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Belland, Eirik. "Alternating Current Corrosion of Carbon Steel." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-16342.
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The objective was to investigate if the established theory concerning corrosion calculations and electrochemical behavior of carbon is valid when steel is exposed to AC in an electrolyte consisting of 3,5 wt% NaCl and distilled water. The experimental work was divided in two main parts. The first part concerned corrosion testing, including weight loss measurements in stagnant conditions in combination with linear polarization resistance experiments. AC-current densities investigated was 0-, 50-, 75-, 100-, 150-, 220- and 500 A/m2. Polarization curves were produced on two weight loss samples, one exposed to 150 A/m2 and the other exposed to 220 A/m2, at the end of the weight loss experiments.From the corrosion testing it was found that the estimated corrosion current densities (icorr) from the weight loss experiments on samples exposed to AC-current densities below 500 A/m2, was in an approximate accordance with the icorr values estimated from LPR. At 500 A/m2 the measured corrosion rates and corresponding corrosion currents were slightly higher than the remainder. The higher corrosion rate measured from the samples exposed to 500 A/m2 is suggested related to a non-faradaic corrosion contribution. The suggested mechanism is a facilitation of grain boundary corrosion at high AC-current densities leading to the loss of grains. This being a non-faradaic corrosion contribution it is not possible to measure with LPR or polarization curves. The constant B [mV] from the Stern-Geary equation was estimated on basis of LPR measurements. The constant displayed a decreasing trend with increasing AC-current densities. This was explained by the lowering of anodic and cathodic tafel slopes with increasing AC-current densities. The polarization resistance (Rp’ - [Ω∙m2]) also showed a decreasing trend with increased AC-current densities. This was explained by the increased current response in the LPR measurements with increasing AC-current densities.The second part was intended to elucidate the effect of AC on electrochemical behavior of the carbon steel through producing polarization curves at different AC-current densities using a rotating electrode experimental setup. Alterations in corrosion current densities, cathodic tafel slopes, limiting current density of oxygen reduction and corrosion potentials on steel without AC and at current densities of 100-, 150-, 220- and 500 A/m2 are investigated during the electrochemical testing.  From the rotating electrode experiments no significant change in corrosion current was found with increasing AC-current densities. The potential range, in which limiting current of oxygen reduction (ilim) appeared, decreased with increasing AC-current densities. This decrease in ilim also affected the corrosion potentials (Ecorr). A decrease in the potential range of ilim leads to a more cathodic Ecorr. A particular observation was found at AC-current densities of 150 A/m2 were the effect of ilim seemed absent. The samples exposed to this AC-current density also attained the most cathodic corrosion potentials at approximately -850mVSCE which was between 200-400mV lower than the samples exposed to the remaining AC-current densities. Cathodic tafel slopes showed a decreasing trend with increasing AC-current density. Anodic rafel slopes were considered absent due to pitting above Ecorr.Pictures of the weight loss samples were captured in the SEM. It was found that the formation of pits occurred on all weight loss samples exposed to AC. On the samples without induced AC no sign of pitting was observed. Hence it was found that the corrosion attacks attained a more local character when AC-current was induced in the steel samples.
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Forthun, Kari. "Alternating Current Corrosion of Aluminium Sacrificial Anodes." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for materialteknologi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22387.
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Direct Electric Heating (DEH) is applied to subsea oil production and transmission pipelines to prevent freezing of hydrates as wax during productions shut downs. To prevent clogging, the pipes are heated by application of alternating current (AC) voltage. As a result, a risk for AC corrosion is introduced, which is the motivation and subject of this thesis. The steel pipes are coated and applied conventional cathodic protection (CP) by use of AlZnIn sacrificial anodes. The present work focused on the risk of increased rates of AC influenced corrosion of the AlZnIn anodes. Anode samples coupled to steel samples were investigated under applied AC by use of laboratory scale test cells in synthetic seawater at room temperature. In these experiments, which lasted for one week, the applied AC was varied in the range 0.5 to 150 A m-2, and the anode-steel area ratio (AR) was set to either 10:1 or 100:1. Corrosion rates were assessed by weight loss measurements and properties of surface deposits and corroded surfaces were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. For better assessment of anode-steel coupling in practice and the significance of anode-steel area, similar tests were performed by using a connection of two identical pairs of parallel-coupled anode-steel, with area ratio of 100:1. Equipment and methodology for investigation of AC corrosion were developed and evaluated. Results show that the anode corrosion rate increased with increasing applied AC level, while steel is sufficiently protected under the experimental conditions specified above. Anode corrosion rate was influenced both by current provided for the protection of the steel and self-corrosion and the attack was characterized by pit formation and coalescence of these at higher AC levels. High self-corrosion rates were attributed to successive alkalization, explained by hydrogen evolution, and acidification of the anode surface at each AC cycle, which destabilized the protective oxide layer. Corrosion was limited at high AC levels, explained by hydrogen blanketing of the anode surface and by hydrogen trapped within pores of the hydroxide surface film. AC corrosion of the anodes depended strongly on the anode-steel area ratio. In experiments with electrode pair configuration as described above, the significance of the steel samples vanished by increasing the anode-steel area ratio to 100:1. The system functioned as an anode?anode galvanic couple, which caused a significant decrease in the potential of the anodes, giving rise to runaway self-corrosion rates. In experiments with one anode-steel couple, the couple potential also decreased once AC was applied, increasingly in extent with applied AC potential. This further increased the current requirement by increasingly cathodic steel, thereby resulting in extreme anode corrosion at high AC levels in experiments with AR of 10:1. A subsequent positive shift in the couple potential to a stable level lower than the DC operation potential (-1.05 VSCE) of the AlZnIn anode was observed within 20 hours, caused by hydrogen evolution on steel. The time until the positive shift increased with applied AC level and decreased AR. Formation of calcareous deposits on the steel surface under DC conditions is an important aspect of CP in seawater because the deposits reduce the current requirement significantly. Such deposits did not appear to have a similar significance in the presence of applied AC. Increased water reduction by AC, causing pH increase on the steel surface higher than the DC case, reduced the protectiveness of the deposits by inhibition of electrically insulating CaCO3 formation. Preconditioning of the steel surface by CP under usual DC conditions to form the desired deposits did not have a clear influence on the AC corrosion of anodes. The decrease of both the AC and DC components of the cell current as a function of time under moderate applied AC levels, however, indicated the formation of calcareous deposits on steel. No calcareous scales were found to deposit on the anode surface. The decrease of cell current with time can also be attributed to the development of corrosion products on the anode surface. Decrease in the cell current was not appreciable for high AC levels (> 2 V RMS) with an AR of 10:1, explained by the destruction and instability of the calcareous deposits due to vigorous gas evolution. In conclusion, these results suggest that the lifetime of the CP system at high levels of applied AC (V(AC) > 2 V AC or iAC > 30 A m-2) may become significantly reduced in relation to the expected lifetime under DC conditions.
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Ahmed, Mustafa M. Abdalla. "Alternating-Current Thin-Film Electroluminescent Device Characterization." Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2008. http://www.nusl.cz/ntk/nusl-233432.
