Dissertations / Theses on the topic 'Very low frequency'

The topics covered in this dissertation are all areas of study involving observations at low radio frequencies. There are three main subject areas: a study of the twin-tailed radio galaxy 3C3.1; a study of both an old and a new sample of radio sources that exhibit very steep radio spectra at low frequency; the design and construction of a new radio telescope operating at low radio frequency together with the making of a new radio source survey. 3C3.1 has been studied by other authors but new high angular resolution, high sensitivity observations at low radio frequency have allowed further progress to be made in understanding the behaviour of this source. It has been thought that 3C3.1 type sources would be responsible for most (if not all) of the very steep spectrum radio sources. 3C3.1 is relatively close, hence easy to study. A model has been developed which explains the previously not understood brightness distribution along the long luminous jets. In order to quantify the predicted behaviour more precisely a set of simple numerical simulations was performed. Very steep spectrum radio sources are by their nature easier to detect at low radio frequencies. In the past, it has been shown that most, if not all, very steep spectrum sources are associated with clusters of galaxies. Both optical and further radio observations of a sample of sources prepared by the author, and a sample prepared by other workers were undertaken. The optical observations of high sensitivity have greatly strengthened the hypothesis that all of such sources are indeed associated with clusters of galaxies. The radio observations, both performed at high and low radio frequencies, have shown that such sources seem to have in general evolved from conventional sources with both 'tailed' and 'double' radio structure. A serious limitation for further work at low radio frequencies is the availibility of high sensitivity, high resolution instruments. A twenty five element interferometer with a one mile baseline operating at 38 MHz was designed and constructed. This allowed an appraisal of the operating conditions at such low frequency. A deep radio survey of the north pole was performed and a new sample of very steep spectrum constructed.

