Alternating-current Components Research Articles

Dynamic resistance of a REBCO tape carrying direct current under a mixture magnetic field of AC field with DC-biased field

Abstract When the REBCO coated conductor tape carries a direct current(DC) transport current whilst exposed to the alternating current(AC) magnetic field, a DC electrical resistance can be observed, which is called “dynamic resistance”. The High Temperature Superconducting(HTS) magnet wound by the REBCO tapes is located in the HTS electrical machine as field winding carrying DC transport current. The operational environment of the HTS electrical machine involves a complex magnetic field, encompassing both AC and DC components. The interaction between the AC magnetic field and the DC transport current induces dynamic resistance and dynamic loss in the REBCO tape which is a distinctive trait of REBCO tape. Additionally, the presence of an extra DC-biased magnetic field can decrease the critical current of the REBCO tape, thereby altering its electromagnetic properties and potentially compromising its safety. As the basis of superconducting magnets, it is particularly important to study the dynamic resistance and loss distribution of the single REBCO tape under a mixture of magnetic field backgrounds, according to the real working environments in various applications. In this paper, the electromagnetic-thermal coupling model of multilayer REBCO tape based on H-formulation is built in COMSOL Multiphysics. The electromagnetic characteristics and dynamic resistance of the tape are presented when the tape is applied AC magnetic field and carries DC transport current. The effects of perpendicular and parallel DC-biased magnetic fields on the dynamic resistance and loss distribution of the REBCO tape are investigated in the paper. And the DC transport current safety margin will be observed in different applied DC-biased magnetic fields. This study comprehensively demonstrates the variation of dynamic resistance and loss distribution under a complex background magnetic field, which is significant for exploring the electromagnetic characteristics and calculating the loss of the HTS magnets in the HTS electrical machine.

Recording physiological and pathological cortical activity and exogenous electric fields using graphene microtransistor arrays in vitro.

Graphene-based solution-gated field-effect transistors (gSGFETs) allow the quantification of the brain's full-band signal. Extracellular alternating current (AC) signals include local field potentials (LFP, population activity within a reach of hundreds of micrometers), multiunit activity (MUA), and ultimately single units. Direct current (DC) potentials are slow brain signals with a frequency under 0.1 Hz, and commonly filtered out by conventional AC amplifiers. This component conveys information about what has been referred to as "infraslow" activity. We used gSGFET arrays to record full-band patterns from both physiological and pathological activity generated by the cerebral cortex. To this end, we used an in vitro preparation of cerebral cortex that generates spontaneous rhythmic activity, such as that occurring in slow wave sleep. This examination extended to experimentally induced pathological activities, including epileptiform discharges and cortical spreading depression. Validation of recordings obtained via gSGFETs, including both AC and DC components, was accomplished by cross-referencing with well-established technologies, thereby quantifying these components across different activity patterns. We then explored an additional gSGFET potential application, which is the measure of externally induced electric fields such as those used in therapeutic neuromodulation in humans. Finally, we tested the gSGFETs in human cortical slices obtained intrasurgically. In conclusion, this study offers a comprehensive characterization of gSGFETs for brain recordings, with a focus on potential clinical applications of this emerging technology.

AC/DC Thermal Nano-Analyzer Compatible with Bulk Liquid Measurements

Nanocalorimetry, or thermal nano-analysis, is a powerful tool for fast thermal processing and thermodynamic analysis of materials at the nanoscale. Despite multiple reports of successful applications in the material sciences to study phase transitions in metals and polymers, thermodynamic analysis of biological systems in their natural microenvironment has not been achieved yet. Simply scaling down traditional calorimetric techniques, although beneficial for material sciences, is not always appropriate for biological objects, which cannot be removed out of their native biological environment or be miniaturized to suit instrument limitations. Thermal analysis at micro- or nano-scale immersed in bulk liquid media has not yet been possible. Here, we report an AC/DC modulated thermal nano-analyzer capable of detecting nanogram quantities of material in bulk liquids. The detection principle used in our custom-build instrument utilizes localized heat waves, which under certain conditions confine the measurement area to the surface layer of the sample in the close vicinity of the sensing element. To illustrate the sensitivity and quantitative capabilities of the instrument we used model materials with detectable phase transitions. Here, we report ca. 106 improvement in the thermal analysis sensitivity over a traditional DSC instrument. Interestingly, fundamental thermal properties of the material can be determined independently from heat flow in DC (direct current) mode, by using the AC (alternating current) component of the modulated heat in AC/DC mode. The thermal high-frequency AC modulation mode might be especially useful for investigating thermal transitions on the surface of material, because of the ability to control the depth of penetration of AC-modulated heat and hence the depth of thermal sensing. The high-frequency AC mode might potentially expand the range of applications to the surface analysis of bulk materials or liquid-solid interfaces.

