Current Required Research Articles

PI‐based controller for low‐power distributed inverters to maximise reactive current injection while avoiding over voltage during voltage sags

In the recently deregulated power system scenario, the growing number of distributed generation sources should be considered as an opportunity to improve stability and power quality along the grid. To make progress in this direction, this work proposes a reactive current injection control scheme for distributed inverters under voltage sags. During the sag, the inverter injects, at least, the minimum amount of reactive current required by the grid code. The flexible reactive power injection ensures that one phase current is maintained at its maximum rated value, providing maximum support to the most faulted phase voltage. In addition, active power curtailment occurs only to satisfy the grid code reactive current requirements. As well as, a voltage control loop is implemented to avoid overvoltage in non-faulty phases, which otherwise would probably occur due to the injection of reactive current into an inductive grid. The controller is proposed for low-power rating distributed inverters where conventional voltage support provided by large power plants is not available. The implementation of the controller provides a low computational burden because conventional PI-based control loops may apply. Selected experimental results are reported in order to validate the effectiveness of the proposed control scheme.

Surface modification of carbon steel reinforcement of concrete

Purpose – The purpose of this paper was to characterize the surface of steel reinforcement of concrete under cathodic protection (CP), submerged in seawater, to understand the surface changes due to the application of CP and their consequences on cathodic current requirements. Design/methodology/approach – Reinforced concrete specimens with applied CP were immersed in natural seawater. The experimental methodology included monitoring of corrosion potential (Ecorr); measurement of galvanic current (Igalv), protection potential (Eprotection) and the depolarization potential of steel during the time of exposure; and electrochemical impedance spectroscopy (EIS). The chemical composition of the steel surface was assessed using X-ray diffraction (XRD). Findings – The application of CP leads to the formation of a deposit on the steel surface that according to XRD results, Pourbaix diagram and physical characteristics, is a protective oxide: magnetite (Fe3O4). This oxide causes a decrease in the corrosion rate and requires application of the protection current. It was found that the surface remained protected even after eight days when the CP system was interrupted. Research limitations/implications – It is necessary to carry out analysis of the chemical composition of deposits formed on the steel surface, perhaps using X-ray photoelectron spectroscopy, Mössbauer, to verify the presence of the magnetite. Practical implications – Determination of the main cause of the decrease in current required for protection and deposit formation conditions will enable the design of a CP system to be optimized and economized. At present, the CP design considers only a constant current value for the duration of the protection time. Originality/value – CP is a technique that has proven effective for the protection of metal structures. However, little attention has been devoted to the surface changes that occur under applied CP and their impact on the electrochemical behavior of the system. This paper describes the phenomena produced at the metal surface and determines kinetic parameters and their consequences on the CP behavior.

Alteration of the threshold stimulus for intraoperative brain mapping via use of antiepileptic medications

Abstract Intraoperative seizures during awake craniotomy with cortical and subcortical mapping are a common occurrence. Patients are routinely treated preoperatively with anti-convulsive medications to reduce seizure occurrence. Historically these drugs have not been believed to significantly affect awake craniotomy procedures. We report a patient undergoing intraoperative mapping with differential response and seizure occurrence based upon antiepileptic drug usage. A 43 year old female presented with history of seizures, right sided hemiparesis, electrical sensations, and difficulty with language function. She was determined to have a mass lesion involving the left frontal and temporal lobes and subsequently elected to undergo resection by awake craniotomy with intraoperative mapping. A first attempt at lesion resection was performed after a missed dose of anti-convulsant medication (levetiracetam) and was subsequently aborted because of repeated seizure activity. The threshold for seizure generation (1.75 mA) was observed to be significantly lower than expected. Therapy was begun with both levetiracetam and phenytoin prior to a second attempted resection one week later. Thresholds for cortical motor response in the second operation were significantly higher than expected (> 9.0 mA), and no intraoperative seizure activity was observed. To our knowledge this is the first quantitative example of antiepileptic drugs affecting the current required for intraoperative mapping. This case highlights the potential for higher current requirements in patients preoperatively treated with high doses of antiepileptic drugs, as well as the importance of confirming adequate dosage of antiepileptic drugs in patients at an increased risk of seizure generation.

