Coherent motion of a hole in a two-dimensional quantum antiferromagnet

1990 ◽  
Vol 78 (2) ◽  
pp. 219-227 ◽  
Author(s):  
R. Eder ◽  
K. W. Becker
Keyword(s):  
Coherent Motion ◽  
Two Dimensional ◽  
Quantum Antiferromagnet

The perception of coherent motion in two-dimensional patterns (abstract only)

1984 ◽  
Vol 18 (1) ◽  
pp. 23-23 ◽  
Author(s):  
Edward H. Adelson ◽  
J. Anthony Movshon
Keyword(s):  
Coherent Motion ◽  
Two Dimensional

scholarly journals Monocular mechanisms determine plaid motion coherence

1996 ◽  
Vol 13 (4) ◽  
pp. 615-626 ◽  
Author(s):  
David Alais ◽  
Maarten J. van der Smagt ◽  
Frans A. J. Verstraten ◽  
W. A. van de Grind
Keyword(s):  
Cortical Area ◽  
The Other ◽  
Coherent Motion ◽  
Spatial Period ◽  
Two Dimensional ◽  
Middle Temporal ◽  
Spatial Frequencies ◽  
Motion Coherence ◽  
Plaid Motion ◽  
Feature Based

AbstractAlthough the neural location of the plaid motion coherence process is not precisely known, the middle temporal (MT) cortical area has been proposed as a likely candidate. This claim rests largely on the neurophysiological findings showing that in response to plaid stimuli, a subgroup of cells in area MT responds to the pattern direction, whereas cells in area V1 respond only to the directions of the component gratings. In Experiment 1, we report that the coherent motion of a plaid pattern can be completely abolished following adaptation to a grating which moves in the plaid direction and has the same spatial period as the plaid features (the so-called “blobs”). Interestingly, we find this phenomenon is monocular: monocular adaptation destroys plaid coherence in the exposed eye but leaves it unaffected in the other eye. Experiment 2 demonstrates that adaptation to a purely binocular (dichoptic) grating does not affect perceived plaid coherence. These data suggest several conclusions: (1) that the mechanism determining plaid coherence responds to the motion of plaid features, (2) that the coherence mechanism is monocular, and thus (3), that it is probably located at a relatively low level in the visual system and peripherally to the binocular mechanisms commonly presumed to underlie two-dimensional (2-D) motion perception. Experiment 3 examines the spatial tuning of the monocular coherence mechanism and our results suggest it is broadly tuned with a preference for lower spatial frequencies. In Experiment 4, we examine whether perceived plaid direction is determined by the motion of the grating components or the features. Our data strongly support a feature-based model.

ChemInform Abstract: Two-Dimensional S = 1 Quantum Antiferromagnet (NiCl)Sr2Ta3O10.

ChemInform ◽  
2010 ◽  
Vol 41 (45) ◽  
pp. no-no
Author(s):  
Hiroshi Kageyama ◽  
et al. et al.
Keyword(s):  
Two Dimensional ◽  
Quantum Antiferromagnet

scholarly journals SCHWINGER-BOSON STUDIES OF THE SINGLE HOLE MOTION IN A 2D QUANTUM ANTIFERROMAGNET

1994 ◽  
Vol 08 (27) ◽  
pp. 3843-3858
Author(s):  
C.Q. WU ◽  
Z.B. SU ◽  
L. YU
Keyword(s):  
Heisenberg Model ◽  
Quantum Spin ◽  
Spin Fluctuations ◽  
Energy Separation ◽  
Antiferromagnetic Order ◽  
Two Dimensional ◽  
Equal Footing ◽  
Anisotropic Heisenberg Model ◽  
Single Hole ◽  
Quantum Antiferromagnet

Within the Schwinger-boson approach for the t-J model, the single hole problem in a two-dimensional quantum antiferromagnet is studied by using the quantum Bogoliubovde Gennes formalism which treats the distortion of the spin background and quantum spin fluctuations on an equal footing. Several self-trapped localized hole states are found in the distorted spin-background as in the case of an anisotropic Heisenberg model. These localized hole states survive at finite temperatures when the antiferromagnetic order becomes short-ranged. The energy separation between the two lowest states is reduced by considering the spin-background distortion, but it remains finite.

