Fluid Pressure Fluctuations Research Articles

Research on reciprocating sealing performance and leakage rate prediction based on GA-PSO-BPNN hybrid algorithm

Purpose This study aims to investigate the sealing performance of reciprocating seals under the effect of rubber abrasion using ABAQUS simulation software, and to propose a prediction framework based on a hybrid algorithm (GA-PSO-BPNN) to predict the leakage of reciprocating seals of downhole gauging instrumentation under different working condition parameters. Design/methodology/approach The authors combined the UMESHMOTION user program with the improved Archard wear model to investigate reciprocating seal performance. GA and a PSO were proposed as ways to enhance the BPNN’s predictive model. Findings The results show that the impact of fluid pressure fluctuations on the wear of the seal lip is more pronounced during the rapid wear phase compared to the steady wear phase. Similarly, variations in compression rate have a greater impact on seal lip wear at different stages of wear. The GA-PSO-BPNN prediction model outperforms the single-prediction model in terms of prediction accuracy. Originality/value The authors investigated sealing performance through simulation software and propose a GA-PSO-BPNN-based fault diagnosis method for rotating machinery. To verify the accuracy of the prediction model, a reciprocating sealing test platform for gauge work cylinders is constructed. Peer review The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-08-2024-0293/

Mathematical modeling and CFD investigation of the novel oscillating shear valve generating sinusoidal signals by fluid pressure fluctuation

The oscillating shear valve pulser is a critical component of advanced downhole high-speed transmission systems, playing a vital role in efficient drilling operations. It is highly valued for its flexible and accurate source signal modulation capabilities, as well as its ability to operate safely without blockages. Specifically, how to ensure that the oscillatory shear valve pulse generator produces high-quality sinusoidal differential pressure source signals is particularly crucial. Consequently, this paper initially considers the motion characteristics of the shear valve in acceleration-uniform speed-deceleration, derives the calculation formula of the throttle area of the valve hole based on the fan-arc-fillet-line, and adopts the latest unsteady-liquid thin-walled cutting-edge throttling mechanism (UTCTM) we discovered, innovatively proposing the mechanism model of the differential pressure signal generation of the oscillatory shear valve. Based on this model, a typical optimized four-blade oscillatory shear valve was obtained. Through a series of CFD computational fluid dynamics studies, the amplitude variation characteristics and sinusoidal morphology evolution laws of the differential pressure signal at different frequencies were revealed, forming a unique design method for oscillatory shear valves, which provides a solid theoretical basis and technical support for the development of a new generation of pulsers.

A new interpretation of soft-sediment deformation features (SSDs) in the Parktown Formation (lower West Rand Group); the physical processes of deformation during deposition

Abstract In the Parktown Formation of the lower West Rand Group (Witwatersrand Supergroup), remarkably well-preserved soft-sedimentary deformation features (SSDs) occur in a number of locations in three stratigraphic horizons across the Vredefort Mountainland and in key sites in Johannesburg. The SSDs were the inevitable products of static liquefaction during early deposition in the Witwatersrand Basin. The trigger to static liquefaction is interpreted to be autogenic and related to cyclic fluctuations in pore fluid pressure(s) during capped dewatering. Allogenic triggers are not indicated. We suggest that static liquefaction was an integral physical process to sediment deposition on the Parktown Formation offshore platform, but a process not previously recognised as important to the modification of the West Rand Group stratigraphy across the Witwatersrand Basin.

Dynamic stress response in reservoirs stimulated by fluctuating fluid pressure during pulsating hydraulic fracturing

