Effects Of Stratification Research Articles

A Simple and Practical Method for Reducing the Disparate Impact of Differential Privacy

Differentially private (DP) mechanisms have been deployed in a variety of high-impact social settings (perhaps most notably by the U.S. Census). Since all DP mechanisms involve adding noise to results of statistical queries, they are expected to impact our ability to accurately analyze and learn from data, in effect trading off privacy with utility. Alarmingly, the impact of DP on utility can vary significantly among different sub-populations. A simple way to reduce this disparity is with stratification. First compute an independent private estimate for each group in the data set (which may be the intersection of several protected classes), then, to compute estimates of global statistics, appropriately recombine these group estimates. Our main observation is that naive stratification often yields high-accuracy estimates of population-level statistics, without the need for additional privacy budget. We support this observation theoretically and empirically. Our theoretical results center on the private mean estimation problem, while our empirical results center on extensive experiments on private data synthesis to demonstrate the effectiveness of stratification on a variety of private mechanisms. Overall, we argue that this straightforward approach provides a strong baseline against which future work on reducing utility disparities of DP mechanisms should be compared.

Effect of stratification on the propagation of a cylindrical gravity current

Direct numerical simulations (DNSs) of three-dimensional cylindrical release gravity currents in a linearly stratified ambient are presented. The simulations cover a range of stratification strengths $0< S\leq 0.8$ (where $S=(\rho _b^*-\rho _0^*)/(\rho _c^*-\rho _0^*), \rho _b^*, \rho _0^*$ and $\rho _c^*$ are the dimensional density at the bottom of the domain, top of the domain and the dense fluid, respectively) at two different Reynolds numbers. A comparison between the stratified and unstratified cases illustrates the influence of stratification strength on the dynamics of cylindrical gravity currents. Specifically, the front velocity in the slumping phase decreases with increasing stratification strength whereas the duration of the slumping phase increases with increments of $S$ . The Froude number calculated in this phase shows a good agreement with models proposed by Ungarish & Huppert (J. Fluid Mech., vol. 458, 2002, pp. 283–301) and Ungarish (J. Fluid Mech., vol. 548, 2006, pp. 49–68), originally developed for planar gravity currents in a stratified ambient. In the inertial phase, the front velocity across cases with different stratification strengths adheres to a power-law scaling with an exponent of $-$ 1/2. Higher Reynolds numbers led to more frequent lobe splitting and merging, with lobe size diminishing as stratification strength increased. Strong interactions among inner vortex rings occurred during the slumping phase, leading to the early formation of hairpin vortices in weakly stratified cases, while strongly stratified cases exhibited delayed vortex formation and less turbulence.

Effect of Sediment Stratification on the Mechanical and Acoustic Properties of Hydrate-Bearing Sediments

Effect of Sediment Stratification on the Mechanical and Acoustic Properties of Hydrate-Bearing Sediments

Dynamic stratification and biogeochemical cycling response of microbial communities in east indian ocean ridge

Marine harbors a diverse and intricate microbial ecosystem crucial for driving biogeochemical and nutrient cycles. To gain insights into the ecological functions of microbial communities in deep-sea sediments and their responses to biogeochemical cycling, this study investigated microbial dynamics within the East Indian Ocean (EIO) ridge, focusing on vertical stratification of sediment communities. Notably, depth-related microbial patterns surpassed regional stratification effects. Environmental factors, such as TN and NO2–-N, significantly shaped community structures, while stochastic processes, particularly homogenizing dispersal, contributed to spatial similarity and structural stability. In this challenging environment, bacterial and archaeal communities established symbiotic relationships for enhanced survival, and dominated carbon and nitrogen biogeochemical cycling processes, respectively. Key bacterial genera acted as bridging agents, orchestrating intricate interactions, while archaeal communities displayed greater dispersion. Metabolic pathways analyses revealed that bacterial community was characterized by denitrification and DNRA processes, while archaea were dominated by the nirK-encoded denitrification pathway. Ultimately, this study shed light on nuanced interactions and ecological roles of microbial communities, contributed to broader understanding of biogeochemical processes and global carbon/nitrogen sinks.

Thermal and mass stratification effects on unsteady parabolic flow past an infinite vertical plate with exponential decaying temperature and variable mass diffusion in porous medium

AbstractThis study looks at how thermal and mass stratification affect the unsteady parabolic flow past an infinite vertical plate with exponentially decaying temperature and variable mass diffusion in a porous medium. The Laplace transform method is applied to solve the governing equations for flow, energy, and mass diffusion. The effects of the both stratification on the flow field, temperature, and mass diffusion are then investigated. The research suggests that the existence of thermal and mass stratification has a considerable influence on the profiles of velocity, temperature, and mass diffusion. It is also found that a stable state is reached for the velocity when both stratification parameters are increased, while stable states are reached for the temperature and concentration when the mass stratification is increased but the thermal stratification is decreased.

