Soil-water resistivity curve of a tropical soil

The evaluation of soil-water characteristic curve is one of the most important procedures in the matter of understanding the soil behaviour during wetting and drying processes. Even though it might be carried out by established methods, this practice is considered a time-consuming technique, and because of this it is still under-used in comparison with its potential applications. In this way, this paper aims to analyse the correlation of soil suction and soil resistivity to produce a time-reduced soil-water characteristic curve (SWCC), based on resistivity measured values. To perform this research, it was used a set of soil samples collected from Nova Friburgo, Rio de Janeiro – Brazil. The material was geotechnically characterized by standard methods. To determine the (SWCC), it was used the filter paper method and the volumetric water content/suctions were obtained by wetting and drying stages for two paths that emerged from the field moisture content. The results revealed a remarkable relationship between suction and the resistivity measured data, emphasizing the feasibility of determining the Soil-Water Characteristic Curve by resistivity measurements, here named Soil-Water Resistivity Curve (SWResC).

ω Phase Transformation and Mechanical Properties in Binary Zr-Nb Biomedical Alloy

The athermal ω phase transformation, magnetic susceptibility and deformation behavior of Zr-xNb alloys (x = 10 and 14) for use in medical devices subjected to magnetic resonance imaging (MRI) were investigated using electrical resistivity measurements, transmission electron microscopy observations and compression tests. The alloy with x = 10 exhibited a positive temperature coefficient in the electrical resistivity curve and the presence of an athermal ω phase at room temperature. On the other hand, the alloy with x = 14 showed an anomalous negative temperature coefficient (NTC) in the resistivity curve. Similar NTCs also appear in β-Ti alloys, which is interpreted as the growth of an athermal ω phase and the appearance of lattice modulation. The ω phase and diffuse satellites, which are possibly related to lattice modulation, were confirmed in the Zr-14Nb alloy at room temperature. The volume fraction of the athermal ω phase and the appearance of lattice modulation are related to the operating deformation mode and Young’s modulus. Thus, controlling the ω phase transformation in Zr-Nb alloys is key to developing medical devices that can be used in MRI.

Early detection of acute transmural myocardial ischemia by the phasic systolic-diastolic changes of local tissue electrical impedance

Myocardial electrical impedance is influenced by the mechanical activity of the heart. Therefore, the ischemia-induced mechanical dysfunction may cause specific changes in the systolic-diastolic pattern of myocardial impedance, but this is not known. This study aimed to analyze the phasic changes of myocardial resistivity in normal and ischemic conditions. Myocardial resistivity was measured continuously during the cardiac cycle using 26 different simultaneous excitation frequencies (1 kHz–1 MHz) in 7 anesthetized open-chest pigs. Animals were submitted to 30 min regional ischemia by acute left anterior descending coronary artery occlusion. The electrocardiogram, left ventricular (LV) pressure, LV dP/d t, and aortic blood flow were recorded simultaneously. Baseline myocardial resistivity depicted a phasic pattern during the cardiac cycle with higher values at the preejection period (4.19 ± 1.09% increase above the mean, P < 0.001) and lower values during relaxation phase (5.01 ± 0.85% below the mean, P < 0.001). Acute coronary occlusion induced two effects on the phasic resistivity curve: 1) a prompt (5 min ischemia) holosystolic resistivity rise leading to a bell-shaped waveform and to a reduction of the area under the LV pressure-impedance curve (1,427 ± 335 vs. 757 ± 266 Ω·cm·mmHg, P < 0.01, 41 kHz) and 2) a subsequent (5–10 min ischemia) progressive mean resistivity rise (325 ± 23 vs. 438 ± 37 Ω·cm at 30 min, P < 0.01, 1 kHz). The structural and mechanical myocardial dysfunction induced by acute coronary occlusion can be recognized by specific changes in the systolic-diastolic myocardial resistivity curve. Therefore these changes may become a new indicator (surrogate) of evolving acute myocardial ischemia.

