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1
Gao, Yan-An, Qing-Shan Yang i Yun Dong. "A Three-Dimensional Pedestrian–Structure Interaction Model for General Applications". International Journal of Structural Stability and Dynamics 18, nr 09 (wrzesień 2018): 1850107. http://dx.doi.org/10.1142/s0219455418501079.
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A three-dimensional (3D) pedestrian–structure interaction (PSI) system based on the biomechanical bipedal model is presented for general applications. The pedestrian is modeled by a bipedal mobile system with one lump mass and two compliant legs, which comprise damping and spring elements. The continuous gaits of the pedestrian are maintained by a self-driven walking kinetic energy, which is a new driven mechanism for the mobile unit. This self-driven mechanism enables the pedestrian to operate at a varying total energy level, as an important component for further modeling of the crowd-structure dynamic interaction. Numerical studies show that the pedestrian walking on the structure leads to a reduction in the natural frequency, but an increase in the damping ratio of the structure. This model can also reproduce the reaction forces between the feet and structure, similar to those measured in the field. In addition, the proposed model can well describe the 3D pedestrian–structure dynamic interaction. It is recommended for use in further study of more complicated scenarios such as the dynamic interaction between a large scale kinetic crowd and slender footbridge.
2
Toso, Marcelo André, i Herbert Martins Gomes. "Biodynamic Synchronized Coupled Model for Crowd-Footbridge Interaction". European Journal of Engineering and Formal Sciences 4, nr 1 (21.02.2020): 64. http://dx.doi.org/10.26417/ejef.v4i1.p64-74.
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Nowadays there are growing interests in vibration serviceability assessments of composite footbridges. The new design trends of composite footbridges make them slender civil structures that may be affected by the load action of walking pedestrians resulting in large deflections or even uncomfortable vibrations. Furthermore, the presence of people on the footbridges causes the addition of mass to the structural system and due to the human body’s ability to absorb vibrational energy, an increase in structural damping. In this paper, the interaction between pedestrian and structure is modelled using data from pedestrian characteristics and vibration data from a measured footbridge as a comparison basis. A previously developed numerical model was used, this model called Biodynamic Synchronized Coupled Model (BSCM) consists of a fully synchronized force model in the longitudinal and lateral direction of pedestrian’s movement and a biodynamic model with mass, damping and stiffness parameters. The model is coupled with the structure using the Finite Element Method at the feet’s contact points. Pedestrians are treated as individuals with intrinsic kinetic and kinematic parameters following a measured correlation matrix obtained by the use of an especially designed force platform. Finally, the adequacy of the proposed model to represent the pedestrians as BSCM for the walking effects on the structure is investigated by experimentally measured accelerations on a footbridge (freely walking). The numerical results show good agreement with the experimental results.
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Touber, Emile, i Nicolas Alferez. "Shock-induced energy conversion of entropy in non-ideal fluids". Journal of Fluid Mechanics 864 (11.02.2019): 807–47. http://dx.doi.org/10.1017/jfm.2019.25.
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From shaping cosmic structures in space to producing intense sounds in aircraft engines, shock waves in fluids ineluctably convert entropy fluctuations into swirling motions and sound waves. Studies of the corresponding conversion from internal energy to kinetic energy have so far been restricted to ideal (or idealised) fluids. Yet, many substances do not obey the ideal-gas law (including those in the above two examples). The present work demonstrates that non-ideal thermodynamic properties provide a remarkable degree of control over the conversion to solenoidal and dilatational kinetic energies. Of particular interest is the ability to suppress much of the emitted acoustic field whilst promoting mixing downstream of the shock. This is made possible by exploiting the convexity (or lack thereof) of the shock adiabats. Whilst illustrated here using dense vapours near the thermodynamic critical point, this ability to design and control specific shock-induced energy transfers extends beyond near-critical-point phenomena; e.g. shocked mixtures (high-speed dusty flows on Mars, nanoparticle formation in supersonic expanders for drug manufacturing), reacting fronts (supersonic combustion, rocket propulsion), ionising shocks (reentry systems, inertial confinement fusion) or fronts in active fluids (bacterial and crowd flows). This theoretical work, which demonstrates the predictive capabilities of linear theory, lays the foundation for future experimental investigations ultimately aimed at delivering novel shock-based flow-control strategies exploiting the thermodynamic properties of the fluid.
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Prasanth, Bathala, Rinika Paul, Deepa Kaliyaperumal, Ramani Kannan, Yellapragada Venkata Pavan Kumar, Maddikera Kalyan Chakravarthi i Nithya Venkatesan. "Maximizing Regenerative Braking Energy Harnessing in Electric Vehicles Using Machine Learning Techniques". Electronics 12, nr 5 (24.02.2023): 1119. http://dx.doi.org/10.3390/electronics12051119.
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Innovations in electric vehicle technology have led to a need for maximum energy storage in the energy source to provide some extra kilometers. The size of electric vehicles limits the size of the batteries, thus limiting the amount of energy that can be stored. Range anxiety amongst the crowd prevents the entire population from shifting to a completely electric mode of transport. The extra energy harnessed from the kinetic energy produced due to braking during deceleration is sent back to the batteries to charge them, a process known as regenerative braking, providing a longer range to the vehicle. The work proposes efficient machine learning-based methods used to harness maximum braking energy from an electric vehicle to provide longer mileage. The methods are compared to the energy harnessed using fuzzy logic and artificial neural network techniques. These techniques take into consideration the state of charge (SOC) estimation of the battery, or the supercapacitor and the brake demand, to calculate the energy harnessed from the braking power. With the proposed machine learning techniques, there has been a 59% increase in energy extraction compared to fuzzy logic and artificial neural network methods used for regenerative energy extraction.
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Palomba, Ilaria, Alberto Doria, Edoardo Marconi, Matteo Bottin i Giulio Rosati. "Vibration Energy Harvesting from Raindrops Impacts: Experimental Tests and Interpretative Models". Applied Sciences 12, nr 7 (23.03.2022): 3249. http://dx.doi.org/10.3390/app12073249.
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The kinetic energy of raindrops is a large and renewable source of energy that nowadays can be exploited by means of piezoelectric harvesters. This study focuses on a new cantilever harvester that uses the impact of a drop on a liquid surface created on the harvester in order to improve the conversion from kinetic energy to electric energy. Experimental tests, carried out both outdoors and indoors, were performed to assess the validity of the proposed design. The voltage obtained with the impact on the liquid surface was about four times larger than the one obtained with the impact on a dry surface. The phenomena that lead to the increased performance of the harvester were analyzed both experimentally, by means of a high-speed camera, and analytically, by means of a mathematical model. The camera footage showed a clear relationship between the waveform of the generated voltage and the various phases of the impact (crown formation, crown collapse, and sloshing). The mathematical model developed herein, which was based on the oscillation of the liquid mass caused by the impact and on the linear momentum equation, is simple and can be used to estimate the measured voltage within a good approximation.
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Gabor, Andreea, Corneliu Mircea Davidescu, Adina Negrea, Mihaela Ciopec i Lavinia Lupa. "Behaviour of Silica and Florisil as Solid Supports in the Removal Process of As(V) from Aqueous Solutions". Journal of Analytical Methods in Chemistry 2015 (2015): 1–10. http://dx.doi.org/10.1155/2015/562780.
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In this study two solid supports, silica and florisil, were impregnated with crown ether (dibenzo-18-crown-6) and Fe(III) ions and their efficiency was compared in the adsorption process of As(V) from aqueous solutions. The solid supports were impregnated with crown ether due to their ability to build complexes with positives ions. Fe(III) was used because of As(V) affinity for it. The impregnated solid supports were characterized by energy dispersive X-ray analysis, scanning electron microscopy, Fourier transform infrared spectroscopy, and the specific surface area. The influence of the solid : liquid ratio on the adsorption process, kinetic studies for the pseudo-first-order and pseudo-second-order, and activation energy were studied. Thermodynamic studies as well as equilibrium studies were carried out. The obtained results showed that, from the two considered materials, impregnated silica presents a higher efficiency with a good selectivity, able to remove As(V) from aqueous solutions containing trace concentrations.
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Zhou, Jun Wei, i Da Zheng Wang. "Parametric Study of Crowned Blade in Horizontal Axial Turbine". Advanced Materials Research 732-733 (sierpień 2013): 443–50. http://dx.doi.org/10.4028/www.scientific.net/amr.732-733.443.
