Maximum Residence Time Research Articles

Prediction of maximum spreading time of water droplet during impact onto hot surface beyond the Leidenfrost temperature

When a water droplet impacts on a heated surface in the film boiling regime, it will spread, recede, and finally bounce off from the heated surface. These unique liquid-solid interactions only occur at high surface temperatures. Our main objective in this research is to measure the maximum spreading and residence time of the droplet and the findings were compared to theory. We focused our study in the film boiling regime. Brass material was selected as the test surface and was polished until it became a mirror polished surface. The temperature range for this experimental work was between 100 °C up to 420 °C. Degassed and distilled water was used as the test liquid. The high speed video camera recorded the images at the rate of 10,000 frames per second (fps). As a result, it was found that the experimental value of maximum spreading and residence time agreed closely with the theoretical calculation. A new empirical formula that can be used to predict the maximum spreading time in the film boiling regime is also proposed.

Incorporating Fish Tolerance to Supersaturated Total Dissolved Gas for Generating Flood Pulse Discharge Patterns Based on a Simulation‐Optimization Approach

AbstractSupersaturated total dissolved gas (STDG) caused by the flood discharge can result in bubble disease and even fish death, posing potential risks to aquatic ecosystems. In order to reduce the impacts of STDG on such ecosystem, a dynamic multi‐objective STDG management model (DMO‐STDGM) with the flood pulse discharge pattern is developed based on the prototype observation and laboratory test analysis, which consists of STDG prediction, fish safety assessment, multi‐objective optimization and 2‐D STDG transport diffusion simulation modules. The proposed model can support generation of flood pulse discharge patterns to reduce the level of STDG and minimize the maximum residence time of STDG water. The developed model is applied to optimize the discharge pattern of Xiluodu project to reduce the effects of STDG on fish. Simulation results of the worst scenario with the flood pulse discharge pattern show that the maximum residence time of STDG for T120%, T125%, T130%, and T140% are 12, 9, 4, 3 and 1 h, which are less than the corresponding LT50s (Mean Lethal Time). It means that the physiological function of fish can recover from the affect of STDG, thus fish can survive in the worst scenario. The established model can also be employed for increasing power generation. Simulation results indicate that the flood pulse discharge pattern with equal weight of ecology and power generation can ensure full load operation of hydropower station with 12,600 MW. The established model is widely applicable and can provide an important theoretical and technical support for water quality and ecosystem management under multiple complexities.

Mathematical approaches to modelling the mass transfer process in solid oxide fuel cell anode

In the recent literature, the influence of lean fuel, type of fuel, velocity profile and the flow direction on the performance operation of solid oxide cells (SOCs) is commonly investigated. SOCs generate electricity when they operate in fuel cell mode (SOFC – Solid Oxide Fuel Cell) or produce hydrogen in electrolysis mode (SOEC – Solid Oxide Electrolyzer Cell). They consist of several layers, including two porous electrodes separated by a gas-tight electrolyte. Typical anode porosity (fuel electrode in SOFC mode) varies from 20% to 50% (after sintering). The porosity value may limit the mass transport and the overall performance of SOC. This work investigates computationally and experimentally, the existing challenge such as diffusion mechanism in porous medium using the example of SOC electrode. A set of mass transport models (Fick's laws, modified Fick's law, Maxwell-Stefan Model, Dusty Gas Model) are described and discussed, highlighting their similarities, differences, advantages, and disadvantages as well as restrictions in usage. Finally, a detailed computational fluid dynamics (CFD) model of the diffusive transport in porous electrode was elaborated and validated. An experimental campaign was conducted using anode supported SOC, fabricated at the Institute of Power Engineering in Poland. Simulations were performed of the mass transport of pure hydrogen and pure water vapor or carbon dioxide (substitute of real product of electrochemical reaction in SOC for validation purposes) through porous anode. Tests were conducted in the wide flow range 10 [ml/min] up to 200 [ml/min] for both gases. The results demonstrate that hydrogen mole fractions reached similar values (0.5–0.6) at both outlets only for the maximum residence time or high porosity of anode. This implies that residence time and gas diffusion can be controlled by a combination of operating and microstructural parameters and can be estimated by numerical simulation using computational fluid dynamics. The main motivation and outcome of this work were to reduce the cost and time required for the optimization of the mass transport process through SOC's porous electrode.

