Adaptive neural network motion control of manipulators with experimental evaluations.

A nonlinear proportional-derivative controller plus adaptive neuronal network compensation is proposed. With the aim of estimating the desired torque, a two-layer neural network is used. Then, adaptation laws for the neural network weights are derived. Asymptotic convergence of the position and velocity tracking errors is proven, while the neural network weights are shown to be uniformly bounded. The proposed scheme has been experimentally validated in real time. These experimental evaluations were carried in two different mechanical systems: a horizontal two degrees-of-freedom robot and a vertical one degree-of-freedom arm which is affected by the gravitational force. In each one of the two experimental set-ups, the proposed scheme was implemented without and with adaptive neural network compensation. Experimental results confirmed the tracking accuracy of the proposed adaptive neural network-based controller.

Frecuencia de la mutación 185delAG en el gen BRCA1 en mujeres chilenas sanas con antecedentes familiares de cáncer de mama / Frequency of the 185delAG mutation in the BRCA1 gene in chilean healthy women with family history of breast cancer

Background: Breast cancer is the most common malignancy among women, and is the second cause of cancer mortality among Chilean women. Female mortality due to breast cancer in Chile has shown a steady increase from 9.5 deaths per 100.000 women in 1985 to 12.8 deaths per 100.000 in 1995. A family history of breast cancer is one of the main risk factors for the development of the disease. BRCA1 and BRCA2 are two major hereditary breast cancer susceptibility genes. Mutations in these genes are associated to inherited breast cancer; 664 predisposing mutations have been described, but in specific populations only some of them, such as 185delAG have been found to be associated with susceptibility to breast cancer. Aim: To establish the frequency of the 185delAG mutation in the BRCA1 gene in Chilean healthy women with a family history of breast cancer. Patients and Methods: The 185delAG mutation was studied by mismatch polymerase chain (PCR) reaction in 382 Chilean healthy women with at least two relatives affected with breast cancer. The PCR products were digested with the restriction enzyme HinfI. Digestion of the normal allele (170 pb fragment) produces a 150 pb fragment; the PCR product for the mutant allele does not contain a site for HinfI and therefore remains as a 170 bp fragment after digestion. Results: One of the 382 healthy women presented the fragment of 170 pb after digestion with HinfI suggesting that she was heterozygous carrier for this mutation. The mutant patient had a mammography without suspicion of cancer. Conclusions: The frequency of the 185delAG mutation in BRCA1 was 0.26 percent (1/382) in Chilean healthy women with a family history of breast cancer

Stable computed-torque control of robot manipulators via fuzzy self-tuning.

Computed-torque control is a well-known motion control strategy for manipulators which ensures global asymptotic stability for fixed symmetric positive definite (proportional and derivative) gain matrices. In this paper, we show that global asymptotic stability also holds for a class of gain matrices depending on the manipulator state. This feature increases the potential of the computed-torque control scheme to handle practical constraint in actual robots such as presence of friction in the joints and actuators with limited torque capabilities. We illustrate this potential by means of a fuzzy self-tuning algorithm to select the proportional and derivative gains according to the actual tracking position error. Experiments on a two degrees of freedom robot arm show the usefulness of the proposed approach.

Cáncer de la vesícula biliar / Gallbladder carcinoma

El cáncer de la vesícula biliar ha aumentado en nuestro país. Se tratan en el Servicio de Cirugía 62 casos entre 1983 y julio de 1987. Fueron del sexo femenino el 76%, con una edad promedio de 65,2 años. El dolor, tumor palpable e ictericia fueron síntomas destacados. Hubo colelitiasis en el 76%. Se intervinieron 56 pacientes, siendo la laparotomía exploradora y biopsia la operación más frecuente por el avanzado estadio de la enfermedad (95% en los estadios III, IV y V). El 97% eran adenocarcinomas. Se infectaron el 25%. Fallecen el 19,6% antes de 30 días. La sobrevida promedio fué de 3,2 meses. Dos pacientes sobreviven a los 30 y 18 meses, operados en estadios I y II respectivamentew con una colecistectomía simple. Ninguno de nuestros pacientes recibió quimio ni radioterapia complementaria. Se enfatiza la gravedad y mal pronóstico de la enfermedad, por la imposibilidad de un diagnóstico precoz, el aumento de su incidencia (3,3% de todas las intervenciones biliares), lo avanzado de las lesiones, el alto número de laparotomías exploradoras y la nula sobrevida en los estadios superiores al I