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The horizontal axial turbine could extract kinetic energy from both wind and tidal stream. In this paper, a type of horizontal axial turbine was designed with a crown stalled on the blade tip and the turbine was analyzed in a tidal stream. Several turbines with different geometries of the crowns were compared, whose power coefficients were numerically simulated by the CFD method. Effects of the crown design parameters, such as crown setting directions and different widths on turbine efficiency were discussed. Furthermore, when the turbine worked at different tip speed ratio, the results were discussed, either. By analysis of the results, it is could be concluded that a circular crown was sufficient to eliminate blade tip loss caused by tip leakage flow. The upstream semicircle crown modified the corresponding side foil pressure distribution to the design value, and so did the downstream semicircle crown. In the ellipse crowns testing, turbine efficiency was approximately in line with the value of crowns width. When the turbine with the circular crown worked at a little higher tip speed ratio than the design value, the crown was effective as before.
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Nanko, Kazuki. "Relationship between Throughfall Kinetic Energy and Tree Height, Crown Bottom Height, and Crown Length for Japanese Cypress Plantation". Journal of the Japanese Forest Society 95, nr 4 (2013): 234–39. http://dx.doi.org/10.4005/jjfs.95.234.
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Cao, Yan, Jingxin Wang i Chunling Zhu. "Numerical Simulation of Microscale Oblique Droplet Impact on Liquid Film". Aerospace 10, nr 2 (26.01.2023): 119. http://dx.doi.org/10.3390/aerospace10020119.
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The oblique impact of microscale water droplets on liquid film is numerically investigated. Two-phase flow problems are simulated using three-dimensional incompressible Navier-Stokes equations, and the level-set method is employed for capturing the gas-liquid interface. The numerical model is verified using experimental results from a normal and oblique impact via the qualitative comparison of crown profile features and quantitative contrast of the crown height and radius varying with time. The article discusses the influence of tangential impact velocity, water film thickness, Reynolds number, and Weber number on the shape characteristics, tangential momentum, and kinetic energy of the annular crown. The results show that the decreasing momentum in the tangential direction can be divided into three clear stages: rapid decrease, slight increase, and continuous decrease. In addition, film thickness and Weber number have significant effects on the momentum decay rate.
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Nishimura, Norio, Tohru Tanaka i Takushi Motoyama. "Additivity of the partial molar volumes of organic compounds". Canadian Journal of Chemistry 65, nr 9 (1.09.1987): 2248–53. http://dx.doi.org/10.1139/v87-375.
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A critical test of additivity for partial molar volume has been made at 25 °C in CCl4 with polyethylene glycol dimethyl ethers, crown ethers, cycloalkanes, n-alkanes, and others. Plots of partial molar volume at infinite dilution [Formula: see text] against the properly chosen number of repeating unit (n) are linear except for small cyclic molecules, and the slopes of homologous straight chain and ring compounds are the same. The values of [Formula: see text] extrapolated to n = 0 for cycloalkanes and crown ethers support the validity of the contribution due to the translational kinetic energy that has been predicted recently on a theoretical basis. The importance of packing efficiencies around the solute molecules has been examined by means of simple models.
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Li, Shi Bin, Ya Ling Qiu, Ping Yu, Hui Luo i Wei Zhang. "Study on Energy-Saving Crown Block Anti-Collision of Oil Drilling Rig". Advanced Materials Research 361-363 (październik 2011): 941–45. http://dx.doi.org/10.4028/www.scientific.net/amr.361-363.941.
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In view of present security problems existing from traveling block’s speed by manual control, a kind of energy-saving automatic anti-collision scheme is put forward. An analysis of the transmission system structure of ZJ70L-ZPD oil drilling rig can obtain the influence that the alteration of diesel engine speed results in the alteration of speed of traveling block rising or falling. Fuzzy control system is established by fuzzy control strategy that concludes input quantity rotation speed deviation and deviation ratio and output quantity throttle aperture, which creates fuzzy control data sheet by offline calculating. Decelerate gradient on the set position of decay area was calculated by detecting the speed of the braking point, through the way that queries the fuzzy control table to real-time adjust output quantity of throttle size so as to achieve the purpose of anti-collision. This kind of anti-collision scheme reduces energy consumption by figuring out the real-time speed deviation to adjust fuel charge, avoids the braking system power dissipation off the kinetic energy by means of frictional heat when traveling block rising, provides new ideas and methods to solve problem of crown block anti-collision.
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Ciopec, Mihaela, Oana Grad, Adina Negrea, Narcis Duţeanu, Petru Negrea, Raluca Vodă i Cătălin Ianăşi. "Highly Efficient Recovery of Ruthenium from Aqueous Solutions by Adsorption Using Dibenzo-30-Crown-10 Doped Chitosan". Polymers 14, nr 8 (11.04.2022): 1551. http://dx.doi.org/10.3390/polym14081551.
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Ruthenium, as an industrial by-product or from natural sources, represents an important economical resource due to its specific applications. A complex problem is represented by ruthenium separation during reprocessing operations, therefore, different materials and methods have been proposed. The present study aims to develop a new material with good adsorbent properties able to be used for ruthenium recovery by adsorption from aqueous solutions. Absorbent material was obtained using chitosan (Ch) surface modification with dibenzo-30-crown-10 ether (DB30C10). Chitosan represents a well-known biopolymer with applicability in different adsorptive processes due to the presence of hydroxyl-, carboxyl-, and nitrogen-containing groups in the structure. Additionally, crown ethers are macromolecules with a good complexation capacity for metallic ions. It is expected that the adsorptive efficiency of newly prepared material will be superior to that of the individual components. New synthesized material was characterized using scanning electron microscopy coupled with energy dispersive X-ray (SEM–EDX), Fourier transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller surface area analysis (BET), and determination of point of zero charge (pZc). Results obtained from the performed kinetic, thermodynamic, and equilibrium studies confirmed the good adsorptive capacity of the prepared material, Ch-DB30C10, obtaining a maximum adsorption capacity of 52 mg Ru(III) per gram. This adsorption capacity was obtained using a solution with an initial concentration of 275 mg L−1, at pH 2, and 298 K. Ru(III) adsorption kinetics were studied by modeling the obtained experimental data with pseudo-first order and pseudo-second order models. Desorption studies established that the optimum eluent was represented by the 5M HNO3 solution. Based on the performed studies, a mechanism for recovery of ruthenium by adsorption was proposed.
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Fyles, Thomas M., i Steven P. Hansen. "Equilibrium and kinetic studies of a chemical model of active transport: Membrane transport of potassium salts by cryptand carriers driven by potassium ion complexation". Canadian Journal of Chemistry 66, nr 6 (1.06.1988): 1445–53. http://dx.doi.org/10.1139/v88-233.
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A theoretical framework of energy transduction in membranes was used as a point of departure for the design of a simple chemical model of primary active transport (reaction pumping). In the model, cryptand carriers transport potassium salts across a bulk liquid membrane, driven by the complexation of potassium by a dicarboxylate crown ether in one aqueous phase. Both the equilibrium position and kinetic behavior of the model system could be predicted from the theoretical framework. Experimental verification of the predictions confirms the fitness of the theoretical framework and provides a design tool for the formulation of new membrane transport systems.
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Ciopec, Mihaela, Oana Grad, Adina Negrea, Narcis Duteanu, Petru Negrea, Cristina Paul, Catalin Ianăși, Giannin Mosoarca i Cosmin Vancea. "A New Perspective on Adsorbent Materials Based Impregnated MgSiO3 with Crown Ethers for Palladium Recovery". International Journal of Molecular Sciences 22, nr 19 (3.10.2021): 10718. http://dx.doi.org/10.3390/ijms221910718.
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The study of new useful, efficient and selective structures for the palladium ions’ recovery has led to the development of a new series of macromolecules. Thus, this study presents a comparative behavior of two crown benzene ethers that modify the magnesium silicate surface used as adsorbent for palladium. These crown ethers are dibenzo18-crown-6 (DB18C6) and dibenzo 30-crown-10 (DB30C10). The obtained materials were characterized by scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX) and Fourier-transform infrared spectroscopy (FT-IR). The specific surface area (BET) and point of zero charge (PZC) of the two materials were determined. The palladium ions’ recovery from synthetic aqueous solutions studies aimed to establish the adsorption mechanism. For this desideratum, the kinetic, equilibrium and thermodynamic studies show that MgSiO3-DB30C10 have a higher adsorption capacity (35.68 mg g−1) compared to MgSiO3-DB18C6 (21.65 mg g−1). Thermodynamic studies highlight that the adsorption of Pd(II) on the two studied materials are spontaneous and endothermic processes. The positive values of the entropy (ΔS0) suggest that the studied adsorption processes show a higher disorder at the liquid/solid interface. Desorption studies were also performed, and it was found that the degree of desorption was 98.3%.
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Negrea, Adina, Adriana Popa, Mihaela Ciopec, Lavinia Lupa, Petru Negrea, Corneliu M. Davidescu, Marinela Motoc i Vasile Mînzatu. "Phosphonium grafted styrene–divinylbenzene resins impregnated with iron(III) and crown ethers for arsenic removal". Pure and Applied Chemistry 86, nr 11 (1.11.2014): 1729–40. http://dx.doi.org/10.1515/pac-2014-0806.
