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We study the Rayleigh--Taylor instability for two miscible, incompressible, inviscid fluids. Scale invariant estimates for the size of the mixing zone and coarsening of internal structures in the fully nonlinear regime are established following techniques introduced for the Saffman--Taylor instability in [G. Menon and F. Otto, Comm. Math. Phys., 257 (2005), pp. 303--317]. These bounds provide optimal scaling laws and reveal the strong role of dissipation in slowing down mixing. [ABSTRACT FROM AUTHOR]

Carbonate‐brucite chimneys are a characteristic of low‐ to moderate‐temperature, ultramafic‐hosted alkaline hydrothermal systems, such as the Lost City hydrothermal field located on the Atlantis Massif at 30°N near the Mid‐Atlantic Ridge. These chimneys form as a result of mixing between warm, serpentinization‐derived vent fluids and cold seawater. Previous work has documented the evolution in mineralogy and geochemistry associated with the aging of the chimneys as hydrothermal activity wanes. However, little is known about spatial heterogeneities within and among actively venting chimneys. New mineralogical and geochemical data (87Sr/86Sr and stable C, O, and clumped isotopes) indicate that the brucite and calcite precipitate at elevated temperatures in vent fluid‐dominated domains in the interior of chimneys. Exterior zones dominated by seawater are brucite‐poor and aragonite is the main carbonate mineral. Carbonates record mostly out of equilibrium oxygen and clumped isotope signatures due to rapid precipitation upon vent fluid‐seawater mixing. On the other hand, the carbonates precipitate closer to carbon isotope equilibrium, with dissolved inorganic carbon in seawater as the dominant carbon source and have δ13C values within the range of marine carbonates. Our data suggest that calcite is a primary mineral in the active hydrothermal chimneys and does not exclusively form as a replacement of aragonite during later alteration with seawater. Elevated formation temperatures and lower 87Sr/86Sr relative to aragonite in the same sample suggest that calcite may be the first carbonate mineral to precipitate. Plain Language Summary: At the Lost City hydrothermal field, warm alkaline fluids are discharging out of uplifted mantle rocks. When vent fluids mix with seawater at the seafloor, carbonate and brucite minerals form spectacular towers up to 60 m high. Systems like Lost City are important because the reaction between water and rocks provides carbon and energy sources for microbial life. However, we still do not fully understand what controls the mineralogy and geochemistry of the Lost City hydrothermal chimneys. In this paper, we suggest that the extent of mixing between the hydrothermal fluids and seawater influences the mineralogy and geochemistry of the chimneys. Calcite, which was previously thought to form only during alteration of aragonite by seawater, can also form during seawater‐hydrothermal fluid mixing. Both calcite and brucite form in the interior of the chimneys where vent fluid is more dominant. Aragonite, on the other hand, forms in the exterior of the structures from seawater‐rich fluids. Lastly, because minerals precipitate rapidly during fluid mixing, the stable isotope geochemistry of the carbonates mostly records the composition and temperature of seawater and not the mixed fluid. Thus, care should be exercised in interpreting mineral geochemical data from similar systems. Key Points: The mineralogy and geochemistry of Lost City chimneys are controlled by the extent of mixing between hydrothermal fluids and seawaterBrucite and calcite precipitate in vent fluid dominated zones while aragonite forms in the exterior of the structures in seawater‐rich zonesCarbonates precipitate in isotopic disequilibrium and record the O and C stable isotope composition of seawater dissolved inorganic carbon [ABSTRACT FROM AUTHOR]

