Thesis (Ph. D.)--Johns Hopkins University, 1916. / Cover title. Vita. "To be presented at the fifth midwinter convention of the American Institute of Electrical Engineers, New York, February 15, 1917." Caption title: The electric strength of air.--VII, by J.B. Whitehead and W.S. Brown. eContent provider-neutral record in process. Description based on print version record. Bibliography: p. 187-188.

O Triodo de corona com corrente constante foi utilizado em medidas da evolução do potencial de superfície de amostras de FEP 12 e 25 &#956m, carregadas com corona positiva e negativa no FEP 12 e 25 &#956m carregadas com corona positiva e negativa no ar e no nitrogênio. Estas medidas permitem concluir que não há diferença a nível de transporte de cargas entre os resultados com os dois gases. Apenas a umidade é importante para a subida e o decaimento do potencial de superfície. A subida do potencial de superfície de amostras de FEP 12 &#956m carregadas com corona negativa foi interpretada por meio da justaposição de dois modelos teóricos. No material só existem armadilhas profundas, em número finito, tanto na superfície quanto no volume; sendo que as de volume estão uniformemente distribuídas. Nenhum decaimento significativo de potencial é observado. A superfície desempenha um papel predominante na captura e injeção de portadores nas amostras de 12 &#956m carrega - das com corona positiva. Um modelo teórico que supõe schubweg dependente do campo médio reproduz os resultados experimentais. / The corona triode with constant current was used to measure the evolution of surface potential of FEP 12 and 25 &#956m samples, charged with positive and negative corona in air and in nitrogen. No difference in the transport properties in thin samples was observed when the gas was changed and this allowed us to conclude that electrons and holes are the carriers responsible by the transport of charge in the material. Only the moisture is important to the build up and decay of surface potential. The build up of surface potential of 12 &#956m samples charged with negative corona was interpreted by means of a deep fast trapping model in the beginning, followed by an increase of the trapping time when saturation is approached. Surface traps are also present. No significative potential decay is observed. The surface performs an important role in the trap¬ ping and injection of carriers into the bulk of 12 &#956m samples charged with positive corona. A theoretical model that assumes schubweg dependent on mean electric field fits the experimental results.

O Triodo de corona com corrente constante foi utilizado em medidas da evolução do potencial de superfície de amostras de FEP 12 e 25 &#956m, carregadas com corona positiva e negativa no FEP 12 e 25 &#956m carregadas com corona positiva e negativa no ar e no nitrogênio. Estas medidas permitem concluir que não há diferença a nível de transporte de cargas entre os resultados com os dois gases. Apenas a umidade é importante para a subida e o decaimento do potencial de superfície. A subida do potencial de superfície de amostras de FEP 12 &#956m carregadas com corona negativa foi interpretada por meio da justaposição de dois modelos teóricos. No material só existem armadilhas profundas, em número finito, tanto na superfície quanto no volume; sendo que as de volume estão uniformemente distribuídas. Nenhum decaimento significativo de potencial é observado. A superfície desempenha um papel predominante na captura e injeção de portadores nas amostras de 12 &#956m carrega - das com corona positiva. Um modelo teórico que supõe schubweg dependente do campo médio reproduz os resultados experimentais. / The corona triode with constant current was used to measure the evolution of surface potential of FEP 12 and 25 &#956m samples, charged with positive and negative corona in air and in nitrogen. No difference in the transport properties in thin samples was observed when the gas was changed and this allowed us to conclude that electrons and holes are the carriers responsible by the transport of charge in the material. Only the moisture is important to the build up and decay of surface potential. The build up of surface potential of 12 &#956m samples charged with negative corona was interpreted by means of a deep fast trapping model in the beginning, followed by an increase of the trapping time when saturation is approached. Surface traps are also present. No significative potential decay is observed. The surface performs an important role in the trap¬ ping and injection of carriers into the bulk of 12 &#956m samples charged with positive corona. A theoretical model that assumes schubweg dependent on mean electric field fits the experimental results.