The role of the AC component in human perception of AC\u2013DC hybrid electric fields

Electric energy is essential to today’s society. To cope with global higher demand while minimizing land use, efficient high voltage direct current (HVDC) power lines are planned to be mounted on existing alternating current (AC) structures leading to electric fields (EFs) from both AC and DC transmission lines in hybrid configurations. Due to the close proximity to residential areas, the investigation of human hybrid EF perception and underlying mechanisms will be useful to project permitting. To specify the influence of the AC component on the whole-body detection thresholds of hybrid EFs and to explore the lower bound of human hybrid EF perception, 51 participants with an EF detection ability above average were exposed in a double-blind laboratory study. A psychophysical method based on the signal detection theory was used. Very low EF strength combinations, e.g. 1 kV/m AC combined with 1 kV/m DC, were reliably perceived by at least one participant. Detection thresholds were significantly lower with increased AC EF strengths, underlining the key role of the AC component in the human perception of hybrid EFs. Findings will contribute to the assessment of public reaction to the perception of EFs around hybrid overhead power lines and to their optimal designs.

Analysis and improvement of non-contact SpO2 extraction using an RGB webcam.

Peripheral oxygen saturation (SpO2), a vital physiological sign employed in clinical care, is commonly obtained by using a contact pulse oximeter. With the rapid popularization of ordinary red-green-blue (RGB) webcams embedded in devices such as smartphones or laptops, there are broad application prospects for exploring techniques for non-contact SpO2 extraction using RGB webcams. However, many issues remain to be solved in the traditional webcam-based SpO2 extraction methods, such as the inherent low signal-to-noise ratio (SNR) of alternating current (AC) components of RGB signals and the potential defects in using RGB signals combination for SpO2 extraction. In this study, we conducted an in-depth examination of the existing research on webcam-based SpO2 extraction techniques, analyzed the practical problems in using them, and explored new ideas to solve the problems. Rather than roughly using the standard deviations (SD) of AC components for calculations, we performed blind source separation for AC components, and then used the energy coefficients retained in the mixed matrix to replace the variables required in the algorithm. Moreover, steady data was selected to compensate for the potential defects in using RGB signals combination. Through these efforts, the anti-noise capability of the algorithm was significantly enhanced, and the related defects were compensated for. The experimental results indicated that the proposed method produced reliable SpO2 estimation that could potentially-with further research-be used in real applications.

Analyzing DC and AC Magnetic Field Intensity, Distribution, and Relationship in a Hyundai IONIQ 2016 Electric Vehicle

This study aimed to evaluate the direct current (DC) and alternating current (AC) electromagnetic field (EMF) intensity and distribution of an electric vehicle (EV). The results revealed that the EV generated DC and AC EMFs, which differed depending on the operation (resting, idling, and driving at speeds of 40 and 80 km/h). A correlation was established between the AC and DC components of the EMF, which was approximately 0.5 when idling and 0.8 at speeds of 40 and 80 km/h. The results obtained were below the harmful limit set by regulatory agencies, specifically the International Commission on Non‐Ionizing Radiation Protection (ICNIRP) and the Institute of Electrical and Electronics Engineers (IEEE). To further contribute to this field of study, the various measurement equipment used in the literature are summarized according to their parameters.

