Journal articles on the topic 'Distance coalescence'
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1
Yang, Zhi Yong, Jian Dong Li, and Guo Hua Zhang. "Numerical Simulation of Bubble Coalescence Based on VOF Method." Applied Mechanics and Materials 148-149 (December 2011): 814–17. http://dx.doi.org/10.4028/www.scientific.net/amm.148-149.814.
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This paper takes bubbles of bubble shell as research object, mainly studies two bubbles arranged in a vertical position. Applying VOF (volume of fluid) method to simulate interaction between two bubbles, analyses the effect of center distances and diameters on deformation and coalescence of bubbles. Results show that coalescence time of two bubbles with same diameters increases as the center distance increases. To two bubbles with different diameters, when the bigger bubble located beneath at the initial time, the smaller bubble moves upward first and then moves downward before two bubbles coalesce. When the smaller bubble located beneath at the initial time, bubble coalescence cannot happen. This paper is the basis of bubble group research, it is of positive significance to the bubble group research and performance improvement of bubble shell.
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Wilkins, Jon F., and John Wakeley. "The Coalescent in a Continuous, Finite, Linear Population." Genetics 161, no. 2 (June 1, 2002): 873–88. http://dx.doi.org/10.1093/genetics/161.2.873.
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Abstract In this article we present a model for analyzing patterns of genetic diversity in a continuous, finite, linear habitat with restricted gene flow. The distribution of coalescent times and locations is derived for a pair of sequences sampled from arbitrary locations along the habitat. The results for mean time to coalescence are compared to simulated data. As expected, mean time to common ancestry increases with the distance separating the two sequences. Additionally, this mean time is greater near the center of the habitat than near the ends. In the distant past, lineages that have not undergone coalescence are more likely to have been at opposite ends of the population range, whereas coalescent events in the distant past are biased toward the center. All of these effects are more pronounced when gene flow is more limited. The pattern of pairwise nucleotide differences predicted by the model is compared to data collected from sardine populations. The sardine data are used to illustrate how demographic parameters can be estimated using the model.
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Wang, Yong Gang, Hong Liang He, Li Li Wang, and Fu Qian Jing. "Percolation-Relaxation Model with Critical Damage for Describing the Dynamic Tensile Spall of Ductile Metals." Key Engineering Materials 324-325 (November 2006): 121–24. http://dx.doi.org/10.4028/www.scientific.net/kem.324-325.121.
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In the framework of percolation theory, a simple void-coalescence model combined with the constitutive relations for describing the stress relaxation and material softening during the void-coalescence process, name as the percolation-relaxation (P-R) model, is proposed to describe the dynamic tensile spallation of ductile metals. A critical damage is introduced and coupled into the model to identify the onset of the void coalescence. Mesoscopically, the critical damage corresponds to the critical intervoid ligament distance (ILD), indicating the start of transition from the void-growth to the void-coalescence.
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Ahmed, Fatma, Nobuyuki Kawahara, and Eiji Tomita. "Binary collisions and coalescence of droplets in low-pressure fuel injector." Thermal Science, no. 00 (2020): 185. http://dx.doi.org/10.2298/tsci191120185a.
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The phenomena of binary collisions and coalescence of droplets was investigated from experimental studies but still are missing from real applications such as from fuel injector. The main purpose of the current study is to investigate the phenomena of binary collisions and coalescence of droplets from a practical port fuel injector (PFI). To accomplish this, direct microscopic images are taken from high-speed video camera coupled with a long-distance microscope and Barlow lens using the backlighting method. Experimental optimization of the spatial resolution and the depth -of -field of the long-distance microscope and Barlow lens are achieved. Experimental results from the direct microscopic images are compared with predictions from empirical equations for different collision regimes. Droplet sizes and velocities of experimental coalescence droplets from collisions are compared with the values predicted by the equations. The main results of this study are: The probability of collision and coalescence is very low in a PFI. The tangential velocity components of small droplets play an essential role in shape deformation during collisions and coalescence of the droplets. The previous published empirical equations to calculate dimensionless parameters, the Weber number (We), the droplet diameter ratio (?), and impact parameter (B) are applicable to the coalescence of droplets in a PFI.
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Fan, Pingyang, Jianxin Liu, Wengui Zuo, Min Wang, and Daoyong Zhang. "Experimental Study of Rock-like Materials with Two Unequal Parallel Preexisting Fissures under Uniaxial Compression." Applied Sciences 12, no. 20 (October 15, 2022): 10404. http://dx.doi.org/10.3390/app122010404.
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Fissures substantially impact the engineering stability of rock masses, making research on rock masses with preexisting fissures essential for engineering activities. The development of specimens with different preexisting fissure types was examined in this study. Three different types of specimens with preexisting fissures can be broadly categorized: specimens with few preexisting fissures, specimens with multiple preexisting fissures, and specimens with preexisting fissures and other flaws. Uniaxial compression tests of specimens with preexisting fissures of two unequal lengths were conducted, and the influence of preexisting fissure angle, the distance between the two fissures and fissure length on the peak strength and coalescence mode of specimens were analyzed. A large preexisting fissure length significantly influenced the peak strength and coalescence, and the uniaxial compressive strength (UCS) values of the rock-like materials decreased. In contrast, increasing the long preexisting fissure length influenced the crack propagation and coalescence more extensively in the case of a long preexisting fissure. The preexisting fissure angle and two preexisting fissure distances had a negligible effect on the UCS values of the rock-like materials. However, with increasing long preexisting fissure length, the short preexisting fissure was subject to crack propagation and coalescence.
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Rousset, François. "Genetic Differentiation and Estimation of Gene Flow from F-Statistics Under Isolation by Distance." Genetics 145, no. 4 (April 1, 1997): 1219–28. http://dx.doi.org/10.1093/genetics/145.4.1219.
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I reexamine the use of isolation by distance models as a basis for the estimation of demographic parameters from measures of population subdivision. To that aim, I first provide results for values of F-statistics in one-dimensional models and coalescence times in two-dimensional models, and make more precise earlier results for F-statistics in two-dimensional models and coalescence times in one-dimensional models. Based on these results, I propose a method of data analysis involving the regression of FST/ (1 – FST) estimates for pairs of subpopulations on geographic distance for populations along linear habitats or logarithm of distance for populations in two-dimensional habitats. This regression provides in principle an estimate of the product of population density and second moment of parental axial distance. In two cases where comparison to direct estimates is possible, the method proposed here is more satisfactory than previous indirect methods.
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Zhang, Fangfang, and Hongjun Li. "Visualization of Coalescence of Multiple Small Bubbles with Closed B-Spline Curve." International Journal of Computer Games Technology 2020 (August 27, 2020): 1–13. http://dx.doi.org/10.1155/2020/8953893.
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The smoothness of surface shape is one of the key issues to simulate coalescence of underwater bubbles. In this paper, B-spline closed curve is used to realize the visual simulation of multibubble coalescence. The main idea of the proposed algorithm is to construct a continuous bubble deformation which is guided by the normal direction of each control point and weighted by the distance from the point to the geometry center of the contour. The advantages of this algorithm include the smoothness of the bubble contour in the processing of deformation and the randomness of dynamic process and coalescence process. Experiment results show that the simulation algorithm works well and can be used in 3D computer games and animations.
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Dai, Bing, Ying Chen, Guoyan Zhao, Weizhang Liang, and Hao Wu. "A Numerical Study on the Crack Development Behavior of Rock-Like Material Containing Two Intersecting Flaws." Mathematics 7, no. 12 (December 11, 2019): 1223. http://dx.doi.org/10.3390/math7121223.
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It is quite often that rocks contain intersecting cracks. Therefore, crack behavior cannot be completely studied by only considering several isolated, single flaws. To investigate the crack behavior of rock or rock-like material containing intersecting flaws under uniaxial loading, numerical simulations were carried out using parallel bonded-particle models containing two intersecting flaws with different inclination angles (varying β) and different intersection angles (varying αα). The crack propagation processes are analyzed and two typical patterns of linkage are observed between two intersecting flaws: (1) One-tip-linkage that contains three subtypes: Coalescence position near the tip; coalescence position at the flaw, but far away from the tip; coalescence position outside the flaw at a certain distance from the tip; and (2) two-tip-linkage with two subtypes: Straight linkage and arc linkage. The geometries of flaws influence the coalescence type. Moreover, the effects of intersection angle α and inclination angle β on the peak stress, the stress of crack initiation, and the stress of crack coalescence are also investigated in detail.
