Overflow Channel Research Articles

Effects of a surface layer cross-flow and slope steepness on the rate of descent of dense water flows along a slope

The pathways and mixing in dense water overflows have been addressed in a range of numerical studies based on the DOME (Dynamics of Overflow Mixing and Entrainment) setup. These studies are motivated by overflows such as the flow of dense and cold water over the ridge between Iceland and Scotland. The main route of this water is through the Faroe-Shetland channel and further through the Faroe Bank Channel. After leaving the Faroe Bank Channel, the dense water continues along the slope along the Iceland-Faroe Ridge. Across this ridge there is also a strong flow of Atlantic water that may affect the pathway and mixing in the dense plume. In the DOME investigations, the slope steepness is assumed to be constant and there is no active background flow in the ambient water masses above the dense plume. With the situation along the Iceland-Faroe Ridge in mind, the setup from the DOME experiment is adjusted to study the effects of i) the slope profile, ii) flows crossing the slope on top of the along-slope flow of dense water, and iii) the topography near the overflow channel of dense water. It is found that the rate of descent is depending on slope steepness, and for a curved slope going from flat on top of a ridge to much steeper away from the ridge, dense water parcels near the ridge top or crest will sink slower than the faster flowing dense water further down along the slope. A cross-flow over the ridge, mimicking the flow of Atlantic water over the Iceland-Faroe Ridge, will force stronger mixing between the dense water and the ambient water above and dense water mixed up into the surface water can be allowed to flow out across the ridge. Furthermore, the dynamical situation along the slope will change and fluid parcels in the deeper part of the plume can experience a faster rate of descent. By removing a barrier in the topography downstream of the overflow channel, dense water can be steered towards the ridge and the starting point of the center of mass of the descending overflow water will be higher up on the slope.

A novel overflow channel design of manifold cold plate for lithium-ion battery: A CFD study

In the realm of electric vehicles, optimizing the thermal management systems for lithium-ion batteries is crucial for enhancing performance and longevity. To improve the cooling effect of the indirect liquid cooling system, this study reports on the CFD investigation of two novel designs of variable cross-section overflow channels of manifold cold plates for lithium-ion batteries. However, the total volume of the overflow channel is kept the same as that of the traditional design. The first type (Type-1) is referred to as the flow-direction variable cross-section. The second type (Type-2) is referred to as the vertical flow-direction variable cross-section. The angle of the flow channels, which is defined using two non-dimension parameters of deflection coefficient (Type-1 (alpha, ɑ), Type-2 (beta, β)) varied ranging from 1/7, 1/5, 1/3, 1/2, 2, 3, 5, 7. The effect of the deflection coefficient on flow and heat transfer characteristics is reported in this study. The result from the new designs is benchmarked with that of the traditional overflow unit. After that, the CFD model is extended to include a manifold unit with 12 Type-2 overflow channel units. The water coolant ranging from 0.1 mL/s to 0.63 mL/s with a temperature of 293 K is set to flow in the flow channel with a uniform heat flux at the bottom boundary wall. The maximum temperature of the heating surface decreased from 305.65 K to 301.93 K, and the average temperature of the heating surface of Type 2 (β = 7, Qinlet = 0.105 mL/s) decreased by 3.65 K compared to the traditional overflow unit. The thermal resistance of the Type-2 overflow unit with β > 1 decreased by a maximum of 30 % in comparison to that of the traditional overflow unit under the same boundary condition. Although the pressure drop of the Type-2 overflow unit has increased, the maximum increase is no more than 19 % compared to the traditional overflow unit. Based on this, a manifold unit is designed containing 12 Type-2 overflow units (optimized design, β = 5). Comparative analysis was conducted under the uniform heat flux condition equivalent to a 5 C discharge of the battery within the range of inlet flow rates of 2–7.2 mL/s. The average temperature of the heating surface of the optimized design decreased by 3.65 K compared to the traditional manifold unit, when the inlet flow rate is 2.39 mL/s, and the mean absolute temperature deviation decreased by 48 %.

