X-ray diffraction and electrochemical impedance spectroscopy study of zinc coated LiNi0.5Mn1.5O4 electrodes

Coating and doping with zinc have been used to modify LiNi_0.5Mn_1.5O₄ powders prepared at 700 and 800 °C. As previously found in the literature, surface treatment with zinc leads to a net improvement of the electrochemical performance of the 5-V electrode in lithium cells. X-ray diffraction reveals the occurrence of surface ZnO, which disappears after heating at 500 °C. This indicates that ZnO forms a coating, although zinc can also be incorporated in the LiNi_0.5Mn_1.5O₄ framework. The electrochemical oxidation of both bare LiNi_0.5Mn_1.5O₄ and zinc treated products has been followed by ex situ X-ray diffraction of charged electrodes. For both materials a decrease in the cubic unit cell parameter and the formation of two cubic phases during lithium extraction has been found. Lattice contraction is significantly larger in the sample modified with zinc. EIS measurements give direct evidence of the better stabilization of the electrode surface in the coated material.     

Validation of impedance cardiography measurements of cardiac output during limited exercise in heart transplant recipients

Abstract. Twenty-one patients were studied at rest and during exercise after heart transplantation to compare cardiac output measured by thermodilution and impedance cardiography. Exercise was performed on a bicycle ergometer over a limited range of work load (25 and 50 watt) whilst metabolic gas exchange was recorded. One patient was studied at rest whilst his circulation was maintained by a Jarvik-7 artificial heart. The values of cardiac output measured by impedance cardiography corresponded closely with the flow rate from the artificial heart. There was also close agreement between the impedance and thermodilution measurements of cardiac output at rest and during exercise. Both measurements followed the changes in heart rate and oxygen consumption. Both thermodilution and impedance cardiography methods elicited good reproducibility of cardiac output measurements at rest and during exercise. These observations suggest that the noninvasive and continuous record of cardiac output obtained by impedance cardiography can be used for the postoperative monitoring of heart transplant recipients.     

Determination of diffusion coefficient of hydrogen in metals and their elastic modulus by generalised impedance

Transport of hydrogen in elastic metals has been analysed in terms of an impedance-like non-linear transfer function (TF). The equilibrium in a membrane specimen is perturbed by a sinusoidal signal of the concentration of hydrogen, of large amplitude, applied to one of its surfaces. The fundamental harmonics of periodically reproducible flux at the same surface is considered as a response. The TF is defined as the ratio of the signal to the response. The power of the said TF in determining the diffusion coefficient of hydrogen in a metal–hydrogen system and its bulk elastic modulus was analysed for the example of α-phase Pd–H and Pd₈₁Pt₁₉–H systems. It has been found that such a TF is suitable for determination of the above parameters. Also, the sensitivity of these estimates to the uncertainty of concentration of hydrogen in the metal, its partial molar volume and the thickness of the specimen has been explored.     

The ensemble-averaged impedance cardiogram: An evaluation of scoring methods and interrater reliability

The interrater reliability and concurrent validity of two methods of scoring the ensemble-averaged impedance cardiogram were evaluated. Impedance cardiographic and electrocardiographic signals were recorded from 40 undergraduate men and women during a baseline rest period and a vocal mental arithmetic task period. Recordings were scored by four raters using a conventional method, involving ensemble averaging after careful editing of beat-to-beat waveforms, and a streamlined method, involving ensemble averaging without beat-to-beat editing. Intraclass correlations for interrater reliability exceeded .92, whereas intraclass correlations for concurrent validity exceeded .97, indicating excellent agreement between raters and scoring methods for all cardiac measures. The streamlined method was significantly faster than the conventional method. The results indicate that variations in beat-to-beat editing do not constitute a serious source of error in the ensemble-averaged impedance cardiogram and support the interrater reliability and concurrent validity of the two scoring methods.     

Impedance study of the electrochemical reduction of adrenochrome on glassy carbon

The electrochemical reduction of adrenochrome on a glassy carbon electrode was investigated by ac impedance in a constant ionic strength McIlvaine buffer solution. When the frequency was lower than 60 kHz, —Z″ against Z′ showed straight lines whose inclined angles with the real axis were within the range 71–76° in the diagrams of the complex impedance plane obtained at different do potentials. In the corresponding admittance diagrams, distorted semicircles appeared. The electrode reaction involves adsorption of electroactive species and the effect of concentration polarization cannot be neglected. Based upon the admittance model of the equivalent circuit, the optimal estimated values of some model parameters were obtained by using a Gauss-Newton algorithm and non-linear curve fitting. The characteristics of the electrode process are also discussed.     

