Articles de revues : « Axial and radial growth »

1

Lohn, Andrew J., Kate J. Norris, Robert D. Cormia, Elane Coleman, Gary S. Tompa et Nobuhiko P. Kobayashi. « Effect of Doping on Nanowire Morphology during Plasma-assisted Chemical Vapor Deposition ». MRS Proceedings 1439 (2012) : 25–31. http://dx.doi.org/10.1557/opl.2012.941.

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ABSTRACTMorphologies of silicon nanowires grown by plasma-assisted metalorganic chemical vapor deposition were studied in the presence of various dopant precursors. The varied precursors affected the axial and radial growth rates over orders of magnitude where triethylborane showed the strongest enhancements for both axial and radial growth, and triethylarsenic and triethylantimony retarded axial growth. Native oxide thickness is also shown to depend strongly on doping condition resulting in increased oxide thicknesses for increased carrier concentration, using shifts in the measured binding energy of the silicon 2p3/2 state as a proxy for carrier concentration.

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Geelhaar, L., C. Chèze, W. M. Weber, R. Averbeck, H. Riechert, Th Kehagias, Ph Komninou, G. P. Dimitrakopulos et Th Karakostas. « Axial and radial growth of Ni-induced GaN nanowires ». Applied Physics Letters 91, n^o 9 (27 août 2007) : 093113. http://dx.doi.org/10.1063/1.2776979.

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Misra, R. K., A. R. Dexter et A. M. Alston. « Maximum axial and radial growth pressures of plant roots ». Plant and Soil 95, n^o 3 (octobre 1986) : 315–26. http://dx.doi.org/10.1007/bf02374612.

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Dubrovskii, Vladimir G. « Theory of MBE Growth of Nanowires on Reflecting Substrates ». Nanomaterials 12, n^o 2 (14 janvier 2022) : 253. http://dx.doi.org/10.3390/nano12020253.

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Selective area growth (SAG) of III-V nanowires (NWs) by molecular beam epitaxy (MBE) and related epitaxy techniques offer several advantages over growth on unpatterned substrates. Here, an analytic model for the total flux of group III atoms impinging NWs is presented, which accounts for specular re-emission from the mask surface and the shadowing effect in the absence of surface diffusion from the substrate. An expression is given for the shadowing length of NWs corresponding to the full shadowing of the mask. Axial and radial NW growths are considered in different stages, including the stage of purely axial growth, intermediate stage with radial growth, and asymptotic stage, where the NWs receive the maximum flux determined by the array pitch. The model provides good fits with the data obtained for different vapor–liquid–solid and catalyst-free III-V NWs.

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Ponsurya, P., Shahid Hussain, B. H. Abbas Shahul Hameed, R. Perumalsamy, R. Thirumamagal, M. Jayachandran et A. Ayeshamariam. « Studies on Growth Mechanism of Annealed Graphite Powder and Gas-Sensor Applications ». Materials Science Forum 832 (novembre 2015) : 102–9. http://dx.doi.org/10.4028/www.scientific.net/msf.832.102.

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High quality micro sheet rhombohedral graphite crystals were synthesized by Hummer method using compounds of MWCNT, K2S2O8and P2O5. The growth mechanisms were discussed by finite element simulation. The synthetic sheet rhombohedral graphite crystals showed a higher growth rate in radial direction than that in axial direction. Raman spectrum and Fourier transform infrared spectrum indicated that synthesized sheet rhombohedral Graphite had fewer crystal lattice distortions with no impurities. Finite element simulations indicated that the solvent metal convection field in the radial direction was stronger than that in the axial direction. As prepared graphite powder was annealed at 1350 oC to obtain diamond nanoparticles. The as-prepared products were exposed to formaldehyde gas.

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Prato, J., et B. Lakshminarayana. « Investigation of Compressor Rotor Wake Structure at Peak Pressure Rise Coefficient and Effects of Loading ». Journal of Turbomachinery 115, n^o 3 (1 juillet 1993) : 487–500. http://dx.doi.org/10.1115/1.2929279.

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This paper reports an experimental study of the three-dimensional characteristics of the mean velocity in the trailing-edge, near-wake, and far-wake regions of a highly loaded low-speed compressor rotor. The wake structure and decay characteristics are compared with the wake data in the same compressor with moderate loading. The experimental investigation was carried out using a rotating five-hole probe. The flow field was surveyed at various radial and axial locations downstream of the compressor rotor. Variations in the axial, tangential, and radial components of mean velocity at various axial and radial locations were derived from the data and compared with earlier data at lower loading to discern the effects of loading. It was found that the higher loading had the following effects: Higher total velocity defects were observed in the hub-wall region, increased wake growth rate in the tip region, faster decay of static pressure difference in the trailing-edge region, larger initial wake width in the trailing-edge region, increased rate of growth of the semi-wake width in the trailing-edge region, increased decay rate of radial velocity in the trailing-edge region, and decreased decay rate of the radial velocity in the far-wake region. Far wake properties were almost identical in both cases.

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NEMOTO, Keisuke, et Koou YAMAZAKI. « Allometric relationships between axial and radial stem growth in rice plants. » Japanese journal of crop science 58, n^o 1 (1989) : 55–59. http://dx.doi.org/10.1626/jcs.58.55.

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Arif, Omer, Valentina Zannier, Francesca Rossi, Daniele Ercolani, Fabio Beltram et Lucia Sorba. « Self-Catalyzed InSb/InAs Quantum Dot Nanowires ». Nanomaterials 11, n^o 1 (13 janvier 2021) : 179. http://dx.doi.org/10.3390/nano11010179.

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The nanowire platform offers great opportunities for improving the quality and range of applications of semiconductor quantum wells and dots. Here, we present the self-catalyzed growth of InAs/InSb/InAs axial heterostructured nanowires with a single defect-free InSb quantum dot, on Si substrates, by chemical beam epitaxy. A systematic variation of the growth parameters for the InAs top segment has been investigated and the resulting nanowire morphology analyzed. We found that the growth temperature strongly influences the axial and radial growth rates of the top InAs segment. As a consequence, we can reduce the InAs shell thickness around the InSb quantum dot by increasing the InAs growth temperature. Moreover, we observed that both axial and radial growth rates are enhanced by the As line pressure as long as the In droplet on the top of the nanowire is preserved. Finally, the time evolution of the diameter along the entire length of the nanowires allowed us to understand that there are two In diffusion paths contributing to the radial InAs growth and that the interplay of these two mechanisms together with the total length of the nanowires determine the final shape of the nanowires. This study provides insights in understanding the growth mechanisms of self-catalyzed InSb/InAs quantum dot nanowires, and our results can be extended also to the growth of other self-catalyzed heterostructured nanowires, providing useful guidelines for the realization of quantum structures with the desired morphology and properties.