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Jádrem této disertační práce bylo studovat optické a elektrické charakteristiky tenkovrstvých elektroluminiscenčních součástek řízených střídavým proudem (ACTFEL) a zejména vliv procesu stárnutí luminiforů na jejich optické a elektrické vlastnosti. Cílem této studie měl být příspěvek ke zvýšení celkové účinnosti luminoforů, vyjádřené pomocí jasu, účinnosti a stability. Vzhledem k tomu, že současnou dominantní technologií plochých obrazovek je LCD, musí se další alternativní technologie plošných displejů porovnávat s LCD. Výhodou ACTFEL displejů proti LCD je lepší rozlišení, větší teplotní rozsah činnosti, větší čtecí úhel, či možnost čtení při mnohem vyšší intenzitě pozadí. Na druhou stranu je jejich nevýhodou vyšší energetická náročnost, problém s odpovídající barevností tří základních barev a podstatně vyšší napětí nutné pro činnost displeje. K dosažení tohoto cíle jsme provedli optická, elektrická a optoelektrická měření ACTFEL struktur a ZnS:Mn luminoforů. Navíc jsme studovali vliv dotování vrstvy pomocí KCl na chování mikrostruktury a na elektroluminiscenční vlastnosti (zejména na jas a světelnou účinnost) ZnS:Mn luminoforů. Provedli jsme i některá, ne zcela obvyklá, měření ACTFEL součástek. Vypočítali jsme i rozptylový poměr nabitých barevných center a simulovali transportní charakteristiky v ACTFEL součástkách. Studovali jsme vliv stárnutí dvou typů ZnS:Mn luminoforů (s vrstvou napařenou či získanou pomocí epitaxe atomových vrstev) monitorováním závislostí svítivost-napětí (L-V), velikost vnitřního náboje - elektrické pole luminoforu (Q-Fp) a kapacitance-napětí (C-V) ve zvolených časových intervalech v průběhu stárnutí. Provedli jsme krátkodobá i dlouhodobá měření a pokusili jsme se i o vizualizaci struktury luminoforu se subvlnovým rozlišením pomocí optického rastrovacího mikroskopu pracujícího v blízkém poli (SNOM). Na praktickém případu zeleného Zn2GeO4:Mn (2% Mn) ACTFEL displeje, pracujícího při 50 Hz, jsme také studovali stabilitu svítivosti pomocí měření závislosti svítivosti na napětí (L-V) a světelné účinnosti na napětí (eta-V). Přitom byl zhodnocen význam těchto charakteristik. Nezanedbatelnou a neoddělitelnou součástí této práce je i její pedagogický aspekt. Předložený text by mohl být využit i jako učebnice pro studenty na mé univerzitě v Lybii.
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Hernández-Morales, José Bernardo. "Electromagnetic stirring with alternating current during electroslag remelting." Thesis, University of British Columbia, 1988. http://hdl.handle.net/2429/28385.
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The electroslag remelting process combines both a chemical refining ability and a better control on solidification which produces materials of more uniform properties. In spite of the advantages of this process, segregation-prone alloys are still difficult to produce via ESR, particularly when large ingot diameters are involved. In this context the study of externally applied electromagnetic fields is of great interest.
An AC operated stirring device was designed and laboratory-scale experiments were conducted. The solidification structures resulting from the stirring as well as the mixing conditions prevailing in the liquid pool were investigated. Also, modelling studies on the electromagnetic body force produced by the stirrer and the resulting thermal field were conducted.
The start of stirring results in a clearly defined band in both steady- and unsteady-state regimes. The microstructure was not significantly modified in the center of the ingot but a loss in directionality was found at the mould wall. It seems apparent that the stirred liquid does not penetrate significantly inside the interdendritic region. Mixing studies revealed that the degree of mixing in the pool is enhanced by the stirring.
The theoretical calculations show that most of the electromagnetic body force is confined to the magnetic skin depth at the mould wall and the metal-slag interface. Using a previously developed two-dimensional heat transfer model it was not possible to reproduce the experimental pool profiles obtained when stirring was applied.Applied Science, Faculty of
Materials Engineering, Department of
Graduate
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Chavez, Reyes Xavier A. "Electrochemical Disinfection of Municipal Wastewater using Alternating Current." ScholarWorks@UNO, 2014. http://scholarworks.uno.edu/td/1907.
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This research focused on chlorine-free disinfection of wastewater by complying with today's regulations. The equipment used was a continuous flow electrochemical reactor connected to an alternating current (AC) power supply. The electrodes used were made out of titanium coated with iridium oxide. To determine the inactivation of Escherichia Coli, a bacterial count method based on the USEPA method 1603 was used.
After several experiments it was determined that electrochemical disinfection using AC was not efficient and economic enough to be classified as a viable alternative to chlorine disinfection. It was demonstrated that chlorine can be produced by electrolysis using AC and that no hydrogen could be noticed as a byproduct of the electrolysis of wastewater. When the results from this investigation were compared to the ones obtained using DC in Acosta (2014), it was determined that the belief that AC and DC are equally efficient at disinfecting wastewater is wrong.
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Salimian, Alireza. "Alternating current electroluminescent properties of zinc sulfide powders." Thesis, University of Greenwich, 2012. http://gala.gre.ac.uk/9154/.
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In order to investigate the alternating current electroluminescent properties of zinc sulfide powders the following experiments were conducted: synthesis of zinc sulfide phosphors (comprised of zinc, sulfur and copper dopant); thermal shocking of phosphor materials (sudden cooling, using liquid nitrogen, of phosphor particles heated up to 500oC) and analysis of their alternating current electroluminescent properties as well as studies of particle crystal structures by synchrotron and conventional X-ray powder diffraction techniques. Inductively coupled plasma mass spectrometry was utilized to investigate the concentration of co-activator atoms within the zinc sulphide crystal lattice. Electroluminescent panels were prepared and the emission properties were evaluated theoretically in order to obtain a mathematical relationship between various parameters involved in the electroluminescent process. Thermal quenching of zinc sulfide phosphor alters its photoluminescent and electroluminescent properties. The dominant wavelength of the material alters from 504 nm to 517 nm. It appears that the blue centres are vulnerable to the thermal quenching procedure carried out as the blue emission deteriorates and the overall blue emission of the material is reduced due to the role that the interstitial Cu+ species play in this mechanism. The interstitial Cu+ is not as stable in its location within the lattice compared to substitutional Cu+ and hence a thermal shock is prone to effect its location or association with the surrounding atoms. The green emission centre, however, appears to be unaffected. Results obtained from layer by layer analysis of the material demonstrate that the surface of the phosphor particles contain most of the copper content (copper to zinc molar ratio of 0.08% in the surface compared to 0.06% at inner levels distributed within the lattice). The location of the outer copper layer may play a key role in the alternating current electroluminescence (ACEL) process; further experiments need to be conducted in order to prove the foregoing hypothesis. Irrespective of the amount of copper impurity (dopnat) initially added to the zinc sulphide precursor, prior to synthesis of the phosphor, during the high temperature firing of the material (above 700˚C) a considerable amount of the copper will be ejected from the lattice and be washed off in the latter steps of the synthesis process (where the newly synthesized phosphor is washed in concentrated ammonia solution); an initial copper content of 1.2% molar ratio is reduced to 0.154%; however, the duration of the high temperature firing is a key factor in the final amount of copper present within the lattice. XRPD experiments of a working ACEL device (i.e., when the AC field is applied across the electroluminescent phosphor) show that the diffraction lines all shift, but remain within the region where broad diffraction intensity is observed for a powder sample (i.e. random orientation). Indeed the sharp diffraction lines are observed to span across each broad diffraction area associated with the sphalerite phase. The panel exhibits a different diffraction pattern when the device is powered in an AC field compared to when it is not exposed to the field. This clearly indicates that the particles possess piezoelectric properties and the electric field causes strain on the crystal lattice. When considering the major drawbacks of ACEL technology, i.e. it’s short life time and degradation characteristics, defining a mathematical model of its emission degradation is a step towards understanding part of the mechanism of the ACEL process. Due to the various number of parameters involved in the phenomenon of electroluminescence (such as particle size, copper content and random distribution of crystal planes) and the fact that emissions arise from certain centres randomly distributed over each phosphor particle, mathematical models are only accurate when they are formulated in relation to the analysis of a particular batch of phosphor sample and used to prepare a particular panel. Hence, no overall mathematical formulation can be produced to measure the emission properties of various ACEL panels produced by different batches of zinc sulfide phosphors. The findings of this research indicate that sample preparation technique which involves addition of raw zinc sulfide to an already copper doped zinc sulfide causes an increase in the occurrence of nano p-n junctions species within the lattice where the cupper locations form the p-type and the n type is formed from the release of some sulfur atoms from zinc sulfide structure during the high temperature firing relative to the conventional phosphor preparation methods. Larger particles have a higher probability of contacting interstitial copper sites during firing and preparation as copper atoms tend to migrate out of the zinc sulfide lattice toward the surface. Hence larger particles (commercial phosphors) demonstrate better emission properties. Thermal quenching affects the interstitial copper sites more than the other luminescent centres formed of substitutional copper sites. Hence the lowered blue emission occurs. Due to the probability of high dispersion of Cu atoms within the ZnS lattice a useful mathematical model cannot easily be developed for an EL panel. EXAFS analysis cannot be fully relied up on in respect of the interstitial copper environment in these phosphors considering that a small fraction of the copper impurity in the phosphor exists at interstitial sites. However, the results from experiments using XANES confirm a change in the electronic configuration of Zn atoms when samples are quenched.