Orientador: João Sinézio de Carvalho Campos / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-20T20:46:43Z (GMT). No. of bitstreams: 1 Lopes_SelmaAparecida_M.pdf: 4679717 bytes, checksum: b44b60b38798f2147b5fd6fe7eacc78f (MD5) Previous issue date: 2012 / Resumo: O material polimérico denominado não tecido de polipropileno (NTPP), após receber adequado tratamento químico, tem sido largamente utilizado na indústria têxtil para confecção de produtos de higiene pessoal, fraldas e absorventes descartáveis. Neste sentido o presente trabalho analisa os efeitos das técnicas de descarga corona (atmosfera ambiente) e plasma por radiofrequência (atmosferas de oxigênio (O2), nitrogênio (N2) e argônio (Ar) causados nas propriedades de superfície de amostras de NTPP em função do tempo de tratamento e nas respectivas atmosferas citadas. Recortam-se amostras de NTPP com geometria retangular (10x30mm) e espessura média de 40?m. Após tratamentos por corona e plasma submetem-se as amostras ás técnicas de medidas de ângulo de contato (método da gota séssil), de espectrometria em infravermelho (FTIR/ATR), de microscopia eletrônica exploratória (SEM) e de calorimetria diferencial exploratória (DSC); as quais têm por objetivo caracterizar a superfície do material em relação à molhabilidade, a formação de grupos polares, alterações morfológicas e comportamento de volume, respectivamente. Realizaram-se as medidas em quintuplicatas e dentre os resultados pode-se destacar que (i) o ângulo de contato tende a diminuir com o aumento do tratamento tanto corona quanto plasma, indicando que está ocorrendo aumento da molhabilidade do material, assim como comprovado por cálculos de energia livre de superfície (por exemplo: sem tratamento 18 mN/m e após tratamento 87 mN/m); (ii) as espectrometrias em infravermelho indicam a formação de grupos polares (hidroxílicos e carboxílicos); (iii) os termogramas em DSC indicam que não há alterações entre amostras com e sem tratamento, preservando assim propriedades de volume do material (estabilidade térmica de 0 á 135ºC e Tm=162ºC). Cabe ressaltar que realizaram-se medidas sobre a durabilidade do tratamento corona e os resultados mostram satisfatória durabilidade até 4 dias / Abstract: The polymeric material known as non-woven polypropylene (NTPP) upon receiving suitable chemical treatment has been widely used in the textile industry for the manufacture of personal hygiene products, diapers and disposable absorbent. In this sense the present paper analyzes the effects of corona discharge techniques (ambient atmosphere) and plasma radiofrequency (atmospheres of oxygen (O2), nitrogen (N2) and argon (Ar) caused the surface properties of samples as a function NTPP treatment time and the respective atmospheres cited. Samples were cut out NTPP rectangular geometry (10x30mm) and an average thickness of 40?m. After corona treatment and plasma samples were subjected techniques measures the contact angle (sessile drop method), infrared spectrometry (FTIR/ATR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) which are intended to characterize the material surface with respect to wettability, the formation of polar groups, and morphological behavior volume, respectively. There were measures in quintuplicatas and among the results can be noted that (i) the contact angle tends to decrease with the increase in both corona treatment and plasma, indicating that it is an increase of the wettability of the material, as evidenced by calculations of surface free energy (for example, untreated 18 mN/m after treatment 87 mN/m; (ii) infrared spectroscopy indicated the formation of polar groups (hydroxyl and carboxyl); (iii) the DSC thermograms show no charges between treated and untreated samples, thus maintaining properties of the material volume (thermal stability of 0 to 135ºC and Tm=162ºC). It should be noted that measurements were performed on the stability of the corona treatment and the results show satisfactory stability up to 4 days / Mestrado / Ciencia e Tecnologia de Materiais / Mestre em Engenharia Química

No description available.