The relationship between Sn–Ag mineralization and mantle magmatism is a topic of high interest in current ore deposit research. Here, we investigate porphyry-, skarn-, and cassiterite-sulfide type Sn-polymetallic deposits associated with granitoids and vein-type Ag–Pb–Zn deposits hosted in sub-volcanic rocks in the southern Great Xing'an Range (SGXR), northeast China, as a case example. We use He, Ar, and S isotopes and isotopic end-member simulation calculations to determine the contribution of mantle-derived fluids/melts to the ore mineralization. Our He–Ar isotope data demonstrate that the ore-forming fluids are mixtures of shallow crust-derived fluid containing radiogenic 4He but no radiogenic 40Ar and magmatic fluids with mantle-derived 3He and 40Ar. The Pb–Zn–Ag deposits have a higher contribution of magmatic volatiles than the Sn-polymetallic deposits. Sulfide δ34S values of − 2.7 to − 0.6‰ in the Pb–Zn–Ag deposits are consistent with a magmatic sulfur source, whereas sulfides with δ34S values of − 12.2 to − 0.15‰ in the Sn-polymetallic deposits signal a possibly bimodal source of sulfur, i.e., crustal light sulfur mixed with magmatic sulfur. The noble gas compositions of the ore fluids are controlled by crustal thickness, high 3He fluxes (24 to 404 at/s/cm2), and low residence time (1 to 18 Myr) of He in the asthenosphere below the SGXR. Non-equilibrium open-system magma degassing is evidenced by the range of elevated values of 4He/40Ar* ratios (4.8–127). The 3He/heat ratio of the ore fluids from the Sn and Pb–Zn–Ag deposits overlap (0.01–0.76 × 10−2 cm3 STP J−1 (cubic centimeter at standard temperature and pressure per joule) and 0.02–1.08 × 10−2 cm3 STP J−1, respectively), indicating a consequence of conduction of mantle-derived heat across the magma-hydrothermal interface. Furthermore, an increasing abundance of Sn reserves in the SGXR deposits can be equated with an increase in the mantle-derived He component in the ore fluids. These findings suggest that a continuous flux of mantle-derived fluids/melts plays an essential role in Sn–Ag–Pb–Zn mineralization. [ABSTRACT FROM AUTHOR]

The Altun orogenic belt is situated along the northern boundary of the Tibetan Plateau. In this study, we present an analysis of the ore deposit, mineral composition, and carbon isotope signatures of the Tugeman graphite deposit within the Altun orogenic belt. The graphite in the Tugeman graphite deposit occurs within graphite-bearing schists and marble. Graphite enrichment is observed in the ductile shear zone. The carbon isotope values of graphite range between −18.90‰ and −10.03‰ (with an average value of −12.70‰). These values differ significantly from those observed in organic matter and marine carbonates, suggesting the occurrence of a mixing process involving reduced carbon fluid derived from biological organic material during regional metamorphism as well as a potential influx of oxidized carbon fluid from external sources. In addition, the metamorphic temperature of Tugeman graphite calculated from Raman spectroscopy is between 494 °C and 570 °C, which indicates that the disordered material is transformed from greenschist-amphibolite facies metamorphism to moderate-crystalline graphite. Combining the geological and carbon isotope characteristics of the Tugeman graphite deposit, we argue that the Tugeman graphite deposit is a regional metamorphic graphite deposit of biogenic origin, and during the late stage of metamorphism, it underwent interaction with fluids. [ABSTRACT FROM AUTHOR]

Carbonate-hosted Pb–Zn deposits are of major economic importance. The Sichuan–Yunnan–Guizhou metallogenetic belt (SYGMB), located on the western margin of the Yangtze Block, comprises over 400 carbonated-hosted Pb–Zn deposits. However, ore-forming fluids recorded in these deposits have led to controversy regarding ore genesis. We investigated a fluid system for the Maoping deposit in the SYGMB, based on fluid inclusions, and H–O–He–Ar isotopic studies. The results showed that ore-forming fluids in the Maoping deposit are characterized by mixing of high-temperature and low-salinity metamorphic fluids and low-temperature and high-salinity basinal brines. The Precambrian basement is considered to produce metamorphic fluids, while the basinal brines are said to originate from the Youjiang Basin. The mineralization at the depositional site appears to reflect the coincidence of the metamorphic fluids, basinal brines, Carboniferous coal seams, and structural-stratigraphic traps. Regional-scale data show large-scale heterogeneity in fluid properties, including basinal brines, metamorphic fluids, and organic fluids. Furthermore, the data suggest a precipitation model for some high-grade Pb–Zn deposits in the SYGMB. These findings will contribute to an understanding of deposit types in the SYGMB. [ABSTRACT FROM AUTHOR]

