A case of meningeal melanocytoma at the foramen magnum is reported in a 62-year-old man. Magnetic resonance (MR) imaging revealed characteristic signal patterns: homogeneous high intensity on the T1-weighted image and low intensity on the T2-weighted image. Light microscopy showed a histological appearance similar to that of melanotic meningioma. The ultrastructural features of the neoplastic cells were compatible with those of melanocytes, but they contained no features of arachnoidal cells. Immunohistochemical bromodeoxyuridine study revealed low proliferative activity among the neoplastic cells. The MR appearance and pathological features in this rare case of meningeal melanocytoma are demonstrated and discussed.

The mutually coupled Hopfield model can determine the local minimum of the energy function in a short time by the steepest descent of the energy function surface [1]. To use its high speed, analog implementation of the Hopfield model by an analog circuit is considered. On the other hand, no thorough study of various problems in the analog circuit, such as the sensitivity of the parameters to deviations of the element values, has been presented. From this viewpoint, this paper attempts a sensitivity analysis of the Hopfield model for the circuit parameters when the model is implemented on an analog circuit. Sensitivity analysis means in this paper a procedure in which error is provided by a normal random variable to a parameter that may be affected by the circuit implementation, and the effect on the solution is examined. It is seen that the Hopfield model is highly sensitive to error. In other words, the realization of low sensitivity is very important in implementing the Hopfield model as an analog circuit. This paper proposes a method where the diagonal element of the coupling weight matrix is set to a nonzero value and reports that the sensitivity to error can be reduced by this approach. The property is verified by a numerical simulation for the traveling salesman problem (TSP). © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(12): 43–53, 1999

SUMMARYThe mutually coupled Hopfield model can determine the local minimum of the energy function in a short time by the steepest descent of the energy function surface [1]. To use its high speed, analog implementation of the Hopfield model by an analog circuit is considered. On the other hand, no thorough study of various problems in the analog circuit, such as the sensitivity of the parameters to deviations of the element values, has been presented. From this viewpoint, this paper attempts a sensitivity analysis of the Hopfield model for the circuit parameters when the model is implemented on an analog circuit. Sensitivity analysis means in this paper a procedure in which error is provided by a normal random variable to a parameter that may be affected by the circuit implementation, and the effect on the solution is examined. It is seen that the Hopfield model is highly sensitive to error. In other words, the realization of low sensitivity is very important in implementing the Hopfield model as an analog circuit. This paper proposes a method where the diagonal element of the coupling weight matrix is set to a nonzero value and reports that the sensitivity to error can be reduced by this approach. The property is verified by a numerical simulation for the traveling salesman problem (TSP). © 1999 Scripta Technica, Electron Comm Jpn Pt 3, 82(12): 4353, 1999