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Cao, Bing Qiang, Hao Ming Wei, Xi Lun Hu et Hai Bo Gong. « Polar and Nonpolar ZnO Nanowire QWs Grown with PLD Using Nanowire Arrays with Tuning Density as Physical Templates ». Materials Science Forum 688 (juin 2011) : 207–12. http://dx.doi.org/10.4028/www.scientific.net/msf.688.207.

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The encountered difficulties that prevent ZnO nanowires from being used as light-emitters are p-type doping and quantum well (QW) integration. The growth of homogenous nanowire quantum wells is usually influenced by the shadowing effect associated with nanowire growth density. In this paper, based on the growth density control of nanowire array, a new two-step pulsed laser deposition (PLD) strategy was demonstrated to grow two kinds of ZnO nanowire QWs, e.g. radial nonpolar QW and axial polar QW. The growth-density control of ZnO nanowires was realised by introducing a wetting layer and adjusting the substrate-target distances. The structural and optical characterizations of these two kinds of nanowire QWs prove that the radial nanowire QWs are more homogenous than axial QWs, which also show better optical properties.

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Sherwood, Owen A., et Evan N. Edinger. « Ages and growth rates of some deep-sea gorgonian and antipatharian corals of Newfoundland and Labrador ». Canadian Journal of Fisheries and Aquatic Sciences 66, n^o 1 (janvier 2009) : 142–52. http://dx.doi.org/10.1139/f08-195.

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Using bomb-14C dating and growth ring counting methods, we calculate life spans and growth rates of six species of deep-sea corals collected at depths of between 400 and 900 m from the continental slope of Newfoundland and Labrador. Bamboo corals ( Acanella arbuscula , Keratoisis ornata ) and antipatharians ( Stauropathes arctica ) secrete concentric growth rings in their axial skeletons, which were proven to form annually for K. ornata and S. arctica. These species had the lowest radial growth rates of 33 ± 11 to 75 ± 11 μm·year–1. Primnoa resedaeformis and Paramuricea spp. had higher radial growth rates of 83 ± 6 to 215 ± 37 μm·year–1. Paragorgia arborea had the highest radial growth rate of 830 ± 120 μm·year–1. Axial growth rates ranged from 0.56 ± 0.05 cm·year–1 for a specimen of Paramuricea spp. to 2.61 ± 0.45 cm·year–1 for a specimen of Primnoa resedaeformis . Life spans ranged from 18 ± 4 years for a live-collected P. resedaeformis to 200 ± 30 years for a subfossil specimen of K. ornata. Because all of the corals were from heavily fished areas, it is likely that age distributions are biased towards smaller and younger colonies. Recovery of deep-sea corals from fishing-induced damage will take decades to centuries.

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Wilczek, Anna B., Muhammad Iqbal, Wieslaw Wloch et Marcin Klisz. « Geometric analysis of intrusive growth of wood fibres in Robinia pseudoacacia ». IAWA Journal 39, n^o 2 (13 juin 2018) : 191–208. http://dx.doi.org/10.1163/22941932-20170204.

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ABSTRACTAll cell types of the secondary xylem arise from the meristematic cells (initials) of the vascular cambium and grow under mechanical constraints emerging from the circular-symmetrical geometry that characterises many tree trunks. The course of intrusive growth of cambial initials has been elucidated, but is yet to be described in the case of xylem fibres. This study explains the geometry of intrusive growth of the secondary xylem fibres in the trunk ofRobinia pseudoacacia.Long series of serial semi-thin sections of the vascular cambium and the differentiating secondary xylem were analysed. Since fibres grow in close vicinity to expanding cells of the derivatives of the vascular cambium, we assumed that they have similar growth conditions. Dealing with the cylindrical tissue of the vascular cambium in a previous study, we used a circularly symmetrical equation for describing the growth mechanism of cambial initials. Like the cambial initials, some of the cambial derivatives differentiating into the various cell types composing the secondary xylem also exhibit intrusive growth between the tangential walls of adjacent cells. As seen in cross sections of the cambium, intrusively growing initials form slanted walls by a gradual transformation of tangential (periclinal) walls into radial (anticlinal) walls. Similarly, the intrusive growth of xylem fibres manifests initially as slants, which are formed due to axial growth of the growing cell tips along the tangential walls of adjacent cells. During this process, the tangential walls of adjacent cells are partly separated and dislocated from the tangential plane. The final shape of xylem fibres, or that of vessel elements and axial parenchyma cells, depends upon the ratio of their intrusiveversussymplastic growths in the axial, circumferential and radial directions.

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Borgström, Magnus T., Jesper Wallentin, Johanna Trägårdh, Peter Ramvall, Martin Ek, L. Reine Wallenberg, Lars Samuelson et Knut Deppert. « In situ etching for total control over axial and radial nanowire growth ». Nano Research 3, n^o 4 (20 mars 2010) : 264–70. http://dx.doi.org/10.1007/s12274-010-1029-x.

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Plante, Martin C., et Ray R. LaPierre. « Analytical description of the metal-assisted growth of III–V nanowires : Axial and radial growths ». Journal of Applied Physics 105, n^o 11 (juin 2009) : 114304. http://dx.doi.org/10.1063/1.3131676.

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Shwartz, Nataliya L., Alla G. Nastovjak et Igor G. Neizvestny. « Peculiarities of axial and radial Ge–Si heterojunction formation in nanowires : Monte Carlo simulation ». Pure and Applied Chemistry 84, n^o 12 (27 mai 2012) : 2619–28. http://dx.doi.org/10.1351/pac-con-11-12-05.