• A fluid-structure interaction model of acoustic resonant system was built. • The dynamic characteristics of the coupled system were systematically analyzed. • The equivalent mass of fluid decreases as the excitation amplitude increases. • Increasing the excitation frequency can enhance dynamic response of the system. This paper investigates the dynamic characteristics of a multi-degree-of-freedom (multi-DOF) acoustic resonant system involving highly viscous fluids. First, a fluid-structure interaction (FSI) model is established to describe the interaction between the multi-DOF acoustic resonant system and the two-phase fluids, and then the effects of various excitation parameters on the dynamic response of the coupled system are studied. Under the influence of vertical acoustic vibration, the fluid in the container undergoes violent and irregular motions, which leads to a decrease and fluctuation in the equivalent mass of the fluid. The reduction in fluid equivalent mass causes the excitation frequency to deviate from the natural frequency of the multi-DOF acoustic resonant system, thus significantly reducing the dynamic response of the coupled system. Furthermore, the fluctuation of the fluid equivalent mass induces a quasi-periodic motion pattern of the acoustic resonant system. Although increasing the excitation amplitude can effectively increase the dynamic response of the coupled system, it can also increase the fluctuation level of the dynamic response to a certain extent. By appropriately increasing the excitation frequency, the coupled system can operate at a new resonant frequency, thereby reducing the influence of fluid motion on the dynamic response of the system. [ABSTRACT FROM AUTHOR]

Utilizing in situ oxygen isotope analysis, we demonstrate the potential of cassiterite as a robust recorder of fluid source and evolution. Cassiterite is an ore mineral, and its mineral–water oxygen isotope fractionation factor is only weakly temperature-dependent. Unlike most explored gangue minerals such as quartz, cassiterite can provide a direct and robust archive of ore-forming fluids, e.g., fluid oxygen isotope composition (δ18O values). Core and rim domains of a representative cassiterite crystal from the Piaotang tin-tungsten (Sn-W) deposit, China, are characterized by contrasting δ18O values. Cassiterite δ18O values are –2.14 ± 0.41 ‰ for the core and 2.36 ± 0.36 ‰ for the rim, which equate to fluid δ18O values of ~ 4.1 ‰ (core) and ~ 8.6 ‰ (rim). Additionally, the cassiterite rim is enriched in niobium (Nb) and tantalum (Ta) compared to the mineral core. The δ18O, and Nb and Ta data are interpreted to reflect core to rim crystallization from distinct pulses of magmatic-hydrothermal fluids that possessed a discrete oxygen isotopic, and Nb and Ta composition. Such a pulsed process could be a common feature for Sn-W deposits, and is critical to the formation of giant deposits with high metal grades. Involvement of meteoric water associated with the first mineralization stage reaches ~ 33%, but is limited (~ 7%) in the second (main) mineralization stage. Therefore, cooling induced by fluid mixing may not be necessary for tin deposition, and our new findings invite a reassessment of the role of meteoric water in other Sn-W deposits. Our petrologic modelling shows that fluids exsolved from a 10 – 15 km3 parental granitic magma can yield the Sn-W endowments recorded at Piaotang. Further, during magma fractionation, Sn and W are preferentially transferred into fluids compared to Nb and Ta. As a consequence, fluid chemistry is the primary factor controlling metal endowment and zoning in W-Sn deposits, as observed at Piaotang, and explains the predominant magmatic origin of Nb–Ta deposits. [ABSTRACT FROM AUTHOR]

The mixing characteristics of two initially stratified high‐viscosity fluids with a free surface under forced vertical vibration were studied experimentally and numerically. The flow characteristics and dynamics of the free surface and interface between liquids were analyzed and the effects of the vibration parameters on the mixing process were evaluated. The degree of mixing was determined by the frequency and amplitude of vibration. Effective mixing could not be achieved by merely using the deformation of the free surface because of the low fluidity of high‐viscosity fluids. However, an increase in vibration intensity disintegrated the free surface and interface, thereby significantly promoting the mixing of fluids and improving the mixing efficiency. [ABSTRACT FROM AUTHOR]

