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Huang, Aiqun, i Aniket Bhattacharya. "DNA confined in a two-dimensional strip geometry". EPL (Europhysics Letters) 106, nr 1 (1.04.2014): 18004. http://dx.doi.org/10.1209/0295-5075/106/18004.
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FORMIGA, J. B., i C. ROMERO. "ON THE GEOMETRICAL CONFINEMENT OF FERMIONS". International Journal of Modern Physics: Conference Series 18 (styczeń 2012): 86–90. http://dx.doi.org/10.1142/s2010194512008252.
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To show the important role that geometry may play in the problem of confining particles to our four-dimensional spacetime, we consider a five-dimensional model where fermions are confined in a hypersurface due to an interaction with geometric fields. We use two different fields which appear in non-Riemannian geometries, namely, the Weyl one-form and the torsion two-form. We show that for suitable choices of these fields one manages to confine fermions in our brane (our four-dimensional world). It turns out that this confinement is independent of the energy and the mass of the fermions.
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Bubeck, R., C. Bechinger, S. Neser i P. Leiderer. "Melting and Reentrant Freezing of Two-Dimensional Colloidal Crystals in Confined Geometry". Physical Review Letters 82, nr 16 (19.04.1999): 3364–67. http://dx.doi.org/10.1103/physrevlett.82.3364.
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Li, Haobo, Jianping Xiao, Qiang Fu i Xinhe Bao. "Confined catalysis under two-dimensional materials". Proceedings of the National Academy of Sciences 114, nr 23 (22.05.2017): 5930–34. http://dx.doi.org/10.1073/pnas.1701280114.
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Confined microenvironments formed in heterogeneous catalysts have recently been recognized as equally important as catalytically active sites. Understanding the fundamentals of confined catalysis has become an important topic in heterogeneous catalysis. Well-defined 2D space between a catalyst surface and a 2D material overlayer provides an ideal microenvironment to explore the confined catalysis experimentally and theoretically. Using density functional theory calculations, we reveal that adsorption of atoms and molecules on a Pt(111) surface always has been weakened under monolayer graphene, which is attributed to the geometric constraint and confinement field in the 2D space between the graphene overlayer and the Pt(111) surface. A similar result has been found on Pt(110) and Pt(100) surfaces covered with graphene. The microenvironment created by coating a catalyst surface with 2D material overlayer can be used to modulate surface reactivity, which has been illustrated by optimizing oxygen reduction reaction activity on Pt(111) covered by various 2D materials. We demonstrate a concept of confined catalysis under 2D cover based on a weak van der Waals interaction between 2D material overlayers and underlying catalyst surfaces.
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Zagorodnev, Igor V., Andrey A. Zabolotnykh, Danil A. Rodionov i Vladimir A. Volkov. "Two-Dimensional Plasmons in Laterally Confined 2D Electron Systems". Nanomaterials 13, nr 6 (8.03.2023): 975. http://dx.doi.org/10.3390/nano13060975.
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The collective oscillations of charge density (plasmons) in conductive solids are basic excitations that determine the dynamic response of the system. In infinite two-dimensional (2D) electron systems, plasmons have gapless dispersion covering a broad spectral range from subterahertz to infrared, which is promising in light-matter applications. We discuss the state-of-the-art physics of 2D plasmons, especially in confined 2D electron systems in stripe and disk geometry, using the simplest approach for conductivity. When the metal gate is placed in the vicinity of the 2D electron system, an analytical description of the plasmon frequency and damping can be easily obtained. We also analyze gated plasmons in the disk when it was situated at various distances from the gate, and discuss in detail the nontrivial behavior of the damping. We predict that it is not a simple sum of the radiative and collisional dampings, but has a nonmonotonic dependence on the system parameters. For high-mobility 2D systems, this opens the way to achieve the maximal quality factor of plasma resonances. Lastly, we discuss the recently discovered near-gate 2D plasmons propagating along the laterally confined gate, even without applied bias voltage and having gapless dispersion when the gate has the form of a stripe, and discrete spectrum when the gate is in the form of disk. It allows for one to drive the frequency and spatial propagation of such plasmons.
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KESSLER, DAVID A., i HERBERT LEVINE. "TIP INSTABILITY DURING CONFINED DIFFUSION-LIMITED GROWTH". Modern Physics Letters B 02, nr 08 (wrzesień 1988): 945–51. http://dx.doi.org/10.1142/s0217984988000746.
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We study diffusion-limited crystal growth in a two dimensional channel geometry. We demonstrate that although there exists a linearly stable steady-state finger solution of the pattern evolution equations, the true dynamical behavior can be controlled by a tip-widening instability. Possible scenarios for the long-time behavior of the system are presented.
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Tian, Jiting, Walter Kob i Jean-Louis Barrat. "Are strongly confined colloids good models for two dimensional liquids?" Journal of Chemical Physics 156, nr 16 (28.04.2022): 164903. http://dx.doi.org/10.1063/5.0086749.
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Quasi-two-dimensional (quasi-2D) colloidal hard-sphere suspensions confined in a slit geometry are widely used as two-dimensional (2D) model systems in experiments that probe the glassy relaxation dynamics of 2D systems. However, the question to what extent these quasi-2D systems indeed represent 2D systems is rarely brought up. Here, we use computer simulations that take into account hydrodynamic interactions to show that dense quasi-2D colloidal bi-disperse hard-sphere suspensions exhibit much more rapid diffusion and relaxation than their 2D counterparts at the same area fraction. This difference is induced by the additional vertical space in the quasi-2D samples in which the small colloids can move out of the 2D plane, therefore allowing overlap between particles in the projected trajectories. Surprisingly, this difference in the dynamics can be accounted for if, instead of using the surface density, one characterizes the systems by means of a suitable structural quantity related to the radial distribution function. This implies that in the two geometries, the relevant physics for glass formation is essentially identical. Our results provide not only practical implications on 2D colloidal experiments but also interesting insights into the 3D-to-2D crossover in glass-forming systems.
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Ciftja, Orion, LeDarion Escamilla i Ryan Mills. "Shape-Dependent Energy of an Elliptical Jellium Background". Advances in Condensed Matter Physics 2015 (2015): 1–4. http://dx.doi.org/10.1155/2015/851356.
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The jellium model is commonly used in condensed matter physics to study the properties of a two-dimensional electron gas system. Within this approximation, one assumes that electrons move in the presence of a neutralizing background consisting of uniformly spread positive charge. When properties of bulk systems (of infinite size) are studied, shape of the jellium domain is irrelevant. However, the same cannot be said when one is dealing with finite systems of electrons confined in a finite two-dimensional region of space. In such a case, geometry and shape of the jellium background play a role on the overall properties of the system. In this work, we assume that the region where the electrons are confined is represented by a jellium background charge with an elliptical shape. It is shown that, in this case, the Coulomb self-energy of the elliptically shaped region can be exactly calculated in closed analytical form by using suitable mathematical transformations. The results obtained reveal the external influence of geometry/shape on the properties of two-dimensional systems of few electrons confined to a small finite region of space.
