Comparison between the AC and DC measurement of electrodermal activity.

Compared to direct current (DC) methods, alternating current (AC) methods have rarely been used in the field of electrodermal research. AC methods, however, have the advantage of enabling analysis of electrodermal activity, including capacitive properties. To establish an easy AC method, a computer-controlled measurement system was developed in this study. The system can automatically measure impedances at three different frequencies on the basis of phase detection and determine an impedance locus. Performance tests using RC parallel circuits showed that the system has sufficient accuracy. Palmar skin impedance was also measured and temporal changes in parameters of the circular arc law were investigated. It was demonstrated that the system can obtain impedance data with a data acquisition time of less than 0.2 s and can easily determine an impedance locus. It is expected that the new system, due to its high level of accuracy and ease of operation, will be used as an AC method of measuring electrodermal activity.

This paper describes the performance of junctions based on self-assembled monolayers (SAMs) as the functional element of a half-wave rectifier (a simple circuit that converts, or rectifies, an alternating current (AC) signal to a direct current (DC) signal). Junctions with SAMs of 11-(ferrocenyl)-1-undecanethiol or 11-(biferrocenyl)-1-undecanethiol on ultraflat, template-stripped Ag (Ag(TS)) bottom electrodes, and contacted by top electrodes of eutectic indium-gallium (EGaIn), rectified AC signals, while similar junctions based on SAMs of 1-undecanethiol-SAMs lacking the ferrocenyl terminal group-did not. SAMs in these AC circuits (operating at 50 Hz) remain stable over a larger window of applied bias than in DC circuits. AC measurements, therefore, can investigate charge transport in SAM-based junctions at magnitudes of bias inaccessible to DC measurements. For junctions with SAMs of alkanethiols, combining the results from AC and DC measurements identifies two regimes of bias with different mechanisms of charge transport: (i) low bias (|V| < 1.3 V), at which direct tunneling dominates, and (ii) high bias (|V| > 1.3 V), at which Fowler-Nordheim (FN) tunneling dominates. For junctions with SAMs terminated by Fc moieties, the transition to FN tunneling occurs at |V| ≈ 2.0 V. Furthermore, at sufficient forward bias (V > 0.5 V), hopping makes a significant contribution to charge transport and occurs in series with direct tunneling (V ≲ 2.0 V) until FN tunneling activates (V ≳ 2.0 V). Thus, for Fc-terminated SAMs at forward bias, three regimes are apparent: (i) direct tunneling (V = 0-0.5 V), (ii) hopping plus direct tunneling (V ≈ 0.5-2.0 V), and (iii) FN tunneling (V ≳ 2.0 V). Since hopping does not occur at reverse bias, only two regimes are present over the measured range of reverse bias. This difference in the mechanisms of charge transport at forward and reverse bias for junctions with Fc moieties resulted in large rectification ratios (R > 100) and enabled half-wave rectification.

ABSTRACTWe present an improved AC (Alternating Current) method for the determination of the Thomson coefficient, which can be used for obtaining the absolute Seebeck coefficient. While previous work has focused on DC (Direct Current) methods, we analyze the influence of an AC current in order to derive the Thomson coefficient of a thin wire from measurable quantities. Our expression requires five parameters including AC current, resistance, temperature gradient, and the temperature changes due to the Thomson and Joule effects. Thus, a prior determination of thermal conductivity and sample geometry is not required, unlike DC methods. In order to validate our analysis, the Thomson coefficient of a thin Pt wire has been measured at several frequencies. The results agree with those obtained from a conventional DC method.

A series of ethylene–octene copolymer (EOC) composites have been prepared by melt‐mixing with different weight ratios of expandable graphite filler (0–50% by weight). Electrical conductivity [both alternating current (AC) and direct current (DC)] and thermal conductivity studies were carried out. Effect of filler loading and frequency on electrical conductivity was studied. DC conductivity has increased from 1.51 × 10 −13 S cm −1 to 1.17 × 10 −1 S cm −1 . Percolation threshold by DC and also AC methods was observed at about 16 vol% of the filler. Real part of permittivity was found to be decreasing with increase in frequency while conductivity was increasing. Thermal conductivity was also found to be increasing gradually from 0.196 to 0.676 Wm −1 K −1 which is about 245% increase. Graphite not only increases the electrical and thermal conductivities but at and above 40 wt%, also acts as a halogen‐free, environmental friendly flame retardant. Shore‐A hardness of EOC/graphite composites shows that even with high graphite loading, the hardness is increased from about 50–68 only so that the rubbery nature of the composite is not affected very much. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers

THE ordinary dynamometer is as well adapted for direct as for alternate current measurements; but while it is generally regarded as the best available instrument for alternate currents, its use with direct currents is almost restricted to standard instruments of the ampere balance type. This is due to the immensely greater sensitiveness obtainable with direct current instruments constructed on the heterostatic principle, as exemplified in galvanometers with permanently magnetised needles or magnets. The latter instruments, due originally to Kelvin and Maxwell, and first developed commercially by Ayrton and Perry, have been brought to a high state of perfection in recent years, with the result that ordinary measurements on direct current circuits are much more precise and satisfactory than those on alternate current circuits.

