Stability Of Stratification Research Articles

Heat transfer and stratification behaviors of internally heated double-layer fluids systems under swinging conditions

To evaluate the safety designs aimed at the stratified corium pools for nuclear reactors applied in the marine environment, it’s important to carry out research on the convection related phenomena inside a layered fluids system under motion conditions. Thus, in this paper, the macroscopic characteristics of heat transfer and stratification for the double-layer fluids systems with internal heat source under motion conditions were studied through visualization experiments, and due to the complexity of actual ocean motions, only swinging motions were considered. In this research, a new dimensionless number Ris was proposed to quantify the effects of swinging motions, which represents the ratio of the characteristic buoyancy to the characteristic centrifugal force caused by swinging motions. Based on experimental results, swinging motions exert the most significant impacts on the layered systems when Ris is less than 1. In this case, the ratio of maximum temperature fT and the ratio of temperature difference between the two layers fΔT both dropped below 0.5, while the ratio of peak heat transfer capacity fQ-peak raised above 1.5, with the ratio of stable heat transfer capacity fQ-stable most probably lying within the range of 1.06 to 1.2. Additionally, several representative types of macroscopic interface deformation or stratification instability was observed, and phenomenon of mixing could appear between the double-layer fluids under intense-enough swinging conditions. These phenomena imply the significantly intensified forced convection inside the layered systems, which explains the sharply decreased temperature difference and the greatly enhanced heat transfer capacity during high-intensity swinging motions. By contrast, when Ris becomes larger than 10, the values of fΔT、fΔT and fQ-peak will be approaching to 1.0, and relatively stable stratification of the layered systems can be maintained, which indicates the increasingly negligible impacts of swinging motions in such cases. Besides, it was found that an increase in the thickness of either the lower-layer or the upper fluid also helped restrain interface deformation and enhanced the stratification stability of the layered systems.

Study of turbulence intermittency in unstable atmospheric surface layer and its effect on saltation sand motion based on wavelet transform

Turbulence in the atmospheric surface layer, especially in deserts and semi-arid regions, significantly affects sand movement. In unstable stratification, turbulence exhibits complex intermittency, complicating its impact on saltation. This study uses wavelet transform analysis to examine the effects of turbulence intermittency in unstable stratification on saltation. Our analysis reveals that in unstable stratification, the energy distribution of turbulence is more dispersed, the intermittent characteristics are more significant, and the intermittent burst duration of streamwise turbulence is longer, while the vertical intermittent burst duration is shorter. The fitting formulas of the energy ratio and stratification stability of the streamwise wind speed, vertical wind speed, and temperature at different frequencies are given. In addition, there is a complex nonlinear relationship between stratification stability and friction velocity on saltation. In unstable stratification, the critical wind speed required for saltation is higher than that of near-neutral, and the jumping speed and horizontal transport are weakened. Moreover, the coherence between wind speed and saltation flux increases significantly at low frequency with the increase in instability, indicating that large-scale motion plays a key role in saltation under these conditions. The more unstable the stratification is, the more obvious the phase difference fluctuation of the low frequency part is, and the more unfavorable the formation of stable saltation sand conditions. This study reveals the turbulence intermittently and its complex effects on sand particle movement in unstable stratification, which is of great significance for predicting and controlling dust storms, land desertification, and soil erosion.

Effect of two-dam coexistence on thermal regime: A special withdrawal measure in Fengman reservoir, China

