Teses / dissertações sobre o tema "Ion current measurements"

The efficiency of combustion processes is assuming nowadays a huge importance, since the energy production, many industrial processes, as well as building heating systems are still mainly based on the combustion of hydrocarbons. The performance of the combustion process depends on many factors and it is a crucial point for the reliability and the efficiency of a plant or a thermal machine that exploits combustion as a primary source of energy. Moreover, the constant increasing of carbon dioxide concentration in atmosphere makes more and more important reducing the emission of this gas as well as the other pollutant/toxic chemical compounds that are produced during combustion. An optimized combustion process allows reducing dramatically the production of chemical compounds like carbon monoxide or nitrogen oxides, and also to releasing in the atmosphere the minimum amount of carbon dioxide per unit of energy produced. There are many studies related to the optimization of the internal combustion of the engines, especially for automotive applications, whereas the literature is less exhaustive for burner combustion optimization. The focus of this work is the study and the development of measurement systems allowing to get information about the combustion characteristics in gas turbines, with the aim of providing tools for monitoring/controlling the combustion parameters and keeping the combustion efficiency as high as possible over time. This activity has been developed in collaboration with Beker Huges (Nuovo Pignone Tecnologie - Florence), one of the world leaders in the design and development of gas turbines. Two different sources of information on the state of the combustion process have been considered in this thesis, namely the density of ions produced by the flame in the combustion chamber and the composition of the exhaust gases. The measurement of the ionic density due to the flame has been used since several years, particularly in the automotive sector, to obtain information about the combustion process: from the postprocessing of the signal obtained using ionization sensors (or ionic current sensors), it is possible to determine, for example, the onset of the combustion, the air–fuel ratio (and therefore the pollutant concentration at the exhaust), as well as to get information about the flame stability and the occurrence of periodic pressure variations in the combustion chamber. On this basis, even if the relationship between combustion parameters and flame induced ion density is highly dependent on the type of fuel, there is room to exploit the information of the ion sensors also with gas turbines, to optimize the operation of the combustor (e.g. reducing instability) and to monitor the polluting emissions. Ion or ionization sensors, which are usually used to measure the ion density in a burning gas, are essentially conductive electrodes capable of generating signals for either the charge transferred to/from the ionized gas and/or the charge induced on the electrodes themselves. The challenging issue concerns the choice of the materials for the sensor (electrodes and electrical insulators) which, being placed in the combustion chamber, must operate in extreme conditions, i.e., for example, in presence of very high temperatures. On the other hand, the conditioning front-end electronics for this kind of sensors is not critical. As far as the measurement of the concentration of toxic/pollutant compounds in exhaust gases is concerned, the most relevant compounds to be considered are carbon monoxide (CO) and nitrogen oxides (NOx). Monitoring CO and NOx in the exhaust gases is important not only from the point of view of environmental pollution, but also because their concentrations are useful and reliable indicators about the combustion efficiency. The drawback is that, due to the measurement procedure, they cannot be used for a timely feedback control of the combustion process, the reason is that the exhaust gases must be sampled from the chimney and pumped to the measurement instrument (gas analyser), and this procedure introduces a significant delay between the instant in which the gases are produced by the combustion and the time at which they are analysed. From the standpoint of the measurement instruments, exhaust gas analysers with different accuracies and costs (which are usually relevant) are available on the market. These devices can be portable or fixed and can exploit different measurement principles. Besides cost, an issue of these devices is that accurate gas sensors need frequent calibration exploiting reference gas tanks, which can be a problem in specific industrial plants such as power generation or oil and gas plants. The possibility to use a more flexible gas analyser, with a better trade-off among cost, measurement accuracy, the calibration intervals and robustness, is a deeply felt need in the oil & gas sector, considering also that these instruments are required to operate in environments that can be severely harsh, especially in terms of temperature and humidity. In this thesis, the developed and tested, in laboratory and in actual real test rigs of two measurement instruments, one for ion current measurements and one for exhaust gas composition measurement is discussed. For the first instrument, a theoretical model of the ion sensor used was also developed, which significantly helped in interpreting the experimental data.

The objective of this report was to implement battery cycling and an intermittent current interruption (ICI) method for determining battery resistance into a simple lithium-ion battery model in the finite element methods (FEM) program COMSOL Multiphysics, andevaluate how accurately the model reflects the behaviour of voltage and internal resistance with respect to experimental results. The ICI technique consists of repeating the steps of first having a longer charging period and then having a short current interruption, where the internal resistance is calculated from the voltage drop that occurs when the current is turned off. The model was evaluated against measurements, made with the same technique (ICI), on assembled NMC-graphite batteries. Codes written in the statistical programming language “R” were used to process the data from both COMSOL and the experiments. Both the batteries and the model were constructed with a reference electrode, to enable measurement of each electrode by itself. The results as documented in this report show that it is possible to simulate the measurement technique in COMSOL, but that both the resistance and voltage profiles differed quite a lot from the behaviour of the tested batteries. The resistance of the positive electrode did however give good results and it was possible to improve the model by changing some parameters. The magnitude of the resistance, which was already quite close, could be improved by changing the porosity and particle size, and the voltage profiles were improved when using voltage-data achieved from the real measurements.