Determining the most effective scheme for fracturing operations depends on accurate calculations of reservoir stress. Traditional fracturing theories usually focus on stable fluid injection modes, which employ static assumptions in modelling and analysis. However, pulsating hydraulic fracturing (PHF) introduces fluctuating fluid pressure to stimulate reservoirs, which requires considering dynamic factors and exploring the dynamic stress response within the reservoir. Furthermore, reservoirs are often classified as homogeneous continuous or porous media materials, but the boundaries between these classifications are sometimes apparent. This paper investigated the development of both an elastodynamics model and a poroelastodynamics model for calculating dynamic stress responses during PHF. The staggered grid finite difference method addressed these models, with the outer boundary employing the perfectly matched layer (PML) method to simulate an infinite reservoir. The numerical simulation results were extensively verified and compared with analytical solutions, and the differences between various models and their relevant conditions were thoroughly analyzed. Analyzing fluid pressure fluctuation parameters revealed noteworthy insights into reservoir stress response characteristics. Results indicate that as the Biot coefficient and permeability increase, the disparities between the elastodynamics and poroelastodynamics models become prominent. In practical terms, high Biot coefficient or high permeability reservoirs necessitate using the poroelastodynamics model for accurate reservoir stress analysis. As the frequency of fluid pressure fluctuation increases, the amplitude of response of reservoir circumferential stress also increases, while the response amplitude of radial stress and fluid pressure decreases. These findings offer valuable theoretical guidance for parameter design in engineering applications during PHF.

Investigation of Energy Loss Mechanism and Vortical Structures Characteristics of Marine Sediment Pump Based on the Response Surface Optimization Method

Marine sediment pumps are extensively applied in marine engineering fields with complex media and harsh flow conditions. Therefore, this study conducts a multi-factor optimization design for a marine sediment pump. The response surface optimization method is utilized to improve the efficiency by optimizing the number of impeller blades, the blade inlet angle, the blade outlet angle, and the blade wrap angle. Next, a response surface regression model is created, and the influence of geometric parameters on the efficiency is determined. Meanwhile, the energy loss mechanism and vortical structure characteristics after optimization are analyzed by applying entropy production and the method for identifying Omega vortices. The findings suggest a 6.33% efficiency enhancement in the optimized model under the design conditions. The impeller’s internal flow field is enhanced, and the entropy generation rate is significantly diminished. The fluid flow adhered more closely to the blade profile, and the velocity and pressure distribution exhibit better uniformity. The presence of large-scale vortices and occurrences of flow separation within the impeller passage experience a notable decrease, and the overall fluid pressure fluctuation amplitude decreased, resulting in a more stable flow. Therefore, the discoveries from the research offer references for the design and selection of marine sediment pumps.

Recurrent reflex syncope in idiopathic intracranial hypertension patient resolved after lumbar puncture: pathogenetic implications

BackgroundIdiopathic intracranial hypertension is a disease characterized by increased intracranial cerebrospinal fluid volume and pressure without evidence of other intracranial pathology. Dural sinuses are rigid structures representing a privileged low-pressure intracranial compartment. Rigidity of dural sinus ensures that the large physiologic fluctuations of cerebrospinal fluid pressure associated with postural changes or to Valsalva effect cannot be transmitted to the sinus. An abnormal dural sinus collapsibility, especially when associated with various anatomical sinus narrowing, has been proposed as a key factor in the pathogenesis of idiopathic intracranial hypertension. This pathogenetic model is based on an excessive collapsibility of the dural sinuses that leads to the triggering of a self-limiting venous collapse positive feedback-loop between the cerebrospinal fluid pressure, that compresses the sinus, and the increased dural sinus pressure upstream, that reduces the cerebrospinal fluid reabsorption rate, increasing cerebrospinal fluid volume and pressure at the expense of intracranial compliance and promoting further sinus compression. Intracranial compliance is the ability of the craniospinal space to accept small volumetric increases of one of its compartments without appreciable intracranial pressure rise. In idiopathic intracranial hypertension, a condition associated with a reduced rate of CSF reabsorption leading to its volumetric expansion, a pathologically reduced IC precedes and accompanies the rise of ICP. Syncope is defined as a transient loss of consciousness due to a transient cerebral hypoperfusion characterized by rapid onset, short duration, and spontaneous complete recovery. A transient global cerebral hypoperfusion represents the final mechanism of syncope determined by cardiac output and/or total peripheral resistance decrease. There are many causes determining low cardiac output including reflex bradycardia, arrhythmias, cardiac structural disease, inadequate venous return, and chronotropic and inotropic incompetence. Typically, syncopal transient loss of consciousness is mainly referred to an extracranial mechanism triggering a decrease in cardiac output and/or total peripheral resistance. Conversely, the association of syncope with a deranged control of intracranial compliance related to cerebral venous outflow disorders has been only anecdotally reported.Case PresentationWe report on a 57-year-old woman with daily recurrent orthostatic hypotension syncope and idiopathic intracranial hypertension-related headaches, which resolved after lumbar puncture with cerebrospinal fluid subtraction.ConclusionsA novel mechanism underlying the triggering of orthostatic syncope in the presence of intracranial hypertension-dependent reduced intracranial compliance is discussed.