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Abstract In the present work a polymer with phosphonium pendant groups impregnated with crown ether (dibenzo-18-crown-6) and loaded with iron ions was investigated for arsenic removal through adsorption from aqueous solutions. The impregnated polymer was loaded with iron ions due to the high affinity of arsenic to it. The characterization of the surface modification of the obtained new adsorbent material was performed on the basis of energy dispersive X-ray analysis; scanning electron microscopy and Fourier transform infrared spectroscopy. The arsenic adsorption was investigated, including effect of pH, arsenic initial concentration, the shaking time and temperature. The effect of the pH was examined over the range 2–11. The adsorption of As(V) increases with pH increasing reaching a maximum at pH higher than 8. Equilibrium, kinetic and thermodynamic studies were carried out to study the adsorption performance of the obtained material in the removal process of arsenic from aqueous solutions. For the studied materials the equilibrium data closely fitted Langmuir model and was achieved a maximum adsorption capacity of 32.6 μg As(V)/g of material. The pseudo-second order kinetic model is suitable for describing the adsorption system. The obtained results show that the studied adsorbent can be used with efficiency in the arsenic removal from underground water even from low influent arsenic concentration solutions.
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Grad, Oana Alexandra, Mihaela Ciopec, Adina Negrea, Narcis Duteanu, Petru Negrea i Raluca Vodă. "Evaluation of Performance of Functionalized Amberlite XAD7 with Dibenzo-18-Crown Ether-6 for Palladium Recovery". Materials 14, nr 4 (20.02.2021): 1003. http://dx.doi.org/10.3390/ma14041003.
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Due to the increased demand for palladium, as well due to its reduced availability in nature, its recovery from diluted waste solutions becomes a necessity, and perhaps an emergency. As a result of economic and technological development, new materials with improved adsorbent properties that are more efficient for metallic ions’ recovery were synthesized and introduced to market. The goal of this study was to obtain a new adsorbent material by functionalizing through impregnation a commercial polymeric support that was both inexpensive and environmentally friendly (Amberlite XAD7) with crown ether (di-benzo-18-crown-6—DB18C6). Crown ethers are known for their ability to form complexes within metallic ions, by including them inside of the ring, regardless of its atomic size. Adsorbent material was prepared by impregnation using the solvent-impregnated resin method (SIR). To highlight the presence of crown ether on the resin surface, a new synthesized material was characterized by scanning electron microscopy (SEM), elemental analysis X-ray energy dispersive spectroscopy (EDX) and Fourier transform infrared spectroscopy (FT-IR). The specific surface of the adsorbent material was also determined by the Brunauer–Emmett–Teller (BET) method. Adsorbent performances of the prepared material were highlighted by kinetic, thermodynamic and equilibrium studies and a possible mechanism was also proposed. The influence of specific parameters for the adsorption process (contact time, temperature, Pd(II) initial concentration) on the maximum adsorption capacity was pursued.
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Goebes, Philipp, Karsten Schmidt, Werner Härdtle, Steffen Seitz, Felix Stumpf, Goddert von Oheimb i Thomas Scholten. "Rule-based analysis of throughfall kinetic energy to evaluate biotic and abiotic factor thresholds to mitigate erosive power". Progress in Physical Geography: Earth and Environment 40, nr 3 (18.01.2016): 431–49. http://dx.doi.org/10.1177/0309133315624642.
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Below vegetation, throughfall kinetic energy (TKE) is an important factor to express the potential of rainfall to detach soil particles and thus for predicting soil erosion rates. TKE is affected by many biotic (e.g. tree height, leaf area index) and abiotic (e.g. throughfall amount) factors because of changes in rain drop size and velocity. However, studies modelling TKE with a high number of those factors are lacking. This study presents a new approach to model TKE. We used 20 biotic and abiotic factors to evaluate thresholds of those factors that can mitigate TKE and thus decrease soil erosion. Using these thresholds, an optimal set of biotic and abiotic factors was identified to minimize TKE. The model approach combined recursive feature elimination, random forest (RF) variable importance and classification and regression trees (CARTs). TKE was determined using 1405 splash cup measurements during five rainfall events in a subtropical Chinese tree plantation with five-year-old trees in 2013. Our results showed that leaf area, tree height, leaf area index and crown area are the most prominent vegetation traits to model TKE. To reduce TKE, the optimal set of biotic and abiotic factors was a leaf area lower than 6700 mm2, a tree height lower than 290 cm combined with a crown base height lower than 60 cm, a leaf area index smaller than 1, more than 47 branches per tree and using single tree species neighbourhoods. Rainfall characteristics, such as amount and duration, further classified high or low TKE. These findings are important for the establishment of forest plantations that aim to minimize soil erosion in young succession stages using TKE modelling.
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Ciopec, Mihaela, Corneliu Mircea Davidescu, Adina Negrea, Narcis Duţeanu, Gerlinde Rusu, Oana Grad i Petru Negrea. "Amberlite XAD7 resin functionalized with crown ether and Fe(III) used for arsenic removal from water". Pure and Applied Chemistry 91, nr 3 (26.03.2019): 375–88. http://dx.doi.org/10.1515/pac-2018-0607.
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Abstract Water represents an essential resource for life and for all natural processes. Our existence and our economic activities are totally dependent on this precious resource. It is well known that into the developing countries the main resource of drinkable water is represented by underground waters, so their contamination with arsenic represents a real problem that needs to be solved. To solve the problem of arsenic water pollution, it was necessary to develop a series of chemical, physicochemical and biological methods to reduce arsenic concentrations from water. From all these methods, adsorption offers many advantages including simple and stable operation, easy handling of waste, absence of added reagents, compact facilities and generally lower operation cost. The goal of this paper is to study the sorption properties of a new adsorbent material prepared by impregnating Amberlite XAD7 resin with crown ether (dibenzo-18-crown-6 ether) and loaded with Fe(III) ions. Solvent impregnated resin (SIR) method was used for functionalization. Amberlite XAD7 resin functionalization was evidenced by energy dispersive X-ray analysis, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis and determination of specific surface by the Brunauer, Emmett and Teller (BET) analysis. Equilibrium, kinetic and thermodynamic studies were performed in order to determine the removal efficiency of the studied adsorbent for arsenic removal from water. In order to study the As(V) adsorption mechanism the experimental data were modelled using pseudo-first-order and pseudo-second order kinetic models. Kinetic of adsorption process was better described by pseudo-second-order model. Experimental data were fitted with three non-linear adsorption isotherm models: Langmuir, Freundlich and Sips. Obtained experimental data were better fitted by Sips adsorption isotherm. The values of thermodynamic parameters (ΔG°, ΔH°, ΔS°) showed that the adsorption process was endothermic and spontaneous. The results proved that Amberlite XAD7 resin with crown ether and loaded with Fe(III) is an efficient adsorbent for the As(V) removal from water. The possibility of reuse the adsorbent material through adsorption and desorption cycles was also studied and it was found that the material can be used in five sorption-desorption cycles. Maximum adsorption capacity obtained experimentally being 18.8 μg As(V)/g material.
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García-Carrillo, Cristina, José Parga-Torres, Héctor Moreno-Casillas i Francisco S. Sellschopp-Sanchez. "Kinetics and Energy Consumption for a Three-Stage Electrocoagulation Process for the Recovery of Au and Ag from Cyanide Leachates". Metals 9, nr 7 (5.07.2019): 758. http://dx.doi.org/10.3390/met9070758.
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The most common processes used for the recovery of gold and silver from cyanide leachates are Merril-Crowe, activated carbon in pulp, and ion exchange resins; the process of electrocoagulation (EC) also is a promising new technique. EC is an electrochemical process whose mechanisms include oxidation, reduction, decomposition, deposition, coagulation, absorption, flotation, and precipitation. It has been used for the treatment of water and wastewater with different degrees of success. This study aimed to determine the kinetics of the reaction and the energy consumption at constant voltage, and at constant current using aluminum electrodes with two different distances between electrodes. EC was run in three stages for the removal of gold and silver from aqueous cyanide solutions from samples supplied by a Mexican mining company. Characterization of the sample showed initial concentrations of 49.48 and 383 mg/L of gold and silver, respectively. Results showed the effectiveness of the process by achieving removals up to 98.59% of gold and 99.43% of silver. Additionally, it was determined that the kinetics of the reaction is of zero order and that the lowest energy consumption can be achieved when working at constant voltage and with a separation of 0.8 cm between electrodes.
