measurement noises during aeroengine transient tests in the intake environmental pressure simulation system (IEPSS), a sliding mode active disturbance rejection controller (SMADRC) is designed. The sliding mode control in SMADRC can deal with unmatched disturbances that are beyond the capabilities of the extended state observer (ESO) in ADRC. And the particle swarm optimization (PSO) algorithm is introduced to tune and optimize the controller parameters to further enhance the performance. To validate the effectiveness of the proposed method, simulations are conducted on the IEPSS software platform. The simulation results clearly demonstrate PSO‐SMADRC can reduce the mean squared error by 60.9%, the input oscillation by 68.7%, and the maximum deviation by 53.9%, compared with LADRC originally applied in the IEPSS.

GIS Environment Based Study of Acute Myocardial Infarction Incidence and Associated Risk Factors at a Major Referral Cardiac Center in Twin City of Rawalpindi and Islamabad, Pakistan

Background: Acute Myocardial Infarction (AMI) is a critical cardiac condition characterized by sudden blood flow blockage to the heart. Previous research indicates associations between AMI risk and factors such as age, gender, lifestyle habits, and preexisting medical conditions. Methods: This cross-sectional spatial analysis study aims to explore the geographically diverse incidence of AMI and associated risk factors in the twin cities of Islamabad and Rawalpindi. Data from 500 AMI patients, collected in April 2022 from a major cardiac center, were analyzed using the Chi-square test to assess associations between AMI risk factors. Results: Significant associations were identified between the lifestyle of AMI patients and diabetes (p = 0.002), and a highly significant association of age was found with diabetes, hypertension, and smoking (p = 0.000). This pioneering spatial analysis of AMI incidence provides valuable insights for developing national health interventions in Pakistan. Conclusion: This study addresses the significant concern of AMI incidence and associated risk factors in data-sparse Pakistan. Utilizing Geographical Information System (GIS), it offers a spatial understanding of AMI distribution and patterns, paving the way for future cardiovascular health research in the country.

A multi-time-scale wall model for large-eddy simulations and applications to non-equilibrium channel flows

The recent Lagrangian relaxation towards equilibrium (LaRTE) approach (Fowleret al.,J. Fluid Mech., vol. 934, 2022, A44) is a wall model for large-eddy simulations (LES) that isolates quasi-equilibrium wall-stress dynamics from non-equilibrium responses to time-varying LES inputs. Non-equilibrium physics can then be modelled separately, such as the laminar Stokes layers that form in the viscous region and generate rapid wall-stress responses to fast changes in the pressure gradient. To capture additional wall-stress contributions due to near-wall turbulent eddies, a model term motivated by the attached eddy hypothesis is proposed. The total modelled wall stress thus includes contributions from various processes operating at different time scales (i.e. the LaRTE quasi-equilibrium plus laminar and turbulent non-equilibrium wall stresses) and is called the multi-time-scale (MTS) wall model. It is applied in LES of turbulent channel flow subject to a wide range of unsteady conditions from quasi-equilibrium to non-equilibrium. Flows considered include pulsating and linearly accelerating channel flow for several forcing frequencies and acceleration rates, respectively. We also revisit the sudden spanwise pressure gradient flow (considered in Fowleret al.,J. Fluid Mech., vol. 934, 2022, A44) to review how the newly introduced model features affect this flow. Results obtained with the MTS wall model show good agreement with direct numerical simulation data over a vast range of conditions in these various non-equilibrium channel flows. To further understand the MTS model, we also describe and test the instantaneous-equilibrium limit of the MTS wall model. In this limit, good wall-stress predictions are obtained with reduced model complexity but providing less complete information about the wall-stress physics.

