Journal articles: 'Laminar layer'

1

Forster, E., C. Kaltschmidt, J. Deng, H. Cremer, T. Deller, and M. Frotscher. "Lamina-specific cell adhesion on living slices of hippocampus." Development 125, no. 17 (September 1, 1998): 3399–410. http://dx.doi.org/10.1242/dev.125.17.3399.

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Laminar distribution of fiber systems is a characteristic feature of hippocampal organization. Ingrowing afferents, e.g. the fibers from the entorhinal cortex, terminate in specific layers, which implies the existence of laminar recognition cues. To identify cues that are involved in the laminar segregation of fiber systems in the hippocampus, we used an in vitro assay to study the adhesion of dissociated entorhinal cells on living hippocampal slices. Here we demonstrate that dissociated entorhinal cells adhere to living hippocampal slices with a lamina-specific distribution that reflects the innervation pattern of the entorhino-hippocampal projection. In contrast, laminae which are not invaded by entorhinal fibers are a poor substrate for cell adhesion. Lamina-specific cell adhesion does not require the neural cell adhesion molecule or the extracellular matrix glycoprotein reelin, as revealed in studies with mutants. However, the pattern of adhesive cues in the reeler mouse hippocampus mimics characteristic alterations of the entorhinal projection in this mutant, suggesting a role of layer-specific adhesive cues in the pathfinding of entorhinal fibers. Lamina-specific cell adhesion is independent of divalent cations, is abolished after cryofixation or paraformaldehyde fixation and is recognized across species. By using a novel membrane adhesion assay, we show that lamina-specific cell adhesion can be mimicked by membrane-coated fluorescent microspheres. Recognition of the adhesive properties of different hippocampal laminae by growing axons, as either a growth permissive or a non-permissive substrate, may provide a developmental mechanism underlying the segregation of lamina-specific fiber projections.

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Giepman, R. H. M., F. F. J. Schrijer, and B. W. van Oudheusden. "A parametric study of laminar and transitional oblique shock wave reflections." Journal of Fluid Mechanics 844 (April 4, 2018): 187–215. http://dx.doi.org/10.1017/jfm.2018.165.

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High-resolution particle image velocimetry measurements were performed on laminar and transitional oblique shock wave reflections for a range of Mach numbers ($M=1.6{-}2.3$), Reynolds numbers ($Re_{x_{sh}}=1.4\times 10^{6}{-}3.5\times 10^{6}$) and flow deflection angles ($\unicode[STIX]{x1D703}=1^{\circ }{-}5^{\circ }$ or $p_{3}/p_{1}=1.11{-}1.64$). The laminar interactions revealed a long, flat and triangular shaped separation bubble. For relatively strong interactions ($p_{3}/p_{1}>1.2$), the bubble grows linearly in the upstream direction with increasing shock strength. Under these conditions, the boundary layer keeps an on average laminar velocity profile up to the shock impingement location, followed by a quick transition and subsequent reattachment of the boundary layer. For weaker interactions ($p_{3}/p_{1}<1.2$), the boundary layer is able to remain laminar further downstream of the bubble, which consequently results in a later reattachment of the boundary layer. The pressure distribution at the interaction onset for all laminar cases shows excellent agreement with the free-interaction theory, therefore supporting its validity even for incipiently separated laminar oblique shock wave reflections.

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Atencio, Craig A., and Christoph E. Schreiner. "Laminar Diversity of Dynamic Sound Processing in Cat Primary Auditory Cortex." Journal of Neurophysiology 103, no. 1 (January 2010): 192–205. http://dx.doi.org/10.1152/jn.00624.2009.

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For primary auditory cortex (AI) laminae, there is little evidence of functional specificity despite clearly expressed cellular and connectional differences. Natural sounds are dominated by dynamic temporal and spectral modulations and we used these properties to evaluate local functional differences or constancies across laminae. To examine the layer-specific processing of acoustic modulation information, we simultaneously recorded from multiple AI laminae in the anesthetized cat. Neurons were challenged with dynamic moving ripple stimuli and we subsequently computed spectrotemporal receptive fields (STRFs). From the STRFs, temporal and spectral modulation transfer functions (tMTFs, sMTFs) were calculated and compared across layers. Temporal and spectral modulation properties often differed between layers. On average, layer II/III and VI neurons responded to lower temporal modulations than those in layer IV. tMTFs were mainly band-pass in granular layer IV and became more low-pass in infragranular layers. Compared with layer IV, spectral MTFs were broader and their upper cutoff frequencies higher in layers V and VI. In individual penetrations, temporal modulation preference was similar across layers for roughly 70% of the penetrations, suggesting a common, columnar functional characteristic. By contrast, only about 30% of penetrations showed consistent spectral modulation preferences across layers, indicative of functional laminar diversity or specialization. Since local laminar differences in stimulus preference do not always parallel the main flow of information in the columnar cortical microcircuit, this indicates the influence of additional horizontal or thalamocortical inputs. AI layers that express differing modulation properties may serve distinct roles in the extraction of dynamic sound information, with the differing information specific to the targeted stations of each layer.

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4

Djenidi, L., F. Anselmet, J. Liandrat, and L. Fulachier. "Laminar boundary layer over riblets." Physics of Fluids 6, no. 9 (September 1994): 2993–99. http://dx.doi.org/10.1063/1.868429.

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5

Anderson, E. J., W. R. McGillis, and M. A. Grosenbaugh. "The boundary layer of swimming fish." Journal of Experimental Biology 204, no. 1 (January 1, 2001): 81–102. http://dx.doi.org/10.1242/jeb.204.1.81.

