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J Kertesz

Publications and source records attributed to J Kertesz.

6 recordsLinked to original sources
PubMed2000

Self-organization, localization of shear bands, and aging in loose granular materials

We introduce a mesoscopic model for the formation and evolution of shear bands in loose granular media. Numerical simulations reveal that the system undergoes a nontrivial self-organization process which is governed by the motion of the shear band and the consequent restructuring of the material along it. High density regions are built up, progressively confining the shear bands in localized regions. This results in an inhomogeneous aging of the material with a very slow increase in the mean density, displaying an unusual glassylike system-size dependence.

Journal Article↗
PubMed2000

Effect of anisotropy on the instability of crack propagation

Dynamics of fracture is investigated in an anisotropic two-dimensional Born-Maxwell model by numerical simulations. From previous studies it is known that the isotropic model shows crack branching and velocity oscillations of the propagating main crack above a critical velocity, similarly with experimental findings in some brittle materials. Here we present studies in which anisotropy has been introduced to the model system. Anisotropy is found to have significant effects on crack propagation and on the pattern it forms. In the case of symmetric anisotropy (relative to the crack direction) we found changes in velocity oscillation and side branching properties. In the case of asymmetric anisotropy two kinds of periodicities occur and strong anisotropy causes different branch patterns to form at two sides of the main crack. In addition, the role of disorder through distributed spring constants has been studied for both types of anisotropy. Finally a simple exactly solvable model for investigating the initial stages of crack branching has been developed and analyzed.

Journal Article↗
PubMed2000

Instability of symmetric couette flow in a granular gas: hydrodynamic field profiles and transport

We investigated the inelastic hard-disk gas sheared by two parallel bumpy walls (Couette flow). In our molecular dynamic simulations we found a sensitivity to the asymmetries of the initial particle positions and velocities and an asymmetric stationary state, where the deviation from (anti)symmetric hydrodynamic fields is stronger as the normal restitution coefficient decreases. For better understanding of this sensitivity we carried out a linear stability analysis of the former kinetic theoretical solution [J. T. Jenkins and M. W. Richman, J. Fluid. Mech. 171, 53 (1986)] and found it to be unstable. The effect of this asymmetry on the self-diffusion coefficient is also discussed.

Journal Article↗
PubMed1996

Progressive deterioration of brainstem auditory evoked potentials in Creutzfeldt-Jakob disease: clinical and electroencephalographic correlation.

Brainstem auditory evoked potentials (BAEP) were recorded and correlated with the clinical and electroencephalographic (EEG) findings in three verified cases of Creutzfeldt-Jakob disease (CJD). In contrast to previous reports, there was progressive deterioration of the BAEPs, through initial asymmetry of wave latencies to abnormal wave morphology, and increased interpeak latencies. Consequently, in two of the patients, disorganization of the wave pattern and generalized conduction-time slowing appeared by the time there was a fully developed clinical picture of CJD with periodic EEG waves. In the third, clinically mild CJD, asymmetry of wave latencies in the BAEP emerged, correlating with the appearance of periodicity on EEG. Our findings are consistent with the late, progressive involvement of the brainstem by the pathological process in CJD.

Brain Death↗
PubMed1986

Wide-field fusional stimulation in strabismus.

The effectiveness of wide-field fusional stimulation was evaluated on 57 strabismics and 29 patients with convergence insufficiency. The strabismics had fusion, normal retinal correspondence (even if it coexisted with anomalous retinal correspondence), a deviation not exceeding 30 delta, and visual acuity of 6/7.5 or better. The strabismics included intermittent exotropes, surgically overcorrected intermittent exotropes, and accomodative esotropes. Of these strabismic patients, 42 responded to therapy in which tropias were converted to phorias or the frequency of the manifest deviation was significantly reduced, fusional amplitudes were significantly enlarged, and in many cases, stereoacuity improved as well. In 16 cases, surgery that was recommended before treatment is no longer being considered. Of the patients with convergence insufficiency, 23 responded to therapy which resulted in the enlargement of fusional amplitudes and the alleviation of symptoms. Follow-up visits (for up to 5 years) confirm that the improvement persists, which indicates the utility and effectiveness of this technique.

Accommodation, Ocular↗