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Chan, Woei Leong, Yongdong Cui, Siddharth Sunil Jadhav, Boo Cheong Khoo, Heow Pueh Lee, Chi Wan Calvin Lim, Like Gobeawan i in. "Experimental study of wind load on tree using scaled fractal tree model". International Journal of Modern Physics B 34, nr 14n16 (10.04.2020): 2040087. http://dx.doi.org/10.1142/s0217979220400871.
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Green urbanism has stimulated more research on the aerodynamics of tree in recent years. The insight gained in studying wind load on trees would mitigate risk of tree falling and enable sustainable landscape planning. However, deciphering the effect of wind on trees is a daunting task because trees come in various species, shapes and sizes. In this study, we aim at conducting wind tunnel tests on various species of trees, including measuring the respective drag coefficient and turbulent flow field using a force balance and particle image velocimetry system. The wind tunnel experiment is conducted using scaled down fractal tree model at 10 and 15 m/s. The 3D-printed tree model is grown based on the data collected on the species-specific tree parameters, such as the height, trunk diameters, crown box dimensions, etc. In this paper, the wind tunnel result of Yellow Flame (Peltophorum pterocarpum) is presented. Results show that the drag coefficient for this inflexible tree model is not sensitive to wind speed. The Reynolds shear stress and turbulence kinetic energy are observed to be the largest at the top and bottom of the crown where the velocity gradients are the highest.
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Testik, F. Y., A. P. Barros i L. F. Bliven. "Toward a Physical Characterization of Raindrop Collision Outcome Regimes". Journal of the Atmospheric Sciences 68, nr 5 (1.04.2011): 1097–113. http://dx.doi.org/10.1175/2010jas3706.1.
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Abstract A comprehensive raindrop collision outcome regime diagram that delineates the physical conditions associated with the outcome regimes (i.e., bounce, coalescence, and different breakup types) of binary raindrop collisions is proposed. The proposed diagram builds on a theoretical regime diagram defined in the phase space of collision Weber numbers We and the drop diameter ratio p by including critical angle of impact considerations. In this study, the theoretical regime diagram is first evaluated against a comprehensive dataset for drop collision experiments representative of raindrop collisions in nature. Subsequently, the theoretical regime diagram is modified to explicitly describe the dominant regimes of raindrop interactions in (We, p) by delineating the physical conditions necessary for the occurrence of distinct types of collision-induced breakup (neck/filament, sheet, disk, and crown breakups) based on critical angle of impact consideration. Crown breakup is a subtype of disk breakup for lower collision kinetic energy that presents distinctive morphology. Finally, the experimental results are analyzed in the context of the comprehensive collision regime diagram, and conditional probabilities that can be used in the parameterization of breakup kernels in stochastic models of raindrop dynamics are provided.
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Kuo, Ting-Yang, Wei-Hsiang Tseng i Chun-hsien Chen. "Force Spectroscopy of Metal-Crown Ether Multivalency: Effect of Local Environments on Energy Landscape and Sensing Kinetics". Angewandte Chemie International Edition 54, nr 32 (18.06.2015): 9213–17. http://dx.doi.org/10.1002/anie.201503948.
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Kuo, Ting-Yang, Wei-Hsiang Tseng i Chun-hsien Chen. "Force Spectroscopy of Metal-Crown Ether Multivalency: Effect of Local Environments on Energy Landscape and Sensing Kinetics". Angewandte Chemie 127, nr 32 (18.06.2015): 9345–49. http://dx.doi.org/10.1002/ange.201503948.
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Sica, R. J., i P. S. Argall. "Seasonal and nightly variations of gravity-wave energy density in the middle atmosphere measured by the Purple Crow Lidar". Annales Geophysicae 25, nr 10 (6.11.2007): 2139–45. http://dx.doi.org/10.5194/angeo-25-2139-2007.
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Abstract. The Purple Crow Lidar (PCL) is a large power-aperture product monostatic Rayleigh-Raman-Sodium-resonance-fluorescence lidar, which has been in operation at the Delaware Observatory (42.9° N, 81.4° W, 237 m elevation) near the campus of The University of Western Ontario since 1992. Kinetic-energy density has been calculated from the Rayleigh-scatter system measurements of density fluctuations at temporal-spatial scales relevant for gravity waves, e.g. soundings at 288 m height resolution and 9 min temporal resolution in the upper stratosphere and mesosphere. The seasonal averages from 10 years of measurements show in all seasons some loss of gravity-wave energy in the upper stratosphere. During the equinox periods and summer the measurements are consistent with gravity waves growing in height with little saturation, in agreement with the classic picture of the variations in the height at which gravity waves break given by Lindzen (1981). The mean values compare favourably to previous measurements when computed as nightly averages, but the high temporal-spatial resolution measurements show considerable day-to-day variability. The variability over a night is often extremely large, with typical RMS fluctuations of 50 to 100% at all heights and seasons common. These measurements imply that using a daily or nightly-averaged gravity-wave energy density in numerical models may be highly unrealistic.
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Maison, Alice, Cédric Flageul, Bertrand Carissimo, Yunyi Wang, Andrée Tuzet i Karine Sartelet. "Parameterizing the aerodynamic effect of trees in street canyons for the street network model MUNICH using the CFD model Code_Saturne". Atmospheric Chemistry and Physics 22, nr 14 (20.07.2022): 9369–88. http://dx.doi.org/10.5194/acp-22-9369-2022.
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Abstract. Trees provide many ecosystem services in cities such as urban heat island reduction, water runoff limitation, and carbon storage. However, the presence of trees in street canyons reduces the wind velocity in the street and limits pollutant dispersion. Thus, to obtain accurate simulations of pollutant concentrations, the aerodynamic effect of trees should be taken into account in air quality models at the street level. The Model of Urban Network of Intersecting Canyons and Highways (MUNICH) simulates the pollutant concentrations in a street network, considering dispersion and physico-chemical processes. It can be coupled to a regional-scale chemical transport model to simulate air quality over districts or cities. The aerodynamic effect of the tree crown is parameterized here through its impact on the average wind velocity in the street direction and the vertical transfer coefficient associated with the dispersion of a tracer. The parameterization is built using local-scale simulations performed with the computational fluid dynamics (CFDs) code Code_Saturne. The two-dimensional CFD simulations in an infinite street canyon are used to quantify the effect of trees, depending on the tree characteristics (leaf area index, crown volume fraction, and tree height to street height ratio) using a drag porosity approach. The tree crown slows down the flow and produces turbulent kinetic energy in the street, thus impacting the tracer dispersion. This effect increases with the leaf area index and the crown volume fraction of the trees, and the average horizontal velocity in the street is reduced by up to 68 %, while the vertical transfer coefficient by up to 23 % in the simulations performed here. A parameterization of these effects on horizontal and vertical transfers for the street model MUNICH is proposed. Existing parameterizations in MUNICH are modified based on Code_Saturne simulations to account for both building and tree effects on vertical and horizontal transfers. The parameterization is built to obtain similar tree effects (quantified by a relative deviation between the cases without and with trees) between Code_Saturne and MUNICH. The vertical wind profile and mixing length depend on leaf area index, crown radius, and tree height to street height ratio. The interaction between the trees and the street aspect ratio is also considered.
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Balakrishnan, Vimal K., Julian M. Dust, Gary W. vanLoon i Erwin Buncel. "Catalytic pathways in the ethanolysis of fenitrothion, an organophosphorothioate pesticide. A dichotomy in the behaviour of crown/cryptand cation complexing agents". Canadian Journal of Chemistry 79, nr 2 (1.02.2001): 157–73. http://dx.doi.org/10.1139/v01-006.
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The rates of displacement of 3-methyl-4-nitrophenoxide ion from the pesticide, fenitrothion, by alkali metal ethoxides in anhydrous ethanol were followed spectrophotometrically. Through product analysis experiments, which included 31P NMR and GC-MS, as well as spectrophotometric analysis, three reaction pathways were identified: nucleophilic attack at the phosphorus centre, attack at the aliphatic carbon, and a minor SNAr route ([Formula: see text]7%). Furthermore, a consecutive process was found to occur on the product of attack at the phosphorus centre. For purposes of kinetic treatment, the processes at the aliphatic and aromatic carbon were combined (i.e., the minor SNAr pathway was neglected), and the observed reaction rate constants were dissected into rate coefficients for nucleophilic attack at phosphorus and at aliphatic carbon. Attack at phosphorus was found to be catalyzed by the alkali metal ethoxides in the order KOEt > NaOEt > LiOEt. Catalysis arises from alkali metal ethoxide aggregates in the base solutions used (01.8 M); treatment of the system as a mixture of free ethoxide, ion-paired metal ethoxide, and metal ethoxide dimers resulted in a good fit with the kinetic data. An unexpected dichotomy in the kinetic behaviour of complexing agents (e.g., DC-18-crown-6, [2.2.2]cryptand) indicated that the dimers are more reactive than free ethoxide anions, which are in turn more reactive than ion-paired metal ethoxide. The observed relative order of reactivity is explained in the context of the Eisenman theory in which the free energy of association of the metal ion with the rate-determining transition state is largely determined by the solvent reorganization parameter. In contrast with displacement at the phosphorus centre, attack at the aliphatic carbon was not found to be catalyzed by alkali metals. In this case, the free ethoxide anion was more reactive than either the ion-paired metal ethoxide or the dimeric aggregate. The differing effects of alkali metals on the two pathways is ascribed largely to the leaving group pKa. For carbon attack, the pKa value estimated for demethyl fenitrothion, 2.15, is sufficiently low that metal ions are not required to stabilize the rate-determining transition state. In contrast, for phosphorus attack, 3-methyl-4-nitrophenoxide, with a pKa of 7.15, requires stabilization by metal ion interactions. Hence, alkali metal ions catalyze attack at phosphorus, but not attack at the carbon centres.Key words: organophosphorothioate, pesticide, fenitrothion, ethanolysis, alkali metal ethoxide, ion-pair reactivity, dimers, catalysis, competitive pathways.