Spectrum Comparative Analysis of the Frequency Domain Complex Cole-Cole Mode

Using MATLAB the spectrum comparative analysis was gived between complex Cole-Cole model and basic Cole-Cole model when theirs parameters change. The results show that the complex resistivity curve shape of complex model is limitted by total variation of two same kind parameters of complex model. The variation rule of the curve shape is consistent with basic mode when same kind parameters change. The influent of polarization rate and frequency correlation coefficient is bigger than time constant parameter. The resistivity curve of parallel complex model and series complex model is very similar. Then points out the difficulties and problems faced by the extraction of IP parameters.

The use and misuse of apparent resistivity in electromagnetic methods

Problems and misunderstandings arise with the concept of apparent resistivity when the analogy between an apparent resistivity computed from geophysical observations and the true resistivity structure of the subsurface is drawn too tightly. Several definitions of apparent resistivity are available for use in electromagnetic methods; however, those most commonly used do not always exhibit the best behavior. Many of the features of the apparent resistivity curve which have been interpreted as physically significant with one definition disappear when alternative definitions are used. It is misleading to compare the detection or resolution capabilities of different field systems or configurations solely on the basis of the apparent resistivity curve. For the in‐loop transient electromagnetic (TEM) method, apparent resistivity computed from the magnetic field response displays much better behavior than that computed from the induced voltage response. A comparison of “exact” and “asymptotic” formulas for the TEM method reveals that automated schemes for distinguishing early‐time and late‐time branches are at best tenuous, and those schemes are doomed to failure for a certain class of resistivity structures (e.g., the loop size is large compared to the layer thickness). For the magnetotelluric (MT) method, apparent resistivity curves defined from the real part of the impedance exhibit much better behavior than curves based on the conventional definition that uses the magnitude of the impedance. Results of using this new definition have characteristics similar to apparent resistivity obtained from time‐domain processing.

Interference Functions, Pair Distribution Functions and Electron Transport Properties of Liquid Mercury-Indium Alloys

X-ray diffraction patterns of liquid Hg-In alloys with 5, 12, 25, 35, 42, 50 and 62 atomic percent In were measured at room temperature (25°C). The interference and radial distribution functions, I(K) and 4 π r2 ρ(r), respectively, were refined by an error analysis program. The position K1=4π sin Θ1/λ of the first peak maximum of I(K) does not change upon alloying, i. e., K1=2.29 A-1. The interference function of In plotted in reduced coordinates K/K1 agrees with that calculated from the hard sphere model with a packing density of 45%. A small asymmetry of the first peak towards larger K values might be discernible in In, whereas the Hg and Hg-In interference functions show a relatively large asymmetry, and their subsequent peaks appear at larger K/K1 values than those of the hard sphere model and In. The interatomic distances r1 and the numbers of electrons ηE in the first coordination shell show only a small deviation from a linear relationship when plotted as a function of concentration.Since 1(K) for K<2 kF, where kF is the FERMI radius, are rather similar for Hg, In and all measured alloys, the electrical resistivity and thermoelectric power were evaluated using the random model and ANIMALU and HEINE pseudopotentials. The predicted resistivity was found to increase from 30µΩcm for pure Hg to 43 µΩcm for 35 atomic per cent In alloy and then to decrease to 24 µΩcm for pure In. The measured values of the resistivity decrease from 96 µΩcm for Hg to 30 µΩcm for pure In. Beyond the first eutectic composition, i. e., about 35 atomic per cent In concentration, the predicted resistivity curve decreases similarly to the measured resistivity curve. The discrepancy is attributed to the low density of states for Hg at the FERMI level. The predicted thermoelectric power decreases gradually from 1.22 µV/°K for pure Hg to 0.23 µV/°K for 62 atomic per cent In alloy, the value for pure In being 0.59 µV/°K. The measured values of thermoelectric power at 100°C decrease first from -6.5 µV/°K for pure Hg to -7.1 µV/°K for 5 atomic per cent In alloy and then increase to -0.7µV/°K for pure In. The discrepancy in the predicted values has been attributed to the energy dependence term of the pseudopotentials near the FERMI surface, particularly for pure Hg.