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Tygier, Samuel C. Tenzing. "High current proton fixed-field alternating-gradient accelerator designs." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/high-current-proton-fixedfield-alternatinggradient-accelerator-designs(ce718c72-3875-458f-92d2-1cd496287993).html.
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To make energy production sustainable and reduce carbon dioxide emissions it is necessary to stop using fossil fuels as our primary energy source. The Accelerator Driven Subcritical Reactor (ADSR) could provide safe nuclear power. It uses thorium as fuel, which is more abundant than uranium, and produces less long lived waste. An ADSR uses neutron spallation, caused by a high power proton beam impacting a metal target, to drive and control the reaction. The beam needs to have an energy of around 1 Ge V and a current of 10 mA with a very high reliability, the combination of which is beyond the capabilities of existing particle accelerators. Cyclotrons and synchrotrons both have trouble producing such a beam, while a suitable linac would be several hundred metres long, and expensive. A more compact accelerator design would allow multiple accelerators to be combined to improve reliability. This thesis examines the use of a Fixed-Field Alternating-Gradient (FFAG) accelerator as the proton driver. FFAGs are compact, and can simultaneously achieve higher energies than a cyclotron at higher repetition rates than a synchrotron. However, it is still a challenge to reach the high currents required. A 35 to 400 MeV non-scaling FFAG was designed to demonstrate issues encountered at high currents. Two methods were investigated in order to increase the number of particle bunches that could be simultaneously accelerated. One uses multiple solutions to the harmonic conditions for acceleration, and the second injects bunches after the acceleration has started. Neither was found to give significant practical improvement in current. Space charge is a destructive force at high currents. Software was developed to simulate the effect of space charge in an FFAG using several models. Space charge tune shifts were measured for a range of energies and currents, and peak currents of above 1 A were found to be unstable. In order to provide 10 mA of average current, acceleration would need to occur in around 100 turns, which will require a very rapid RF sweep.
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Aldayel, Abdulaziz A. "Comparison of acute physiological effects between alternating current and pulsed current electrical muscle stimulation." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2010. https://ro.ecu.edu.au/theses/131.
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Electrical muscle stimulation (EMS) is widely used in rehabilitation and sport training, and alternating current and pulsed current EMS are commonly used. However, no systematic comparison between alternating and pulsed current EMS has been made in the previous studies. The main aim of this research was to compare acute physiological responses between the alternating and pulsed current EMS. The secondary purpose of the research was to investigate further muscle damage induced by EMS-evoked isometric contractions. Three experimental studies were conducted in the thesis project together with literature review about EMS.
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Joós, Géza. "The nature of torsional interactions in synchronous generators /." Thesis, McGill University, 1986. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=74033.
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Perumal, Ajay Kumar. "Alternating current electroluminescence (AC-EL) with organic light emitting material." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2012. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-89750.
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We demonstrate a new approach for fabricating alternating current driven organic electroluminescent devices using the concept of doping in organic semiconductors. Doped charge transport layers are used for generation of charge carriers within the device, hence eliminating the need for injecting charge carriers from external electrodes.
The device is an organic-inorganic hybrid: We exploit the mechanical strength and chemical stability of inorganic semiconductors and combine it with better optical properties of organic materials whose emission color can be chemically tuned so that it covers the entire visible spectrum. The device consists of an organic electroluminescence (EL) layer composed of unipolar/ambipolar charge transport materials doped with organic dyes (10 wt% ) as well as molecularly doped charge generation layers enclosed between a pair of transparent insulating metal oxide layers. A transparent indium doped tin oxide (ITO) layer acts as bottom electrode for light outcoupling and Aluminium (Al) as top reflective electrode. The electrodes are for applying field across the device and to charge the device, instead of injection of charge carriers in case of direct current (DC) devices. Bright luminance of up to 5000 cd m-2 is observed when the device is driven with an alternating current (AC) bias. The luminance observed is attributed to charge carrier generation and recombination, leading to formation of excitons within the device, without injection of charge carriers through external electrodes.
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Farrow, C. "Characterisation and optimisation of alternating current thin film electroluminescent displays." Thesis, Nottingham Trent University, 2014. http://irep.ntu.ac.uk/id/eprint/84/.
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This Thesis presents research undertaken to investigate the electro-optical characterisation and optimisation of Thin Film Electroluminescent (TFEL) devices and Laterally Emitting Thin Film Electroluminescent (LETFEL) devices with respect to device lifetime and aging. Post deposition localised laser annealing as an alternative to thermal annealing has been previously described in the literature. The effects of laser annealing on various devices is investigated and described within this Thesis. In particular, the novel use of ArF laser annealing at a wavelength of 193nm as a post deposition annealing process for ZnS:Mn thin films deposited by RF magnetron sputtering has been presented and compared to KrF laser annealing (248nm wavelength). Additionally the use of KrF laser annealing on a new deposition method, High Target Utilisation Sputtering (HiTUS) is presented, with successful results obtained on heat sensitive substrates. Results presented show that the use of KrF produces slightly better performance in respect to maximum luminance, however the use of ArF laser annealing can allow for achievement of higher luminance at lower applied voltages. Research is also presented regarding methods for tackling the issue of reduced performance of devices over time. Investigations are undertaken to determine the extent to which the burn-in parameters used affect the lifetime of devices. A series of experiments in which the step-time, voltage and therefore overall burn-in time are altered are described. Results show that the lifetime of the device can be significantly altered by small changes to these parameters, with significant improvements in lifetime observed and described. As a result of the experiments and analysis described in this Thesis, areas for further research are suggested with the aim of further device optimisation in regards to post deposition heat treatment and the burn-in process.
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Bloomfield, Aaron Paul. "A High Frequency Alternating Current Battery Heater for Military Vehicles." University of Toledo / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1302312903.
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Fröbel, Markus. "Novel Concepts For Alternating Current Operated Organic Light-Emitting Devices." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-221652.
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Inorganic alternating current electroluminescent devices (AC-ELs) are known for their ruggedness and extreme long-term reliability, which is why they can often been found in industrial and medical equipment as well as in applications in the military sector. In contrast to the inorganic phosphors used in AC-ELs, organic materials offer a number of advantages, in particular a significantly higher efficiency, easier processibility, and a wide selection of emitter materials spanning the entire visible spectrum. Several efforts towards alternating current driven organic light-emitting devices have recently been made, however, important operating mechanism are still not well understood. In the first part of this theses, alternating current driven, capacitively coupled, pin-based organic light-emitting devices are investigated with respect to the influence of the thickness of the insulating layer and the intrinsic organic layer on the driving voltage. A three-capacitor model is employed to predict the basic behavior of the devices and good agreement with the experimental values is found. The proposed charge regeneration mechanism based on Zener tunneling is studied in terms of field strength across the intrinsic organic layers. A remarkable consistency between the measured field strength at the onset point of light emission (3–3.1 MV/cm) and the theoretically predicted breakdown field strength of around 3 MV/cm is obtained. The latter value represents the field required for Zener tunneling in wide band gap organic materials according to Fowler-Nordheim theory. In a second step, asymmetric driving of capacitively coupled OLEDs is investigated. It is found that different voltages and/or pulse lengths for positive and negative half-cycle lead to significant improvements in terms of brightness and device efficiency.