Gas–droplet–liquid transitions and fluctuations in soft nano-confinement

One permanent characteristic of the thermodynamics of small systems is environment-dependence, also known as ensemble-dependence. Fluid molecules in soft (deformable) nano-confinement offer a special ensemble that acts as a bridge between classical isobaric (NPT) and isochoric (NVT) ensembles. Here, we discuss the gas–liquid transition taking place in a soft nano-confinement where the cell volume is not fixed but changes when the system pressure is changed. The free energy of the system is calculated as a function of the size of the liquid droplet that appears in the gas phase. We discuss how the phase behavior changes when the condition of the confinement changes from rigid confinement to very soft confinement. For the simple fluid model studied, the coexistence and critical phase behaviors are found to be uniquely determined by αK (αK is the dimensionless elasticity constant of the wall of confined space and is proportional to its ability to resist deformation), and the confinement with moderate softness exhibits richer phase behavior. We then study the fluctuations of pressure, volume, and droplet size for fluid in soft confined spaces, which is again closely related to the wall softness. Under moderate softness, large fluctuations in both fluid pressure and volume are seen in the transition region where fluid pressure increases with volume expansion, accompanied by the strengthened fluctuation of droplet size.

Mathematical modeling of pulsations in the drillingfluid

Purpose. To improve the efficiency of cleaning wells from drilled rock by using a pulsating flow of drilling fluid. to study the effect of cuttings concentration and distance from the pulse source on the parameters of its oscillations. The methods. Based on the analysis of the peculiarities of the well flushing process, the possibility of using an uneven flow of drilling mud created by fluid pressure fluctuations at the bottom of the well mathematical modeling of fluctuations in the two-phase environment of the flow of drilling fluid with drilled rock was carried out. In order to construct a mathematical model of oscillatory vibrations, the initial and boundary conditions for solving the homogeneous wave equation of the third order are set. The solution of this equation is realized using the Fourier method. Based on the results of the analytical calculations, a program in the JavaScript environment was developed to study the effect of cuttings concentration and distance from the pulse source on the vibration parameters. Findings. Using the developed program, the dependence of the change in the intrinsic vibration displacement of a two-phase medium on time was investigated when the cuttings concentration varies from 0 to 13 % in the drilling fluid and the distance from the pulse source varies from 1 to 1000 m. It was found that the vibration displacement in time is a sinusoidal curve with a certain period. It was found that the pulsation frequency decreases in hyperbolic dependence with distance from the pulse source due to attenuation in a two-phase medium. It was found that pulsations propagate effectively at a distance of up to 300 m from the pulse source. The effect of the cuttings concentration in the drilling fluid on the pulsation frequency is investigated. The originality. A mathematical model of the process of rock particles removal through the annular space of the well by a pulsating flow of drilling fluid is created. Practical implementation. Software has been developed to assess the effect of cuttings concentration and distance from the pulse source on the oscillation parameters, which will allow to evaluate and improve the process of well cleaning with a pulsating flow of drilling fluid.

Characteristics of Slow Slip Events Explained by Rate‐Strengthening Faults Subject to Periodic Pore Fluid Pressure Changes