Effect of Stratification and Joule Heating on MHD Dusty Viscoelastic Fluid Flow Through Inclined Channels in Porous Medium in Presence of Molecular Diffusivity

An analysis is carried out to study laminar MHD convection flow of a second order dusty viscoelastic fluid in porous medium through an inclined parallel plate channel in the presence of molecular diffusivity. The plates are maintained at two different temperatures that decay with time. The study is done under the consideration that viscosity and density of the fluid are variable to the extent that it causes stratification and joule heating effect in the process of the flow. The purpose of the study is to examine how stratification and joule heating affect the flow in relation to the physical quantities namely, Stratification factor, Hartmann number, Viscoelastic coefficient, Joule heating parameter, Prandtl number, Eckert number, Schmidt number and Porosity of the medium etc. The non-dimensional governing equations are solved analytically by using regular perturbation technique, and the graphs are plotted using MATLAB programming language. The mathematical expressions for fluid and particle velocity, fluid temperature, fluid concentration, skin friction for fluid and particle, flow flux for fluid and particle, Nusselt number, Sherwood number at the plates are evaluated and their nature of variations for different numerical values of physical parameters are shown graphically, discussed and conclusions are drawn.

Failure mechanism and infrared radiation characteristic of hard siltstone induced by stratification effect

Failure mechanism and infrared radiation characteristic of hard siltstone induced by stratification effect

Vertically stratified interactions of nectarivores and nectar-inhabiting bacteria in a liana flowering across forest strata.

Vertical stratification is a key feature of tropical forests and plant-frugivore interactions. However, it is unclear whether equally strong patterns of vertical stratification exist for plant-nectarivore interactions and, if so, which factors drive these patterns. Further, nectar-inhabiting bacteria, acting as "hidden players" in plant-nectarivore interactions, might be vertically stratified, either in response to differences among strata in microenvironmental conditions or to the nectarivore community serving as vectors. We observed visitations by a diverse nectarivore community to the liana Marcgravia longifolia in a Peruvian rainforest and characterized diversity and community composition of nectar-inhabiting bacteria. Unlike most other plants, M. longifolia produces inflorescences across forest strata, enabling us to study effects of vertical stratification on plant-nectarivore interactions without confounding effects of plant species and stratum. A significantly higher number of visits were by nectarivorous bats and hummingbirds in the midstory than in the understory and canopy, and the visits were strongly correlated to flower availability and nectar quantity and quality. Trochiline hummingbirds foraged across all strata, whereas hermits remained in the lower strata. The Shannon diversity index for nectar-inhabiting bacterial communities was highest in the midstory. Our findings suggest that vertical niche differentiation in plant-nectarivore interactions seems to be partly driven by resource abundance, but other factors such as species-specific preferences of hummingbirds, likely caused by competition, play an important role. We conclude that vertical stratification is an important driver of a species' interaction niche highlighting its role for promoting biodiversity and ecosystem functioning.

Acoustic tomography in a deep stratified lake; toward reliable estimates of large-scale currents by differential travel time

Lakes worldwide are under increasing stress. For example climate change tends to strengthen stratification, promoting hypoxia and other nefarious effects. Targeting scientific investigation of such changes, and operational monitoring, we have been developing the lacustrine application of Coastal Acoustic Tomography (“CAT”) at Lake Biwa. The largest lake in Japan, Biwa supplies water to 14 million, and has a mean depth in its main basin of 41 m. Since November 2016, we have used M-sequences (5 kHz carrier) to execute the first successful tests of CAT at multikilometer ranges in any lake, with multiweek deployment of 3 (5) stations in Nov 2017 (2018). In 2021, we confirmed reciprocal transmission in spring through early summer between two stations at 7 km. In autumn, we often observed two distinct groups of arrivals. Ray-tracing simulations, based on sound-speed distributions from realistic hydrodynamic simulations, revealed a warm “surface channel” and cold “deep channel” whose predicted arrival times corresponded well with the observations. In continuing work to be reported, we are targeting reliable measurement of raypath-averaged currents by differential travel time, as already achieved by the second author’s team for the stronger tidal currents in the Seto Inland Sea at ranges of 3 km. Preliminary processing has revealed continuous evolution of phase difference between reciprocal receptions. By exploiting such phase differences we hope to achieve a useful level of accuracy in differential travel time despite the weak currents.