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Yakush, S. E., N. S. Sivakov, V. I. Melikhov i O. I. Melikhov. "Modelling of water jet impact on molten metal". Journal of Physics: Conference Series 2119, nr 1 (1.12.2021): 012073. http://dx.doi.org/10.1088/1742-6596/2119/1/012073.
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Abstract Splashes of high-temperature melt spreading over a water pool bottom can be a reason for the formation of a zone where melt, water and steam are mixed, providing conditions for powerful steam explosions. The paper considers the formation of melt splashes arising from the impact of a water jet on the surface of the melt. Numerical simulations are performed in 3D formulation, using the VOF method and an improved phase change model. The evolution of melt surface following the water jet impact is demonstrated, including the formation of a cavern, a primary melt splash known as the crown, as well as a secondary splash following the collapse of the cavern, known as the cumulative jet. Parametric study for the melt splash height dependence on the water jet geometry and velocity is carried out. The results of numerical analysis are discussed from the point of view of the similarity with respect to the momentum and kinetic energy of water jet. The significance of the results for the steam explosion problem is discussed.
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Kralj, Bogdan, Oleg S. Timofeev, Dušan Žigon, Tatjana I. Kirichenko i JožE Marsel. "A study of protonated molecules of crown ethers containing two thiourea segments by collision-induced dissociation mass analysed ion kinetic energy spectrometry". Rapid Communications in Mass Spectrometry 9, nr 2 (1995): 160–66. http://dx.doi.org/10.1002/rcm.1290090211.
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Sagane, Fumihiro, Masaki Matsui i Kiyoshi Kanamura. "The Effect of the Solvation Ability Towards Mg2+-ion on the Kinetic Behavior of Mg3Bi2 Electrode". Journal of The Electrochemical Society 169, nr 3 (1.03.2022): 030517. http://dx.doi.org/10.1149/1945-7111/ac593a.
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Intermetallic compounds are expected to be used as the negative electrode for Mg-ion batteries, due to their relatively large capacity and the excellent electrochemical performance in the non-ethereal solutions. In the present study, the reaction mechanism of Mg3Bi2 is focused. By comparing the reactivity towards the same electrode sheet in various electrolyte solutions, it is found that the effect of MgF2 based surface film, which is formed by the decomposition of Mg(N(CF3SO2)2)2 (Mg(TFSA)2), is not large necessarily. The reactivity in Mg(TFSA)2+crown ether/acetonitrile solution fairly varies by the size of crown ethers. From the results, it is indicated that the de-solvation process will also be the critical factor for the Mg2+-ion insertion/extraction into the Mg3Bi2 electrode.
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Marston, J. O., E. Q. Li i S. T. Thoroddsen. "Evolution of fluid-like granular ejecta generated by sphere impact". Journal of Fluid Mechanics 704 (1.05.2012): 5–36. http://dx.doi.org/10.1017/jfm.2012.141.
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AbstractWe present results from an experimental study of the speed and shape of the ejecta formed when a solid sphere impacts onto a granular bed. We use high-speed imaging at frame rates up to 100 000 f.p.s. to provide direct measurement of individual grain velocities and ejecta angles as well as the overall evolution of the granular ejecta. For larger grain sizes, the emergence velocities of the grains during the ‘early stage flow’, i.e. before the main ejecta ‘curtain’ forms, increase with the kinetic energy of the impacting sphere but are inversely proportional to the time from impact. We also observe that the fastest grains, which can obtain velocities up to five times that of the impacting sphere (${V}_{g} / {V}_{0} = 5$), generally emerge at the earliest times and with the lowest ejection angles. As the grain size is decreased, a more ‘fluid-like’ behaviour is observed whereby the ejected material first emerges as a thin sheet of grains between the sphere and the bed surface, which is also seen when a sphere impacts a liquid pool. In this case, the sheet velocity is approximately double that of the impacting sphere (${V}_{s} / {V}_{0} = 2$) and independent of the bulk packing fraction. For the finest grains we provide evidence of the existence of a vortex ring inside the ejecta curtain where grains following the air flow are entrained through the curtain. In contrast to predictions from previous studies, we find that the temporal evolution of the ejecta neck radius is not initially quadratic but rather approaches a square-root dependence on time, for the finest grains with the highest impact kinetic energy. The evolution therefore approaches that seen for the crown evolution in liquid drop impacts. By using both spherical glass beads and coarse sands, we show that the size and shape distribution are critical in determining the post-impact dynamics whereby the sands exhibit a qualitatively different response to impact, with grains ejected at lower speeds and at later times than for the glass beads.
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Li, Cuiwei, i Liang Qiao. "Rapid Prediction Algorithm for Economic Development Trend of Tourism Using Markov Chain". Mobile Information Systems 2022 (21.06.2022): 1–8. http://dx.doi.org/10.1155/2022/8726206.
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The environment for tourist development will be increased further if the people-centered development concept is fully implemented, and people’s desire for a colorful tourism life will be boosted. This includes the new kinetic energy of digitalization and networking, which has contributed more and more to economic development. The people-centered development concept also includes the sudden new crown pneumonia outbreak that has had a major influence on the tourism sector; the tourism industry’s robust expansion will not change as a result. There is a reason to assume that tourism will become a key business that contributes to the long-term economic and social growth of China. With the Markov chain to forecast the development tendency of the tourism economy, this paper constructs characteristic indicators such as the number of duty-free shopping on outlying islands, the per capita spending of outlying island rabbit tax shopping, and the number of ecological civilization villages, using the era of free trade ports as a backdrop. The experimental results shows that the proposed idea of this paper is realistic and can have a significant impact towards designing a national ecological civilization pilot zone, international tourism consumption center, and the creation of tropical rainforest national parks.
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Tsegaw, Assefa Asmare, i Fang Jung Shiou. "Development of a Self-Propelled Multi-Jet Polishing Tool for Ultra Precision Polishing". Advanced Materials Research 939 (maj 2014): 481–90. http://dx.doi.org/10.4028/www.scientific.net/amr.939.481.
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As the needs of optical glasses are on the rise, the precision on shape, form, surface qualities and the scaling down of sizes are rising, too. The standards and surface finish of reference mirrors used in measuring appliances are crucial; hence, enhancement of the surface finish is indispensable in manufacturing industries. This paper proposes a self-propelled multi jet polishing technique for ultra precision polishing process in which bladelessTesla turbinewas used as a prime mover. The turbine is characterized by high swirling velocity at the outlet; therefore, high kinetic energy in the course of away from the turbine was used as polishing energy. Simulation of the flow of the field of turbine blades using computational fluid dynamics software (CFD) has also been presented. With a newly designed and manufactured polishing tool, this paper investigates the optimal polishing parameters for surface roughness improvement of crown optical glasses using Taguchis experimental approach; signal-to-nose (S/N) ratio and ANOVA analysis was also carried out to determine the effect of main factors on the surface roughness. Consequently, a 2.5μm size of Al2O3abrasive, 10wt% abrasive concentration, 80rpm of polishing head, 6 numbers of nozzles, 6 kg/cm2of pressure, and 45min. of polishing time have been found to be the optimal parameters. It was observed that about 94.44% improvements on surface roughness; Ra, from 0.360μm to 0.020μm has been achieved using the optimal parameters. In addition to this; angular speed of polishing head, pressure and polishing time were found to have significant effect on surface roughness improvement.
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Nagasubramanian, G., i S. Di Stefano. "12‐Crown‐4 Ether‐Assisted Enhancement of Ionic Conductivity and Interfacial Kinetics in Polyethylene Oxide Electrolytes". Journal of The Electrochemical Society 137, nr 12 (1.12.1990): 3830–35. http://dx.doi.org/10.1149/1.2086309.