The epidural electric stimulation test does not predict local anesthetic spread or consumption in labour epidural analgesia

The epidural electrical stimulation test (EEST) is a highly specific and sensitive test for confirming placement of the epidural catheter in the epidural space. The purpose of this study was to investigate if the EEST could predict the spread and consumption of local anesthetic solutions during labour epidural analgesia. This observational study was conducted in labouring parturients requesting epidural analgesia. The EEST was performed after the epidural catheter placement (T0) and repeated five minutes after a test dose with 2% lidocaine 3 mL (T1). The minimum current required to elicit the motor response at each time point was recorded. A loading dose of 0.125% bupivacaine 10 mL and fentanyl 50 μg was administered and followed by patient-controlled epidural analgesia with 0.0625% bupivacaine and fentanyl 2 μg·mL(-1) (baseline infusion 10 mL·hr(-1), bolus dose 5 mL, lockout interval ten minutes, maximum dose 20 mL·hr(-1)). The primary outcome was the correlation between the current required to elicit motor responses at T0 and T1 and the consumption of bupivacaine in the first two hours of epidural administration. The secondary outcomes included the muscle contraction patterns determined by the EEST and the incidence of failed, inadequate, or asymmetric blocks. The study was conducted in 102 parturients. The mean electric current required to elicit muscle response was 4.43 mA (range 1-10 mA) at T0, 5.97 mA (range 1-14 mA) at T1, and the mean Δ (T1-T0) current was 1.54 mA (range 0-8 mA). There was no correlation between either the mean baseline current required or the Δ (T1-T0) current and the total bupivacaine consumption at two hours. The incidence of inadequate blocks at two hours was 18%; however, none of the catheters required replacement. Unilateral left (34%) or right (31%) leg contraction was the most frequent pattern elicited by the EEST. The EEST shows a wide range of electrical current requirements and elicits a variety of muscle twitch patterns on the lower limbs. Although it confirms the epidural placement of the catheter, the EEST cannot be used to predict the spread or consumption of the local anesthetic solution during labour epidural analgesia.

Online purchases of an expanded range of condom sizes in comparison to current dimensional requirements allowable by US national standards

Across studies, 35-50% of men describe condoms as fitting poorly. Rates of condom use may be inhibited in part due to the inaccessibility of appropriately sized condoms. As regulated medical devices, condom sizes conform to national standards such as those developed by the American Society for Testing and Materials (ASTM) or international standards such as those developed by the International Organisation for Standardisation (ISO). We describe the initial online sales experience of an expanded range of condom sizes and assess uptake in relation to the current required standard dimensions of condoms. Data regarding the initial 1000 sales of an expanded range of condom sizes in the United Kingdom were collected from late 2011 through to early 2012. Ninety-five condom sizes, comprising 14 lengths (83-238mm) and 12 widths (41-69mm), were available. For the first 1000 condom six-pack units that were sold, a total of 83 of the 95 unique sizes were purchased, including all 14 lengths and 12 widths, and both the smallest and largest condoms. Initial condom purchases were made by 572 individuals from 26 countries. Only 13.4% of consumer sales were in the ASTM's allowable range of sizes. These initial sales data suggest consumer interest in an expanded choice of condom sizes that fall outside the range currently allowable by national and international standards organisations.