A rheological and computational analysis on Buongiorno nanofluid model featuring magnetohydrodynamics

This research captures nonlinear thermo-solutal buoyancy (i.e., nonlinear mixed convection) impact in nanofluid flow based on magnetized Casson model. The generalized porosity concept (i.e., Darcy–Forchheimer relationship) is employed by considering incompressible liquid that saturates the porous space. Effects of thermophoresis, Robin conditions, thermo-solutal stratifications and Brownian diffusion are accounted. Consideration of transpiration phenomenon captures suction/injection aspects. Fluid mechanics basic laws are depleted to simplify the governing rheological expressions. A transformation procedure is then employed to convert the nonlinear governing partial systems into differential systems. Homotopy methodology is used to obtain analytical solutions and convergence is ensured. Graphical and tabular outcomes are presented to address the importance of emerging variables.

The influence of supersonic spatial-temporal coupling disturbance on detonation in an expanded chamber

At present, the most researches on perturbed detonation only considers single factor effects, and there are few studies on the impact of multi-factor coupled perturbations on detonation. In order to match the complex inflow conditions in real situation, the initiation and propagation process of detonation disturbed by spatial-temporal coupling have been studied. This study adopts an adaptive mesh refinement program. It can dynamically capture the structure change of detonation and reduce the total calculation amount. The N-S (Navier-Stokes) equation and single-step reaction model was used in this study. The calculation model is the classic expansion channel that can enhance thrust. After analyze the effects of disturbance amplitudes and disturbance stratification, the results indicates that the stratification phenomenon of disturbance has different effects on the characteristics of flow field. The expansion wall can weaken the disturbance intensity, but its effect is limited. It can only achieve good results when the disturbance on the straight wall side is weak, but the weakening effect of expansion wall also exacerbates the instability of wave. On the other hand, the stability of detonation waves under spatial stratification is stronger, which helps to maintain the intensity of detonation wave.

The effect of flow stratification on ship performance: a numerical study

ABSTRACT If a layer of low-density water settles on top of higher density water, such as fresh water melting from a glacier and settling on top of colder seawater, a body of water can stratify into stable, distinct layers. A vessel advancing in such a stratified fluid can generate internal waves between these layers. The generation of internal waves requires energy and thus increases the resistance experienced by the vessel, a phenomenon known as the dead water effect which can result in a severe reduction in speed and loss of steering power. This study uses Computational Fluid Dynamics (CFD) to investigate the increase in ship resistance caused by the dead water effect. The results show that the presence of a stratified flow can increase total resistance approximately sixfold in extreme conditions. At standard operating conditions, total resistance may increase by approximately 6% as a result of flow stratification.

High propulsive performance by an oscillating foil in a stratified fluid

We investigate numerically the propulsion characteristics of an oscillating foil undergoing coupled heave and pitch motion in a linearly density-stratified flow. A parameter space defined by the internal Froude number ( $1 \le Fr \le 10$ ) and the maximum angle of attack ( $5^\circ \le {\alpha _0} \le 30^\circ$ ) is considered in our study. The results demonstrate a significant enhancement in both thrust production and propulsive efficiency due to the stratification influence. Notably, the highest efficiency exceeding $80\,\%$ is achieved under moderate stratification conditions, surpassing the performance observed in a homogeneous fluid. We attribute this optimum performance to the proper match between the stratification effect and foil kinematics, which gives rise to intense vortex interactions and sufficient wave–mean flow interactions in the near wake of the oscillating foil. Consequently, the energy is transferred towards wake structures to form a high-intensity momentum jet in close proximity to the foil's trailing edge, indicating efficient propulsion. Furthermore, we find that the stratifications within the moderate-to-strong transitional regime display a reduced dependence of propulsive efficiency on the maximum angle of attack, primarily due to the delaying and alleviating effects on dynamic-stall events. Such a mechanism enables the oscillating foil to maintain a satisfactory performance by sufficiently high angles of attack without the penalty of stall events. Based on our findings, we propose that animals or artificial vehicles utilising oscillatory propulsion can benefit from the presence of density stratification in the surrounding fluid.