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Chen, Rou, Huidan(Whitney) Yu, and Likun Zhu. "Effects of initial conditions on the coalescence of micro-bubbles." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, no. 3 (November 24, 2017): 457–65. http://dx.doi.org/10.1177/0954406217742941.
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The effects of initial conditions on the coalescence of two equal-sized air micro-bubbles ( R0) in water are studied using the lattice Boltzmann method. The focus is on effects of two initial set-ups of parent bubbles, separated by a small distance d and connected with a neck bridge radius r0, on the neck bridge growth at the early stage of the bubble coalescence. A sophisticated free energy lattice Boltzmann method model based on the Cahn-Hilliard diffuse interface approach is employed. This lattice Boltzmann method model has been demonstrated suitable for handling a large density ratio of two fluids up to 1000 and capable of minimizing the nonphysical spurious current. In both initial scenarios, the neck bridge evolution exhibits a half power-law scaling, [Formula: see text] after a development time. The half power-law agrees with the recent analytical prediction and experimental results. It has been found that smaller initial separation distance or smaller initial neck bridge radius results in faster growth of neck bridge and bubble coalescence, which is similar to the effects of these two initial scenarios on droplet coalescence. The physical mechanism behind each behavior has been explored. For the initial connected case, faster neck growth and longer development time corresponding to smaller initial neck radius is due to the significant bias between the capillary forces contributed by the meniscus curvature and the neck bridge curvature, whereas in the case of initial separated scenario, faster growth and shorter development time corresponding to shorter separation distance is due to the formation of elongated neck bridge. The prefactor A0 that represents the growth of neck bridge radius at the characteristic time ti captured in each case is in good agreement with the experimental results.
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Bustamante, Danilo E., Manuel Oliva, Santos Leiva, Jani E. Mendoza, Leidy Bobadilla, Geysen Angulo, and Martha S. Calderon. "Phylogeny and species delimitations in the entomopathogenic genus Beauveria (Hypocreales, Ascomycota), including the description of B. peruviensis sp. nov." MycoKeys 58 (September 9, 2019): 47–68. http://dx.doi.org/10.3897/mycokeys.58.35764.
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The genus Beauveria is considered a cosmopolitan anamorphic and teleomorphic genus of soilborne necrotrophic arthropod-pathogenic fungi that includes ecologically and economically important species. Species identification in Beauveria is difficult because of its structural simplicity and the lack of distinctive phenotypic variation. Therefore, the use of multi-locus sequence data is essential to establish robust species boundaries in addition to DNA-based species delimitation methods using genetic distance, coalescent, and genealogical concordance approaches (polyphasic approaches). In this regard, our study used multilocus phylogeny and five DNA-based methods to delimit species in Beauveria using three molecular makers. These polyphasic analyses allowed for the delimitation of 20–28 species in Beauveria, confirming cryptic diversity in five species (i.e. B. amorpha, B. bassiana, B. diapheromeriphila, and B. pseudobassiana) and supporting the description of B. peruviensis as a new taxon from northeastern Peru. The other five species were not evaluated as they did not have enough data (i.e. B. araneola, B. gryllotalpidicola, B. loeiensis, B. medogensis, and B. rudraprayagi). Our results demonstrate that the congruence among different methods in a polyphasic approach (e.g. genetic distance and coalescence methods) is more likely to show reliably supported species boundaries. Among the methods applied in this study, genetic distance, coalescent approaches, and multilocus phylogeny are crucial when establishing species boundaries in Beauveria.
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Yao, Shouguang, Tao Huang, Kai Zhao, Jianbang Zeng, and Shuhua Wang. "Simulation of flow boiling of nanofluid in tube based on lattice Boltzmann model." Thermal Science 23, no. 1 (2019): 159–68. http://dx.doi.org/10.2298/tsci160817006y.
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In this study, a lattice Boltzmann model of bubble flow boiling in a tube is established. The bubble growth, integration, and departure of 3% Al2O3-water nanofluid in the process of flow boiling are selected to simulate. The effects of different bubble distances and lateral accelerations a on the bubble growth process and the effect of heat transfer are investigated. Results showed that with an increase in the bubble distance, the bubble coalescence and the effect of heat transfer become gradual. With an increase in lateral acceleration a, the bubble growth is different. When a = 0.5e?7 and a = 0.5e?6, the bubble growth includes the process of bubble growth, coalescence, detachment, and fusion with the top bubble and when a = 0.5e?5 and a = 0.5e?4, the bubbles only experience growth and fusion, and the bubbles do not merge with the top bubble directly to the right movement because the lateral acceleration is too large, resulting in the enhanced effect of heat transfer in the tube.
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Jiang, Fang, Guo Guang Cheng, and Hai Kuo Yang. "Effect of Gas Injection with Multi-hole Orifices on Bubble Behavior during Metal Refining." Advanced Materials Research 233-235 (May 2011): 1940–45. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.1940.
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Cold model experiments have been conducted to make clear the effect of orifices on bubble behavior based on the comparison of 1-hole and 4-hole configurations. It is found that this effect is closely related to the gas flow rate and the orifice configuration. For 1-hole orifices, bubble behavior is influenced by the hole diameter at low gas flow rate. Nevertheless, in the region of high gas flow rate, this effect becomes less obvious. However, bubble behavior is strongly affected even at high gas flow rate when 4-hole orifices are used. It is also shown there exists an optimal distance between holes for 4-hole orifices. Below this value, the hole distance is too small to adequately avoid bubble coalescence in the radial direction. Above this value, little further contribution to avoidance of bubble coalescence can be made, but weight and cost of the orifices will increase.
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Slatkin, Montgomery. "Inbreeding coefficients and coalescence times." Genetical Research 58, no. 2 (October 1991): 167–75. http://dx.doi.org/10.1017/s0016672300029827.
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SummaryThis paper describes the relationship between probabilities of identity by descent and the distribution of coalescence times. By using the relationship between coalescence times and identity probabilities, it is possible to extend existing results for inbreeding coefficients in regular systems of mating to find the distribution of coalescence times and the mean coalescence times. It is also possible to express Sewall Wright's FST as the ratio of average coalescence times of different pairs of genes. That simplifies the analysis of models of subdivided populations because the average coalescence time can be found by computing separately the time it takes for two genes to enter a single subpopulation and time it takes for two genes in the same subpopulation to coalesce. The first time depends only on the migration matrix and the second time depends only on the total number of individuals in the population. This approach is used to find FST in the finite island model and in one- and two-dimensional stepping-stone models. It is also used to find the rate of approach of FST to its equilibrium value. These results are discussed in terms of different measures of genetic distance. It is proposed that, for the purposes of describing the amount of gene flow among local populations, the effective migration rate between pairs of local populations, M^, which is the migration rate that would be estimated for those two populations if they were actually in an island model, provides a simple and useful measure of genetic similarity that can be defined for either allozyme or DNA sequence data.
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Barbier, E., and Nik Petrinic. "Multiple Crack Growth and Coalescence in Meshfree Methods with Adistance Function-Based Enriched Kernel." Key Engineering Materials 560 (July 2013): 37–60. http://dx.doi.org/10.4028/www.scientific.net/kem.560.37.
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Distance fields are functions defining the minimum distance between any generic point inspace and the boundaries of an object. This paper shows some important properties of these fields andtheir derivatives. In fact, for polygonal lines, the derivatives of distance fields are discontinuous overthe finite length of the segment, but continuous all around the end-points. An immediate consequenceis their application as intrinsic enrichment of weight functions in meshless methods, for the treatmentof multiple arbitrary cracks. By introducing such explicitly known function for the distance fields,discontinuities can be easily incorporated in the kernel in a simple, multiplicative manner. The result-ing method allows a more straightforward implementation and simulation of the presence of multiplecracks in a meshless framework without using any of the existing algorithms such as visibility, trans-parency and diffraction. Furthermore, one of the main advantages of this approach is the automaticcoalescence of multiple interacting cracks, i.e. no particular enrichment functions are necessary at thejunction points.