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GATICA, SILVINA M., M. MERCEDES CALBI, GEORGE STAN, R. ANDREEA TRASCA i MILTON W. COLE. "QUASI-ONE DIMENSIONAL FLUIDS THAT EXHIBIT HIGHER DIMENSIONAL BEHAVIOR". International Journal of Modern Physics B 24, nr 25n26 (20.10.2010): 5051–59. http://dx.doi.org/10.1142/s0217979210057195.
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Fluids confined within narrow channels exhibit a variety of phases and phase transitions associated with their reduced dimensionality. In this review paper, we illustrate the crossover from quasi-one dimensional to higher effective dimensionality behavior of fluids adsorbed within different carbon nanotubes geometries. In the single nanotube geometry, no phase transitions can occur at finite temperature. Instead, we identify a crossover from a quasi-one dimensional to a two dimensional behavior of the adsorbate. In bundles of nanotubes, phase transitions at finite temperature arise from the transverse coupling of interactions between channels.
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Gauthier, Guillaume, Matthew T. Reeves, Xiaoquan Yu, Ashton S. Bradley, Mark A. Baker, Thomas A. Bell, Halina Rubinsztein-Dunlop, Matthew J. Davis i Tyler W. Neely. "Giant vortex clusters in a two-dimensional quantum fluid". Science 364, nr 6447 (27.06.2019): 1264–67. http://dx.doi.org/10.1126/science.aat5718.
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Adding energy to a system through transient stirring usually leads to more disorder. In contrast, point-like vortices in a bounded two-dimensional fluid are predicted to reorder above a certain energy, forming persistent vortex clusters. In this study, we experimentally realize these vortex clusters in a planar superfluid: a 87Rb Bose-Einstein condensate confined to an elliptical geometry. We demonstrate that the clusters persist for long time periods, maintaining the superfluid system in a high-energy state far from global equilibrium. Our experiments explore a regime of vortex matter at negative absolute temperatures and have relevance for the dynamics of topological defects, two-dimensional turbulence, and systems such as helium films, nonlinear optical materials, fermion superfluids, and quark-gluon plasmas.
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Park, Bum Jun, Bomsock Lee i Taekyung Yu. "Pairwise interactions of colloids in two-dimensional geometric confinement". Soft Matter 10, nr 48 (2014): 9675–80. http://dx.doi.org/10.1039/c4sm01823k.
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Ou, Meng-Jun, i Ji-Xuan Hou. "Harmonically confined Bose–Einstein condensation on the surface of a cylinder". Modern Physics Letters B 35, nr 17 (31.03.2021): 2150285. http://dx.doi.org/10.1142/s0217984921502857.
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It is well known that Bose–Einstein condensation cannot occur in a free two-dimensional (2D) system. Recently, several studies have showed that BEC can occur on the surface of a sphere. We investigate BEC on the surface of cylinder on both sides of which atoms are confined in a one-dimensional (1D) harmonic potential. In this work, only the non-interacting Bose gas is considered. We determine the critical temperature and the condensate fraction in the geometry using the semi-classical approximation. Moreover, the thermodynamic properties of ideal bosons are also studied using the grand canonical partition function.
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Zhang, Jie, Haitao Dai, Chao Yan, Degang Xu, Yanjun Liu, Dan Luo i Xiaowei Sun. "Lasing properties from dye-doped holographic polymer dispersed liquid crystal confined in two-dimensional cylindrical geometry". Optical Materials Express 6, nr 4 (28.03.2016): 1367. http://dx.doi.org/10.1364/ome.6.001367.
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Cosentino Lagomarsino, Marco, Marileen Dogterom i Marjolein Dijkstra. "Isotropic–nematic transition of long, thin, hard spherocylinders confined in a quasi-two-dimensional planar geometry". Journal of Chemical Physics 119, nr 6 (8.08.2003): 3535–40. http://dx.doi.org/10.1063/1.1588994.
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Swan, James W., i John F. Brady. "The hydrodynamics of confined dispersions". Journal of Fluid Mechanics 687 (17.10.2011): 254–99. http://dx.doi.org/10.1017/jfm.2011.351.
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AbstractA method is proposed for computing the low-Reynolds-number hydrodynamic forces on particles comprising a suspension confined by two parallel, no-slip walls. This is constructed via the two-dimensional analogue of Hasimoto’s solution (J. Fluid Mech., vol. 5, 1959, pp. 317–328) for a periodic array of point forces in a viscous, incompressible fluid, and, like Hasimoto, the summation of interactions is accelerated by substitution and superposition of ‘Ewald-like’ forcing. This method is akin to the accelerated Stokesian dynamics technique (J. Fluid Mech., vol. 448, 2001, pp. 115–146) and models the suspension dynamics with log–linear computational scaling. The effectiveness of this approach is demonstrated with a calculation of the high-frequency dynamic viscosity of a colloidal dispersion as function of volume fraction and channel width. Similarly, the short-time self-diffusivity for and the sedimentation rate of spherical particles in a confined suspension are determined. The results demonstrate the influence of confining geometry on the transport of small particles, which is becoming increasingly important for micro- and biofluidics.
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Lefauve, Adrien, J. L. Partridge, Qi Zhou, S. B. Dalziel, C. P. Caulfield i P. F. Linden. "The structure and origin of confined Holmboe waves". Journal of Fluid Mechanics 848 (5.06.2018): 508–44. http://dx.doi.org/10.1017/jfm.2018.324.
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Finite-amplitude manifestations of stratified shear flow instabilities and their spatio-temporal coherent structures are believed to play an important role in turbulent geophysical flows. Such shear flows commonly have layers separated by sharp density interfaces, and are therefore susceptible to the so-called Holmboe instability, and its finite-amplitude manifestation, the Holmboe wave. In this paper, we describe and elucidate the origin of an apparently previously unreported long-lived coherent structure in a sustained stratified shear flow generated in the laboratory by exchange flow through an inclined square duct connecting two reservoirs filled with fluids of different densities. Using a novel measurement technique allowing for time-resolved, near-instantaneous measurements of the three-component velocity and density fields simultaneously over a three-dimensional volume, we describe the three-dimensional geometry and spatio-temporal dynamics of this structure. We identify it as a finite-amplitude, nonlinear, asymmetric confined Holmboe wave (CHW), and highlight the importance of its spanwise (lateral) confinement by the duct boundaries. We pay particular attention to the spanwise vorticity, which exhibits a travelling, near-periodic structure of sheared, distorted, prolate spheroids with a wide ‘body’ and a narrower ‘head’. Using temporal linear stability analysis on the two-dimensional streamwise-averaged experimental flow, we solve for three-dimensional perturbations having two-dimensional, cross-sectionally confined eigenfunctions and a streamwise normal mode. We show that the dispersion relation and the three-dimensional spatial structure of the fastest-growing confined Holmboe instability are in good agreement with those of the observed confined Holmboe wave. We also compare those results with a classical linear analysis of two-dimensional perturbations (i.e. with no spanwise dependence) on a one-dimensional base flow. We conclude that the lateral confinement is an important ingredient of the confined Holmboe instability, which gives rise to the CHW, with implications for many inherently confined geophysical flows such as in valleys, estuaries, straits or deep ocean trenches. Our results suggest that the CHW is an example of an experimentally observed, inherently nonlinear, robust, long-lived coherent structure which has developed from a linear instability. We conjecture that the CHW is a promising candidate for a class of exact coherent states underpinning the dynamics of more disordered, yet continually forced stratified shear flows.