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The process of axial and radial Si–Ge heterostructure formation during nanowire growth by vapor–liquid–solid (VLS) mechanism was studied using Monte Carlo (MC) simulation. It was demonstrated that radial growth can be stimulated by adding chemical species that decrease the activation energy of precursor dissociation or the solubility of semiconductor material in catalyst drop. Reducing the Si adatom diffusion length also leads to Si shell formation around the Ge core. The influence of growth conditions on the composition and abruptness of axial Ge–Si heterostructures was analyzed. The composition of the GexSi1–x axial heterojunction (HJ) was found to be dependent on the flux ratio, the duration of Si and Ge deposition, and the catalyst drop diameter. Maximal Ge concentration in the HJ is dependent on Ge deposition time owing to gradual changing of catalyst drop composition after switching Ge and Si fluxes. The dependence of junction abruptness on the nanowire diameter was revealed: in the adsorption-induced growth mode, the abruptness decreased with diameter, and in the diffusion-induced mode it increased. This implies that abrupt Ge–Si HJ in nanowires with small diameter can be obtained only in the chemical vapor deposition (CVD) process with negligible diffusion component of growth.

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Liu, Shi Biao, Ke Lu Wang, Shi Qiang Lu, Xin Li et Xian Juan Dong. « Feed Speed Design and Optimization in Radial-Axial Ring Rolling Process by FEM ». Advanced Materials Research 421 (décembre 2011) : 513–21. http://dx.doi.org/10.4028/www.scientific.net/amr.421.513.

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Radial-axial ring rolling is an important component of advanced manufacturing technology, but it has characteristics of high nonlinear on geometry and physics, so the radial-axial ring rolling process becomes very complex. In addition, the feeding mode of core roller has enormous influence on the quality of the rolled ring as well as the stability of the process. In this paper, a 3D rigid-plastic FE model of radial-axial ring rolling process is established, then three kinds of feed speed design ((1)constant of feed speed; (2)constant of feed in one rotary; (3)variation of feed speed)are offered. The difference of outer radius growth velocity, distribution of effective strain and temperature, rolling force, size of ring are analysised for the three kinds of feed methods. And, an optimized feed method is proposed base on analytic results, the optimized feed method can improve the quality of formed ring, and decrease the requirement of ring rolling mill.

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Arif, Omer, Valentina Zannier, Vladimir G. Dubrovskii, Igor V. Shtrom, Francesca Rossi, Fabio Beltram et Lucia Sorba. « Growth of Self-Catalyzed InAs/InSb Axial Heterostructured Nanowires : Experiment and Theory ». Nanomaterials 10, n^o 3 (10 mars 2020) : 494. http://dx.doi.org/10.3390/nano10030494.

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The growth mechanisms of self-catalyzed InAs/InSb axial nanowire heterostructures are thoroughly investigated as a function of the In and Sb line pressures and growth time. Some interesting phenomena are observed and analyzed. In particular, the presence of In droplet on top of InSb segment is shown to be essential for forming axial heterostructures in the self-catalyzed vapor-liquid-solid mode. Axial versus radial growth rates of InSb segment are investigated under different growth conditions and described within a dedicated model containing no free parameters. It is shown that widening of InSb segment with respect to InAs stem is controlled by the vapor-solid growth on the nanowire sidewalls rather than by the droplet swelling. The In droplet can even shrink smaller than the nanowire facet under Sb-rich conditions. These results shed more light on the growth mechanisms of self-catalyzed heterostructures and give clear route for engineering the morphology of InAs/InSb axial nanowire heterostructures for different applications.

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Rajput, Kishore S., et K. S. Rao. « SECONDARY GROWTH IN THE STEM OF SOME SPECIES OF ALTERNANTHERA AND ACHYRANTHES ASPERA (AMARANTHACEAE) ». IAWA Journal 21, n^o 4 (2000) : 417–24. http://dx.doi.org/10.1163/22941932-90000257.

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Secondary growth in Achyranthes aspera, Alternanthera polygamous, A. pungens, A. sessilis, and A. triandra was achieved by the development of a cambial variant resulting in successive rings of xylem and phloem. Each new cambium was developed at a distance about two to three cells external to the phloem produced by the previous cambium. The development of phloem was not synchronous in the species studied. Phloem development started either simultaneously with xylem or after the formation of a few xylem derivatives. In Achyranthes, xylem production started first followed by the development of phloem. Phloem mother cells differentiated into sieve tube elements, companion cells and axial parenchyma. Xylem was storied and exclusively composed of axial elements. Radial elements were absent in all the xylem rings of the stem. Vessels were angular and mostly solitary, but radial and tangential multiples were also observed occasionally. Xylem fibres were nonseptate and nucleated. Development of phloem and the rayless nature of the xylem is discussed.

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Jackson, A. D. « Stall Cell Development in an Axial Compressor ». Journal of Turbomachinery 109, n^o 4 (1 octobre 1987) : 492–98. http://dx.doi.org/10.1115/1.3262138.

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An experimental investigation of stall inception and stall cell development in a single-stage axial compressor is described. The stall inception was found to be naturally nonrandom: By artificially perturbing the flow the inception could be accurately fixed at a known location in the compressor. The stall cell was first detected behind the rotor at a small distance from the tip. The stall cell grew very rapidly in circumferential extent, but slowly in radial extent. After reaching the hub the cell decreased in size before reaching full development as a single full span rotating stall cell. Relationships between various parameters of the stall cell growth are presented. The growth is explained in terms of the cell blockage, and the mechanism for multiple stall inception is discussed.

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Chen, Shu Xian, Jia Dong Hou et Xiao Ming Tan. « Growth of Semi-Insulating GaAs Crystal with Uniform Si Doping ». Advanced Materials Research 1015 (août 2014) : 675–78. http://dx.doi.org/10.4028/www.scientific.net/amr.1015.675.

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An improved double crucible method of melt replenishing to counteract the dopant segregation effect in order to grow homogeneous doped GaAs crystals is brought forward, and its validity and feasibility are demonstrated by analytical and numerical study. The numerical results show that the new method can suppress the increase of dopant concentration near the growth interface and can maintain the homogeneity of dopant distribution along the radial direction. The positions of replenishing melt exit almost have no effects on the axial and radial distribution homogeneity of dopant Si in the crystal. So the new method has many distinct advantages: it can improve the crystallization rate and size, the operation is flexible, etc.