A single hole in a quantum antiferromagnet: selfconsistent Green’s function approach

1991 ◽  
Vol 05 (01n02) ◽  
pp. 207-217 ◽  
Author(s):  
Gerardo Martínez ◽  
Peter Horsch
Keyword(s):  
Born Approximation ◽  
Complete Characterization ◽  
Exact Diagonalization ◽  
Low Energy ◽  
Spin Polaron ◽  
Two Dimensional ◽  
Effective Masses ◽  
Single Hole ◽  
Quantum Antiferromagnet

We solved numerically the integral equation for the selfenergy which describes the motion of a single hole in a two-dimensional quantum antiferromagnet (AF) within the selfconsistent Born approximation. This formulation stresses the similarity of the AF-spin polaron with the standard polaron problem. We confine our calculation to finite cluster geometries and compare with results from previous exact diagonalization studies. The spectral function is characterized by a narrow quasiparticle (qp) peak at the low energy side of the spectra, which appears to be well separated from the incoherent band part for large enough J values. For small J we find a reduced width of ~7t for the incoherent band. The bottom of the coherent qp band always occurs at (±π/2, ±π/2). Its bandwidth initially increases with J until J≃t and then decreases as 2t2/J. A complete characterization of our solution is given, including the dispersion relation and effective masses of this quasiparticle. The comparison with exact diagonalization studies for a 4×4 cluster is remarkably good. From our results we see that a lattice of 16×16 sites describes adequately the thermodynamic limit. We conclude that the simple Born approximation is a valuable scheme to characterize the dynamics of one hole in the t-J model. both in the perturbative and the strong coupling regimes.

Are Mechanisms for Perception of Biological Motion Different from Mechanisms for Perception of Nonbiological Motion?

2002 ◽  
Vol 95 (3_suppl) ◽  
pp. 1301-1310 ◽  
Author(s):  
Leo Poom ◽  
Henrik Olsson
Keyword(s):  
Biological Motion ◽  
Three Dimensional ◽  
Constant Time ◽  
Coherent Motion ◽  
Two Dimensional ◽  
Dimensional Shape ◽  
Perception Of Biological Motion ◽  
Three Dimensional Shape ◽  
Over Time ◽  
Unidirectional Motion

We compared the integration of information over space and time for perceiving different configurations of moving dots: a walking person (biological motion), rigid three-dimensional shapes, and unidirectional coherent motion of all dots (translation). No performance differences in judging walking direction and coherent translation direction were obtained in conditions with constant presentation times and varying number of target dots (integration over space). Depending on the speed of the two-dimensional configurations judgments were either worse or better than the judgments of walking direction. The results for conditions with different presentation times (integration over time) show that information about biological motion is integrated over time that increases with increasing gait period, while two-dimensional unidirectional motion is integrated over constant time independent of speed. The effect is not due to the oscillatory nature of the biological motion since information about a rigid three-dimensional shape is summed over a constant time independent of the period of the motion cycle. This could be interpreted as different neural mechanisms mediating the temporal summation for walking direction compared to detecting the orientation of rigid structure, or the direction of two-dimensional unidirectional motion. Since biological motion is characterized by nonrigidity, it is possible that the form itself is integrated over time and not the motion pattern.

Phase diagram of the two-dimensional quantum antiferromagnet in a magnetic field

2006 ◽  
Vol 99 (8) ◽  
pp. 08H503 ◽  
Author(s):  
Alessandro Cuccoli ◽  
Giacomo Gori ◽  
Ruggero Vaia ◽  
Paola Verrucchi
Keyword(s):  
Magnetic Field ◽  
Phase Diagram ◽  
Two Dimensional ◽  
Quantum Antiferromagnet
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