Research on Real-Time Monitoring and Warning Technology for Multi-Parameter Underground Debris Flow

Sudden debris flows in underground mines are characterized by strong burstiness, great destructiveness, and difficult monitoring. Traditional single monitoring methods can only roughly judge the probability of underground debris flow occurrences through one-sided potential phenomena, making it difficult to accurately predict sudden underground debris flows. Therefore, effective monitoring methods can prevent or reduce waste and damage to mineral resources caused by mine debris flow disasters. This study is based on the theoretical foundations of rainfall automatic identification program, unsteady flow theory, and wavelet threshold denoising theory. It preprocesses key data such as rainfall, groundwater, and surface displacement with the aim of reducing criterion errors and improving the accuracy of determination. By utilizing the underground debris flow warning determination program, warning determination algorithm, and information management system hosted on the monitoring and warning platform, a comprehensive underground debris flow warning system is integrated. This system incorporates determining parameters such as rainfall, water inflow, groundwater level, surface subsidence, pore water pressure, surrounding rock stress, microseismic phenomena, and underground video recognition, with the innovative approach of “weather-surface-underground” multi-directional monitoring. The system was successfully installed and applied in the Pulang Copper Mine in Yunnan Province, demonstrating good application effectiveness. The results indicate that compared to traditional single monitoring methods, the multi-directional monitoring and warning system for underground debris flows has advantages such as low fault tolerance and high accuracy, making it more suitable for ensuring safe mining in mining areas.

Research and experiments on low throttle loss switched inertance hydraulic systems based on inertive elements

Switching hydraulic inertial systems (SIHS) manipulate the interaction of inertial and capacitive components through switching valves to achieve the efficient and rapid pressure regulation. However, the opening and closing of the switching valve lead to fluid expansion and compression in the switched volume, which generates throttling losses in the switching valve transition cycle, resulting in substantial energy loss. Hydraulic soft switching is an essential means to solve the loss of switching valves. However, the poor resonance performance of the hydraulic system leads to arduousness in the soft switching design. Therefore, this paper proposes that a mechanical-hydraulic coupling mechanism can realize the soft switching. A new approach is proposed to realize soft switching with a parallel double-motor mechanism based on the new idea. The approach connects inertive elements, at the back, to the switching valve to suppress the sudden flow increase caused by the compressed fluid in the switched volume during the opening transition stage of the switching valve, thus effectively reducing the loss caused by the throttling flow of the switching valve. The new approach has been experimentally verified to reduce the throttling flow by 33%, resulting in an increase of the SIHS output efficiency by 10%–15%.

Numerical simulation of turbidity currents using consistent particle method

This paper expands the Consistent Particle Method (CPM) to simulation of turbidity currents with focus on turbulent water-sediment flow. A mixture model is adopted in solving the sediment transport equation to simulate the sediment mass transfer due to settling convection and turbulent diffusion. To compute the gravity-driven convection term, the proposed CPM-upwind scheme is relatively easy to implement as it avoids the use of a kernel function which has the requirements of symmetry and unity. Two sand settling problems demonstrate the good accuracy of the CPM-upwind scheme. For suspended sediment diffusion caused by turbulence, CPM is able to model anisotropic diffusion without the averaging effect caused by the isotropy requirement if a kernel function is used. The validated CPM methodology is then applied to simulate a sudden flow of water-sediment mixture into ambient water. The results of the mixture front motion and sediment deposit density agree well with published experimental results.

Analysis of the flow phenomenon of fluid undergoing a sudden contraction to an annular gap

The paper presents the visualization results of the sudden contraction flow field with an annular gap downstream of the contraction cross section. The contraction ratio directly influences the flow phenomena. No stationary vortices were observed upstream of the contraction cross section, and flow separation divided the flow field within the annular gap into a recirculation zone, a shear layer, and a mainstream zone. Vena-contracta point and reattachment point occurred within the flow field of the annular gap. The production of Reynolds stress varied with the contraction ratio, and the momentum exchange mainly occurred in the recirculation zone and the shear layer, while the flow state in the mainstream zone tended to become isotropic. Rapid changes in turbulent kinetic energy primarily occurred in the shear layer, and the production term of turbulent kinetic energy contributed the most. Applying computational fluid dynamics and experimental results, this study has formulated an expression for the contraction coefficient of the proposed model. The axial positions of the vena-contracta point and reattachment point have a strong correlation with the contraction ratio, which can be represented by an exponential function.