The Fengman Reservoir in China employs a distinctive approach termed two-dam coexistence to mitigate the risks associated with aging and hazardous dams. This method involves the partial demolition of the old dam and construction of a new dam downstream, which allows the remaining part of the old dam to act as a retaining wall for selective water withdrawal. Through a comprehensive study, long-term water temperature data were analyzed, along with the characteristics of the two-dam coexistence system, to comprehend its effects on thermal stratification in the main basin near the dams and the withdrawal water temperature (WWT) regime. The results revealed that the metalimnion shifted upwards, strengthening stratification, and the temperature gradient expanded from 0–0.9 °C/m to 0–10.5 °C/m compared to that under the one-dam condition. Vertical mixing was reduced, causing the temperature difference between surface and bottom waters to range from 6.8 to 26.8 °C. This enhanced the stratification stability by 1.8 times compared with the one-dam condition, with some annual variability. Thus, the buoyancy frequency decreased accordingly. Furthermore, two-dam coexistence influenced the WWT, resulting in higher WWT during the warming period (averaging 4.3 °C from May to June) and lower WWT during the freeze-up period (averaging 0.1 °C from January to February) than that of the one-dam condition. The most significant temperature difference between the main basin near the old dam and the one near the new dam occurred at the bottom of the reservoir (ranging from 3.5 to 12.0 °C), confirming that the old dam functioned as a retaining wall, allowing the thermal regime to change. Owing to the two-dam coexistence, the withdrawal layer shifted by 20.0 m from near the intake to close to the demolition elevation. These changes in stable stratification and variations in WWT play crucial roles in reservoir management. This study offers practical insights for treating similar aging and hazardous reservoirs and serves as a reference for optimizing water quality management strategies.

An investigation of the effect of stratification stability and saltation sand flux on the anisotropy of atmospheric surface layer wall turbulence

In the atmospheric surface layer (ASL), the anisotropic characteristics of turbulence become more complex due to the strong influence of heat flux and particle motion. In this paper, the effects of stratification stability and total saltation sand flux on turbulent anisotropy of ASL wall turbulence are systematically analyzed by using high-frequency 3D velocity, temperature, and saltation sand flux measured in the field. Our results show that the temperature gradient intensifies the spanwise turbulent motion and enhances the vertical motion asymmetry. Although the buoyancy-driven turbulence enhances the spanwise variation, the momentum transfer mode between the streamwise–vertical and spanwise–vertical does not change. With the increase in instability, the large-scale motions (LSM) of the spanwise velocity may be destroyed and more spanwise small-scale motions (SSM) formed. In addition, saltation increases the sharpness, randomness, and extreme frequency of spanwise velocity distribution, but does not change the momentum transfer mode. Saltation may enlarge the fluctuation range and scale of the spanwise velocity, but may not be the main factor affecting the anisotropy of SSM. These results can deepen people's understanding of wind-blown sand movement and turbulence properties in ASL, and provides empirical data and insights that can significantly contribute to the development and refinement of turbulence models, particularly those that need to account for the complex interplay between stratification stability, saltation sand flux, and turbulence anisotropy.

Numerical investigation of thermal-mixing characteristics at vertically oriented T-junction pipelines

When hot and cold fluids are mixed at pipeline tees, temperature fluctuations are generated and can lead to thermal fatigue damage in the piping materials. At the University of Stuttgart in Germany, experimental investigations have been performed for understanding the flow mixing mechanism causing thermal fatigue. It was found that the inlet flow rate is one of the decisive factors on the mixing behaviors at a horizontal T-junction.In this study, the influence of the inlet flow rate on the flow mixing behaviors at the vertical T-junction is investigated using the large-eddy simulation (LES) method. The simulations are validated with the previous experiments and provide a good overview of the mixing flow. The LES method shows the advantage of illustrating the collision of two flow streams at the T-junction, which leads to different behaviors of the mixing flow. Generally, the temperature fluctuation in the mixing flow as well as the stability of thermal stratification decreases along the flow direction due to the dissipation of the turbulent kinetic energy in the mixing flow. The decrease in the main flow rate shows the impact of the increase in thermal stratification stability and the reverse flow distance. The decrease in the branch flow leads to a slight increase of the thermal stratification stability downstream of the T-junction and significant turbulent penetration in the branch pipe. The maximum temperature fluctuation at the pipeline inner surface is located at the joint position of the pipelines with a value higher than 30 K. Moreover, the flow collision at the T-junction leads to significant secondary flow in the mixing region, which can be influenced by the variations in the inlet flow rate. In particular, the secondary flow due to cold fluid presents a phenomenon of counter-rotating vortex pair (CRVP), and generates a temperature fluctuation with a frequency of approximately 1.1 Hz, which is recorded by the monitor points at both horizontal sides of the pipeline. In comparison with the previous work at the horizontal T-junction, the complete flow collision at the vertical T-junction is the reason for the totally different mixing phenomenon.