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Tineo, Daniel, Danilo E. Bustamante, Martha S. Calderon, Jani E. Mendoza, Eyner Huaman, and Manuel Oliva. "An integrative approach reveals five new species of highland papayas (Caricaceae, Vasconcellea) from northern Peru." PLOS ONE 15, no. 12 (December 10, 2020): e0242469. http://dx.doi.org/10.1371/journal.pone.0242469.
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The assignment of accurate species names is crucial, especially for those with confirmed agronomic potential such as highland papayas. The use of additional methodologies and data sets is recommended to establish well-supported boundaries among species of Vasconcellea. Accordingly, six chloroplast (trnL-trnF, rpl20-rps12, psbA-trnH intergenic spacers, matK and rbcL genes) and nuclear (ITS) markers were used to delimit species in the genus Vasconcellea using phylogeny and four DNA-based methods. Our results demonstrated congruence among different methodologies applied in this integrative study (i.e., morphology, multilocus phylogeny, genetic distance, coalescence methods). Genetic distance (ABGD, SPN), a coalescence method (BPP), and the multilocus phylogeny supported 22–25 different species of Vasconcellea, including the following five new species from northern Peru: V. badilloi sp. nov., V. carvalhoae sp. nov., V. chachapoyensis sp. nov., V. pentalobis sp. nov., and V. peruviensis sp. nov. Genetic markers that gave better resolution for distinguishing species were ITS and trnL-trnF. Phylogenetic diversity and DNA-species delimitation methods could be used to discover taxa within traditionally defined species.
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Schlottke, Jan, Winfried Straub, Klaus Dieter Beheng, Hassan Gomaa, and Bernhard Weigand. "Numerical Investigation of Collision-Induced Breakup of Raindrops. Part I: Methodology and Dependencies on Collision Energy and Eccentricity." Journal of the Atmospheric Sciences 67, no. 3 (March 1, 2010): 557–75. http://dx.doi.org/10.1175/2009jas3174.1.
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Abstract Binary collisions of large raindrops moving with terminal fall velocity are numerically investigated using FS3D, a direct numerical simulation (DNS) code based on the “volume of fluid” method. The result of this process can be a permanent coalescence or a temporal coalescence followed by a breakup of the coalesced system into smaller-sized remnants of the original raindrops and a number of fragment droplets of different sizes. In total, 32 drop pairs are studied with sizes chosen to cover nearly completely the entire size parameter range relevant to breakup. This is an important extension of investigations performed in 1982 by Low and List, who studied 10 drop pairs only. Moreover, eccentricity has been introduced as an additional parameter controlling the collision outcome. Eccentricity is defined as the horizontal distance of the initial drops’ centers with values equal to approximately 0 for centric and 1 for grazing collisions. The main results include numerically calculated data of coalescence efficiencies and fragment size distributions with emphasis on eccentricity effects. It is shown that eccentricity largely determines the appearance of specific breakup modes and consequently the respective fragment size distributions. Comparisons are made with the main findings of Low and List. Coalescence efficiency values larger than those derived by Low and List show up for very small Weber numbers. Additionally, the existence of their definite limit value of collision kinetic energy necessary for coalescence could not be confirmed. The fragment size distributions are in some cases similar to those measured by Low and List but there are also major differences for other cases. The presented results are used for parameterizations of coalescence efficiencies and fragment size distributions as well as for calculations of stationary drop spectra shown in Part II of this study.
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Abbasi, Muhammad Salman, Husnain Ali, Ali Hussain Kazim, Tariq Nawaz Chaudhary, Muhammad Usman, Sheraz Afzaal, Muhammad Usman, and Douhadji Abalo. "Emulsion Droplet Pair Coalescence under a Direct Current Electric Field." Mathematical Problems in Engineering 2022 (June 2, 2022): 1–9. http://dx.doi.org/10.1155/2022/8420722.
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We investigate the dynamics of the droplet pair coalescence and its stability under a direct current (DC) electric field strength by using simulation and theoretical analyses. We conduct a parametric study to investigate the effects of electric capillary number ( C a e = ε o ε out E o 2 R o / γ , the ratio of the electrical Maxwell stress to interfacial capillary stress), droplet size ratios (R/Ro, where R and Ro are the radii of the coalescing drops, respectively), and the droplet interfacial separation distance (S) on the coalescence process. We show that unequal-sized droplets undergo unique dynamics owing to the generation of velocity gradient between the coalescing droplets. Moreover, using theoretical analysis, we delineate the stable and unstable regimes of a coalesced droplet under an electric field. Results show that if the semimajor axis of the coalesced droplet becomes greater than 1.5 times, it continuously stretches and becomes unstable. We believe that the study will be useful for essential physical insights pertaining to the coalescence process and valuable for their applications in various areas of biological engineering, chemical sciences, material sciences, and lab on a chip.
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Dong, Hui, Yan Han, Yong Zhou, Xiao Li, Jian-Tao Yao, and Yan Li. "The Temperature Distribution in Plasma-Sprayed Thermal-Barrier Coatings During Crack Propagation and Coalescence." Coatings 8, no. 9 (September 4, 2018): 311. http://dx.doi.org/10.3390/coatings8090311.
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A Finite-Element Model (FEM) for thermal-barrier coatings was employed to elaborate the temperature distribution on yttria-stabilized zirconia (YSZ) free surface during cracks coalescing, then the influence of sintering of YSZ induced by heat-transfer overlapping on energy release rate was quantificationally evaluated. A three-dimensional model including three layers was fabricated. Two types of cracks, with and without depth variations in YSZ coating, were introduced into the model, respectively. The temperature rise of YSZ coating over the crack is independent of each other at the beginning of crack propagation. As crack distance shortens, the independent temperature-rise regions begin to overlap, while maximum temperature is still located at the crack center before crack coalescence. The critical distance that the regions of temperature rise, just overlapping, is the sum of half lengths of two coalescing cracks (i.e., a1 + a2), which is independent of cracking path. The maximum temperature in YSZ sharply increases once cracks coalesce. Compared with one delamination crack, the effective energy-release rate induced by heat-transfer overlapping increases in the range of 0.2%–15%, depending on crack length and crack distance, which is on some level comparable to that of deterioration of thermal expansion misfit induced by temperature jump between crack faces.
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Qian, XiKun, ZhengZhao Liang, and ZhiYi Liao. "A Three-Dimensional Numerical Investigation of Dynamic Fracture Characteristics of Rock Specimens with Preexisting Surface Flaws." Advances in Civil Engineering 2018 (October 18, 2018): 1–18. http://dx.doi.org/10.1155/2018/8027582.
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FEM-based numerical investigation was conducted to investigate the fracture characteristics of heterogeneous rocks with preexisting surface flaws under dynamic loadings. Different types of cracks from initiation to coalescence of the specimen with a single flaw were reproduced in numerical tests, which were very highly agreed with experimental results. Numerical testing on specimens with a single flaw demonstrated that the crack behaviors, including its path, length, and cracking velocity, were significantly different on the surface of and inside the rock specimen. In addition, the higher the incident pressure level applied, the longer the cracking distance propagated; the more the AE count is, the larger the AE energy released and the greater the fragmentized. Furthermore, the cutting depth of flaw could significantly affect crack propagation patterns and AE characteristics. When the cutting depth of flaw is equal to the thickness of the specimen, there would be no shell-like crack emerged. Subsequently, testing results of the multi-preexisting flaws indicated that the surface flaws on the specimen made the crack initiation and coalescence behaviors more complicated. The coalescence between flaw tips is not easy, and the coalescence of preexisting flaws needs two or multiple cracks to achieve. The coalescence points occurred not only in the preexisting flaw but also in the trajectory of the wing cracks and antiwing cracks. The accumulative AE energy and AE counts are positively correlated with the amounts of preexisting flaws. Finally, crack evolution under dynamic and static loading was compared. Short tensile cracks are found to be the most common crack type, which are responsible for specimen failure. These findings could give a better explanation on the crack initiation and propagation of rock specimen with preexisting flaw, which is the phenomenon that has not been observed in many dynamic experiments.
