8,046 research outputs found
Propagation of an Acoustic Pulse of Finite Amplitude in a Granular Medium
A study of propagation of a wide-band acoustic signal in a granular medium is reported. Experimental data on the propagation of pulses with an amplitude up to 3 MPa and characteristic length about 1 µs through a sample of cobalt-manganese nodules are compared with a computer model of the process. An anomalous sig'rfal absorption in the high-frequency range observed with relatively weak sounding pulses is explained under the assumption of a fractal sample structure on a certain scale. When the signal amplitude increases, the ahsorption assumes a normal power form which is evidence of substance structural changes
Algebro-Geometric Solutions of the Boussinesq Hierarchy
We continue a recently developed systematic approach to the Bousinesq (Bsq)
hierarchy and its algebro-geometric solutions. Our formalism includes a
recursive construction of Lax pairs and establishes associated
Burchnall-Chaundy curves, Baker-Akhiezer functions and Dubrovin-type equations
for analogs of Dirichlet and Neumann divisors. The principal aim of this paper
is a detailed theta function representation of all algebro-geometric
quasi-periodic solutions and related quantities of the Bsq hierarchy.Comment: LaTeX, 48 page
Possible ferro-spin nematic order in NiGa2S4
We explore the possibility that the spin-1 triangular lattice magnet NiGa2 S4
may have a ferro-nematic ground state with no frozen magnetic moment but a
uniform quadrupole moment. Such a state may be stabilized by biquadratic spin
interactions. We describe the physical properties of this state and suggest
experiments to help verify this proposal. We also contrast this state with a
`non-collinear' nematic state proposed earlier by Tsunetsugu and Arikawa for
NiGa2S4
Zeros of the Partition Function for Higher--Spin 2D Ising Models
We present calculations of the complex-temperature zeros of the partition
functions for 2D Ising models on the square lattice with spin , 3/2, and
2. These give insight into complex-temperature phase diagrams of these models
in the thermodynamic limit. Support is adduced for a conjecture that all
divergences of the magnetisation occur at endpoints of arcs of zeros protruding
into the FM phase. We conjecture that there are such arcs for , where denotes the integral part of .Comment: 8 pages, latex, 3 uuencoded figure
Complex-Temperature Properties of the Ising Model on 2D Heteropolygonal Lattices
Using exact results, we determine the complex-temperature phase diagrams of
the 2D Ising model on three regular heteropolygonal lattices, (kagom\'{e}), , and (bathroom
tile), where the notation denotes the regular -sided polygons adjacent to
each vertex. We also work out the exact complex-temperature singularities of
the spontaneous magnetisation. A comparison with the properties on the square,
triangular, and hexagonal lattices is given. In particular, we find the first
case where, even for isotropic spin-spin exchange couplings, the nontrivial
non-analyticities of the free energy of the Ising model lie in a
two-dimensional, rather than one-dimensional, algebraic variety in the
plane.Comment: 31 pages, latex, postscript figure
The Yang Lee Edge Singularity on Feynman Diagrams
We investigate the Yang-Lee edge singularity on non-planar random graphs,
which we consider as the Feynman Diagrams of various d=0 field theories, in
order to determine the value of the edge exponent.
We consider the hard dimer model on phi3 and phi4 random graphs to test the
universality of the exponent with respect to coordination number, and the Ising
model in an external field to test its temperature independence. The results
here for generic (``thin'') random graphs provide an interesting counterpoint
to the discussion by Staudacher of these models on planar random graphs.Comment: LaTeX, 6 pages + 3 figure
On Darboux transformation of the supersymmetric sine-Gordon equation
Darboux transformation is constructed for superfields of the super
sine-Gordon equation and the superfields of the associated linear problem. The
Darboux transformation is shown to be related to the super B\"{a}cklund
transformation and is further used to obtain super soliton solutions.Comment: 9 Page
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