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Samsam-Khayani, Hadi, Shabnam Mohammadshahi i Kyung Chun Kim. "Experimental Study on Physical Behavior of Fluidic Oscillator in a Confined Cavity with Sudden Expansion". Applied Sciences 10, nr 23 (3.12.2020): 8668. http://dx.doi.org/10.3390/app10238668.
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In this study, two-dimensional time-resolved particle image velocimetry (2D-TR-PIV) was used to investigate the effect of the external domain on oscillating jets from double-feedback fluidic oscillators. Two different cases with different Re numbers (2680–10,730), as free external domain and fully confined were studied. Time-averaged results showed although a self-oscillating jet was attained for the free external domain, it could not be achieved for a fully confined geometry. For a fully confined geometry at Re = 2680, two symmetric vortices did not allow the jet to oscillate and at Re = 6440, the flow pattern in the external region became non-symmetric due to the Coanda vortex, subsequently, the self-oscillating jet was not observed. At Re = 10,730, the strength of the jet was inclined to cope with such vortices and tended to oscillate. However, strong vortices were created near the exit region of the fluidic oscillator, which led to an almost non-symmetric pattern. In addition, the proper orthogonal decomposition (POD) method and phase-averaged analysis were applied to obtain the unsteady behavior of flow and the most energetic dynamic structure. Interestingly, at Re = 6440, the third mode was still energetic for fully confined, but for other cases, the first two modes were the most energetic modes, which showed vigorous coherent structures.
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Zajec, Boštjan, Marko Matkovič, Nejc Kosanič, Jure Oder, Blaž Mikuž, Jan Kren i Iztok Tiselj. "Turbulent Flow over Confined Backward-Facing Step: PIV vs. DNS". Applied Sciences 11, nr 22 (10.11.2021): 10582. http://dx.doi.org/10.3390/app112210582.
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Particle Image Velocimetry measurements of the liquid velocity fields in the flow over the backward-facing step were performed in the same flow configuration as in the existing Direct Numerical Simulation (DNS). The experiment and the simulation were performed in an identical cross-section geometry with step expansion rate 2.25 and the square shape of the outlet duct at the Reynolds number in an inlet part of the section 7100. The experiment was performed in transparent test section, 1.2 m long, with 20 × 45 mm2 cross-section upstream and 45 × 45 mm2 downstream, while a domain that was three times shorter was used in the DNS. A 2D-2C PIV system with a single high-speed camera and a pulse laser was used for a series of two-dimensional measurements of the velocity field at several cross-sections from two different perspectives. Variables analyzed in the experiment are time-averaged fluid velocities, velocity RMS fluctuations and two components of the Reynolds stress tensor. The key novelty is the comparison of two very accurate approaches, PIV and DNS, in the same cross-section geometry. Comparison of the similarities, and especially the differences between the two approaches, elucidates uncertainties of both studies and answers the question on what kind of agreement is expected when two very accurate approaches are compared.
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Witkowski, K. K., i T. K. Kopeć. "Dimensional Crossover in the Bose–Einstein Condensation Confined to Anisotropic Three-Dimensional Lattices". Journal of Low Temperature Physics 201, nr 3-4 (25.07.2020): 340–72. http://dx.doi.org/10.1007/s10909-020-02499-y.
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Abstract The Bose–Einstein condensation (BEC) in three-dimensional (3D) anisotropic lattices is studied. We present theoretical results for the critical temperature for BEC, chemical potential, condensate fraction and relevant thermodynamic quantities like: internal energy, entropy, specific heat and compressibility as a function of anisotropy parameter being the ratio of the nearest-neighbor in-plane ($$t_\parallel$$ t ‖ ) and out-of-plane ($$t_\perp$$ t ⊥ ) hopping amplitudes. In particular, considered scenarios include weakly coupled two-dimensional (2D) planes ($$t_\perp /t_\parallel \ll 1$$ t ⊥ / t ‖ ≪ 1 , relevant for layered structures) as well as a rod-like geometry of interacting one-dimensional (1D) chains ($$t_\parallel /t_\perp \ll 1$$ t ‖ / t ⊥ ≪ 1 ). The impact of the dimensional crossover as the system is tuned away from a set of disconnected 2D layers, or traverses from a set of separate 1D chains to a regime where a fully isotropic 3D structure emerges is elucidated. Both numerical and analytic approaches are employed, (the latter in a form of series expansions involving $$t_\parallel ,t_\perp$$ t ‖ , t ⊥ amplitudes) for internal energy, entropy, specific heat and isothermal compressibility. The theoretical outcome of the present study may be of interest to a number of scenarios in solid-state physics, where the relevant quasi-particles are bosonic-like, as well as might be applicable to the physics of cold bosons loaded in artificially engineered 3D optical lattices.
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Proskokov, A. V., i S. I. Petrushin. "Process Chip Formation with a Single Conditional Shear Surface". Applied Mechanics and Materials 682 (październik 2014): 304–12. http://dx.doi.org/10.4028/www.scientific.net/amm.682.304.
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Most research on chip formation is based on free cutting with a single shear plane (the approach proposed by I.A. Time). No account is taken of the two-dimensional blade geometry nor of the three-dimensional character of the deformation source in the cut layer. It is assumed that the transformation of the cut layer into chip is confined to a very narrow zone adjacent to the shear plane. By contrast, constrained cutting is characterized by a conditional threedimensional shear surface, which is analogous to the shear plane.
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Dollet, B., A. Scagliarini i M. Sbragaglia. "Two-dimensional plastic flow of foams and emulsions in a channel: experiments and lattice Boltzmann simulations". Journal of Fluid Mechanics 766 (9.02.2015): 556–89. http://dx.doi.org/10.1017/jfm.2015.28.
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AbstractIn order to understand the flow profiles of complex fluids, a crucial issue concerns the emergence of spatial correlations among plastic rearrangements exhibiting cooperativity flow behaviour at the macroscopic level. In this paper, the rate of plastic events in a Poiseuille flow is experimentally measured on a confined foam in a Hele-Shaw geometry. The correlation with independently measured velocity profiles is quantified by looking at the relationship between the localisation length of the velocity profiles and the localisation length of the spatial distribution of plastic events. To complement the cooperativity mechanisms studied in foam with those of other soft glassy systems, we compare the experiments with simulations of dense emulsions based on the lattice Boltzmann method, which are performed both with and without wall friction. Finally, unprecedented results on the distribution of the orientation of plastic events show that there is a non-trivial correlation with the underlying local shear strain. These features, not previously reported for a confined foam, lend further support to the idea that cooperativity mechanisms, originally invoked for concentrated emulsions (Goyon et al., Nature, vol. 454, 2008, pp. 84–87), have parallels in the behaviour of other soft glassy materials.