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Xie, Zexing, Meiying Xie, Tingting Tang, Fan Yang, Liyan Xue i Zhengming Jiang. "β-Diketone-Driven Deep Eutectic Solvent for Ultra-Efficient Natural Stable Lithium-7 Isotope Separation". Separations 10, nr 2 (4.02.2023): 111. http://dx.doi.org/10.3390/separations10020111.
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6Li and 7Li are strategic resources. Because Li+ ions have no outermost electrons and the radii of 6Li and 7Li differ by only one neutron, the separation of the naturally stable isotopes of Li, especially by solvent extraction, is recognized as a difficult problem worldwide. Therefore, in this paper, an advanced β-diketone-driven deep eutectic solvent (DES) extraction system containing 2-thenoyltrifluoroacetone (HTTA) and tri-n-octyl phosphine oxide (TOPO) is introduced to the extraction and separation of 6Li+ and 7Li+ ions. Compared with those of reported HTTA extraction systems and crown ether extraction systems, the separation coefficient (β7Li/6Li) of the β-diketone-driven DES extraction system can reach the best value of 1.068, which is now the highest known β-value reported in the extraction system. From the intramolecular hydrogen bond of HTTA to the intermolecular hydrogen bond of DES, the bond energy increases by 47.8%. Because the active site of the proton in DES provides a higher energy barrier for the separation of 7Li, the β7Li/6Li is significantly increased. The extractions were characterized by spectrum, using 1H nuclear magnetic resonance (NMR) spectroscopy, Fourier-transform infrared (FT-IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS). The mechanism was determined on the basis of the reaction kinetics and density functional theory (DFT). The DES extractant shows excellent cycle performance with regard to stripping and reusability. In conclusion, the highly efficient, economical, and stable β-diketone-driven DES extraction system can be used for the separation of naturally stable Li isotopes, which provides good industrial application prospects.
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Clark, Kenneth L., Warren E. Heilman, Nicholas S. Skowronski, Michael R. Gallagher, Eric Mueller, Rory M. Hadden i Albert Simeoni. "Fire Behavior, Fuel Consumption, and Turbulence and Energy Exchange during Prescribed Fires in Pitch Pine Forests". Atmosphere 11, nr 3 (29.02.2020): 242. http://dx.doi.org/10.3390/atmos11030242.
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Prescribed fires are conducted extensively in pine-dominated forests throughout the Eastern USA to reduce the risk of wildfires and maintain fire-adapted ecosystems. We asked how fire behavior and fuel consumption during prescribed fires are associated with turbulence and energy fluxes, which affect the dispersion of smoke and transport of firebrands, potentially impacting local communities and transportation corridors. We estimated fuel consumption and measured above-canopy turbulence and energy fluxes using eddy covariance during eight prescribed fires ranging in behavior from low-intensity backing fires to high-intensity head fires in pine-dominated forests of the New Jersey Pinelands, USA. Consumption was greatest for fine litter, intermediate for understory vegetation, and least for 1 + 10 hour wood, and was significantly correlated with pre-burn loading for all fuel types. Crown torching and canopy fuel consumption occurred only during high-intensity fires. Above-canopy air temperature, vertical wind velocity, and turbulent kinetic energy (TKE) in buoyant plumes above fires were enhanced up to 20.0, 3.9 and 4.1 times, respectively, compared to values measured simultaneously on control towers in unburned areas. When all prescribed fires were considered together, differences between above-canopy measurements in burn and control areas (Δ values) for maximum Δ air temperatures were significantly correlated with maximum Δ vertical wind velocities at all (10 Hz to 1 minute) integration times, and with Δ TKE. Maximum 10 minute averaged sensible heat fluxes measured above canopy were lower during low-intensity backing fires than for high-intensity head fires, averaging 1.8 MJ m−2 vs. 10.6 MJ m−2, respectively. Summed Δ sensible heat values averaged 70 ± 17%, and 112 ± 42% of convective heat flux estimated from fuel consumption for low-intensity and high-intensity fires, respectively. Surprisingly, there were only weak relationships between the consumption of surface and understory fuels and Δ air temperature, Δ wind velocities, or Δ TKE values in buoyant plumes. Overall, low-intensity fires were effective at reducing fuels on the forest floor, but less effective at consuming understory vegetation and ladder fuels, while high-intensity head fires resulted in greater consumption of ladder and canopy fuels but were also associated with large increases in turbulence and heat flux above the canopy. Our research quantifies some of the tradeoffs involved between fire behavior and turbulent transfer of smoke and firebrands during effective fuel reduction treatments and can assist wildland fire managers when planning and conducting prescribed fires.
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Wang, Tianbo, Lanchun Zhang, Li Li, Jiahui Wu i Hongchen Wang. "Numerical Comparative Study on the In-Cylinder Mixing Performance of Port Fuel Injection and Direct Injection Gas-Fueled Engine". Energies 15, nr 14 (19.07.2022): 5223. http://dx.doi.org/10.3390/en15145223.
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In recent decades, research on alternative fuel engines is becoming more and more popular. Compressed natural gas (CNG) has the advantages of abundant reserves and a lower cost. It can reduce vehicle emissions relatively quickly and has little impact on the entire transportation infrastructure. As the fourth generation of a gas fuel supply method, gas fuel direct injection (DI) technology can effectively avoid volumetric efficiency reduction and power reduction problems of the port fuel injection (PFI) method. However, the former’s mixing path and duration are shortened greatly, which often leads to poor mixing uniformity. In order to improve the in-cylinder mixing uniformity, the in-cylinder mixing process of the CNG-fueled engine is taken as the research object in this study. The computational fluid dynamics (CFDs) models of the mixing process for the PFI and DI modes are established, and their mixing uniformities are compared. Besides, based on the authors’ previous research, the influence mechanism of the piston crown shape and fuel injection angle on the mixing process of the CNG DI engine is explored. The results show that the probability distribution frequency (PDF) of the best mixture concentration region (BMCR) is as high as 72% for the PFI mode, which is much higher than for the DI mode. The shorter jet impingement distance of the flat top piston leads to higher turbulent kinetic energy (TKE) intensity, and the in-cylinder mixing uniformity will be improved. When gas fuel is injected into an area with a higher in-cylinder TKE, the average in-cylinder TKE will be higher, and the in-cylinder mixture will be more homogeneous.
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Brière, Kathleen M., i Christian Detellier. "Solvent effects in the metal interchange of crown ether – alkali metal cation complexes. Transition from an associative exchange in nitromethane to a dissociative exchange in acetonitrile studied by 23Na nuclear magnetic resonance". Canadian Journal of Chemistry 70, nr 10 (1.10.1992): 2536–43. http://dx.doi.org/10.1139/v92-321.
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The role of the solvent in the dissociation kinetics and cation exchange mechanisms of the complex sodium–monobenzo-15-crown-5 (Na: B15C5)+ was examined by 23Na NMR. In nitromethane (NM), the cationic exchange between the complexes takes place via an associative metal interchange mechanism, 1M. In acetonitrile (AN), it takes place via a dissociative (dissociation/recombination) mechanism. In AN–NM binary mixtures, the rate constant of the dissociative exchange (k−1) increases with the AN molar fraction, XAN, from 1.1 × 10−2 s−1 for XAN = 0 to 89 × 10−2 s−1 for XAN = 0.400 (corresponding to a decrease of the free energy of activation, ΔGdi≠ from 62.1 to 51.1 kJ mol−1 respectively, at 301.5 K). The activation parameters were ΔHdi≠ = 48 kJ mol−1 and ΔSdi≠ = −20 J K−1, mol−1 for XAN = 0.200. This rate increase was related to the concentration increase in solution of the AN monosolvated complex (AN: Na: B15C5)+. In the whole range of AN mole fractions studied, the rate constant of the associative exchange, k2, was not dependent upon XAN in the error limits: k2 ≈ 9 × 104 M−1 s−1 at 301.5 K (ΔGas≠ = 45 kJ mol−1). The activation parameters were determined to be ΔHas≠ = 23 kJ mol−1 and ΔHas≠ = −75 J K−1 mol−1. These findings are in good agreement with an associative exchange controlled mainly by the conformational changes of the ligand during the concerted partial decomplexation of a sodium cation and partial complexation of a second one, while solvation of the complexed cation plays a major role in the dissociative mechanism.
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Y., Gerasymchuk,, Adamenko, O., Lavrishchev, A. i Novoselytskiy, Y. "Determination parameters of the precipitating electrode of the electrotechnical means for cleaning air of livestock buildings from harmful gases and bacterial contamination". Mehanization and electrification of agricultural, nr 9(108) (2019): 141–48. http://dx.doi.org/10.37204/0131-2189-2019-9-17.