Are fire temperatures and residence times good predictors of survival and regrowth for resprouters in Florida, USA, scrub?

BackgroundFire is a dominant ecological disturbance in many ecosystems. Post-fire resprouting is a widespread response to fire, but resprouting vigor varies with many components of the fire regime, including fire intensity. We measured responses in 46 species of resprouting plants of Florida, USA, scrub and related habitats, marking and measuring individual plants before fires. We then measured fire temperatures and residence times (time above 60 °C) during 13 fires, at the base of each plant. We measured post-fire plant sizes for up to six years. We hypothesized that high temperatures and long residence times would reduce survival and growth, and that these vital rates would vary by burn season, habitat type, and species group.ResultsFires had variable intensities with maximum temperatures ranging from 47 to 890 °C (mean temperature = 549 °C) and residence times ranging from 0 to 83 minutes (mean time = 10 minutes). Consumed plants experienced higher fire intensity than scorched plants, and residence times were higher during the wet season (July through October), than the dry season (November through April), and fire season (May to June) and with drier conditions. Across all species affected by fire, 86% of plants survived and resprouted post fire. First year survival was unrelated to fire variables, with high survival across all maximum temperatures and residence times. Burn season, habitat, and species group did not significantly affect survival. On average across all species, post-fire growth recovered to pre-fire heights within four years. Growth was not significantly affected by species group or burn season.ConclusionResprouting perennial plants that dominate Florida scrub and surrounding habitats appear resilient to a wide range of fire intensities, as measured by maximum temperatures and residence times. Post-fire growth was rapid, with recovery of pre-fire heights in four years. Species groups varied in post-fire recovery rates. In these habitats, fire is critical to maintain the habitat structure for many animals and plants, including many rare species. The slower recovery of biomass for resprouting shrubs results in the longer availability of gaps for rare herbaceous species. In addition, variability in post-fire survival and growth among species groups likely contributes to the persistence of species diversity and complexity across habitats. However, variation in fire intensity appears to have little effect on resprouting species or subsequent habitat structure. A range of fire regimes can be used in prescribed fire management without having major impacts on resprouting plants in Florida scrub and related vegetation.

Use of trihalomethanes as a surrogate for haloacetonitrile exposure introduces misclassification bias

Epidemiologists have used trihalomethanes (THMs) as a surrogate for overall disinfection byproduct (DBP) exposure based on the assumption that THM concentrations are proportional to concentrations of other DBP classes. Toxicological evidence indicates THMs are less potent toxins than unregulated classes like haloacetonitriles (HANs). If THMs are not proportional to the DBPs driving toxicity, the use of THMs to measure exposure may introduce non-trivial exposure misclassification bias in epidemiologic studies. This study developed statistical models to evaluate the covariance and proportionality of HAN and THM concentrations in a dataset featuring over 9500 measurements from 248 public water systems. THMs only explain ∼30% of the variance in HANs, whether the data is pooled in a classic linear regression or hierarchically grouped by water system in a multilevel linear regression. The 95% prediction interval on HANs for the median THM concentration exceeds the interquartile range of HANs. Mean HAN:THM ratios range from ∼2.4% to ∼80% across water systems, and varied with source water category, season, disinfectant sequence and distribution system location. The HAN:THM ratio was 265% higher in groundwater systems than in surface water systems and declined by ∼40% between finished effluent and maximum residence times in surface water systems with chlorine-chlorine disinfection. A maximum likelihood approach was used to estimate the misclassification bias that may result from using THMs to construct risk-ratios, assuming that HANs represent the “true” DBP exposure risk. The results indicate an odds ratio of ∼2 estimated with THM concentrations could correspond to a true odds ratio of 4–5. These findings demonstrate the need for epidemiologic studies to evaluate exposure by measuring DBPs that are likely to drive toxicity.

