scholarly journals Two-Dimensional Soil Geometric Tortuosity Model Based on Porosity and Particle Arrangement

Minerals ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 43
Author(s):  
Jin Gan ◽  
Zhiquan Yang ◽  
Zhiwei Zhang ◽  
Chaoyue Li ◽  
Yi Yang ◽  
...  
Keyword(s):  
Functional Relationship ◽  
Geometric Analysis ◽  
Anisotropy Parameter ◽  
Two Dimensional ◽  
Soil Permeability ◽  
Theoretical Derivation ◽  
Permeability Characteristics ◽  
Physical Mechanisms ◽  
Particle Arrangement ◽  
Fluid Seepage

Porosity and particle arrangement are important parameters affecting soil tortuosity, so it is of great significance to determine the intrinsic relationship between them when studying soil permeability characteristics. Theoretical derivation and geometric analysis methods are used to derive a two-dimensional geometric tortuosity model. The model is a function of particle arrangement parameters (m and θ) and porosity. An analysis of the model and its parameters shows that: (1) The arrangement of particles is one of the reasons for the different functional relationship between tortuosity and porosity, which proved that the tortuosity is not only related to the porosity but also affected by the particle arrangement. (2) The greater the anisotropy parameter m is, the greater the tortuosity is, indicating m varies when fluid passes through the soil from different sides resulting in different values of permeability. (3) The tortuosity increases with the increase in the blocking parameters θ. (4) With increasing porosity, the influence of the parameters m and θ on the tortuosity gradually decreases, suggesting that the influence of particle arrangement on tortuosity gradually decreases. The results presented here increase the understanding of the physical mechanisms controlling tortuosity and, hence, the process of fluid seepage through soil.

scholarly journals Mechanisms of Up-Valley Winds

2004 ◽  
Vol 61 (24) ◽  
pp. 3097-3111 ◽  
Author(s):  
Gabriele Rampanelli ◽  
Dino Zardi ◽  
Richard Rotunno
Keyword(s):  
Three Dimensional ◽  
The Other ◽  
Two Dimensional ◽  
Free Atmosphere ◽  
Valley Wind ◽  
Main Contributor ◽  
Physical Mechanisms ◽  
Thermally Driven ◽  
Hydrostatic Approximation ◽  
Temperature Contrast

Abstract The basic physical mechanisms governing the daytime evolution of up-valley winds in mountain valleys are investigated using a series of numerical simulations of thermally driven flow over idealized three-dimensional topography. The three-dimensional topography used in this study is composed of two, two-dimensional topographies: one a slope connecting a plain with a plateau and the other a valley with a horizontal floor. The present two-dimensional simulations of the valley flow agree with results of previous investigations in that the heated sidewalls produce upslope flows that require a compensating subsidence in the valley core bringing down potentially warmer air from the stable free atmosphere. In the context of the three-dimensional valley–plain simulations, the authors find that this subsidence heating in the valley core is the main contributor to the valley– plain temperature contrast, which, under the hydrostatic approximation, is the main contributor to the valley– plain pressure difference that drives the up-valley wind.

scholarly journals The Influences of Category Learning on Perceptual Reconstructions

2020 ◽  
Author(s):  
Marina Dubova ◽  
Robert Goldstone
Keyword(s):  
Visual System ◽  
Perceptual Learning ◽  
Category Learning ◽  
Human Visual System ◽  
Functional Relationship ◽  
Experimental Designs ◽  
Two Dimensional ◽  
Learning Models ◽  
Learning Mechanisms ◽  
Feature Structure

We explore different ways in which the human visual system can adapt for perceiving and categorizing the environment. There are various accounts of supervised (categorical) and unsupervised perceptual learning, and different perspectives on the functional relationship between perception and categorization. We suggest that common experimental designs are insufficient to differentiate between hypothesised perceptual learning mechanisms and reveal their possible interplay. We propose a relatively underutilized way of studying potential categorical effects on perception, and test the predictions of different perceptual learning models using a two-dimensional, interleaved categorization-plus-reconstruction task. We find evidence that human visual encodings adapt to the feature structure of the environment, allocate encoding resources with respect to categorization utility, and adapt to prevent miscategorizations.

scholarly journals Coherent Scattering of Ultraviolet Light by Avian Feather Barbs

The Auk ◽  
2003 ◽  
Vol 120 (1) ◽  
pp. 163-170 ◽  
Author(s):  
Richard O. Prum ◽  
Staffan Andersson ◽  
Rodolfo H. Torres
Keyword(s):  
Rayleigh Scattering ◽  
Power Spectra ◽  
Coherent Scattering ◽  
Mie Scattering ◽  
Two Dimensional ◽  
Structural Colors ◽  
Physical Mechanisms ◽  
Spatial Frequencies ◽  
Transmission Electron ◽  
Alternative Hypotheses

