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An analysis of DC distribution systemsAjitkumar, Rohit 05 April 2011 (has links)
The Master's Thesis research focuses on analyzing the possibilities of using Direct Current distribution systems to distribute power to end users. Considering the shift in load types in the past few decades and also a growing demand of distributed generation, DC distribution can potentially offer higher efficiencies and cost savings to utilities. The incorporation of DC distribution offers the opportunity to eliminate multiple conversion stages for devices which are powered using DC electricity. The integration of power sources such as photovoltaics and fuel cells, which produce DC power, offer further incentives to consider the use of DC systems. Using DC systems can help eliminate the conversion losses associated with rectifiers and inverters which would be part of the infrastructure if AC distribution was used. In the literature, the study of DC distribution has been limited to customized systems. The objective of this research is to analyze DC distribution when applied to systems based on standard IEEE test feeder systems. The IEEE 13 node test feeder and the IEEE 37 node test feeder will be used as the basis for the analysis. Issues such as associated costs, protection and integration of appliances will also be addressed.
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Cellular electrofusion utilizing corona fields and DC pulse technologyStein, Joshua 01 June 2007 (has links)
Cell fusion is an important technique that is used in the field of medicine and biomedical research. For instance, fusion can be used to create hybridomas and novel types of secretory hybrid cells. It may also be used to engineer cultured insulin-secreting pancreatic B-cell lines for the treatment of diabetes. Historically, the applications listed above have been accomplished by a number of methodologies including dielectrophoresis, centrifugation, polyethylene glycol (PEG) and viral fusion proteins. However, these approaches often fail to produce the desired results due to poor cell viability, lack of 1:1 fusion, and use of non-physiological environments. It is proposed that the application of an electrical field generated by corona charge (corona fields) and subsequent treatment with direct current (DC) pulse technology will overcome these deficiencies. Isolated and pre-labeled neuronally committed human teratocarcinoma (NT2) cells in monoculture or co-culture, were seeded in chambers, constructed in the laboratory, and allowed to adhere to the chamber bottom prior to corona treatment.
A corona generator, also constructed in the laboratory, was used to expose cells to positive and negative electrical charges to induce cell-cell contact. The cells were then pulsed with DC voltage to induce fusion. During the experiments, cells were photographed sequentially to record cell movement/contact and fusion. The project was designed to identify optimal corona-based electrofusion parameters for viable, 1:1 cell fusion. Optimal results for cell-cell contact were obtained using a cell density of 2.35 times ten to the fourth power cells per microliter Dulbecco's Modified Eagle Medium (DMEM) in a grounded circular plate corona chamber following at least 3 minutes of settling time. Corona charges from (+) 6.1 kilivolt and (-) 5.5 kilivolt potentials were determined as being most favorable for cell movement and viability.
Fusion was best achieved by first exposing either a circular or square ungrounded corona chamber configuration to 3 minutes (+) corona charge followed by 3 minutes (--) corona charge; disturbing the cells in the chamber with mechanical force; and then exposing them to 8-15 sequences of a 2,500 Volts per centimeter DC pulse at 100 microseconds.
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Verstärkung des antinozizeptiven Effekts der kathodalen transkraniellen Gleichstromstimulation durch den Dopaminagonisten Pergolid / Enhancement of the antinozizeptive effect of cathodal trancranial direct current stimulation by the dopamine-agonist PergolideBergmann, Inga 11 May 2010 (has links)
No description available.
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Combining Transcranial Electrical Stimulation With Magnetic Resonance Imaging In Behavioural Measurements In Health And DiseaseSaiote, Catarina 31 January 2014 (has links)
No description available.
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Modulation Of Neuroplasticity In Humans By Advanced Stimulation Protocols And NeuromodulatorsBatsikadze, Giorgi 27 February 2014 (has links)
No description available.
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Plasma Characteristics of the DC Saddle Field Glow DischargeLeong, Keith R. 10 January 2014 (has links)
Plasma enhanced chemical vapor deposition systems are massively deployed to grow numerous thin film coatings including hydrogenated amorphous silicon. A new deposition chamber was designed, procured, and constructed to investigate the plasma properties of a 100% silane (SiH4) glow discharge with varying chamber pressure and inter-electrode spacing. A Hiden EQP1000 ion mass spectrometer sampled the plasma from the substrates point of view. Ion energy distributions were obtained using four different excitation sources +DC, –DC, radio frequency (at 13.56 MHz), and the DC Saddle Field (DCSF) in the tetrode configuration.