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Dietzel, Charles, Hakan Oguz, Jeffery J. Hemphill, Keith C. Clarke, and Nicholas Gazulis. "Diffusion and Coalescence of the Houston Metropolitan Area: Evidence Supporting a New Urban Theory." Environment and Planning B: Planning and Design 32, no. 2 (April 2005): 231–46. http://dx.doi.org/10.1068/b31148.
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The authors build on a recent development in urban geographic theory, providing evidence of an oscillatory behavior in spatiotemporal patterns of urban growth. With the aid of remotely sensed data, the spatial extent of urban areas in the Houston (USA) metropolitan region from 1974 to 2002 was analyzed by spatial metrics. Regularities in the spatial urban growth pattern were identified with temporal periods as short as thirty years by means of spatial metric values, including mean nearest-neighbor distance, mean patch area, total number of urban patches, and mean patch fractal dimension. Through changes in these values, a distinct oscillation between phases of diffusion and coalescence in urban growth was revealed. The results suggest that the hypothesized process of diffusion and coalescence may occur over shorter time periods than previously thought, and that the patterns are readily observable in real-world systems.
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Telles, Mariana Pires de Campos, and José Alexandre Felizola Diniz-Filho. "Null expectation of spatial correlograms under a stochastic process of genetic divergence with small sample sizes." Genetics and Molecular Biology 23, no. 4 (December 2000): 739–43. http://dx.doi.org/10.1590/s1415-47572000000400007.
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An Ornstein-Uhlenbeck process was used to simulate the exponential relationship between genetic divergence and geographic distances, as predicted by stochastic processes of population differentiation, such as isolation-by-distance, stepping-stone or coalescence models. These simulations were based only on the spatial coordinates of the local populations that defined a spatial unweighted pair-group method using arithmetic averages (UPGMA) link among them. The simulated gene frequency surfaces were then analyzed using spatial autocorrelation procedures and Nei's genetic distances, constructed with different numbers of variables (gene frequencies). Stochastic divergence in space produced strong spatial patterns at univariate and mutivariate levels. Using a relatively small number of local populations, the correlogram profiles varied considerably, with Manhattan distances greater than those defined by other simulation studies. This method allows one to establish a range of correlogram profiles under the same stochastic process of spatial divergence, thereby avoiding the use of unnecessary explanations of genetic divergence based on other microevolutionary processes.
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Voelter, Christian, and Joachim Rösler. "Growth and Coalescence of γ’-Precipitates in Nickel-Based Alloy 115NC during Slow Cooling for Membrane Manufacturing." Metals 12, no. 1 (January 11, 2022): 134. http://dx.doi.org/10.3390/met12010134.
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By coarsening of the γ’-precipitates and selective extraction of one of the two existing phases, porous structures can be produced from nickel-based superalloys. There are two basic approaches to achieve a bicontinuous γ/γ’-microstructure—directional and incoherent coarsening. Single crystalline superalloy membranes are produced by the so-called rafting of the microstructure, i.e., directional coarsening. Unlike this process, incoherently coarsened membranes lack a detailed understanding of the mechanisms leading to cross-linking of the precipitates. In this paper, the growth and coalescence of precipitates during initial slow cooling from above the γ’ solvus temperature was studied. In addition to the three-dimensional morphological changes of the precipitates, it is also shown that only little coalescence of the particles occurs despite the high γ’ content and, therefore, their very small distance. The loss of coherency that occurs during this part of coarsening must first advance through further aging before a bicontinuous microstructure is formed.
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Сундуков, Сергей, Sergey Sundukov, Равиль Нигметзянов, Ravil Nigmetzyanov, Дмитрий Фатюхин, and Dmitriy Fatyukhin. "Technology improvement of ultrasonic refinement of machinery work surfaces based on phenomenological investigation of cavity formations." Science intensive technologies in mechanical engineering 2, no. 1 (January 31, 2017): 16–21. http://dx.doi.org/10.12737/24207.
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The study of processes based on cavitation use required a clear definition of phenomena arising in liquid at high-frequency oscillation impact upon it. For the in-depth study of the phenomena under investigation in the given work there was used a high-speed video filming.
As the analysis of high-speed filming has shown after closing a bubble is divided into many pieces which, in their turn, pulse in-phase. At the same time there is observed a formation of complex bubble formations which are offered to be called clusters (Fig. 3).
Bubbles formed under the influence of variable acoustic pressure and located at a small distance from each other combine. Two processes take place simultaneously – bubbles combining (coalescence) and the integration of small bubbles in larger ones under the influence of cohesion forces with the formation of general structures (coagulation). The coalescence is followed with the transition of a system in a state with lower free energy.
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Xu, Shu Sheng, Xiang Guo Zeng, and Hua Yan Chen. "Molecular Dynamics Study on Interaction between Voids for Pure Aluminum." Key Engineering Materials 452-453 (November 2010): 845–48. http://dx.doi.org/10.4028/www.scientific.net/kem.452-453.845.
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The voids in pure Aluminum always exit in the manufacturing process. The Modified Embedded Atom Method (MEAM) potential is employed in the molecular dynamics (MD) simulation at atomic scale to investigate the interaction between voids under the impact loading for pure Aluminum. The distance between the voids distributed along the loading orientation affects the failure mechanism seriously. The results show that there are 3 kinds of mechanisms with the change of the distance between voids: 1) coalescence takes place within a critical distance between voids under extra loading, 2) when the distance between voids reaches a certain value, each void cracks at 4 locations along with the slide direction <110> of face-centered cubic (fcc), respectively, 3) a stress shield zone appears when the ligament between the voids is at the size between the cases mentioned above, which brings out the phenomena that each of the voids cracks only at 2 locations, and no crack appeared at the stress shield zone.
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Wang, Jianming, Zhonghui Chen, and Lingfan Zhang. "Unloading-Induced Crack Propagation of Two Collinear Unequal Length Flaws in Brittle Rocks." Geofluids 2020 (June 5, 2020): 1–18. http://dx.doi.org/10.1155/2020/9385749.
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The propagation and coalescence of numerous discontinuous joints significantly contribute to landslide instability during excavation unloading. The tip expression of stress intensity factors of two collinear unequal length cracks in a typical rock mass under unloading conditions was calculated based on the superposition principle and fracture mechanics to determine the meso-influence law of intermittent joint interaction in the slope under the action of excavation. The effects of many factors on this interaction were also analyzed theoretically. Unloading tests were conducted on rock-like specimens with two collinear unequal length cracks in addition to numerical simulation and theoretical analysis. The results show decreased interaction between the two cracks with increased crack distance, increased influence of the main crack on a secondary crack with increased length of the main crack, and decreased influence of the secondary crack on the main crack with decreased length of the secondary crack. Wing tensile cracks first appear at the tip of flaws, and the propagation of these cracks occurs with the generation of secondary tensile cracks and shear cracks during unloading. Propagation and coalescence between cracks lead to tension and shear mixed failure of a rock bridge, and tensile cracks appear near the unloading surface. The axial initiation and peak stress of a crack increase with increased flaw distance, and the theoretical calculations were confirmed by lateral unloading test results.
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Abasova Inara. "DEVELOPMENT OF A PROCESS CONTROL SYSTEM FOR DYNAMIC SEDIMENT OF OIL EMULSION." World Science 1, no. 3(43) (March 31, 2019): 15–18. http://dx.doi.org/10.31435/rsglobal_ws/31032019/6399.
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Using heat balance and geometric features of horizontal cylindrical sedimentation, a new method and algorithm for controlling the dynamic sediment of emulsified water drops of oil emulsion have been developed. The mechanism of oil emulsion dynamic sediment on the proposed method is that the redistribution of the flow contributes to the cyclic change in the flow rate of the oil emulsion in the settling apparatus and the oscillatory motion (compression and expansion) of the intermediate emulsion layers, leading to the destruction of armoring casings, coalescence of emulsified water drops and transfer mechanical impurities into water cushion of the settling apparatus, as a result of which the quality of commercial oil increases (the content of water and mineral salts decrease in the prepared oil) and the risk of flooding the settling apparatus decreases. In the settling apparatus, where the volume of the oil emulsion is greater than the average value, the intermediate emulsion layer expands, the kinetic energy increases, and it increases the efficiency of collisions between the drops, leading to the destruction of the armoring casings and coalescence of the drops. When the volume is less than the average value, the intermediate emulsion layer is compressed, the distance between the drops decreases, leading to a coalescence of the drops and an increase in the efficiency of oil preparation.