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Tangential and normal velocity profiles of the boundary layer surrounding live swimming fish were determined by digital particle tracking velocimetry, DPTV. Two species were examined: the scup Stenotomus chrysops, a carangiform swimmer, and the smooth dogfish Mustelus canis, an anguilliform swimmer. Measurements were taken at several locations over the surfaces of the fish and throughout complete undulatory cycles of their propulsive motions. The Reynolds number based on length, Re, ranged from 3×10(3) to 3×10(5). In general, boundary layer profiles were found to match known laminar and turbulent profiles including those of Blasius, Falkner and Skan and the law of the wall. In still water, boundary layer profile shape always suggested laminar flow. In flowing water, boundary layer profile shape suggested laminar flow at lower Reynolds numbers and turbulent flow at the highest Reynolds numbers. In some cases, oscillation between laminar and turbulent profile shapes with body phase was observed. Local friction coefficients, boundary layer thickness and fluid velocities at the edge of the boundary layer were suggestive of local oscillatory and mean streamwise acceleration of the boundary layer. The behavior of these variables differed significantly in the boundary layer over a rigid fish. Total skin friction was determined. Swimming fish were found to experience greater friction drag than the same fish stretched straight in the flow. Nevertheless, the power necessary to overcome friction drag was determined to be within previous experimentally measured power outputs. No separation of the boundary layer was observed around swimming fish, suggesting negligible form drag. Inflected boundary layers, suggestive of incipient separation, were observed sporadically, but appeared to be stabilized at later phases of the undulatory cycle. These phenomena may be evidence of hydrodynamic sensing and response towards the optimization of swimming performance.

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Zhang, Jiaojiao, Shengna Liu, and Liancun Zheng. "Turbulent boundary layer heat transfer of CuO–water nanofluids on a continuously moving plate subject to convective boundary." Zeitschrift für Naturforschung A 77, no. 4 (December 21, 2021): 369–77. http://dx.doi.org/10.1515/zna-2021-0268.

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Abstract The turbulent boundary layer (TBL) heat transfer of CuO–water nanofluids on a continuously moving plate subject to convective boundary are investigated. Five different shapes of nanoparticles are taken into account. Prandtl mixing length theory is adopted to divide the TBL into two parts, laminar sub-layer and turbulent region. The numerical solutions are obtained by bvp4c and accuracy is verified with previous results. It is found that the transfer of momentum and heat in the TBL is more obvious in laminar sub-layer than in turbulent region. The rise of velocity ratio parameter increases the velocity and temperature while decreases the local friction coefficient. The heat transfer increases significantly with the increase of velocity ratio parameter, Biot number, and nanoparticles volume fraction. For nanoparticles of different shapes, the heat transfer characteristics are Nu x (sphere) < Nu x (hexahedron) < Nu x (tetrahedron) < Nu x (column) < Nu x (lamina).

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7

Raić, Karlo. "Simplification of laminar boundary layer equations." Metallurgical and Materials Engineering 24, no. 2 (July 2, 2018): 93–102. http://dx.doi.org/10.30544/347.

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The laminar boundary layer theory has been involved in two domains of transport phenomena: (i) steady-state flow (via Blasius eq.) and (ii) unsteady state flow and/or nonflow (via Newton, Fourier and/or Fick’s equations). Listed partial differential equations with the similarity of solutions enable the substitution of the observed phenomena by only one-second order differential equation. Consequently, an approach established on the general polynomial solution is described. Numerical verification of the concept is presented. Experimental notifications are documented. Finally, the new simulation strategy is suggested.

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8

Alston, Thomas M., and Ira M. Cohen. "Decay of a laminar shear layer." Physics of Fluids A: Fluid Dynamics 4, no. 12 (December 1992): 2690–99. http://dx.doi.org/10.1063/1.858456.

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9

Qiu, Jinhao, Junji Tani, Toshiyuki Hayase, and Takashi Okutani. "Active control of laminar boundary layer." Matériaux & Techniques 90 (2002): 13–17. http://dx.doi.org/10.1051/mattech/200290120013s.

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10

Kuz’min, A. I., and S. S. Kharchenko. "Self ignition in laminar mixing layer." Combustion, Explosion, and Shock Waves 35, no. 1 (January 1999): 23–30. http://dx.doi.org/10.1007/bf02674382.

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11

McConnell, SK, and CE Kaznowski. "Cell cycle dependence of laminar determination in developing neocortex." Science 254, no. 5029 (October 11, 1991): 282–85. http://dx.doi.org/10.1126/science.254.5029.282.

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The neocortex is patterned in layers of neurons that are generated in an orderly sequence during development. This correlation between cell birthday and laminar fate prompted an examination of how neuronal phenotypes are determined in the developing cortex. At various times after labeling with [3H]thymidine, embryonic progenitor cells were transplanted into older host brains. The laminar fate of transplanted neurons correlates with the position of their progenitors in the cell cycle at the time of transplantation. Daughters of cells transplanted in S-phase migrate to layer 2/3, as do host neurons. Progenitors transplanted later in the cell cycle, however, produce daughters that are committed to their normal, deep-layer fates. Thus, environmental factors are important determinants of laminar fate, but embryonic progenitors undergo cyclical changes in their ability to respond to such cues.

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12

Polivanov, Pavel A., Andrey A. Sidorenko, and Anatoly A. Maslov. "Effective plasma buffet and drag control for laminar transonic aerofoil." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, no. 1 (August 29, 2018): 58–67. http://dx.doi.org/10.1177/0954410018795542.

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The effect of plasma actuators on shock wave–laminar boundary layer interaction was studied experimentally on transonic laminar aerofoil. The unsteady characteristics of the separation zone including the transonic buffet were measured. Two kinds of electrical discharge actuators were used for the flow control. Successful suppression of separated flow and laminar transonic buffet by plasma actuators was demonstrated. An analysis of the effect of power and frequency of the discharge on shock wave–laminar boundary layer interaction was carried out. High efficiency ratio of the separation control by plasma actuators was achieved in the experiments.

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13

Lysenko, Vladimir, Boris Smorodsky, Yuri Yermolaev, Sergey Gaponov, Aleksandr Kosinov, Nikolay Semionov, and Alex Yatskih. "Influence Of Heavy Gas Blowing Into The Wall Layer Of Supersonic Boundary-Layer On Its Transition." Siberian Journal of Physics 12, no. 1 (March 1, 2017): 50–56. http://dx.doi.org/10.54362/1818-7919-2017-12-1-50-56.

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The experimental investigation of the influence of the distributed blowing of heavy gas (sulfur hexafluoride of SF6) into the wall layer of supersonic flat-plate boundary layer (at free-stream Mach number M = 2) on the laminar-turbulent transition have been performed. For the first time experimentally it is shown that in case of such blowing there is a boundary-layer stabilization, and the laminar-turbulent transition is removed from the model leading edge.

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14

Sawa, Sayuki, and Shinzo Yoshikado. "Evaluation of Laminated Thin-Film ZnO Varistor by PLD." Key Engineering Materials 350 (October 2007): 217–20. http://dx.doi.org/10.4028/www.scientific.net/kem.350.217.

