Computer aided evaluation of pipeline current near toroidal HVDCground electrodes

The effect of the return current of an HVDC toroidal electrode on underground metallic installations such as pipelines and cables is evaluated. In order to quantify the effect of HVDC electrodes on the buried conductor, an equivalent model is first presented that takes into account the electrical properties of the pipeline and its surrounding. In particular, infinitely long pipelines with different coatings are considered. The pipelines are assumed to be continuously buried in homogeneous soil and are located in the vicinity of the HVDC electrode. It is found that the voltage gradient in the vicinity of the electrode results in return currents in grounded conductors, the effects of which can extend several kilometers. Protective coatings reduce stray current from local voltage disturbances but have limited effect against distant electrodes     

HVDC ground electrode heat dissipation in an N-layer soil

The temperature distribution in an N-layer soil, due to high-voltage direct-current (HVDC) injection via ground electrodes, was computed using finite-difference methods. The temperature profiles for various ground electrode shapes buried in a two-layer soil were computed using these same techniques. The results obtained were then compared with results obtained experimentally in the laboratory. A sensitivity analysis was performed on the effect of the height of the top layer of a two-layer earth model. The computed results agree very well with those obtained experimentally. The effect of varying the height of the top layer of a two-layer earth was then investigated. The computations indicate that the temperature can be predicted as a function of this height     

Uterine pressure-flow relationships during early gestation

Placental and myoendometrial pressure-flow relationships were determined in 17 gravid ewes between 29 and 110 gestational days with the use of radioactive-labeled microsphere injections under flow meter guidance. Myoendometrial relationships were consistently curvilinear with convexity toward the flow axis. From 29 to 40 days, caruncular-cotyledonary relationships were similar to myoendometrial ones. After 50 days, the relationship was slightly but significantly curvilinear with convexity toward the pressure axis. From 42 to 50 days, responses were intermediate. The changes in caruncle-cotyledon vascular reactivity correlated with the onset and maturation of interdigitation of fetal and maternal tissues during definitive placentation. A hypothesis for these changes in vascular reactivity is presented.     

HVDC Ground Electrode Heat Dissipation

The temperature distribution in the soil surrounding High Voltage Direct Current (HVDC) ground electrodes is determined by using a finite-difference method. This, commonly used numerical method of solution, was selected due to its practicability in obtaining engineering solutions involving both complex ground electrode geometries and boundary conditions. Temperature profiles obtained using this method are also presented.     

Evaluation of the effect of vertical faults on the voltagedistribution around HVDC electrodes using a supercomputer

An effective method for evaluating the electric field, the voltage distribution, and the current density near geological faults in the earth is presented. In order to quantify the effect of HVDC (high-voltage direct current) electrodes, it is necessary to determine the voltage distribution and current flow in the ground. Electrostatic theory is used to generate a voltage solution which must satisfy the Laplace equation and boundary conditions along vertical faults. The voltage distribution around a HVDC toroidal electrode is shown for an actual case. The image theory is used to account for the effect of vertical faults and horizontal soil layers. A supercomputer is utilized to generate a sufficient amount of images to insure that the boundary conditions are met within a desired accuracy     

Appendictiis in pregnancy

Twenty-nine cases of acute appendicitis during pregnancy are presented, and the recent literature is reviewed. Occurring once in 1,600 gestations, appendicitis carries a pregnancy loss of 10.8%. Difficulties in diagnosis and delays in treatment increase with advancing gestational age. Aggressive management may minimize the resultant maternal morbidity and fetal mortality.     

Stochastic control of processes having moving boundaries—An experimental study

A general state estimator requiring only discrete time measurements has been developed for nonlinear distributed parameter systems having moving boundaries. The state estimator has been combined with an optimal linear-quadratic feedback controller to provide a stochastic feedback control scheme for this class of problem. Both the state estimation and control algorithms were implemented in real time for a laboratory casting process and were found to perform well. The state estimation scheme would seem to hold the most interest for industrial applications.     

Heat dissipation computations of a HDVC ground electrode using asupercomputer

The temperature of soil surrounding a high-voltage direct current (HVDC) toroidal ground electrode of practical dimensions in both homogeneous and nonhomogeneous soils was computed at incremental points in time using finite-difference methods on a supercomputer. The results obtained validated the expected result, that the time constant of the system is large, requiring long-term and short-term simulation curves, as shown. It is concluded that by being able to compute the thermal response and by calculating the thermal time constant, the option for possible improved design is available     

Effects of Cis- and trans-clomiphene on the uterine blood flow of oophorectomized ewes

Changes in the left uterine artery blood flow (YBF) after intraarterial administration of estradiol-17beta and cis- and trans-clomiphene citrate to conscious, oophorectomized ewes were monitored by chronically implanted electromagnetic flow probes. Cis-clomiphene produced UBF increases comparable to or greater than those produced by estradiol-17beta but at dose levels 20 times greater. Comparison of UBF response curves for cis-clomiphene with those for estradiol-17beta showed a delayed onset of initial vasodilation and a delayed peak response. The duration of uterine vasodilation produced by cis-clomiphene was dose-dependent and exceeded that produced by estradiol-17beta. Similar reponses were observed with trans-clomiphene but at dose levels at least 1,000 times those of estradiol-17beta. The characteristics of clomiphene-induced UBF responses that differed from those after estradiol-17beta may reflect differences in estrogen receptor activation between the compounds.     

Transient analysis of heat dissipation due to a HVDC groundelectrode

The temperature of the soil surrounding a high-voltage direct-current (HVDC) ground electrode was computed at various points in time using finite difference methods. The temperature response for various ground electrodes was computed using these same techniques. The results were then compared with results obtained experimentally in a laboratory. It is suggested that peak temperature calculations may be desirable for periodic short-term operation of a HVDC ground electrode. Since the surrounding soil temperatures may not have reached a steady state, a transient analysis may be necessary