Thermophoresis and Brownian motion effect on hybrid nanoparticles flow over a wedge surface by considering double stratification effects

This research looks at the flow of hybrid nanoparticles across a wedge-shaped surface. In addition to this, Brownian motion and thermal stratification are used to model how heat moves through a system. The mass expression also deals with the thermophoresis effect and mass stratification. The governing equations involve the continuity, momentum, energy, and mass equation of hybrid nanofluids that are modified into ODE's by applying similarity transformation. The solutions are obtained from two well-known numerical routines, RKF-45 and the profiles embodying f ′ ( η ) , θ ( η ) , and P ( η ) are interpreted under the influence of several physical parameters. The results showed that as the Prandtl number goes up, temperature profiles of fluid flow go down, and as Brownian motion factors go up, temperature profiles go up. It is found that the fluid’s thermal flow rate slows down as the Brownian motion and thermophoretic elements get stronger. On the other hand, the thermal flow rate of fluid goes up as the thermal stratification parameter goes up.

Twin forces: similarity between rotation and stratification effects on wall turbulence

Can the similarity between rotation and stratification provide quantitative predictions for complex turbulence? In this work, we focus on plane Couette turbulence as the background flow, which allows us to eliminate the key differences between Rayleigh–Bénard and Taylor–Couette turbulence, and facilitates a quantitative mapping across many complex turbulent systems involving rotation, stratification and curvature effects. To characterize the separated or coupled effects of rotation and stratification, we introduce an overall Richardson number ${Ri}_\chi$ which is the sum of the Coriolis Richardson number $Ri_\theta$ and the buoyancy Richardson number $Ri_T$ . When the Prandtl number $Pr=1$ , the heat and inertial-frame momentum transport almost coincide and mainly depend on ${Ri}_\chi$ and the Reynolds number, regardless of the specific ratio between $Ri_\theta$ and $Ri_T$ . When $Pr$ varies, the weighted average ${Nu}_\chi$ of the transport coefficients can still remain approximately invariant in most cases. Furthermore, the large-scale structures in purely rotating and purely stratified cases exhibit strikingly similar features. These findings not only indicate a more reasonable analogy for the ultimate Taylor–Couette turbulence but also pave the way for developing new predictive models for natural and industrial processes.

The impact of soil layering and groundwater flow on energy pile thermal performance

Shallow geothermal energy pile systems have emerged as cost-effective and low-carbon alternatives for heating and cooling buildings, compared to traditional air-conditioning systems. Geothermal applications have been researched extensively in recent years under the assumption of ground homogeneity, and the effect of ground stratification remains mostly unexplored. To investigate this, a 3D finite element numerical model is developed and validated against laboratory-scale experimental data, to study the transient diffusion-convection heat transfer linked with Darcy groundwater flow around energy piles in multi-layered lithology. The model is used to undertake long-term assessments under balanced and unbalanced thermal loads to evaluate the thermal effects of soil layering and discrepancies against commonly assumed equivalent homogeneous stratum, for soil profiles with different thermal conductivity distributions. The groundwater flow effect at various depths and seepage velocities on the thermal performance of the energy pile is investigated as well. Results demonstrate the need to account for the spatial variability in thermal properties, particularly for unbalanced thermal loading scenarios. The thermal yield can be underestimated by up to 19.6 % due to an inaccuracy of 48.2 % in the accumulated temperature after 25-year of operation with respect to an equivalent homogeneous ground with depth-weighted average thermal conductivity. This discrepancy grows as the contrast between layers increases. An empirical derived formula is presented and tested, presenting a correction to the effective thermal conductivity of the layered systems in this study that considers the thermal contribution of the ground beneath the pile. Groundwater seepage is shown to have a positive impact on the heat exchanger efficiency, and in the layered geology the efficiency under-estimation becomes more critical at low to moderate Darcy velocities, if neglected or inaccurately measured. These findings contribute to a broader understanding of energy piles and can assist engineers and practitioners in optimising energy geo-structure design, boosting the technology’s viability.

Polygenic scores for tobacco use provide insights into systemic health risks in a diverse EHR-linked biobank in Los Angeles

Tobacco use is a major risk factor for many diseases and is heavily influenced by environmental factors with significant underlying genetic contributions. Here, we evaluated the predictive performance, risk stratification, and potential systemic health effects of tobacco use disorder (TUD) predisposing germline variants using a European- ancestry-derived polygenic score (PGS) in 24,202 participants from the multi-ancestry, hospital-based UCLA ATLAS biobank. Among genetically inferred ancestry groups (GIAs), TUD-PGS was significantly associated with TUD in European American (EA) (OR: 1.20, CI: [1.16, 1.24]), Hispanic/Latin American (HL) (OR:1.19, CI: [1.11, 1.28]), and East Asian American (EAA) (OR: 1.18, CI: [1.06, 1.31]) GIAs but not in African American (AA) GIA (OR: 1.04, CI: [0.93, 1.17]). Similarly, TUD-PGS offered strong risk stratification across PGS quantiles in EA and HL GIAs and inconsistently in EAA and AA GIAs. In a cross-ancestry phenome-wide association meta-analysis, TUD-PGS was associated with cardiometabolic, respiratory, and psychiatric phecodes (17 phecodes at P < 2.7E-05). In individuals with no history of smoking, the top TUD-PGS associations with obesity and alcohol-related disorders (P = 3.54E-07, 1.61E-06) persist. Mendelian Randomization (MR) analysis provides evidence of a causal association between adiposity measures and tobacco use. Inconsistent predictive performance of the TUD-PGS across GIAs motivates the inclusion of multiple ancestry populations at all levels of genetic research of tobacco use for equitable clinical translation of TUD-PGS. Phenome associations suggest that TUD-predisposed individuals may require comprehensive tobacco use prevention and management approaches to address underlying addictive tendencies.

