Symmetry and Uprightness in Visually Perceived Forms

2017 ◽  
Author(s):  
Lydia M. Maniatis
Keyword(s):  
Visual System ◽  
Retinal Image ◽  
Mirror Symmetry ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Two Dimensional ◽  
Retinal Projection ◽  
Retinal Surface ◽  
Axis Of Symmetry

Why do some two-dimensional (2D) drawings look three-dimensional (3D)? The answer is because their projection on our retinas is consistent with a 3D percept that has a “better” shape and orientation than the 2D figure. Whenever a retinal projection is interpreted by the visual system as the projection of a surface that is not frontoparallel (i.e., not parallel to the retinal surface), then the retinal image will differ in shape from the source of the projection in (a) the sizes of its internal angles and/or (b) the relative extents of its surfaces. The latter differences arise because, when an extent is assumed to be receding, then it must also be assumed to have undergone foreshortening in the projection. Using pictures, we can show that the visual system likes more, rather than less, mirror symmetry and a vertical axis of symmetry more than a tilted one.

scholarly journals A Fast Two-Dimensional Numerical Method for the Wake Simulation of a Vertical Axis Wind Turbine

Energies ◽  
2020 ◽  
Vol 14 (1) ◽  
pp. 49
Author(s):  
Zheng Yuan ◽  
Jin Jiang ◽  
Jun Zang ◽  
Qihu Sheng ◽  
Ke Sun ◽  
...  
Keyword(s):  
Velocity Distribution ◽  
Numerical Method ◽  
Three Dimensional ◽  
Particle Method ◽  
Vortex Method ◽  
Vertical Axis ◽  
Two Dimensional ◽  
Vertical Axis Wind Turbine ◽  
Wake Effect ◽  
Array Design

In the array design of the vertical axis wind turbines (VAWT), the wake effect of the upstream VAWT on the downstream VAWT needs to be considered. In order to simulate the velocity distribution of a VAWT wake rapidly, a new two-dimensional numerical method is proposed, which can make the array design easier and faster. In this new approach, the finite vortex method and vortex particle method are combined to simulate the generation and evolution of the vortex, respectively, the fast multipole method (FMM) is used to accelerate the calculation. Based on a characteristic of the VAWT wake, that is, the velocity distribution can be fitted into a power-law function, a new correction model is introduced to correct the three-dimensional effect of the VAWT wake. Finally, the simulation results can be approximated to the published experimental results in the first-order. As a new numerical method to simulate the complex VAWT wake, this paper proves the feasibility of the method and makes a preliminary validation. This method is not used to simulate the complex three-dimensional turbulent evolution but to simulate the velocity distribution quickly and relatively accurately, which meets the requirement for rapid simulation in the preliminary array design.

scholarly journals Theoretical Gravity Anomalies of Glaciers Having Parabolic Cross-Sections

1964 ◽  
Vol 5 (38) ◽  
pp. 255-257 ◽  
Author(s):  
Charles E. Corbató
Keyword(s):  
Cross Sections ◽  
Lower Boundary ◽  
Gravity Anomalies ◽  
Vertical Axis ◽  
Two Dimensional ◽  
Axis Of Symmetry ◽  
Upper Boundary

AbstractEquations and a graph are presented for calculating gravity anomalies on a two-dimensional glacier model having a horizontal upper boundary and a lower boundary which is a parabola with a vertical axis of symmetry.

Occlusion Constraints and Stereoscopic Slant

Perception ◽  
1997 ◽  
Vol 26 (1) ◽  
pp. 29-38 ◽  
Author(s):  
Jukka Häkkinen ◽  
Göte Nyman
Keyword(s):  
Binocular Vision ◽  
Retinal Image ◽  
Three Dimensional ◽  
Vertical Axis ◽  
The Other ◽  
Necessary Condition ◽  
Slant Perception ◽  
Frontoparallel Plane ◽  
Reduction Effect

In binocular vision horizontal magnification of one retinal image leads to a percept of three-dimensional slant around a vertical axis. It is demonstrated that the perception of slant is diminished when an occlusion interpretation is possible. A frontoparallel plane located in the immediate vicinity of a slanted surface in a location which allows a perception of occlusion reduces the magnitude of perceived slant significantly. When the same plane is placed on the other side, the slant perception is normal because there is no alternative occlusion interpretation. The results indicate that a common border between the occluder and a slanted surface is not a necessary condition for the reduction effect. If the edges are displaced and the edge of the slanted surface is placed in a location in which it could be occluded, the effect still appears.