THE IMPACT OF MINING EXCAVATIONS (VOIDS) ON THE WATER QUALITY MANAGEMENT IN THE NORTH KALIMANTAN PROVINCE

The presence of a coal mining business permit not only has an economic impact but can also cause environmental problems. The objectives of this research are (1) to analyze the impact of PT XXX's overflowing voids on water management and water quality, and (2) to carry out spatial analysis, mapping and estimation of coal reserves that cannot be extracted by PT YYY. The research method is a case study selected by purposive sampling at two companies in North Kalimantan Province using water quality test analysis with grab sampling and estimating the potential loss of coal reserves using the rule of gradual changes and rule of nearest point methods as well as aerial photography. The research results show that in general the water use meets Class 3, namely: Water that can be used for cultivating freshwater fish, animal husbandry, water for irrigating crops, and/or other uses that require the same water quality as that use. Apart from that, PT XXX has built an overflow water channel into the PT YYY area without management approval, thus having a negative impact on PT YYY's mining plans which are dominated by peat land. Map of PT YYY's lost coal potential of 714,688 MT with an affected area of 15.16 hectares with details of 6.4 ha being the void area included in PT YYY's IUP area, 1.86 ha being the road and buffer zone area and 6.9 ha is a potential lost area of PT YYY.

The study of heat exchange processes during induction heating of the casing string in relation to the determination of behind-the-casing flows

One of the promising methods of geophysical survey of existing wells is active thermometry. The technology for conducting research using this method includes induction heating of a section of a metal casing string, registration and analysis of temperature changes in the range of induction exposure. As a result of heat exchange with the heated section of the column, a thermal disturbance is created in the fluid flow moving inside the column or in the behind-the-casing flow channel. The analysis of non-stationary temperature in the process of induction action allows solving actual practical problems, for example, determining the presence of fluid overflows in the space behind the casing string. In this work, on the basis of numerical simulation, the features of the formation of a temperature field in the process of inductive heating of the casing string are studied in relation to the determination of behind-the-casing fluid flows. Numerical simulation was performed using the Ansys Fluent software package. Fluid movement in the well is described by the Navier–Stokes equation in the Boussinesq–Oberbeck approximation, and its temperature is calculated taking into account forced and free convection. To calculate the temperature in the inductor, casing string, rocks and cement sheath, a non-stationary heat equation is used. The application of induction heating in diagnosing behind-the-casing flows in the sump, localized below the working perforated formations, in the annular space between the casing string and the cement ring is considered. The distribution curves of the cross-sectional average temperature in the casing string body in the induction heating interval at different flow rates in the casing cross-flow channel are plotted. It is shown that with an increase in the volume flow in the overflow channel, the maximum heating of the column decreases due to more intense heat transfer to the flow in the overflow channel. It has been established that the temperature curves show a “pull” of temperature (temperature disturbances in the body of the casing string propagate in the direction of flow in the overflow channel), the value of which increases with the flow rate in the overflow channel. It is shown that the temperature “pull” (the distance over which the thermal disturbance propagates) during upward flow exceeds the “pull” during downward flow, which is due to the influence of natural thermal convection in the fluid inside the casing string. On the example of the modeling conditions adopted in the work, it was found that up and down flows of more than 0.5 m3/day can be reliably determined from temperature measurements during the induction effect.

Age and Origin of Fluvial Deposits in the Vistula River Valley Near Tarnobrzeg (Sandomierz Basin, Poland): Insights from Sediment Dating and Analysis

Abstract The present research aimed to determine the age and origin of a 4-m sequence of fluvial deposits located in Siedleszczany on the western side of the Tarnobrzeg Monadnock in the Vistula River valley. Initially, these deposits were thought to be sediments of the overflood (Vistulian) terrace. The study revealed that the sand deposits are relatively young Late Holocene sediments, spanning from the 8th century AD to the 15th–16th centuries AD, and the organic material originated from erosion of older Holocene deposits of various ages. This finding was supported by palynological analysis, which identified, besides Holocene pollen grains, also those from Late Glacial and other Quaternary periods, and even from pre-Quaternary ones. Extreme floods in the Vistula valley may be specified as the origin of the sandy sediments in Siedleszczany. Similar large floods occurred in the past when ice jams blocked the main riverbed, leading to the formation of overflow channels. These floods caused rapid erosion of the flood-plain and deposition of sandy sediments in the sheltered marginal areas of the valley, away from high-velocity flood flows. As a result, the fluvial deposits in Siedleszczany, in the Vistula valley, resemble palaeoflood slackwater deposits observed in various regions worldwide.