Quasi-periodic disturbances have been observed in the outer solar atmosphere for many years. Although first interpreted as upflows (Schrijver et al. (1999)), they have been widely regarded as slow magneto-acoustic waves, due to their observed velocities and periods. Here we conduct a detailed analysis of the velocities of these disturbances across several wavelengths using the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We analysed 41 examples, including both sunspot and non-sunspot regions of the Sun. We found that the velocities of propagating disturbances (PDs) located at sunspots are more likely to be temperature dependent, whereas the velocities of PDs at non-sunspot locations do not show a clear temperature dependence. This suggests an interpretation in terms of slow magneto-acoustic waves in sunspots but the nature of PDs in non-sunspot (plage) regions remains unclear. Finally, we found that removing the contribution due to the cooler ions in the 193 wavelength suggests that a substantial part of the 193 emission of sunspot PDs can be attributed to the cool component of 193. Phase mixing is a well known and studied phenomenon in the solar corona, to enhance the dissipation of Alfvén waves (Heyvaerts and Priest (1982)). In this study we run numerical simulations of a continuously driven Alfvén wave in a low beta plasma along a uniform magnetic field. We model phase mixing by introducing a density inhomogeneity. Thermal conduction is then added into the model in the form of Braginskii thermal conduction. This acts to transport heat along the magnetic field. A parameter study will be carried out to investigate how changing the density structure and other parameters changes the results. We go on to consider the effect of wave reflection on phase mixing. We found that wave reflection has no effect on the damping of Alfvén waves but increases the heat in the system. We also consider a more realistic experiment where we drive both boundaries and study how the loop is heated in this situation. We also study what effect changing the frequency of one of the drivers so there is a small difference between the frequencies (10%) and a large difference (50%). We find the general behaviour is similar, but the heat is tilted. We have investigated basic phase mixing model which incorporates the mass exchange between the corona and the chromosphere. Chromospheric evaporation is approximated by using a non dimensional version of the RTV (Rosner et al. (1978)) scaling laws, relating heating (by phase mixing of Alfvén waves), density and temperature. By combining this scaling law with our numerical MHD model for phase mixing of Alfvén waves, we investigate the modification of the density profile through the mass up flow. We find a rapid modification of the density profile, leading to drifting of the heating layers. We also find that similar results are own seen in the propagating Alfvén wave case when we incorporate the effects of reflection.

MSc., Faculty of Science, University of the Witwatersrand, 2011 / In this thesis, a novel type of electrostatic thruster is introduced. The Corona Ionization (CorIon) Space Propulsion system is an electrostatic propulsion system intended for use on satellites and for deep space probes. It makes use of the corona ionization mechanism to create the needed propellant ions. This same mechanism is also responsible for the thrust, thereby reducing its size and complexity. First, the effects of incomplete ionization of propellant molecules is discussed and conclusions drawn. Next, a mathematical model describing the electric field characteristics is derived. Considering the needle tip as a point charge and the exhaust plume to be cylindrically symmetric with a constant spread angle, the resultant electric field of both the needle tip and the produced ions obeys Poisson‘s equation. The charge density is obtained from the relationship between the drift velocity and the current. In order to solve the differential equation, we consider the electric field to only change in the radial direction so that Poisson‘s Equation is reduced to its radial part. This differential equation is solved to yield the electric field of the system. Some results are discussed. By integrating the electric field the relationship between the potential difference and the current of propellant ions is obtained. This relationship also yields insight into the ionization efficiency. Following this, an expression for the thrust is derived via two different methods: The first uses the energy conservation, and is termed ―Vector heating‖. The ions are viewed as a current heating the neutrals in the plume in the direction away from the needle. A temperature can be derived for the plume, and the resulting average gas velocity estimated from molecular theory. Finally, using the rocket thrust equation, an expression for the thrust is obtained. iv The second, more conventional method uses electrostatic repulsion to calculate the recoil on the needle: from the electric field computed for the system, an expression for the Coulomb forces on the ionized propellant can be derived. The recoil on the needle will experience the same force, resulting in thrust. Finally, the theoretical predictions for the various parameters are compared to experimental data. From this comparison, it is seen that there is a reasonable agreement between the experimental data and the model even though the electrostatic prediction underestimates the thrust of the system.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 1997. / Results are reported on an initial investigation into corona power loss and its relationship to corona initiated audible noise. The work has the goal of being able to accurately predict the corona power loss, from a transmission line, from knowledge of the audible noise on the line. Corona power loss and its relationship to corona current, applied voltage and electric field is also exarr-ined. Experiments were performed using two single phase, different diameter, corona cages. Although the corona cage test results showed no correlation between corona initiated broad band audible noise and corona power loss, a linear empirical relationship, with excellent correlation, was found to exist between corona power loss and 100Hz Hum (dBA above 20jlPa). Results showed that, at the same magnitude of electric field, within the l h o different diameter corona cages, the corona current is the same magnitude and the corona power loss is proportional to the applied voltage. / MT2017

none

No description available.