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Jiang, Bin, Xiangtong Shi, Qun Zheng, Qingfang Zhu, Zhongliang Chen et Zhitao Tian. « The Relationship of Spike Stall and Hub Corner Separation in Axial Compressor ». International Journal of Turbo & ; Jet-Engines 37, n^o 1 (26 mars 2020) : 1–16. http://dx.doi.org/10.1515/tjj-2016-0046.

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AbstractThe onset of spike stall induced by the interaction of hub corner separation flow with the tip leakage flow is investigated in detail by numerical method in this paper. The time resolved results indicate that the remarkable radial secondary flow from hub to tip near the trailing edge is formed when the compressor approaching rotating stall. The radial secondary flow is unstable and cross-passages propagates, which flows in and away out of the tip region periodically. The disturbance caused by radial secondary flow will influence the tip leakage flow directly by reforming the vortexes in blade tip region. A secondary vortex which comes from the radial migration of corner separation and is induced by the tip leakage vortex appears in the tip region. The simulation result demonstrates that the generation of the secondary vortex is an important symbol of blockage growth in the tip region at the stall inception phase. The disturbance produced by secondary vortex is an incentive of the leading edge overflow and the intensity of secondary vortex could be used as a criterion of rotating stall before leading edge spillage.

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DYSON, R. J., et O. E. JENSEN. « A fibre-reinforced fluid model of anisotropic plant cell growth ». Journal of Fluid Mechanics 655 (5 juillet 2010) : 472–503. http://dx.doi.org/10.1017/s002211201000100x.

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Many growing plant cells undergo rapid axial elongation with negligible radial expansion. Growth is driven by high internal turgor pressure causing viscous stretching of the cell wall, with embedded cellulose microfibrils providing the wall with strongly anisotropic properties. We present a theoretical model of a growing cell, representing the primary cell wall as a thin axisymmetric fibre-reinforced viscous sheet supported between rigid end plates. Asymptotic reduction of the governing equations, under simple sets of assumptions about the fibre and wall properties, yields variants of the traditional Lockhart equation, which relates the axial cell growth rate to the internal pressure. The model provides insights into the geometric and biomechanical parameters underlying bulk quantities such as wall extensibility, and shows how either dynamical changes in wall material properties or passive fibre reorientation may suppress cell elongation.

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Liu, Bin, Yanduo Fu, Luyao He, Hao Geng et Lijian Yang. « Weak Magnetic Internal Signal Characteristics of Pipe Welds under Internal Pressure ». Sensors 23, n^o 3 (19 janvier 2023) : 1147. http://dx.doi.org/10.3390/s23031147.

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Weak magnetic detection technology is an effective method to identify stress-induced damage to ferromagnetic materials, and it especially possesses great application potential in long-distance oil and gas pipeline weld crack detection. In the process of pipeline operation, due to internal pressure and external loads, local stress concentration may be generated, and partial stress concentration may lead to local cracks and expansion of the pipe. In order to improve the accuracy of magnetic signal analysis for ferromagnetic materials under internal pressure, the causes of magnetic signal generation at pipeline welds were analyzed from a microscopic perspective. The distributions of magnetic signals at pipeline welds, weld cracks, and base metal cracks under different internal pressures were numerically analyzed. The variation trends of magnetic signal characteristics, such as peak values of axial and radial components, gradient K, maximum gradient Kmax, and gradient energy factor S(K), were analyzed. In addition, experiments were carried out to verify the numerical data. It was revealed that with the elevation of internal pressure, the peak values of the axial and radial components, gradient K, maximum gradient Kmax, and gradient energy factor S(K) linearly increased. However, the magnitude and average change of S(K) were larger, which can more directly indicate variations of magnetic signals. The radial growth rate νy of S(K) was 3.24% higher than the axial growth rate νx, demonstrating that the radial component of the magnetic signal was more sensitive to variations of stress. This study provided a theoretical and experimental basis for detection of stress-induced damage to long-distance oil and gas pipelines.

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Ok Lim, Dong. « Spiral Growth in Cudrania Tricuspidata Caused by Liana Entwinement ». IAWA Journal 17, n^o 2 (1996) : 133–39. http://dx.doi.org/10.1163/22941932-90001442.

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The anatomy of Cudrania tricuspidata stemwood that grew spirally due to liana entwinement has been examined. In the first three years after entwinement by the liana (Pueraria thunbergiana) annual radial growth of the stemwood increased by 1.2 to 5.0 times . Thereafter the radial increment declined markedly as the liana continued to develop, producing abnormal growth in the tree stem. The wood of the liana-affected stem showed distinct differences in both cell orientation and anatomical characteristics compared with normal wood. In the first three year s after entwinement, the vessels became inclined to the stem axis. In later growth all the axial cells contributed to spiral grain angles up to 30° to the stem axis. Dimensions of vessels and fibres were also found to be affected. Physiological aspects of severe liana entwinement on the wood anatomy of the host stem are discussed.

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Halder, Nripendra N., Shimon Cohen, David Gershoni et Dan Ritter. « Growth of large diameter pure phase wurtzite GaP nanowires by a two-step axial-radial growth approach ». Applied Physics Letters 112, n^o 13 (26 mars 2018) : 133107. http://dx.doi.org/10.1063/1.5020425.

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Khine, Y. Y., et J. S. Walker. « Thermoelectrically Driven Melt Motion During Floating Zone Crystal Growth With an Axial Magnetic Field ». Journal of Fluids Engineering 120, n^o 4 (1 décembre 1998) : 839–43. http://dx.doi.org/10.1115/1.2820748.

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During semiconductor crystal growth with an externally applied magnetic field, thermoelectric currents may drive a melt circulation which affects the properties of the crystal. This paper treats a model problem for a floating zone process with a uniform axial magnetic field, with planar solid-liquid interfaces, with a cylindrical free surface, with a parabolic temperature variation along the crystal-melt interface, and with an isothermal feed rod-melt interface. The ratio of the electrical conductivities of the liquid and solid is a key parameter. The azimuthal velocity is much larger than the radial or axial velocity. There is radially outward flow near the crystal-melt interface which should be beneficial for the mass transport of dopants and species.