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Xu, Zhihua, Xingzheng Lu, Wenliang Wang, Ershaui Xu, Rongjun Qin, Yiru Niu, Xu Qiao, Feng Yang i Rui Yan. "Monocular Video Frame Optimization Through Feature-Based Parallax Analysis for 3D Pipe Reconstruction". Photogrammetric Engineering & Remote Sensing 88, nr 7 (1.07.2022): 469–78. http://dx.doi.org/10.14358/pers.21-00066r3.
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Structure-from-motion (SfM) techniques have been widely used for three-dimensional (3D) scene reconstruction from sequential video frames. However, for reconstructing narrow and confined spaces such as the interior of drainage pipes, selecting geometrically optimal frames is a major challenge, not only to reduce the number of needed frames but also to yield better geometry. This paper introduces a coarse-to-fine method to optimize the selection of monocular video frames based on a geometric criterion called feature-based parallax analysis for 3D pipe reconstruction. The proposed method was applied in two experiments with a monocular camera fixed on a customized robot. Experimental results show that our approach only requires respectively 9.66% and 3.15% of the number of frames. The spatial distribution of the retrieved frames was uniform and reasonable, enabling the successful SfM process to achieve a complete reconstruction of the pipe geometry.
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KUZNETSOV, N. G., i M. J. SIMON. "A note on uniqueness in the linearized water-wave problem". Journal of Fluid Mechanics 386 (10.05.1999): 5–14. http://dx.doi.org/10.1017/s0022112099004668.
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The uniqueness theorem of Simon & Ursell (1984), concerning the linearized two-dimensional water-wave problem in a fluid of infinite depth, is extended in two directions. First, we consider a two-dimensional geometry involving two submerged symmetric bodies placed sufficiently far apart that they are not confined in the vertical right angle having its vertex on the free surface as the theorem of Simon & Ursell requires. A condition is obtained guaranteeing the uniqueness outside a finite number of bounded frequency intervals. Secondly, the method of Simon & Ursell is generalized to prove uniqueness in the axisymmetric problem for bodies violating John's condition provided the free surface is a connected plane region.
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Rusby, D. R., G. E. Cochran, A. Aghedo, F. Albert, C. D. Armstrong, A. Haid, A. J. Kemp i in. "Enhanced electron acceleration by high-intensity lasers in extended (confined) preplasma in cone targets". Physics of Plasmas 30, nr 2 (luty 2023): 023103. http://dx.doi.org/10.1063/5.0127580.
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We report on experimental results from a high-intensity laser interaction with cone targets that increase the number (×3) and temperature (×3) of the measured hot electrons over a traditional planar target. This increase is caused by a substantial increase in the plasma density within the cone target geometry, which was induced by 17 ± 9 mJ prepulse that arrived 1.5 ns prior to the main high intensity (>1019 W/cm2). Three-dimensional hydrodynamic simulations are conducted using hydra which show that the cone targets create substantially longer and denser plasma than planar targets due to the geometric confinement of the expanding plasma. The density within the cone is a several hundred-micron plasma “shelf” with a density of approximately 1020 n e/cc. The hydra simulated plasma densities are used as the initial conditions for two-dimensional particle-in-cell simulations using EPOCH. These simulations show that the main acceleration mechanism is direct-laser-acceleration, with close agreement between experimentally measured and simulated electron temperatures. Further analysis is conducted to investigate the acceleration of the electrons within the long plasma generated within a compound parabolic concentrator by the prepulse.
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Khosronejad, Ali, i C. D. Rennie. "Three-dimensional numerical modeling of unconfined and confined wall-jet flow with two different turbulence models". Canadian Journal of Civil Engineering 37, nr 4 (kwiecień 2010): 576–87. http://dx.doi.org/10.1139/l09-172.
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Wall-jet flow is an important flow field in hydraulic engineering, and its applications include flow from the bottom outlet of dams and sluice gates. An in-house three-dimensional (3-D) finite-volume Reynolds-averaged-Navier-Stokes (RANS) numerical model predicts the hydrodynamic characteristics of wall jets with square and rectangular source geometry. Either the low-turbulence Reynolds number k–ω or the standard k–ε turbulence closure models are applied. The calculated results for velocity profile and bed shear stress in both longitudinal and vertical directions compare favourably with both the published experimental results and the FLUENT® finite volume model. The two closure models are compared with the k–ω model, displaying 4% greater average accuracy than the k–ε model. Finally, the influence of lateral confinement of the receiving channel on wall-jet hydrodynamics is investigated, with decreased longitudinal deceleration and decreased bed shear stress observed in a confined jet. This has important implications for sediment transport in the receiving channels downstream of sluice gates.
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Kummali, Mohammed Musthafa, David Cole i Siddharth Gautam. "Effect of Pore Connectivity on the Behavior of Fluids Confined in Sub-Nanometer Pores: Ethane and CO2 Confined in ZSM-22". Membranes 11, nr 2 (5.02.2021): 113. http://dx.doi.org/10.3390/membranes11020113.
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The behavior of fluids under nano-confinement varies from that in bulk due to an interplay of several factors including pore connectivity. In this work, we use molecular dynamics simulations to study the behavior of two fluids—ethane and CO2 confined in ZSM-22, a zeolite with channel-like pores of diameter 0.55 nm isolated from each other. By comparing the behavior of the two fluids in ZSM-22 with that reported earlier in ZSM-5, a zeolite with pores of similar shape and size connected to each other via sinusoidal pores running perpendicular to them, we reveal the important role of pore connectivity. Further, by artificially imposing pore connectivity in ZSM-22 via inserting a 2-dimensional slab-like inter-crystalline space of thickness 0.5 nm, we also studied the effect of the dimensionality and geometry of pore connectivity. While the translational motion of both ethane and CO2 in ZSM-22 is suppressed as a result of connecting the pores by perpendicular quasi-one-dimensional pores of similar dimensions, the effect of connecting the pores by inserting the inter-crystalline space is different on the translational motion of the two fluids. For ethane, pores connected via inter-crystalline space facilitate translational motion but suppress rotational motion, whereas in the case of CO2, both types of motion are suppressed by pore connection due to the strong interaction of CO2 with the surface of the substrate.
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CARAM, H. S., i D. C. HONG. "DIFFUSING VOID MODEL FOR GRANULAR FLOW". Modern Physics Letters B 06, nr 13 (10.06.1992): 761–71. http://dx.doi.org/10.1142/s0217984992000843.
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The gravitational flow pattern of granular media in a confined geometry is assumed to be caused by the upward motion of voids generated at the discharge orifices. The model describes some well known and unique features of granular flows such as the deformation of the free surface, the formation of dead zones, the flow around obstacles with its companion void regions and the formation of cascading zones. It also predicts an unexpected velocity profile in a flow expansion as well as the propagation of dilation waves whose scaling solutions are presented. These thin two-dimensional beds are also found to behave very differently from three-dimensional beds.