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Laminar-type thin-film ZnO varistors were fabricated on sintered alumina substrates using visible light (532nm) pulsed laser deposition (PLD). The structure of the laminar-type thin-film varistor is Ni / Co-added ZnO / impurity layer / Co-added ZnO / Ni. Many droplets were observed on the deposited Bi2O3+MnO2 compared with the deposited Co-added ZnO thin film. Moreover, for droplets on the Bi2O3+MnO2 layer, the content of Mn was higher than that of Bi. The V-I characteristics of the deposited ZnO+CoCl2 or Bi2O3+MnO2 thin film were ohmic. However, V-I characteristics of laminar-type thin film including the Bi2O3+MnO2 impurity layer deposited for 30min showed nonlinearity. The non linearity index α was approximately 2 and the varistor voltage was approximately 1V. Thermal annealing in N2 gas atmosphere at 700°C for 10 min was carried out to improve the crystallinity of the thin film. After annealing, both the varistor voltage and the current at which nonlinearity appeared decreased. Moreover, the value of non linearity index α was approximately 2.8.

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15

Boiko, Andrey V., Kirill V. Demyanko, Yuri M. Nechepurenko, and Grigory V. Zasko. "On the Use of Probability-Based Methods for Estimating the Aerodynamic Boundary-Layer Thickness." Fluids 6, no. 8 (July 28, 2021): 267. http://dx.doi.org/10.3390/fluids6080267.

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In this paper, known probabilistic methods for estimating the thickness of the boundary layer of a two-dimensional laminar flow of viscous incompressible fluid are extended to three-dimensional laminar flows of a viscous compressible medium. Their applicability to the problems of boundary-layer stability is studied with the LOTRAN3 software package, which allows us to compute the position of laminar-turbulent transition in three-dimensional aerodynamic configurations.

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16

Pierucci, Mauro, and Pedro Morales. "Interaction between a laminar boundary layer and an elastic layer." Journal of the Acoustical Society of America 80, S1 (December 1986): S15—S16. http://dx.doi.org/10.1121/1.2023674.

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17

Desai, A. R., and S. K. McConnell. "Progressive restriction in fate potential by neural progenitors during cerebral cortical development." Development 127, no. 13 (July 1, 2000): 2863–72. http://dx.doi.org/10.1242/dev.127.13.2863.

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During early stages of cerebral cortical development, progenitor cells in the ventricular zone are multipotent, producing neurons of many layers over successive cell divisions. The laminar fate of their progeny depends on environmental cues to which the cells respond prior to mitosis. By the end of neurogenesis, however, progenitors are lineally committed to producing upper-layer neurons. Here we assess the laminar fate potential of progenitors at a middle stage of cortical development. The progenitors of layer 4 neurons were first transplanted into older brains in which layer 2/3 was being generated. The transplanted neurons adopted a laminar fate appropriate for the new environment (layer 2/3), revealing that layer 4 progenitors are multipotent. Mid-stage progenitors were then transplanted into a younger environment, in which layer 6 neurons were being generated. The transplanted neurons bypassed layer 6, revealing that layer 4 progenitors have a restricted fate potential and are incompetent to respond to environmental cues that trigger layer 6 production. Instead, the transplanted cells migrated to layer 4, the position typical of their origin, and also to layer 5, a position appropriate for neither the host nor the donor environment. Because layer 5 neurogenesis is complete by the stage that progenitors were removed for transplantation, restrictions in laminar fate potential must lag behind the final production of a cortical layer. These results suggest that a combination of intrinsic and environmental cues controls the competence of cortical progenitor cells to produce neurons of different layers.

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18

Aggoune, S., and El Hachemi Amara. "Dynamical Study of a Molten Boundary Layer Ejected by Laminar Gas Flow." Defect and Diffusion Forum 348 (January 2014): 88–93. http://dx.doi.org/10.4028/www.scientific.net/ddf.348.88.

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We consider in the present work the fusion laser cutting of stainless steel sheets under a nitrogen laminar gas jet. The molten metal is treated as a laminar and steady viscous incompressible fluid. The mathematical model describing our problem is set in terms of Navier-Stokes equations, solved numerically using the finite differences method, where the effect of the gas jet velocity on the molten boundary layer is considered. The generated shear stress occurring on the gas-liquid interface and its contribution in the momentum is carried out, and it is found that when the skin friction and the shear stress decrease, the thickness and the velocity at the edge of the molten boundary layer increase along the kerf surface. The layer thickness reduces when the assisting gas velocity is increased.

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Han, B., and P. Kunthong. "Micro-Mechanical Deformation Analysis of Surface Laminar Circuit in Organic Flip-Chip Package: An Experimental Study." Journal of Electronic Packaging 122, no. 4 (May 15, 2000): 294–300. http://dx.doi.org/10.1115/1.1290000.

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Thermo-mechanical deformations of microstructures in a surface laminar circuit (SLC) substrate are quantified by microscopic moire´ interferometry. Two specimens are analyzed; a bare SLC substrate and a flip chip package assembly. The specimens are subjected to a uniform thermal loading of ΔT=−70°C and the microscopic displacement fields are documented at the identical region of interest. The nano-scale displacement sensitivity and the microscopic spatial resolution obtained from the experiments provide a faithful account of the complex deformation of the surface laminar layer and the embedded microstructures. The displacement fields are analyzed to produce the deformed configuration of the surface laminar layer and the strain distributions in the microstructures. The high modulus of underfill produces a strong coupling between the chip and the surface laminar layer, which produces a DNP-dependent shear deformation of the layer. The effect of the underfill on the deformation of the microstructures is investigated and its implications on the package reliability are discussed. [S1043-7398(00)01304-9]

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Ninomiya, Taihei, Kacie Dougherty, David C. Godlove, Jeffrey D. Schall, and Alexander Maier. "Microcircuitry of agranular frontal cortex: contrasting laminar connectivity between occipital and frontal areas." Journal of Neurophysiology 113, no. 9 (May 2015): 3242–55. http://dx.doi.org/10.1152/jn.00624.2014.