Terrain effects of the Tibetan Plateau on dust aerosol distribution over the Tarim Basin, China

Dust events are frequent in the Tarim Basin because of its underlying desert surface; moreover, meteorological conditions under the influence of the surrounding high terrains, especially the Tibetan Plateau, may also trigger dust events. However, the terrain effect of the Tibetan Plateau on the dust aerosol distribution over the Tarim Basin remains unclear. This study aimed to investigate the impact of the Tibetan Plateau terrain on the dust aerosol variations in three dust events over the Tarim Basin using the Weather Research and Forecasting Chemistry model. With decreasing altitude of the Tibetan Plateau, dust concentration (DC) decreased in the upper layers and increased in the low layers. The DC within the entire atmospheric layers increased by 8.52%, 24.03%, and 43.05% on average during three dust events at Tibetan Plateau altitudes of 3000 m, 2000 m, and 1000 m, respectively, thereby indicating that the DC in the lower layers increasingly dominated the entire atmospheric layers as the Tibetan Plateau altitude decreased. Low-elevation terrain enhanced the planetary boundary layer height, near-surface wind speed, and surface air temperature, but weakened atmospheric stratification stability, all of which are beneficial for strengthening dust emissions and vertical mixing in the lower layers of the Tarim Basin. Furthermore, a decrease in the Tibetan Plateau altitude led to forming a vertical circulation, with the south to rise and the north to sink over the Tarim Basin. Meteorological field and vertical circulation could adequately explain the changes in the distribution of dust aerosols over the Tarim Basin. Overall, this study enhances our understanding of the effect of the Tibetan Plateau terrain on changes in the dust aerosol in the Tarim Basin and surrounding central Asian regions.

Characteristics and interactions of fluctuation velocities, saltation mass flux, and temperature in the atmospheric surface layer

The essence of wind-blown sand movement is a particle movement system driven by high Reynolds number wall turbulence in the atmospheric surface layer (ASL). Understanding this phenomenon is crucial as the law and mechanism of sand movement have not been effectively revealed at present. In this study, we utilize the high-frequency time series data from the Oceano site, a renowned location for such studies, which includes streamwise wind velocity (u), wall-normal wind velocity (w), temperature (T), and total saltation mass flux (q) to delve deeper into wind-blown sand movement. The results indicate a positive correlation between T and w. Interestingly, this correlation not only escalates with height but also intensifies with the increase of the stratification stability parameters (z/L). Sand influences the intensity ratio of each quadrant to Reynolds stress without altering the time ratio. Both the ejection and sweep processes correlate well with z/L. Similarly, q also exhibits a good correlation with z/L. The buoyancy's impact on the low-frequency fluctuations of q might be through its effect on the low-frequency fluctuations of w, enhancing the sand transport capacity of w. This discovery holds profound implications for the study of two-phase flow in ASL and the precise prediction of surface sediment transport.

Comparisons of temperature structures with turbulent structures in thermally stratified channel flows by direct numerical simulation