Study on the association of wall shear stress and vessel structural stress with atherosclerosis: An experimental animal study

Background and aimsArtery is subject to wall shear stress (WSS) and vessel structural stress (VSS) simultaneously. This study is designed to explore the role of VSS in development of atherosclerosis. MethodsSilastic collars were deployed on the carotid to create two constrictions on 13 rabbits for a distinct mechanical environment at the constriction. MRI was performed to visualize arteries’ configuration. Animals with high fat (n = 9; Model-group) and normal diet (n = 4; Control-group) were sacrificed after 16 weeks. 3D fluid-structure interaction analysis was performed to quantify WSS and VSS simultaneously. ResultsTwenty plaques were found in Model-group and 3 in Control-group. In Model-group, 8 plaques located proximally to the first constriction (Region-1, close to the heart) and 7 distally to the second (Region-2, close to the head) and 5 plaques were found on the contralateral side of 3 rabbits. Plaques at Region-1 tended to be bigger than those at Region-2 and the macrophage density at these locations was comparable. Minimum time-averaged WSS (TAWSS) in Region-1 was significantly higher than that in Region-2, and both maximum oscillatory shear index (OSI) and particle relative residence time (RRT) were significantly lower. Peak and mean VSS in Region-1 were significantly higher than those in Region-2. Correlation analyses indicated that low TAWSS, high OSI and RRT were only associated with plaque in Region-2, while lesions in Region-1 were only associated with high VSS. Moreover, only VSS was associated with wall thickness of plaque-free regions in both regions. ConclusionsVSS might contribute to the initialization and development of atherosclerosis solely or in combination with WSS.

The mixing sensitivity of toluene and ethylbenzene sulfonation using fuming sulfuric acid studied in a rotor-stator spinning disc reactor

The mixing sensitivity was studied for the sulfonation of two alkylbenzenes (ArH’s), toluene and ethylbenzene, by using a rotor-stator spinning disc reactor (SDR). Fuming sulfuric acid (FSA), containing 30 wt. % free sulfur trioxide, was used as a sulfonating agent, which resulted in a fast, exothermic, and viscous liquid-liquid reaction system. Experiments were conducted by varying the SDRs’ rotational speed between 50 and 9000 rpm. In addition, different molar flow ratios (ArH:FSA) were investigated, ranging from 0.8 to 3.2, while operating at a maximum residence time of 7.1 s. The selectivity towards mono-sulfonated products was found to increase significantly at a higher rotational speed. This was observed consistently for both alkylbenzenes and all molar flow ratios, confirming the mixing sensitivity of the two alkylbenzene sulfonation reactions. Furthermore, it was proposed that the mixing sensitivity arises from a competition that exists between the desired and highly reactive primary sulfonation and the much less reactive consecutive sulfonation step to disulfonic acids.

Investigation and evaluation of salinity gradient power in Arvand River estuary using pressure retarded osmosis (PRO) method

The salinity gradient power is the energy of the entropy of mixing the two solutions at different salt concentrations. The estuary of the river as a place of the mixture of seawater and freshwater has great potential of this kind of renewable energy. In this research, this potential in Arvand River estuary and its effective factors is analyzed and evaluated. By examining the calculations on the data of three hydrometric stations located on Arvand River, in Khorramshahr station, the mixture of 1.26 m3 of seawater with salinity of 40 ppt with 0.174 m3of river water with 1.17 ppt of salinity leads to the highest energy at 739.85 MW. Also, the penetration length of saline water and water residence time on the estuaries of the rivers leading to the Persian Gulf has a significant effect on the salinity gradient power. According to the calculations carried out under HWS and Arvand River mean discharge, the maximum saline water penetration length into estuary associated with Arvand River is 41 km. The maximum residence time of seawater in Arvand River estuary is 8.9 days.

Hyporheic exchange mechanism driven by flood wave

AbstractTo study the hyporheic exchange driven by a single peak flood‐induced water level fluctuation (i.e., flood wave), a method combining numerical simulation with theoretical derivation was proposed based on the Inbuk Stream, Korea, where flooding occurs frequently. The hyporheic exchanges induced by different flood waves were investigated by varying amplitude (A), duration (T), wave type parameter (r), and rising duration (tp), which were adopted from the real‐time stream stage fluctuations. Additionally, the idea of constant upstream flood volume (CUFV) condition for flood waves was put forward, and the effects of “Botan” (T/A) and peak number (N) on hyporheic exchange were studied. The results showed that the hyporheic exchange flux (q) was controlled by the water level h (sine‐type) and its change rate v (cosine‐type), and was proportional to the polynomial of them q ∝ (ω∙h + v), where ω is the angular frequency of the flood wave. Based on this mechanism, the influence principles on hyporheic exchanges of the typical flood wave parameters (A, T, r and tp) as well as T/A and N under CUFV condition were clarified. The main characteristic variables of hyporheic exchange, which were maximum aquifer storage and residence time, were positively correlated. They also had positive relations to the integral of the flood wave over time, which increased when the wave became higher, wider, rounder and less skewed. However, when CUFV condition was imposed, the residence time was positively correlated with T/A, whereas the maximum aquifer storage was negatively correlated with T/A. With the increase in N, water exchanged more frequently and some water returned to the stream early, leading to the slight decrease in maximum aquifer storage and residence time. These findings enriched the theory of hyporheic exchange driven by surface water fluctuation and be of great significance to enhance pollutant degradation in the hyporheic zone downstream of reservoirs.