• Physiological surface tension had a negligible effect on ADV-mediated PO 2 reduction. • Fluid protein concentration was uncorrelated with PO 2 reduction. • Viscosity had a transient effect on PO 2 reduction. • Fluid mixing accelerated PO 2 reduction at physiologic viscosities. • Reduction in the PO 2 in whole blood was demonstrated. Acoustic droplet vaporization (ADV) has been shown to reduce the partial pressure of oxygen (PO 2) in a fluid. The goals of this study were three-fold: 1) to determine the ADV pressure amplitude threshold in fluids that had physiologically relevant values for surface tension, protein concentration, and viscosity; 2) to assess whether these parameters and fluid mixing affect ADV-mediated PO 2 reduction; and 3) to assess the feasibility of ADV-mediated PO 2 reduction in plasma and whole blood. In vitro ADV experiments were conducted using perfluoropentane droplets (number density: 5 × 106 ± 0.2 × 106/mL) dispersed in fluids (saline, polyvinylpyrrolidone solutions, porcine plasma, or porcine whole blood) that had a physiological range of surface tensions (62–68 mN/m), protein concentrations (0 and 68.7 mg/mL), and viscosities (0.7–4 cP). Droplets were exposed to pulsed ultrasound (5 MHz, 4.25 MPa peak negative pressure) while passing through a 37 °C flow system with inline PO 2 sensors. In select experiments, the fluid also passed through mixing channels after ultrasound exposure. Our results revealed that the ADV pressure thresholds were the same for all fluids. Surface tension and protein concentration had no effect on PO 2 reduction. Increasing viscosity attenuated PO 2 reduction. However, the attenuated effect was absent after fluid mixing. Furthermore, ADV-mediated PO 2 reduction in whole blood (30.8 ± 3.2 mmHg) was less than that in a polyvinylpyrrolidone solution (40.2 ± 2.1 mmHg) with equal viscosity. These findings should be considered when planning clinical studies of ADV-mediated PO 2 reduction and other biomedical applications of ADV. [ABSTRACT FROM AUTHOR]

Thermal convection and fluid mixing are involved in the formation of many mineral deposits, but their relationships and roles in mineralization remain poorly understood because they are generally investigated separately in different studies. Here we present a case study combining thermal convection and fluid mixing to examine the critical factors that controlled the formation of high-grade, world-class unconformity-related uranium (URU) deposits in the Athabasca Basin (Canada). Reactive transport modeling of various scenarios with different degrees of involvement of thermal convection and fluid mixing shows that significant URU mineralization occurs at the intersection of a basement fault with the basin-basement unconformity only if thermal convection and basin-basement fluid mixing take place concurrently. If there is no thermal convection in the basin, only sparse U mineralization occurs along the unconformity. If insufficient amount of reducing fluid is provided from the basement along the fault, no significant U mineralization occurs either. Furthermore, no significant U mineralization occurs if the U concentration in the basinal fluid is low. We conclude that the exceptionally rich U endowment in the Athabasca Basin is the result of coupling of three critical factors: high-permeability sandstone favoring thermal convection in the basin, ample supply of reducing agents by basement fluids along reactivated basement faults, and abundant U-rich basinal fluid available in the basin sequences. Similar coupling of fluid processes may be essential for the formation of other types of mineral deposits. • Reactive transport modeling reproduces unconformity-related U mineralization. • Thermal convection and fluid mixing must occur simultaneously for U mineralization. • Permeable sandstone is critical for initiating and maintaining thermal convection. • Permeable basement faults linked with regional faults can provide ample reductant. • Availability of U-rich basinal fluids in sandstone is vital for U mineralization. [ABSTRACT FROM AUTHOR]

Mixing between two different fluids with a mutual interface must be initiated by fluid transporting across this fluid interface, caused, for example, by applying an unsteady velocity agitation. In general, there is no necessity for this physical flow barrier between the fluids to be associated with extremal or exponential attraction, as might be revealed by applying Lagrangian coherent structures, finite-time Lyapunov exponents or other methods on the fluid velocity. It is shown that streaklines are key to understanding the breaking of the interface under velocity agitations, and a theory for locating the relevant streaklines is presented. Simulations of streaklines in a cross-channel mixer and a perturbed Kirchhoff elliptic vortex are quantitatively compared to the theoretical results. Additionally, a methodology for quantifying the unsteady advective transport between the two fluids using streaklines is presented and verified numerically for the same two examples. [ABSTRACT FROM AUTHOR]