Numerical analysis of demolition waste‐based thermal energy storage system for concentrated solar power plants

AbstractThermal energy storage (TES) is an enabling system that provides uninterrupted energy from concentrated solar power (CSP) plants. Packed‐bed TES systems have great opportunity to significantly enhance the cost‐effectiveness, efficiency, and sustainability of CSP plants by employing an affordable and sustainable packing material. The objective of this study is to design a demolition waste‐based packed bed TES system with a maximum storage capacity of 40 kWh, specifically tailored to store heat within the temperature range of 290°C to 565°C using solar salt as heat transfer fluid (HTF), thereby making it suitable for integration into CSP plants. Performance and thermal behavior of demolition waste‐based packed‐bed TES system was assessed through numerical analysis. The results demonstrate that a high discharging efficiency of 76.0% was achieved when the HTF flow rate was set at 100 kgh−1. However, it is important to note that at lower HTF flow rate, heat loss increases, leading to a decrease in discharging efficiency to 70%. The experiment also revealed a uniform thermal gradient within the packed‐bed TES system, up to a fluid flow rate of 300 kgh−1. It is worth mentioning that lower flow rates can further improve the stratification effect; however, they may also result in increased heat loss and reduced storage capacity. Based on these findings, an optimal flow rate range of 100 to 200 kgh−1 is recommended to achieve the best performance for the packed‐bed TES system.

Prediction model of buoyancy-driven flow rate in inclined tunnels with a localized buoyancy source: Emphasis on stratification effects

In inclined narrow and long spaces such as tunnels, the buoyancy-driven flow pattern and the resulting ventilation flow rate are different from those in enclosure-type buildings, because of their large length-to-width aspect ratios. In this paper, the buoyancy-driven flow rate induced by a localized heat source in inclined tunnels was investigated. Theoretical analysis and three series of experiments including non-isothermal or isothermal buoyancy sources, i.e., large-scale fire tests, brine-water tests and helium-air tests were performed. Two typical buoyant flow patterns were identified in the experiments, which are stratified and well-mixed patterns, respectively. Both the stratification pattern and the longitudinal decay rate of temperature rise were proved to be correlated with a dimensionless factor, η=B01/3ΔLsina/(g0′1/2H3/2), which is composed of characteristic parameters referring to both buoyancy source and geometrical configuration. The flow stratification results in stack effect attenuation and consequently ventilation flow rate reduction. A model for predicting the buoyancy-driven flow rate in such spaces was proposed, with special emphasis on the effects of stratification pattern. The predictions were validated with the experimental data, and the necessity for accounting for the stack effect attenuation caused by stratification was proved. The prediction model possesses an explicit expression and can thus provide a convenient tool for design calculations.

Hyporheic Flows in Stratified Sediments: Implications on Residence Time Distributions

AbstractThe fate of nutrients and contaminants in fluvial ecosystems is strongly affected by the mixing dynamics between surface water and groundwater within the hyporheic zone, depending on the combination of the sediment's hydraulic heterogeneity and dune morphology. This study examines the effects of hydraulic conductivity stratification on steady‐state, two‐dimensional, hyporheic flows and solute residence time distribution. First, we derive an integral transform‐based semi‐analytical solution for the flow field, capable of accounting for the effects of any functional shape of the vertically varying hydraulic conductivity. The solution considers the uneven distribution of pressure at the water‐sediment interface (i.e., the pumping process) dictated by the presence of dune morphology. We then simulate solute transport using particle tracking. Our modeling framework is validated against numerical and tracer data from flume experiments and used to explore the implication of hydraulic conductivity stratification on the statistics and pdf of the residence time. Finally, reduced‐order models are used to enlighten the dependence of key residence time statistics on the parameters characterizing the hydraulic conductivity stratification.