‘Generic-View Principle’ for Three-Dimensional-Motion Perception: Optics and Inverse Optics of a Moving Straight Bar

Perception ◽  
1996 ◽  
Vol 25 (7) ◽  
pp. 797-814 ◽  
Author(s):  
Michiteru Kitazaki ◽  
Shinsuke Shimojo
Keyword(s):  
Visual System ◽  
Motion Perception ◽  
Retinal Image ◽  
General Framework ◽  
Three Dimensional ◽  
Image Motion ◽  
Optical Process ◽  
Retinal Image Motion ◽  
The Subject ◽  
Three Components

The generic-view principle (GVP) states that given a 2-D image the visual system interprets it as a generic view of a 3-D scene when possible. The GVP was applied to 3-D-motion perception to show how the visual system decomposes retinal image motion into three components of 3-D motion: stretch/shrinkage, rotation, and translation. First, the optical process of retinal image motion was analyzed, and predictions were made based on the GVP in the inverse-optical process. Then experiments were conducted in which the subject judged perception of stretch/shrinkage, rotation in depth, and translation in depth for a moving bar stimulus. Retinal-image parameters—2-D stretch/shrinkage, 2-D rotation, and 2-D translation—were manipulated categorically and exhaustively. The results were highly consistent with the predictions. The GVP seems to offer a broad and general framework for understanding the ambiguity-solving process in motion perception. Its relationship to other constraints such as that of rigidity is discussed.

Two-Dimensional Photoelasticity as a Method of Approximation to the Stresses in Three-Dimensional Problems with a Plane or Axis of Symmetry

1962 ◽  
Vol 66 (615) ◽  
pp. 193-196 ◽  
Author(s):  
M. L. Meyer ◽  
A. N. Oak
Keyword(s):  
Three Dimensional ◽  
Two Dimensional ◽  
Slide Rule ◽  
Layer Technique ◽  
Axis Of Symmetry ◽  
Great Simplicity

The fundamental advantage of two-dimensional photoelasticity is its great simplicity. Neither the frozen-stress three-dimensional method nor the photoelastic layer technique share this simplicity as yet. Whereas the frozen-stress and layer techniques are most suitable for final investigation into the strength of a finished design, the simple plane photoelasticity can be used as a tool by the designer at every stage of his design, as a specialised slide rule, so to say, that gives sometimes faster and frequently more accurate answers than complicated stress calculations. The consequences of given changes in the outlines of a component can often be studied more conveniently and cheaply by this method than by almost any other.

Stochastic Modeling of Icicle Formation

1994 ◽  
Vol 116 (3) ◽  
pp. 180-184 ◽  
Author(s):  
K. Szilder ◽  
E. P. Lozowski
Keyword(s):  
Water Flux ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Cylindrical Symmetry ◽  
Diameter Growth ◽  
Two Dimensional ◽  
Fluid Element ◽  
Pendant Drop ◽  
Dimensional Model ◽  
Supply Rate

A discrete random walk model has been developed to simulate icicle formation. A three-dimensional icicle is represented by a two-dimensional model with cylindrical symmetry around the vertical axis. The water flux along the icicle is divided into fluid elements which follow a stochastic path downwards towards the tip. During its walk, a fluid element may freeze on the icicle’s lateral surface or at the tip. The fluid elements can also form a pendant drop which may drip from the icicle tip. The freezing probability and the shedding parameter, which are the discrete model’s parameters, are expressed as functions of the heat loss to the airstream and the water supply rate, using simple analytical considerations. The predicted rates of icicle length and diameter growth agree well with experimental data. In addition, the model icicles exhibit the characteristic icicle ribs.

Variable pitch control for vertical-axis wind turbines

2018 ◽  
Vol 42 (2) ◽  
pp. 128-135 ◽  
Author(s):  
S Horb ◽  
R Fuchs ◽  
A Immas ◽  
F Silvert ◽  
P Deglaire
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Turbine ◽  
Three Dimensional ◽  
Vertical Axis ◽  
Two Dimensional ◽  
Vertical Axis Wind Turbine ◽  
Horizontal Axis Wind Turbine ◽  
Variable Pitch ◽  
Pitch Control

NENUPHAR aims at developing the next generation of large-scale floating offshore vertical-axis wind turbine. To challenge the horizontal-axis wind turbine, the variable blade pitch control appears to be a promising solution. This article focuses on blade pitch law optimization and resulting power and thrust gain depending on the operational conditions. The aerodynamics resulting from the implementation of a variable blade pitch control are studied through numerical simulations, either with a three-dimensional vortex code or with two-dimensional Navier-stokes simulations (two-dimensional computational fluid dynamics). Results showed that the three-dimensional vortex code used as quasi-two-dimensional succeeded to give aerodynamic loads in very good agreement with two-dimensional computational fluid dynamics simulation results. The three-dimensional-vortex code was then used in three-dimensional configuration, highlighting that the variable pitch can enhance the vertical-axis wind turbine power coefficient ( Cp) by more than 15% in maximum power point tracking mode and decrease it by more than 75% in power limitation mode while keeping the thrust below its rated value.