Direct numerical simulation (DNS) in the thermally stratified turbulent channel flow with the Boussinesq approximation at Reynolds number Reτ≈395, Prandtl number Pr=0.71 and Richardson number Riτ=−10,0 and 10 is performed in this study. Based on the DNS data, the three-dimensional structure of temperature fluctuations and the effect of stratification stability on temperature structure morphology, scale and volume are investigated. Results show that thermal buoyancy has a significant effect on the temperature structure under different stratifications. Specially, the three-dimensional structure of temperature fluctuations has similar morphological characteristics to that of streamwise velocity fluctuations only in the near-wall region under stable and neutral stratifications. The streamwise length of the temperature structure decreases with the height, but the structure volume increases linearly with the height. However, under the unstable stratification (Riτ=−10), the thermal buoyancy makes the turbulence form a quasi-streamwise large-scale convective structure directly enhancing the large-scale temperature structure. So the streamwise length and spanwise width of the temperature structure increase with the height, and the spanwise width exhibits a discontinuous jump with the height. At the same time, the scale size of the temperature structure in the outer regions is almost constant, thus the structure volume increases nonlinearly with the height. In addition, the temperature fluctuations are also affected by thermal buoyancy. The thermal buoyancy enhances the large-scale temperature structure in the near wall region through the modulation of the large-scale turbulent structure in the outer regions on the temperature large-scale fluctuations near the wall. Which results in the similarity between the temperature structure and streamwise velocity structure in the near-wall region being destroyed.

Optimization of selective withdrawal strategy in a warm monomictic reservoir based on thermal stratification

Selective withdrawal from reservoirs is an effective strategy for balancing economic goals and environmental demands. Multilevel intake operation (MIO) is one of the main options for improving the thermal regime of deep reservoirs. In this study, a combination of measured data and a two-dimensional hydrodynamic model (CE-QUAL-W2) was utilized to analyze the impact of MIO processes on the thermal stability of a reservoir and the improvement effect of the withdrawal water temperature (WWT). The purpose of this study was to identify an optimal selective withdrawal strategy to meet the water temperature needs of fish downstream during their spawning and breeding activities. The results showed that the MIOs raised the withdrawal water intake position (8.3–11.2 m) for the WWT. Meanwhile, MIOs resulted in statistically significant changes in the water temperature structure of the reservoir (p < 0.01). The stratification stability of the water column weakened (6.8 %-34.5 %), and there were interannual differences. The WWT increased by 0.0 °C∼1.9 °C every ten days, and the time to reach the optimum temperature (18 °C) for fish spawning was 7 to 17 days earlier. There was a statistically significant positive correlation between the WWT improvement and the stability index (SI) (R = 0.7817, p < 0.01). The threshold values of the SI (above the water intake) for average WWT improvements of 0.5 and 1.0 °C were 90.3 and 221.9 kg/m2, respectively, and the recommended operating period was from early-April to May. Under MIOs, the weakening stratification and the increasing WWT during the warming period reduced risks to the water quality and ecological health in the reservoir and downstream rivers. This study provides a helpful reference for the implementation of selective withdrawal operations and the optimization of water quality management strategies in similar large, deep reservoirs.

Future projections of thermal regimes and mixing characteristics in a monomictic reservoir under climate change

Stratified structures are basic physical characteristics of lakes and reservoirs, which play important roles in vertical convection and mixing processes. Global warming is expected to alter the thermal regimes and stratified characteristics of lakes and reservoirs, leading to potential environmental risks and ecological problems. In this study, we used a two-dimensional hydrodynamic model to explore the response characteristics of the thermal regime to climate change in the Xiluodu Reservoir. The study is conducted based on four representative concentration pathways (RCP 2.6, RCP 4.5, RCP 6.0, and RCP 8.5). The results show that the projected surface water temperature of the reservoir will significantly increase (0.13 °C/10a-0.34 °C/10a) from 2022 to 2099, and the warming rate of the water in the epilimnion and thermocline will be greater than that in the hypolimnion, leading to enhanced vertical stratification in the reservoir. The stratification stability index (SI) will increase by 14.4 % under RCP 8.5 compared to that under RCP 2.6. The main responses of the reservoir to climate change are earlier start date and later end date of stratification, which may increase the duration of hypoxia in the hypolimnion and promote the succession of planktonic algal communities. The withdrawal water temperature in the reservoir will significantly increase under the climate warming scenarios (0.03 °C/10a-0.22 °C/10a). Furthermore, our research results indicate that selective withdrawal is still needed to mitigate the adverse effects of cold water from the reservoir during the fish spawning period under the strongest warming scenario, and can also be an effective adaptive management strategy to regulate thermal stability in the reservoir. This study provides a scientific and theoretical reference for the sustainable management of similar deep monomictic reservoirs under climate change.

