Dynamic Resistance Measurement Research Articles

Rapid crack propagation in plastic water pipes: measurement of dynamic fracture resistance

A classical analysis of Irwin and Corten relates the minimum pressure to sustain crack propagation along a pipeline to the dimensions, elastic modulus and fracture resistance of the pipe wall. Although the model is inapplicable to gas pressurisation, it is here modified to become sufficiently accurate for water pressurised thickwalled pipe to provide the basis of a dynamic fracture resistance test. Results for three commonly used water pipe grade polymers agree well with the predictions of the ‘Thermal Decohesion’ model, and with other experimental data where available. Rapid crack propagation behaviour, in both test and service pipeline configurations, is dominated by the ratio of crack speed to fluid decompression wave speed. This ratio can be adjusted in a controlled test environment.

Effects on contact resistance of passing electrical current through wiping palladium contacts

A study has been carried out to evaluate the effect of passing electrical current through wiping palladium contacts. Different magnitudes of dc current, from 0 to 4 A, are used, and at 0 A the wipe amplitudes change from 50 /spl mu/m to 1 mm. Two types of contact resistance are examined: one is dynamic contact resistance monitored and stored during wiping by a digital oscilloscope, and the other is static contact resistance measured at the start of sliding by a digital voltmeter. In light of dynamic contact resistance measurements we propose a tentative mechanism for explaining the contact resistance degrading process; the comparison of static contact resistance during wiping with and without current demonstrates that passing electrical current through the wiping contacts can restrict the contact resistance degradation. This occurs by a self-cleaning action which scrapes the wear debris accumulated at the end of the wear track far away from the contact spot caused by thermal expansion. The evidence demonstrates that the critical wiping number, (N/sub c/), where the contact resistance begins to increase rapidly, is strongly dependent on the wipe amplitude at 0 A, but slightly affected by current. AES analysis results show that oxides mainly exist within the wear track, while polymers concentrate at the ends of the wear track.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Safety pharmacology of the respiratory system: Techniques and study design

AbstractThe known effects of drugs from a variety of pharmacologic/therapeutic classes on the respiratory system and worldwide regulatory requirements support the need for conducting respiratory evaluations in safety pharmacology. The objective of these studies is to evaluate the potential for drugs to cause secondary pharmacologic or toxicologic effects that influence respiratory function. Changes in respiratory function can result either from alterations in the pumping apparatus that controls the pattern of pulmonary ventilation or from changes in the mechanical properties of the lung that determine the transpulmonary pressures (work) required for lung inflation and deflation. Defects in the pumping apparatus are classified as hypo‐ or hyperventilation syndromes and are evaluated by examining ventilatory parameters in a conscious animal model. The ventilatory parameters include respiratory rate, tidal volume, minute volume, peak (or mean) inspiratory flow, peak (or mean) expiratory flow, and fractional inspiratory time. Defects in mechanical properties of the lung are classified as obstructive or restrictive disorders and can be evaluated in animal models by performing flow‐volume and pressure‐volume maneuvers, respectively. The parameters used to detect airway obstruction include peak expiratory flow, forced expiratory flow at 25 and 75% of forced vital capacity, and a timed forced expiratory volume, while the parameters used to detect lung restriction include total lung capacity, inspiratory capacity, functional residual capacity, and compliance. Measurement of dynamic lung resistance and compliance, obtained continuously during tidal breathing, is an alternative method for evaluating obstructive and restrictive disorders, respectively, and is used when the response to drug treatment is expected to be immediate (within minutes post‐dose). The species used in the safety pharmacology studies conducted in our laboratory are the same as those used in toxicology studies since pharmacokinetic and toxicologic/pathologic data are available in these species. These data can be used to help select test measurement intervals and doses and to aid in the interpretation of functional change. The techniques and procedures for measuring respiratory function parameters are well established in guinea pigs, rats, and dogs.

Analysis of airway function of immature whole lung transplants versus mature lobar transplants

For the pediatric patient with end-stage lung disease in need of transplantation, two potential donor options currently exist: size-matched immature whole lungs or reduced-size mature lobes. To determine which of these options provides superior long-term function, we studied airway mechanics in a chronic porcine model of pediatric lung transplantation. Three groups of animals were studied: the first group underwent left upper lobectomrny at 9 ± 1 weeks of age (innervated left lower lobes). These animals served as controls. A second group of 9-week-old animals received an immature whole left lung allograft from age-matched donors. The third group received a reduced-size mature left lower lobe from 6-monat-old donors. Measurements of dynamic airway resistance, pulmonary compliance, and functional residual capacity of the isolated lobes or lungs, and of the nonoperated right lungs, were recorded 12 ± 1 weeks later, and mean values were calculated for each group. Results showed that transplantation of an immature whole lung resulted in abnormal dynamic airway resistance to airflow, which was not seen in the mature lobar transplants. In addition, compliance was impaired most significantly in the immature whole lung transplants. We conclude that in this experimental model of pediatric lung transplantation, transplantation of a mature lobar segment results in superior long-term airway function when compared with immature whole lung transplants.