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Polovinkina, Marina V., Amar Debbouche, Igor P. Polovinkin et Sergio A. David. « Stability of stationary solutions for the glioma growth equations with radial or axial symmetries ». Mathematical Methods in the Applied Sciences 44, n^o 15 (13 janvier 2021) : 12021–34. http://dx.doi.org/10.1002/mma.7194.

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Mohan, Premila, Junichi Motohisa et Takashi Fukui. « Controlled growth of highly uniform, axial/radial direction-defined, individually addressable InP nanowire arrays ». Nanotechnology 16, n^o 12 (20 octobre 2005) : 2903–7. http://dx.doi.org/10.1088/0957-4484/16/12/029.

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Stefani, Jerry A., John K. Tien, Kwang Su Choe et John P. Wallace. « Multifrequency eddy current diagnostics of axial and radial thermal profiles during silicon crystal growth ». Journal of Crystal Growth 106, n^o 4 (décembre 1990) : 611–21. http://dx.doi.org/10.1016/0022-0248(90)90034-i.

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Joslyn, H. D., et R. P. Dring. « Axial Compressor Stator Aerodynamics ». Journal of Engineering for Gas Turbines and Power 107, n^o 2 (1 avril 1985) : 485–92. http://dx.doi.org/10.1115/1.3239754.

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Axisymmetric, through-flow calculations, currently the “backbone” of most multistage turbomachinery design systems, are being pushed to their limit. This is due to the difference between the complex, three-dimensional flows that actually occur in turbomachinery and the two-dimensional flow assumed in this type of analysis. To foster the development of design analyses that account more accurately for these three-dimensional effects, there is a need for detailed flow field data in a multistage environment. This paper presents a survey of the initial results from a detailed experimental study of the aerodynamics of the second stage of a large scale, two-stage axial compressor. Data were acquired over a range of flow coefficients. The data presented here are for the second stator and include airfoil and endwall flow visualization, and radial-circumferential traverse measurements presented in the form of fullspan contour plots of total pressure. Also presented are the spanwise distributions of total and static pressures, axial velocity, air angles, and blockage. The effect of increased loading on the growth of the hub corner stall and its impact on these parameters is discussed.

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Snitko, S. A., A. V. Yakovchenko, V. V. Pilipenko et N. I. Ivleva. « Modeling of ring billets rolling on radial-axial ring-rolling mill ». Izvestiya. Ferrous Metallurgy 63, n^o 8 (8 octobre 2020) : 665–73. http://dx.doi.org/10.17073/0368-0797-2020-8-665-673.

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On the basis of radial-axial rolling of ring billets, resource-saving technologies for metal forming have been created. Determining the rational parameters of this process is the actual scientific and technical task at development of new profiles. The method of three-dimensional finite element modeling is the most effective tool for improving the technological conditions of ring rolling process. However, as practice has shown, the finite element modeling method requires adaptation to each process of metal forming. This is the subject of the present work. The expediency of using dependency for calculating the metal flow stress for finite-element modeling of ring-rolling processes is substantiated. This dependence was developed on the basis of a theory that takes into account the chemical composition of structural carbon steel, its temperature, strain rate, accumulated deformation, and also the processes of dynamic transformation of the metal structure during hot rolling. A computer program for automated determination of dependency parameters has been developed. The analysis of the accuracy of the obtained dependence was performed in relation to the experimental data. In the course of these calculations, the method of automated determination of the metal flow stress was used by spline interpolation of the experimental data included in the computer database of digital information for a particular steel grade. The average relative error of calculated values of the metal flow stress was 8 % relative to the experimental ones. An improved method is proposed for calculating the parameters of ring billets rolling and reaching the required growth rate of the ring diameter implemented in a finite element modeling system, which is similar to the way the control system of the ring-rolling mill works in solving the same problem (reaching the required growth rate of the ring diameter) when implemented appropriate rolling in practice. When calculating the size of the compression, the iterative process and the method of half division were used. The average deviations of calculated values of the parameters of ring billets rolling from the experimental did not exceed 12.4 %, which makes it possible to apply the proposed approach to study the patterns of the rings rolling process and to improve the rolling technology.

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Yang, Hong-Jie, Sheng-Yan He et Hsing-Yu Tuan. « Simultaneous axial screw dislocation-mediated growth and radial layer-by-layer deposition for controlled synthesis of asymmetric axial ZnO nanospindles ». Nanoscale 6, n^o 15 (27 juin 2014) : 9034. http://dx.doi.org/10.1039/c4nr01888e.

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Nolan, David S. « Three-dimensional instabilities in tornado-like vortices with secondary circulations ». Journal of Fluid Mechanics 711 (19 septembre 2012) : 61–100. http://dx.doi.org/10.1017/jfm.2012.369.

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AbstractTornadoes and other intense atmospheric vortices are known to occasionally transition to a flow structure with multiple vortices within their larger circulations. This phenomenon has long been ascribed to fluid dynamical instability of the inner-core circulation, and many previous studies have diagnosed low-wavenumber unstable modes in tornado-like vortices that resemble the observed structures. However, relatively few of these studies have incorporated the strong vertical motions of the inner-core circulation into the stability analysis, and no stability analyses have been performed using a complete, frictionally driven secondary circulation with strong radial inflow near the surface. Stability analyses are presented using the complete circulations generated from idealized simulations of tornado-like vortices. Fast-growing unstable modes are found that are consistent with the asymmetric structures present in these simulations. Attempts to correlate the structures and locations of these modes with instability conditions for vortices with axial jets derived by Howard & Gupta and by Leibovich & Stewartson produce only mixed results. Analyses of perturbation energy growth show that interactions between eddy fluxes and the radial shear of the azimuthal wind contribute very little to the growth of the dominant modes. Rather, the radial shear of the vertical wind and the vertical shear of the vertical wind (corresponding to deformation in the axial direction) are the primary energy sources for perturbation growth. Relatively weak axisymmetric instabilities are also identified that have some similarity to symmetric oscillations that have been observed in tornadoes.

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Vijendra Rao, R., R. Dayal, B. L. Sharma et Luxmi Chauhan. « Reinvestigation of the Wood Structure of Thottea Siliquosa (Aristolochiaceae) ». IAWA Journal 13, n^o 1 (1992) : 17–20. http://dx.doi.org/10.1163/22941932-90000557.

