Explore the vast range of titles available.

In this work we study strong spectral properties of Ruelle transfer operators related to a large family of Gibbs measures for contact Anosov flows. The ultimate aim is to establish exponential decay of correlations for Hölder observables with respect to a very general class of Gibbs measures. The approach invented in 1997 by Dolgopyat in “On decay of correlations in Anosov flows” and further developed in Stoyanov (2011) is substantially refined here, allowing to deal with much more general situations than before, although we still restrict ourselves to the uniformly hyperbolic case. A rather general procedure is established which produces the desired estimates whenever the Gibbs measure admits a Pesin set with exponentially small tails, that is a Pesin set whose preimages along the flow have measures decaying exponentially fast. We call such Gibbs measures regular. Recent results in Gouëzel and Stoyanov (2019) prove existence of such Pesin sets for hyperbolic diffeomorphisms and flows for a large variety of Gibbs measures determined by Hölder continuous potentials. The strong spectral estimates for Ruelle operators and well-established techniques lead to exponential decay of correlations for Hölder continuous observables, as well as to some other consequences such as: (a) existence of a non-zero analytic continuation of the Ruelle zeta function with a pole at the entropy in a vertical strip containing the entropy in its interior; (b) a Prime Orbit Theorem with an exponentially small error.

With climate change, population growth and the resulting escalating water shortage, humanity is increasingly turning to non-renewable and even fossil groundwater resources, which poses a major challenge to sustainable water management. In this study, 2D basin-scale numerical simulations were carried out on the COMSOL Multiphysics ® finite element numerical platform to identify non-renewable water resources in the Central Pannonian Basin (Central Europe, Hungary) based on the lack of hydraulic connection to recharge areas. The concept and boundary conditions (fixed water table configuration at the top, pressure-elevation profiles on the lateral sides, and constant pressure on the bottom) were derived from a previous basin-scale hydraulic data evaluation study, while the hydrostratigraphic subdivision was based on seismic and well log interpretations. As a result, topography-driven groundwater flow systems fed by meteoric water infiltration were separated from a transition zone, which contains non-renewable groundwater resources and covers 85% area of the simulated 110 km long and roughly 1600 m deep cross-section what was previously thought to be fully renewable. Such complex flow pattern and re-interpretation of the renewable and non-renewable groundwater resources can be expected in any terrestrial sedimentary basin with over-pressured flow domains.

Inspired by the electrical discharge mechanism of electric fish, we report a bio‐inspired power source based on agarose hydrogels. The device generates electrical energy by exploiting ion concentration gradients across high‐ and low‐salinity hydrogels, in combination with polyelectrolyte membrane gels exhibiting ion selectivity based on Donnan exclusion. Systematic optimization of hydrogel composition identified optimal ion concentrations and agarose content that balance energy output and mechanical stability. To further enhance performance, asymmetric redox pairs—ferrocyanide/ferricyanide at the anode and vanadium oxide at the cathode—were introduced, boosting both voltage and current outputs. Additionally, a continuous flow system was incorporated to replenish ionic gradients, addressing limitations from ion gradient depletion during extended operation. Simulations and experimental results confirmed that the flow‐assisted configuration maintained stable ion distributions, enabling sustained power output over time. This work demonstrates a safe, scalable, and environmentally friendly platform for water‐based energy harvesting, with potential applications in bio‐interfacing and soft energy devices.

A continuous Dean flow UV-C system was designed using fluorinated ethylene propylene tubing with UV-C transmission ≈60% wrapped in a serpentine path to improve axial mixing with a Dean number > 140. The microbial inactivation efficiency of the system was evaluated using Salmonella Typhimurium, E. coli O157:H7, Staphylococcus aureus , Saccharomyces Cerevisiae , and T1UV inoculated in almond milk (AM) and treated at various fluence levels at an optimized flow rate of 515 mL/min. In addition, a detailed examination of the velocity magnitude at various locations in a dean flow system, especially at the bends, was quantified. The findings indicate that a reduction > 4 log 10 CFU/mL was attained for all specified microorganisms with a reduction equivalent fluence of 22.05 mJ/cm 2 . Additionally, computational fluid dynamics were employed to examine the velocity magnitude and incident radiation field within the tubing. In summary, the system demonstrated effectiveness in inactivating target microorganisms present in almond milk. Incorporating UV treatment in the production line allows for more environmentally sustainable practices, reducing energy consumption, and may eliminate the need for additional preservatives in plant-based beverage manufacturing.