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ISO, SATOSHI. "LONG DISTANCE UNIVERSALITY OF LAUGHLIN STATE AND CALOGERO-SUTHERLAND MODEL". Modern Physics Letters A 09, nr 23 (30.07.1994): 2123–37. http://dx.doi.org/10.1142/s0217732394001982.
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We study the universal long distance behavior of the Laughlin state for the fractional quantum Hall effect and the ground state of the Calogero-Sutherland model (one-dimensional 1/r2 interaction model). In particular, it is shown that these two wave functions coincide exactly when Laughlin state is confined in a narrow cylinder geometry. The seeming difference of dimensionality is merely a difference of representation of wave functions. We also give a recipe to interpret operators acting on states in the lowest Landau level in terms of the usual one-dimensional fermion operators, which is important for extracting the Tomonaga-Luttinger liquid behavior of the edge states.
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Wang, Ming Bo, Rui He Wang i Xian Yong Liu. "Numerical Simulation of a Semi-Confined Slot Turbulent Impinging Jet". Advanced Materials Research 268-270 (lipiec 2011): 345–50. http://dx.doi.org/10.4028/www.scientific.net/amr.268-270.345.
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A Realizable k-ε turbulence model in conjunction with a standard wall function has been applied to the prediction of a fully-developed two-dimensional jet impinging within a semi-confined space. A single geometry with a Reynolds number of 10,000 and a nozzle –to-plate spacing of eight diameters has been considered at different inlet boundary conditions. The numerical results, including the time-averaged velocities and the turbulent intensity, have been compared with the experimental data reported by Yoshida (ref 5). It is found that the trends in the axial velocity, the radial velocity and the turbulent intensity are fairly predicted. The fully-developed boundary condition is generally better than the constant velocity boundary condition. The differences between the numerical and experimental results can be attributed to the turbulence model and the treatment of the low Reynolds number zone near the wall.
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Mosaddeghi, Mohammad. "Two dimensional simulation of laminar flow by three- jet in a semi-confined space". Nonlinear Engineering 9, nr 1 (7.02.2020): 111–17. http://dx.doi.org/10.1515/nleng-2020-0001.
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AbstractEquipment performance improvement in a wide range of working conditions is one of the major goals of aerodynamics. This goal can be achieved by the deformation of the object being examined or by using flow control techniques in active or inactive modes. In different researches, how to change the development ratio on the semi-confined space with input jet system is surveyed. In this study, two-dimensional simulation of the flow has been investigated in three-jet laminar flow in a semi-confined space. To determine the effective and optimal mixing in a laminar flow, critical Reynolds numbers were determined to distinguish when the flow in the channel from a steady-state symmetric flowformed downstream recirculation and ultimately transient flow. To better understand the flow characteristics, the simulations were changed at a fixed jet spacing (input jets distance to height of space ratio). Also, in this paper, for comparison, four jets were considered. Based on the results, it was observed that in all cases, mixing occurred in the space between three jets. Placing the jet along the walls of the semi-confined space allows the best combination, and increase in the distance between the first and third jets and reduction of the particle coefficient caused to reach the critical Reynolds number faster and, as a result, mixing in a laminar flow with geometric changes of the semi-confined space.
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de Pádua Santos, A., F. Moraes, F. A. N. Santos i S. Fumeron. "An Abelian Higgs model for disclinations in nematics". Condensed Matter Physics 26, nr 1 (2023): 13506. http://dx.doi.org/10.5488/cmp.26.13506.
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Topological defects in elastic media may be described by a geometric field akin to three-dimensional gravity. From this point of view, disclinations are line defects of zero width corresponding to a singularity of the curvature in an otherwise flat background. On the other hand, in two dimensions, the Frank free energy of a nematic liquid crystal may be interpreted as an Abelian Higgs Lagrangian. In this work, we construct an Abelian Higgs model coupled to ``gravity'' for the nematic phase, with the perspective of finding more realistic disclinations. That is, a cylindrically symmetric line defect of finite radius, invariant under translations along its axis. Numerical analysis of the equations of motion indeed yield a +1 winding number ``thick'' disclination. The defect is described jointly by the gauge and the Higgs fields, that compose the director field, and the background geometry. Away from the defect, the geometry is conical, associated to a dihedral deficit angle. The gauge field, confined to the defect, gives a structure to the disclination while the Higgs field, outside, represents the nematic order.
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Hasan, Wajeeh, i Mohammed Mahmood. "Transient Three-Dimensional Natural Convection in Confined Porous Media with Time-Periodic Boundary Conditions". Journal of Al-Rafidain University College For Sciences ( Print ISSN: 1681-6870 ,Online ISSN: 2790-2293 ), nr 2 (17.10.2021): 195–227. http://dx.doi.org/10.55562/jrucs.v32i2.334.
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Transient three-dimensional natural convection in confined fluid-saturated porous media had been investigated numerically through this work. The geometry selected is a box with time-periodic temperature variation at the vertical sides and constant wall temperature at the top and bottom. In this investigation, the momentum equation of flow through fluid-saturated porous media had been transformed to a vector potential form and solved numerically using the Successive Over Relaxation method while the energy equation is solved using the three-dimensional Alternating Direction Implicit method. The values of the Rayleigh number under investigation are (150, 200, 250 and 300). The results are presented in a form of contour maps for the temperature and a velocity vector maps for the velocity. The results reveal that the temperature within the box is increased as the time or Rayleigh number increase.The Nusselt number varies inversely with the time and directly with the Rayleigh number. Two cell convective patterns are obtained in the y-z
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Short, Mark, i James J. Quirk. "The effect of compaction of a porous material confiner on detonation propagation". Journal of Fluid Mechanics 834 (17.11.2017): 434–63. http://dx.doi.org/10.1017/jfm.2017.736.
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The fluid mechanics of the interaction between a porous material confiner and a steady propagating high explosive (HE) detonation in a two-dimensional slab geometry is investigated through analytical oblique wave polar analysis and multi-material numerical simulation. Two HE models are considered, broadly representing the properties of either a high- or low-detonation-speed HE, which permits studies of detonation propagating at speeds faster or slower than the confiner sound speed. The HE detonation is responsible for driving the compaction front in the confiner, while, in turn, the high material density generated in the confiner as a result of the compaction process can provide a strong confinement effect on the HE detonation structure. Polar solutions that describe the local flow interaction of the oblique HE detonation shock and equilibrium state behind an oblique compaction wave with rapid compaction relaxation rates are studied for varying initial solid volume fractions of the porous confiner. Multi-material numerical simulations are conducted to study the effect of detonation wave driven compaction in the porous confiner on both the detonation propagation speed and detonation driving zone structure. We perform a parametric study to establish how detonation confinement is influenced both by the initial solid volume fraction of the porous confiner and by the time scale of the dynamic compaction relaxation process relative to the detonation reaction time scale, for both the high- and low-detonation-speed HE models. The compaction relaxation time scale is found to have a significant influence on the confinement dynamics, with slower compaction relaxation time scales resulting in more strongly confined detonations and increased detonation speeds. The dynamics of detonation confinement by porous materials when the detonation is propagating either faster or slower than the confiner sound speed is found to be significantly different from that with solid material confiners.