Abstract Ultraviolet (UV) structural colors of avian feathers are produced by the spongy medullary keratin of feather barbs, but various physical mechanisms have been hypothesized to produce those colors, including Rayleigh scattering, Mie scattering, and coherent scattering (i.e. constructive interference). We used two-dimensional Fourier analysis of transmission electron micrographs of the medullary keratin of UV-colored feather barbs of the Blue Whistling Thrush (Myiophonus caeruleus) (Turdidae) to test the alternative hypotheses for production of those UV structural hues. The two-dimensional Fourier power spectra of the tissue reveal a ring-like distribution of peak periodicity at intermediate spatial frequencies (∼0.078 nm −1), which documents that Myiophonus medullary keratin is substantially nanostructured and equivalently ordered in all directions. This nanoscale spatial order falsifies a basic assumption of both the Rayleigh scattering and Mie scattering. A predicted reflectance spectrum based on the Fourier power spectra matches hue of the measured reflectance spectra of the feathers (345 nm). These results demonstrate that the Myiophonus medullary keratin is ordered at the appropriately nanoscale to produce the observed UV hues by coherent scattering.

Three-Dimensional Geometric Analysis of the Plunge Centreless Grinding Process

1987 ◽  
Vol 201 (5) ◽  
pp. 309-320 ◽  
Author(s):  
N G Subramanya Udupa ◽  
M S Shunmugam ◽  
V Radhakrishnan
Keyword(s):  
Simulation Model ◽  
Geometric Analysis ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Grinding Process ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Two Dimensional Model

The grinding action and the rounding mechanism are highly complex in centreless grinding. The axis of the workpiece not only moves laterally but also tilts during the grinding process. Rowe and Barash have developed a two-dimensional model for an infeed centreless grinding neglecting the tilt of the workpiece. In this paper, an attempt has been made to develop a simulation model which incorporates the tilt of the workpiece. The theoretical and experimental investigations have been carried out with workpieces having specific geometries and the results are discussed.

scholarly journals Unraveling the Effect of Defects, Domain Size, and Chemical Doping on Photophysics and Charge Transport in Covalent Organic Frameworks

2021 ◽  
Author(s):  
Raja Ghosh ◽  
Francesco Paesani
Keyword(s):  
Charge Transport ◽  
Domain Size ◽  
Chemical Doping ◽  
Two Dimensional ◽  
Covalent Organic Frameworks ◽  
Physical Mechanisms

Understanding the underlying physical mechanisms that govern charge transport in two-dimensional (2D) covalent organic frameworks (COFs) will facilitate the development of novel COF-based devices for optoelectronic and thermoelectric applications. In this...

scholarly journals Knudsen Number Effects on Two-Dimensional Rayleigh–Taylor Instability in Compressible Fluid: Based on a Discrete Boltzmann Method

Entropy ◽  
2020 ◽  
Vol 22 (5) ◽  
pp. 500 ◽  
Author(s):  
Haiyan Ye ◽  
Huilin Lai ◽  
Demei Li ◽  
Yanbiao Gan ◽  
Chuandong Lin ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Knudsen Number ◽  
Compressible Fluid ◽  
Two Dimensional ◽  
Helmholtz Instability ◽  
Physical Mechanisms ◽  
Rayleigh Taylor Instability ◽  
Boltzmann Method ◽  
Rt Instability ◽  
Non Equilibrium

Based on the framework of our previous work [H.L. Lai et al., Phys. Rev. E, 94, 023106 (2016)], we continue to study the effects of Knudsen number on two-dimensional Rayleigh–Taylor (RT) instability in compressible fluid via the discrete Boltzmann method. It is found that the Knudsen number effects strongly inhibit the RT instability but always enormously strengthen both the global hydrodynamic non-equilibrium (HNE) and thermodynamic non-equilibrium (TNE) effects. Moreover, when Knudsen number increases, the Kelvin–Helmholtz instability induced by the development of the RT instability is difficult to sufficiently develop in the later stage. Different from the traditional computational fluid dynamics, the discrete Boltzmann method further presents a wealth of non-equilibrium information. Specifically, the two-dimensional TNE quantities demonstrate that, far from the disturbance interface, the value of TNE strength is basically zero; the TNE effects are mainly concentrated on both sides of the interface, which is closely related to the gradient of macroscopic quantities. The global TNE first decreases then increases with evolution. The relevant physical mechanisms are analyzed and discussed.

scholarly journals Efficient online handwritten Chinese character recognition system using a two-dimensional functional relationship model

