A simple vibrating sample magnetometer for macroscopic samples.

We here present a simple model of a vibrating sample magnetometer (VSM). The system allows recording magnetization curves at room temperature with a resolution of the order of 0.01 emu and is appropriated for macroscopic samples. The setup can be mounted with different configurations depending on the requirements of the sample to be measured (mass, saturation magnetization, saturation field, etc.). We also include here examples of curves obtained with our setup and comparison curves measured with a standard commercial VSM that confirms the reliability of our device.

Influence of electrodes on the 448 kHz electric currents created by radiofrequency: A finite element study.

Radiofrequency is a technology used in physical rehabilitation by physicians and physiotherapists for more than fifteen years, although there exist doubts on how it works. Indiba is a particular method that applies a voltage difference of 448 KHz between two electrodes, creating an electric current between them. These electrodes are an active one that is placed on different areas of the body and a passive one that is left on the same position during the treatment. There are two different types of active electrodes: the capacitive one and the resistive one. In this paper, it has been studied how the different electrodes affect the current density inside the body and thus how they affect the efficacy of the treatment. It shows how finite element calculations should help physicians in order to better understand its behavior and improve the treatments.

In vivo measurements of electrical conductivity of porcine organs at low frequency: new method of measurement.

Calculations of the induced currents created in the human body by external electromagnetic fields would be more accurate provided that more realistic experimental values of the electrical properties of the body were available. The purpose of this work is to experimentally obtain values for the conductivity of living organs in conditions close to the real situation. Two-electrode in vivo measurements of the bioimpedance of some porcine organs have been performed. From these measurements and taking into account geometrical considerations, the electrical conductivity for the kidney, liver, heart, and spinal cord has been obtained and were found to be higher than the values reported in the literature. Furthermore, a new experimental procedure is proposed where the conductivity is determined from the values of the electrical potential and currents that are induced by an external electromagnetic field created by a coil placed close to the organ under study.

Short-term fatigue testing can predict medium-term pericardium behaviour.

The medium-term fatigue behaviour of calf pericardium (similar to the one used to manufacture cardiac bioprostheses valve leaflets) has been studied. 96 samples were tested under fatigue subjecting them to biaxial stress at 1 Hz frequency for 5000 cycles, in 4 series of 24 samples, at several supra-physiological mean pressures and pressure amplitudes. Short-term damage parameters such as the accumulated energy consumption in 10 cycles (E10) and medium-term ones after 5000 cycles like total energy consumption (Et) and maximum displacement of the membrane (Dt) have been evaluated. E10 showed exponential growing tendency with pressure and linear tendency with pressure amplitude when only one parameter curve was plotted. Similar results were found when analysing Et and Dt. Linear correlation models were established between E10 and Et and E10 and Dt. Similar results were achieved in the four series, with excellent determination coefficients. The results confirm that the fatigue behaviour from the very first cycles of the test can predict the medium-term behaviour of the tissue by means of measurement of suitable damage markers. The tendencies observed between the parameters seem to show that the results could have been the same ones if the test had been performed at physiological pressures and amplitudes. This work opens the door to a non-destructive test of the tissue prior to employ it to manufacture valve leaflets.

Time dependence of electrical bioimpedance on porcine liver and kidney under a 50 Hz ac current.

The purpose of this work is to study the changes of the bioimpedance from its 'in vivo' value to the values measured in a few hours after the excision from the body. The evolution of electrical impedance with time after surgical extraction has been studied on two porcine organs: the liver and the kidney. Both in vivo and ex vivo measurements of electrical impedance, measuring its real and imaginary components, have been performed. The in vivo measurements have been carried out with the animal anaesthetized. The ex vivo measurements have been made more than 2 h after the extraction of the organ. The latter experiment has been carried out at two different stabilized temperatures: at normal body temperature and at the standard preservation temperature for transplant surgery. The measurements show a correlation between the biological evolution and the electrical bioimpedance of the organs, which increases from its in vivo value immediately after excision, multiplying its value by 2 in a few hours.