The shape of the ion energy distributions was constant for the capacitively coupled +DC, –DC, and rf (at higher pressures of 75 and 160 mTorr) glow discharges. The shape of the ion energy distributions for the DCSF plasma exhibited a double peak or saddle structure analogous to radio frequency plasmas. The width between the peaks (peak separation) was controlled by the pressure and the semi-transparent cathode to semi-transparent anode distance. Ion energy distributions from the DCSF plasma concurred with rf and +DC ion energy distributions at specific pressures and inter-electrode distances. This result demonstrates the versatility of the DCSF glow discharge system. Moreover, control of the peak separation is modeled to be
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equivalent to controlling the critical ratio (ion transit time in the sheath to the electron oscillating period), and/or the inferred electron oscillating sheath potential.
The DCSF possesses a fusion of rf and +DC methods. The long high energy tail or constant background are indicative of a +DC high voltage sheath in which there is an increasing fraction of collisionless ions as the anode-cathode distance increases. These collisionless ions are provided by the oscillating electrons (or rf nature) of the DCSF method. Higher order silane (silicon containing) ions increase in relative intensity with increasing inter-electrode spacing for the +DC, –DC, and rf plasmas. These higher order silane ions are also detected in the DCSF plasma, and can be reduced at either lower pressure or lower cathode to anode or cathode to substrate distances.
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Plasma Characteristics of the DC Saddle Field Glow DischargeLeong, Keith R. 10 January 2014 (has links)
Plasma enhanced chemical vapor deposition systems are massively deployed to grow numerous thin film coatings including hydrogenated amorphous silicon. A new deposition chamber was designed, procured, and constructed to investigate the plasma properties of a 100% silane (SiH4) glow discharge with varying chamber pressure and inter-electrode spacing. A Hiden EQP1000 ion mass spectrometer sampled the plasma from the substrates point of view. Ion energy distributions were obtained using four different excitation sources +DC, –DC, radio frequency (at 13.56 MHz), and the DC Saddle Field (DCSF) in the tetrode configuration.
The shape of the ion energy distributions was constant for the capacitively coupled +DC, –DC, and rf (at higher pressures of 75 and 160 mTorr) glow discharges. The shape of the ion energy distributions for the DCSF plasma exhibited a double peak or saddle structure analogous to radio frequency plasmas. The width between the peaks (peak separation) was controlled by the pressure and the semi-transparent cathode to semi-transparent anode distance. Ion energy distributions from the DCSF plasma concurred with rf and +DC ion energy distributions at specific pressures and inter-electrode distances. This result demonstrates the versatility of the DCSF glow discharge system. Moreover, control of the peak separation is modeled to be
iii
equivalent to controlling the critical ratio (ion transit time in the sheath to the electron oscillating period), and/or the inferred electron oscillating sheath potential.
The DCSF possesses a fusion of rf and +DC methods. The long high energy tail or constant background are indicative of a +DC high voltage sheath in which there is an increasing fraction of collisionless ions as the anode-cathode distance increases. These collisionless ions are provided by the oscillating electrons (or rf nature) of the DCSF method. Higher order silane (silicon containing) ions increase in relative intensity with increasing inter-electrode spacing for the +DC, –DC, and rf plasmas. These higher order silane ions are also detected in the DCSF plasma, and can be reduced at either lower pressure or lower cathode to anode or cathode to substrate distances.
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Bird streamer initiated breakdowns under HVDC conditions.Naidoo, Kribashen. January 2007 (has links)
This dissertation describes the role played by bird streamers in transmission line faults under HVDC conditions. The research was initiated due to the lack of knowledge of these faults under HVDC conditions. An explanation as to what bird streamers faults are, the role they play in the breakdown of air-gaps and a means of preventing bird streamer caused faults from occurring is made Experimental work has been carried out in order to gain an understanding of these faults under HVDC conditions. The overall aim of the experiments was to find a horizontal distance (protected zone) on an HVDC tower top, in order to prevent birds from perching around the centre of the tower. This will lead to a reduction of bird streamer caused faults. A brass rod was used as the artificial streamer in the experiments, under both negative and positive polarity (voltages in the range 0 to 220 kV DC were applied). Later in the experimental phase, a string soaked in a saline solution was used as a more realistic simulation of a bird streamer. QuickField™, an FEM package, was used to simulate the electric field in the region of the live conductor fitting and the tip of the bird streamer, to assess the degree of distortion of the electric field caused by the introduction of the bird streamer. These simulations served as means of verifying the laboratory experiments. This dissertation has proposed a relationship between the breakdown voltage and the protected zone length, based on the air-gap breakdown voltages for both I-String and V-String insulator configurations in the air-gap range 0 to 350 mm. These curves can be used in the design of transmission lines, as a means of reducing bird streamer faults. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, 2007.
