scholarly journals Human identification by spatio-temporal symmetry

2003 ◽  
Author(s):  
J.B. Hayfron-Acquah ◽  
M.S. Nixon ◽  
J.N. Carter
Keyword(s):  
Human Identification ◽  
Spatio Temporal ◽  
Temporal Symmetry

scholarly journals Disrupting the spatio-temporal symmetry of the electron dynamics in atmospheric pressure plasmas by voltage waveform tailoring

2019 ◽  
Vol 28 (1) ◽  
pp. 01LT01 ◽  
Author(s):  
Andrew R Gibson ◽  
Zoltán Donkó ◽  
Layla Alelyani ◽  
Lena Bischoff ◽  
Gerrit Hübner ◽  
...  
Keyword(s):  
Atmospheric Pressure ◽  
Electron Dynamics ◽  
Voltage Waveform ◽  
Atmospheric Pressure Plasmas ◽  
Spatio Temporal ◽  
Temporal Symmetry

scholarly journals Mode competition in modulated Taylor–Couette flow

2008 ◽  
Vol 601 ◽  
pp. 381-406 ◽  
Author(s):  
M. AVILA ◽  
M. J. BELISLE ◽  
J. M. LOPEZ ◽  
F. MARQUES ◽  
W. S. SARIC
Keyword(s):  
Couette Flow ◽  
Physical Experiment ◽  
Mode Competition ◽  
Taylor Vortex ◽  
Coexistence Region ◽  
Narrow Region ◽  
Taylor Couette ◽  
Spatio Temporal ◽  
Temporal Symmetry ◽  
Taylor Couette Flow

The effects of harmonically oscillating the inner cylinder about a zero mean rotation in a Taylor–Couette flow are investigated experimentally and numerically. The resulting time-modulated circular Couette flow possesses a Z2 spatio-temporal symmetry which gives rise to two distinct modulated Taylor vortex flows. These flows are initiated at synchronous bifurcations, have the same spatial symmetries, but are characterized by different spatio-temporal symmetries and axial wavenumber. Mode competition between these two states has been investigated in the region where they bifurcate simultaneously. In the idealized numerical model, the two flows have been found to coexist and be stable in a narrow region of parameter space. However, in the physical experiment, neither state has been observed in the coexistence region. Instead, we observe noise-sustained flows with irregular time-dependent axial wavenumber. Movies are available with the online version of the paper.

Flow over a thin circular disk at low to moderate Reynolds numbers

2008 ◽  
Vol 605 ◽  
pp. 253-262 ◽  
Author(s):  
A. R. SHENOY ◽  
C. KLEINSTREUER
Keyword(s):  
Lift Coefficient ◽  
Three Dimensional ◽  
Circular Disk ◽  
Vortex Structures ◽  
Separation Region ◽  
Three Dimensional Flow ◽  
Dimensional Flow ◽  
Vortex Loops ◽  
Spatio Temporal ◽  
Temporal Symmetry

Computation of viscous flow over a circular disk of aspect ratio 10 (thickness/diameter) in the Reynolds number (Re) range of 10 to 300 was performed. The following flow regimes were observed: (I) steady axisymmetric flow when Re < 135, with the presence of a toroidal vortex behind the disk; (II) regular bifurcation with loss of azimuthal symmetry but with planar symmetry and a double-threaded wake, for 135 ≤ Re < 155; (III) three-dimensional flow with periodic shedding of double-sided hairpin-shaped vortex structures and periodic motion of the separation region for 155 ≤ Re < 172; (IV) regular shedding of double-sided hairpin-shaped vortex structures with planar and spatio-temporal symmetry for 172 ≤ Re < 280; (V) periodic three-dimensional flow with irregular rotation of the separation region when Re = 280–300. This transition process for the disk differs from that for the sphere as we observe a loss of the symmetry plane in Regime III due to a twisting motion of the axial vorticity strands in the wake of the disk. The periodic flow was characterized by double-sided hairpin structures, unlike the one-sided vortex loops observed for the sphere. This resulted in the drag coefficient oscillating at twice the frequency of the axial velocity. In Regime IV, the vortex loops were shed from diametrically opposite locations and with equal strength, resulting in the lift coefficient oscillating symmetrically about a zero mean. These results imply the presence of spatio-temporal symmetry.