Assessment of Runoff Control Effect with Improved Stepped Bioretention System (ISBS) under Various Rainwater Conditions

Stepped bioretention systems have been increasingly used for rainwater treatment in hillside areas. However, the depth of aquifer and soil permeability coefficient limit the treatment effect of runoff rainwater, resulting in a large amount of overflow water, particularly during extreme rainfall events. Here, in contrast to the ordinary stepped bioretention system (OSBS), an improved stepped bioretention system (ISBS) was developed by changing the overflow channel and the inflow and overflow were analyzed under various rainwater conditions. ISBS has high stability and the ability to control runoff rainwater. The runoff rainwater volume reduction rate reached 51.5–100% and the removal rate of suspended solid, chemical oxygen demand, total phosphorus and total nitrogen were 31.2–47.9%, 27.1–51.7%, 26.5–59.0% and 26.7–46.9%, respectively. According to the working principle of the continuous stirred tank reactor (CSTR), the permeable water concentration of other rainfall events can be predicted by using the parameters obtained from extreme rainfall events. In general, ISBS is a very promising runoff rainwater treatment technology, which can reduce the overflow quantity and recharge groundwater under various rainwater conditions.

Shell helium-burning hot subdwarf B stars as candidates for blue large-amplitude pulsators

Blue large-amplitude pulsators (BLAPs) are a newly discovered type of variable star. Their typical pulsation periods are on the order of a few tens of minutes, with relatively large amplitudes of 0.2–0.4 mag in optical bands, and their rates of period changes are on the order of 10−7 yr−1 (both positive and negative). They are extremely rare objects and attempts to explain their origins and internal structures have attracted a great deal of attention. Previous studies have proposed that BLAPs may be pre-white dwarfs, with masses around 0.3 M⊙, or core-helium-burning stars in the range of ∼0.7 − 1.1 M⊙. In this work, we use a number of MESA models to compute and explore whether BLAPs could be explained as shell helium-burning subdwarfs type B (SHeB sdBs). The models that best match existing observational constraints have helium core masses in the range of ∼0.45 − 0.5 M⊙. Our model predicts that the positive rate of period change may evolve to negative. The formation channels for SHeB sdBs involve binary evolution and although the vast majority of BLAPs do not appear to be binaries (with the exception of HD 133729), the observational constraints are still very poor. Motivated by these findings, we explored the Roche lobe overflow channel. Of the 304 binary evolution models we computed, about half of them are able to produce SHeB sdBs in long-period binaries that evade detection from the limited observations that are currently available.

Analysis of Volcanic Development Model and Main Controlling Factors of Oil Distribution in the Third Member of Shahejie Formation in Zaoyuan Oilfield

In order to clarify the influence in the volcanic mode and structure on the oil reservoirs, the volcanic reservoir characteristics, volcanic eruption pattern, and volcanic eruption period of the third member of the Shahejie formation in the Dagang Oilfield Zao35 fault block are studied by combining logging, 3D seismic, and production data, and to provide geological basis for the subsequent development of volcanic reservoirs. The results show that the volcanic body of the Zao35 fault block is jointly controlled by the fissure-centered eruption mode, and there are three strings of bead-shaped eruption centers as well as a fault overflow channel. Based on the seismic response characteristics, the volcanic rocks can be divided into three main eruption cycles. Moreover, combined with the relatively stable mudstone interlayer encountered by the single well, it can be further divided into eight volcanic eruption periods. There are three different lava units in the overflow facies of each stage, namely thick layer dense basalt, basalt with pores developed at the top and dense at the bottom, and basalt with pores developed at the top and dense in the middle. Influenced by the volcanic development model, the oil is mainly distributed in the volcanic reservoir on the slope belt between the central eruption and the fracture eruption. Affected by volcanic eruption periods, the pore basalt at the top and bottom of each period controls the distribution of the oil reserves. Therefore, the thick layer stomatal basalt located between the two eruption modes is the key target of the next development.