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Barker, Daniel, and Martin Landrø. "An alternative method for modeling close-range interactions between air guns." GEOPHYSICS 79, no. 2 (March 1, 2014): P1—P7. http://dx.doi.org/10.1190/geo2013-0141.1.
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We evaluated the problem of modeling the decay of the primary pulse amplitudes of air-gun clusters caused by the traditional assumption of sphericality. This was done by generalizing the Rayleigh equation to work with arbitrary bubble shapes, while retaining the assumption of incompressibility. To approximate the coalescence of the bubbles, we let the shapes be isosurfaces of the velocity potential. With this method, it is possible to model the firing of clustered air guns at any separation distance, including small distances that would cause two spherical bubbles to overlap. In this way, we obtained results matching the relative decay shown to be present for air-gun clusters. In addition, this method also allowed a way of calibrating the model such that effects created by the presence of the gun, compared to just a single spherical air bubble, may be estimated and included.
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Cai, Minglei, Tedi Kujofsa, Xinkang Chen, Md Tanvirul Islam, and John E. Ayers. "Interaction Length for Dislocations in Compositionally-Graded Heterostructures." International Journal of High Speed Electronics and Systems 27, no. 03n04 (September 2018): 1840022. http://dx.doi.org/10.1142/s0129156418400220.
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Several simple models have been developed for the threading dislocation behavior in heteroepitaxial semiconductor materials. Tachikawa and Yamaguchi [Appl. Phys. Lett., 56, 484 (1990)] and Romanov et al. [Appl. Phys. Lett., 69, 3342 (1996)] described models for the annihilation and coalescence of threading dislocations in uniform-composition layers, and Kujofsa et al. [J. Electron. Mater., 41, 2993 (2013)] extended the annihilation and coalescence model to compositionally-graded and multilayered structures by including the misfit dislocation-threading dislocation interactions. However, an important limitation of these previous models is that they involve empirical parameters. The goal of this work is to develop a predictive model for annihilation and coalescence of threading dislocations which is based on the dislocation interaction length Lint. In the first case if only in-plane glide is considered the interaction length is equal to the length of misfit dislocation segments while in the second case glide and climb are considered and the interaction length is a function of the distance from the interface, the length of misfit dislocations, and the density of the misfit dislocations. In either case the interaction length may be calculated using a model for dislocation flow. Knowledge of the dislocation interaction length allows predictive calculations of the threading dislocation densities in metamorphic device structures and is of great practical importance. Here we demonstrate the latter model based on glide and climb. Future work should compare the two models to determine which is more relevant to typical device heterostructures.
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Islam, Md Tanvirul, Xinkang Chen, Tedi Kujofsa, and John E. Ayers. "Threading Dislocations in Metamorphic Semiconductor Buffer Layers Containing Chirped Superlattices." International Journal of High Speed Electronics and Systems 27, no. 03n04 (September 2018): 1840028. http://dx.doi.org/10.1142/s0129156418400281.
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Metamorphic realization of semiconductor devices has become increasingly important due to the great freedom it affords in layer compositions and thicknesses. However, metamorphic growth is often accompanied by the introduction of high densities of threading dislocation defects. This behavior may be understood by using an annihilation and coalescence model for the threading dislocation behavior which is based on the dislocation interaction length Lint. For its application we considered only glide of dislocations, so the interaction length was assumed to be equal to the length of misfit dislocation segments LMD. The length of misfit segments was determined approximately by the Matthews, Mader, and Light model [J. Appl. Phys., 41, 3800 (1970)] for lattice relaxation, and was assumed to be independent of the distance from the interface. Within this framework we have applied the annihilation and coalescence model to chirped semiconductor superlattices to evaluate these superlattices as strainrelaxed buffers for metamorphic devices. In this work we have studied two basic types of InGaAs/GaAs chirped superlattice buffers: type I superlattices are compositionally modulated while type II superlattices are thickness modulated.
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Nath, A., and A. Khare. "Transient evolution of multiple bubbles in laser induced breakdown in water." Laser and Particle Beams 29, no. 1 (December 22, 2010): 1–9. http://dx.doi.org/10.1017/s0263034610000662.
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AbstractPulsed laser induced plasma in water produces multiple bubbles with the passage of laser pulse. Shadowgraphy and beam deflection set-up is used to study the temporal and spatial evolution of these bubbles as a function of distance from the laser focus. The formation of multiple bubbles, bubble coalescence, and their effect onto cavity dynamics is reported. Bubble radius and the corresponding velocities from shadowgraphy is used to calculate the maximum gas pressure inside the bubble using Neppiras model. The maximum pressure inside the cavity is found to be 0.4 MPa at the laser focus.
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Bense, Alexandre, Mathieu Lizee, Thibault Guillet, and Guilhem Gallot. "Spatial distribution of air bubbles created by an imping water jet into a free water surface." Emergent Scientist 6 (2022): 3. http://dx.doi.org/10.1051/emsci/2022001.
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In this paper we study the rise to the surface, radial motion and disappearance of the bubbles created by a water jet pouring into a container, in particular their density at the surface as a function of the impact velocity. We first focus on their emergence radius at the surface which follows a log-normal distribution. Next, we establish experimentally a law relating the bubble velocity to the distance to the jet. We also investigate their disappearance, caused at low density mainly by explosion, and at high density predominantly by coalescence. Finally, we build an accurate model for the density of bubbles.
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Anjos, Gustavo R. "Numerical Investigation of Two-Phase Flows in Corrugated Channel with Single and Multiples Drops." Fluids 6, no. 1 (December 31, 2020): 13. http://dx.doi.org/10.3390/fluids6010013.
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This work aims at investigating numerically the effects of channel corrugation in two-phase flows with single and multiples drops subject to buoyancy-driven motion. A state-of-the-art model is employed to accurately compute the dynamics of the drop’s interface deformation using a modern moving frame/moving mesh technique within the arbitrary Lagrangian–Eulerian framework, which allows one to simulate very large domains. The results reveal a complex and interesting dynamics when more than one drop is present in the system, leading eventually in coalescence due to the amplitude of the corrugated sinusoidal channel and distance between drops.
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Kumar, M. S. N., D. Arzoumanian, A. Men’shchikov, P. Palmeirim, M. Matsumura, and S. Inutsuka. "Filament coalescence and hub structure in Mon R2." Astronomy & Astrophysics 658 (February 2022): A114. http://dx.doi.org/10.1051/0004-6361/202140363.
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There is growing evidence of the role of hub-filament systems (HFS) in the formation of stars from low to high masses. As of today, however, the detailed structures of these systems are still not well described. Here we study the Mon R2 star-forming region, which has a rich network of filaments joining in a star cluster forming hub, and aim to understand the hub structure and to examine the mass fraction residing in the hub and in the filaments, which is a key factor that influences massive star formation. We conducted a multi-scale, multi-component analysis of the Herschel column density maps (resolution of 18.2′′ or ~0.07 pc at 830 pc) of the region using a newly developed algorithm getsf to identify the structural components, namely, extended cloud, filaments, and sources. We find that cascades of lower column density filaments coalesce to form higher-density filaments eventually merging inside the hub (0.8 pc radius). As opposed to the previous view of the hub as a massive clump with ~1 pc radius, we find it to be a network of short high-density filaments. We analyse the orientations and mass per unit length (M∕L) of the filaments as a function of distance from the hub centre. The filaments are radially aligned towards the centre of the hub. The total mass reservoir in the Mon R2 HFS (5 pc × 5 pc) is split between filaments (54%), an extended cloud (37%), and sources (9%). The M∕L of filaments increases from ~10 M⊙ pc−1 at 1.5 pc from the hub to ~100 M⊙ pc−1 at its centre, while the number of filaments per annulus of 0.2 pc width decreases from 20 to two in the same range. The observed radial column density structure of the HFS (filament component only) displays a power-law dependence of NH2 ∝ r−2.17 up to a radius of ~2.5 pc from the central hub, resembling a global collapse of the HFS. We present a scenario where the HFS can be supported by magnetic fields which interact, merge, and reorganise themselves as the filaments coalesce. We plotted the plane-of-the-sky magnetic field line geometry using archival Planck data to support our scenario. In the new view of the hub as a network of high-density filaments, we suggest that only the stars located in the network can benefit from the longitudinal flows of gas to become massive, which may explain the reason for the formation of many low-mass stars in cluster centres. We show the correlation of massive stars in the region to the intertwined network-like hub, based on which we updated the implications of the filaments to clusters (F2C) model for massive star formation.