Electrical Resistance and Stress of Bilayer Co(P)/Cu and Ni(P)/Cu Thin Films

The electrical resistance of the metallic bilayer was measured in situ using a resistance furnace. In the isothermal resistance measurements the sheet resistance was measured as a function of time, up to 20 h, at the constant temperature of 400°C. Results show that the sheet resistance of Co(P)/Cu system stays constant for 19 h, while that for the Ni(P)/Cu system continuously changes with time. In the dynamic resistance measurements the sheet resistance was measured as a function of temperature, from 25 to 500°C at the heating rate of 10°C/min. Results show that the dependence of the sheet resistance on temperature for the bilayer Ni(P)/Cu and Co(P)/Cu thin films is at first linear and then deviates from linearity as the temperature increases from room temperature to 500°C. This dependence exhibited irreversibility. The stress of the bimetallic bilayers was measured in situ as a function of temperature in the range from 50 to 500°C using a modified Flexus Z2400S apparatus. Results show that the initial stress at room temperature is compressive. During the first heating cycle the stress state remains compressive and the stress level at the maximum temperature of 450°C is slightly higher than the stress in the as‐deposited film. During the cooling cycle the compressive stress changes into the tensile and continues to accumulate with the decreasing temperature, reaching a maximum value at room temperature.

Corrections to low-frequency resistance measurements of self-heated metal microstructures

The resistance of self-heated mesoscopic structures has been used for some time as a way to prove the characteristics of electrons and phonons in these systems. In this paper, the authors consider the differences between low-frequency dynamic and static resistance measurements of mesoscopic systems in the steady state. They present a general description of these non-equilibrium experiments, and discuss the connection to an integration procedure used to determine the differences between the two methods of resistance measurements. The authors have applied the analysis to electron-heating experiments and have shown that the difference between the static and dynamic resistance depends on the electron-phonon coupling and the acoustic coupling appropriate for the mesoscopic structure.

More Than One Type of Conductance is Activated During Responses of Blowfly Monopolar Neurones

ABSTRACT The principal second-order neurones in the blowfly compound eye, the large monopolar neurones (LMCs), were studied using intracellular recording and discontinuous current-clamp techniques, in combination with measurement of dynamic input resistance. The LMCs had resting potentials of –35 to –45 mV and showed a linear current-voltage relationship in the lamina in the physiological voltage range. The hyperpolarizing light-on transient was associated with a drop in input resistance from 17 ± 5 to 3 ± 1MΩ, and had a reversal potential between –60 and –90 mV. The dynamic input resistance of saturated responses and the properties of reversed responses suggested that more than one conductance was activated during the response of the LMCs. In lamina recordings, the input resistance increased beyond the resting level during repolarization, which can be interpreted in terms of a continuous release of transmitter by the photoreceptor terminals, even in darkness. The input resistance of LMCs in axon recordings in darkness and during the light-on response was generally higher than in the lamina recordings. The responses to light in axons also differed from those recorded in lamina by showing regenerative properties.

Nonlinear conductivity of an In-Y1Ba2Cu3O7−x interface

We report dynamic resistance (dV/dI) measurements of a large, macroscopic interface between In metal and polycrystalline Y1Ba2Cu3O7−x. The interface was prepared by pressing a 3-mm2 In pellet onto a freshly prepared Y1Ba2Cu3O7−x polycrystalline ceramic surface. Although this interface covered about 105 crystallites of the superconductor, the electrical characteristics were very similar to those observed in point contact measurements on both single-crystal and polycrystalline specimens. A slowly varying bias-dependent background resistivity, narrow resistance peaks, and a zero-bias resistance anomaly were all features of the dV/dI spectra. Both the temperature and magnetic field dependencies of the interface conductivity are reported.

Respiratory mechanics measured by a simple device.

A simple and inexpensive apparatus is described which permits the semi-automatic measurements of pulmonary dynamic compliance (Cdyn) and airway resistance (Raw) while rapid changes of these factors during the experimental induction of pneumopathies can be followed. A diaphragm is used as a pneumotachograph because it was found to be quite sensitive and pulmonary secretions did not disturb the measurements. Volume base line drift is prevented.

Tunnelling in junctions with CdS barriers

Junctions having an Al–CdS–Al configuration exhibited both a temperature-dependent zero-bias anomaly and a double energy gap when dynamic resistance measurements were made. The zero-bias anomaly and the double energy gap can be explained by assuming that Cd particles are embedded in the CdS synthetic tunneling barrier. The first energy gap corresponds with that of Al. The second is assumed to arise as a result of tunneling through Cd particles embedded in the CdS. Employing a double tunneling process, one corresponding to direct tunneling through CdS and the other involving Cd particles embedded in the CdS, quantitative agreement with experimental results was achieved.

Measurement of dynamic resistance to breathing in unanesthetized dogs

Measurements of air-flow resistance were made using unanesthetized dogs prepared with exteriorized tracheas. Pressure-flow relationships obtained from these experiments adhered to Rohrer's equation. Drugs that are classically known to alter tone of bronchial musculature substantially change the pressure-flow relationship in these animals. Submitted on October 6, 1960