AbstractGeophysical observations suggest that temporal changes in pore fluid pressure correlate with slow slip events (SSEs) at some subduction zones, including the Hikurangi and Cascadia subduction zones. These fluctuations in pore fluid pressure are attributed to fluid migration before and during SSEs, which may modulate SSE occurrence. To examine the effect of pore fluid pressure changes on SSE generation, we develop numerical models in which periodic pore‐pressure perturbations are applied to a stably sliding, rate‐strengthening fault. By varying the physical characteristics of the pore‐pressure perturbations (amplitude, characteristic length and period), we find models that reproduce shallow Hikurangi SSE properties (duration, magnitude, slip, recurrence) and SSE moments and durations from different subduction zones. The stress drops of modeled SSEs range from ∼20–120 kPa while the amplitudes of pore‐pressure perturbations are several MPa, broadly consistent with those inferred from observations. Our results indicate that large permeability values of ∼10−14 to 10−10 m2 are needed to reproduce the observed SSE properties. Such high values could be due to transient and localized increases in fault zone permeability in the shear zone where SSEs occur. Our results suggest that SSEs may arise on faults in rate‐strengthening frictional conditions subject to pore‐pressure perturbations.

Sucrose transport inside the phloem: Bridging hydrodynamics and geometric characteristics

In plants, the delivery of the products of photosynthesis is achieved through a hydraulic system labeled as phloem. This semi-permeable plant tissue consists of living cells that contract and expand in response to fluid pressure and flow velocity fluctuations. The Münch pressure flow theory, which is based on osmosis providing the necessary pressure gradient to drive the mass flow of carbohydrates, is currently the most accepted model for such sucrose transport. When this hypothesis is combined with the conservation of fluid mass and momentum as well as sucrose mass, many simplifications must be invoked to mathematically close the problem and to resolve the flow. This study revisits such osmotically driven flows by developing a new two-dimensional numerical model in cylindrical coordinates for an elastic membrane and a concentration-dependent viscosity. It is demonstrated that the interaction between the hydrodynamic and externally supplied geometrical characteristic of the phloem has a significant effect on the front speed of sucrose transport. These results offer a novel perspective about the evolutionary adaptation of plant hydraulic traits to optimize phloem soluble compounds transport efficiency.

Dynamics modeling and stress response solution for liquid-filled pipe system considering both fluid velocity and pressure fluctuations

Dynamics modeling and stress response solution of the liquid-filled pipe system (LFPS) are necessary to predict the reliability of the pipe. However, the existing methods still need further research to solve the stress response of pipe system, and the influence of fluid velocity and pressure (FVAP) fluctuations on the vibration response is not considered. Based on this, a dynamics modeling method named FEM-TMM is proposed to solve the natural characteristics and stress response of the LFPS based on the combination of the finite element method (FEM) and transfer matrix method (TMM), which can consider the fluctuations of FVAP. The incompatible solid (Solid-NC) and virtual beam (VBeam) elements are constructed to establish the finite element models of the solid and fluid domains respectively, and the coupling elements are introduced to couple the solid and fluid domains. TMM is used to solve the FVAP fluctuations of the LFPS under external excitation, and the steady-state resonant frequency and vibration mode are obtained based on the iteration method. The virtual force iteration and stress smoothing methods are adopted to solve the stress response of the LFPS, then the dynamics modeling method FEM-TMM is obtained, and the rationality of the modeling method is verified by experiments. Finally, the analysis results show that the influence of velocity fluctuation on resonance frequency and stress response can be ignored. The critical pressures of resonant frequencies are less than or equal to those of resonant frequencies without considering pressure fluctuation. There are multiple stress barriers and valleys in the different-order stress responses of the LFPS, and the pressure fluctuation will change the distribution laws and maximum peak values of the stress barriers.

Fluid-solid coupling model and biological features of large vestibular aqueduct syndrome.

Objective: Computed tomography (CT) images of the temporal bone of large vestibular aqueduct syndrome (LVAS) patients were used to establish 3D numerical models based on the structure of the inner ear, which are, in turn, used to construct inner ear fluid-solid coupling models. The physiological features and pathophysiology of LVAS were analyzed from a biomechanical perspective using finite element analysis. Methods: CT images of the temporal bone were collected from five children attending the Second Hospital of Dalian Medical University in 2022. The CT images were used to build 3D models of the inner ear containing the vestibular aqueduct (VA) by Mimics and Geomagic software, and round window membrane models and fluid-solid coupling models were built by ANSYS software to perform fluid-solid coupling analysis. Results: By applying different pressure loads, the deformation of the round window membranes occurred, and their trend was basically the same as that of the load. The deformation and stress of the round window membranes increased with the increase in load. Under the same load, the deformation and stress of the round window membranes increased with the expansion of the midpoint width of the VA. Conclusion: CT images of the temporal bone used clinically could establish a complete 3D numerical model of the inner ear containing VA. Fluctuations in cerebrospinal fluid pressure could affect inner ear pressure, and VA had a limiting effect on the pressure from cerebrospinal fluid. The larger the VA, the smaller the limiting effect on the pressure.