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Neocortex is striking in its laminar architecture. Tracer studies have uncovered anatomical connectivity among laminae, but the functional connectivity between laminar compartments is still largely unknown. Such functional connectivity can be discerned through spontaneous neural correlations during rest. Previous work demonstrated a robust pattern of mesoscopic resting-state connectivity in macaque primary visual cortex (V1) through interlaminar cross-frequency coupling. Here we investigated whether this pattern generalizes to other cortical areas by comparing resting-state laminar connectivity between V1 and the supplementary eye field (SEF), a frontal area lacking a granular layer 4 (L4). Local field potentials (LFPs) were recorded with linear microelectrode arrays from all laminae of granular V1 and agranular SEF while monkeys rested in darkness. We found substantial differences in the relationship between the amplitude of gamma-band (>30 Hz) LFP and the phase of alpha-band (7–14 Hz) LFP between these areas. In V1, gamma amplitudes in L2/3 and L5 were coupled with alpha-band LFP phase in L5, as previously described. In contrast, in SEF phase-amplitude coupling was prominent within L3 and much weaker across layers. These results suggest that laminar interactions in agranular SEF are unlike those in granular V1. Thus the intrinsic functional connectivity of the cortical microcircuit does not seem to generalize across cortical areas.

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21

Förster, Eckart, Shanting Zhao, and Michael Frotscher. "Hyaluronan-associated adhesive cues control fiber segregation in the hippocampus." Development 128, no. 15 (August 1, 2001): 3029–39. http://dx.doi.org/10.1242/dev.128.15.3029.

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In various brain regions, particularly in the hippocampus, afferent fiber projections terminate in specific layers. Little is known about the molecular cues governing this laminar specificity. To this end we have recently shown that the innervation pattern of entorhinal fibers to the hippocampus is mimicked by the lamina-specific adhesion of entorhinal cells on living hippocampal slices, suggesting a role of adhesion molecules in the positioning of entorhinal fibers. Here, we have analyzed the role of extracellular matrix components in mediating this lamina-specific adhesion. We show that hyaluronidase treatment of hippocampal slices abolishes lamina-specific adhesion as well as layer-specific growth of entorhinal fibers to the dentate outer molecular layer in organotypic slice cultures. We conclude that hyaluronan-associated molecules play a crucial role in the formation of the lamina-specific entorhinal projection to the hippocampus.

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22

Nelson, P. A., M. C. M. Wright, and J. L. Rioual. "Automatic Control of Laminar Boundary-Layer Transition." AIAA Journal 35, no. 1 (January 1997): 85–90. http://dx.doi.org/10.2514/2.66.

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23

Semin, N. V., V. V. Golub, G. E. Elsinga, and J. Westerweel. "Laminar superlayer in a turbulent boundary layer." Technical Physics Letters 37, no. 12 (December 2011): 1154–57. http://dx.doi.org/10.1134/s1063785011120285.

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24

Nasr, H., I. A. Hassanien, and H. M. El-Hawary. "Chebyshev solution of laminar boundary layer flow." International Journal of Computer Mathematics 33, no. 1-2 (January 1990): 127–32. http://dx.doi.org/10.1080/00207169008803843.

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25

Mihaela, CALUDESCU. "LAMINAR STABILITY ANALYSIS IN BOUNDARY LAYER FLOW." INCAS BULLETIN 1, no. 1 (September 24, 2009): 33–36. http://dx.doi.org/10.13111/2066-8201.2009.1.1.7.

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26

Kachanov, Y. S. "Physical Mechanisms of Laminar-Boundary-Layer Transition." Annual Review of Fluid Mechanics 26, no. 1 (January 1994): 411–82. http://dx.doi.org/10.1146/annurev.fl.26.010194.002211.

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27

Bogolepov, V. V. "Small perturbations of a laminar boundary layer." Journal of Applied Mechanics and Technical Physics 28, no. 5 (1988): 706–16. http://dx.doi.org/10.1007/bf00912023.

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28

Bejan, Adrian. "Theory of Unsteady Laminar Boundary Layer Flow." International Journal of Heat and Mass Transfer 28, no. 6 (June 1985): 1241. http://dx.doi.org/10.1016/0017-9310(85)90134-6.

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Nelson, P. A., M. C. M. Wright, and J. L. Rioual. "Automatic control of laminar boundary-layer transition." AIAA Journal 35 (January 1997): 85–90. http://dx.doi.org/10.2514/3.13467.

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Hicks, Peter D., and Pierre Ricco. "Laminar streak growth above a spanwise oscillating wall." Journal of Fluid Mechanics 768 (March 6, 2015): 348–74. http://dx.doi.org/10.1017/jfm.2015.98.

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The use of spanwise wall oscillations to attenuate the growth of laminar streaks within the incompressible Blasius boundary layer is investigated. As in the case of the flow above a stationary flat plate, studied by Leib et al. (J. Fluid Mech., vol. 380, 1999, pp. 169–203), free-stream convected gusts interact with the boundary layer to drive the streak growth. Spanwise wall oscillations can either reduce or increase the total energy of the laminar streaks, depending upon the wall oscillation amplitude and frequency, as well as the free-stream gust properties. Reductions in streak energies of up to 90 % are obtained, indicating that spanwise wall oscillations are an effective technique for attenuating the laminar streak growth. Therefore they may suppress secondary boundary-layer instabilities and delay transition. The laminar boundary-layer base flow matches the Blasius profile in the streamwise and wall-normal directions, while in the spanwise direction a generalized version of the classical Stokes layer profile (generated by a wall oscillating beneath a quiescent fluid) occurs, which evolves downstream due to non-parallel flow effects. Via a Wentzel–Kramers–Brillouin–Jeffreys analysis, this generalized Stokes layer is shown to approach the classical Stokes layer in the limit of large downstream distances or high-frequency plate oscillations. The laminar streaks forced by the generalized and the classical Stokes flows differ significantly, which implies that the choice of the spanwise base flow may affect the secondary instability and transition in this flow. The analysis also proves that the use of the classical Stokes layer as spanwise base flow, as employed by Hack & Zaki (Phys. Fluids. vol. 24 (3), 2012, 034101), is inappropriate.

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Poels, Allison, Xavier Collin, Azemi Benaissa, and Dominique Poirel. "Mode and regime identification for a static NACA0012 airfoil at transitional Reynolds numbers." Mechanics & Industry 21, no. 6 (2020): 620. http://dx.doi.org/10.1051/meca/2020094.

