RESUMEN
The critical Casimir effect appears when critical fluctuations of an order parameter interact with classical boundaries. We investigate this effect in the setting of a Landau-Ginzburg model with continuous symmetry in the presence of quenched disorder. The quenched free energy is written as an asymptotic series of moments of the model's partition function. Our main result is that, in the presence of a strong disorder, Goldstone modes of the system contribute either with either an attractive or a repulsive force. This result was obtained using the distributional zeta-function method without relying on any particular ansatz in the functional space of the moments of the partition function.
RESUMEN
We discuss the Sherrington-Kirkpatrick mean-field version of a spin glass within the distributional zeta function method (DZFM). In the DZFM, since the dominant contribution to the average free energy is written as a series of moments of the partition function of the model, the spin-glass multivalley structure is obtained. Also, an exact expression for the saddle points corresponding to each valley and a global critical temperature showing the existence of many stables or at least metastable equilibrium states is presented. Near the critical point, we obtain analytical expressions of the order parameters that are in agreement with phenomenological results. We evaluate the linear and nonlinear susceptibility and we find the expected singular behavior at the spin-glass critical temperature. Furthermore, we obtain a positive definite expression for the entropy and we show that ground-state entropy tends to zero as the temperature goes to zero. We show that our solution is stable for each term in the expansion. Finally, we analyze the behavior of the overlap distribution, where we find a general expression for each moment of the partition function.
RESUMEN
We describe an analog model for quantum gravity effects in condensed matter physics. The situation discussed is that of phonons propagating in a fluid with a random velocity wave equation. We consider that there are random fluctuations in the reciprocal of the bulk modulus of the system and study free phonons in the presence of Gaussian colored noise with zero mean. We show that, in this model, after performing the random averages over the noise function a free conventional scalar quantum field theory describing free phonons becomes a self-interacting model.
RESUMEN
We discuss the density fluctuations of a fluid due to zero point motion, assuming a linear dispersion relation. We argue that density fluctuations in a fluid can be a useful analog model for better understanding fluctuations in relativistic quantum field theory. We calculate the differential cross section for light scattering by the zero point density fluctuations, and find a result proportional to the fifth power of the light frequency. We give some estimates of the relative magnitude of this effect compared to the scattering by thermal density fluctuations, and find that it can be of the order 13% for liquid neon at optical frequencies. This relative magnitude is proportional to frequency and inversely proportional to temperature. Although the scattering by zero point density fluctuation is small, it may be observable.
RESUMEN
A survey was carried out in a hospital of Nova Iguaçu, Rio de Janeiro, Brazil, in the period from July 1999 to March 2002, to determine the infection rate of Listeriamonocytogenes in HIV+ patients with diarrhea symptoms; 134 samples were processed by microbiological methods. The results demonstrated 12.68% of positive samples. However, no statistical differences were observed for age or sex in the studied group, suggesting that this microorganism should be regarded in the differential diagnosis of infectious processes in HIV+ patients in the area.
RESUMEN
A survey was carried out in a hospital of Nova Iguaçu, Rio de Janeiro, Brazil, in the period from July 1999 to March 2002, to determine the infection rate of Listeria monocytogenes in HIV+ patients with diarrhea symptoms; 134 samples were processed by microbiological methods. The results demonstrated 12.68% of positive samples. However, no statistical differences were observed for age or sex in the studied group, suggesting that this microorganism should be regarded in the differential diagnosis of infectious processes in HIV+ patients in the area