Case study: Analysis and research on pipeline vibration of liquid oxygen kerosene of rocket engine and vibration reduction measures Measures

Abnormal vibration often occurs in the liquid oxygen kerosene transmission pipe- line of rocket engines, seriously threatening the safety of rocket engines. Improper handling will result in rocket launch failure and enormous economic losses. Therefore, the vibration of the transmission pipeline must be studied. In this paper, a three-dimensional high-pressure transmission pipeline model comprising a corrugated pipe, a multi-section bending pipe, and other auxiliary structures is established. Using the two-way fluid–solid coupling method, vibration analysis is performed on the pipeline under external pressure pulse excitation. The accuracy of the computation results is verified by a thermal test. Two vibration reduction strategies are presented and validated by simulation in accordance with the findings of the vibration study. The main conclusions are as follows: (1) At the same frequency, the amplitude distribution of vibration acceleration significantly correlates with the flow field pressure, indicating that fluid pressure fluctuation is the root cause of the abnormal vibration of the pipeline, and the vibration of the pipeline increases with the average pressure. (2) The time-average value and fluctuation amplitude of the larger stress and strain are mainly concentrated in the two supports, namely, the inside of the elbow and the bellows, which is different from the distribution of vibration acceleration. Such places are prone to structural failure and should be given attention. (3) The guide plate and the support enhancement method can reduce the vibration, but the support enhancement method has a better effect, reducing the vibration velocity and acceleration by 86.4% and 93%, respectively.

Numerical Analysis of the Flow-induced Whistling Noise of Ventilation Wall Based on Fluid-structure Coupling Method

As a widely used device in the field of air cooling and heat dissipation of electronic equipment, ventilation walls often have the problem of whistling caused by airflow. This paper presents a numerical study on the flow-induced whistling noise of a ventilation wall. Firstly, the interior flow field of the ventilation wall under typical working conditions was calculated. Secondly, the structure wet mode of the ventilation wall was calculated considering the airflow influence on the structural vibration. Thirdly, taking the fluid pressure fluctuation at the surfaces of the ventilation wall as excitation source, the structural vibration and radiation noise of ventilation wall was simulated, respectively. Finally, the structure of the ventilation wall was optimized to reduce the whistling noise. The results show that the high velocity airflow causes strong fluid-structure coupling of the ventilation wall. Besides, the peak frequency band of whistling noise ranges from 112Hz to 125Hz, and the maximum sound pressure level (SPL) reaches 87.3dB. Moreover, by improving the structure of ventilation wall, the maximum SPL of whistling noise deceases about 10.5dB, which significantly reduces the flow-induced noise. In conclusion, this paper could provide a method for reducing the flow-induced noise of ventilation walls.

Spatial coupling relationship between faults and gold deposits in the Jiaodong ore concentration area and the effect of thermal doming-extension on mineralisation

As the third largest gold ore-forming province in the world, the deep metallogenic potential of and exploration strategies for Jiaodong gold deposits have attracted substantial attention. By applying three-dimensional (3D) geological modelling to these super-giant and giant gold deposits, this study reveals the 3D morphological characteristics of the ore-bearing faults and the ore-related granites, analyses the relationships between ore body locations and slope dip angle changes in the faults, and discusses the coupling relationships among gold mineralisation, ore-controlling faults, and magmatic activities. In the 3D model, the dip angles of ore-controlling faults gradually decrease downwards and alternate between steep and gentle along the fault dip direction. The ore bodies mainly occur in areas with relatively high fault-dip-angle change rates. Hence, positions with fault dip angles of 20°–50° and change rates of ≥0.91 should be considered as target areas for prospecting deep gold ore bodies. In-depth analysis suggests that the ore-hosting faults, granites, and gold mineralisation resulted from regional thermal doming and extensional movements. Gold ore bodies in the Jiaodong Peninsula occur inside or on the periphery of Mesozoic granite. Strong magmatic activities during the transition from enriched to depleted mantle provided the necessary metallogenic and thermal dynamic environment for gold mineralisation. In particular, the magmatic evolution provided abundant ore-forming materials. The detachment faults with varied dip angles provided favourable space for gold mineralisation, as the fluctuations of ore-forming fluid pressure caused by sudden changes in these dip angles served as the primary mechanism underlying the step-like gold mineralisation pattern.