A control approach for alternating current disturbance signal of fuel cells based on MOSFET high‐speed switch

AbstractInternal resistance is currently one of the most effective ways to achieve the performance improvement, control optimization, and on‐line fault diagnosis of fuel cells. In the fuel cell internal resistance test (FCIRT) system (FCIRTS), the alternating current (AC) disturbance signal is mainly achieved through the use of DC/DC converters or other expensive program‐controlled equipments, which are expensive and large, and it is not conducive to the commercial application of low‐cost FCIRTS. In particular, for the fuel cell vehicles based on dual‐source motors, the DC/DC structure is cancelled. Therefore, a new method should be used in the FCIRTS. To solve this problem, a low‐cost fuel cell AC disturbance signal control approach based on MOSFET high‐speed switch was proposed in this paper. In the approach, a circuit model of MOSFET high‐speed regulation was built, and the AC control of the fuel cells was achieved finally by simulation analysis and experimental verification. The proposed approach can not only independently control the AC components, but also save the system space and cost because of reducing reliance on DC/DC converters and dedicated equipments. Therefore, it is of great value to the development of low‐cost, high‐precision, and real‐time FCIRTS.

A framework of generative adversarial networks with novel loss for JPEG restoration and anti-forensics

Both JPEG restoration and anti-forensics remove the artifacts left by JPEG compression, and recover the JPEG compressed image. However, how to restore the high-frequency details of a JPEG compressed image for JPEG restoration and how to deceive the existing JPEG compression detectors without sacrificing visual quality in JPEG anti-forensics remain challenging. To address these issues, a framework of generative adversarial networks (GAN) with novel loss functions for JPEG restoration and anti-forensics (JRA-GAN) is proposed to allow a JPEG compressed image to be translated into a reconstructed one. Since JPEG compression causes impairment to high-frequency components, an alternating current (AC)-component loss function that measures the loss of AC components is proposed in JRA-GAN to recover these components. To prevent forensic detection, a calibration loss function is also introduced in JRA-GAN to mitigate the variance gap in the high-frequency subbands between a generated image and its calibrated version. Our experimental results demonstrate that the proposed JPEG restoration method outperforms existing methods in terms of image quality, and the JPEG anti-forensic scheme achieves better visual quality and anti-forensic performance that is comparable to the existing state-of-the-art anti-forensic methods. Our code is available in this page: https://github.com/wujianyuan/JRG-GAN .

Quantum scattering and its impact on the source–drain current with defect generation in the channel of nanoscale transistors

The electrons scattered by the defects in the channel can be described by the time-dependent Schrodinger equation. An analytical and physical model of the time evolution of the source–drain current in a transistor at a given defect density has been proposed. It clearly shows that the source–drain current is composed of direct-current and a lot of alternating-current components. And thus the source–drain current will be sensitive to the defect density in the channel. Further, an analytical and physical relation between the phase shift of alternating-current components and the defect density in the channel is derived. Phase shift obtained from time-evolution experimental data of the source–drain current in aging process of nanoscale memory devices agrees well with the theoretical prediction.

The influence of a power source and an induction-capacitance device on the process of nickel deposition

The influence of the type of power source and the parameters of an induction-capacitance device (inductance and capacitance) on the kinetics of nickel deposition, the spectrum of alternating-current components, and the morphology of coating growth is studied in this work. It is shown that the type of the power source and the conditions of device adjustment substantially affect the process of nickel deposition and its structure.