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This work examines the flow structure modes in the boundary layer and in the wake of a NACA0012 airfoil in static conditions at transitional chord-based Reynolds numbers (Rec), for small angles of attack (α). A laminar mode, with a laminar separation of the boundary layer and laminar Kármán streets in the wake, was first observed for Rec < 61400 and α = 0°. For 77 000 < Rec < 118600, which corresponds to a regime between laminar and transitional mode called subcritical mode, the boundary layer exhibited a long separation bubble reattached close to the trailing edge, and the wake showed a turbulent Kármán street. Finally, for higher Rec and α, a critical transition mode consisted of a long bubble followed by a turbulent separation, and a less structured vortex street in the wake of the airfoil.

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Levitt, M. D., C. A. Fetzer, J. M. Kneip, J. H. Bond, and D. G. Levitt. "Quantitative assessment of luminal stirring in the perfused small intestine of the rat." American Journal of Physiology-Gastrointestinal and Liver Physiology 252, no. 3 (March 1, 1987): G325—G332. http://dx.doi.org/10.1152/ajpgi.1987.252.3.g325.

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We measured the resistance (RL) to CO absorption that resulted from poor luminal stirring in the constantly perfused rat jejunum. RL or calculated unstirred layer thickness was greater for 30-cm than 10-cm long segments, indicating lack of a uniform thickness of unstirred layer. The possibility that laminar flow existed in the gut was first tested by calculating expected CO absorptions from fluid moving with laminar flow. These values agreed closely with observed absorption rates. Laminar flow also was supported by the observation that CO absorption was independent of perfusate viscosity. Lastly, after sudden addition of phenolsulfonphthalein (PSP) to the perfusate, PSP outflow concentration was similar in tygon tubing (which has laminar flow) and a gut segment of comparable dimension. We conclude that flow in the perfused gut is laminar and that this laminar flow has many implications for studies carried out with the constant-perfusion technique.

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Lasauskas, Eduardas. "INFLUENCE OF TRANSITION LOCATION ON AIRFOIL DRAG." Aviation 9, no. 3 (September 30, 2005): 19–22. http://dx.doi.org/10.3846/16487788.2005.9635906.

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A comparison of predicted and measured laminar‐turbulent transition on the airfoil is presented. The MSES code is used for a prediction. The experimental data are taken from an experiment of W. Würz. Comparison of calculated results with measured data shows that the envelope of calculated individual frequencies coincides well with measured data in the transitional region for the attached boundary layer and for the separated laminar shear layer. For minimum drag, the laminar flow should be as long as possible and the shape parameter of the boundary layer at the transition should not exceed the value of 3.8. The optimum value of the shape parameter is 3.65 at Reynolds numbers from 1 to 2 million.

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QUADRIO, MAURIZIO, and PIERRE RICCO. "The laminar generalized Stokes layer and turbulent drag reduction." Journal of Fluid Mechanics 667 (November 16, 2010): 135–57. http://dx.doi.org/10.1017/s0022112010004398.

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This paper considers plane channel flow modified by waves of spanwise velocity applied at the wall and travelling along the streamwise direction. Both laminar and turbulent regimes for the streamwise flow are studied. When the streamwise flow is laminar, it is unaffected by the spanwise flow induced by the waves. This flow is a thin, unsteady and streamwise-modulated boundary layer that can be expressed in terms of the Airy function of the first kind. We name it the generalized Stokes layer because it reduces to the classical oscillating Stokes layer in the limit of infinite wave speed. When the streamwise flow is turbulent, the laminar generalized Stokes layer solution describes well the space-averaged turbulent spanwise flow, provided that the phase speed of the waves is sufficiently different from the turbulent convection velocity, and that the time scale of the forcing is smaller than the life time of the near-wall turbulent structures. Under these conditions, the drag reduction is found to scale with the Stokes layer thickness, which renders the laminar solution instrumental for the analysis of the turbulent flow. A classification of the turbulent flow regimes induced by the waves is presented by comparing parameters related to the forcing conditions with the space and time scales of the turbulent flow.

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Epstein, M., G. M. Hauser, and R. E. Henry. "Thermophoretic Deposition of Particles in Natural Convection Flow From a Vertical Plate." Journal of Heat Transfer 107, no. 2 (May 1, 1985): 272–76. http://dx.doi.org/10.1115/1.3247410.

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An analysis is made for thermophoretic transport of small particles through a free-convection boundary layer adjacent to a cold, vertical deposition surface. The gas-particle, boundary layer equations are solved numerically for both laminar and turbulent flow. The numerical results indicate that, for a fixed set of boundary conditions and physical properties, the particle concentration at the wall in the laminar flow is very close to that in turbulent flow. A simple expression is suggested relating the particle transport rate to the heat transfer coefficient for the laminar and turbulent flow regimes.

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36

LINGWOOD, R. J. "On the impulse response for swept boundary-layer flows." Journal of Fluid Mechanics 344 (August 10, 1997): 317–34. http://dx.doi.org/10.1017/s0022112097006149.

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Swept-wedge flows are used to study the effects of pressure gradient and flow angle on the stability of three-dimensional laminar boundary layers. It is shown that the flow is absolutely unstable in the chordwise direction, i.e. disturbances grow in time at every chordwise location, for certain parameter combinations. However, laminar–turbulent transition may still be a convective process.

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Avramenko, A. A., A. O. Tyrinov, N. P. Dmitrenko, and Yu Yu Kovetska. "HEAT TRANSFER IN GRADIENT LAMINAR FLOWS." Thermophysics and Thermal Power Engineering 43, no. 3 (October 8, 2021): 30–35. http://dx.doi.org/10.31472/ttpe.3.2021.4.

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The development of new areas of research in the field of theoretical thermophysics requires reliable analytical solutions that could take into account the main aspects of physical parameters in the studied objects. One such analytical technique is symmetry groups. On the basis of symmetry groups the problem of heat transfer in gradient laminar flows is solved in the paper. For the first time, the symmetries of the energy equation for the boundary layer at an arbitrary changing velocity at marching direction are obtained. Examples of the use of group analysis methods for the study of heat transfer in the boundary layer of an incompressible fluid are demonstrated. The problems of heat transfer in the boundary layer on a heat-conducting wall with a constant temperature and on a heat-insulated wall are considered. Analytical relations for temperature and heat transfer coefficients distribution are obtained.