The cold pressor test: Vascular and myocardial response patterns and their stability

The purposes of the present study were to compare the cardiovascular response patterns evoked by three versions of the cold pressor test (either forehead stimulation or hand or foot immersion) and to determine the reproducibility of the responses over a 2-week interval. Blood pressure, heart rate, stroke volume, cardiac output, total peripheral resistance, and systolic time intervals were obtained during rest and during the cold pressor test in 42 young men. Across conditions, the pressor response was supported by peripheral resistance increases with concomitant stroke volume decreases. Although the response panerns were generally similar across sites, exceptions were apparent for heart rate. Forehead stimulation was characterized by no significant change in heart rate, whereas limb (hand or foot) immersion was associated with significant heart rate acceleration. The responses elicited by the three cold pressor test conditions were reliable and showed little evidence of attenuation over the test-retest interval.     

Evaluation of the impedance tonometers TGDc-01 and iCare according to the international ocular tonometer standards ISO 8612

BACKGROUND: Two new tonometers have been introduced that are based on the impedance principle. Both the TGDc-01 (transpalpebral measurement) and the iCare (corneal measurement) do not require corneal anaesthesia. The present work presents an evaluation of both devices. METHODS: Comparative measurements using one of the new tonometers and applanation tonometry were performed by one investigator according to the international standard for ocular tonometer (ISO 8612). Measurements were performed on 445 eyes without corneal pathology from 243 patients. Six measurements were performed for iCare and 3 for TGDc, immediately followed by 3 applanation tonometry measurements. RESULTS: The correlation coefficient with respect to applanation tonometry was 0.81 for TGDc and 0.95 for iCare. TGDc-01 measurements showed an average deviation of 3.1 +/- 2.6 mmHg to those of Perkins applanation tonometry. The maximum difference was 28.7 mmHg below and 9.8 mmHg above the results of applanation tonometry. iCare showed an average deviation of 2.5 +/- 1.1 mmHg to Goldmann tonometry. The maximum difference was 14.5 mmHg below and 9.8 mmHg above. CONCLUSIONS: The results of both new tonometers showed a good correlation with the reference applanation tonometric methods, but the strict requirements of ISO 8612 are not fulfilled by either tonometer at present. Additionally, transpalpebral measurements with the TGDc-01 showed unacceptably high variability.     

Impedance of goat eye lens at different DC voltages

A computer assisted AC impedance system is used to measure the DC voltage—current (V-I) characteristics and AC impedance of a goat eye lens using a two-probe Ag−AgCl electrode system. The measurement of the V-I characteristics shows that when a DC voltage from 0mV to 30mV is applied, the resultant current decreases from an initial value of 0.58μA to 0.006μA. However, when the voltage is increases beyond 30mV, the current increases and reaches a value of 0.9μA at 100mV. The data on the frequency response (0.01–10 Hz) of the impedance of lens tissue show an inverse relationship with frequency. The effect of various DC voltages, namely 0, 30, 50, 100 and 200 mV, on the impedance of the eye lens is also investigated over a frequency range of 0.01–10 Hz. The measurement results for both V-I characteristics and AC impedance further suggest the presence of a 30 mV voltage compartment in the goat eye lens.     

急性肾衰大鼠肾阻抗容积脉波的改变及三种莨菪药的治疗作用

用自己建立的阻抗法描记大鼠肾容积脉波，研究油酸致急性肾衰时肾阻抗容积脉波的改变及樟柳碱、东莨菪碱、山莨菪碱对这些改变的影响。结果表明：左肾动脉注射油酸后１０ｍｉｎ、１ｈ、６ｈ出现低平及平顶波，波高及流入容积速度明显低于注射前及生理盐水对照组。三种莨菪药治疗后，低平及平顶波明显减少或消失，波高及流入容积速度明显提高。结果说明：急性肾衰早期肾内脉动血管弹性降低，紧张度增高，周围阻力增加，肾组织血液灌流量降低；三种莨菪药均可改善肾内脉动血管的功能，提高肾组织血液灌流量