Characterization and numerical evaluation of flow and blood damage in a pulsatile left ventricular assist device

Each year, thousands of people lose their lives due to left-sided heart failure. Left ventricular assist device (LVAD) is a mechanical pump utilized to aid the function of the left ventricle of the weakened heart. This study investigates flow dynamics, hemolytic and thrombocytopathic characteristics of LVAD with pulsatile flow. To this end, computational fluid dynamics simulations are utilized to predict the levels of hemolysis, thrombosis susceptibility potential and particle residence time in a quantitative manner, and furthermore, we perform dye ejection analysis to understand the pump’s capability to eject old materials. Thus, a set of time-dependent nonlinear partial differential equations are coupled with each other. Blood flow is acquired by solving continuity and momentum equations and levels of hemolysis are computed by coupling two additional scalar transport equations based on a Eulerian transport approach with the governing equations of fluid flow. Additionally, we assess particle residence time and rate of dye ejection according to a continuum-based model. It is depicted, the value of maximum velocity in the pump is much smaller than the axial ones which causes to reduction in red blood cell damage. Average hemolysis obtained its maximum value at the clearance zone, and hemolysis index at the exit of pump is one order lower compared to continuous ones. It is also observed that for all instances of the cycle the maximum residence time concentrates near the outlet domain representing the no accumulation of particles in interior of the pump and capability of the pump to eject material efficiently.

Predicting potential cambium damage and fire resistance in Pinus nigra Arn. ssp. salzmannii

Fire management can play a key role in ensuring stand maintenance in future scenarios of global change, particularly in Pinus nigra stands, which are known to be adapted to low-intensity surface fires through characteristics such as thick bark. In this study, laboratory tests were carried out to quantify cambium damage and fire resistance in P. nigra, by using a mass loss colorimeter device in a vertical configuration for the first time. In addition, low-intensity prescribed burning treatments were conducted in the field, and the field and laboratory data were compared. The following variables were used as proxy measures to assess cambium damage: time that temperature remained above 60 °C, heating rate and maximum absolute temperature in the inner bark area. The data were analysed using a Bayesian hierarchical approach (generalized linear mixed model). A threshold heat flux (25 kW m−2) for the time to ignition of bark was identified. A critical temperature of 60 °C was reached in the cambium during the combustion phase, after the flame was extinguished. The laboratory experiments showed, for the first time, the influence of flame residence time on the potential cambium damage. A bark thickness of 17 mm can be considered the threshold level for preventing critical temperatures being reached in Pinus nigra stands. The influence of bark thickness on protection against fire was confirmed, as was the importance of the coefficient of variation of bark thickness. The field results showed that flame characteristics (maximum temperature and residence time) were the most significant predictors of cambium damage. The combination of fire intensity and exposure time at low heat fluxes is more important than bark in determining cambium damage and may have important implications in the field of forest fuel management and in the ecology of pine forests.

Reconstruction of the paleo-environments of northern and southern slopes of the Alborz Mountain chain based on preserved evidence in soils

The purpose of this study was reconstruction of dominant paleo-environments on northern and southern slopes of Alborz Mountain based on the modern and old environmental evidences preserved in the soils. Totally 691 soil profiles in 14 separate segments (9 segments in northern slope and 5 segments in southern slope) with an area of 783,850 ha (251 pedons in northern slope with about 123,600 ha; 440 pedons in southern slope with about 660,350 ha) in Alborz Mountains were studied. Morphological, physical, chemical, mineralogical, micromorphological, and geochemical analyses of the studied sites carried out using standard methods and demonstrated significant differences between the soils of northern and southern slopes. Micromorphological data showed that the calcite coatings in northern slope pedons have formed before the clay coatings however, while the opposite conditionings for calcite and clay coatings in southern slope were observed. The geochemical analyses results were in agreement with the results obtained from micromorphological analyses and further confirmed the addition of aeolian materials into the studied pedons in southern slope. Biological features and the organic and inorganic residues were extremely different in the northern and southern slopes. The maximum and minimum mean residence times (MRTs) in the subsurface layers were 4467 ± 50 years in deciduous forest and 4410 ± 48 years in coniferous forest in northern slope. However, the MRTs for burnt woods from the depths of 1.6 and 2.68 m of soil in southern slope were 3665 ± 61 and 6083 ± 84 years, respectively. Soils as archives of ecosystems contain very informative data for paleo-environmental and paleogeographic reconstructions. The results of this study demonstrated that the southern slope has been heavily influenced by glacial and aeolian deposits that in some cases have led to the top-down reverse distribution of the element oxides in the soil.