The Redshift Evolution of the Binary Black Hole Merger Rate: A Weighty Matter

Gravitational-wave detectors are starting to reveal the redshift evolution of the binary black hole (BBH) merger rate, R BBH(z). We make predictions for R BBH(z) as a function of black hole mass for systems originating from isolated binaries. To this end, we investigate correlations between the delay time and black hole mass by means of the suite of binary population synthesis simulations, COMPAS. We distinguish two channels: the common envelope (CE), and the stable Roche-lobe overflow (RLOF) channel, characterized by whether the system has experienced a common envelope or not. We find that the CE channel preferentially produces BHs with masses below about 30 M ⊙ and short delay times (t delay ≲ 1 Gyr), while the stable RLOF channel primarily forms systems with BH masses above 30 M ⊙ and long delay times (t delay ≳ 1 Gyr). We provide a new fit for the metallicity-dependent specific star formation rate density based on the Illustris TNG simulations, and use this to convert the delay time distributions into a prediction of R BBH(z). This leads to a distinct redshift evolution of R BBH(z) for high and low primary BH masses. We furthermore find that, at high redshift, R BBH(z) is dominated by the CE channel, while at low redshift, it contains a large contribution (∼40%) from the stable RLOF channel. Our results predict that, for increasing redshifts, BBHs with component masses above 30 M ⊙ will become increasingly scarce relative to less massive BBH systems. Evidence of this distinct evolution of R BBH(z) for different BH masses can be tested with future detectors.

Design, design analysis and calculation of structural and technological characteristics of a flat-chamber electromembrane apparatus for purification of solutions of machine-building and chemical industries

The design of an electric baromembrane apparatus of a flat-chamber type for the purification of technological solutions of machine-building and chemical industries is developed. An optimized version of the apparatus with an increased effective solution separation area and the volume of the separated solution is presented, the volume and mass of its elements are calculated. The developed design of the apparatus makes it possible to reduce the hydraulic resistance in the overflow channels for the circulation of the separated solution, to increase the productivity and effectiveness of the separation of the solution, to reduce stagnation effects in the path of output of the near-cathode, near-anode permeates. Keywords: electromembrane apparatus, design, calculation. kdn1979dom@mail.ru, sseedd@mail.ru

River flooding response to ENSO-related monsoon precipitation: Evidence from late Holocene core sediments in the Jianghan Plain

In the Jianghan Plain, known as the province of thousands of lakes, monsoon precipitation-induced floods carrying large amounts of sediments can shape the depositional landscape, particularly after frequent river flooding. Therefore, the sediments document abundant information on climate change and its interaction with the fluviolacustrine system and paleoflooding. To date, late Holocene paleoflood records are limited, as continuous paleoflood archives are scarce. Here, using grain size end-members and sensitive components in combination with element records from the JH001 sediment core in the Jianghan Plain, nine continuous paleoflood regimes were identified during 3400–3000, 2750–2550, 2050–1820, 1800–1650, 1550–1500, 1350–1100, 1050–1000, 800–750, and 620–600 cal yr BP, respectively. Exploration of the climatic driving factors on flood regimes indicated a good agreement among paleoflood regimes and El Niño-Southern Oscillation (ENSO)-related hydrological records in the Middle Yangtze Valley (MYV) and reconstructed ENSO records. This suggests that ENSO is the dominant influence on flood occurrence in the Jianghan Plain. Strong ENSO activity exerted a southward shift in the subtropical high in the western Pacific and produced a long-lasting rainbelt in the mid-lower Yangtze Valley, which induced the occurrence of floods in the Jianghan Plain. The evolution pattern of sedimentary environment demonstrated that the floods led to river overflow and overbank expansion, even causing the rivers to divert and bifurcate. The overflow channels carried and deposited silt sediments in the floodplain, which shaped the specific alluvial-lacustrine landscape of the Jianghan Plain. Our results indicate that the grain size of core sediments is sensitive to the occurrence of paleofloods, and that ENSO-related paleofloods significantly influenced the fluviolacustrine sedimentary evolution. These findings are highly useful for regional flood planning and environmental protection in the eastern Jianghan Plain in the context of global warming.