Minimum Current Requirements for Epidural Stimulation Test Confirmation of Epidural and Intrathecal Catheter Placement

The typical blind insertion of a catheter into the epidural space risks catheter misplacement into the intrathecal space. The epidural stimulation test is designed to confirm the correct epidural location of a catheter but may also detect unintended intrathecal catheter placement by evaluating the minimum electrical current required for appropriate motor stimulation. Using this test, we observed the minimum current requirements for appropriate motor stimulation of catheters placed in the epidural and intrathecal spaces. In this prospective observational study, patients scheduled for epidural catheter placement and intrathecal catheter placement were evaluated by the epidural stimulation test. The epidural space was localized by using a loss-of-resistance technique with normal saline, and the intrathecal space was identified by advancing a Tuohy needle until a continuous flow of clear cerebrospinal fluid was obtained. Afterward, a catheter was placed in the appropriate space, and a nerve stimulator delivered progressively, increasing electrical current until an appropriate muscle contraction was palpated. The minimum milliamperage required for this muscle contraction was our primary outcome measure. Of 37 catheters intentionally placed in the epidural space, the mean current required to produce an appropriate palpable motor contraction was 7.8 +/- 3.3 mA with a range of 2 to 14 mA. Of the 11 catheters intentionally placed in the intrathecal space, the mean current required to produce an appropriate palpable motor contraction was 1.3 +/- 0.8 mA with a range of 0.05 to 2.4 mA. We conclude that the epidural stimulation test minimum electrical current requirement seems to be lower for intrathecal compared with epidural catheter placement.

Initial plasma results from the Electric Tokamak*

The Electric Tokamak, a low field ITER sized device with R = 5 m, has been operating with well equilibrated clean plasmas since January 2000. Short, 0.9 s, discharges with a central energy confinement time τE(0) = 150 ms are now routinely obtained at a toroidal field B = 0.1 T with kTe, kTi≃120 eV. The discharges are feedback controlled in up/down position and in plasma current. Biased electrode driven H modes have been obtained that compare well with the results obtained on CCT by R.J. Taylor and align with the `neoclassical bifurcation' theory of K.C. Shaing. Very successful second harmonic ion heating has been demonstrated with the ICRF antenna outside the vacuum system and with 50% single pass absorption. ICRF heated discharges indicate that poloidal rotation sufficient for edge bifurcation (H mode) may soon be achieved by ICRF induced fast ion losses. The threshold electrode biasing current required for bifurcated poloidal rotation has so far been reduced by 70% owing to ICRH driven ion orbit loss. The remaining critical ICRF item needed for the exploration of high beta plasma equilibria is the demonstration of the required current profile shaping. It is expected that mode conversion in the ion-ion hybrid regime, with high field side launch, will allow the current drive required to approach and exceed the Troyon beta limit. In 1-D full wave calculations, high harmonic current drive appears most promising at higher beta. Achieving the goal of plasma equilibration near unity beta will require 10 s long discharges (at kT = 3 keV, ne = 3×1019 m-3, B = 0.25 T) because of current profile shaping requirements.

Slow outward tail currents in molluscan bursting pacemaker neurons: two components differing in temperature sensitivity

Bursting pacemaker neurons of Tritonia and Aplysia were studied in voltage-clamp experiments to determine the ionic requirements of the slow outward tail current. This current is important for terminating bursts and hyperpolarizing the neuron during the interval between bursts and therefore contributes to the timing of pacemaker activity. A method for rapid extracellular perfusion of the neuron soma with solutions of different ionic composition was used to study the ionic dependence of the tail current. Measurements of the current-voltage relationship were made at different times during the decay of the tail current to determine the reversal potential in different ionic solutions. These experiments showed that 2 or more slow outward currents contribute to the tail current. Temperature had a large effect on these currents. At cold temperatures (10-15 degrees C), the tail current was predominantly a K current. At warm temperatures (20-23 degrees C), both a K current and a K-insensitive outward current were seen. Bursting pacemaker activity occurred throughout this temperature range. Both the K current and the K-insensitive current required Ca influx for activation. These findings help to reconcile conflicting reports in the literature concerning the ionic dependence of the slow outward tail current and suggest a mechanism for temperature compensation of bursting activity in these pacemaker cells.

Energy and current requirements for ventricular defibrillation using trapezoidal waves.