Part two of this work demonstrates a device concept for highly efficient organic light-emitting devices whose emission color can be easily adjusted from, e.g., deep-blue through cold-white and warm-white to saturated yellow. The presented approach exploits the different polarities of the positive and negative half-cycles of an alternating current driving signal to independently address a fluorescent blue emission unit and a phosphorescent yellow emission unit vertically stacked on top of each other. The electrode design is optimized for simple fabrication and driving and allows for two-terminal operation by a single source. The presented approach for color-tunable OLEDs is versatile in terms of emitter combinations and meets application requirements by providing a high device efficiency of 36.2 lm/W, a color rendering index of 82 at application relevant brightness levels of 1000 cd/m², and warm-white emission color coordinates.
The final part demonstrates an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows to efficiently generate every color that is a superposition of spectra of the individual emission units. The device is built in a top-emission geometrywhich is highly desirable for display fabrication as the pixel can be directly deposited onto the back-plane electronics. Furthermore, the presented device design requires only three independently addressable electrodes which simplifies fabrication and electrical driving.
The electrical performance of each individual unit is on par with standard pin single emission unit OLEDs, showing very low leakage currents and achieving high brightness levels at moderate voltages of around 3–4 V.
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Tidd, Chad N. "Hardware model of a shipboard Zonal Electrical Distribution System (ZEDS) Alternating Current/Direct Current (AC/DC)." Thesis, Cambridge Massachusetts Institute of Technolog, 2010. http://hdl.handle.net/10945/4936.
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CIVINSApproved for public release; distribution is unlimited
A hardware model of a shipboard electrical distribution system based on aspects of the DDG 51 Flight IIA, Arleigh Burke class, 60Hz Alternating Current (AC) and the future direct current (DC), zonal electrical distribution system (ZEDS). These distribution boards were designed and built for the purpose of testing electrical system components at the Massachusetts Institute of Technology's Laboratory for Electromagnetic and Electronic Systems (LEES). Two 5 kW generators serve as electrical generation for the ZEDS benchtop emulator boards. The hardware models support experimentation with AC and DC ZEDS power loading and protection. The hardware models reflect the AC ZEDS architecture employed on the DDG-51 class destroyers. The emulator is a three phase electrical system with both port and starboard buses, a computer interface to control the generators and contactors or solid state relays through a graphic user interface (GUI). The system is capable of being configured and operated in a split plant, parallel or single generator plant configuration.
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Tidd, Chad N. (Chad Norman). "Hardware model of a shipboard zonal electrical distribution system (ZEDS) : alternating current/direct current (AC/DC)." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61908.
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Thesis (Nav. E.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering; and, (S.M. in Engineering and Management)--Massachusetts Institute of Technology, Engineering Systems Division, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 91-92).
A hardware model of a shipboard electrical distribution system based on aspects of the DDG 51 Flight IIA, Arleigh Burke class, 60Hz Alternating Current (AC) and the future direct current (DC), zonal electrical distribution system (ZEDS). These distribution boards were designed and built for the purpose of testing electrical system components at the Massachusetts Institute of Technology's Laboratory for Electromagnetic and Electronic Systems (LEES). The combination of existing electrical generators and the newly created electrical distribution boards will provide a hereto unattained level of access for testing and evaluating a number of research topics currently being worked on at LEES. The level of reality inherent in this system will enable the user to refine experimental hardware and software in a safe and controlled environment. The user will benefit from a quicker product development process. Additionally, the ability to easily produce verifiable records to demonstrate the effectiveness/applicability of their individual experiments will help to progress research at LEES along the product development path. Two 5 kW generators serve as electrical generation for the ZEDS benchtop emulator boards. The hardware models support experimentation with AC and DC ZEDS power loading and protection. The hardware models reflect the AC ZEDS architecture employed on the DDG-51 class destroyers. The emulator is a three phase electrical system with both port and starboard buses, a computer interface to control the generators and contactors or solid state relays through a graphic user interface (GUI). The system is capable of being configured and operated in a split plant, parallel or single generator plant configuration.
by Chad N. Tidd.
S.M.in Engineering and Management
Nav.E.
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Chaichimansour, Mohammad. "Electro-optical characterization of alternating-current thin-film electroluminescence (ACTFEL) devices." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/15502.
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Wu, Zhenkun. "Metal-reduced graphene oxide for supercapacitors and alternating current line-filters." Diss., Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/53941.
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We design a facile approach to investigate the role benzene derivatives play in the capacitance enhancement of graphene-based supercapacitors. The main reason is attributed to the pseudocapacitance of the aromatic molecules rather than the former one. Meanwhile, we find that the para and ortho substituted benzene derivatives contribute much more than the meta substituted ones.
In addition, we fabricate an all-solid-state flexible MSC based on metal-reduced GO. The as-fabricated MSC shows high areal capacitance and excellent reliability, which makes it a promising energy storage candidate for wearable electronics. Based on the work of MSC, we achieve a flexible ac line-filter that is not only competitive against commercial product but also suitable for mass production.
Meanwhile, we produce a three-dimensional graphene/polydimethylsiloxane composite that gives a thermal resistance as small as 14 mm2K/W, which is comparable to commercial products. What’s more, a convenient transient program that saves much time is developed to measure the thermal resistance.
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Vyakaranam, Bharat GNVSR. "DYNAMIC HARMONIC DOMAIN MODELING OF FLEXIBLE ALTERNATING CURRENT TRANSMISSION SYSTEM CONTROLLERS." Cleveland State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=csu1324673091.
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Henz, Dieter. "Heating Effect of Alternating Current on Lithium-IonBatteries at Subzero Temperatures." Thesis, KTH, Maskinkonstruktion (Inst.), 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-226325.
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Electrification of transport is a distinct goal of many authorities. Electric vehicles are locally emission-free and can help to improve the air quality in cities. Despite several stimuli to promote electric vehicles, customers do not accept them at the desired level. One reason is the poor ratio between driving range and purchase cost. One possibility to tackle this poor ratio is to reduce complexity and weight of a battery pack, which helps to reduce its costs while increasing the driving range at the same time. Recent batteries in electric vehicles use lithium-ion technology. This type of batteries have a limited operating temperature, which requires pre-heating in cold ambient. In many electric vehicles pre-heating is realized with a heating element in the battery pack. This heating element does not only bring along additional weight but requires extra energy for distributing the heat. The idea of this study is to propose a more efficient heating method which is called alternating current (AC) heating. This method uses the internal impedance of a battery to generate dissipative heat, heating it up from inside. This work consists of practical measurements and experiments on a cell level as well as simulations. First, a literature research is conducted to present the latest heating technologies. Then, an impedance measurement is performed. The result of the impedance measurement is used to define the operating points for the following experiment. The experiment shows how AC frequency and amplitude influence the heating effect. The results from the impedance measurement and the experiment are further used to construct a cell simulation model that connects the thermal properties with the electrical properties. After verification of the model, the simulation is expanded to a battery pack level. The conclusion of the study is that it is generally possible to heat lithium-ion batteries with alternating current. Lower frequencies provide better heating effect at the same current amplitude and a higher current amplitude gives better heating effect than lower amplitudes. Therefore, the study also shows that further research is necessary to determine how the AC frequency affects aging of lithium-ion batteries at low temperatures. Finally, a method for increasing the current amplitude is proposed.Att göra trafiken eldriven är ett tydligt mål hos många myndigheter i hela världen. Lokalt sett är elektriska fordon utsläppslösa och kan därför bidra till att förbättra luftkvaliteten i snabbt växande städer. Trots att det finns många anledningar till att stödja elektriska fordon accepterar konsumenterna dem inte på en önskad nivå. En grund till den låga populariteten är det dåliga förhållandet mellan körsträcka och inköpskostnad. En möjlighet till att förbättra förhållandet är att minsta antalet komponenter i batteripaketet, eftersom kostnaderna då sjunker samtidigt som körsträckan ökar. Moderna batterier i elektriska fordon bygger på litiumjon teknologin. Denna typ av batterier har ett begränsd brukstemperaturområde och behöver därför värmas upp vid kalla förhållanden. I många elektriska fordon blir batteriet uppvärmt via ett eget värmeelement som byggs in i batteripaketet. Detta värmeelement orsakar mer komplexitet och behöver energi för att fördela värmen över batteriet. I den här studien undersöks möjligheten att använda en ny metod som kallas växelströmvärmning. Denna metod utnyttjar värmeutvecklingen i batteriets inre impedansen för att värma upp batteriet inifrån. Arbetet innehåller både en praktiskt del och en del med simulationer. En litteraturstudie över moderna uppvärmningsmetoder är presenterad i början av rapporten. Efter det finns en impedansmätning av två battericeller. Därefter testas olika driftpunkter för att bestämma hur växelströms frekvens och amplitud påverkar uppvärmningseffekt i en cell. Resultatet av impedansmätningen används för att bestämma driftpunkter för ett följande experiment och härleda ett ekvivalentskrets-schema för en battericell. Studiens slutsats är att det i allmänhet är möjligt att värma litiumjonbatterier med växelström. Låga frekvenser har bättre uppvärmningseffekt på samma strömamplitud och höga strömamplituder har bättre effekt än låga strömamplituder. På grund av detta visar studien också att det behöver genomföras flera undersökningar som fokuserar på hur frekvensen är kopplad med åldringen av batterikapaciteten vid låga temperaturer. Avslutningsvis presenteras en idé som visar hur det är möjligt att höja strömmen i batteriet för att förbättra uppvärmningseffekten.