Advances in seismic fluid geochemistry and its application in earthquake forecasing

<p indent="0mm">Earthquakes are one of the most serious natural disasters of the world, with huge potential to cause serious injury and damage to humans and society. Earthquake forecasting, however, still remains a worldwide unsolved problem. The generation and occurrence of an earthquake—Accompanied by material migration, energy transmission and abrupt changes of underground conditions—Can result in the migration and evolution of geochemical elements and isotopes in natural fluids. Active fault zones are not only earthquake-prone areas but also deep fluid overflow channels. The geochemical characteristics of fluids in active faults act as good indicators for tectonic and seismic activities due to their high sensitivities to the changes of stress, temperature and permeability in the crust. The spatial and temporal variations of fluids in the active fault zones are closely related to the deep geological process and as well as the type, scale, and state of the active faults. On the contrary, the state change of an active fault can continue to affect the evolution and migration process of the deep fluids. The close relationship between fluid geochemistry and active faults makes fluid geochemistry not only an important role in earthquake forecasting but also an effective means to explain the changes of materials and conditions that take place during an earthquake. Before the occurrence of an earthquake, the stress and strain can lead to complex changes of chemical elements and isotopes in subsurface water, gas, soil and/or other media, that is, seismic fluid geochemistry anomalies. Therefore, in active fault zones or seismically active areas, monitoring the fluid geochemistry in these surface media and effectively identifying anomalies related to earthquakes have been identified as promising methods for earthquake forecasting. In recent years, seismic fluid geochemistry has been widely used to forecast earthquakes around the world due to its comparatively low costs and the advantages of its timeliness, simplicity, and convenience. Furthermore, with the accumulation of observation data, improved data processing methods and summaries of earthquake cases, more and more fluid geochemistry anomalies are being detected before the occurrence of earthquakes, particularly that of big earthquakes. As a result of the early detection of geochemistry anomalies, some earthquakes have even been successfully predicted. In addition, new analytical techniques play a more significant role in studies of the mechanism of earthquake precursors and seismic physical processes. However, most earthquake predictions are currently based on phenomenon correspondence and/or empirical statistics, and the lack of research on the genetic mechanism of seismic fluid geochemistry anomalies leads to difficulties in the further application of this method. As such, there remains significant room for improvement for the construction of a prediction model based on seismic fluid geochemistry. In this paper, the recent research progress of seismic fluid geochemistry in the field of earthquake forecasting is summarised and combined with our research results and insights to provide guidance for future works in earthquake forecasting methods.

Study of new designs of spillway channels with artificial roughness

The effective functioning of agriculture and, as a consequence, the solution of the food problem is impossible without the use of scientifically based measures for water supply for food production. The paper presents the ways of regulating the transporting capacity of the grade-control structures and their new designs. For comparison, the works of leading experts in this field of were considered. The basis of the methodological and theoretical studies were the studies by Kazakhstani and CIS scientists on the problems of improving and researching new designs of overflow channels with artificial roughness. To solve the set tasks, general scientific methods were used to study improved designs of spillway channels. The results of experimental studies of new designs of spillway channels with artificial roughness are given; theory, methods, research data, and new designs of interfacing structures obtained on the basis of the findings of experimental studies in the Training Center for the Safety of Hydraulic Structures at the Department of Water Resources of the Taraz State University named after M.Kh. Dulaty. Taking into account the experimental studies of the structure under consideration, recommendations are proposed for conducting experimental studies of the structures of spillway channels with artificial roughness. The main conclusions and practical recommendations can be used as a methodological basis for further study of spillway channels with artificial roughness. A method has been developed for determining the position, alignment of the beginning of energy extinguishing under the condition of a fast flow regime (at the transit part of the flow) at the end section of the flume with artificial roughness. The results of calculations by the proposed method show good compatibility with the data of field studies.