Experimental investigation and analysis on the pressure stabilization of subcooled liquid nitrogen circulation for the HEPS

The High Energy Photon Source (HEPS) is a fourth generation radiation source, where lots of optical equipment are cooled down to the liquid nitrogen temperature for the better performance. The subcooled liquid nitrogen circulation is a very advantageous cooling method of monochromators and undulators, which are sensitive to fluid pressure fluctuations. Although the pressure stabilization matters a lot but it has rarely been studied. In this paper, the causes of pressure fluctuations are analyzed, and accordingly the principle of thermal balance is proposed. Based on the analysis, three pressure stabilization methods were suggested and tested. A partially liquid nitrogen filled tank was connected to the subcooled liquid nitrogen circulation serving as a pressure fluctuation buffer. The side effect is that the heat load of the tank raises the pressure gradually. Therefore, the cold source buffer and its induced heat load need good compromise. The tank heat load was cooled by saturated nitrogen, bypass liquid nitrogen and direct gas absorption: The saturated nitrogen reuses the sensible heat of cold gas; the bypass liquid nitrogen avoids the influence of circulation heat load variation and the gas absorption prevents the heat exchanger in the tank. The test results show that the peak-to-peak value of the pressure fluctuation can be controlled in the level of ± 4.0 mbar and the RMS value less than 1.0 mbar. The pressure affect factors were empirically studied.

Improving mining development modelling based on the thermal methods

Introduction. The problem of oil recovery growth and oil reserves management improvement in active oil fields is growing annually. It is possible to increase oil recovery and improve oil reserves management by introducing the thermal methods of oil production. This method was applied at the Yarega oil field. The thermal mining development technology is currently being implemented at the Yarega territory on an industrial scale. Lyael territory is developed by SAGD technology. Heat capacity and thermal conductivity are crucial characteristics of rocks. Reference books and databases lack reliable data on sedimentary rocks thermal properties. The traditional experimental base of thermal petrophysics cannot provide representative information on the thermal properties of rocks, considering rock heterogeneity and anisotropy, various fluid saturation, and pressure and temperature fluctuations. Results. According to special petrophysical studies of the Yarega highly viscous oil field core, ambiguity has been revealed in the thermal properties of rocks, including anisotropy, heat capacity and thermal conductivity. When applying laboratory results in modeling, divergence in oil production and cumulative steam oil ratio can reach 60%. Main ambiguity arising in the course of thermal mine development modeling has been identified. The ambiguity is associated with the account of production for a well, a large number of underground wells, and low reservoir pressure (lower than atmospheric pressure). These problems are successfully solved by specialists of the Yarega field, who maintain highly viscous oil development. At low reservoir pressures, the simulator encounters errors on low pressure values during well operation. Conclusions. At the Yarega field, permanent geological and technological model is currently actively being implemented. It is aimed at solving technological problems of ambiguity in the development of highly viscous oil by thermal methods using advanced software.