Estructura poblacional de Morpho helenor peleides kollar, 1850 (lepidoptera: nymphalidae) en un paisaje de bosque seco tropical, departamento de Bolivar, Colombia.

Teniendo en cuenta la alta tasa de destrucción de los bosques en la región Caribe colombiana y la escasa información disponible sobre la ecología poblacional de las mariposas del género Morpho, se analizó la variación de estructura poblacional de Morpho helenor peleides Kollar, 1850 en un paisaje de Bosque seco tropical (BST) en los Montes de María, Caribe colombiano. Metodología. Para el estudio de la mariposa, se utilizó el método de captura-marca-recaptura (CMR) en siete estaciones, en las cuales se instalaron trampas Van Someren-Rydon cebadas con una mezcla de frutas fermentadas. Resultados. La abundancia total fue de 287 individuos, con 59 recapturas (20,5%). Se obtuvieron tamaños poblacionales entre 8 y 339 individuos. La proporción sexual macho-hembra fue 3:1. Se capturaron mayores porcentajes de mariposas nuevas (41,8%) e intermedias (38,6%). El tiempo de residencia máximo registrado fue de 38 días. Se calcularon distancias totales de vuelo entre 149 y 1,231m, aunque las hembras presentaron los mayores promedios (303.7±189.4m) de distancia recorrida; pero no se encontraron diferencias significativas entre las distancias recorridas entre sexos (U= 265,5, p>0,05). Conclusiones: La estructura poblacional de M. helenor peleides presentó una variación espacial y temporal en el paisaje de bosque seco estudiado. Adicionalmente, se determinó que la cobertura de dosel natural juega un papel importante en la dinámica temporal y la distribución de la abundancia de este grupo de mariposas en el bosque seco tropical y se resalta la importancia de este ecosistema en la conservación de esta especie.

Transient and Steady-State Analysis of Multistage Production Lines With Residence Time Limits

Residence time limits for the intermediate products are commonly seen in production systems due to quality requirements. A part in a buffer typically needs to be scrapped or reworked if its residence time exceeds the maximum allowable residence time, while a part needs to keep waiting in the buffer if its residence time is less than the minimum required residence time. Such limits could be required at multiple stages of the production line, making it difficult to analyze both the steady-state and transient production system performance. The problem under study is formulated as a multistage geometric serial production line with residence time limits. To deal with its large state space, a two-machine-one-buffer subsystem isolated from a multistage geometric serial production line is first analyzed for both steady-state and transient performance. Furthermore, a novel aggregation method, including the steady-state analysis and transient analysis, is proposed to evaluate the overall system performance. The proposed aggregation method substantially reduces the complexity of the problem and makes the analysis of the problem tractable. Compared with the simulation, the aggregation method maintains high accuracy in estimating both steady-state and transient performance measures. Such a method provides quantitative tools for effective performance evaluation and prediction on the factory floor.

Leveraging flow mechanics to determine critical process and scaling parameters in a continuous viral inactivation reactor.

A continuous viral inactivation (CVI) chamber has been designed to operate with acceptable residence time distribution (RTD) characteristics. However, altering the CVI's geometry and operation to accommodate the scale was not obvious. In this work, we elucidate the influence of Dean vortices and leverage the transition into the weak turbulent regime to establish relationships between input variables and process outputs. This study was targeted to understand and quantify the impact of viscosity, Dean number, internal diameter, and path length on the RTD. When the Dean number exceeds 70, radial mixing generated by the Dean vortices began to consistently alter the axial dispersive effects experienced by the pulse injection. Increasing to a Dean number of >100, the axial dispersive effects were dominated by the Dean vortices which allowed the calculation of the minimum and maximum residence time to be generated. This work provides a method to calculate operational solutions for a tubular incubation reactor in terms of path length, internal diameter, flow rate, and target minimum and maximum residence time specifications that assures both viral residence times while also establishing criteria to maximize product quality during continuous operation.