In the last 20 years, the use of high voltage direct current (HVDC) power transmission has grown considerably. With the increase in the number of HVDC transmission lines and in the transmission voltages, concern has increased as to possible health effects. For research on these health effects to be carried out, it is necessary to measure the electrical environment ofHVDC transmission lines accurately. The electrical environment ofHVDC transmission lines is characterised by: Electric field strength E [Vim];Ion current density J [A/m²] ;Space charge density p [C/m³ ]. Typical values measured under HVDC transmission lines are: E = lOkV/m, J = 400nA/m² . This thesis describes the design, construction and testing of an electric field mill capable of measuring electric field strength from 0 to 25kV/m (resolution = lOV/m), and ion current density from 0 to 1000 nA/m² (resolution = 20nA/m² ). The electric field readings have an accuracy of ±8%. The ion current density readings have an accuracy of ±12%. The field mill was tested in the laboratory in a simulated HVDC environment, and found to give good performance. For operation under a HVDC line, the field mill design will need some alterations to make it weatherproof. The design considerations described in this thesis should be helpful in the design of electric field mills in general.

In my thesis I describe the improvements of the Penning trap mass spectrometer SMILETRAP. The objective of these improvements have been to increase the reliability and the accuracy with which an atomic mass can be measured using highly charged ions. The improvements have been achieved by stabilizing both the electric and magnetic fields of the trap and by improving the technical performance of the trap system. As a result it has been possible to measure accurately the mass of several atoms ranging from hydrogen to mercury using charge states from 1+ to 52+. It was only possible to use the highest charge states after applying a successful cooling of these ions with Helium during the charge breeding. The technical improvements made a number of interesting accurate mass measurements possible. The measurements of the 3H, 3He, and 4He masses showed that the previously values were wrong. The mass difference between 3H and 3He which is the Q-value of the tritium beta decay has been determined to 18.588(3) keV. The Q-value of the double β-decay of 76Ge was measured at an accuracy of 50 eV. This value is indispensable for the evaluation the Heidelberg-Moscow experiment which aims at finding a possible neutrino-less decay which if present would be a violation of the standard model. The mass ratio of mCs/mp is used to determine the fine structure constant independent of QED calculations. The two decades old anomaly in the mass values of Hg was solved by the mass determination of 198Hg and 204Hg. The mass of 24Mg was measured at an uncertatinty of 0.6 ppb and will be used in the determination of the g-factor of a bound electron in a hydrogen like ions.

The aim of this thesis was to study the effects of extremely low frequency (ELF) electromagnetic magnetic fields on potassium currents in neural cell lines ( Neuroblastoma SK-N-BE ), using the whole-cell Patch Clamp technique. Such technique is a sophisticated tool capable to investigate the electrophysiological activity at a single cell, and even at single channel level. The total potassium ion currents through the cell membrane was measured while exposing the cells to a combination of static (DC) and alternate (AC) magnetic fields according to the prediction of the so-called ‘ Ion Resonance Hypothesis ’. For this purpose we have designed and fabricated a magnetic field exposure system reaching a good compromise between magnetic field homogeneity and accessibility to the biological sample under the microscope. The magnetic field exposure system consists of three large orthogonal pairs of square coils surrounding the patch clamp set up and connected to the signal generation unit, able to generate different combinations of static and/or alternate magnetic fields. Such system was characterized in term of field distribution and uniformity through computation and direct field measurements. No statistically significant changes in the potassium ion currents through cell membrane were reveled when the cells were exposed to AC/DC magnetic field combination according to the afore mentioned ‘Ion Resonance Hypothesis’.

The aim of this thesis was to study the effects of extremely low frequency (ELF) electromagnetic magnetic fields on potassium currents in neural cell lines ( Neuroblastoma SK-N-BE ), using the whole-cell Patch Clamp technique. Such technique is a sophisticated tool capable to investigate the electrophysiological activity at a single cell, and even at single channel level. The total potassium ion currents through the cell membrane was measured while exposing the cells to a combination of static (DC) and alternate (AC) magnetic fields according to the prediction of the so-called ‘ Ion Resonance Hypothesis ’. For this purpose we have designed and fabricated a magnetic field exposure system reaching a good compromise between magnetic field homogeneity and accessibility to the biological sample under the microscope. The magnetic field exposure system consists of three large orthogonal pairs of square coils surrounding the patch clamp set up and connected to the signal generation unit, able to generate different combinations of static and/or alternate magnetic fields. Such system was characterized in term of field distribution and uniformity through computation and direct field measurements. No statistically significant changes in the potassium ion currents through cell membrane were reveled when the cells were exposed to AC/DC magnetic field combination according to the afore mentioned ‘Ion Resonance Hypothesis’.