Analysis of Water Vapor Transport and Trigger Mechanisms for Severe Rainstorms Associated with a Northeast China Cold Vortex in 2022

Rainstorms always occur in the southeast and northeast quadrants of the Northeast China Cold Vortex (NCCV), resulting in significant flooding. This study investigated water vapor and trigger mechanisms for rainstorms within these two regions of an NCCV event during 11–14 June 2022 in terms of Lagrangian backward tracking, stratification stability, and upward motion using the ERA5 reanalysis. In the mid-troposphere, a quasi-stationary “ridge-NCCV-ridge” pattern resided over northeastern China, with an “anticyclonic-cyclonic-anticyclonic” airflow in the lower troposphere. As a result, water vapor originated from the Yellow Sea and was transported in an “L” shape toward both two regions. The southeast region was influenced by southwesterly and northwesterly airflows, resulting in the convergence of moist air from the Yangtze River and Lake Baikal and significant vertical shear of positive vorticity advection. This dynamic created deep and pronounced upward currents in the southeast of the NCCV, leading to the development of intensive and extensive rainstorms in situ. In contrast, the northeast region of the NCCV was dominated by southerly airflow. The moist air converged against the lee side of the Great Khingan Mountains and generated shallow, unstable stratification. The upward motion in this area was relatively weaker and thus induced regional rainstorms.

Thermal expansion of atmosphere and stability of vertically stratified fluids

The influence of thermal expansion of the Earth's atmosphere on the stability of vertical stratification of fluid density and temperature is studied. We show that such an influence leads to the instability of incompressible flows. Modified by the thermal expansion coefficient, a new expression for the Brunt-Väisälä frequency is derived, and a critical value of the thermal expansion coefficient for which the instability occurs is revealed.

Stability of smoke stratification under the impact of water sprays with various droplet size ranges in longitudinally ventilated road tunnels

This paper presents a simplified model of tunnel smoke stratification, which can be used to study the effect of sprinkler water spray on stratified stability. The stratified flow downstream of a tunnel fire is represented by a two-layer thermal flow, with the hot upper layer representing the smoke and the cold lower layer representing the ventilation air. The dragging effects of sprays from sprinkler nozzles with various K-factors were numerically studied using FDS code (version 6.7.3). Experiment data reported in the literature successfully validated the accuracy of the CFD method. Spray-induced smoke movements, including the smoke logging distance and the horizontal movement, were determined by releasing a series of massless tracers from the smoke layer inlet. The findings of the work indicate that the dragging effect of a water spray is droplet-size-dependent. The smaller the droplets, the larger the dragging force for a given volumetric spray rate. By applying dimensional analysis and introducing the volume mean diameter into the governing parameters, some correlation models that account for the droplet size were proposed to predict the spray-induced smoke movements and smoke layer heat loss. The new correlation models help complete previous work by the authors and are of practical use for tunnel fire safety design where water sprays are included alongside a longitudinal ventilation system.

Severity Differences and Mechanisms of Algal Blooms Among Sections in Pengxi River of the Three Gorges Reservoir