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A study of fire-induced air-gap voltage breakdown characteristics under HVDC conditions.Ntshangase, Zola. January 2012 (has links)
This dissertation investigates the role that is played by high temperatures of air gaps on the
breakdown voltage levels under DC positive and negative polarity applied voltages. Due to
past experience of AC transmission lines tripping as a result of sugar-cane fires that occur
under these lines during cultivation seasons, this study was initiated to investigate this effect
under DC applied voltages.
Results were obtained from laboratory work conducted and these were closely analysed to
understand the behaviour of air gaps under these conditions. A 17mm2 square-cut brass rodrod
electrode configuration was used to carry out these tests at the various air gap
temperatures. These were induced by a gas burner for both the positive and negative
polarities at 200C – 3000C for the 10 mm – 150 mm air gap range and 200C – 1500C for the
200 mm – 500 mm air gap range. Later particles were introduced into the air gap to
determine the subsequent behaviour. These were introduced vertically from the top into an
air gap via a vibrating micro sieve mechanism to regulate the consistency of the introduction
of these particles in the air gap.
A reduction of 55% and 50% was observed on the breakdown voltage under positive and
negative polarity applied voltages respectively from ambient conditions to 3000C.
Additionally the breakdown behaviour of both negative and positive DC was found to be
linear which is similar to the AC case. However, air gaps subjected to positive DC applied
voltages were found to portray an inferior dielectric strength as opposed to the equivalent
negative DC polarity.
The study found that the effect of particles in the air gap is practically negligible and that for
practical purposes, only the temperature effect plays a role due to the reduced air density at
high temperatures.
Empirical models for both the positive and negative DC polarities have been proposed by the
study that incorporate the effect of the temperature in the air gap to enable the determination
or prediction of the breakdown voltage level at various temperatures. These models may be
utilised for DC transmission line design for servitudes in areas that are known to be prone to
fires. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2012.
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Maximum power point tracking algorithm for photovoltaic home power supply.Nkashama, Cedrick Lupangu. January 2011 (has links)
Solar photovoltaic (PV) systems are distributed energy sources that are an environmentally friendly
and renewable source of energy. However, solar PV power fluctuates due to variations in radiation
and temperature levels. Furthermore, when the solar panel is directly connected to the load, the power
that is delivered is not optimal. A maximum peak power point tracker is therefore necessary for
maximum efficiency.
A complete PV system equipped maximum power point tracking (MPPT) system includes a solar
panel, MPPT algorithm, and a DC-DC converter topology. Each subsystem is modeled and simulated
in a Matlab/Simulink environment; then the whole PV system is combined with the battery load to
assess the overall performance when subjected to varying weather conditions.
A PV panel model of moderate complexity based on the Shockley diode equation is used to predict
the electrical characteristics of the cell with regard to changes in the atmospheric parameter of
irradiance and temperature.
In this dissertation, five MPPT algorithms are written in Matlab m-files and investigated via
simulations. The standard Perturb and Observe (PO) algorithm along with its two improved versions
and the conventional Incremental Conductance (IC) algorithm, also with its two-stage improved
version, are assessed under different atmospheric operating conditions. An efficient two-mode MPPT
algorithm combining the incremental conductance and the modified constant voltage methods is
selected from the five ones as the best model, because it provides the highest tracking efficiencies in
both sunny and cloudy weather conditions when compared to other MPPT algorithms.
A DC-DC converter topology and interface study between the panel and the battery load is performed.
This includes the steady state and dynamic analysis of buck and boost converters and allows the
researcher to choose the appropriate chopper for the current PV system. Frequency responses using
the state space averaged model are obtained for both converters. They are displayed with the help of
Bode and root locus methods based on their respective transfer functions. Following the simulated
results displayed in Matlab environment for both choppers, an appropriate converter is selected and
implemented in the present PV system. The chosen chopper is then modeled using the Simulink
Power Systems toolbox and validates the design specifications.
The simulated results of the complete PV system show that the performances of the PV panel using
the improved two-stage MPPT algorithm provides better steady state and fast transient characteristics
when compared with the conventional incremental conductance method. It yields not only a reduction
in convergence time to track the maximum power point MPP, but also a significant reduction in
power fluctuations around the MPP when subjected to slow and rapid solar irradiance changes. / Thesis (M.Sc.Eng)-University of KwaZulu-Natal, Durban, 2011.
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