Importance of Body Stance in Fog Droplet Collection by the Namib Desert Beetle

The fog-basking behavior of the Onymacris unguicularis, a beetle species living in the coastal regions of the Namibian desert, has recently caught the attention of the engineering community, as suggesting a viable biomimetic approach to address the problem of harvesting water in arid regions of the globe. Previous research has focused on observation and analysis of the beetle’s elytron properties and how these affect fog-collection rates. The head stance taken by the Onymacris unguicularis when fog basking is well documented. However, how this stance affects droplet collection has not been studied up to now. The present paper addresses this problem from a computational fluid dynamics perspective, where three-dimensional numerical simulations are used to characterize the fog flow properties around a simplified geometry mimicking the beetle’s body. The simulations employ two-way coupling between the gas flow and the dispersed fog phase to account for feedback effects of fog droplets on the carrier fluid (air), and assume that droplets are captured after hitting the elytron surface. The study considers several combinations of free-stream velocity and droplet volume fraction. The analysis reveals that there is a range of head-stance angles, corresponding to an inclination of the beetle between 35 deg and 45 deg with respect to the horizon, that maximizes water collection on the beetle’s back, in qualitative agreement with observations in nature and laboratory experiments. A rationale is proposed to explain this phenomenon, finding that the specific head stance corresponds to the maximum residence time of fluid particles above the beetle’s elytron surface. This, in turn, designates the maximum likelihood for water droplets to be captured in the boundary layer developing over the beetle and subsequently hit the surface where they get captured. The results reveal the importance of the fluid flow pattern around the beetle’s body in addition to the microphysical properties of the elytron when reliable predictions of the water droplet collection efficiency are sought.

The impact of CO gradients on C. ljungdahlii in a 125 m3 bubble column: Mass transfer, circulation time and lifeline analysis

Successful scale-up of biological fermentations requires the prevention of any performance losses from lab to production scale. Modelling large-scale conditions, in particular, so-called lifeline analysis, is a proper approach to unravel potential risks and to guide the way for preventing non-wanted under-performance. This study focuses on synthesis gas fermentations in bubble columns which are particularly challenging because of poor carbon (C) -source solubility and low bacterial energy availability under such anaerobic conditions. As a model case, Clostridium ljungdahlii DSM 13528 is studied in a 125 m3 bubble column reactor investigating bacterial motion patterns, circulation time, short- and long-term responses. A pseudo-stationary gas gradient respectively fermentations ‘snap-shot’ was conducted with computational fluid dynamics in an Euler-Euler approach while the movement of the microorganism was simulated as Lagrangian massless particles. Cells were assigned uptake and product formation kinetics. Statistical lifeline analysis revealed that 97% of all cells experienced substrate limitations, whereas 84% were likely to undergo transcriptional changes after exposure in stress-inducing zone longer than 70 s. Bacteria movements predominately occurred between low and moderate product biomass yield regions with longer residence times in the latter. The circulation time derived from mixing time analysis is similar to the mean circulation time of a single bacterium. The latter was deduced from regime transition studies. Maximum residence times over 100 s as minimum regime crossing times of 10 s could also be identified. These findings show the high potential of Lagrange trajectories analysis in bubble column gas gradients which can be used for performance prediction and therefore risk minimization in scale-up.

Designing the incineration process for improving the cementitious performance of sewage sludge ash in Portland and blended cement systems

Currently, there is little doubt that the global temperature increase is a consequence of the concentrations of manmade greenhouse gases. Sustainable alternatives such as the use of supplementary cementitious materials and the reduction of sanitary landfills through the incineration of sewage sludge hold promise for the reduction of these gases.An experimental design is proposed to make the incineration of sewage sludge (SS) more efficient, thereby improving the sewage slush ash (SSA) produced as a supplementary cementitious material. Different maximum temperatures and residence times were studied in the partial replacement of Portland and blended cements; the resulting SSAs contributed to the mechanical behavior of concrete through improved hydraulic and pozzolanic activity in addition to intense interactions with cement.The particle size distributions of the SSAs were similar to those of the cements, but the specific surface areas of the SSAs were up to 18 times higher than those of the cements. This vast difference is explained by the presence of micropores after the incineration process. Consequently, the specific surface area of the SSA particles was the most important property explaining the pozzolanic activity and interaction effects with cement. Lower incineration temperatures and higher incineration times increased the specific surface area, therefore increasing the cementitious performance of SSA. The SSA cementitious performance was lower in blended cement than in Portland cement; however, the replacement of blended cement by SSA increased the compressive strength at early and late ages.