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Nath, Saurabh, S. Farzad Ahmadi, Hope A. Gruszewski, Stuti Budhiraja, Caitlin E. Bisbano, Sunghwan Jung, David G. Schmale, and Jonathan B. Boreyko. "‘Sneezing’ plants: pathogen transport via jumping-droplet condensation." Journal of The Royal Society Interface 16, no. 155 (June 2019): 20190243. http://dx.doi.org/10.1098/rsif.2019.0243.
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We show that condensation growing on wheat leaves infected with the leaf rust fungus, Puccinia triticina , is capable of spontaneously launching urediniospores off the plant. This surprising liberation mechanism is enabled by the superhydrophobicity of wheat leaves, which promotes a jumping-droplet mode of condensation powered by the surface energy released from coalescence events. We found that urediniospores often adhere to the self-propelled condensate, resulting in liberation rates of approximately 10 cm −2 h −1 for leaves infected with rust. Urediniospores were catapulted up to 5 mm from the leaf’s surface, a distance sufficient to clear the laminar boundary layer for subsequent dispersal even in gentle winds.
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Shavlov, A. V., V. A. Dzhumandzhi, and E. S. Yakovenko. "Electrocoalescence of Water Droplets." Plasma 6, no. 1 (March 1, 2023): 127–38. http://dx.doi.org/10.3390/plasma6010011.
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An experimental setup has been created to study the electrocoalescence of submillimeter- and millimeter-sized water droplets on a hydrophobic dielectric surface. The dependences of the interdroplet distance on the droplet radius are studied. It is shown that drops on a hydrophobic surface exhibit patterns of spatial arrangement that are characteristic of drops of a droplet cluster and fog. The electric field strengths at which mass coalescence of droplets begin are measured. A new model of electrocoalescence based on the state diagram of a drop-ion plasma is proposed. The possible role of electrocoalescence in the problem of rapid rain formation in atmospheric clouds is discussed.
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Yuan, Junjie, Xin Ye, and Yanguang Shan. "Two-dimensional lattice Boltzmann method to study the influence of nucleation distance on heat flux during bubble coalescence." International Journal of Thermal Sciences 172 (February 2022): 107353. http://dx.doi.org/10.1016/j.ijthermalsci.2021.107353.
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Lu, Wenbin, Paz Beniamini, and Clément Bonnerot. "On the formation of GW190814." Monthly Notices of the Royal Astronomical Society 500, no. 2 (November 2, 2020): 1817–32. http://dx.doi.org/10.1093/mnras/staa3372.
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ABSTRACT The LIGO–Virgo collaboration recently reported a puzzling event, GW190814, with component masses of 23 and 2.6 M⊙. Motivated by the relatively small rate of such a coalescence (1–$23\rm \, Gpc^{-3}\, yr^{-1}$) and the fact that the mass of the secondary is close to the total mass of known binary neutron star (bNS) systems, we propose that GW190814 was a second-generation merger from a hierarchical triple system; i.e. the remnant from the bNS coalescence was able to merge again with the 23 M⊙ black hole (BH) tertiary. We show that this occurs at a sufficiently high probability provided that the semimajor axis of the outer orbit is less than a few au at the time of bNS coalescence. It remains to be explored whether the conditions for the formation of such tight triple systems are commonly realized in the Universe, especially in low-metallicity (≲0.1 Z⊙) environments. Our model provides a number of predictions. (1) The spin of the secondary in GW190814-like systems is 0.6–0.7. (2) The component mass distribution from a large sample of LIGO sources should have a narrow peak between 2.5 and ∼3.5 M⊙, whereas the range between ∼3.5 and ∼5 M⊙ stays empty (provided that stellar evolution does not generate such BHs in the ‘mass gap’). (3) About 90 per cent (10 per cent) of GW190814-like events have an eccentricity of e ≳ 2 × 10−3 (≳0.1) near gravitational wave frequency of $10\,$ mHz. (4) A significant fraction (${\gtrsim}10\, \rm {per\, cent}$) of bNS mergers should have signatures of a massive tertiary at a distance of a few au in the gravitational waveform. (5) There are 105 undetected radio-quiet bNS systems with a massive BH tertiary in the Milky Way.
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LAI, ANN, NICOLAS BREMOND, and HOWARD A. STONE. "Separation-driven coalescence of droplets: an analytical criterion for the approach to contact." Journal of Fluid Mechanics 632 (July 27, 2009): 97–107. http://dx.doi.org/10.1017/s0022112009007320.
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Recent microfluidic experiments by Bremond, Thiam & Bibette (Phys. Rev. Lett., vol. 100, 2008, paper no. 024501), along with simulations by Yoon et al. (Phys. Fluid, vol. 19, 2007, paper no. 102102) and near-contact experiments and simulations by Manica et al. (Langmuir, vol. 24, 2008, pp. 1381–1390), have demonstrated that two droplets can coalesce as they are separating rather than upon their collision. We analyse the experimental microfluidic flow configuration for the approach to contact with a two-dimensional model: we apply a lubrication analysis followed by the method of domain perturbation to determine the droplet deformation as a function of time. We find the approximate shape for the deformed droplet at the time of contact. In particular, for droplets of radius R, moving apart according to h0(t) = h0(0) + αt2, where 2h0(t) is the separation distance, we define a non-dimensional parameter A=4CμR2α1/2/πγ[h0(0)]3/2, where μ is the viscosity of the continuous phase; γ is the interfacial tension; and C depends on the viscosity ratio between the droplets and the continuous phase. Our model suggests that there exists a critical value Acrit = 16/33/2 ≈ 3.0792, below which separation is unlikely to facilitate the coalescence of the droplets. The predictions are in good agreement with available experimental data.
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Ababou, Y., P. Desjardins, R. A. Masut, A. Yelon, and G. L'Espérance. "Metalorganic vapor phase epitaxy and structural characterization of InP on Si(111)." Canadian Journal of Physics 74, S1 (December 1, 1996): 108–11. http://dx.doi.org/10.1139/p96-843.
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We report the growth of InP layers using low-pressure metalorganic vapor phase epitaxy on buffered HF-treated Si(111) surfaces, both normally oriented and 3.8° off, toward [Formula: see text]. The InP layers grown on normally oriented Si(111) show the presence of roughly regular terraces, which may be associated with antiphase domains, whose width increases rapidly with the epilayer thickness. The average dislocation density at the top surface is as low as 4 × 105 cm−2 for 4.8 μm thick epilayers. Transmission electron microscopy observations show a rapid decrease of threading dislocation densities with increasing distance from the interface, due principally to their coalescence, as determined from X-ray diffraction analysis. This indicates a high reaction constant between dislocations, of 1.8 × 10−5 cm.
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Xu, C., and X. Wu. "The Equations of Motion for Binary Systems with Relativistic Quadrupole-Quadrupole Moments Interaction." Symposium - International Astronomical Union 188 (1998): 346–47. http://dx.doi.org/10.1017/s0074180900115463.