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Hagen, Catalina H. Musinoi. "The Influence of Alternating Current on the Polarization Behavior of Stainless Steels." Thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for kjemi, 2013. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-22419.
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In later years direct electrical heating (DEH) based on the use of alternating current (AC) has replaced traditional chemical based methods for hydrate formation control in subsea flow lines. The problem with the AC-method is the increased risk of corrosion. A number of publications have been presented on the effect of AC on carbon steel since the early 1900s and there is a general understanding that higher alternating currents lead to higher risk of AC corrosion. However the mechanism is still not completely understood and besides - little is known about the AC-induced corrosion on stainless steels. The purpose of this study is to provide accurate and thorough understanding of the mechanism and severity of applied AC on steels in general and stainless steels in particular. The cathodic polarization behavior of 316L stainless steel has been studied and compared with the polarization behavior of X65 carbon steel, at the direct current (DC) potentials -800 mV and -1050 mV (SCE) for a range of applied AC current densities - from 0 to 1000 A/m2 . An investigation of the passivity of stainless steels with and without AC was carried out on 25Cr under open circuit conditions and under anodic bias. A total of 55 experiments were performed in 3.5 wt% sodium chloride (NaCl) for this study. The experiments were conducted at 25 oC with a stagnant working electrode and lasted 96 hours at the most. The current responses were recorded. Weight losses were measured. Surface morphologies were studied both visually, with Scanning Electron Microscopy (SEM) and Energy-dispersive spectroscopy (EDS). Cathodic current densities for 316L were found to increase with one order of magnitude at -800 mV and two orders of magnitude at -1050 mV when AC was increased from 0 to 1000 A/m2. The highest cathodic current density, 3.35*10-3 A/cm2, was found for 316L at -1050 mV and 1000 A/m2 AC. The highest corrosion rate (CR) for 316L - 0.113 mm/y - was measured at -800 mV and 1000 A/m2AC. Cathodic current densities for X65 were found to be of same magnitude at -800 mV, but increased with one order of magnitude at -1050 mV when AC was increased from 0 to700 A/m2. The highest cathodic current density for X65 was 2.18 *10-3 A/cm2 at -1050 mV and 700 A/m2 AC. The highest CR for X65, 0.205 mm/y and 0.236 mm/y, were measured when 500 A/m2 AC was applied at -800 mV and -1050 mV respectively. When AC densities higher than 100 A/m2 were applied on 25Cr, hydrogen evolution was found to control the corrosion kinetics and the passive region disappeared.The results indicate a significant acceleration of cathodic kinetics with applied AC. Weight loss measurements indicate also an increase in the corrosion rate with applied AC. However, the cathodic reaction rates were much higher than the anodic reaction rates at the applied DC potentials. The results implicate that the presence of AC decreases the effectiveness of cathodic protection systems. A possible model for the AC mechanism has been proposed.
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Wung, Peter Yu-Pu. "Operating point dependent modeling of synchronous reluctance motors and its implication on vector controlled motor performance." Diss., Georgia Institute of Technology, 1993. http://hdl.handle.net/1853/15042.
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余志偉 and Chi-wai Yu. "An axial field inductor alternator." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1986. http://hub.hku.hk/bib/B31208022.
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吳熾華 and Che-wa Ng. "An advanced ac drive system for an electric van." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1990. http://hub.hku.hk/bib/B31231937.
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Ng, Che-wa. "An advanced ac drive system for an electric van /." [Hong Kong : University of Hong Kong], 1990. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12691276.
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White, Terence H. "A three-phase hybrid dc-ac inverter system utilizing hysteresis control." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2004. http://library.nps.navy.mil/uhtbin/hyperion/04Jun%5FWhite%5FTerence.pdf.
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Bichaud, Emmanuelle. "Frittage « flash » de céramiques sous courant alternatif." Thesis, Université Grenoble Alpes (ComUE), 2016. http://www.theses.fr/2016GREAI028/document.
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Le procédé de frittage ultra rapide « flash sintering » a vu le jour il y a cinq ans. Cette technique permet le frittage de céramiques conductrices en moins de 5 secondes, avec des températures de four beaucoup plus basses que le frittage conventionnel. L’utilisation des capacités du flash sintering en tant que procédé nécessite d’en comprendre les mécanismes, qui sont encore mal connus et très discutés. L’objectif cette thèse est la compréhension du phénomène de flash sintering et de son origine. Les travaux se sont concentrés sur la zircone et les composites alumine-zircone, et sur les phénomènes observés lorsqu’un champ électrique constant est appliqué. Ils s’appuient sur deux types d’expériences : le chauffage à vitesse constante et le frittage en palier de température. Une attention particulière a été portée à la conductivité effective des matériaux. En s’appuyant sur le frittage conventionnel de ces matériaux et des mesures d’évolution de leur conductivité, ce travail a permis de montrer que l’origine du frittage ultrarapide est la puissance dissipée par effet Joule dans le matériau. Cette dissipation couplée à l’activation thermique de la conductivité ionique provoque un emballement couplé de la température et du courant électrique. Cette interprétation est en accord avec l’ensemble des données expérimentales, qui ne nécessitent pas l’existence d’autres effets du courant ou du champ, même s’ils ne peuvent être exclus a priori“Flash sintering” is an ultrafast sintering technique which enables the densification of conductive ceramics in less than 5 seconds, using furnace temperatures far below the usual temperatures required by pressureless sintering. The use of flash sintering as an industrial technique however needs understanding the involved mechanisms, which are still widely controversial.This PhD work aims at understanding the flash sintering phenomenon and its origin. The investigations have been focused on zirconia and zirconia-alumina composites, and on the phenomena observed when a constant electric field is applied. They are based on two types of experiments: constant heating rate and isothermal stage sintering. Particular attention was paid to the effective conductivity of the materials. Using the knowledge on conventional sintering of the studied materials and measurements of the evolution of their conductivity with temperature, the present work shows that ultrafast sintering is mainly driven by the Joule power dissipated inside the material. This dissipation, coupled with the thermally activated conductivity, leads to thermal and electrical runaway. This analysis is consistent with the whole set of experimental data obtained in this work, which do not need any specific effects of current and/or electrical field to explain the results, although such effects cannot be excluded
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Chapariha, Mehrdad. "Modeling alternating current rotating electrical machines using constant-parameter RL-branch interfacing circuits." Thesis, University of British Columbia, 2013. http://hdl.handle.net/2429/45565.