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38

Obara, Clifford J., and C. P. van Dam. "Keel Design for Low Viscous Drag." Journal of Ship Research 33, no. 02 (June 1, 1989): 145–55. http://dx.doi.org/10.5957/jsr.1989.33.2.145.

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Foil and planform parameters which govern the level of viscous drag produced by the keel of a sailing yacht are discussed. It is shown that the application of laminar boundary-layer flow offers great potential for increased boat speed resulting from the reduction in viscous drag. Three foil shapes have been designed and it is shown that their hydrodynamic characteristics are very much dependent on location and mode of boundary-layer transition. The planform parameter which strongly affects the capabilities of the keel to achieve laminar flow is leading-edge sweep angle. The two significant phenomena related to keel sweep angle which can cause premature transition of the laminar boundary layer are crossflow instability and turbulent contamination of the leading-edge attachment line. These flow phenomena and methods to control them are discussed in detail. The remaining factors that affect the maintainability of laminar flow include surface roughness, surface waviness, and freestream turbulence. Recommended limits for these factors are given to insure achievability of laminar flow on the keel. In addition, the application of a simple trailing-edge flap to improve the hydrodynamic characteristics of a foil at moderate-to-high leeway angles is studied.

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Bogey, Christophe, and Roberto Sabatini. "Effects of nozzle-exit boundary-layer profile on the initial shear-layer instability, flow field and noise of subsonic jets." Journal of Fluid Mechanics 876 (August 1, 2019): 288–325. http://dx.doi.org/10.1017/jfm.2019.546.

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The influence of the nozzle-exit boundary-layer profile on high-subsonic jets is investigated by performing compressible large-eddy simulations (LES) for three isothermal jets at a Mach number of 0.9 and a diameter-based Reynolds number of $5\times 10^{4}$, and by conducting linear stability analyses from the mean-flow fields. At the exit section of a pipe nozzle, the jets exhibit boundary layers of momentum thickness of approximately 2.8 % of the nozzle radius and a peak value of turbulence intensity of 6 %. The boundary-layer shape factors, however, vary and are equal to 2.29, 1.96 and 1.71. The LES flow and sound fields differ significantly between the first jet with a laminar mean exit velocity profile and the two others with transitional profiles. They are close to each other in these two cases, suggesting that similar results would also be obtained for a jet with a turbulent profile. For the two jets with non-laminar profiles, the instability waves in the near-nozzle region emerge at higher frequencies, the mixing layers spread more slowly and contain weaker low-frequency velocity fluctuations and the noise levels in the acoustic field are lower by 2–3 dB compared to the laminar case. These trends can be explained by the linear stability analyses. For the laminar boundary-layer profile, the initial shear-layer instability waves are most strongly amplified at a momentum-thickness-based Strouhal number $St_{\unicode[STIX]{x1D703}}=0.018$, which is very similar to the value obtained downstream in the mixing-layer velocity profiles. For the transitional profiles, on the contrary, they predominantly grow at higher Strouhal numbers, around $St_{\unicode[STIX]{x1D703}}=0.026$ and 0.032, respectively. As a consequence, the instability waves rapidly vanish during the boundary-layer/shear-layer transition in the latter cases, but continue to grow over a large distance from the nozzle in the former case, leading to persistent large-scale coherent structures in the mixing layers for the jet with a laminar exit velocity profile.

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Khapko, T., P. Schlatter, Y. Duguet, and D. S. Henningson. "Turbulence collapse in a suction boundary layer." Journal of Fluid Mechanics 795 (April 14, 2016): 356–79. http://dx.doi.org/10.1017/jfm.2016.205.

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Turbulence in the asymptotic suction boundary layer is investigated numerically at the verge of laminarisation using direct numerical simulation. Following an adiabatic protocol, the Reynolds number $Re$ is decreased in small steps starting from a fully turbulent state until laminarisation is observed. Computations in a large numerical domain allow in principle for the possible coexistence of laminar and turbulent regions. However, contrary to other subcritical shear flows, no laminar–turbulent coexistence is observed, even near the onset of sustained turbulence. High-resolution computations suggest a critical Reynolds number $Re_{g}\approx 270$, below which turbulence collapses, based on observation times of $O(10^{5})$ inertial time units. During the laminarisation process, the turbulent flow fragments into a series of transient streamwise-elongated structures, whose interfaces do not display the characteristic obliqueness of classical laminar–turbulent patterns. The law of the wall, i.e. logarithmic scaling of the velocity profile, is retained down to $Re_{g}$, suggesting a large-scale wall-normal transport absent in internal shear flows close to the onset. In order to test the effect of these large-scale structures on the near-wall region, an artificial volume force is added to damp spanwise and wall-normal fluctuations above $y^{+}=100$, in viscous units. Once the largest eddies have been suppressed by the forcing, and thus turbulence is confined to the near-wall region, oblique laminar–turbulent interfaces do emerge as in other wall-bounded flows, however only transiently. These results suggest that oblique stripes at the onset are a prevalent feature of internal shear flows, but will not occur in canonical boundary layers, including the spatially growing ones.

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Schrauf, G. "Status and perspectives of laminar flow." Aeronautical Journal 109, no. 1102 (December 2005): 639–44. http://dx.doi.org/10.1017/s000192400000097x.

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AbstractAfter identifying the ecological and economic drivers for use of laminar flow technology, we outline the mechanisms of laminarturbulent boundary layer transition and review the status of natural laminar flow (NLF) and hybrid laminar flow control (HLFC). New ways to reduce the complexity of HLFC systems are presented, and the remaining steps to achieve technology readiness are discussed.

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Jonker, A. S., J. J. Bosman, E. H. Mathews, and L. Liebenberg. "Flow over a glider canopy." Aeronautical Journal 118, no. 1204 (June 2014): 669–82. http://dx.doi.org/10.1017/s0001924000009428.

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Abstract In order to minimise drag, the front part of most modern glider fuselages is shaped so that laminar flow is preserved to a position close to the wing-to-fuselage junction. Experimental investigations on a full-scale JS1 competition glider however revealed that the laminar boundary layer in fact trips to turbulent flow at the fuselage-to-canopy junction position, increasing drag. This is possibly due to ventilation air leaking from the cockpit to the fuselage surface through the canopy seal, or that the gap is merely too large and therefore trips the boundary layer to turbulent flow. The effect of air leaking from the fuselage-to-canopy gap as well as the size of the gap was thus investigated with the use of computational fluid dynamics. It was found that if air was leaking through this gap the boundary layer would be tripped from laminar to turbulent flow. It was also found that the width of the canopy-to-fuselage gap plays a significant role in the preservation of laminar flow. If the gap is less than 1mm wide, the attached boundary layer is able to negotiate the gap without being tripped to turbulent flow, while if the gap is 3mm and wider, it will be tripped from laminar to turbulent flow. The work shows that aerodynamic drag on a glider can be significantly minimised by completely sealing the fuselage-to-canopy gap and by ensuring a seal gap-width of less than 1mm.

