RESUMO
In this work, the Generalized Hubbard Model on a square lattice is applied to evaluate the electrical current density of high critical temperature d-wave superconductors with a set of Hamiltonian parameters allowing them to reach critical temperatures close to 100 K. The appropriate set of Hamiltonian parameters permits us to apply our model to real materials, finding a good quantitative fit with important macroscopic superconducting properties such as the critical superconducting temperature (Tc) and the critical current density (Jc). We propose that much as in a dispersive medium, in which the velocity of electrons can be estimated by the gradient of the dispersion relation ∇ε(k), the electron velocity is proportional to ∇E(k) in the superconducting state (where E(k)=(ε(k)-µ)2+Δ2(k) is the dispersion relation of the quasiparticles, and k is the electron wave vector). This considers the change of ε(k) with respect to the chemical potential (µ) and the formation of pairs that gives rise to an excitation energy gap Δ(k) in the electron density of states across the Fermi level. When ε(k)=µ at the Fermi surface (FS), only the term for the energy gap remains, whose magnitude reflects the strength of the pairing interaction. Under these conditions, we have found that the d-wave symmetry of the pairing interaction leads to a maximum critical current density in the vicinity of the antinodal k-space direction (π,0) of approximately 1.407236×108 A/cm2, with a much greater current density along the nodal direction (π2,π2) of 2.214702×109 A/cm2. These results allow for the establishment of a maximum limit for the critical current density that could be attained by a d-wave superconductor.
RESUMO
Objective: a Web-based Fuzzy Inference Tool for cardiovascular risk assessment has been developed. The tool makes use of inference rules from evidence-based medicine for membership classification. Methods: the system framework allows adding variables such as gender, age, weight, height, medication intake, and blood pressure, with various types of membership functions based on classification rules. Results: the tool allows health professional to enter patient clinical data and obtain a prediction of cardiovascular risk. The tool can also be later used to predict other types of risks including cognitive and physical disease conditions.
Objetivo: desarrollar una herramienta Fuzzy de Inferencia basada en Web para la evaluación del riesgo cardiovascular. La herramienta hace uso de reglas de inferencia de medicina basada en evidencia para la clasificación de membresía. Métodos: el marco del sistema permite la adición de variables como el género, la edad, el peso, la altura, la ingesta de medicamentos, y la tensión arterial, con varios tipos de funciones de pertenencia basada en reglas de clasificación. Resultados: la herramienta permite a los profesionales de la salud ingresar los datos clínicos del paciente y obtener una predicción del riesgo cardiovascular. La herramienta también puede ser utilizada más adelante para predecir otros tipos de riesgos, incluyendo condiciones de la enfermedad cognitivas y físicas.
Assuntos
Humanos , Sistema Cardiovascular , Fármacos Cardiovasculares , Acidente Vascular Cerebral , Técnicas de Diagnóstico CardiovascularRESUMO
A portable, Internet-based EEG/Auditory Evoked Potential (AEP) monitoring system was developed for remote electrophysiological studies during sleep. The system records EEG/AEP simultaneously at the subject's home for increased comfort and flexibility. The system provides simultaneous recording and remote viewing of EEG, EMG and EOG waves and allows on-line averaging of auditory evoked potentials. The design allows the recording of all major AEP components (brainstem, middle and late latency EPs) and constituent single sweep EEG epochs. Auditory stimulation is remotely controlled from any internet-connected PC. The developed platform consists of a portable server computer for data acquisition and secured data transmission to the Internet, a web server for temporary storage, and a remote viewing station. During operation, signals are acquired during sleep and transmitted to the secured web server for controlled access viewing. The remote viewer station allows the user to continuously visualize the auditory evoked potentials, modify auditory stimuli at any time and adjust system parameters for its online computation. The developed internet-based EEG/EP system has been tested in a laboratory environment. Preliminary results demonstrate feasibility of remote real-time acquisition and viewing of EEG and EPs and future potential for home monitoring and telemedicine applications.