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BHATTACHARYA, S. "Exact analytical solutions for steady three-dimensional inviscid vortical flows". Journal of Fluid Mechanics 590 (15.10.2007): 147–62. http://dx.doi.org/10.1017/s0022112007007938.
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Vortical flows with an axial (z-axis) swirl and a toroidal circulation (in the (rho,z)-plane) can be observed in a wide range of fluid mechanical phenomena such as flow around rotary machines or natural vortices like tornadoes and hurricanes. In this paper, we obtain exact analytical solutions for a general class of steady systems with such three-dimensional circulating structures. Assuming incompressible ideal fluid, a general single-variable equation, known as the Squire–Long equation, can be constructed which can uniquely describe the velocity fields with steady axial and toroidal circulations. In this paper, we consider the case where this type of flow can be analysed by solving a linear homogeneous partial differential equation. The derived equation resembles the governing equation of the hydrogen problem. As a result, we obtain a quantization relation which is similar to the expression for the quantized energy states in a hydrogen atom.For circulating flows, this formalism provides a complete set of orthogonal basis functions which are regular and localized. Hence, each of the basis solutions can be used as a simplified model for a realistic phenomenon. Moreover, an arbitrary circulating field can be expanded in terms of these orthogonal functions. Such an expansion can be potentially useful in the study of more general vortices. As illustrations, we present a few examples where we solve the linear homogeneous equation to analyse fluid mechanical systems which can be models for circulating flow in confined geometry. First, we consider three-dimensional vortices confined between two parallel planar walls. Our examples include flows between two infinite planar walls, inside and outside a vertical cylinder bounded at the ends by horizontal plates, and in an axially confined annular region. Then we describe the special way in which the basis functions should be superposed so that a complicated steady velocity-field with three-dimensional vortical structures can be constructed. Two such cases are discussed to indicate that the derived solutions can be used for complicated fluid mechanical modelling.
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Sullivan, P. A., P. A. Charest i T. Ma. "Heave Stiffness of an Air Cushion Vehicle Bag-and-Finger Skirt". Journal of Ship Research 38, nr 04 (1.12.1994): 302–7. http://dx.doi.org/10.5957/jsr.1994.38.4.302.
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The heave stiffness of a bag-and-finger flexible skirt air cushion is investigated analytically and experimentally. The investigations use a two-dimensional section of the skirt confined between end-plates and moving in heave. This simplified geometry facilitates analysis involving a minimum of empiricism. Experiments show that the airflows, including leaks between fingers and at the end-plates, can be modeled as orifice-like. The analysis assumes that the fingers can be modeled as rigid massless bodies. Three models of the bag, based on combinations of massless inelastic membranes and rigid links, are investigated. The predictions and experiments are in good agreement and show that modest geometry changes can have large effects on heave stiffness. It is suggested that these simple skirt models can provide useful insights into the dynamics.
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Jahanshaloo, Leila, Nor Azwadi Che Sidik i Emad Kermani. "Application of the Lattice Boltzmann Method for Fluid Flow around Complex Geometry". Applied Mechanics and Materials 554 (czerwiec 2014): 230–35. http://dx.doi.org/10.4028/www.scientific.net/amm.554.230.
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In recent years, several strategies have been proposed to deal with complex geometry to study particle-fluid interaction using lattice Boltzmann method. Curved boundary treatments have been suggested to improve the accuracy of the stair-shaped approximation in conventional lattice Boltzmann simulations. This paper presents numerical analysis of three interpolation methods for confined flow around blockage positioned inside a channel. A two-dimensional nine velocity lattice arrangement was chosen to discretize the fluid domain and single relaxation time technique is applied in this study. The results are presented in terms of velocity contour, lift and drag forces variation for three different shapes of blockage. The simulations results are then compared with those obtained using the three different interpolating treatments. Some of these methods show more adaptability for force evaluating on distinct surfaces.
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Lanzerstorfer, Daniel, i Hendrik C. Kuhlmann. "Global stability of the two-dimensional flow over a backward-facing step". Journal of Fluid Mechanics 693 (3.11.2011): 1–27. http://dx.doi.org/10.1017/jfm.2011.399.
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AbstractThe two-dimensional, incompressible flow over a backward-facing step is considered for a systematic variation of the geometry covering expansion ratios (step to outlet height) from 0.25 to 0.975. A global temporal linear stability analysis shows that the basic flow becomes unstable to different three-dimensional modes depending on the expansion ratio. All critical modes are essentially confined to the region behind the step extending downstream up to the reattachment point of the separated eddy. An energy-transfer analysis is applied to understand the physical nature of the instabilities. If scaled appropriately, the critical Reynolds number approaches a finite asymptotic value for very large step heights. In that case centrifugal forces destabilize the flow with respect to an oscillatory critical mode. For moderately large expansion ratios an elliptical instability mechanism is identified. If the step height is further decreased the critical mode changes from oscillatory to stationary. In addition to the elliptical mechanism, the strong shear in the layer emanating from the sharp corner of the step supports the amplification process of the critical mode. For very small step heights the basic state becomes unstable due to the lift-up mechanism, which feeds back on itself via the recirculating eddy behind the step, resulting in a steady critical mode comprising pronounced slow and fast streaks.
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Reynolds, Robert R., Jack H. Cole i Zhen Yuan. "Effects of Geometry on the Performance of a Downhole Orbital Vibrator". Journal of Energy Resources Technology 124, nr 2 (28.05.2002): 77–82. http://dx.doi.org/10.1115/1.1467600.
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The influence of geometry on the pressure field within the confined, water-filled annulus between a central, vibrating cylinder and an outer, rigid enclosure is determined. A two-dimensional model is constructed using the finite element (FE) method and parameters are identified to characterize the eccentricity of the nominal cylinder position, the size of the annulus relative to the inner cylinder and the degree to which the annulus is not circular (i.e., it is elliptic). The FE solution is verified using a closed-form solution for the special case of a concentric cylinder and annulus. It is shown that the system acts as a force multiplier. Analyses of the asymmetrical geometries indicate that while the pressure field on the surface of the cylinder and enclosure can be highly asymmetric, the system is relatively insensitive to minor variations in annulus shape except when the vibrating cylinder is not centrally located within the fluid region or the annulus size itself is small.
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Buonomo, Bernardo, Oronzio Manca, Nadezhda S. Bondareva i Mikhail A. Sheremet. "Thermal and Fluid Dynamic Behaviors of Confined Slot Jets Impinging on an Isothermal Moving Surface with Nanofluids". Energies 12, nr 11 (30.05.2019): 2074. http://dx.doi.org/10.3390/en12112074.