Since the impoundment of the Three Gorges Dam, 50% of the first-order tributaries in the reservoir area have had frequent algal blooms but with variations regarding the geographical locations of the seriously bloomed sections and the scope of the latter being influenced by the mainstream. This study took the Pengxi River, a first-order tributary of the reservoir area, as an example in order to explore the difference in eutrophication among the river sections and the influence of the Yangtze River on its tributaries. During the spring bloom season of 2019, sampling was carried out in one-week intervals for a total duration of one month. Seven sampling sections (PX1-PX7) were set up from the confluence to upstream. According to the profiles of vertical water temperature and conductivity of each section, the influence scope and form of the backwater of the Yangtze River were inferred; in addition, severity differences and mechanisms of algal blooms among sections were explored through the comparison of the hydrology, water quality, and sediment nutrients among Gaoyang Lake (PX5), which has had serious algal blooms, and the upstream (PX6) and downstream (PX4) sections of PX5, which are both 4 km away from PX5. The results showed that during the sampling month, the average ρ(Chl-a) in the confluence area of the Pengxi River (PX1-PX4) and in the upstream (PX5-PX7) were in the range of 14.55-44.00 μg·L-1 and 42.66-175.40 μg·L-1, respectively. The ρ(Chl-a) of PX5 was up to 413.00 μg·L-1, which was significantly higher than that of other sections (P<0.05). Temperature and conductivity results showed that the backwater from Yangtze River flowed into the Pengxi River from the middle and bottom layers during the period from April to May. The confluence (PX1-PX4) sections were in the intersection area of the backwater from Yangtze River and the upstream of the Pengxi River; thus, the waterbody was unstable, which was not conducive to the formation of algal blooms. However, the upstream (PX5-PX7) sections were not directly affected by the backwater from Yangtze River, leading the nutrient exchange mainly vertically. Most averages of n(TN)/n(TP) and n(DTN)/n(DTP) of PX4-PX6 were all greater than 16, indicating a phosphorus-limited state. During sampling, the average sediment total phosphorus of PX5 was 91% of that in upstream PX6, which was only 4 km away, whereas the surface water total phosphorus of PX5 was 180% of that in PX6. The important reason for this phenomenon is that the water surface width of PX5 was 3.6-4.7 times that of PX6, indicating longer wind fetch in the former section. Owing to the mountainous landscape in the Three Gorges Reservoir (TGR) region where windy weather is rare, the disturbance effect of wind and waves on PX5 was stronger than that of PX6, and the nutrients released from the sediment at the PX5 section caused by wind and waves resupplied the surface water more easily, causing more serious algal blooms at PX5 than those at the remaining sections in the Pengxi River. The main causes of the algal blooms in the tributaries of the TGR area lied in the stability of water stratification and the supply of internal phosphorus. The stability of water stratification was mainly affected by the backwater from Yangtze River, and the supply of internal phosphorus in the algal bloom season was affected by the special water stratification phenomenon of the tributaries of TGR-the "surface density layers." The duration and degree of weather disturbance to the surface density layers can be used to predict the time and scale of algal blooms.

Two-Dimensional Modelling of the Mixing Patterns in a Tropical Semiarid Reservoir

Tropical semi-arid regions suffer with recurrent droughts and uncertain water availability, but a few research studies have been conducted to further understand those complexities and their relationships with reservoir hydrodynamics. This study assessed the hydrodynamic processes of a multiple-use reservoir located in the Brazilian semiarid region. The aim was to apply the CE-QUAL-W2 model to understand the lake’s thermal structure and its variabilities in time and space by using the Richardson’s number (Ri) as a reference. Meteorological patterns were also investigated. Results show that: (1) no significant changes were found by analysing the spatial variabilities of stratification; (2) seasonal changes were relevant as more robust stratification stability was observed in the wet period when water availability may be impacted by poor water quality; (3) from meteorological evaluations, rainfall showed a strong coefficient of determination with Ri (r² of 0.77); and (4) a threshold value of 60 mm in monthly precipitation was found as an indication of a stable stratification in the water column. Wind speed and water level partly influenced Ri’s variabilities, while low impact was noted for air temperature and inflow. These results can promote an improvement in water-resources management by linking rainfall regime and reservoir hydrodynamics.