Characterization of a gamma spectrometer–neutron counter background correlation in mobile radiological search systems

The mobile radiological search system (MRSS) is frequently employed to locate radiological material that may be used in nuclear terrorism. Because they are mobile, an MRSS has difficulties characterizing the radiation background during operations, particularly in their neutron counters. Operators of these systems noted a potential relationship between the MRSS’s background neutron count rate and the count rate in its scintillator’s “overflow” channel (a channel that counts all signals with energies greater than 3 MeV). Previous work indicated that this overflow channel is the result of muons. That result coupled with the fact that both muons and background neutrons are produced by cosmic ray interactions meant that the neutron-overflow channel relationship is non-trivial. To fully characterize the neutron–muon relationship, this research collected and analyzed MRSS data from throughout the continental United States. These data were collected by three different organizations (one university and two MRSS operators), each with a unique MRSS setup. The locations measured accounted for the changes in neutron and muon background as a result of three variables: elevation, latitude, and the local environment (i.e. nearby buildings). Analysis of this data indicated that the average neutron count rate varied with the average muon count rate by a power law function. This relationship sufficiently accounts for all three variables that change both count rates, and its presence indicates that an MRSS can estimate its background neutron count rate by simply measuring the muon count rate. However, the data also indicated one complication with applying this relationship more broadly: each organization’s relationship had slightly different power law equations, which appears to be dependent on individual MRSS setup.

The supply of the public lacus of Pompeii, estimated from the discharge of their overflow channels

The term lacus generally identified the public fountains in the main streets of ancient Roman towns, providing for the population daily water demand. The simplest lacus consisted of a stone basin and a spout stone, concealing one or two supply pipes. 35 street fountains of this type have been surveyed in Pompeii, to gather information on their supply and its variation in time. A new method was devised for calculating the discharge through the overflow channel of each lacus, and this value was taken as an estimate of the water supplied to each fountain. The overflow channel internal cross-section width was measured at four elevations, and the cross-section profile was reconstructed based on these data. Three water levels of 1 cm, half of the cross-section height and entire cross section height, were considered at each channel’s inlet, obtaining a corresponding channel discharge. The values obtained, ranging from 0.03 to 2.9 l/s, were checked against the trajectory of the fountain water jet, making sure that it remained within the basin length. For 28 fountains the average discharge was found to be 0.08 l/s when the water was at the lowest level, 0.43 l/s for the intermediate level and 1.18 l/s for a full inlet. The average time of residence of the water, in the lacus draw basin, was estimated between 11 min and 3 h. An estimate of the demand of all the town lacus was compared with the capacity of the aqueduct channel entering at Porta Vesuvio: the town lacus could have been supplied contemporaneously at the minimum and intermediate discharges.

The impact of D-shaped jaggedness on heat transfer enhancement technique using Al2O3 based nanoparticles

Abstract The study focused on analyzing the dimpled surface's impact over the mini channel on the flow parameters and heat transfer over a circular flow regime using a numerical approach. Alumina nano-fluid evaluated as thermo-fluid with different volume fractions was analyzed to observe the heat transfer enhancement over the dimpled channel under laminar flow conditions. Through varying stream-wise spacing (x/d) and span-wise spacing (y/d), the investigations identify the impact of dimpled surface in the heat transfer enhancement under constant and uniform heat flux. The results concluded that the dimpled flow channel could enhance heat transfer compared to a smooth channel with a 27% increase in thermal efficiency. The results showed that the dimpled channel with a 4% volume fraction of alumina nano-fluid has an increase in thermal efficiency up to 32%, followed by a 1% volume fraction having a thermal efficiency of 29%. The evaluation also made that the decrease in stream-wise spacing (x/d) and span-wise spacing (y/d) increases Nusselt number and friction factors. Further studies are going to analyze the nanoparticle clogging overflow channel using numerical simulations.

Post-eruption evolution of maar lakes and potential instability: The Lake Pavin case study, French Massif Central