Developing Long-Distance Power-Distribution Systems

The vision of installing large subsea production facilities in remote offshore locations is today, simply not feasible. The problem is that subsea power systems are not designed to transmit high-voltage electricity to a production facility or pipeline tieback that may be under thousands of feet of water and 100 miles away from the nearest power plant. Today’s subsea power-distribution technology is largely based on alternating- current (AC) technology, which, because of its electrical characteristics, can only be efficiently transmitted across a distance of 90 miles. In most cases, however, the effective distance is much less. On average, subsea tiebacks receive power from a platform or vessel located not more than 10 miles away and, in the case of most subsea processing systems, even closer. In an AC-supplied system, the flow of electricity alternates back and forth across the transmission line and is the form of electricity most commonly used in homes and businesses around the world. When long distances are involved, AC power distribution becomes a complicated operation and requires a great amount of attention to detail because of the physics involved with voltage regulation. The search for an alternative to conventional AC systems has revealed the need for multiple technological advancements, from pressure compensated electrical switches to highly-conductive cables able to deliver power more efficiently. About 5 years ago, “We were looking at going to farther distances with alternating current instead of direct current (DC) because most of the equipment we have right now is AC powered,” said James Pappas, vice president of the Research Partnership to Secure Energy for America’s (RPSEA) ultradeepwater program. He said that, after studying the issue, however, it was determined that using AC power could result in a 35% power loss in a 100-mile-long cable because of resistivity and other factors. Not long after that conclusion was reached, General Electric (GE) approached RPSEA with a concept to transfer all the power to a deepwater field with DC and then use a subsea transformer module located within the field to convert some of the power to AC. With this system, the expected power loss over 100 miles could be as low as 25%. “So, if you have AC components, it can convert power to AC for those components, and if you need DC, then it has DC components,” Pappas said. “It all sounds pretty simple until you want to put it in a package and then set it down in 10,000 ft of salt water.”

Mesoscopic entangled coherent states implemented with a circuit quantum electrodynamics system

We show a scheme to generate entangled coherent states in a circuit quantum electrodynamics system, which consists of a nanomechanical resonator, a superconducting Cooper-pair box (CPB), and a superconducting transmission line resonator. In the system, the CPB plays the role of a nonlinear medium and can be conveniently controlled by a gate voltage including direct-current and alternating-current components. The scheme provides a powerful tool for preparing the multipartite mesoscopic entangled coherent states.

Noninvasive Estimation of Arterial Viscoelastic Indices Using a Foil-type Flexible Pressure Sensor and a Photoplethysmogram

This paper proposes a noninvasive method for estimating the viscoelastic characteristics of arterial walls using pulse waves measured in various parts of the body using a foil-type pressure sensor (FPS) and a photoplethysmogram. The FPS was employed to measure pulse waves based on the tonometry approach for its characteristics of high sensitivity and flexibility as well as its ability to continuously measure the alternating-current component of pulse waves. First, in order to accurately measure the amplitude variation of blood pressure waves, suitable mechanical forces externally applied to the FPS were examined, and it was found that values of 5 - 25 (N) yielded the best performance. Next, to verify the time characteristics of pulse waves, the brachial-ankle pulse wave velocity (baPWV) was measured. The results showed that baPWV determined using the FPS and that found with a noninvasive vascular screening device were almost the same. Estimation was then performed to establish arterial viscoelastic indices for the radial artery and the dorsal pedis artery during the application of mechanical pain stimuli. The results suggested that the estimated indices could be used to quantitatively assess vascular response caused by sympathicotonia. Thus, it was concluded that the proposed method enabled noninvasive measurement of pulse waves and estimation of viscoelastic indices.

Noninvasive Monitoring of Arterial Viscoelastic Indices Using a Foil-type Pressure Sensor

This paper proposes a noninvasive method for estimating the dynamic characteristics of arterial walls using pulse waves measured in various parts of the body by a foil-type pressure sensor. The sensor not only has high sensitivity and flexibility but also features the ability to continuously measure the alternating-current component of pulse waves. These capabilities make it suitable for estimating the dynamic characteristics of arterial walls. In this paper, a foil-type pressure sensor was employed to measure pulse waves based on the tonometry approach, and a method of estimating changes in arterial viscoelastic indices was proposed based on the measured pulse waves and photoplethysmograms. In order to accurately measure blood pressure, first, we examined suitable mechanical forces to the sensor, and found that values of 5-25[N] yielded the best performance. We then estimated the arterial viscoelastic indices of a radial artery and a dorsal pedis artery when mechanical pain stimuli were applied to the subjects. The results suggested that the estimated indices can be used to quantitatively assess vascular response caused by sympathicotonia. We thus concluded that the proposed method enabled noninvasive measurement of pulse waves in the dorsal pedis artery and estimation of arterial viscoelastic indices.