With the expansion of today's digital era, the use of electronic equipment is increasing exponentially at home, office, and plants. The common denominator of these electronic equipment is that they all use Direct current (DC) power internally by converting Alternating Current (AC) power to DC power using local converters. All these converters produce losses, heat, and are prone to failures which in turn impact the equipment efficiency, life span, and reliability. In addition, these converters increase the cost of equipment they are powering and their required footprint. The issue of reliability and cost reduction is more stressing for data centers where servers, Uninterruptable Power Supply (UPS) systems, and IT equipment constituting the majority of the load can be powered directly through a DC grid. This paper presents a case study that compares AC and DC technologies for powering a typical data center and outlines the main advantages and limitations of each technology. This study will present a comparative analysis of a DC power system against a typical AC distribution for critical datacenter loads. It also presents a real case study of existing AC powered data center and compare the benefits of powering the center via DC instead of AC. Analytical reliability, safety and efficiency models are developed, and quantitative results are obtained based on a set of real data. The study indicates that the DC system would be more reliable, efficient and will achieve less Capex and Opex values than the AC.

Bulk barium titanate (BaTiO3 ) ceramic specimens with bimodal microstructures are prepared and their dielectric and fatigue strengths are investigated under an alternating current (AC) electric field and a direct current (DC) electric field. It is found that under AC electrical loading, both the dielectric and fatigue strengths decrease with increasing amount of coarse abnormal grains. The scatter of the AC fatigue strength is characterized with the Weibull statistics. The extent of scatter of the AC fatigue strength data correlates strongly with the size distribution of the coarse grains. Such correlation is resulted from the presence of intrinsic defects within the microstructure. For DC electrical loading, the time to failure of the specimens with coarse abnormal grains is significantly shorter than the lifetimes of the specimens with only small normal grains. It is found that under a DC electric field of 6 MVm−1, the BaTiO3 specimens would fail within 200 h when abnormal grains are present in the microstructure. However, the lifetimes of the specimens containing abnormal grains vary significantly from one to another. The Weibull statistical analysis indicates that the amount of abnormal grains has little influence on the lifetime performance of bulk BaTiO3 ceramics under large DC electric fields. In most of the failed BaTiO3 specimens under DC electrical loading, regardless of their lifetimes, large through-thickness round holes with recrystallization features are present. A mixed failure mode consisting of avalanche and thermal breakdowns is proposed for the failed specimens.

A simple and low-cost alternating current (AC)-based method, without electrolyte correction, is proposed (Electrochemical Impedance Spectroscopy (EIS)-Zero Gap Cell) for the determination of ohmic contribution of diaphragms. The effectiveness of the proposed methodology was evaluated by using a commercial Alkaline Water Electrolysis (AWE) diaphragm (Zirfon®). Furthermore, the results were compared with two conventional electrochemical methodologies for calculating the separator resistance, based on direct current (DC), and AC measurements, respectively. Compared with the previous techniques, the proposed approach reported more accurate and precise values of resistance for new and aged samples. Compared with the manufacturer reference, the obtained error values for new samples were 0.33%, 5.64%, and 41.7%, respectively for EIS-Zero gap cell, AC and DC methods, confirming the validity and convenience of the proposed technique.

Electrical stunning is considered one of less stressful fish stunning method. However, for its efficiency, it is important to determine the best way of application of the electrical variables. The aim of this study was to evaluate the effect of different voltages (100, 150, and 200 V) of alternating current (AC) or direct current (DC), frequency of 50 Hz, for 180 s exposure, concerning the aspects of behavior and meat quality of pacu (Piaractus mesopotamicus). Fish subjected to AC remained unconscious longer, evaluated by behavior analysis, when compared to DC. The pacu subjected to 100 AC, 200 AC and 100 DC showed less bleeding in the fillets. The lightness (L*) of the fillets were higher in 150 AC, 150 DC and 100 DC, followed by 200 and 100 AC. The redness (a*) in pacu fillets were moderate in treatments 200 and 150 AC and less intense in treatments 100 DC and 100 AC. The yellowness (b*) was higher in fish fillets treatment 150 DC and lower in 100 AC. Therefore, the 200 V alternating current (AC) used in water stunning caused apparent unconsciousness of up to 4 min. after exposure and less bleeding in fillets, thus it is a suitable stunning method to be recommended for the pacu processing industry.