Formation of the high-grade Triple R uranium deposit revealed by Fe and S isotopes in pyrite

The Patterson Lake corridor, located on the southwestern margin of the Athabasca Basin, contains several basement-hosted uranium deposits that formed via protracted, structurally controlled fluid–rock interactions. Using multiple generations of pyrite grains (pre-, syn- and post-mineralization) from the Triple R deposit, in situ iron isotopic analyses revealed large intra-sample and -grain variations ( δ 56 Fe values ranging from −2.21 to +1.67‰) whereas sulfur isotopes yielded minor variations ( δ 34 S values ranging from −4.44 to +5.3‰) relative to natural isotopic variations for both elements. The wide range in δ 56 Fe values supports textural and chemical evidence that fluctuating oxidation states and chemistry in the fault zone fluids caused multiple generations of pyrite oxidation and precipitation. Sulfur isotope data from shallower mineralized zones show a slight enrichment in heavier isotopes, consistent with limited Rayleigh fractionation. However, when coupled with iron isotope data, the overall dataset supports a sulfur-rich, open system wherein heat from intrusions at depth and fault movements drove sulfur-bearing fluids upwards, causing precipitation of pre-mineralization pyrite and graphite. During fault reactivation, fluid pressure fluctuations between hydrostatic and sub-hydrostatic regimes drew oxidizing, uranium-bearing, basinal brines down into the basement to react with sulfides in the host rocks and deeply sourced, H 2 S-bearing reducing fluids. These redox reactions and fluid mixing resulted in precipitation of uraninite and syn-mineralization pyrite. These results further support the importance of structural control, repeated faulting and thermal anomalies in the basement for mineralization, necessitating re-examination of the current exploration model for unconformity-related uranium deposits. Supplementary material: Plot of δ 57 Fe versus δ 56 Fe values of all samples is available at https://doi.org/10.6084/m9.figshare.c.6026621 Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathways

Decompression induced enrichment and precipitation of gold in the polymetallic sulfide stage of the northwest Jiaodong gold deposits, eastern North China Craton

Mechanisms for the enrichment and re-precipitation of gold in the giant Jiaodong gold deposits (eastern North China Craton) remain poorly constrained. To better understand the mineralization mechanism, we did in situ analyses of S isotopes on sulfides such as pyrite, pyrrhotite, galena and chalcopyrite from the disseminated (altered-rock type) and quartz-vein type gold deposits by femtosecond laser ablation coupled multi-collector inductively coupled plasma mass spectrometry. Pyrites from the altered-rock type gold deposit show δ34S values in the range from 7.4 to 11.3 ‰, which is obviously heavier than the quartz-vein type gold deposits with δ34S = 6.2 ∼ 8.8 ‰. Traditionally, the difference of sulfur isotopic compositions between the two types of gold deposits was attributed to the change in oxygen fugacity. However, we found that, from early to late metallogenic stage, sulfur isotopes of pyrites from the altered rock type gold deposits tend to decrease gradually and pyrrhotites can always be observed in the third stage. Moreover, the S isotopic compositions (δ34S = 7.9 to 8.2 ‰) of the pyrites coexisting with magnetite are comparable with those (δ34S = 6.2 to 8.0 ‰) of the pyrites coexisting with pyrrhotite in the quartz vein type gold deposits. These features indicate that the decrease of sulfur isotopes in pyrites was not caused by increase of oxygen fugacity. We suggest that the S isotopic and fO2 variation could be ascribed to an increase of pH of the ore-forming fluid, which is supported by the typically quartz dissolution and common occurrence of calcite and pyrrhotite in the late metallogenic stage (the third stage) and an overall decrease of aluminum contents of quartz from core to rim. We further proposed that the variation of pH of ore-forming fluids is probably related to a process of decompression due to development and enlargement of fractures filled with ore-forming fluids. Gold enrichment in the main ore-forming stage of the northwest Jiaodong gold deposit probably was realized by multiple phases of fluid pressure fluctuation, which subsequently led to repeatedly dissolution and re-precipitation of Au from pyrites due to decreasing oxygen fugacity and increasing pH values of the ore-forming fluids.

Problems in CSF and Ophthalmic Disease Research.

There has been significant interest and progress in the understanding of cerebrospinal fluid pressure and its relationship to glaucoma and other ophthalmic diseases. However, just as every physiologic fluid pressure fluctuates, cerebrospinal fluid pressure (CSFP) is similarly dynamic. Coupling this with the difficulty in measuring the pressure, there are many obstacles in furthering this field of study. This review highlights some of the difficulties in CSFP research, including fluid compartmentalization, estimation equations, and pressure fluctuation. Keeping these limitations in mind will hopefully improve the quality and context of this burgeoning field.