Point-of-load (POL) converters are used extensively in IT products. Every piece of the integrated circuit (IC) is powered by a point-of-load (POL) converter, where the proximity of the power supply to the load is very critical in terms of transient performance and efficiency. A compact POL converter with high power density is desired because of current trends toward reducing the size and increasing functionalities of all forms of IT products and portable electronics. To improve the power density, a 3D integrated POL module has been successfully demonstrated at the Center for Power Electronic Systems (CPES) at Virginia Tech. While some challenges still need to be addressed, this research begins by improving the 3D integrated POL module with a reduced DCR for higher efficiency, the vertical module design for a smaller footprint occupation, and the hybrid core structure for non-linear inductance control. Moreover, as an important category of the POL converter, the voltage regulator (VR) serves an important role in powering processors in today's electronics. The multi-core processors are widely used in almost all kinds of CPUs, ranging from the big servers in data centers to the small smartphones in almost everyone's pocket. When powering multiple processor cores, the energy consumption can be reduced dramatically if the supply voltage can be modulated rapidly based on the power demand of each core by dynamic voltage and frequency scaling (DVFS). However, traditional discrete voltage regulators (VRs) are not able to realize the full potential of DVFS since they are not able to modulate the supply voltage fast enough due to their relatively low switching frequency and the high parasitic interconnect impedance between the VRs and the processors. With these discrete VRs, DVFS has only been applied at a coarse timescale, which can scale voltage levels only in tens of microseconds (which is normally called a coarse-grained DVFS). In order to get the full benefit of DVFS, a concept of an integrated voltage regulator (IVR) is proposed to allow fine-grained DVFS to scale voltage levels in less than a microsecond. Significant interest from both academia and industry has been drawn to IVR research. Recently, Intel has implemented two generations of very high frequency IVR. The first generation is implemented in Haswell processors, where air core inductors are integrated in the processor's packaging substrate and placed very closely to the processor die. The air core inductors have very limited ability in confining the high frequency magnetic flux noise generated by the very high switching frequency of 140MHz. In the second generation IVR in Broadwell processors, the inductors are moved away from the processor substrate to the 3DL PCB modules in the motherboard level under the die. Besides computers, small portable electronics such as smartphones are another application that can be greatly helped by IVRs. The smartphone market size is now larger than 400 billion US dollars, and its power consumption is becoming higher and higher as the functionality of smartphones continuously advances. Today's multi-phase VR for smartphone processors is built with a power management integrated circuit (PMIC) with discrete inductors. Today's smartphone VRs operate at 2-8MHz, but the discrete inductor is still bulky, and the VR is not close enough to the processor to support fine-grained DVFS. If the IVR solution can be extended to the smartphone platform, not only can the battery life be greatly improved, but the total power consumption of the smartphone (and associated charging time and charging safety issues) can also be significantly reduced. Intel's IVR may be a viable solution for computing applications, but the air core inductor with un-confined high-frequency magnetic flux would cause very severe problems for smartphones, which have even less of a space budget. This work proposes a three-dimensional (3D) integrated voltage regulator (IVR) structure for smartphone platforms. The proposed 3D IVR will operate with a frequency of tens of MHz. Instead of using an air core, a high-frequency magnetic core without an air gap is applied to confine the very high frequency flux. The inductor is designed with an ultra-low profile and a small footprint to fit the stringent space requirement of smartphones. A major challenge in the development of the very high frequency IVR inductor is to accurately characterize and compare magnetic materials in the tens of MHz frequency range. Despite the many existing works in this area, the reported measured properties of the magnetics are still very limited and indirect. In regards to permeability, although its value at different frequencies is often reported, its saturation property in real DC-biased working conditions still lacks investigation. In terms of loss property, the previous works usually show the equivalent resistance value only, which is usually measured with small-signal excitation from an impedance/network analyzer and is not able to represent the real magnetic core loss under large-signal excitation in working conditions. The lack of magnetic properties in real working conditions in previous works is due to the significant challenges in the magnetic characterization technique at very high frequencies, and it is a major obstacle to accurately designing and testing the IVR inductors. In this research, an advanced core loss measurement method is proposed for very high frequency (tens of MHz) magnetic characterization for the IVR inductor design. The issues of and solutions for the permeability and loss measurement are demonstrated. The LTCC and NEC flake materials are characterized and compared up to 40MHz for IVR application. Based on the characterized material properties, both single-phase and multi-phase integrated inductor are designed, fabricated and experimentally tested in 20MHz buck converters, featuring a simple single-via winding structure, small size, ultra-low profile, ultra-low DCR, high current-handling ability, air-gap-free magnetics, multi-phase integration within one magnetic core, and lateral non-uniform flux distribution. It is found that the magnetic core operates at unusually high core loss density, while it is thermally manageable. The PCB copper can effectively dissipate inductor heat with 3D integration. In addition, new GaN device drivers and magnetic materials are evaluated and demonstrated with the ability to increase the IVR frequency to 30MHz and realize a higher density with a smaller loss. In summary, this research starts with improving the 3D integrated POL module, and then explores the use of the 3D integration technique along with the very high frequency IVR concept to power the smartphone processor. The challenges in a very high frequency magnetic characterization are addressed with a novel core loss measurement method capable of 40MHz loss characterization. The very high frequency multi-phase inductor integrated within one magnetic component is designed and demonstrated for the first time. A 20MHz IVR platform is built and the feasibility of the concept is experimentally verified. Finally, new GaN device drivers and magnetic materials are evaluated and demonstrated with the ability to increase the IVR frequency to 30MHz and realize higher density with smaller loss.<br>Ph. D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, and the Woods Hole Oceanographic Institution, 1994.<br>Includes bibliographical references (leaves 235-245).<br>by Christopher Robert Bradley.<br>Ph.D.

Publicación a texto completo no autorizada por el autor<br>Aclara las bases teóricas de los cables de media tensión (en especial XLPE), como son el tipo de aislamiento, parámetros, los mecanismos de degradación de los cables, etc. También realizaremos una comparación entre dos pruebas de soporte tanto en DC como en VLF, con el objetivo de demostrar que este último es la mejor elección en este tipo de pruebas y que ya los métodos tradicionales de inyección DC no son recomendables.<br>Tesis

<p> On August 21, 2017 a total solar eclipse occurred over the United States commencing on the west coast moving across to the east coast providing an opportunity to observe how the rapid day-night-day transition changed the ionosphere&rsquo;s D-region electron density and how very low frequency (VLF) electromagnetic wave propagation was affected. To observe the solar obscurity effects, VLF receivers were deployed in two locations: one in the path of totality in Lakeside, Nebraska and another south of the totality path in Hugo, Colorado. The locations were chosen to achieve an orthogonal geometry between the eclipse path and propagation path of U. S. Navy VLF transmitter in North Dakota, which operates at 25.2 kHz and has call sign NML. VLF amplitude and phase changes were observed in both Lakeside and Hugo during the eclipse. A negative phase change was observed at both receivers as solar obscuration progressively increased. The observed phase changes became positive as solar obscuration reduced. The opposite trend was observed for the amplitude of the transmitted signal: growth as max totality approached and decay during the shadow&rsquo;s recession. The Long Wave Propagation Capability (LWPC) code developed by the US Navy was used to model the observations. LWPC is a modal solution finder for Earth-ionosphere waveguide propagation that takes into account the D-region density profile. In contrast to past efforts where a single ionosphere profile was assumed over the entire propagation path, a degree of spatial resolution along the path was sought here by solving for multiple segments of length 100-200 km along the path. LWPC modeling suggests that the effective reflection height changed from 71 km in the absence of the eclipse, to 78 km at the center of the path of totality during the total solar eclipse and is on agreement with past work.</p><p>

