17,037 research outputs found

### Calculation of the incremental stress-strain relation of a polygonal packing

The constitutive relation of the quasi-static deformation on two dimensional
packed samples of polygons is calculated using molecular dynamic simulations.
The stress values at which the system remains stable are bounded by a failure
surface, that shows a power law dependence on the pressure. Below the failure
surface, non linear elasticity and plastic deformation are obtained, which are
evaluated in the framework of the incremental linear theory. The results shows
that the stiffness tensor can be directly related to the micro-contact
rearrangements. The plasticity obeys a non-associated flow rule, with a plastic
limit surface that does not agree with the failure surface.Comment: 11 pages, 20 figur

### Monte Carlo study of the spin-glass phase of the site-diluted dipolar Ising model

By tempered Monte Carlo simulations, we study site-diluted Ising systems of
magnetic dipoles. All dipoles are randomly placed on a fraction x of all L^3
sites of a simple cubic lattice, and point along a given crystalline axis. For
x_c< x<=1, where x_c = 0.65, we find an antiferromagnetic phase below a
temperature which vanishes as x tends to x_c from above. At lower values of x,
we find an equilibrium spin-glass (SG) phase below a temperature given by k_B
T_{sg} = x e_d, where e_d is a nearest neighbor dipole-dipole interaction
energy. We study (a) the relative mean square deviation D_q^2 of |q|, where q
is the SG overlap parameter, and (b) xi_L/L, where xi_L is a correlation
length. From their variation with temperature and system size, we determine
T_{sg}. In the SG phase, we find (i) the mean values and decrease
algebraically with L as L increases, (ii) double peaked, but wide,
distributions of q/ appear to be independent of L, and (iii) xi_L/L rises
with L at constant T, but extrapolations to 1/L -> 0 give finite values. All of
this is consistent with quasi-long-range order in the SG phase.Comment: 15 LaTeX pages, 15 figures, 3 tables. (typos fixed in Appendix A

### Critical point symmetries in boson-fermion systems. The case of shape transition in odd nuclei in a multi-orbit model

We investigate phase transitions in boson-fermion systems. We propose an
analytically solvable model (E(5/12)) to describe odd nuclei at the critical
point in the transition from the spherical to $\gamma$-unstable behaviour. In
the model, a boson core described within the Bohr Hamiltonian interacts with an
unpaired particle assumed to be moving in the three single particle orbitals
j=1/2,3/2,5/2. Energy spectra and electromagnetic transitions at the critical
point compare well with the results obtained within the Interacting Boson
Fermion Model, with a boson-fermion Hamiltonian that describes the same
physical situation.Comment: Phys. Rev. Lett. (in press

### Encoding algebraic power series

Algebraic power series are formal power series which satisfy a univariate
polynomial equation over the polynomial ring in n variables. This relation
determines the series only up to conjugacy. Via the Artin-Mazur theorem and the
implicit function theorem it is possible to describe algebraic series
completely by a vector of polynomials in n+p variables. This vector will be the
code of the series. In the paper, it is then shown how to manipulate algebraic
series through their code. In particular, the Weierstrass division and the
Grauert-Hironaka-Galligo division will be performed on the level of codes, thus
providing a finite algorithm to compute the quotients and the remainder of the
division.Comment: 35 page

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