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Williams, James C. "Singularities in solutions of the three-dimensional laminar-boundary-layer equations." Journal of Fluid Mechanics 160 (November 1985): 257–79. http://dx.doi.org/10.1017/s0022112085003470.

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The three-dimensional steady laminar-boundary-layer equations have been cast in the appropriate form for semisimilar solutions, and it is shown that in this form they have the same structure as the semisimilar form of the two-dimensional unsteady laminar-boundary-layer equations. This similarity suggests that there may be a new type of singularity in solutions to the three-dimensional equations: a singularity that is the counterpart of the Stewartson singularity in certain solutions to the unsteady boundary-layer equations.A family of simple three-dimensional laminar boundary-layer flows has been devised and numerical solutions for the development of these flows have been obtained in an effort to discover and investigate the new singularity. The numerical results do indeed indicate the existence of such a singularity. A study of the flow approaching the singularity indicates that the singularity is associated with the domain of influence of the flow for given initial (upstream) conditions as is prescribed by the Raetz influence principle.

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Vijgen, P. M. H. W., C. P. van Dam, and C. J. Obara. "Turbulence Effects on the Design and Performance of Low-Drag Keels." Journal of Ship Research 36, no. 03 (September 1, 1992): 268–79. http://dx.doi.org/10.5957/jsr.1992.36.3.268.

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Achievement of laminar boundary-layer flow over the keel of sailing yachts offers great potential for increased boat speed resulting from the reduction in viscous drag. The intensity and the spectral energy distribution of small-scale turbulence in the upper layer of the ocean can have a large effect on the extent of laminar flow and, hence, the drag reduction. A detailed summary and interpretation is provided of measured turbulent intensities and length scales in the upper ocean. An analysis is given of the effect of small-scale turbulence on boundary-layer transition and profile drag for two laminar-flow foils at zero and moderate leeway angles. Using the modified en-transition criterion it is shown that the level of small-scale oceanic turbulence is an important parameter in the design of a laminar-flow foil. At high turbulence levels, the foil with a more forward location of the minimum-pressure point generates less drag than the foil with a more aft location of the minimum-pressure point at the same flow conditions.

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45

Ó Náraigh, Lennon, Peter D. M. Spelt, and Stephen J. Shaw. "Absolute linear instability in laminar and turbulent gas–liquid two-layer channel flow." Journal of Fluid Mechanics 714 (January 2, 2013): 58–94. http://dx.doi.org/10.1017/jfm.2012.452.

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AbstractWe study two-phase stratified flow where the bottom layer is a thin laminar liquid and the upper layer is a fully developed gas flow. The gas flow can be laminar or turbulent. To determine the boundary between convective and absolute instability, we use Orr–Sommerfeld stability theory, and a combination of linear modal analysis and ray analysis. For turbulent gas flow, and for the density ratio $r= 1000$, we find large regions of parameter space that produce absolute instability. These parameter regimes involve viscosity ratios of direct relevance to oil and gas flows. If, instead, the gas layer is laminar, absolute instability persists for the density ratio $r= 1000$, although the convective/absolute stability boundary occurs at a viscosity ratio that is an order of magnitude smaller than in the turbulent case. Two further unstable temporal modes exist in both the laminar and the turbulent cases, one of which can exclude absolute instability. We compare our results with an experimentally determined flow-regime map, and discuss the potential application of the present method to nonlinear analyses.

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Higuera, F. J. "The hydraulic jump in a viscous laminar flow." Journal of Fluid Mechanics 274 (September 10, 1994): 69–92. http://dx.doi.org/10.1017/s0022112094002041.

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The hydraulic jump appearing in the viscous laminar flow of a thin liquid layer over a finite horizontal plate is studied using the boundary-layer approximation for the flow in and around the jump. The position and structure of the jump are determined by numerically solving the resulting problem with a boundary condition at the edge of the plate that expresses the matching of the layer with the shorter region where the liquid turns around and falls under the action of gravity. When the Froude number of the flow ahead of the jump is very large, the jump is much shorter than the horizontal extent of the layer, though still much longer than its depth. An asymptotic description of the inner structure of such a jump is given, building upon the analysis of Bowles & Smith for the short interaction region at the leading end of the jump. This structure consists of a fast moving separated flow in the upper part of the layer that progressively slows down by ingesting new fluid across its lower boundary, until the hydrostatically generated adverse pressure gradient makes it recirculate in the lower part of the layer. The effects of the surface tension and the cross-stream pressure variation owing to the curvature of the streamlines are taken into account in the jump and in the flow approaching the edge of the plate, showing that they can lead to quantitative and also qualitative changes of the jump structure, including a local breakdown of the boundary-layer approximation.

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Yamagata, M., and J. R. Sanes. "Target-independent diversification and target-specific projection of chemically defined retinal ganglion cell subsets." Development 121, no. 11 (November 1, 1995): 3763–76. http://dx.doi.org/10.1242/dev.121.11.3763.