scholarly journals Spatio-Temporal Symmetry—Point Groups with Time Translations

Symmetry ◽  
2017 ◽  
Vol 9 (9) ◽  
pp. 187 ◽  
Author(s):  
Haricharan Padmanabhan ◽  
Maggie Kingsland ◽  
Jason Munro ◽  
Daniel Litvin ◽  
Venkatraman Gopalan
Keyword(s):  
Symmetry Point ◽  
Point Groups ◽  
Spatio Temporal ◽  
Temporal Symmetry

Nonlinear mode interactions in a counter-rotating split-cylinder flow

2017 ◽  
Vol 816 ◽  
pp. 719-745 ◽  
Author(s):  
Paloma Gutierrez-Castillo ◽  
Juan M. Lopez
Keyword(s):  
Steady States ◽  
Mode Competition ◽  
Meridional Plane ◽  
Vortex Lines ◽  
Counter Rotation ◽  
Pulse Waves ◽  
Group Orbit ◽  
Spatio Temporal ◽  
Cylinder Flow ◽  
Temporal Symmetry

The flow in a split cylinder with each half in exact counter rotation is studied numerically. The exact counter rotation, quantified by a Reynolds number $\mathit{Re}$ based on the rotation rate and radius, imparts the system with an $O(2)$ symmetry (invariance to azimuthal rotations as well as to an involution consisting of a reflection about the mid-plane composed with a reflection about any meridional plane). The $O(2)$ symmetric basic state is dominated by a shear layer at the mid-plane separating the two counter-rotating bodies of fluid, created by the opposite-signed vortex lines emanating from the two endwalls being bent to meet at the split in the sidewall. With the exact counter rotation, the additional involution symmetry allows for steady non-axisymmetric states, that exist as a group orbit. Different members of the group simply correspond to different azimuthal orientations of the same flow structure. Steady states with azimuthal wavenumber $m$ (the value of $m$ depending on the cylinder aspect ratio $\unicode[STIX]{x1D6E4}$) are the primary modes of instability as $\mathit{Re}$ and $\unicode[STIX]{x1D6E4}$ are varied. Mode competition between different steady states ensues, and further bifurcations lead to a variety of different time-dependent states, including rotating waves, direction-reversing waves, as well as a number of slow–fast pulse waves with a variety of spatio-temporal symmetries. Further from the primary instabilities, the competition between the vortex lines from each half-cylinder settles on either a $m=2$ steady state or a limit cycle state with a half-period-flip spatio-temporal symmetry. By computing in symmetric subspaces as well as in the full space, we are able to unravel many details of the dynamics involved.

Serial Movement Timing and Musical Experience

1985 ◽  
Vol 60 (1) ◽  
pp. 31-36 ◽  
Author(s):  
L. R. T. Williams
Keyword(s):  
Temporal Patterns ◽  
Musical Experience ◽  
Serial Pattern ◽  
Timing Error ◽  
Movement Timing ◽  
Internal Representations ◽  
Musical Practice ◽  
Timing Task ◽  
Spatio Temporal ◽  
Temporal Symmetry

Musicians and non-musicians were compared on a serial movement-timing task incorporating six continuous 11-cm segments. The serial pattern was structured for both spatial and temporal symmetry. There were seven subjects in each group and 50 test trials were analyzed for timing error. The non-musicians were less accurate and more variable for certain parts of the pattern. The findings supported the view that musical practice can assist the process of mapping internal representations of serial relations to novel spatio-temporal patterns of movement.