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Transient simulation programs are used extensively for modeling and simulation of various electrical power and energy systems that include rotating alternating current machines as generators and motors. In simulation programs, traditionally, the machine models are expressed in qd-coordinates (rotational reference frame) and transformed variables, and the power networks are modeled in abc-phase coordinates (physical variables), which represents an interfacing problem. It has been shown in the literature that the method of interfacing machine models and the electric network models plays an important role in numerical accuracy and computational performance of the overall simulation.
This research considers the state-variable-based simulation programs and proposes a unified constant-parameter decoupled RL-branch circuit in abc-phase coordinates (with optional zero-sequence). The proposed circuits are based on voltage-behind-reactance (VBR) formulation and can be used for interfacing both induction and synchronous machine models. The new models achieve a direct and explicit interface with arbitrary external electrical networks, which results in many computational advantages. Extensive computer studies are presented to verify the proposed models and to demonstrate their implementation in several commonly-used simulation programs. The new models are shown to offer significant improvements in accuracy and numerical efficiency over the existing state-of-the-art models due to their direct interface. It is further envisioned that the proposed models will receive a wide acceptance in research community and simulation software industry, and may enable the next generation of power systems simulation tools.
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Vossen, Alexandra Yvonne. "Modulation of neural oscillations and associated behaviour by transcranial Alternating Current Stimulation (tACS)." Thesis, University of Glasgow, 2017. http://theses.gla.ac.uk/7958/.
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Transcranial alternating current stimulation (tACS) is a non-invasive brain stimulation method that involves the application of weak electric currents to the scalp. tACS has the potential to be an inexpensive, easily administrable, and well-tolerated multi-purpose tool for cognitive and clinical neuroscience as it could be applied to establish the functional role of rhythmic brain activity, and to treat neural disorders, in particular those where these rhythms have gone awry. However, the mechanisms by which tACS produces both "online" and "offline" effects (that is, those that manifest during stimulation and those that last beyond stimulation offset) are to date still poorly understood. If the potential of tACS is to be harnessed effectively to alter brain activity in a controlled manner, it is fundamental to have a good understanding of how tACS interacts with neuronal dynamics, and of the conditions that promote its effect. This thesis describes three experiments that were conducted to elucidate the mechanisms by which tACS interacts with underlying neural network activity. Experiments 1 and 2 investigated the mechanism by which tACS at alpha frequencies (8 12 Hz, α-tACS) over occipital cortex induces the lasting aftereffects on posterior α power that were previously described in the literature. Two mechanisms have been suggested to underlie alpha power enhancement after α tACS: entrainment of endogenous brain oscillations and/or changes in oscillatory neural networks through spike timing-dependent plasticity (STDP). In Experiment 1, we tested to what extent plasticity can account for tACS-aftereffects when controlling for entrainment characteristics. To this end, we used a novel, intermittent α-tACS protocol and investigated the strength of the aftereffect as a function of phase continuity between successive tACS episodes, as well as the match between stimulation frequency and individual alpha frequency (IAF). Alpha aftereffects were successfully replicated with enhanced α power after intermittent stimulation compared to sham. These aftereffects did not exhibit any of the expected characteristics of prolonged entrainment in that they were independent of tACS phase-continuity and did not show stable phase alignment or synchronisation to the stimulation frequency. These results indicate that prolonged entrainment is insufficient to explain the aftereffects and suggest that the latter emerge through some form of network plasticity. To clarify the nature of these plasticity mechanisms, we then aimed to assess whether STDP could explain the α power increase. We developed a conceptual STDP model that predicted bi-directional changes in α power depending on the relative mismatch between the tACS frequency and IAF. After observing in Experiment 1 that tACS at frequencies slightly lower than the IAF produced α enhancement, Experiment 2 used a similar intermittent protocol that manipulated tACS frequency to be either slightly lower or higher than IAF to respectively enhance or suppress α activity. In addition, a control condition with continuous stimulation aimed to replicate previous results from other groups. However, we did not observe a systematic α power change in any of the active conditions. The lack of consistency between the two experiments raises concerns regarding the reproducibility and effect size of tACS aftereffects. The third experiment investigated the mechanism of online effects and tested predictions that were based on the assumption that entrainment is the underlying process mediating behavioural changes during tACS. We capitalised on two well-described phenomena: firstly, the association between α power lateralisation and visuospatial attention, and secondly, the fluctuation of perceptual performance with α phase. Specifically, the experiment tested whether event-related α-tACS applied over right parieto-occipital cortex can induce a visuospatial bias in a peripheral dot detection task that would reflect α power lateralisation, and whether detection performance depends on the phase of the tACS waveform. In control trials either no tACS or 40 Hz-tACS (gamma) was applied to make use of the putative opposing roles of alpha and gamma oscillations in visual processing. As expected from lateralised enhancement of alpha oscillations, visual detection accuracy was weakly impaired for targets presented in the left visual field, contralateral to tACS. However, this effect was neither frequency specific nor waveform phase-dependent. Therefore, it is unlikely that the negative effect of tACS on visuospatial performance reflects entrainment. Overall, the results of these experiments only partially met our hypotheses. Experiment 1 produced the α enhancement that was expected based on the literature while the follow-up experiment failed to reproduce these results under similar conditions. This outcome demonstrates at best that tACS aftereffects on α activity are not robust, may vary widely across individuals, and might be extremely sensitive to small changes in experimental parameters and state variables. The results of the third experiment call into question the assumption of online entrainment as basis for the observed behavioural effect. These findings point to the need for improved methodology, for more systematic and exhaustive exploration of the relative effects of tACS across different parameter settings, tasks, and individuals; and for the replication of promising but thus far often anecdotal results. They also inspire guidelines for more informative experimental designs.
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Zaporozhchenko, A., S. A. Nepijko, and G. Schonhense. "Influence of alternating low voltage component on field photoemission current forma semiconductor tip." Thesis, Sumy State University, 2014. http://essuir.sumdu.edu.ua/handle/123456789/39931.
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In this work we considered the influence of low alternating voltage of up to 100 V on the field photoemission process from a semiconductor tip under high voltage of 0.7-5.0 kV and photon excitation of 1.3 eV energy.
Considered cathodes were made of high-resistivity silicon with p-type conductivity.
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Lamanda, Ariana Corinne. "Alternating Current Electrokinetic Manipulation and Concentration of Free Circulating DNA from Blood Samples." Thesis, The University of Arizona, 2014. http://hdl.handle.net/10150/332828.
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Molecular analysis of free circulating (fc)DNA has the potential to change the face of medicine, specifically in cancer diagnostics and in monitoring the efficacy of cancer treatments. In this study, a microfluidic device using AC electrokinetics is developed for rapid concentration and detection of fcDNA from blood. The device concentrates fcDNA using a combination of AC electrothermal flow and dielectrophoresis. The electrothermal fluid motion drives fcDNA towards the center of the electrode where dielectrophoretic trapping occurs. Once fcDNA is collected at the center, the concentration in the sample can be determined by fluorescent analysis using an intercalating dye binding to the double-stranded DNA. Effects of operating parameters are investigated to optimize the device's design. The electrokinetic device isolates high molecular weight DNA and can distinguish from low molecular weight DNA. Quantitative detection of fcDNA in physiologically relevant concentrations is demonstrated toward rapid diagnostics of cancer and monitoring of treatment efficacy.
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Zhang, Lei, and 張磊. "First principle calculation: current density in AC electric field." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43278437.
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Zhang, Lei. "First principle calculation : current density in AC electric field /." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43278437.
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Antaloae, C. C. "Feasibility of high frequency alternating current power distribution for the automobile auxiliary electrical system." Thesis, Cranfield University, 2011. http://dspace.lib.cranfield.ac.uk/handle/1826/6792.