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Purpose. Get dependence to determine the mass of the chemical adsorbent which is contained on the rotating precipitating electrode of the electrotechnical means, taking into account the kinetics of the process of air purification of livestock buildings from harmful gases and bacterial contamination with the complex use of electrophysical and chemical methods of decontamination and air purification. Methods. Analysis of the influence of chemical adsorbent and crown discharge field on the efficiency of air purification of livestock buildings from harmful gases and bacterial contamination. Experimental researches for determination of basic parameters of a precipitating electrode of an electrotechnical means. Results. Scheme of the electrotechnical means with the complex using of electrophysical and chemical methods of purification and disinfection of recirculation air of ventilation emissions from ammonia, carbon dioxide, hydrogen sulfide and bacterial contamination. Polynomial dependence for determining the mass of a chemical adsorbent which is contained on a rotating depositing electrode. Conclusions. Complex using of the electrotechnical means for air purification from harmful gases and bacterial contamination of the recirculation air flow and the utilization heat of ventilation emissions with the implementation anti-icing protection heat exchange surface of the recuperative heat utilizers allows to reduce the level of air exchange and significantly reduce energy costs to provide regulatory airspace of livestock buildings in the cold season. On the disks of precipitating electrodes of an electrotechnical mean for cleaning and disinfection of recirculation air of ventilation emissions, it is necessary to fix a polymer mesh with an area of cellules of 16 mm2, and the frequency rotation of the discs to support within the range from 0.25 s-1 to 1 s-1. Keywords: microclimate, heat utilizer, recuperate, air purification, corona discharge, precipitating electrode.
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Cheng, Shyuan, Mahmoud Elgendi, Fanghan Lu i Leonardo P. Chamorro. "On the Wind Turbine Wake and Forest Terrain Interaction". Energies 14, nr 21 (2.11.2021): 7204. http://dx.doi.org/10.3390/en14217204.
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Future wind power developments may be located in complex topographic and harsh environments; forests are one type of complex terrain that offers untapped potential for wind energy. A detailed analysis of the unsteady interaction between wind turbines and the distinct boundary layers from those terrains is necessary to ensure optimized design, operation, and life span of wind turbines and wind farms. Here, laboratory experiments were carried to explore the interaction between the wake of a horizontal-axis model wind turbine and the boundary layer flow over forest-like canopies and the modulation of forest density in the turbulent exchange. The case of the turbine in a canonical boundary layer is included for selected comparison. The experiments were performed in a wind tunnel fully covered with tree models of height H/zhub≈0.36, where zhub is the turbine hub height, which were placed in a staggered pattern sharing streamwise and transverse spacing of Δx/dc=1.3 and 2.7, where dc is the mean crown diameter of the trees. Particle image velocimetry is used to characterize the incoming flow and three fields of view in the turbine wake within x/dT∈(2,7) and covering the vertical extent of the wake. The results show a significant modulation of the forest-like canopies on the wake statistics relative to a case without forest canopies. Forest density did not induce dominant effects on the bulk features of the wake; however, a faster flow recovery, particularly in the intermediate wake, occurred with the case with less dense forest. Decomposition of the kinematic shear stress using a hyperbolic hole in the quadrant analysis reveals a substantial effect sufficiently away from the canopy top with sweep-dominated events that differentiate from ejection-dominated observed in canonical boundary layers. The comparatively high background turbulence induced by the forest reduced the modulation of the rotor in the wake; the quadrant fraction distribution in the intermediate wake exhibited similar features of the associated incoming flow.
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Zhang, A., Y. Z. Wei, M. Kumagai i T. Koyama. "Kinetics of the adsorption of strontium(II) by a novel silica-based 4,4',(5')-di(tert-butylcyclohexano)-18-crown-6 extraction resin in nitric acid medium". Journal of Radioanalytical and Nuclear Chemistry 262, nr 3 (2004): 739–44. http://dx.doi.org/10.1007/s10967-004-0502-y.
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Zhang, A., Y. Z. Wei, M. Kumagai i T. Koyama. "Kinetics of the adsorption of strontium(II) by a novel silica-based 4,4?,(5?)-di(tert-butylcyclohexano)-18-crown-6 extraction resin in nitric acid medium". Journal of Radioanalytical and Nuclear Chemistry 262, nr 3 (styczeń 2005): 739–44. http://dx.doi.org/10.1007/s10967-005-0502-6.
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Zamani Asl, Mohammad Mehdi, i Zahra Dastyar. "Droplet Impingement into a Liquid Film; Numerical Study of Surface Tension Effect on the Crown Formation". European Journal of Computational Mechanics, 22.01.2022. http://dx.doi.org/10.13052/ejcm2642-2085.304610.
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An axisymmetric numerical model is conducted to study the droplet impingement into a liquid film and crown formation. Through numerical modeling and experimental validation, the effect of different parameters such as surface tension, Weber number, and film thickness on crown evolution is investigated. Surfactant is added to water, aiming reduction of the surface tension in the surfactant-water mix. It was shown that the crown rim diameter increases with Weber in both water and surfactant-water mixture cases. Likewise, crown rim diameter increases with the film thickness in both different cases of fluids. Additionally, results revealed that surface tension does not affect the crown rim diameter. Nevertheless, crown height increases as surface tension decreases. At low values of surface tension, secondary droplets and the de-wetting region appear. These outcomes can be attributed to the domination of kinetic energy of crown rims in cases with low surface tensions.
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Zan Tong, Yinli Yang, Jing Xu, Wei Liu i Liang Chen. "Helium separation performance of crown ether-graphane membranes: a theoretical study". Acta Physica Sinica, 2023, 0. http://dx.doi.org/10.7498/aps.72.20222183.
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Helium (He) is widely used in many scientific and industrial fields, and 9 the shortage of He resources and the growing demand make He 10 separation extremely important. In this paper, the He separation 11 performance of a series of graphanes containing crown ether nanopores 12 (crown ether graphane, CG-n, n=3, 4, 5, 6) was studied by first-principles 13 calculations. At first, the minimum energy paths of He and other 10 gas 14 molecules (Ne, Ar, H<sub>2</sub>, CO, NO, NO<sub>2</sub>, N<sub>2</sub>, CO<sub>2</sub>, SO<sub>2</sub> and CH<sub>4</sub>) passing 15 through CG-n membranes were calculated, and the factors affecting the 16 energy barriers were also investigated. The calculated results show that 17 He was the easiest to pass through all the CG-n membranes with energy 18 barriers of 4.55 eV, 1.05 eV, 0.53 eV and 0.01 eV, respectively. He can be 19 separated by CG-5 and CG-6 with very low energy barriers, and the 20 energy barrier of He passing through CG-6 is the lowest so far as we 21 know. Moreover, all gas molecules can pass through CG-6 with low energy barriers, including many molecules with large kinetic diameters, such as CO (0.13 eV) and N<sub>2</sub> (0.16 eV). Therefore, CG-6 is also expected to be used in the screening field of other gas molecules. In addition, it was found that the energy barriers of gas molecules passing through CG-n were synergistically affected by the sizes of the crown ether nanopores, the kinetic diameters and the types of the gas molecules. Secondly, the diffusion rates of gas molecules passing through CG-5 and CG-6 and the He selectivity towards other 10 gases of CG-5 and CG-6 at different temperatures were calculated. It was found that CG-5 exhibited extremely high He selectivity at a wide temperature range (0-600 K). In summary, crown ether graphanes CG-5 and CG-6 can act as excellent He separation membranes with high He selectivity. This work is expected to inspire experimentalists to develop other graphene-based two-dimensional separation membranes for the separation of He and other gas molecules.
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Xia, Yingchun, Ziyuan Song, Zhengzhong Tan, Tianrui Xue, Shiqi Wei, Lingyang Zhu, Yingfeng Yang i in. "Accelerated polymerization of N-carboxyanhydrides catalyzed by crown ether". Nature Communications 12, nr 1 (2.02.2021). http://dx.doi.org/10.1038/s41467-020-20724-w.
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AbstractThe recent advances in accelerated polymerization of N-carboxyanhydrides (NCAs) enriched the toolbox to prepare well-defined polypeptide materials. Herein we report the use of crown ether (CE) to catalyze the polymerization of NCA initiated by conventional primary amine initiators in solvents with low polarity and low hydrogen-bonding ability. The cyclic structure of the CE played a crucial role in the catalysis, with 18-crown-6 enabling the fastest polymerization kinetics. The fast polymerization kinetics outpaced common side reactions, enabling the preparation of well-defined polypeptides using an α-helical macroinitiator. Experimental results as well as the simulation methods suggested that CE changed the binding geometry between NCA and propagating amino chain-end, which promoted the molecular interactions and lowered the activation energy for ring-opening reactions of NCAs. This work not only provides an efficient strategy to prepare well-defined polypeptides with functionalized C-termini, but also guides the design of catalysts for NCA polymerization.