Vortex evolution and merging mechanism across 180° sharp bend for laminar inflow

The present study deals with the fundamentals of vortex evolution and merging across a 180° sharp bend for laminar inflow (Re = 800). A three-dimensional flow and pressure distribution across the bend are analyzed by using particle image velocimetry measurements. The results show that the sudden flow redirection and adverse pressure gradient create a recirculation region in the vicinity of the divider wall. The vorticity and turbulent kinetic energy distribution highlight the presence of a shear layer between the recirculation and mainstream turning flow. A Rayleigh instability analysis shows the existence of centrifugal instabilities outside the shear layer in the mainstream turning flow. The imbalance of centrifugal and pressure forces act in unison to produce a net force that creates Dean instability across the mainstream turning flow. Consequently, two pairs of counter-rotating Dean vortices develop after the first turn, possibly merging into a single pair after the subsequent 90° turn. Finally, the evolution and merging of Dean vortices are explained with the help of a conceptual diagram illustrating the force interaction and the formation of counter-rotating currents.

Detections of Infrasound Waves From Water Discharges at a Hydroelectric Dam: Implementation of Timely Warnings for Unexpected Discharge Events

AbstractWater discharges at hydroelectric dams on the Imjin River, which flows through North and South Korea, generate abrupt water level increases downstream. We assessed infrasound signals from water discharges using an infrasound array located ∼32 km from the source and applied infrasound detection in a flash flood alert system. Using infrasound signals, there was a 79% detection rate for 48 water level increase events occurring in the river downstream during a 14‐year period (2008–2021). The detected signals had a low amplitude, long duration, and broad frequency range (0.5–15 Hz). The energy curves of the detected infrasound signals for selected events showed good correlations with the onset times and water level variations in water level records. These results demonstrate that infrasound monitoring can serve as a practical early warning system for impending flash floods resulting from unnoticed water discharges or sudden debris flows in mountainous regions.

МЕТОДИКА ОБОСНОВАНИЯ СТРУКТУРЫ И ХАРАКТЕРИСТИК СИСТЕМЫ РЕМОНТНО-ОБСЛУЖИВАЮЩЕЙ БАЗЫ, ОБЕСПЕЧИВАЮЩЕЙ РАБОТОСПОСОБНОСТЬ СОВРЕМЕННОЙ ТЕХНИКИ

The effective operation of the machine and tractor fleet (MTF) of a modern agro-industrial complex requires monitoring of its technical condition by a system of repair and maintenance bases (RMB). A methodology for substantiating the structure and characteristics of the ROB system using special decision support systems (SDSS) is proposed, which will make it possible to implement the maintenance strategy “by actual state”, as well as reduce the recovery time of the MTF. The methodology includes a set of interrelated models: forecasting and diagnosing the technical condition of the MTF, the functioning of the system for ensuring the operability of the MTP and the formation of cost dependencies on the functioning of the RMB system. Algorithms were applied: redistribution of costs between maintenance activities (TO) and current repairs (TR); solution of the optimization problem based on the modified Nelder-Mead method. It was revealed that the small value of the maintenance interval allows to achieve sufficiently high values for the coefficient of technical readiness (Kg). It is shown that the main measure that allows to reduce operating costs and positively influence the value of Kg is the rational distribution of time for carrying out checks used during maintenance of the MTF sample. The use of 2-6 specialists makes it possible to ensure the duration of maintenance according to the state of the ICC unit from two to four hours. Deviations of more than 30 minutes at TR from the normative values of the recovery time led to a sharp decrease in the level of availability at the current level of the sudden failure flow parameter. Attracting an average of 3 - 4 specialists is required to complete the TR. It has been established that the main condition for the optimal operation of the MTF sample is individual monitoring of its technical condition, which makes it possible to reduce the duration of adjustment and repair measures by 40%. The condition for the effectiveness of the RMB system is the presence of at least four people of engineering and technical staff in the teams that carry out these activities. The total cost reduction for ensuring the working condition of the studied equipment was about 18 - 20%.