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An accurate deseription of the wood structure of Thottea siliquosa is presented for the first time. Earlier deseriptions for this species were based on ineorreetly identified sampies. Wood is diffuse-porous with distinet growth rings. Vessels are small , solitary, in radial multiples and also in clusters, forming a distinet radial pattern. Perforations are simple, intervessel pits small, alternate without vestures. Vaseular traehe ids are present. Axial parenehyma is diffuse and diffuse-in-aggregates. Rays are very high and broad, heterogeneous. Fibres thick-walled and non-septate. Oil eells are absent.

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Chen, Yanglong, Xianying Wang, Shufan Xie, Jian Liu, Hongbin Cheng, Xuejun Zheng, Fang Liu et Junhe Yang. « Temperature Effect on the Microstructures and Optical Properties of ZnO Nanowires ». Journal of Nanomaterials 2012 (2012) : 1–5. http://dx.doi.org/10.1155/2012/172312.

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Temperature effects on the microstructures and optical properties of ZnO nanowires were investigated extensively. Furnace calibration results showed that temperatures inside the tube furnace had Gaussian distribution. Both radial and axial growth rates of ZnO nanowires in the Arrhenius plot fall on straight lines. With the increase of temperatures, ZnO nanowires exhibited larger diameters, better crystal qualities, and preferred growth along 〈0002〉 directions. Enhanced UV emission with the increase of growth temperatures was observed, while green emission was greatly reduced.

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CHOI, JAEHYUG, CHAO-TSUNG HSIAO, GEORGES CHAHINE et STEVEN CECCIO. « Growth, oscillation and collapse of vortex cavitation bubbles ». Journal of Fluid Mechanics 624 (10 avril 2009) : 255–79. http://dx.doi.org/10.1017/s0022112008005430.

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The growth, oscillation and collapse of vortex cavitation bubbles are examined using both two- and three-dimensional numerical models. As the bubble changes volume within the core of the vortex, the vorticity distribution of the surrounding flow is modified, which then changes the pressures at the bubble interface. This interaction can be complex. In the case of cylindrical cavitation bubbles, the bubble radius will oscillate as the bubble grows or collapses. The period of this oscillation is of the order of the vortex time scale, τV = 2πrc/uθ, max, where rc is the vortex core radius and uθ, max is its maximum tangential velocity. However, the period, oscillation amplitude and final bubble radius are sensitive to variations in the vortex properties and the rate and magnitude of the pressure reduction or increase. The growth and collapse of three-dimensional bubbles are reminiscent of the two-dimensional bubble dynamics. But, the axial and radial growth of the vortex bubbles are often strongly coupled, especially near the axial extents of the bubble. As an initially spherical nucleus grows into an elongated bubble, it may take on complex shapes and have volume oscillations that also scale with τV. Axial flow produced at the ends of the bubble can produce local pinching and fission of the elongated bubble. Again, small changes in flow parameters can result in substantial changes to the detailed volume history of the bubbles.

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Stout, Eric, et Fazle Hussain. « External turbulence-induced axial flow and instability in a vortex ». Journal of Fluid Mechanics 793 (16 mars 2016) : 353–79. http://dx.doi.org/10.1017/jfm.2016.123.

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External turbulence-induced axial flow in an incompressible, normal-mode stable Lamb–Oseen (two-dimensional) vortex column is studied via direct numerical simulations of the Navier–Stokes equations. Azimuthally oriented vorticity filaments, formed from external turbulence, advect radially towards or away from the vortex axis (depending on the filament’s swirl direction), resulting in a net induced axial flow in the vortex core; axial flow increases with increasing vortex Reynolds number ($Re=$ vortex circulation/viscosity). This contrasts the viscous mechanism for axial flow generation downstream of a lifting body, wherein an axial pressure gradient is produced by viscous diffusion of the swirl (Batchelor, J. Fluid Mech., vol. 20, 1964, pp. 645–658). Analysis of the self-induced motion of an arbitrarily curved external filament shows that any non-axisymmetric filament undergoes radial advection. We then studied the evolution of a vortex column starting with an imposed optimal transient growth perturbation. For a range of Re values, axial flow develops and initially grows as (time)$^{5/2}$ before decreasing after two turnover times; for $Re=10\,000$ – the highest computationally achievable – axial flow at late times becomes sufficiently strong to induce vortex instability. Contrary to a prior claim of a parent–offspring mechanism at the outer edge of the core, vorticity tilting within the core by axial flow is the underlying mechanism producing energy growth. Thus, external perturbations in practical flows (at $Re\sim 10^{7}$) produce destabilizing axial flow, possibly leading to the sought-after vortex breakup.

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Berg, Alexander, Kilian Mergenthaler, Martin Ek, Mats-Erik Pistol, L. Reine Wallenberg et Magnus T. Borgström. « In situetching for control over axial and radial III-V nanowire growth rates using HBr ». Nanotechnology 25, n^o 50 (25 novembre 2014) : 505601. http://dx.doi.org/10.1088/0957-4484/25/50/505601.

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Guo, Jingwei, Hui Huang, Xiaomin Ren, Xin Yan, Shiwei Cai, Wei Wang, Yongqing Huang, Qi Wang et Xia Zhang. « Realizing Zinc Blende GaAs/AlGaAs Axial and Radial Heterostructure Nanowires by Tuning the Growth Temperature ». Journal of Materials Science & ; Technology 27, n^o 6 (janvier 2011) : 507–12. http://dx.doi.org/10.1016/s1005-0302(11)60099-6.

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Chang, Yongqin, Yingdong Lu, Mingwen Wang, Yi Long et Rongchang Ye. « Self-assembly growth of ZnO-based axial and radial junctions via a two-step method ». Applied Surface Science 264 (janvier 2013) : 687–91. http://dx.doi.org/10.1016/j.apsusc.2012.10.096.

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Evtukh, A. A., Anatoly Druzhinin, I. Ostrovskii, A. Kizjak, A. Grigoriev, O. Steblova et S. Nichkalo. « Formation of Ordered Si Nanowires Arrays on Si Substrate ». Advanced Materials Research 854 (novembre 2013) : 83–88. http://dx.doi.org/10.4028/www.scientific.net/amr.854.83.