The Effects of Lake Level and Area Changes of Poyang Lake on the Local Weather

Poyang Lake is the largest freshwater lake in China and is characterized by significant intra-annual variation, with higher water levels and area in the wet season compared to the dry season. However, the effects of the seasonal variation in Poyang Lake on the local weather are still not well-recognized. With the help of the weather research and forecasting (WRF) model, we designed one control experiment (CTL) using the default Poyang Lake level and area data and two sensitivity experiments, EXPT1 and EXPT2, the former representing the higher lake level and the greater area of Poyang Lake in the wet season and the latter representing the lower lake level and the smaller area of Poyang Lake in the dry season, to assess how these changes affect the local weather. The results of EXPT1 show that, as the lake’s level and area increase, the latent heat flux (LH), the sensible heat flux (SH), and the land surface temperature (LST) in the lake area decrease compared to those of the CTL. Meanwhile, the planetary boundary layer height (PBL), the convective available potential energy (CAPE), the wind speed, and the vapor flux over the lake decrease as well, indicating increased atmospheric stratification stability and resulting in a domain-averaged decline in precipitation of −22.3 mm. However, the low lake level and less area in EXPT2 show increasing SH, LST, PBL, and wind speed, and decreasing LH and CAPE compared to those of the CTL. The increasing SH and weakened atmospheric stratification stability in EXPT2 cause a significantly higher wind speed over the eastern part of the lake. As a result, more water vapor is transported to the east side of the lake by westerly upper winds, leading to a decreasing precipitation on the western side of the lake and a slightly increasing precipitation on the eastern side, resulting ultimately in a domain-averaged decline in precipitation of −23.8 mm in the simulation of the low level and less area of Poyang Lake. Although the LH and CAPE decline both in EXPT1 and EXPT2, the main cause is the higher water thermal capacity and lower lake-surface temperature with more lake water for EXPT1 and the lower evaporation with less lake water for EXPT2. Overall, a deeper and larger Poyang Lake will reduce the local temperature, inhibit water evaporation from the lake surface, and make the near-surface atmosphere more stable, resulting in restrained local precipitation. A shrinking lake level and area will raise the local temperature and the instability of the near-surface atmosphere but reduce water vapor and enlarge local wind and circulation, resulting in declining precipitation and a changing fall zone.

A case study of thermal and chemical stratification in a drinking water reservoir

Thermal stratification has an important impact on the cycling of reservoir water quality. Uneven vertical distribution of water quality factors, such as dissolved oxygen and nutrients, occurs during seasonal stratification, which creates chemical stratification. Typically, thermocline and chemocline characteristics vary across different reservoirs. In this study, a field study was conducted in the Zhoucun Reservoir (ZCR), China, to investigate the variation in water quality during periods of thermal stratification. The results revealed the maximum water depth as 15 m at 122 mamsl, which is relatively shallow for stratified reservoirs. However, an extremely high thermocline strength index (TSI) was recorded, which indicates that the thermal stratification of ZCR water is very stable, contrary to our common understanding that stratification is more obvious at greater water depths. The chemical stratification strength index (IC-i) was compared with the TSI and the relative water column stability (RWCS). The TSI had a high correlation with IC-i, which explains the high stability of ZCR chemical stratification. Moreover, it highlights the suitability of TSI for characterising the chemical stability of reservoir stratification. Finally, this study also found that the formation and disappearance of thermal and chemical stratification in the ZCR were synchronous. As stratification directly influences a reservoir water quality regime, this study may be a helpful reference for optimising water quality management.

Patient-reported outcomes in a Chinese cohort of osteogenesis imperfecta unveil psycho-physical stratifications associated with clinical manifestations