2010 ◽  
Vol 20 (4) ◽  
pp. 727-738 ◽  
Author(s):  
Yun Chang ◽  
Jia Lee ◽  
Omar Rijal ◽  
Syed Bakar
Keyword(s):  
Character Recognition ◽  
Functional Relationship ◽  
Chinese Character ◽  
Graph Transformation ◽  
Recognition Rate ◽  
Recognition System ◽  
Two Dimensional ◽  
Chinese Character Recognition ◽  
Handwritten Chinese Character Recognition ◽  
Relationship Model

Efficient online handwritten Chinese character recognition system using a two-dimensional functional relationship modelThis paper presents novel feature extraction and classification methods for online handwritten Chinese character recognition (HCCR). TheX-graph andY-graph transformation is proposed for deriving a feature, which shows useful properties such as invariance to different writing styles. Central to the proposed method is the idea of capturing the geometrical and topological information from the trajectory of the handwritten character using theX-graph and theY-graph. For feature size reduction, the Haar wavelet transformation was applied on the graphs. For classification, the coefficient of determination (R2p) from the two-dimensional unreplicated linear functional relationship model is proposed as a similarity measure. The proposed methods show strong discrimination power when handling problems related to size, position and slant variation, stroke shape deformation, close resemblance of characters, and non-normalization. The proposed recognition system is applied to a database with 3000 frequently used Chinese characters, yielding a high recognition rate of 97.4% with reduced processing time of 75.31%, 73.05%, 58.27% and 40.69% when compared with recognition systems using the city block distance with deviation (CBDD), the minimum distance (MD), the compound Mahalanobis function (CMF) and the modified quadratic discriminant function (MQDF), respectively. High precision rates were also achieved.

scholarly journals Dynamics and instabilities of the free boundary of a two-dimensional dry active nematic aggregate

2021 ◽  
Author(s):  
Hsuan-Yi Chen ◽  
Li-Shing Lin
Keyword(s):  
Free Boundary ◽  
Bulk Modulus ◽  
Nematic Phase ◽  
Particle Density ◽  
Two Dimensional ◽  
Active Stress ◽  
Long Wavelength ◽  
Physical Mechanisms ◽  
Critical Wavelength ◽  
The Stability

Abstract The dynamics of of the free boundary of a two-dimensional aggregate of active rod-shaped particles in the nematic phase is considered theoretically. The aggregate is in contact with a hard boundary at $y=0$, a free boundary at $y=H(x,t)$, and in the $x$-direction the aggregate is of infinite size. The analysis shows that the behavior for an aggregate with steady-state particle density $\rho _s$, strength of active stress $\chi$, bulk modulus $\rho_s \beta$, and particles aligned perpendicular to the boundaries can be mapped to one with active stress strength $- \chi$, bulk modulus $\rho_s(\beta - \chi)$, and particles aligned parallel to the boundaries. For a contractile aggregate, when the particles are aligned parallel to the boundaries, the system is unstable in long wavelengths at any strength of contractility for any $H$, and the critical wavelength increases as $H$ increases; when the particles are aligned perpendicular to the boundaries, the system acquires a finite-wavelength instability at a critical active stress whose strength decreases as $H$ increases. The stability of an extensile aggregate can be obtained from the analysis for contractile aggregates and the aforementioned mapping, even though the corresponding physical mechanisms for the instabilities are different. Finally, in the limit $H \rightarrow \infty$, the free boundary is unstable for any contractile or extensile systems in the long wavelength limit.

Considerations for Use of Square-Paddle Resonators for Arrays of Micro- and Nanoscale Devices

2009 ◽  
Author(s):  
John A. Judge ◽  
Teresa J. Woods ◽  
Joseph F. Vignola
Keyword(s):  
Vibration Mode ◽  
Experimental Studies ◽  
Two Dimensional ◽  
Quality Factors ◽  
Fundamental Vibration ◽  
Beam Resonator ◽  
Physical Mechanisms ◽  
Beam Geometry ◽  
Simple Geometry ◽  
Potential Applications

Mechanically coupling microscale or nanoscale resonators in more than one dimension requires a departure from classic beam resonator designs. A square paddle resonator is a simple geometry that allows easy coupling into two-dimensional arrays. These resonators can have high quality factors in the fundamental vibration mode if operated in vacuum. In this paper we summarize the behavior of such a resonator and describe several design considerations. We develop an expression for the inter-resonator coupling in terms of coupling beam geometry, estimate energy dissipation due to a variety of physical mechanisms, and empirically determine the vibration amplitude at which geometric nonlinearity becomes significant. Future experimental studies can exploit the expressions presented here, which facilitate design of two-dimensional arrays of square-paddle resonators that will be useful for a variety of potential applications.

Sign in / Sign up

Export Citation Format

Share Document