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The paper deals with investigation of silicon nanowires formation by LP CVD method on Si substrate using gold films as a mask. The average diameter of Si nanowires grown by LP CVD was about 60 nm. It was shown that using of Si-Au droplets as the mask allows to obtain vertically aligned silicon nanowires with average diameter of about 60 nm. The kinetics of radial and axial growth was investigated, the growth rates and kinetic coefficient of growth were calculated, which showed a good accordance to experimental data.

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Ma, Nancy, John Walker, David Bliss et George Bryant. « Forced Convection During Liquid Encapsulated Crystal Growth With an Axial Magnetic Field ». Journal of Fluids Engineering 120, n^o 4 (1 décembre 1998) : 844–50. http://dx.doi.org/10.1115/1.2820749.

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This paper treats the forced convection, which is produced by the rotation of the crystal about its vertical centerline during the liquid-encapsulated Czochralski or Kyropoulos growth of compound semiconductor crystals, with a uniform vertical magnetic field. The model assumes that the magnetic field strength is sufficiently large that convective heat transfer and all inertial effects except the centripetal acceleration are negligible. With the liquid encapsulant in the radial gap between the outside surface of the crystal and the vertical wall of the crucible, the forced convection is fundamentally different from that with a free surface between the crystal and crucible for the Czochralski growth of silicon crystals. Again unlike the case for silicon growth, the forced convection for the actual nonzero electrical conductivity of an indium-phosphide crystal is virtually identical to that for an electrically insulating crystal. The electromagnetic damping of the forced convection is stronger than that of the buoyant convection. In order to maintain a given balance between the forced and buoyant convections, the angular velocity of the crystal must be increased as the magnetic field strength is increased.

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Riscob, B., Indranil Bhaumik, S. Ganesamoorthy, R. Bhatt, N. Vijayan, Khavangkhui Zimik, A. K. Karnal, G. Bhagavannarayana et P. K. Gupta. « Crystal growth of Ru-doped congruent LiNbO3and investigation of crystalline perfection and optical properties ». Journal of Applied Crystallography 48, n^o 6 (30 octobre 2015) : 1753–60. http://dx.doi.org/10.1107/s1600576715018464.

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Single crystals of undoped and Ru-doped congruent LiNbO3(LN) were successfully grown by the Czochralski method. The axial and radial gradient of the radio frequency furnace was controlled in order to obtain crack-free single crystals. Wafers were cut from the grown Ru-doped single crystal at different axial positions along the growth direction and subjected to various characterization analyses. Good optical homogeneity and low residual strain in the grown crystal is confirmed by the conoscopy patterns. Further, it is confirmed that Ru doping does not influence the optical sign of the crystal. From a high-resolution X-ray diffractometry analysis, it is evident that the as-grown undoped LN crystal exhibited better crystalline perfection with a single and sharp diffraction curve in comparison to the Ru-doped crystals, which are characterized by a broader diffraction curve. Absorption coefficient and band-gap analysis across the axial length revealed a concentration variation of Ru across the length. Refractive index measurements carried out using a prism coupler showed variation in the optical birefringence, also due to the variation of Ru concentration at different positions of the grown single crystal.

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Khine, Yu Yu, et John S. Walker. « Thermocapillary convection in a cylinder with a strong non-uniform axisymmetric magnetic field ». Journal of Fluid Mechanics 276 (10 octobre 1994) : 369–88. http://dx.doi.org/10.1017/s0022112094002600.

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This paper treats a surface-tension-driven liquid-metal flow in a cylinder with a steady externally applied non-uniform axisymmetric magnetic field. The top boundary consists of an annular free surface around a solid disk, modelling the Czochralski growth of silicon crystals. A radial temperature gradient produces a decrease of the surface tension from the disk edge to the vertical cylinder wall. The magnetic flux density is sufficiently large that inertial effects and convective heat transfer are negligible. First we present large-Hartmann-number asymptotic solutions for magnetic fields with either a non-zero or a zero axial component at the free surface. The asymptotic solutions indicate that a purely radial magnetic field at the free surface represents a singular limit of more general magnetic fields. Secondly we present numerical solutions for arbitrary values of the Hartmann number, and we treat the evolution of the thermocapillary convection as the axial magnetic field at the free surface is changed continuously from the full field strength to zero.

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Tsuchiya, Ryouta, et Ikuo Furukawa. « Radial Variation in the size of Axial Elements in Relation to Stem Increment in Quercus Serrata ». IAWA Journal 30, n^o 1 (2009) : 15–26. http://dx.doi.org/10.1163/22941932-90000199.

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In Quercus serrata, radial variations of wood fibre length, earlywood vessel element length, and earlywood vessel lumen diameter were investigated and maturation ages of them were estimated using nonlinear segmented regression analysis as proposed by Peszlen (1994). In addition, the age at the maximum point of current annual increment and mean annual increment were estimated by using the Gompertz growth function fitted to the variation of cumulative ring width with ring number from the pith. In the same radial strip, the maturation ages both of wood fibre length and the earlywood vessel element length were similar, and those were close to the ages at the maximum point of current annual increment, whereas the maturation age of earlywood vessel lumen diameter was generally greater, close to the age at the maximum point of mean annual increment. These results indicate that earlywood vessel lumen diameter is the best indicator of the three anatomical properties tested and that a relationship exists between the maturation ages of the size of axial elements and radial stem increment.

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Meunier, Félicien, Valentin Couvreur, Xavier Draye, Mohsen Zarebanadkouki, Jan Vanderborght et Mathieu Javaux. « Water movement through plant roots – exact solutions of the water flow equation in roots with linear or exponential piecewise hydraulic properties ». Hydrology and Earth System Sciences 21, n^o 12 (21 décembre 2017) : 6519–40. http://dx.doi.org/10.5194/hess-21-6519-2017.