Kyoto University (京都大学)
0048
新制・課程博士
博士(理学)
甲第12109号
理博第3003号
新制||理||1448(附属図書館)
23945
UT51-2006-J104
京都大学大学院理学研究科地球惑星科学専攻
(主査)教授 町田 忍, 教授 家森 俊彦, 教授 淡路 敏之
学位規則第4条第1項該当

Oxide related research has increased as standard oxides reach their operational limits and new classes of devices are imagined that can only be realized through the use of man-made compounds. Many of these devices require high quality films in order to reach their highest potential. Molecular beam epitaxy (MBE) is poised to become a key producer of high quality oxides. One of the most promising oxides is lithium niobate, LiNbO3, which can potentially deliver novel electronic, optic, and hybrid devices not currently possible. Growing lithium niobate using MBE is difficult. Several concepts are presented that will make this task easier. First, high temperature refractory metals can be delivered to the substrate through a novel use of low temperature chloride compounds such as niobium (V) chloride. This chloride chemistry allows low temperature sources to deliver high temperature materials to the substrate. Second, a precision, vapor-phase source and control system is prototyped for these chloride compounds achieving improved flux accuracy and expanding the capability of standard MBEs to support many sources. Chloride sources have high vapor pressures and are sensitive to temperature changes causing flux drift. The vapor-phase source removes the temperature sensitivity and eliminates thermal drifts. Third, a novel method of measuring flux with spontaneous ionzation current has been developed. This design utilizes a low noise design to measure femtoamp currents generated as an evaporant spontaneously ionizes. The measured current with additional predicted data has the potential for directly counting the atoms evaporated and controlling evaporation from a source. The design is sensitive enough to detect outgassing of the cell and cell "spitting" or other non-idealities. Monitoring these non-idealities can help improve other processes by ensuring the cell is fully outgassed and stable. Finally, a miniaturized RF induction cell prototype is shown that can eliminate the need for incandescent filaments in an oxide based MBE. The RF cell has the potential to increase reliability of MBEs for oxide work and achieve higher operating temperatures without the need for densely wound incandescent filaments or electron beam sources.

The diploma thesis deals with measurement of former Peklo inn in Tišnov and creates a documentation of its building. Measurement is connected to the binding reference system – the S-JTSK coordinate sytem and Baltic Vertical Datum Bpv. The thesis countains a description of the place of interest and history of the building, preparatory work, choice of instruments and tools. In the next part measurement, processed of recorded data, requirements of creating documentation of the ground plan and vertical section, testing results of the work, are described. The thesis countains ground plan of the cellar, ground plan of the second floor and the vertical section of the building in scale of 1:50. Outcomes of thesis will serve as documentation of the current conditions of the building.

This Master thesis deals with low-current measurement in order of picoamps up to a few tens of femtoamps. Such low currents measuring is necessary for determination of air ions concentration. Disturbances, which are otherwise negligible for ordinary measurements must be considered. For example, leakage currents and noise generated in measuring device circuit. The choice of a precise operation amplifier with low input bias current is as important as the selection of low noise passive components. The aim of the thesis is to design and implement a precise low-level amplifier for the purposes of air ions concentration measurements.

碩士
國立臺灣師範大學
物理學系
101
This study is about measuring ion current of single atom tip by using micro-channel plat and Faraday cap with field ion microscope and improving its application. The experiment has two parts : iridium covered tungsten tip and pure iridium tip. For iridium covered tungsten tip, after annealing to 870K~1080K several times,(111) would facet to a pyramid structure with one-atom-top. Because there is only one atom on the top, the field ion current would befocus. In this study, we change the tip radius to investigate how to raise the field ion current per unit area.The investigationshowed that if the radius is larger, more image gas atom could adsorb the surface. It’s easier to supply with ions, so the field ion current could be larger. But the increasing range of ion current would go down because of the raise of shank angle. For iridium tip, after covering oxygen and annealing to 780K , (210) would facet to a pyramid, but the range of annealing temperature is narrow. If the tip temperatureover 780K, the surface would become equilibrium structure which is caused crest line between (311),(111),(100) and (110).Otherwise, iridium (110) easily cause (1×2) or (1×3) restructure after annealing. Miss rowcould change the faceting pyramid structure, andlet the formation of single atom tip become more difficult.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1994.
Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 170-175).