Few studies have focused on the post-eruption evolution of maar craters and associated lake level changes, although breaching of the crater rim poses mass-flow and flood hazards long after the initial eruption. Lake Pavin is a maar lake in the French Massif central formed by an eruption c. 6700 years ago. The maar is perched on the edge of a glacially-shaped valley and the rim overlooks the surrounding subdued landscape. The rim is breached to the north by an overflow channel, and to the south the maar has cut into the flank of the Montchal scoria cone and lava flows. Incision of the lake outlet led to the growth of an alluvial fan that pushed the Couze Pavin River towards the north side of the Gelat valley.Two lake terraces within the crater are used to determine stages in the evolution of the lake. The highstand Stage 1 terrace +18 m above the current lake level indicates that the post-eruption lake surface and volume was 15% and 38% larger than the present-day lake, respectively, prior to the 5-7th Century CE. The poorly preserved Stage 2 bench, +4.35 m on the west side of the natural dam, indicates that incision paused between Stage 1 and achievement of present lake level (Stage 3) before the 18th Century. Four units of streamflow deposits (c. 0.087 km2 in area and 0.14–0.18 km3 in volume) that formed the fan at the mouth of the outlet in the Gelat valley have been 14C dated to between the 9th and 16th Century. From the fan sedimentology, we infer that the lake level dropped slowly between highstand Stages 1 and 2, when the outlet cut down through the rim saddle. The lake level drop accelerated between Stage 2 and Stage 3 before the 14th Century, inducing small debris flows. The latter may have resulted from heavy rainstorms, but there is no evidence for catastrophic events. Stepwise downcutting of the north rim saddle was also governed by contrasted properties of the deposits forming the dam. The current lake level has been stable since at least the early 18th Century, but the long-term stability of the dam is at risk.

Analytical solution of hyporheic exchange in natural rivers with non-point source pollution loads

Issues of pollution pervade the eco-environment, including water sources, resulting from constant pollutant release into river channels from varying sources. The presence of hyporheic zones in rivers play a role in the fate of pollutants in water systems. This paper studies pollutant transport in a natural river with hyporheic zone exchange and non-point source inflows. A non-point source, hyporheic exchange, Hybrid Cells in Series model is proposed and derived analytically. The proposed model is simulated under varying time delays between the hyporheic zone and the overflow channel. The Breakthrough curves produced from the simulations are in good agreement with field tracer test results, as presented in most studies. The model adequately captures the elongated arrival and trailing tails of field data breakthrough profiles. The proposed model's overall performance shows that the model adequately predicts pollutants' transport and fate along a natural river.

Hot Subdwarf Stars Identified in Gaia DR2 with Spectra of LAMOST DR6 and DR7. II.Kinematics

Abstract Combining LAMOST radial velocities with Gaia parallaxes and proper motions, we present 3D Galactic space motions and the orbits of 182 single-lined hot subdwarf stars. These stars were identified by Lei et al. in Gaia DR2 with LAMOST DR6 and DR7 spectra. He-rich hot subdwarf stars with show the largest standard deviations of the Galactic velocity components and orbital parameters, while those with exhibit the second largest standard deviations. The two groups of He-deficient stars with show similar standard deviations, which are systematically lower compared to He-rich stars. We also present a kinematic population classification of the four hot subdwarf helium groups based on their positions in the U − V velocity diagram, the eccentricity diagram, and their Galactic orbits. The overall tendency of the fractional distributions of the four hot subdwarf helium groups in the halo, thin disk, and thick disk is largely consistent with the findings reported by Luo et al. based on LAMOST DR5, which appears to support predictions of binary population synthesis. He-deficient stars with likely originate from a stable Roche lobe overflow channel, He-deficient stars with from the common envelope ejection channel, and He-rich stars with from the merger channel of double He white dwarf stars. The fraction of He-rich hot subdwarf stars with in the thin disk and the halo is far higher than that in the thick disk, which implies that these stars have different formation channels in the thin disk and in the halo.

The Pre-He White Dwarfs in Eclipsing Binaries. I. WASP 0131+28

Abstract We report the first BV light curves and high-resolution spectra of the post-mass transfer binary star WASP 0131+28 to study the absolute properties of extremely low-mass white dwarfs. From the observed spectra, the double-lined radial velocities were derived, and the effective temperature and rotational velocity of the brighter, more massive primary were found to be K and = 55 ± 10 km s−1, respectively. The combined analysis of the Transiting Exoplanet Survey Satellite (TESS) archive data and ours yielded the accurate fundamental parameters of the program target. The masses were derived to about 1.0% accuracy and the radii to 0.6%, or better. The secondary component's parameters of , , = 11,186 ± 235 K, and are in excellent agreement with the evolutionary sequence for a helium-core white dwarf of mass 0.203 , and indicates that this star is halfway through the constant luminosity phase. The results presented in this article demonstrate that WASP 0131+28 is an EL CVn eclipsing binary in a thin disk, which is formed from the stable Roche-lobe overflow channel and composed of a main-sequence dwarf with a spectral type A0 and a pre-He white dwarf.