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A two-dimensional numerical investigation of turbulent convective heat transfer due to a confined slot jet impinging on an isothermal moving surface is accomplished. The confined geometry has an upper adiabatic surface parallel to the heated moving plate and the slot jet is in the middle of the confining adiabatic wall. The working fluids are pure water or a nanofluid, which in this case was a mixture of water and Al2O3 nanoparticles. The governing equations are written adopting the k-ε turbulence model with enhanced wall treatment and the single-phase model approach for the nanofluids. The numerical model is solved using the finite volume method with the Ansys Fluent code. Two geometric configurations regarding two values of the jet distance from the target surface are considered in the simulations. The concentration of nanoparticles ranges from 0% to 6%, with a single diameter equal to 30 nm, Reynolds numbers ranging from 5000 to 20000, and a moving surface-jet velocity ratio between 0 and 2 are examined in the investigation. The aim is to study the system behaviors by means of local and average Nusselt numbers, local and average friction factor/skin friction factor, stream function, and temperature fields. Results show that the presence of nanoparticles determines an increase in the dimensionless heat transfer but, as expected, does not affect the friction factor. The local and average increase in Nusselt numbers is also due to a combined effect of the moving plate and nanofluids.
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AVAGLIANO, AARON, i NHAN PHAN-THIEN. "Torsional flow: effect of second normal stress difference on elastic instability in a finite domain". Journal of Fluid Mechanics 359 (25.03.1998): 217–37. http://dx.doi.org/10.1017/s0022112097008434.
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A rotational shear flow is examined in the bounded parallel-plate geometry for a four-constant Oldroyd-type fluid which has a constant viscosity, and constant first and second normal stress coefficients. A new type of Galerkin spectral technique is introduced to solve the resulting two-dimensional stiff boundary value problem. We show that even a small second normal stress difference can lead to a significant increase (nearly 100%) in the stability of the base torsional flow. Beyond a critical Deborah number the secondary flow, in the form of travelling waves, appears to be confined between two critical radii, in qualitative agreement with the experimental results of Byars et al. (1994). The mechanism behind this instability is investigated for dilute polymer solutions.
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Lanzerstorfer, Daniel, i Hendrik C. Kuhlmann. "Three-dimensional instability of the flow over a forward-facing step". Journal of Fluid Mechanics 695 (21.02.2012): 390–404. http://dx.doi.org/10.1017/jfm.2012.28.
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AbstractThe global, temporal stability of the two-dimensional, incompressible flow over a forward-facing step in a plane channel is investigated numerically. The geometry is varied systematically covering constriction ratios (step-to-inlet height) from 0.23 to 0.965. A three-dimensional linear stability analysis shows that the stability boundary is a smooth continuous function of the constriction ratio. If the critical Reynolds and wavenumbers are scaled appropriately, they approach a linear asymptotic behaviour for large step heights. The critical mode is found to be stationary and confined to the region of separated flow downstream of the step for all constriction ratios. An energy-transfer analysis reveals that the basic flow becomes unstable due to a combined effect involving lift-up and flow deceleration, leading to a critical mode exhibiting steady streaks. Moreover, the receptivity of the flow to initial as well as to structural perturbations is studied by means of an adjoint analysis.
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Al-Hemyari, Mohammed, Mohammad O. Hamdan i Mehmet F. Orhan. "Optimization of a Confined Jet Geometry to Improve Film Cooling Performance Using Response Surface Methodology (RSM)". Processes 8, nr 2 (18.02.2020): 232. http://dx.doi.org/10.3390/pr8020232.
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This study investigates the interrelated parameters affecting heat transfer from a hot gas flowing on a flat plate while cool air is injected adjacent to the flat plate. The cool air forms an air blanket that shield the flat plate from the hot gas flow. The cool air is blown from a confined jet and is simulated using a two-dimensional numerical model under three variable parameters; namely, blowing ratio, jet angle and density ratio. The interrelations between these parameters are evaluated to properly understand their effects on heat transfer. The analyses are conducted using ANSYS-Fluent, and the performance of the air blanket is reported using local and average adiabatic film cooling effectiveness (AFCE). The interrelation between these parameters and the AFCE is established through a statistical method known as response surface methodology (RSM). The RSM model shows that the AFCE has a second order relation with the blowing ratio and a first order relation with both jet angle and density ratio. Also, it is found that the highest average AFCE is reached at an injection angle of 30 degree, a density ratio of 1.2 and a blowing ratio of 1.8.
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HEIN, STEFAN, WERNER KOCH i LOTHAR NANNEN. "Fano resonances in acoustics". Journal of Fluid Mechanics 664 (26.10.2010): 238–64. http://dx.doi.org/10.1017/s0022112010003757.
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In contrast to completely open systems, laterally confined domains can sustain localized, truly trapped modes with nominally zero radiation loss. These discrete resonant modes cannot be excited linearly by the continuous propagating duct modes due to symmetry constraints. If the symmetry of the geometry is broken the trapped modes become highly localized quasi-trapped modes which can interfere with the propagating duct modes. The resulting narrowband Fano resonances with resonance and antiresonance features are a generic phenomenon in all scattering problems with multiple resonant pathways. This paper deals with the classical scattering of acoustic waves by various obstacles such as hard-walled single and multiple circular cylinders or rectangular and wedge-like screens in a two-dimensional duct without mean flow. The transmission and reflection coefficients as well as the (complex) resonances are computed numerically by means of the finite-element method in conjunction with two different absorbing boundary conditions, namely the complex scaling method and the Hardy space method. The results exhibit the typical asymmetric Fano line shapes near the trapped-mode resonances if the symmetry of the geometry is broken.
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Orlova, Svetlana, i Alexander Lopota. "Scene recognition for confined spaces in mobile robotics: current state and tendencies". Robotics and Technical Cybernetics 10, nr 1 (marzec 2022): 14–24. http://dx.doi.org/10.31776/rtcj.10102.
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The article discusses the problem of scene recognition for mobile robotics. Subtasks that have to be solved to implement a high-level understanding of the environment are considered. The basis here is an understanding of the geometry and semantics of the scene, which can be decomposed into subtasks of robot localization, mapping and semantic analysis. Simultaneous localization and mapping (SLAM) techniques have already been successfully applied and, although they have some as yet unresolved problems for dynamic environments, do not present a problem for this issue. The focus of the work is on the task of semantic analysis of the scene, which assumes three-dimensional segmentation. The field of 3D segmentation, like the field of image segmentation, has been decomposed into semantic and object segmentation, contrary to the needs of many potential applications. However, at present, panoptic segmentation is beginning to develop, combining the two previous ones and most fully describing the scene. The paper reviews the methods of 3D panoptic segmentation, identifies promising approaches. The actual problems of the scene recognition problem are also discussed. There is a clear trend towards the development of complex incremental methods of metric-semantic SLAM, which combine segmentation with SLAM methods, and the use of scene graphs, which allow describing the geometry, semantics of scene elements and the relationship between them. Scene graphs are especially promising for the field of mobile robotics, since they provide a transition from low-level representations of objects and spaces (for example, segmented point clouds) to describing a scene at a high level of abstraction, close to a human one (a list of objects in a scene, their properties and location relative to each other).