Aircraft secondary flow systems are small-flow circulation devices that are used for thermal and cold management, flow control, and energy generation on aircraft. The aerodynamic characteristics of main-flow-based inlets have been widely studied, but the secondary-flow-based small inlets, jets, and blowing and suction devices have seldom been studied. Two types of secondary flow systems embedded in a supersonic aircraft wing, a ram-air intake and a submerged intake, are researched here. Firstly, wind tunnel tests under subsonic, transonic, and supersonic conditions are carried out to test the total pressure recovery and total pressure distortion. Secondly, numerical simulations are used to analyze the flow characteristics in the secondary flow systems. The numerical results are validated with experimental data. The calculating errors of the total pressure recovery on the ram-air and submerged secondary flow systems are 8% and 10%, respectively. The simulation results demonstrate that the total pressure distortion tends to grow while the total pressure recovery drops with the increasing Mach number. As the Mach number increases from 0.4 to 2, the total pressure recovery of the ram-air secondary flow system decreases by 68% and 71% for the submerged system. Moreover, the total pressure distortion of the ram-air and submerged secondary flow systems is increased by 19.7 times and 8.3 times, respectively. Thirdly, a detailed flow mechanism is studied based on the simulation method. It is found that the flow separation at the front part of the tube is induced by adverse pressure gradients, which primarily determine the total pressure recovery at the outlet. The three-dimensional vortex in the tube is mainly caused by the change in cross-sectional shape, which influences the total pressure distortion.

The stagnant zones in nested flow systems have been assumed to be critical to accumulation of transported matter, such as metallic ions and hydrocarbons in drainage basins. However, little quantitative research has been devoted to prove this assumption. In this paper, the transport of age mass is used as an example to demonstrate that transported matter could accumulate around stagnation points. The spatial distribution of model age is analyzed in a series of drainage basins of different depths. We found that groundwater age has a local or regional maximum value around each stagnation point, which proves the accumulation of age mass. In basins where local, intermediate and regional flow systems are all well developed, the regional maximum groundwater age occurs at the regional stagnation point below the basin valley. This can be attributed to the long travel distances of regional flow systems as well as stagnancy of the water. However, when local flow systems dominate, the maximum groundwater age in the basin can be located around the local stagnation points due to stagnancy, which are far away from the basin valley. A case study is presented to illustrate groundwater flow and age in the Ordos Plateau, northwestern China. The accumulation of age mass around stagnation points is confirmed by tracer age determined by 14C dating in two boreholes and simulated age near local stagnation points under different dispersivities. The results will help shed light on the relationship between groundwater flow and distributions of groundwater age, hydrochemistry, mineral resources, and hydrocarbons in drainage basins. Key Points Groundwater age distribution is closely related to groundwater flow systems Age mass can accumulate around local stagnation points due to stagnancy The anomalous age in the Ordos Plateau is explained by the stagnation points

Jindong coal basin is one of the 14 large coal basins planned and constructed by the state, and groundwater resources play an important role in supporting the sustainable development of the coal basin. To improve the understanding of deep karst hydrogeological characteristics of the coal basin, the combination of techniques (i.e., 1:50,000 and 1:100,000 surveys, geophysical prospecting, drilling, dynamic monitoring, hydrochemistry and isotopes, etc.) was used to characterize the hydrogeological structures of deep-buried aquifers and analyze the evolution characteristics of groundwater systems under the conditions of long-term and large-scale coal mining. Deep Cambrian Zhangxia formation oolitic limestone water-rich aquifer was newly discovered in this survey, which characterized by the development of karstic fissures and strong water-richness in the effective structural zone. The dissolubility of the Cambrian Zhangxia formation oolitic limestone is weaker than that of the Ordovician Majiagou formation and Carboniferous Taiyuan formation limestone, but stronger than that of the Ordovician and Cambrian dolomite. Controlled by Jinhuo fault zone, there are many large karst groundwater-bearing basins distributed on both sides, such as Jincheng basin, Yangcheng basin, Changzhi basin, etc., and water yield in the center of the basins can reach more than 10,000 m3/days. Main types of karst groundwater storage structures in study area are syncline basin type, fault fracture zone type and permeable-impermeable contact zone type. Affected by coal mining, the dynamic conditions of karst groundwater have changed significantly, mainly manifested in the movement of the boundary of the karst groundwater system, the decline of the groundwater level, the attenuation of karst springs flow, and the complex conversion of multi-source water. The variation characteristics of the spring flow can be subdivided into three stages, namely relatively stable stage, rapid decline stage and slow decline stage. The main controlling factors of these three stages are atmospheric precipitation, coal mining and karst water exploitation, respectively. The regional groundwater circulation pattern under coal mining can be divided into shallow groundwater flow system, deep groundwater flow system and local groundwater flow system. The local groundwater flow system was mainly affected by coal mining, which was manifested as the concentrated discharge of groundwater to goaf. The results of this study will provide scientific basis for groundwater exploration and exploitation and sustainable development of coal basins.