scholarly journals Connecting mirror symmetry in 3D and 2D via localization

2014 ◽  
Vol 29 (32) ◽  
pp. 1530004 ◽  
Author(s):  
Heng-Yu Chen ◽  
Hsiao-Yi Chen ◽  
Jun-Kai Ho
Keyword(s):  
Mirror Symmetry ◽  
Gauge Theories ◽  
Three Dimensional ◽  
High Energy ◽  
Partition Functions ◽  
Two Dimensional ◽  
Abelian Gauge ◽  
Fusion Procedure ◽  
Mirror Pair ◽  
Simple Limit

We explicitly apply localization results to study the interpolation between three- and two-dimensional mirror symmetries for Abelian gauge theories with four supercharges. We first use the ellipsoid [Formula: see text] partition functions to verify the mirror symmetry between a pair of general three-dimensional 𝒩 = 2 Abelian Chern–Simons quiver gauge theories. These expressions readily factorize into holomorphic blocks and their antiholomorphic copies, so we can also obtain the partition functions on S1×S2 via fusion procedure. We then demonstrate S1×S2 partition functions for the three-dimensional Abelian gauge theories can be dimensionally reduced to the S2 partition functions of 𝒩 = (2, 2) GLSM and Landau–Ginzburg model for the corresponding two-dimensional mirror pair, as anticipated previously in M. Aganagic et al., J. High Energy Phys.0107, 022 (2001). We also comment on the analogous interpolation for the non-Abelian gauge theories and compute the K-theory vortex partition function for a simple limit to verify the prediction from holomorphic block.

Detecting Sudden Changes in Dynamic Rotation Displays

2010 ◽  
Vol 23 (3) ◽  
pp. 241-261
Author(s):  
Rachael Thiel ◽  
J. Timothy Petersik
Keyword(s):  
Visual System ◽  
Three Dimensional ◽  
Two Dimensional ◽  
3D Motion ◽  
Axis Of Rotation ◽  
Dynamic Rotation

AbstractFour experiments and controls were run in order to determine the ability of the visual system to detect slight changes in three-dimensional (3D) rotating stimuli in comparison to two-dimensional (2D) controls. A small number of observers (between 5 and 8) viewed computerized displays of pixel-defined transparent rotating spheres or circular patches of pixels drifting linearly in opposite directions. Halfway through the circuit of rotation a letter was briefly displayed and the rotation continued with some change introduced. Our results showed that for horizontal shifts of the stimulus on the X-axis, changes in the axis of rotation, and additions/deletions of pixels, observers were better at detecting the changes associated with 3D motion than 2D motion. There was no good 2D control for approaching and receding stimuli, but on the basis of other results it was concluded that 3D movement had no advantage. It is suggested that rotation in 3D is more readily monitored by the visual system than simultaneous 2D motions in opposite directions.

An Upward-Facing Surface Appears Darker: The Role Played by the Light-From-Above Assumption in Lightness Perception

Perception ◽  
2019 ◽  
Vol 48 (6) ◽  
pp. 500-514
Author(s):  
Yuki Kobayashi ◽  
Kazunori Morikawa
Keyword(s):  
Light Intensity ◽  
Visual System ◽  
Human Visual System ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Surface Reflectance ◽  
Two Dimensional ◽  
Illusory Effect ◽  
Lightness Perception ◽  
Extract Information

The human visual system can extract information on surface reflectance (lightness) from light intensity; this, however, confounds information on reflectance and illumination. We hypothesized that the visual system, to solve this lightness problem, utilizes the internally held prior assumption that illumination falls from above. Experiment 1 showed that an upward-facing surface is perceived to be darker than a downward-facing surface, proving our hypothesis. Experiment 2 showed the same results in the absence of explicit illumination cues. The effect of the light-from-left prior assumption was not observed in Experiment 3. The upward- and downward-facing surface stimuli in Experiments 1 and 2 showed no difference in a two-dimensional configuration or three-dimensional structure, and the participants’ perceived lightness appeared to be affected by the observers’ prior assumption that illumination is always from above. Other studies have not accounted for this illusory effect, and this study’s finding provides additional insights into the study of lightness perception.

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