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The study of binary systems is one of the most important problems in astronomy. Especially recently, gravitational wave detection made possible by Laser Interferometer Gravitational wave Observatory - LIGO and VIRGO, LISA opens up a completely new window for the observation of our universe, it becomes one of the most important and forward area in the modern general relativistic astrophysics. Coalescing binary neutron star (NS) systems are believed to be the most important source emitted high-frequency gravitational wave. Therefore the study of NS coalescence is regarded as a major challenge in modern relativistic astrophysics. Indeed, if the two-body problem could be solved with a sufficient accuracy, the wealth of information might be extracted from the waveforms of coalescing binaries. Many early works to derive and investigate the gravitational two-body system with spin and quadrupole moment interaction have been done already. A detail appraisal of their works has been made by Xu, Wu and Schäfer where they derived the first post-Newtonian equations of motion for binary systems with monopole, spin and quadrupole interaction by making use of the scheme developed by Damour, Soffel and Xu (DSX)As we know, in the last stages of coalescence in binary system, the distance between two stars is closer, the tidal force is stronger, so the nonspherical size l is larger, l2/r2 can reach the level of v2/c2, where r is the distance between two bodies. In this case, the relativistic qudrupole-quadrupole term is of 3-PN order, so one can not neglect the 1-PN contribution of the q-q terms when 3-PN equations of motion (for mass-monopole) are considered. In order to fit the requirement of more accurate solution for binary system, the relativistic q-q terms in the post Newtonian equation of motion have been calculated in this paper. Our work is the first to obtain explicit 1-PN equations of motion for binary systems with relativistic quadrupole-quadrupole interaction in terms of only collective coordinates and B-D moments.
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Yang, Weidong, Zhiguo Luo, Nannan Zhao, and Zongshu Zou. "Numerical Analysis of Effect of Initial Bubble Size on Captured Bubble Distribution in Steel Continuous Casting Using Euler-Lagrange Approach Considering Bubble Coalescence and Breakup." Metals 10, no. 9 (August 27, 2020): 1160. http://dx.doi.org/10.3390/met10091160.
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A mathematic model considering the bubble coalescence and breakup using the Euler-Lagrange approach has been developed to study the effect of the initial bubble size on the distribution of bubbles captured by the solidification shell. A hard sphere model was applied for dealing with the bubble collision. Advanced bubble coalescence and breakup models suitable for the continuous casting system and an advanced bubble captured criteria have been identified established with the help of user-defined functions of FLUENT. The predictions of bubble behavior and captured bubble distribution agree with the water model and plant measurements well respectively. The results show that the number of small bubbles captured by solidification shell is much higher than that of large bubbles. What is more, the number of captured bubbles at the sidewalls decreases with the distance from the meniscus. For the case of large gas flow rate (gas flow fraction of 8.2%), the initial size of bubbles has little effect on bubble captured distribution under various casting speeds. When the gas flow rate is small (gas flow fraction of 4.1%), the number density of captured bubbles increases as the initial bubble size increases, and the effect of initial bubbles size on captured bubble number density is amplified when the casting speed decreases. The average captured bubble diameter is about 0.12–0.14 mm. Additionally, for all cases, the initial bubble size hardly affects the average size of captured bubbles.
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Qiu, Ren-Zheng, Yi-Chen Lin, and Te-Hua Fang. "Fatigue crack growth characteristics of Fe and Ni under cyclic loading using a quasi-continuum method." Beilstein Journal of Nanotechnology 9 (March 27, 2018): 1000–1014. http://dx.doi.org/10.3762/bjnano.9.93.
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A quasi-continuum (QC) method based on the embedded atom method (EAM) potential was employed to investigate the fatigue crack growth and expansion characteristics of single-crystal Fe and Ni under cyclic loading modes I and II. In particular, the crack growth and expansion characteristics of Fe and Ni under cyclic loading were evaluated in terms of atomic stress fields and force–distance curves. The simulation results indicated that under cyclic loading, the initially damaged area of the crack will coalesce again after compression or shear to the initial geometry leading to a strengthening of the material. If no coalescence appears, the crack spreads rapidly and the material breaks. Moreover, under the cyclic loading of shear at any orientation, the slip dislocation observed in the materials considerably affects the release of stress.
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Drissi-Habti, Monssef, Das Raj-Jiyoti, Soumianarayanan Vijayaraghavan, and Ech-Cheikh Fouad. "Numerical Simulation for Void Coalescence (Water Treeing) in XLPE Insulation of Submarine Composite Power Cables." Energies 13, no. 20 (October 19, 2020): 5472. http://dx.doi.org/10.3390/en13205472.
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Due to the growing demand for offshore renewable energy, the development of durable submarine power cables is critical. Submarine power cables are expected to have a service life of over 20 years. However, it has been shown that these cables suffer from water-tree flaws that progressively extend to conductors and corrode copper, which may lead to premature failure. Water treeing is caused by the of interconnection of voids (of a few nanometers) that are present in the insulator after manufacturing or formed during operation. The economic consequences of a breakdown can be drastic due to the heavy maintenance required. In the current study, the insulator is modelled as cubic unit cells containing water voids in the form of ellipsoids. The displacement field of ellipsoids is found to be dependent on its distribution in the cubic cell and on the applied electric field. Von Mises stress and effective plastic strain at the tips of the ellipsoid are found to be significant when either the relative distance between the two ellipsoids is short or the applied electric field is high. The proposed model is intended to provide insights into the ageing of cross-linked polyethylene (XPLE), which is extremely difficult to predict experimentally due to the excessive time needed to achieve coalescence of voids.
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Hardalupas, Y., and J. H. Whitelaw. "Interaction Between Sprays From Multiple Coaxial Airblast Atomizers." Journal of Fluids Engineering 118, no. 4 (December 1, 1996): 762–71. http://dx.doi.org/10.1115/1.2835507.
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Phase Doppler measurements of size, velocity, liquid flux, and average mass fractions were obtained in sprays produced by three identical coaxial airblast atomizers, with their axes placed in a triangular arrangement at distances of two air jet diameters from each other; the arrangement simulates the spray interaction in the preburner of the space shuttle main engine with water and air respectively replacing the liquid oxygen and hydrogen of the preburner sprays. Each nozzle comprised a liquid jet with exit diameter of 2.3 mm centred in a 8.95 mm diameter air stream. Two liquid flowrates were examined, while the air flowrate was kept constant, resulting in Weber number at the exit of the nozzle around 1100, air-to-liquid momentum ratio 8.6 and 38, velocity ratio 24 and 51, mass flowrate ratio 0.35 and 0.75, liquid jet Reynolds number 10,000 and 21,000 and air jet Reynolds number around 108,000. The air flow characteristics were compared to the flow without liquid injection. Up to 10 air jet diameters from the nozzle exit, individual spray characteristics dominated and maximum Sauter mean diameters, typically around 150 μm, and liquid flux were observed on the geometrical axes of the nozzles. Spray merging was strong in the region between the nozzle axes, where the Sauter mean diameter reduced and the liquid flux and the mean and rms of the fluctuations of the axial velocity of the droplets and the air flow increased relative to the single spray. Downstream of 25 air jet diameters from the nozzle exit, the multiple sprays merged to a single spray-like flow produced by a nozzle located at the centre of the triangular region between the nozzle axes. Reduction of the liquid flowrate by 50 percent, improved atomization by 25 percent, shortened the axial distance from the nozzles where the individual spray characteristics disappeared by 30 percent and increased the air flow turbulence by 20 percent. Droplet coalescence was negligible for high liquid flowrates, but for reduced liquid flowrates coalescence became important and the Sauter mean diameter increased with the axial distance from the exit by around 15 percent. Spray merging increased the air flow turbulence and the local mass fraction distribution of the air in the region between the nozzle axes by around 50 and 40 percent respectively relative to the single sprays, resulting in a fuel rich region with increased gas flow turbulence which may influence the ignition process in the preburner of the space shuttle main engine.
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Liu, Meng, and Yufeng Duan. "Predicting the Liquid Film Thickness and Droplet–Gas Flow in Effervescent Atomization: Influence of Operating Conditions and Fluid Viscosity." International Journal of Chemical Reactor Engineering 11, no. 1 (September 10, 2013): 393–405. http://dx.doi.org/10.1515/ijcre-2013-0073.
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Abstract The droplet–gas flow in effervescent atomization was simulated using a comprehensive numerical model. Liquid film thicknesses in the nozzle exit orifice and droplet size distribution at the downstream of spray were calculated. The thickness of liquid film in the nozzle exit orifice increased and approached the droplet size in the primary atomization, as the air–liquid ratio increased. The primary breakup model can accurately predict the Sauter mean diameter in the primary atomization when gas–liquid two-phase flow belongs to the annular flow in the nozzle exit orifice. The viscosity of fluid had minimal influence on the liquid film thickness for spray with fluids, the viscosity of which is significantly greater than that of water. Droplet size initially decreased and then increased along the axial distance because of the secondary atomization and droplet coalescence at the downstream of spray.