We show that the linear drift of the Brownian motion on the universal cover of a closed connected smooth Riemannian manifold is

Investigating and studying groundwater flow systems is important for water resources management, for pollution prevention and for maintaining the ecological balance in arid and semi-arid areas. Systematic geophysics and hydrogeological investigations allow us to define the thickness of the Quaternary sedimentary layer, the lateral boundary of the groundwater system, and the depth and basement of water circulation. Hydrogeochemistry and environmental isotopes are used to gain insights into the recharge process, water–rock interactions, hydraulic characteristics and groundwater retention time and to identify groundwater flow systems at all levels in the Aksu River Basin. Owing to the dissolution of carbonate and gypsum minerals and evaporites, cation exchange between Ca2+ (Mg2+) and Na+ (K+), and the evaporation–concentration effect, concentrations of SO42−, Cl−, Na+ and total dissolved solids gradually increase along the flow direction and decrease with depth, indicating that they belong to different groundwater flow systems. Furthermore, the interpretation of stable isotope concentrations such as δ18O values suggests different degrees of depletion in the horizontal and vertical directions. Combined with the unique structural framework, the particle size variation of loose sediments and the distribution and aggregation of phreatic water with high F and As and soil salinization show the existence of the surface water and groundwater interaction mixing zones and the distribution pattern of multiple local groundwater flow systems. The vertical zonation of 3H and 14C isotope concentrations and unconformable distribution of groundwater residence time further illustrate the hydrodynamic cycle of the local and regional groundwater flow systems. The hydrodynamic and hydrochemical characteristics confirmed the distribution of groundwater flow systems and the complex mixing relationships between groundwater flow systems in the Aksu River Basin under the tectonic conditions since the Neogene in the South Tianshan Mountains.

Coastal groundwater flow investigations at the Cutler site of the Biscayne Bay south of Miami, Florida, gave rise to the dominating concept of density-driven flow of seawater into coastal aquifers indicated as a saltwater wedge. Within that wedge, convection-type return flow of seawater and a dispersion zone were concluded to be the cause of the Biscayne aquifer ‘seawater wedge.’ This conclusion was merely based on the chloride distribution within the aquifer and on an analytical model concept assuming convection flow within a confined aquifer without taking non-chemical field data into consideration. This concept was later labeled the ‘Henry problem,’ which any numerical variable-density flow program has to be able to simulate to be considered acceptable. Revisiting the summarizing publication with its record of piezometric field data (heads) showed that the so-called seawater wedge was actually caused by discharging deep saline groundwater driven by regional gravitational groundwater flow systems. Density-driven flow of seawater into the aquifer was not found reflected in the head measurements for low and high tide which had been taken contemporaneously with the chloride measurements. These head measurements had not been included in the assumption of a seawater wedge and associated dispersion zone and convection cell. The Biscayne situation emphasizes the need for any chemical interpretation of flow pattern to be backed up by head data as energy indicators of flow fields. At the Biscayne site density-driven flow of seawater did not and does not exist. This conclusion was confirmed by five independent methods. The hydrostatic use of vertical buoyancy forces needs, under hydrodynamic boundary conditions, to be replaced with buoyancy forces along the direction of the pressure potential forces [(grad p)/density] which, in the subsurface, can be pointed in any direction in space.