70 research outputs found
Imprinting the memory into paste and its visualization as crack patterns in drying process
In the drying process of paste, we can imprint into the paste the order how
it should be broken in the future. That is, if we vibrate the paste before it
is dried, it remembers the direction of the initial external vibration, and the
morphology of resultant crack patterns is determined solely by the memory of
the direction. The morphological phase diagram of crack patterns and the
rheological measurement of the paste show that this memory effect is induced by
the plasticity of paste.Comment: 4 pages, 3 figures, submitted to JPS
Pattern formation and selection in quasi-static fracture
Fracture in quasi-statically driven systems is studied by means of a discrete
spring-block model. Developed from close comparison with desiccation
experiments, it describes crack formation induced by friction on a substrate.
The model produces cellular, hierarchical patterns of cracks, characterized by
a mean fragment size linear in the layer thickness, in agreement with
experiments. The selection of a stationary fragment size is explained by
exploiting the correlations prior to cracking. A scaling behavior associated
with the thickness and substrate coupling, derived and confirmed by
simulations, suggests why patterns have similar morphology despite their
disparity in scales.Comment: 4 pages, RevTeX, two-column, 5 PS figures include
Polyakov Lines in Yang-Mills Matrix Models
We study the Polyakov line in Yang-Mills matrix models, which include the
IKKT model of IIB string theory. For the gauge group SU(2) we give the exact
formulae in the form of integral representations which are convenient for
finding the asymptotic behaviour. For the SU(N) bosonic models we prove upper
bounds which decay as a power law at large momentum p. We argue that these
capture the full asymptotic behaviour. We also indicate how to extend the
results to some correlation functions of Polyakov lines.Comment: 19 pages, v2 typos corrected, v3 ref adde
Effect of Interaction on the Formation of Memories in Paste
A densely packed colloidal suspension with plasticity, called paste, is known
to remember directions of vibration and flow. These memories in paste can be
visualized by the morphology of desiccation crack patterns. Here, we find that
paste made of charged colloidal particles cannot remember flow direction. If we
add sodium chloride into such paste to screen the Coulombic repulsive
interaction between particles, the paste comes to remember flow direction. That
is, one drop of salt water changes memory effect in the paste and thereby we
can tune the morphology of desiccation crack patterns more precisely.Comment: 10 pages, 11 figures, Title change
Stable propagation of an ordered array of cracks during directional drying
We study the appearance and evolution of an array of parallel cracks in a
thin slab of material that is directionally dried, and show that the cracks
penetrate the material uniformly if the drying front is sufficiently sharp. We
also show that cracks have a tendency to become evenly spaced during the
penetration. The typical distance between cracks is mainly governed by the
typical distance of the pattern at the surface, and it is not modified during
the penetration. Our results agree with recent experimental work, and can be
extended to three dimensions to describe the properties of columnar polygonal
patterns observed in some geological formations.Comment: 8 pages, 4 figures, to appear in PR
Matrix Models
Matrix models and their connections to String Theory and noncommutative
geometry are discussed. Various types of matrix models are reviewed. Most of
interest are IKKT and BFSS models. They are introduced as 0+0 and 1+0
dimensional reduction of Yang--Mills model respectively. They are obtained via
the deformations of string/membrane worldsheet/worldvolume. Classical solutions
leading to noncommutative gauge models are considered.Comment: Lectures given at the Winter School on Modern Trends in
Supersymmetric Mechanics, March 2005 Frascati; 38p
Development and geometry of isotropic and directional shrinkage crack patterns
We have studied shrinkage crack patterns which form when a thin layer of an
alumina/water slurry dries. Both isotropic and directional drying were studied.
The dynamics of the pattern formation process and the geometric properties of
the isotropic crack patterns are similar to what is expected from recent
models, assuming weak disorder. There is some evidence for a gradual increase
in disorder as the drying layer become thinner, but no sudden transition, in
contrast to what has been seen in previous experiments. The morphology of the
crack patterns is influenced by drying gradients and front propagation effects,
with sharp gradients having a strong orienting and ordering effect.Comment: 8 pages, 11 figures, 8 in jpg format, 3 in postscript. See also
http://mobydick.physics.utoronto.ca/mud.htm
Axial anomaly in the reduced model: Higher representations
The axial anomaly arising from the fermion sector of \U(N) or \SU(N)
reduced model is studied under a certain restriction of gauge field
configurations (the ``\U(1) embedding'' with ). We use the
overlap-Dirac operator and consider how the anomaly changes as a function of a
gauge-group representation of the fermion. A simple argument shows that the
anomaly vanishes for an irreducible representation expressed by a Young tableau
whose number of boxes is a multiple of (such as the adjoint
representation) and for a tensor-product of them. We also evaluate the anomaly
for general gauge-group representations in the large limit. The large
limit exhibits expected algebraic properties as the axial anomaly.
Nevertheless, when the gauge group is \SU(N), it does not have a structure
such as the trace of a product of traceless gauge-group generators which is
expected from the corresponding gauge field theory.Comment: 21 pages, uses JHEP.cls and amsfonts.sty, the final version to appear
in JHE
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