Non-Invasive Estimation of Systolic Blood Pressure and Diastolic Blood Pressure Using Photoplethysmograph Components

PurposePhotoplethysmography (PPG) is a noninvasive optical technology that detects changes in blood volume in the vascular system. This study aimed to investigate the possibilities of monitoring the cardiovascular system status by using PPG.Materials and MethodsForced hemodynamic changes were induced using cardiac stimulants; dopamine and epinephrine, and PPG components were recorded by a noninvasive method at the peripheral blood vessels. The results were compared among 6 dogs. Endotracheal intubation was performed after an intramuscular injection of 25 mg/kg ketamine sulfate, and anesthesia was maintained with 2% enflurane. After stabilizing the animals for 15 min, 16 mg/mL diluted dopamine was injected into a vein for 2 min at 20 µg/kg· min-1 by using an infusion pump. Thereafter, the infusion pump was stopped, and 1 mg epinephrine was injected intravenously. Fluid administration was controlled to minimize preload change in blood pressure.ResultsAfter stimulant administration, systolic blood pressure (SBP) and diastolic blood pressures (DBP) increased. The direct current (DC) component, which reflects changes in blood volume, decreased while the alternating current (AC) component, which reflects changes in vascular compliance and resistance, increased. The correlation coefficient between SBP and the foot of the DC component was 0.939 (p < 0.01), while it was 0.942 (p < 0.01) for DBP and the peak of the DC component. The AC component could predict the increase in vascular resistance from a stable pulse blood volume, even with increased pulse pressure.ConclusionsThese results support the possibility that PPG components may be used for easy and noninvasive measurement of hemodynamic changes in the cardiovascular system.

Effects of acupuncture at the Hoku acupoint on the pulsatile laser Doppler signal at the heartbeat frequency.

We aimed to assess the effects of acupuncture by analyzing the alternating current (AC) component of skin blood-flow signals (around the heartbeat frequency) simultaneously recorded at the Hoku acupoint, which is an important acupoint in oriental medicine, and two nearby non-acupoints following acupuncture stimulation (AS). Laser Doppler flowmetry signals were measured in 28 experiments on nine volunteers. Each experiment involved the recording of a 20-min control-data sequence and two sets of effects data recorded 0-20 min and 50-70 min after the AS had been stopped. The direct current (DC) and AC components (DCflux and ACflux, respectively), pulse width (PW), and foot delay time (FDT) of the flux signal were calculated. The DCflux, ACflux, PW, and FDT were all significantly increased only at Hoku following AS. Regression analysis between the DCflux and ACflux revealed that the slope was largest (>1) at Hoku among the measurement sites. Our results indicated that both the DCflux and ACflux in the microcirculatory perfusion were increased by stimulation at the Hoku acupoint, with the change being greatest for the latter. Parameters calculated from the pulsatile flux waveform, such as the PW and FDT, could contribute to noninvasive evaluations of the sympathetic neural activities and of the improvement in perfusion following AS.

Character of the dissolution and partial electrode processes at the alternating-current infralow-frequency polarization of brasses in chloride media. II. Cu44Zn β-brass

The dissolution of β-brasses in a chloride medium at a pulse anodic polarization proceeds at first (up to ∼1 min) nearly uniformly, but when the charge of anodic pulse is carried out partly on the ionization of zinc and partly on the ionization of copper, it becomes selective. In this case the most part of the copper component does not oxidize, but rearranges to form the individual phase, which causes a substantial destruction of the brass electrode. When the cathodic alternating-current component is also switched on and hydrogen evolution begins, pH of the layer near electrode increases preventing the formation of soluble oxidation products in the subsequent anodic half-period. Thus, on a β-brass electrode, the partial cathodic processes affect the anodic oxidation of copper and zinc.

