In this work we discuss the behavior of the microcanonical temperature ∂S(E) ∂E obtained by means of numerical entropic sampling studies. It is observed that in almost all cases the slope of the logarithm of the density of states S(E) is not infinite in the ground state, since as expected it should be directly related to the inverse temperature 1 T . Here we show that these finite slopes are in fact due to finite-size effects and we propose an analytic expression a ln(bL) for the behavior of ∆S ∆E when L → ∞. To test this idea we use three distinct two-dimensional square lattice models presenting second-order phase transitions. We calculated by exact means the parameters a and b for the two-states Ising model and for the q = 3 and 4 states Potts model and compared with the results obtained by entropic sampling simulations. We found an excellent agreement between exact and numerical values. We argue that this new set of parameters a and b represents an interesting novel issue of investigation in entropic sampling studies for different models.

Mostramos que placas em forma de triângulo retângulo com mesma hipotenusa que oscilam livremente em torno de um eixo perpendicular a elas, passando pelo vértice doângulo reto, exibe um isocronismo semelhante ao do pêndulo simples, onde o período depende de umúnico parâmetro geométrico, queé o comprimento do fio. Neste caso o parâmetroé o semi-comprimento da hipotenusa e mostramos ainda que o centro de oscilação localiza-se exatamente no centro da borda oposta. Palavras-chave: isocronismo, triângulos retângulos, pêndulo físico.We show that plates having the shape of right triangles with equal hypotenuses which are free to swing about a perpendicular axis passing through the vertex of the right angle exhibit an isochronism similar to that of the simple pendulum, where the period depends on a single geometric parameter, namely the length of the string. In this case the parameter is the half-length of the hypotenuse and we show in addition that the center of oscillation is located exactly at the center of the opposite edge.

In this work we apply a refined Wang–Landau simulation to a simple polymer model which has an exact solution both in the microcanonical and the canonical formalisms. We investigate the behavior of the microcanonical and canonical averages during the Wang–Landau simulation. The simulations were carried out using conventional Wang–Landau sampling (WLS) and the 1/t scheme. Our results show that updating the density of states only after every N monomer moves leads to a much better precision. During the simulations the canonical averages such as the location of the maximum of the specific heat calculated from independent runs tend asymptotically to values around the correct value obtained from the exact calculations of the density of states and remain unchanged for some final modification factor. Since this f final is found for the model analyzed, one has a criterion to stop the simulations. We compare our results with the exact value and with those of the 1/t scheme.

Mostramos que placas em forma de triângulo retângulo com mesma hipotenusa que oscilam livremente em torno de um eixo perpendicular a elas, passando pelo vértice do ângulo reto, exibe um isocronismo semelhante ao do pêndulo simples, onde o período depende de um único parâmetro geométrico, que é o comprimento do fio. Neste caso o parâmetro é o semi-comprimento da hipotenusa e mostramos ainda que o centro de oscilação localiza-se exatamente no centro da borda oposta.

We study a restricted-height version of the one-dimensional Oslo sandpile with conserved density, using periodic boundary conditions. Each site has a limiting height which can be either two or three. When a site reaches its limiting height it becomes active and may topple, loosing two particles, which move randomly to nearest-neighbor sites. After a site topples it is randomly assigned a new limiting height. We study the model using meanfield theory and Monte Carlo simulation, focusing on the quasi-stationary state, in which the number of active sites fluctuates about a stationary value. Using finite-size scaling analysis, we determine the critical particle density and associated critical exponents.