ABSTRACT
Conductive polymer composites are manufactured by randomly dispersing conductive particles along an insulating polymer matrix. Several authors have attempted to model the piezoresistive response of conductive polymer composites. However, all the proposed models rely upon experimental measurements of the electrical resistance at rest state. Similarly, the models available in literature assume a voltage-independent resistance and a stress-independent area for tunneling conduction. With the aim of developing and validating a more comprehensive model, a test bench capable of exerting controlled forces has been developed. Commercially available sensors-which are manufactured from conductive polymer composites-have been tested at different voltages and stresses, and a model has been derived on the basis of equations for the quantum tunneling conduction through thin insulating film layers. The resistance contribution from the contact resistance has been included in the model together with the resistance contribution from the conductive particles. The proposed model embraces a voltage-dependent behavior for the composite resistance, and a stress-dependent behavior for the tunneling conduction area. The proposed model is capable of predicting sensor current based upon information from the sourcing voltage and the applied stress. This study uses a physical (non-phenomenological) approach for all the phenomena discussed here.
ABSTRACT
The parasitic infection neurocysticercosis may give rise to a variety of psychiatric manifestations that resemble, but are different from, primary psychiatric disorders. The aim of this study was to determine if among individuals from a neurocysticercosis-endemic area of Colombia who apparently had a psychiatric manifestation with associated neurological finding ('cases'), some could have been infected with Taenia solium cysticerci. This case-control study was done in individuals hospitalized in two mental institutions. The control-1 individuals were those classified with primary psychiatric disease, and the control-2 group consisted of healthy, non-hospitalized individuals. A serological test for cysticercosis was positive in 5/96 (5.1%) cases, 4/153 (2.6%) psychiatric controls, and 5/246 (2%) healthy controls. The data analysis indicated a weak association between the cases and a positive serology for neurocysticercosis (odds ratio > 2; P > 0.05). The lower education level of the cases influenced this association.
Subject(s)
Mental Disorders/etiology , Neurocysticercosis/complications , Adult , Aged , Aged, 80 and over , Animals , Antibodies, Helminth/isolation & purification , Case-Control Studies , Colombia , Educational Status , Female , Hospitals, Psychiatric , Humans , Male , Mental Disorders/classification , Middle Aged , Neurocysticercosis/blood , TaeniaABSTRACT
Muchas sustancias pueden producir efectos sobre el sistema nervioso central, incluso las que se usan primariamente por sus acciones periféricas; además, los agentes cuyo beneficio terapéutico se basa en una acción central, se prescriben comúnmente para tratar algunos trastornos psiquiátricos. A lo anterior se agrega que millones de personas se automedican con sustancias fáciles de adquirir y favorecedoras centrales de la adicción. Es importante recordar que los efectos de un fármaco dependen tanto de la dosis como del estado biológico de quien lo recibe. Por lo tanto, no es de extrafíar que inesperadamente una droga administrada a la dosis estándar, produzca excitación o depresión del sistema nervioso central. De esta forma se puede entender por qué es común el desarrollo de síntomas psiquiátricos en las personas que utilizan una variedad de fármacos sean prescritos, de venta libre o ilícita. Estos efectos pueden aparecer con las dosis terapéuticas ya niveles plasmáticos dentro de la ventana terapéutica, reflejando tal vez una reacción de hiperreactividad. Un médico consciente de este hecho, puede ser capaz de diferenciar si cuadros como el delirio, las alucinaciones, la ansiedad y la agresión son de origen endógeno o debidos a una acción exotóxica. Se discuten casos clínicos relacionados con ansiedad, ag resión y delirio inducidos por medicamentos y que demuestran la Importancia de una historia clínica y farmacológica completa en la evaluación de cada paciente que se presente con síntomas psiquiátricos.
Many substances can produce effects on the central nervous system, even those primarily used for its peripheral effects. Agents with therapeutic action at the central level are prescribed for the treatment of some psychiatric disorders, while many persons are under automedication with substances that induce central adiction and are very easily acquired. It Is Important to remember that drug effects depend on the dose and the biological s1tuatlon of the patient; therefore, it is possible that a drug at the standard dose can induce central nervous system excitation or depression. The pharmacological effects can appear at the therapeutic window level indicating a hypereactivity situation. Physicians should be aware of this fact In order to be able to dillucidate whether the psychiatric manifestations are exotoxic or endogenous. Clinical cases of drug. lnduced psychiatric disorders are presented In order to illustrate the importance of a thorough pharmacological and clinical history In every patient whit psychiatric disorders