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Abstract. In 1978, Landsberg and Fowkes presented a solution of the water flow equation inside a root with uniform hydraulic properties. These properties are root radial conductivity and axial conductance, which control, respectively, the radial water flow between the root surface and xylem and the axial flow within the xylem. From the solution for the xylem water potential, functions that describe the radial and axial flow along the root axis were derived. These solutions can also be used to derive root macroscopic parameters that are potential input parameters of hydrological and crop models. In this paper, novel analytical solutions of the water flow equation are developed for roots whose hydraulic properties vary along their axis, which is the case for most plants. We derived solutions for single roots with linear or exponential variations of hydraulic properties with distance to root tip. These solutions were subsequently combined to construct single roots with complex hydraulic property profiles. The analytical solutions allow one to verify numerical solutions and to get a generalization of the hydric behaviour with the main influencing parameters of the solutions. The resulting flow distributions in heterogeneous roots differed from those in uniform roots and simulations led to more regular, less abrupt variations of xylem suction or radial flux along root axes. The model could successfully be applied to maize effective root conductance measurements to derive radial and axial hydraulic properties. We also show that very contrasted root water uptake patterns arise when using either uniform or heterogeneous root hydraulic properties in a soil–root model. The optimal root radius that maximizes water uptake under a carbon cost constraint was also studied. The optimal radius was shown to be highly dependent on the root hydraulic properties and close to observed properties in maize roots. We finally used the obtained functions for evaluating the impact of root maturation versus root growth on water uptake. Very diverse uptake strategies arise from the analysis. These solutions open new avenues to investigate for optimal genotype–environment–management interactions by optimization, for example, of plant-scale macroscopic hydraulic parameters used in ecohydrogolocial models.

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Georgievskaia, E. V. « APPLICATION OF BREAKDOWN MECHANICS FOR PREDICTING THE RESOURCE OF AXIAL RADIAL HYDROTURBINS ». Proceedings of the higher educational institutions. ENERGY SECTOR PROBLEMS 20, n^o 9-10 (24 janvier 2019) : 71–78. http://dx.doi.org/10.30724/1998-9903-2018-20-9-10-71-78.

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To plan for timely reconstruction, modernization, repairs or replacement of equipment it is important to reliably predict the instant of its transition to the limiting state that determines the lifetime. Currently, there are no regulatory methods for assessing the lifetime of hydraulic turbines at the operation stage. The approach presented in this paper uses the fracture mechanics methods to build a long-term individual forecast of the dangerous development defects in the main elements of hydraulic turbines taking into account design, technological and operational features. The forecast is based on three-dimensional mathematical models that describe the change in the technical condition of the equipment during time under actual operation. The ANSYS software is used for calculations. Models take into account the size and position of detected or possible defects. Crack growth is determined by the combination of low- and high-frequency loads. The critical length of the crack corresponds to the instant of change of the crack development mechanism, when the failure risk increases sharply. Proposed approach can significantly reduce the possibility of unplanned or emergency shutdown of the hydraulic unit due to its destruction during the overhaul period.

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Helińska-Raczkowska, Lidia, et Ewa Fabisiak. « Radial Variation and Growth Rate in the Length of the Axial Elements Of Sessile Oak Wood ». IAWA Journal 12, n^o 3 (1991) : 257–62. http://dx.doi.org/10.1163/22941932-90001254.

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Radial variability of the axial element length in oak-wood is most prominent in the juvenile wood which inc1udes approximately 30 annual rings. The length of fibres, tracheids and vessel elements increases from the pith outwards according to a second degree curve. This dependence is most apparent for wood fibres, whereas it is the least distinct for vesseI elements. In the mature zone, anatomical elements are, on average, 10 to 20% Ion ger than in juvenile wood. With deteriorating conditions of tree growth, the length of the anatomical elements tends to increase. There is a negative correlation between length of the measured elements and growth ring width; this is most c1early so for fibres. A similar relationship exists between the length of anatomical elements and wood density.

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Gong, Xiaojing, Pinar Dogan, Xiaoliang Zhang, Uwe Jahn, Ke Xu, Lifeng Bian et Hui Yang. « Atomic-scale behavior of adatoms in axial and radial growth of GaN nanowires : Molecular dynamics simulations ». Japanese Journal of Applied Physics 53, n^o 8 (9 juillet 2014) : 085601. http://dx.doi.org/10.7567/jjap.53.085601.

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Isaeva, Valeria V., et Nickolay V. Kasyanov. « Symmetry Transformations in Metazoan Evolution and Development ». Symmetry 13, n^o 2 (20 janvier 2021) : 160. http://dx.doi.org/10.3390/sym13020160.

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In this review, we consider transformations of axial symmetry in metazoan evolution and development, the genetic basis, and phenotypic expressions of different axial body plans. In addition to the main symmetry types in metazoan body plans, such as rotation (radial symmetry), reflection (mirror and glide reflection symmetry), and translation (metamerism), many biological objects show scale (fractal) symmetry as well as some symmetry-type combinations. Some genetic mechanisms of axial pattern establishment, creating a coordinate system of a metazoan body plan, bilaterian segmentation, and left–right symmetry/asymmetry, are analysed. Data on the crucial contribution of coupled functions of the Wnt, BMP, Notch, and Hedgehog signaling pathways (all pathways are designated according to the abbreviated or full names of genes or their protein products; for details, see below) and the axial Hox-code in the formation and maintenance of metazoan body plans are necessary for an understanding of the evolutionary diversification and phenotypic expression of various types of axial symmetry. The lost body plans of some extinct Ediacaran and early Cambrian metazoans are also considered in comparison with axial body plans and posterior growth in living animals.

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Tsuchiya, Ryouta, et Ikuo Furukawa. « Synchronized Maturation of Vessel Diameter and ray width in Zelkova Serrata ». IAWA Journal 31, n^o 3 (2010) : 269–82. http://dx.doi.org/10.1163/22941932-90000022.

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This study describes radial variation in fibre length, vessel element length, vessel lumen diameter, and ray width (number of cells) in relation to the developmental stages in radial stem increment in Zelkova serrata trees. Maturation age (the age at which the size of the wood elements is stabilized) was compared to the ages at the boundary between the early and middle stages (age t1), and the middle and late stages (age t2) of radial stem increment. The maturation age was estimated by nonlinear segmented regression analysis. Ages t1 and t2 were estimated by the Gompertz growth function. The maturation age for the length of axial elements (wood fibres and vessel elements) was not related to either age t1 or age t2. However, the maturation ages for vessel lumen diameter and ray width were close, and both were related to age t2. This indicates that the maturation of vessel lumen diameter and ray width was synchronized and both were related to the stage of radial stem increment.

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