BackgroundOsteogenesis imperfecta (OI) is a rare congenital disorder of the skeletal system, inflicting debilitating physical and psychological distress on patients and caregivers. Over the decades, much effort has been channeled towards understanding molecular mechanisms and developing new treatments. It has recently become more apparent that patient-reported outcome measurements (PROM) during treatment, healing and rehabilitation are helpful in facilitating smoother communication, refining intervention strategies and achieving higher quality of life. To date, systematic analyses of PROM in OI patients remain scarce.ResultsHere, utilizing a PROM Information System, we report a cross-sectional and longitudinal study in a southern Chinese cohort of 90 OI patients, covering both the child and adult age-groups. In the child group where both self and parental surveys were obtained, we identified two clusters of comparable sizes showing different outlooks in physical mobility and emotional experiences. One cluster (Cluster 1) is more negative about themselves than the other (Cluster 2). A concordance of 84.7% between self and parental assessments was recorded, suggesting the stability and validity of PROM-based stratification. Clinical subtyping, deformity, leg length discrepancy, and limited joint mobility were significantly associated with this stratification, with Cluster 1 showing higher percentages of severe phenotypes than Cluster 2. Since OI is a genetic disorder, we performed genetic testing on 72 of the 90 patients, but found no obvious association between genotypes and the PROM stratification. Analyses of longitudinal data suggested that patients tended to stay in the same psychological state, in both clusters. Adult patients also showed a continuous spectrum of self-evaluation that matches their clinical manifestations.ConclusionBy systematically analyzing patient-reported outcomes, our study demonstrated the link between the sociopsychological wellbeing of OI patients, and their clinical manifestations, which may serve as the basis for evaluating clinical interventions and help achieve better patient-centric medical practices. The lack of genotype-PROM association may be due to the diverse mutational spectrum in OI, which warrants further investigation when a larger sample size is available.

The Structuring Effects of Salinity and Nutrient Status on Zooplankton Communities and Trophic Structure in Siberian Lakes

Many continental saline lakes are under the effects of salinity increase and anthropogenic eutrophication exacerbated by global change. The response of the food web to these drivers of change is not straightforward. To understand the consequences of salinity and eutrophication interactive effects on the food web, we studied the seasonal dynamics of zooplankton and phytoplankton and water quality parameters in 20 lakes of different salinity (from freshwater to hypersaline) and nutrient status (from oligotrophic to eutrophic) located in southern Siberia. We observed a pronounced bottom-up effect of nutrients, which induced an increase in the biomass of phytoplankton and zooplankton and a decline in water quality. A significant decrease in the species abundance of zooplankton was observed at a threshold salinity of 3 g L−1 and the disappearance of fish at 10 g L−1. The top-down effect induced by salinity manifested itself in an increase in the biomass of zooplankton with the disappearance of fish, and in the change of the size distribution of phytoplankton particles with an increase in the proportion of cladocerans in the zooplankton. Even though we observed that with the salinity increase the food web in saline lakes transformed from three-trophic to two-trophic without fish, we conclude that in the salinity range from 10 to 20–30 g L−1 this transition in most cases will not increase the ability of zooplankton to control phytoplankton. Interactive effects of salinity and eutrophication strongly depend on the size and depth of the lake, as deep stratified lakes tend to have a better water quality with lower biomasses of both phyto- and zooplankton. Thus, the salinity per se is not the driver of the decline in water clarity or the uncontrolled development of phytoplankton. Moreover, for deep lakes, salinity may be a factor affecting the stability of stratification, which mitigates the consequences of eutrophication. Thus, small shallow lakes will be the most vulnerable to the joint effect of salinity increase and eutrophication with the degradation of ecosystem functioning and water quality at moderate salinities of 3–20 g L−1.

Experimental investigation of tank stratification in liquid air energy storage (LAES) system

Liquid air energy storage technology is a technology that stores liquid air in case of excess power supply and evaporates the stored liquid air to start a power generation cycle when there is an electric power demand. When liquid air is stored for a long-time during operation, safety and performance degradation can be caused or mitigated by the tank stratification. To investigate the tank stratification phenomenon and associated issues, an experimental facility is constructed. The heat ingress is controlled with respect to changing vacuum level in the experiment. Furthermore, the conditions under which stratification occurs are defined in terms of temperature and concentration, and based on this, the stratification stability ratio and the stability map are defined and evaluated experimentally. The results show that the time required for destratification is 8–29% shorter for liquid air mixture cases than for liquid nitrogen. Moreover, the time required for destratification is 2.4 times longer for the high tank pressure cases, and it is 39% shorter for the case of high heat ingress. From experimental observations, an operation strategy utilizing stratification inside the liquid air storage tank is newly suggested that can minimize the boil-off gas of liquid air in the tank.