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Liu, Huan, Bo Pang i Kai Zhang. "Breath figure templated self-assembly of surface-acylated cellulose nanowhiskers confined as honeycomb films". Cellulose 28, nr 17 (13.10.2021): 10939–51. http://dx.doi.org/10.1007/s10570-021-04245-3.
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AbstractThe self-assembly of cellulose nanowhiskers (CNWs) in confined geometries provides a powerful method for the fabrication of novel structures. Herein, ordered honeycomb microporous films were first prepared with surface-acylated CNWs (CNWs-SU) through the breath figure method. Resulting films showed highly porous order over large regions and the iridescent color was only displayed by their rims, which is different from traditional dish-cast CNW films showing the iridescent color over the whole area. This is mainly due to the condensation of water droplets forming three-dimensional (3D) geometry, which forced CNWs-SU to self-assemble into cholesteric architectures in confined geometry and resulted in the iridescent color of the rims after drying. The mechanism was further studied by investigating the critical influencing factors, primarily the concentration of CNW-SU suspensions, the relative humidity of the atmosphere and the surface-attached moieties. In particular, CNW-SU suspensions with a concentration of 3 mg/mL at the relative humidity of 75% preferentially formed honeycomb films with uniform pores. Too low or too high concentrations of CNW-SU suspensions or relative humidity are not preferable for uniform porous films. CNWs-SU with further immobilized octadecane or fluoroalkyl groups on their surface strongly affected the formation of uniform porous films because of higher hydrophobicity and accompanying inhomogeneous condensation of water droplets. This work provides a novel method to study the interactions of CNWs beyond the planar geometry and the formation of uniform porous films solely with CNWs with structural colors open up interesting possibilities for broad application in photonic nanomaterials. Graphic abstract
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Klemenčič, Eva, Pavlo Kurioz, Milan Ambrožič, Charles Rosenblatt i Samo Kralj. "Annihilation of Highly-Charged Topological Defects". Crystals 10, nr 8 (3.08.2020): 673. http://dx.doi.org/10.3390/cryst10080673.
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We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order parameter was used in an effectively two-dimensional Cartesian coordinate system, where spatial variations along the z-axis were neglected. A pair of {m=3/2,m=−3/2} was enforced by an appropriate surface anchoring field, mimicking an experimental sample realization using the atomic force microscope (AFM) scribing method. Furthermore, defects were confined within a rectangular boundary that imposes strong tangential anchoring. This setup enabled complex and counter-intuitive annihilation processes on varying relevant parameters. We present two qualitatively different annihilation paths, where we either gradually reduced the relative surface anchoring field importance or increased an external in-plane spatially homogeneous electric field E. The creation and depinning of additional defect pairs {12,−12} mediated the annihilation in such a geometry. Furthermore, we illustrate the absorption of TDs by sharp edges of the confining boundary, accompanied by m=±1/4↔∓1/4 winding reversal of edge singularities, and also E-driven zero-dimensional to one-dimensional defect core transformation.
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Biancofiore, Luca. "Crossover between two- and three-dimensional turbulence in spatial mixing layers". Journal of Fluid Mechanics 745 (18.03.2014): 164–79. http://dx.doi.org/10.1017/jfm.2014.85.
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AbstractWe investigate how the domain depth affects the turbulent behaviour in spatially developing mixing layers by means of large-eddy simulations based on a spectral vanishing viscosity technique. Analyses of spectra of the vertical velocity, of Lumley’s diagrams, of the turbulent kinetic energy and of the vortex stretching show that a two-dimensional behaviour of the turbulence is promoted in spatial mixing layers by constricting the fluid motion in one direction. This finding is in agreement with previous works on turbulent systems constrained by a geometric anisotropy, pioneered by Smith, Chasnov & Waleffe (Phys. Rev. Lett., vol. 77, 1996, pp. 2467–2470). We observe that the growth of the momentum thickness along the streamwise direction is damped in a confined domain. An almost fully two-dimensional turbulent behaviour is observed when the momentum thickness is of the same order of magnitude as the confining scale.
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GUGLIELMINI, LAURA, R. RUSCONI, S. LECUYER i H. A. STONE. "Three-dimensional features in low-Reynolds-number confined corner flows". Journal of Fluid Mechanics 668 (13.12.2010): 33–57. http://dx.doi.org/10.1017/s0022112010004519.
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In recent microfluidic experiments with solutions of bacteria we observed the formation of biofilms in the form of thread-like structures, called ‘streamers’, which float in the middle plane of the channel and are connected to the side walls at the inner corners. Motivated by this observation, we discuss here the pressure-driven low-Reynolds-number flow around a corner bounded by the walls of a channel with rectangular cross-section. We numerically solve the flow field in a channel of constant cross-section, which exhibits 90° sharp corners, or turns with constant curvature, or portions with slowly changing curvature along the flow direction, for finite, but small, values of the Reynolds numbers and including the limit of vanishingly small Reynolds numbers. In addition, we develop a matched asymptotic expansion solution for the flow around two boundaries intersecting at an angle α and spanning the small gap h between two horizontal plates. We illustrate the basic features of the flow in these channel geometries by describing the three-dimensional velocity field and the distribution of streamwise vorticity and helicity, and comparing the numerical solutions with predictions based on the asymptotic approach. We demonstrate that near a corner or a change in the curvature of the side wall the flow is three-dimensional and pairs of counter-rotating vortical structures are present, as identified by Balsa (J. Fluid Mech., vol. 372, 1998, p. 25). Finally, we discuss how this secondary flow depends on the significant geometric parameters, the aspect ratio of the channel cross-section, the radius of curvature of the turn and, more generally, the variation of the curvature of the channel side boundary. We believe that these three-dimensional secondary flow structures are relevant to transport problems where accumulation of material at the boundary is possible.
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Choudhury, Kaushik, R. K. Singh, Surya Narayan, Atul Srivastava i Ajai Kumar. "Time resolved interferometric study of the plasma plume induced shock wave in confined geometry: Two-dimensional mapping of the ambient and plasma density". Physics of Plasmas 23, nr 4 (kwiecień 2016): 042108. http://dx.doi.org/10.1063/1.4947032.
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Tieszen, S., H. Merte, V. S. Arpaci i S. Selamoglu. "Crevice Boiling in Steam Generators". Journal of Heat Transfer 109, nr 3 (1.08.1987): 761–67. http://dx.doi.org/10.1115/1.3248155.
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Experimental results are presented on the influence of confinement (normal to heated surface) on nucleate boiling in forced flow. The forced flow conditions and confinement geometry studied are similar to those found for boiling between a primary-fluid tube and a tube-support plate in steam generators of pressurized-water-reactor nuclear power plants. Visual observations of the boiling process within the confined region (crevice) between the tube and its support plate, obtained by high-speed photography, are related to simultaneous two-dimensional temperature maps of the hot primary-fluid-tube surface. The results demonstrate the existence of three confinement-dependent boiling regimes in forced flow conditions that are similar to those found in pool boiling conditions. These regimes are shown to be associated with the Weber number.