Multidecadal pre- and post-collapse dynamics of the northern Larsen Ice Shelf

Rapid retreat of Antarctic ice shelves in a warmer climate remains challenging to predict, contributing to uncertainties in projections of sea level rise. The collapse of the Larsen B Ice Shelf on the Antarctic Peninsula in 2002 was perhaps the most dramatic example of ice shelf retreat on record. Despite a general consensus that regional climate warming is associated with ice shelf collapse, knowledge of the precise details leading to and following collapse is limited. Here we examine a comprehensive set of satellite observations, modeling experiments, and climate reanalysis data to elucidate calving behavior, flow dynamics, and mechanical conditions of the northern Larsen Ice Shelf since the mid-1960s. Our analysis reveals that the Larsen B collapse in March 2002 was the last phase of a calving sequence that began in 1998, and was controlled by both atmospheric and oceanic anomalies that weakened the ice shelf structure over time. The collapse was preceded by a transition from infrequent calving of large tabular-icebergs and localized flow acceleration to frequent calving of small-icebergs and ice-shelf-wide acceleration. The intermittent pulses of the calving sequence were triggered by failure of the northern shear margin, most likely due to ocean-driven weakening by incision of sub-ice-shelf channels, and were further controlled by the location of effective buttressing sources and preexisting crevasses. The limited observational data indicate a similar process for the Larsen A ice shelf. These calving events corresponded with warm anomalies associated with a La Niña / positive Southern Annular Mode teleconnection pattern. The results suggest that warm climate anomalies control the occurrence of calving, while the extent and speed of calving are governed by ice shelf geometry and mechanical conditions, in particular, the sturdiness of the “weakest” shear margin. Sudden widespread flow acceleration and frequent small-iceberg calving may serve as quantifiable precursors for ice shelf destabilization.

Microstructure and Cavitation Damage Characteristics of GX40CrNiSi25-20 Cast Stainless Steel by TIG Surface Remelting

Cavitation erosion degrades the surface of engineering components when the material is exposed to turbulent fluid flows. Under conditions of local pressure fluctuations, a nucleation of gas or vapor bubbles occurs. If the pressure suddenly drops below the vapor pressure, these bubbles collapse violently when subjected to higher pressure. This collapse is accompanied by the sudden flow of the liquid, which is manifested by stress pulses capable of causing plastic deformations on solid surfaces. Repeating these stress conditions can cause material removal and ultimately failure of the component itself. The present study aims to reduce the negative impact of this phenomenon on the mechanical systems components, using the TIG local surface remelting technique. Cavitation erosion tests were performed in accordance with the ASTM G32-2016 standard on samples taken from a cast high-alloy stainless steel. The alloy response for each melting current value was investigated by measuring mass loss as a function of cavitation attack time and by analyzing the damaged surfaces using optical and scanning electron microscopes. It was highlighted that the TIG remelted layers provide an increase in cavitation erosion resistance of 5-6 times as a consequence of the fine graining and microstructure induced by the technique applied.

Hazard assessment and formation mechanism of debris flow outbursts in a small watershed of the Linxia Basin

The Linxia Basin is located in the transition zone between the Qinghai–Tibet Plateau and the Loess Plateau in China. Collapse–landslide–debris flow geological disasters are particularly prevalent in this region. Taking a debris flow that occurred in Zhangjiayuan gully, Dongxiang County, as an example, the characteristics and formation mechanism were studied through field investigation and remote sensing interpretation methods. The hazard zoning and influence range of the debris flow were analysed under different precipitation conditions using numerical simulations. The results show that the debris flow in Zhangjiayuan gully experienced medium-to small-scale, rapid and catastrophic viscous mud flows, with activity frequencies ranging from medium to low. Because large numbers of landslides, collapses and overland flows developed on the gully bank slope, material sources for debris flows were abundant but were supplied intermittently. Induced by heavy rainfall, the landslides on the bank slipped into the gully, and then the landslide mass blocked the channel and formed a weir dam. As water converged in the gully, the dam body softened to mud, seepage deformation occurred, and the dam then burst to form a debris flow. This disaster mode represents a kind of rainfall-type landslide–blockage–debris flow disaster chain. Under varying conditions in which heavy rainfall occurs once every 10 years or once every 50 years, debris flows may break out in Zhangjiayuan gully, and the Zheda highway and the associated tunnels located below the gully are in medium–high debris flow danger zones. When a debris flow rushes out of the gully mouth and cannot be discharged in time, it accumulates and buries the highway and tunnels. Therefore, attention should be given to preventing such small-scale sudden debris flow disasters and strengthening the early warning capacity of debris flow prevention to ensure the safe operation of highway.

Optimization of Emergency Evacuation Behavior for Sudden High Passenger Flow in Resilient Hubs

Optimization of Emergency Evacuation Behavior for Sudden High Passenger Flow in Resilient Hubs