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Pan, Yaoyu, Xiufeng Yang, Song-Charng Kong, Foo Chern Ting, Claudia Iyer i Jianwen Yi. "Characterization of fuel drop impact on wall films using SPH simulation". International Journal of Engine Research, 17.02.2021, 146808742199288. http://dx.doi.org/10.1177/1468087421992888.
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The ability to accurately predict the outcome of the drop/wall interaction is essential to engine spray combustion modeling. In this paper, the process of fuel drop impact on a wet wall was simulated using a numerical method based on smoothed particle hydrodynamics (SPH). The present numerical method was first validated using experimental data on the crown height and crown diameter resulting from water drop impact on a liquid film. Then, the impact process of iso-octane drops on wet walls under engine relevant conditions were studied. The presence of a wall film will affect not only the splash threshold but also the crown evolution and the secondary droplets ejected from the rim of the crown. Numerical results show that the splash threshold increases with the film thickness; the splashed mass ratio increases as the kinetic energy of the incident drop increases. The effect of film thickness on the splashed mass ratio is determined by two competing mechanisms. On the one hand, as the film thickness increases, more incident energy will be absorbed and transferred into the crown, thus producing more secondary droplets. On the other hand, more impinging energy will be dissipated during the spreading as the film thickness increases, thus generating fewer secondary droplets. The properties of the secondary droplets are very different as the film thickness increases. Instead of moving outward, the secondary droplets will move upward and even congregate to the center when the film becomes thicker. The impact angle will affect not only the distributions of the secondary droplets but also the splashed mass. The locations and velocities of the secondary droplets were analyzed. These outcomes were incorporated into formulas that can be further developed into a model for simulating engine spray/wall interactions.
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Kim, Jisoo, Jisoo Shin, Donghwan Kim, Yousang Son i Sungwook Park. "Effects of piston crown designs on in-cylinder flow and mixture formation in gasoline direct injection engine under the lean burn condition". International Journal of Engine Research, 19.04.2023, 146808742311669. http://dx.doi.org/10.1177/14680874231166982.
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In this study, the effects of piston shapes on in-cylinder flow characteristics and mixture formation in the lean condition was analyzed using the PIV method and CFD (CONVERGE v2.4). The four-piston geometries were concave, flat, convex, and base pistons, and the pistons were mounted on a GDI engine with transparent quartz. To quantify in-cylinder flow characteristics, the mean velocity, tumble ratio, turbulent kinetic energy, and tumble center were calculated. In addition, to analyze the effects of the difference in piston shapes in detail, the velocity fraction was calculated by dividing the cylinder area into three. In-cylinder flow was compared for the case without injection and the case with injection. There were four timed injections at C.A. 420°, 480°, 540°, and 600°, and the mixture characteristics were investigated in the cases of 480° and 600° injection. In the intake process and early compression process, there was no significant difference in the quantitative values for the shape of the piston regardless of the presence or absence of injection. However, the effects of the piston crown designs increased in the later compression process. As a result, the highest turbulent kinetic energy was found using a flat piston with a relatively high tumble ratio and swirl ratio in the absence of injection. The mixture formation was similar for all piston crown designs when injected at the crank angle of 480°. However, when the crank angle of 600° was injected, a stagnant fuel area was formed using the base-type piston, so it was difficult to secure sufficient fuel near the center of the cylinder.
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Liang, Xinghui, Jang‐Yeon Hwang i Yang‐Kook Sun. "Practical Cathodes for Sodium‐Ion Batteries: Who Will Take The Crown?" Advanced Energy Materials, 17.08.2023. http://dx.doi.org/10.1002/aenm.202301975.
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AbstractIn recent decades, sodium‐ion batteries (SIBs) have received increasing attention because they offer cost and safety advantages and avoid the challenges related to limited lithium/cobalt/nickel resources and environmental pollution. Because the sodium storage performance and production cost of SIBs are dominated by the cathode performance, developing cathode materials with large‐scale production capacity is the key to achieving commercial applications of SIBs. Therefore, developing host materials with high energy density, long cycling life, low production cost, and high chemical/environmental stability is crucial for implementing advanced SIBs. Among the developed cathode materials for SIBs, O3‐type sodiated transition‐metal oxides have attracted extensive attention owing to their simple synthesis methods, high theoretical specific capacity, and sufficient Na content. However, the relatively large Na‐ion radius leads to sluggish diffusion kinetics and inevitable complex phase transitions during the deintercalation/intercalation process, resulting in poor rate capability and cycling stability. Therefore, this review comprehensively summarizes the research progress and modification strategies for O3‐type cathodes, including the component design, surface modification, and optimization of synthesis methods. This work aims to guide the development of commercial layered oxides and provide technical support for the next generation of energy‐storage systems.
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Bao, Minle, Yali Guo, Luyuan Gong i Shengqiang Shen. "Interface evolution characteristics of dual droplet successive oblique impact on liquid film". Physics of Fluids, 4.06.2022. http://dx.doi.org/10.1063/5.0096585.
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The dynamic characteristics of dual droplets successive oblique impact on a thin liquid film are numerically studied by using the coupled level set and volume of fluid (CLSVOF) model. This three-dimensional model effectively predicts the evolution of crown and crater, which is validated qualitatively and quantitatively by comparing with experimental observations. Some interesting interface features during the collision and coalescence of crowns are revealed in the present simulations, such as the gas cavity, liquid crest, and air gap. In addition, the crater contour takes on different phases with time in the case of dual droplets impact. The evolution characteristics of crater contours in front view and side view have been summarized within a certain time period. Furthermore, the variations of the maximum crater radius in upstream, downstream, and lateral directions as time are quantitatively analyzed. It is found that in the circumferential direction of the crater, the radial kinetic energy of the liquid decreases gradually from the upstream to the downstream direction. This research establishes a foundation for industrial and agricultural applications involving droplets impact.
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Susan-Resiga, Romeo, Sebastian Muntean, Vlad Hasmatuchi, Ioan Anton i François Avellan. "Analysis and Prevention of Vortex Breakdown in the Simplified Discharge Cone of a Francis Turbine". Journal of Fluids Engineering 132, nr 5 (27.04.2010). http://dx.doi.org/10.1115/1.4001486.
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We perform a numerical analysis of the decelerated swirling flow into the discharge cone of a model Francis turbine operated at variable discharge and constant head, using an axisymmetric turbulent swirling flow model and a corresponding simplified computational domain. Inlet boundary conditions correspond to velocity and turbulent kinetic energy profiles measured downstream the Francis runner. Our numerical results are validated against experimental data on a survey section further downstream in the cone, showing that the Reynolds stress turbulence model with a quadratic pressure-strain term correctly captures the flow field. It is shown that the diffuser performance quickly deteriorates as the turbine discharge decreases, due to the occurrence and development of vortex breakdown, with a central quasistagnant region. We investigate a novel flow control technique, which uses a water jet injected from the runner crown tip along the axis. It is shown that the jet discharge can be optimized for minimum overall losses, while the vortex breakdown is eliminated. This flow control method is useful for mitigating the Francis turbine flow instabilities when operating at partial discharge.
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Lloyd, C. J., K. Mittal, S. Dutta, R. M. Dorrell, J. Peakall, G. M. Keevil i A. D. Burns. "Multi-fidelity modelling of shark skin denticle flows: insights into drag generation mechanisms". Royal Society Open Science 10, nr 2 (luty 2023). http://dx.doi.org/10.1098/rsos.220684.
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We investigate the flow over smooth (non-ribletted) shark skin denticles in an open-channel flow using direct numerical simulation (DNS) and two Reynolds averaged Navier–Stokes (RANS) closures. Large peaks in pressure and viscous drag are observed at the denticle crown edges, where they are exposed to high-speed fluid which penetrates between individual denticles, increasing shear and turbulence. Strong lift forces lead to a positive spanwise torque acting on individual denticles, potentially encouraging bristling if the denticles were not fixed. However, DNS predicts that denticles ultimately increase drag by 58% compared to a flat plate. Good predictions of drag distributions are obtained by RANS models, although an underestimation of turbulent kinetic energy production leads to an underprediction of drag. Nevertheless, RANS methods correctly predict trends in the drag data and the regions contributing most to viscous and pressure drag. Subsequently, RANS models are used to investigate the dependence of drag on the flow blockage ratio (boundary layer to roughness height ratio), finding that the drag increase due to denticles is halved when the blockage ratio δ / h is increased from 14 to 45. Our results provide an integrated understanding of the drag over non-ribletted denticles, enabling existing diverse drag data to be explained.