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This study investigates the feasibility and potential benefits of high frequency
alternating current (HFAC) for vehicle auxiliary electrical systems.
A 100Vrms, 50kHz sinusoidal AC bus is compared with 14V DC and 42V DC electrical
systems in terms of mass and energy efficiency. The investigation is focused on the four
main sub-systems of an on-board electrical network, namely: the power generation,
power distribution, power conversion and the electrical loads. In addition, a systemlevel
inquiry is conducted for the HFAC bus and a comparable 42V DC system.
A combination of computer simulation, analytical analysis and experimental work has
highlighted benefits for the HFAC power distribution sub-system and for low-torque
motor actuators. Specifically, the HFAC conductor mass is potentially 70% and 30%
lighter than comparable 14V DC and 42V DC cables, respectively. Also, the proposed
cable is expected to be at least 80% more energy efficient than the current DC
conductor technology. In addition, it was found that 400Hz AC machines can
successfully replace DC motor actuators with a rated torque of up to 2Nm. The former
are up to 100% more efficient and approximately 60% lighter and more compact than
the existing DC motors in vehicles. However, it is argued that the HFAC supply is not
feasible for high-torque motor actuators. This is because of the high energy losses and
increased machine torque ripple associated with the use of HFAC power.
The HFAC power conversion sub-system offers benefits in terms of simple power
converter structure and efficient HFAC/DC converters. However, a significant limitation
is the high power loss within HFAC/AC modules, which can be as high as 900W for a
2.4kW load with continuous operation. Similar restrictions are highlighted for the
HFAC power generation sub-system, where up to 400W is lost in a 4kW DC/HFAC
power module.
The conclusion of the present work is that the HFAC system offers mass and energy
efficiency benefits for the conventional vehicle by leveraging the use of compact lowtorque
motor actuators and lightweight wiring technology.
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Otero, Barros Sara. "Enhancement of the light outcoupling of alternating current laterally emitting thin film electroluminescent devices." Thesis, Nottingham Trent University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314336.
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Wang, Zheng, and 王政. "Chaoization and stabilization of electric motor drives and their industrial applications." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2008. http://hub.hku.hk/bib/B40687594.
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Wang, Zheng. "Chaoization and stabilization of electric motor drives and their industrial applications." Click to view the E-thesis via HKUTO, 2008. http://sunzi.lib.hku.hk/hkuto/record/B40687594.
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Pei, Ruilin. "Measurement and analysis of critical current and AC loss of HTS tapes in a superconducting machine." Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609019.
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Mukhedkar, Radnya A. "Flexible alternating current transmission systems for the prevention of voltage collapse in electrical power systems." Thesis, University of the West of England, Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.252564.
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Meier, Jan Verfasser], and Christoph [Akademischer Betreuer] [Mulert. "Modulation of Interhemispheric Auditory Communication by Transcranial Alternating Current Stimulation / Jan Meier ; Betreuer: Christoph Mulert." Hamburg : Staats- und Universitätsbibliothek Hamburg, 2020. http://nbn-resolving.de/urn:nbn:de:gbv:18-103775.
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Fitzpatrick, Rose. "Transcranial alternating current stimulation over the pre-SMA and rIFG can improve response inhibition performance." Thesis, Fitzpatrick, Rose (2018) Transcranial alternating current stimulation over the pre-SMA and rIFG can improve response inhibition performance. Honours thesis, Murdoch University, 2018. https://researchrepository.murdoch.edu.au/id/eprint/41750/.
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Response inhibition refers to the ability to withhold or cancel a dominant action, and plays a vital role in daily functioning and safety. However, the exact neural mechanisms underpinning response inhibition still require further elucidation. Previous neurophysiological research has found the pre-supplementary motor area (pre-SMA) and the right inferior frontal gyrus (rIFG) are involved in response inhibition, with evidence showing that they work together for successful inhibitory control. The current study aimed to explore if transcranial alternating current stimulation (tACS) could improve response inhibition performance by synchronising oscillatory activity between the pre-SMA and rIFG to facilitate communication. It also aimed to examine the effect of tACS on the P3 and the N2, event-related potentials (ERPs) that are commonly associated with response inhibition. Twenty-two right-handed participants, (mean age = 23.55 years, equal number of males and females) participated in a double-blind experiment. It consisted of two sessions with either synchronised or desynchronised tACS. Response inhibition was measured using a stop-signal task. The study found that synchronised tACS effectively improved response inhibition performance. However, there were no significant changes in the peak amplitudes or onset latencies of N2 and P3 as a result of stimulation. This study has shown tACS is effective at improving response inhibition performance when synchronised stimulation is applied to two regions involved. This approach should be built upon by future research to develop tACS into a treatment tool for improving response inhibition.
Keywords: response inhibition, transcranial alternating current stimulation, tACS, stop-signal task, SST, N2, P3
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Tsao, Yu-Che, and 曹宇喆. "Asymmetric alternating current electrophoretic deposit graphene." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/rauk7u.
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碩士國立彰化師範大學
機電工程學系所
105
In this study, graphene oxide (GO) was prepared by Hummer method using natural graphite powder as raw material. The graphene film was prepared by using asymmetric AC electrophoresis with Advantac # 1 filter paper as the substrate, and the graphene film was prepared by using reduced graphene oxide (rGO) after hydrogen reduction. The effect of AC electrophoresis on the conductivity of this graphene coating was discussed. The composition of the carbon atoms and the chemical bonding of the surface impurity atoms were analyzed by Raman and FTIR. The initial AC electrophoresis deposition experiment was carried out to adjust and design a fixed AC electrophoresis output signal. The electrophoresis time was fixed for 2 hours. The AC voltage peak was changed to the peak and frequency parameters, and the lowest chip resistance value was found. The results show that the chip resistance increases irregularly with the decrease of the peak value of the output voltage and the decrease of the output frequency, and the decrease of the output voltage and the decrease of the output frequency will cause the chip resistance of the graphene film The value of more and more difficult to control. In this experiment, the lowest sheet resistance value of 0.9 Ω / can be obtained at 400 V with 350 Hz.
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Hsiang, Yeh-Cheng, and 葉呈祥. "Alternating Current Prediction For Digital Watermarking System." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/27685847764197930679.
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碩士開南大學
資訊管理學系
96
Digital Watermarking is mainly applied for the protection of intellectual property. It undergoes several processing to embed watermark into multimedia such as test file, static images, dynamic images and audio signals for purpose of protecting intellectual property. This article proposes a kind of blind watermarking technique which information is embed without access to the host data. This paper uses the Integer Discrete Cosine Transformation (IntDCT) which is used in the H.264 translate algorithm. Three new watermarking systems are proposed. In this paper the first method is to select every nine 4×4 blocks as one group, in which watermark bits can be embedded by modulating the AC(0,1),AC(1,0). The second method is to select every nine 4×4 blocks as one group, in which watermark bits can be embedded by modulating the AC(1,1). The third is to select every nine 4×4 blocks as one group, in which watermark bits can be embedded by modulating the AC(1,1) according to the rule of DC value in the center block. The experiments show that the first and second methods are robust. The third method is robust against compression attacks, but is vulnerable other attacks. It is a good kind of weak watermarking system.
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Ojo, Joseph Olorunfemi. "Saturation effects in alternating current electric machines." 1987. http://catalog.hathitrust.org/api/volumes/oclc/17003368.html.
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Thesis (Ph. D.)--University of Wisconsin--Madison, 1987.Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 150-160).
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Chang, Song Chu, and 張松助. "Development of Current Sensorless Vector-Controlled Drives for Alternating Current Machines." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/47809802227271793549.