Symmetry Breaking and Mode-Interaction in Vortex-Structure Interaction

2002 ◽  
Author(s):  
Njuki W. Mureithi ◽  
Hiroshi Kanki ◽  
Syuki Goda ◽  
Tomomichi Nakamura ◽  
Tomoharu Kashikura
Keyword(s):  
Vortex Structure ◽  
Frequency Ratio ◽  
Flow Direction ◽  
Temporal Structure ◽  
Experimental Tests ◽  
Mode Interaction ◽  
Structure Interaction ◽  
Shedding Frequency ◽  
Spatio Temporal ◽  
Temporal Symmetry

This paper presents some results of experiments and numerical computations on various aspects of vortex-structure interaction. Experimental tests were conducted in a small wind tunnel to investigate the effect of mechanical cylinder oscillation in the flow direction on the wake vortex structure. Depending on the excitation to Karman shedding frequency ratio, mode locked states, in the form of spatio-temporally repeatable patterns, could be observed. Symmetrical excitation leads to breaking of the Karman mode spatial-temporal symmetry. Depending on the excitation to Karman frequency ratio, modes lacking the usual Karman symmetry is observed. The existence of a stable spatio-temporal structure appears to be strongly dependent on the interaction (lock-in) between the near wake symmetrical shedding and the ‘established’ far wake Karman pattern. Preliminary work based on symmetry (group) theory is presented to support the foregoing experimental observations. By considering two oscillators having the Dm (κ,2π / m) inline shedding symmetry and the Karman wake having the spatio-temporal symmetry Z2 (κ,π), the possible symmetries of subsequent flow perturbations resulting from the modal interaction are determined. A mode having the reduced symmetry, Z2 (I,π2) was theoretically predicted and confirmed in the experiments. Finally, experimental tests show strong subharmonic lockin for forcing at rational ratios the vortex shedding frequency in the range 1 &lt; m/n &lt; 2. This phenomenon was also predicted theoretically.

scholarly journals Modulated waves in a periodically driven annular cavity

2010 ◽  
Vol 667 ◽  
pp. 336-357 ◽  
Author(s):  
H. M. BLACKBURN ◽  
J. M. LOPEZ
Keyword(s):  
Symmetry Group ◽  
Temporal Dynamics ◽  
Travelling Waves ◽  
Temporal Structure ◽  
Three Dimensional ◽  
Spanwise Direction ◽  
Two Dimensional ◽  
Periodically Driven ◽  
Spatio Temporal ◽  
Temporal Symmetry

Time-periodic flows with spatio-temporal symmetry Z2 × O(2) – invariance in the spanwise direction generating the O(2) symmetry group and a half-period-reflection symmetry in the streamwise direction generating a spatio-temporal Z2 symmetry group – are of interest largely because this is the symmetry group of periodic laminar two-dimensional wakes of symmetric bodies. Such flows are the base states for various three-dimensional instabilities; the periodically shedding two-dimensional circular cylinder wake with three-dimensional modes A and B being the generic example. However, it is not easy to physically realize the ideal flows owing to the presence of end effects and finite spanwise geometries. Flows past rings are sometimes advanced as providing a relevant idealization, but in fact these have symmetry group O(2) and only approach Z2 × O(2) symmetry in the infinite aspect ratio limit. The present work examines physically realizable periodically driven annular cavity flows that possess Z2 × O(2) spatio-temporal symmetry. The flows have three distinct codimension-1 instabilities: two synchronous modes (A and B), and two manifestations of a quasi-periodic (QP) mode, either as modulated standing waves or modulated travelling waves. It is found that the curvature of the system can determine which of these modes is the first to become unstable with increasing Reynolds number, and that even in the nonlinear regime near onset of three-dimensional instabilities the dynamics are dominated by mixed modes with complicated spatio-temporal structure. Supplementary movies illustrating the spatio-temporal dynamics are available at journals.cambridge.org/flm.

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