Increasing electronic appliances in residential buildings have caused researchers to study direct current (DC) powered systems in homes. In this paper, we state a scenario that a home with traditional alternating current (AC) powered appliances are replaced with DC devices. The questions which devices can be replaced, how much savings in terms of energy and electric bill is provided, what are economical, technical, social and environmental problems in this AC-DC transition and which system between DC and AC for residential buildings are much preferable based on the AHP method are answered in the presented study. Results show that 74.126-percentage cost saving in the electric bill is provided. However, the problems that nonexistence in some residential DC devices in the market, immaturity of DC system in terms of technical issue, added system costs, less information about DC by experts and related people, and a public bias that DC is unsafe to exist. In this study, based on these defined advantages and disadvantages of DC and AC system, criteria and sub-criteria have been determined for the analytic hierarchy process (AHP) method. By way of AHP, the result that DC system is much preferable than the AC system for residential buildings has been reached.KeywordsDirect currentAlternating currentAnalytic hierarchy process

Evaluation of constant current alternating current iontophoresis for transdermal drug delivery

As mentioned earlier, a LD is an electrical device that needs a source of electrical energy with the output characteristic of a CCS or CPS for power. This chapter examines the types of available sources. There are a variety of devices designed to produce and supply electricity to consumers. They transform carriers of nonelectric energy, e.g., from oil, gas, chemical reactions, water, wind, sunlight, etc., into electrical energy (the technical literature refers to them as the "primary sources of electrical energy"). This transformed energy is either direct current (DC) or alternating current (AC). Most applications of this energy use two types of primary sources: electric batteries (used in mobile objects such as vehicles and flashlights) and AC generators with an associated AC grid (in which the energy from many primary sources is combined to power stationary equipment). There are also mobile generators, which generate electricity with parameters that match an AC grid. The primary sources of electrical energy can only directly power limited types of electrical devices, such as the incandescent bulbs in flashlights powered by batteries. Some AC motors and incandescent lamps are powered directly from an AC line. Most electrical devices (electrical loads) require either AC sources with a different AC voltage and/or frequency, or DC sources with an output characteristic of a CVS, CCS, or CPS. This arrangement involves an intermediate device connected between the primary electric source and the load that converts electrical energy from the primary source into electrical energy that has the characteristics needed by the load. These devices are called "secondary sources of electrical energy." In the American technical literature, they are usually called power supplies (PSs). In relation to powering LDs, secondary sources are identified as LDDs. An understanding of the characteristics of electrical sources and electrical loads, as well as the interaction between them, is necessary for competent LDD design. One of the primary goals of this book is to present the design principles and characteristics of the secondary sources of electrical energy devoted to powering LDs. The following section considers the characteristics of primary sources.

The introduction of Smart Meter (SM) is a first stage towards Smart Grid to develop future energy system. The main difference of a SM with a traditional meter is that instead of only showing the current usage on the meter itself, it can also communicate the usage details directly to a Distribution System Operator. In order to make overall reduction in energy consumption, increasing awareness about the energy consumption is an important factor. The SM data gives that facility by visualizing the energy consumption in real time. The energy consumption can also be reduced by using low voltage Direct Current (DC) distribution in houses and offices. Several factors have increased the recent interest in DC power system. The number of devices that operate on DC continues to increase in both homes and offices. Most of the devices require Alternating Current (AC) to DC conversion between the AC supply and the DC side of the device. These need of conversion from 230V AC to low voltage DC inside the DC power consuming apparatus results in a low overall efficiency of the AC system. This work focused on feasibility of using 230V AC to 48V DC converter with SM for a house with low voltage DC distribution system.

It is of great significance to study the direct current (DC) breakdown characteristics of the alternating current (AC) cross-linked polyethylene (XLPE) for converting AC XLPE cables into DC operation. The AC and DC breakdown experiments were carried out on 10 kV AC XLPE samples under three different dwell times (1 min, 5 min and 15 min). The characteristics between the breakdown electric field and the breakdown time under AC and DC voltage was obtained according to the date of breakdown experiments. The results show that the 1 h AC and DC breakdown electric field is 69.80 MV/m and 170.96 MV/m respectively, and the DC breakdown electric field is always higher than the AC breakdown electric field in the range of 1 h to 40 a.

The purpose of this study was to determine the effect of alternating current (AC) and direct current (DC) on the bend testing results of low carbon steel welding joints. The results of this study are expected to determine the cracks that occur from the root bend and face bend testings in the AC and DC welding process. This study used experimental method, where the research was done by giving AC and direct polarity DC (DC-) SMAW welding treatments. The material used in this research was low carbon steel plate DIN 17100 Grade ST 44, thickness 10 with E7016 electrode type. The process of welding joints used a single V seam, strong current of 90A, and the welding position of 1G. The testing of welding joints was carried out by bend testing using the standard acceptance of AWS D1.1 root bend and face bend testing results. The results of the bend testing showed that the AC welding root bend test specimen held no cracks while the DC welding root bend test held cracks with incompelete penetration and open crack defects. On the contrary, the AC welding face bend test had open crack defects and in the DC welding face bend test was found a crack. Thus, there was a difference in the crack resistance of the welding joint from the types of current used through the root bend test and face bend test. Therefore, it can be summarized that AC welding is better for root welding and DC welding is good for capping welding.