Effects of electrophoresis and electroosmosis during alternating current iontophoresis across human epidermal membrane

Previous studies in our laboratory have demonstrated that skin electrical resistance can be controlled by an alternating current (AC) electric field. By maintaining constant skin resistance, AC iontophoresis has been shown to reduce the iontophoretic flux variability of neutral permeants. Recently, it was found that symmetric square‐wave AC could enhance iontophoretic transport of both neutral and ionic permeants by means of electrophoresis and/or electroosmosis in a synthetic membrane system, and a model was presented to describe the experimental results. The objective of the present study was to assess the effects of AC voltage and frequency and direct current (DC) offset on the flux of neutral and ionic model permeants with human epidermal membrane (HEM). Experiments were conducted under two different conditions: constant AC voltage iontophoresis and iontophoresis using constant HEM resistance with DC offset voltage. The following are the main findings in these experiments. In the constant AC voltage study, when the permeability data were compared at the same HEM electrical resistance, it was demonstrated that AC even at high frequency (≈1 kHz) could enhance the transport of the ionic permeant (tetraethylammonium ion) across HEM, but no enhancement was observed for the neutral permeant (arabinose). For the ionic permeant flux enhancement, the higher the applied AC voltage, the greater the flux enhancement. There was little or no AC frequency dependence of the flux enhancement in the frequency range of 50–1000 Hz. In the constant HEM resistance study of AC with DC offset, approximately linear relationships were observed between flux enhancement and the DC offset voltage for both the neutral and ionic permeants, and these results were found to be consistent with predictions of the modified Nernst‐Planck model for conventional constant voltage DC iontophoresis. When the DC offset voltage was increased, the AC component of the flux enhancement for the ionic permeant decreased, eventually appearing to contribute negligibly to the total flux enhancement at high DC offset voltages. © 2005 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:547–558, 2005

Influence of combined AC-DC magnetic fields on free radicals in organized and biological systems. Development of a model and application of the radical pair mechanism to radicals in micelles.

The effect of an alternating current (AC) magnetic field (MF) on radical behavior is identical to that exerted by a direct current (DC) field of the same instantaneous strength provided that the frequency is low enough in comparison with radical pair dynamics. This criterion is easily met by environmental fields. In general, combined AC/DC fields will lead to increased radical concentrations and oscillating free radical concentrations. Interestingly, the frequency of oscillation for radical concentration seldom follows exactly the pattern of the external AC component of the MF. Even the simple case of an AC-only field at 60 Hz can lead to oscillations in radical concentrations at 120 Hz. The concentration time dependence patterns can be even more complex when the singlet and triplet levels of the radical pair are not degenerate. Further, the effects can change dramatically depending upon the absolute and relative values of the AC and DC components, thus providing a possible explanation for MF windows for certain effects reported experimentally. Effects on the average radical concentration are probably relevant only for fields higher than about 0.1 gauss. Oscillating radical concentrations may influence signal transduction processes or other cellular mechanisms; at the present time there is not enough knowledge available to establish a reasonable threshold for these types of effects. This contribution aims at providing a solid foundation to guide the experimentalist in the design of meaningful experiments on the possible role of MF perturbations of radical chemistry on biological response.

Quantitative determination of the effect of induced alternating currents on the integration of autologous spongiosa transplants

In a right-left experiment on the ulna of beagles, the authors investigate the influence of induced alternating current on the number of healed-in autologeous spongiosa grafts taken from the same side of the body. At first an atrophic pseudarthrosis is produced in both ulnae of twenty animals by bone resection and electrocoagulation over six months. Following to spongiosa transplantation and plate osteosynthesis, the ulnae are stimulated during eight weeks with a sinusoidal current of 38 cps and an electromagnetically induced alternating-current voltage of 600 mV on an average. The blindfold evaluation of the X-ray picture is performed by four experts and shows significantly better results in the stimulated side. By variance analysis of the results of electronic planimetry of serial layers in the region of transplantation represented by microradiography, it is demonstrated that the greater bone density of the stimulated grafts compared to the control grafts is statistically significant. It has to be considered that these results refer strictly to the electric data and treatment times applied by the authors. Particularly the results are not valid for the unique application of electromagnetic fields without alternating-current component.