This work describes a new fabrication method to produce nitrocellulose-based microfluidic devices using CO 2 laser ablation. This method requires only two simple steps: thermal bonding of a nitrocellulose membrane to a waxy film, and selective ablation of the membrane. The hollow microstructures created by selective ablation offer robust fluid barriers. With the optimized laser power and laser speed, two-dimensional fluid flow devices (2D) can be fabricated with fluid barrier width of 117 ± 11 µm and narrowest channel width of 81 ± 11 µm. This simple yet high resolution method can also be used for fabrication of a three-dimensional fluid flow device (3D) by simply bonding a stack of fabricated 2D devices. Fluidic delay and mixing tools in form of micropillar structures were created concurrently to device fabrication using the CO 2 laser ablation. The phenomena of the fluidic delay and mixing were also evaluated by mathematical simulation which showed that micropillar structures not only delay the flow but also lead it into different directions and velocities causing passive fluidic mixing. A new nitrocellulose well plate fabricated using this method exhibited flexibility of device fabrication, superior sensitivity, less reagent consumption, and shorter analysis time than the conventional well plate. • New laser patterned nitrocellulose-based microfluidic devices are fabricated. • A three-dimensional device can be produced by stacking and bonding method. • Flow delay and mixing tools can be concurrently embedded via laser ablation. • A new nitrocellulose-based well plate format for an immunoassay is demonstrated. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple fluid sources are identified by variation range of Cl isotopes and Cl/Br ratios from. • Vein-type Zn-Pb mineralization is triggered by mixing of evaporated seawater and magmatic hydrothermal fluids. • Quantitative model shows that the mixing volume ratios of both sources are between 1:9 and 4:6. Numerous hydrothermal vein-type Zn–Pb deposits worldwide are characterized by low-temperature metallogeny, no spatial relationship with plutons, and strong water-rock interaction, which result in the difficulty of constraining the fluid origin and the process of ore formation by traditional geochemistry. In this study, we employ chemical and chlorine isotopic composition of bulk fluid inclusions from ore-bearing and ore-barren quartz veins to constrain the possible sources of ore-forming fluids and the process of metal precipitation in the hydrothermal systems of the economic vein-type mineralization in eastern Guizhou Province, SW China. Our new geochemical data are indicative of two end-members in the systems, one identified in the ore-bearing veins with high K/Na, Li/Na, Cl/Br ratios, and δ37Cl values representing magmatic hydrothermal fluids, another distinguished in the ore-barren veins with low Cl/Br ratios and δ37Cl values representing evaporated seawater. We conclude there is a systematic variation of these geochemical data as the results of the mixing between the former and the latter end-member. In the meantime, the mixing is quantitively assessed to study the mixing volume ratios of both end-members. Based on our data and our own previous study, a genetic fluid mixing model involving the magmatic hydrothermal fluids related to deep magma activity and the evaporated seawater is established for the formation of the vein-type Zn–Pb deposits. This study provides a novel geochemical approach for recognizing hydrothermal mineralizing systems. [ABSTRACT FROM AUTHOR]

Abstract: The stirring of a body of viscous fluid using multiple stirring rods is known to be particularly effective when the rods trace out a path corresponding to a nontrivial mathematical braid. The optimal braid is the so-called “pigtail braid”, in which three stirring rods execute the usual “over-under” motion associated with braiding (plaiting) hair. We show how to achieve this optimal braiding motion straightforwardly: one stirring rod is driven in a figure-of-eight motion, while the other two rods are baffles, which rotate episodically about their common centre. We also explore the extent to which the physical baffles may be replaced by flow structures (such as periodic islands). [Copyright &y& Elsevier]

Mixing of shear-thinning fluids with yield stress is investigated in a three-dimensional (3-D) flow both in experiments and in simulations. Experiments are conducted in a stirred tank using tracer visualization and velocity measurements. Bulk flow visualization shows the familiar cavern formation around the impeller with stagnant zones surrounding it. Detailed flow visualization inside caverns reveals the main ingredients of chaotic flow: lobe formation, stretching, folding, and self-similar mixing patterns. For multiple impeller systems, however, we find strong compartmentalization characterized by robust segregation between adjacent caverns, hindering mixing performance. Mixing efficiency is enhanced by moving the shaft off-center, which breaks spatial symmetry. The displacement of the shaft from the tank centerline has a beneficial effect on manifold structure: segregated regions are destroyed, separatrices are eliminated, and sheaaxial circulation is improved. Numerical simulations are performed by solving the incompressible Reynolds Averaged Navier Stokes equation with a Galerkin Least-Squares finite-element formulation and a macroscopic rheological model. Simulations are able to capture the main features of the flow and are used to investigate stretching statistics and scale behavior. [ABSTRACT FROM AUTHOR]