The threshold energy and current required for ventricular defibrillation was determined in dogs ranging in weight from 6.4 to 38 kg and in ponies ranging in weight from 40 to 101 kg. Trapezoidal waves, 10 ms in duration, with 10%, 50%, 70%, and 90% tilt were applied to transchest electrodes. For all values of tilt, the energy and current required increased with body weight. The energy dose (joules per kilogram of body weight) was higher for the heavier animals, whereas the current dose (peak amperes per kilogram of body weight) was essentially the same for dogs and ponies. In both species and for all four waveforms, the percent success increased with increasing energy and current dose. For all four waveforms and for both species, the threshold average current required for defibrillation was between 0.38 and 0.48 A/kg, indicating that average current may be a convenient unit to compare the efficacy of different waveforms.

The effect of changes in rate and rhythm on supernormal excitability in the isolated Purkinje system of the dog. A possible role in re-entrant arrhythmias.

Microelectrode techniques were used to investigate the effects of rate and rhythm changes upon the period of supernormal excitability during repolarization in isolated canine right and left bundle branch and Purkinje fibers. The same microelectrode was used for both intracellular stimulation and recording. Excitability curves (strength-interval curves) were measured as the minimum depolarizing current required to re-excite the fiber during repolarization of a conducted action potential. During the supernormal period it required an average of 17.0 ± 4.6 SD % less than diastolic current to re-excite the fibers throughout the left and right bundle branch-Purkinje system. The supernormal period of excitability in the bundle branch-Purkinje system was voltage dependent, reaching minimum current requirements at 74.3 ± 5.8 SD mV. Excitability curves of conducted action potentials were determined at basic cycle lengths ranging from 1000 to 300 msec and following single and multiple premature beats. The decrease in action potential durations associated with shorter cycle lengths was not accompanied by a corresponding shortening of the supernormal period of excitability. Therefore, at shorter cycle lengths the supernormal period encompassed a greater proportion of the total action potential; in some cases as much as 50% of the total action potential duration exhibited a period of supernormal excitability. The supernormal period of excitability could be eliminated by perfusing the tissues in elevated potassium (5.0 and 7.5 mM) Tyrode's solution. The possible implications for the generation of re-entrant arrhythmias are discussed.

Supernormal excitability and conduction in the His-Purkinje system of the dog.

The electrophysiological characteristics of the period of supernormal excitability and supernormal conduction were investigated in the isolated canine His-Purkinje system. Strength-interval curves were determined as the minimum transmembrane current required to bring the impaled fiber to threshold potential following a conducted action potential. During the period of supernormal excitability, 17.0 ± 4.6% (SD) less current than that required during diastole was needed to reexcite fibers throughout the left and right bundle branch-Purkinje system. A period of supernormal excitability was not found in the His bundle proximal to its pseudobifurcation or in ventricular muscle. The period of supernormal excitability was voltage dependent in the bundle branch-Purkinje system; it began during phase 3 at full repolarization (88.8 ± 5.6 [SD] mv) and reached minimum current requirements at about 74.3 ± 5.8 mv. Action potentials evoked during this period were conducted faster than they were during diastole. The maximum rates of depolarization of these supernormally conducted action potentials were not greatly depressed compared with control rates. A period of supernormal conduction was not observed in the His bundle. When the external potassium concentration was increased from 2.7 mM to 5.0 um or 7.5 mM, both the supernormal period of excitability and the period of supernormal conduction were eliminated in Purkinje fibers.

Current Requirement for Cathodic Protection Of Oil Well Casing★

Abstract Methods at present used to indicate the minimum applied current required to give complete cathodic protection are discussed and evaluated in terms of their scientific basis and their applicability to the protection of oil well casing. Laboratory experiments are described involving the application of cathodic protection currents to a series assembly of galvanic cells. The results of these experiments lead to a modification of the log current—potential criterion of complete protection widely used at the present time. The experiments also indicate the amount of corrosion repressed as a function of the applied protection current, information which is of considerable value when an economic balance is involved. 5.2.4