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博士國立臺灣科技大學
電機工程研究所
84
This dissertation presents a novel method for controlling a current sensorless AC drive using partial state estimator to estimate the torque current and a voltage predictor to predict the voltage of voltage source inverter(VSI).. The proposed method is applied to an induction motor and a permanent-magnet synchronous motor(PMSM) speed control systems. In the induction motor speed control system, a speed controller, a torque current estimator, a voltage-predictive voltage-source inverter( VPVSI) and a slip calculator are included, while in the PMSM speed control system, a speed controller, a torque current estimator and a VPVSI are adopted. A new speed control method, sliding mode proportional integral structure, is also presented. Fast response and adaptive field weakening feature above the base speed of induction motor are achieved through a direct software control system based on field orientation with recursive operation between partial state estimation and voltage prediction. A concurrent programming method, multi- task time-sharing structure, is applied in the direct software control program. This results in high efficiency and easy maintenance features for the program. Besides low cost, the simplicity of the proposed hardware system yields high reliability and good maintainability.
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陳奕安. "Study of Alternating Current Type Megneto-hydrodynamic Pump." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/26454626501530092117.
Full textAbstract:
碩士國立清華大學
動力機械工程學系
98
The objective of this thesis is to investigate the basic structure of alternating-current type Magneto-hydrodynamic (MHD) pumps. Driven by Lorenz Force based upon the interactions of magnetic and electric field, the pumps maintain alternating magnetic and electric field to suppress the electrolysis in electrolyte. A magneto-static field is generated inside a ring made of Halbach Array for providing a strong and uniform magnetic field inside the large air-gap. Then, rotating Halbach Array generates the alternating field inside the stationary air-gap. Two electrodes further provide the alternating electric field for synchronization of electric current to the alternating magnetic field. With a MHD pump made of plastics tube by 5 by 10 mm in width and height, this study has focused on the velocity of fluids made of various concentrations in NaCl solutions ranging from 0.15 M (biocompatible Saline) to 2 M. The verifications on the ac MHD pumps explore the feasibility of bio-medical applications for future lab-on-chips potential.
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Ifill, Roy Oswald. "Alternating current electrocoagulation (AC/EC) of fine particulate suspensions." 2010. http://hdl.handle.net/10048/990.
Full textAbstract:
Thesis (Ph. D.)--University of Alberta, 2010.Title from pdf file main screen (viewed on June 18, 2010). A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Chemical Engineering, Department of Chemical and Materials Engineering, University of Alberta. Includes bibliographical references.
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Yuan, Quan. "OPTIMIZATION OF ALTERNATING CURRENT ELECTROTHERMAL MICROPUMP BY NUMERICAL SIMULATION." 2010. http://trace.tennessee.edu/utk_gradthes/762.
Full textAbstract:
Microfluidic technology has been grown rapidly in the past decade. Microfluidics can find wide applications in multiple fields such as medicine, electronics, chemical and biology. Micro-pumping is an essential part of a microfluidic system. This thesis presents the optimization process of AC electro-thermal micropump with respect to the geometry of electrode array and channel height.The thesis first introduces the theories of AC electrokinetic including dielectrophoresis, AC electro-osmosis (ACEO) and AC electro-thermal (ACET). Also presented are the basic theory and governing equations of microfluidics, the continuity equation, the Navier-Stokes equation, and the conservation of energy equation. AC electro-thermal effect results from the interplays between electric field, temperature field and fluid mechanics. Since the governing equations are highly non-linear, numerical simulation is extensively used to understand the effects of factors such as the electrode dimensions and channel height. By interfacing finite element analysis software COMSOL Multiphysics with Matlab, to the simulation model is able to scan the geometry variables so as to find the optimal micropump design. The optimization has been performed with respect to flow rate and power efficiency of the micropump.
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Ifill, Roy O. "Alternating current electrocoagulation (AC/EC) of fine particulate suspensions." Phd thesis, 2010. http://hdl.handle.net/10048/990.
Full textAbstract:
Poor settling of solids increases land requirement for tailings containment and imposes severe constraints on the water balance. Consequent to these considerations, the alternating current electrocoagulation (AC/EC) technique emerged as a candidate for enhancing the settling behaviour of suspensions in the mineral, coal and oil sands industries. Hence, a fundamental study of AC/EC was undertaken with aluminum electrodes. Ground silica (d50 = 20 m), which formed a stable suspension, served as the model tailings solid at 5.0 wt % in water.
The AC/EC process consisted of two developmental stages: coagulation, marked by pH decrease in the silica suspension; and floc growth, characterized by pH increase from the minimum (i.e., the end of coagulation). AC/EC enhanced the initial settling rate of silica by over three orders of magnitude, and exhibited remarkable flexibility by virtue of the wide range of process parameters that could be optimized. For example, AC/EC can be operated in either the indirect or direct mode. The settling behaviour of bentonite (estimated d50 < 1 m) was more enhanced by indirect AC/EC, while that of silica benefited more from direct AC/EC.
Any condition that increased aluminum dosage (e.g., current, retention time), increased the initial settling rate of silica. Over the feed water pH range of 3.0 to 9.1, AC/EC was effective in enhancing the settling behaviour of silica. AC/EC was also effective over a wide range of temperatures (23 to 85C).
High electrical energy demand by AC/EC was observed throughout this study. Its optimization was beyond the scope of this work.
Dilution of a sample of Syncrude mature fine tailings (MFT) to 4.6 wt % solids sustained a stable suspension. Settling occurred after AC/EC treatment, a crystal-clear supernatant resulted and bitumen was recovered as froth. Entrained solids were easily spray-washed from the froth with water.
The settling behaviour of a Luscar Sterco fine coal tailings sample was not augmented by AC/EC, possibly due to contamination by the companys own electrocoagulation operation.
After having been stored dry for more than a year, electrocoagulated silica was an effective coagulant for as-received silica and Syncrude MFT.Chemical Engineering
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Baukol, Beau. "Alternating-current thin-film electroluminescent device fabrication and characterization." Thesis, 2001. http://hdl.handle.net/1957/30102.
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Cleary, Bradford A. "Alternating-current thin-film electroluminescent device optical excitation experiments." Thesis, 1998. http://hdl.handle.net/1957/33448.
Full textAbstract:
This thesis investigates two methods of optical excitation of alternating-current
thin-film electroluminescent (ACTFEL) devices. The two experimental methods investigated in this thesis are the photo-induced charge (PIQ) and luminescence (PIL),
and the subthreshold-voltage induced transferred charge (VIQ) techniques. PIQ/PIL
experiments utilize an above-bandgap laser pulse to investigate the transport properties
of photo-injected electrons and holes within the phosphor layer of the ACTFEL
device. VIQ experiments use a broadband xenon lamp pulse to optically reset traps
which are ionized by subthreshold bipolar voltage pulses. Both experiments characterize
traps within the phosphor layer.
PIQ/PIL experiments are performed on evaporated ZnS:Mn ACTFEL devices
possessing phosphor layers with thicknesses of 950, 700, and 300 nm. From the
PIQ/PIL experiment, an impact excitation threshold electric field for evaporated
ZnS:Mn is found to be ~1 MV/cm. Evidence of hole-trapping is also obtained from
the PIQ experiment. The holes in evaporated ZnS:Mn ACTFEL devices are found
to possess a drift length of ~180 �� 70 nm, a hole lifetime of ~2 ps, and a capture
cross-section of ~7 x 10������� cm��. It is speculated that the trap responsible for hole
capture is a zinc vacancy or zinc vacancy complex.
VIQ experiments are performed on evaporated, atomic layer epitaxy [ALE] (Cl),
and ALE (DEZ) ZnS:Mn ACTFEL devices. Data obtained via VIQ experiments yield
evidence for the generation of space charge below the EL conduction threshold, as well
as providing a means of estimating the physical location, energy depth, density, and
capture cross-section of traps responsible for VIQ. The depth of the traps responsible
for VIQ in evaporated, ALE (C1), and ALE (DEZ) ZnS:Mn are estimated to be ~1.1,
~0.3, and ~0.8 eV, respectively. It is speculated that the traps responsible for VIQ
are due to sulfur vacancies, chlorine, and oxygen, for evaporated, ALE (Cl), and
ALE (DEZ), respectively.Graduation date: 1999