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In diverse vertebrate species, defined subsets of retinal ganglion cells (RGCs, the neurons that project from retina to brain) are distinguishable on the basis of their dendritic morphology, physiological properties, neurotransmitter content and synaptic targets. Little is known about when this diversity arises, whether diversification requires target-derived signals, and how subtype-specific projection patterns are established. Here, we have used markers for two chemically defined RGC subsets in chick retina to address these issues. Antibodies to substance P (SP) and the nicotine acetylcholine receptor (AChR) beta 2 subunit label two small (< 10%), mutually exclusive groups of RGCs in mature retina. SP and AChRs accumulate in distinct RGCs before retinotectal synapses have formed. Moreover, both populations of RGCs form in retinae that develop following tectal ablation or transplantation to the coelomic cavity. Thus, RGC subsets acquire distinct neurotransmitter phenotypes in the absence of extraretinal cues. In the mature optic tectum, SP- and AChR-positive RGC axonal arbors are confined to distinct retinorecipient (synaptic) laminae. In the developing tectum, SP- and AChR-positive axons are initially intermingled in a superficial fiber layer, but then enter and arborize in appropriate laminae soon after those laminae form. Importantly, SP-positive axons, which synapse in a superficial lamina, never extend into the deeper, AChR-positive lamina. Tectal interneurons rich in SP receptors are concentrated in the lamina to which SP-positive RGC axons project, and a set of cholinergic (choline acetyltransferase-positive) tectal projection neurons elaborate dendrites in the lamina to which AChR-positive RGC axons project. These populations of tectal neurons, which are likely targets of the RGC subsets, form in tecta that develop following enucleation. Thus, RGCs and their targets can diversify in each others absence. Accordingly, we propose that the lamina-selective connectivity we observe reflects the presence of complementary cues on RGC subsets and their laminar targets.

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Stankovic, P., M. Vasic, V. Djukic, Lj Janosevic, and M. Vukasinovic. "Vocal fold masses removal: The sub epithelial micro flap technique." Acta chirurgica Iugoslavica 55, no. 4 (2008): 43–47. http://dx.doi.org/10.2298/aci0804043s.

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Vocal fold mass removal techniques were significantly modified back in 1970s by Hirano's laminar vocal structure and physiology of phonation works, as well as Titze's vibratory vocal cycle works. New methods were to come. Removing the lession by maximum preservation of vocal laminar microstructure (lamina propria and epithelium) and minimal damage of surrounding normal vocal tissue, was pointed out. Microflap technique is based on presenting the superficial layer of lamina propria with the lesion and removing the lession without damage of the mucosa. Preserving of the mucosal layer provides the shield for vibratory substructures. There are two elementary approaches for microflap: lateral and medial. Lateral microflap technique enables better identification of vocal ligament and lowers the risk of it's injury, particularly when scars and tightly adherent lessions are present. This technique has been used in case of big or diffuse lesions, such as vocal oedema or vocal lygament identification difficulties (e.g. vocal scarification). Medial microflap technique seems to be appropriate in removing smaller, localized lessions, such as cysts and vocal polyps. Our 45 patients experience is presented in this article , in 30 patients lessions were removed by lateral microflap technique (46 vocal cords in total), while 15 patients were treated by medial microflap technique. The outcome was assumed by endovideolaryngostroboscopic analysis of glottal occlusion and mucosal wave prior and following to the procedure. Reinke oedema management results were analysed separately.

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Beyene, Shiferaw D., Beshah Ayalew, and Srikanth Pilla. "On the Inter-Laminar Shear Strength of Composites Manufactured via a Stepped-Concurrent UV Curing and Layering Process." Journal of Composite Materials 53, no. 28-30 (June 12, 2019): 4149–59. http://dx.doi.org/10.1177/0021998319846550.

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In this paper, we set to examine the inter-laminar shear strength of a fiber-reinforced composite part manufactured via a stepped-concurrent ultraviolet curing and layering process. This process was specifically proposed for making epoxy-based thick parts, whereby a layer-by-layer, model-based, optimal layering time and ultraviolet control scheme is set up with the objective of minimizing the degree of cure deviation across the final thick part. We focus on a cationic curing process wherein additional energy savings are possible by switching off the ultraviolet source after initiating the curing reaction with the ultraviolet source at each layer addition. Since the inter-laminar sheer strength of parts made via a layering process is often a concern, we consider the application of in-situ consolidation pressure in the layering process. We then characterize the inter-laminar shear strength by manufacturing samples with application of different in-situ consolidation pressures and measuring the inter-laminar shear strength of each sample by the short-beam shear test. The results showed that the inter-laminar shear strength of composite parts fabricated with the proposed stepped-concurrent curing, and layering process increases with the applied consolidation pressure up to a point. Scanning electron microscopy of samples cured at different in-situ consolidation pressure showed that the sample with optimum consolidation pressure has relatively uniform fiber to resin distribution and hence improved inter-laminar shear strength.

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Kopić, Janja, Alisa Junaković, Iva Salamon, Mladen-Roko Rasin, Ivica Kostović, and Željka Krsnik. "Early Regional Patterning in the Human Prefrontal Cortex Revealed by Laminar Dynamics of Deep Projection Neuron Markers." Cells 12, no. 2 (January 5, 2023): 231. http://dx.doi.org/10.3390/cells12020231.

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Early regional patterning and laminar position of cortical projection neurons is determined by activation and deactivation of transcriptional factors (TFs) and RNA binding proteins (RBPs) that regulate spatiotemporal framework of neurogenetic processes (proliferation, migration, aggregation, postmigratory differentiation, molecular identity acquisition, axonal growth, dendritic development, and synaptogenesis) within transient cellular compartments. Deep-layer projection neurons (DPN), subplate (SPN), and Cajal–Retzius neurons (CRN) are early-born cells involved in the establishment of basic laminar and regional cortical architecture; nonetheless, laminar dynamics of their molecular transcriptional markers remain underexplored. Here we aimed to analyze laminar dynamics of DPN markers, i.e., transcription factors TBR1, CTIP2, TLE4, SOX5, and RBP CELF1 on histological serial sections of the human frontal cortex between 7.5–15 postconceptional weeks (PCW) in reference to transient proliferative, migratory, and postmigratory compartments. The subtle signs of regional patterning were seen during the late preplate phase in the pattern of sublaminar organization of TBR1+/Reelin+ CRN and TBR1+ pioneering SPN. During the cortical plate (CP)-formation phase, TBR1+ neurons became radially aligned, forming continuity from a well-developed subventricular zone to CP showing clear lateral to medial regional gradients. The most prominent regional patterning was seen during the subplate formation phase (around 13 PCW) when a unique feature of the orbitobasal frontal cortex displays a “double plate” pattern. In other portions of the frontal cortex (lateral, dorsal, medial) deep portion of CP becomes loose and composed of TBR1+, CTIP2+, TLE4+, and CELF1+ neurons of layer six and later-born SPN, which later become constituents of the expanded SP (around 15 PCW). Overall, TFs and RBPs mark characteristic regional laminar dynamics of DPN, SPN, and CRN subpopulations during remarkably early fetal phases of the highly ordered association cortex development.

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Journal articles on the topic 'Laminar layer'

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