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Goulpeau, Arnaud, Benoit Penel, Marie-Eugénie Maggia, Daniel Fernández Marchán, Dirk Steinke, Mickaël Hedde, and Thibaud Decaëns. "OTU Delimitation with Earthworm DNA Barcodes: A Comparison of Methods." Diversity 14, no. 10 (October 13, 2022): 866. http://dx.doi.org/10.3390/d14100866.
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Although DNA barcodes-based operational taxonomic units (OTUs) are increasingly used in earthworm research, the relative efficiency of the different methods available to delimit them has not yet been tested on a comprehensive dataset. For this study, we used three datasets containing 651, 2304 and 4773 COI barcodes of earthworms from French Guiana, respectively, to compare five of these methods: two phylogenetic methods—namely Poisson Tree Processes (PTP) and General Mixed Yule Coalescence (GMYC)—and three distance matrix methods—namely Refined Single Linkage (RESL, used for assigning Barcode Index Numbers in the Barcode of Life Data systems), Automatic Barcode Gap Discovery (ABGD), and Assemble Species by Automatic Partitioning (ASAP). We found that phylogenetic approaches are less suitable for delineating OTUs from DNA barcodes in earthworms, especially for large sets of sequences. The computation times are unreasonable, they often fail to converge, and they also show a strong tendency to oversplit species. Among distance-based methods, RESL also has a clear tendency to oversplitting, while ABGD and ASAP are less prone to mismatches and have short computation times. ASAP requires less a priori knowledge for model parameterisation than AGBD, provides efficient graphical outputs, and has a much lower tendency to generate mismatches.
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Li, Chunyuan, and Victor Zakkay. "Hydrodynamics and Erosion Modeling of Fluidized Bed Combustors." Journal of Fluids Engineering 116, no. 4 (December 1, 1994): 746–55. http://dx.doi.org/10.1115/1.2911845.
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Hydrodynamics and erosion of Fluidized Bed Combustors (FBCs) containing tubes have been analyzed through the use of the hydrodynamic model, which has been developed at New York University, utilizing a CRAY Y-MP/832 supercomputer and a CONVEX C210 minisupercomputer. Particle velocity fields and bed dynamics including bubble formation and motion and bed expansion and collapse were analyzed for high pressure cold and hot beds. The cold beds were studied by (a) optimizing tube models for simulating a circular tube, (b) varying the distance from distributor plate to the tubes, (c) changing tube size, and (d) using vertical tubes. Atmospheric and pressurized fluidized bed combustors were also simulated and compared to each other for bubble size, bubble frequencies, particle jets, and tube erosion. In particular, the computation revealed bubble coalescence which causes high particle jets. Threshold velocity has been analyzed utilizing Hertz contact theory and the maximum shear theory (Tresca). Tube erosion was predicted utilizing the Finnie erosion model and the modified Finnie model, which considers the threshold velocity and compared to each other. Computed results show that the distance from distributor to the tubes, tube size, tube orientation and operating pressure have significant effect on bed dynamics and tube erosion. The threshold velocity is found to significantly influence the prediction of erosion.
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Driessen, Theo, Pascal Sleutel, Frits Dijksman, Roger Jeurissen, and Detlef Lohse. "Control of jet breakup by a superposition of two Rayleigh–Plateau-unstable modes." Journal of Fluid Mechanics 749 (May 16, 2014): 275–96. http://dx.doi.org/10.1017/jfm.2014.178.
Full textAbstract:
AbstractWe experimentally, numerically and theoretically demonstrate a novel method of producing a stream of widely spaced high-velocity droplets by imposing a superposition of two Rayleigh–Plateau-unstable modes on a liquid jet. The wavelengths of the two modes are chosen close to the wavelength of the most unstable mode. The interference pattern of the two superimposed modes causes local asymmetries in the capillary tension. The velocity of the initial droplets depends on these local asymmetries. Due to their different velocities, the droplets coalesce to produce a stream of larger droplets spaced at a much larger distance than the initial droplets. We analytically derive the perturbations that robustly induce this process and investigate the influence of the nonlinear interactions of the two Rayleigh–Plateau-unstable modes on the coalescence process. Experiments and numerical simulations demonstrate that the jet breakup and the subsequent droplet merging are fully governed by the selected modes.
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Lu, Sheng-You, Ching-I. Peng, Yu-Ping Cheng, Kuo-Hsiang Hong, and Tzen-Yuh Chiang. "Chloroplast DNA phylogeography of Cunninghamia konishii (Cupressaceae), an endemic conifer of Taiwan." Genome 44, no. 5 (October 1, 2001): 797–807. http://dx.doi.org/10.1139/g01-074.
Full textAbstract:
In this study, we investigated the genetic structure and phylogeographic pattern of the genus Cunninghamia, a member of the Cupressaceae restricted to mainland China and Taiwan, based on sequences of the trnDtrnT noncoding spacer of the chloroplast DNA. Maternal inheritance of chloroplasts was determined experimentally. No paternal leakage was detected. Both parsimony and neighbor-joining analyses revealed the polyphyly of Cunninghamia konishii, populations of which were nested in clades of C. lanceolata from mainland China. The nucleotide diversity of chloroplast DNA sequences within C. konishii (0.0118) was higher than that between species (0.0104), which agrees with a previous allozyme investigation. Based on mutational differences between sequences, a minimum spanning network consisting of five clades was constructed. Significant genetic differentiation (ΦST = 0.130, P < 0.001) was detected between the clades based on AMOVA analyses. We infer several possible refugia in the Yunnan, Zhejiang, and Guangdong provinces of south China, all located in the minimum network as interior nodes. We also infer possible migration routes of Cunninghamia populations. The phylogeographic pattern shown in the reconstructed network suggests that the present-day Cunninghamia populations in Taiwan were derived from six different sources in continental Asia via long-distance seed dispersal. A migrant-pool model explains the heterogeneous composition of the organelle DNA in Taiwan's populations and the low differentiation between populations of Taiwan and China (ΦCT = 0.012, P = 0.454). In contrast with the genetic heterogeneity within geographic populations, many local populations have attained coalescence at the trnDtrnT alleles, which has led to significant differentiation at the population level.Key words: AMOVA, coalescence, cpDNA, Cunninghamia konishii, Cunninghamia lanceolata, minimum spanning network, phylogeography.
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Williams, Christopher R. "Reflectivity and Liquid Water Content Vertical Decomposition Diagrams to Diagnose Vertical Evolution of Raindrop Size Distributions." Journal of Atmospheric and Oceanic Technology 33, no. 3 (March 2016): 579–95. http://dx.doi.org/10.1175/jtech-d-15-0208.1.
Full textAbstract:
AbstractThis study consists of two parts. The first part describes the way in which vertical air motions and raindrop size distributions (DSDs) were retrieved from 449-MHz and 2.835-GHz (UHF and S band) vertically pointing radars (VPRs) deployed side by side during the Midlatitude Continental Convective Clouds Experiment (MC3E) held in northern Oklahoma. The 449-MHz VPR can measure both vertical air motion and raindrop motion. The S-band VPR can measure only raindrop motion. These differences in VPR sensitivities facilitates the identification of two peaks in 449-MHz VPR reflectivity-weighted Doppler velocity spectra and the retrieval of vertical air motion and DSD parameters from near the surface to just below the melting layer.The second part of this study used the retrieved DSD parameters to decompose reflectivity and liquid water content (LWC) into two terms, one representing number concentration and the other representing DSD shape. Reflectivity and LWC vertical decomposition diagrams (Z-VDDs and LWC-VDDs, respectively) are introduced to highlight interactions between raindrop number and DSD shape in the vertical column. Analysis of Z-VDDs provides indirect measure of microphysical processes through radar reflectivity. Analysis of LWC-VDDs provides direct investigation of microphysical processes in the vertical column, including net raindrop evaporation or accretion and net raindrop breakup or coalescence. During a stratiform rain event (20 May 2011), LWC-VDDs exhibited signatures of net evaporation and net raindrop coalescence as the raindrops fell a distance of 2 km under a well-defined radar bright band. The LWC-VDD is a tool to characterize rain microphysics with quantities related to number-controlled and size-controlled processes.