Computational Fluid Dynamics Analysis of Carotid–Ophthalmic Aneurysms with Concomitant Ophthalmic Artery Infundibulum in a Patient-Specific Model

Although previous studies have reported cases of coexistence of carotid-ophthalmic aneurysm and ophthalmic artery (OA) infundibulum, the hemodynamic characteristics of this complicated structure and its damaging effects on vision remain to be elucidated. The aim of the present study was to analyze this artery structure using computational fluid dynamics (CFD) techniques. We have presented the case of a patient with a diagnosis of carotid-ophthalmic aneurysm, who had been experiencing blurred vision. A transient analysis was performed to investigate the blood flowing in the parent artery. Hemodynamic parameters such as streamline, wall shear stress (WSS), oscillatory shear index (OSI), and relative residence time were obtained. When the inlet velocity of the parent artery was at the second peak, the flow rate and intensity of the vortex reached their maximum. In the aneurysm neck, a region of high time-averaged WSS (TAWSS) and a region of low TAWSS with a high OSI coexisted. In addition, a relaxation area was found. In the aneurysm dome, the minimum TAWSS was 2.5 Pa, the maximum OSI was 0.48, and the 2 regions did not overlap. In the OA infundibulum, the maximum OSI and relative residence time were 0.47 and 39.2, respectively; the minimum TAWSS was 0.59 Pa. We detected aneurysm regions that were susceptible to further expansion and assessed the rupture risk of each region. The relaxation area could promote aneurysm progression. In addition, the location of the vortex shear force center varied with time. Finally, double vortex streamlines influenced the blood supply through the OA, impairing the vision. Infundibulum might promote thrombus formation and, hence, retard OA blood flow.

Characteristics of Dew Formation in the Semi-Arid Loess Plateau of Central Shaanxi Province, China

Compared to rain, dew is an important supplementary source of water for the survival of certain plants and animals in drylands. However, the hydrology of dew has not yet been fully investigated due to difficulties in measuring the amount and duration of it. In this study, a 3-year in-situ monitoring experiment was conducted from 2014 to 2016 in the semi-arid Sanyuan County, Shaanxi Province of China, using a leaf wetness sensor (LWS) and four associated meteorological instruments. Results showed that the average annual total dewfall was 32.8 mm with a daily maximum of 0.88 mm. The majority of daily dew occurred in the night from 18:00 to 8:00 with the maximum condensation rate occurring at around 4:00. The maximum dew residence time was about 18 h/day on the dew days in all seasons. However, the actual dew production period was about 14 h in spring (March–May), autumn (September–November), and winter (December–February), and only 11 h in summer (June–August). The maximum intensity and amount of dew always occurred in autumn (with an average amount of 12.2 mm or 37% of the annual total), followed closely by spring (11.4 mm, 35%), with much less in summer (6.6 mm, 20%) and winter (2.6 mm, 8%). The annual dew distribution by months showed a double crest variation, with two peaks in April–May and October–November, and two valleys in January–February and July. Comparatively, annual dewfall is only about 1/18th of the rainfall in this region, but the number of dew days (224 days, or 61% of year) is 2.6 times that of rain days (87 days, 24%), making dew a critical supplementary source of water for mitigating dry periods and supporting native plants and animals. Rain and dew are highly complementary as dew occurs in cloudless nights while the rain occurs in different and on much fewer occasions in the region. The dew amount was highly and positively correlated to the relative humidity of the air above the threshold of 81% (r = 0.78, p < 0.01), negatively correlated to the difference between air temperature Ta and dewpoint Td, when (Ta − Td) is less than 4 °C (r = −0.66, p < 0.01), and weakly correlated to wind speed (0.2 to 2 m·s−1), wind direction, surface soil moisture, and temperature. In the Sanyuan region, two general wind directions, 30°–90°and 210°–270°, were more favorable for the formation of dew.