Com o objetivo de complementar estudos hidrogeológicos efetuados durante o processo de locação de poços tubulares, em áreas formadas por rochas ígneas e metamórficas, foram realizados trabalhos de prospecção geofísica utilizando o método VLF \"Very Low Frequency\" . Após um levantamento bibliográfico sobre a metodologia e seus principais métodos de interpretação, foram realizados dois tipos de levantamentos de campo em áreas distintas, sendo um onde já haviam poços perfurados para se tentar estabelecer uma correlação entre as anomalias e os poços e, outro efetivamente visando a locação e posterior perfuração de poços. O método de interpretação utilizado se baseia na filtragem dos dados de campo e na confecção de pseudo-secções de densidade de corrente. Os resultados alcançados podem ser considerados satisfatórios, pois a margem de erro que foi de aproximadamente 5%, no mapeamento e identificação das zonas de fraturas, pode ser considerado insignificante, embora o ideal fosse que estes erros não ocorressem.<br>The VLF \" Very Low Frequency\" geophysical method was used as a complementary field method to locate most favorable points to be drilled for deep water wells. This application was used in the Bahia and Ceará States, Brazil, on pre-Cambrian formed rocks areas. This field work was done after a bibliographic evaluation of the methodology and principal interpretation techniques. Considering the rare examples of application of VLF in Brazil, this research was divided in two phases. The first phase was developed in Bahia, where previous drilled deep-wells existed to permit to stablish a correlation between the field VLF data and the available hydrogeological informations. The second area, Ceará, the VLF field work was used to locate most favorable points for deep-wells to be drilled. The interpretation of the VLF field data was based on the filtration and the construction of pseudo-sections of current density. The obtained results may be considered as satisfactory, since, in Ceará, the error factor was of about 5% for the location of fractured rocks for the new located deep-wells.

Made available in DSpace on 2016-03-15T19:37:41Z (GMT). No. of bitstreams: 1 Jorge Enrifque Samanes Cardenas.pdf: 3561395 bytes, checksum: ba28ce6fbd3bd0e1573255ccacb30d17 (MD5) Previous issue date: 2012-02-17<br>Fundo Mackenzie de Pesquisa<br>Deep amplitude minima are observed in the daily records of Very Low Frequency (VLF, between 3 - 30 kHz) wave amplitudes. Amplitude minima are attributed to modal interference and modal conversion of waves propagating in the Earth - Ionosphere waveguide. The time of amplitude minima is related with the localization of the Terminator line and, therefore, is denominated of Terminator Time or TT time. In this work, we developed a methodology based on the monitoring of TT time to infer the distance of modal interference D and its temporal variation in relation to atmospheric and natural phenomena. For this purpose, we used data provided by the South America VLF Network (SAVNET) to the period 2007 - 2011. The results showed that the methodology is a promising tool to study the dynamics of the lower ionosphere, by means of the daily values of the undisturbed nighttime ionospheric height(hN). We identified short-term and long-term time variations of hN, where the long-term variation is possibly related with the solar activity cycle. We propose the use of this method to search for seismic- electromagnetic effects, and that it should be applied to medium and short propagation paths. Using the Long Wave Propagation Capability (LWPC) code, we simulated TT times and the results show good agreement with the observations, so a value for nighttime height hN = 88 km is suggested. This work will contribute to a greater viability of the use of the VLF technique for the study of the lower ionosphere and the forcings acting on this region of the atmosphere.<br>Pronunciados mínimos de amplitude são observados nos registros diários de sinais de muito baixa frequência ou VLF (do inglês Very Low Frequency, entre 3 - 30 kHz). A presença destes mínimos é atribuída a interferência e conversão modal de ondas se propagando no guia de onda Terra - Ionosfera. Os tempos de ocorrência destes mínimos são relacionados com a localização do Terminadouro e, por isso, são denominados de tempos de Terminadouro ou Tempos TT. Neste trabalho, desenvolvemos uma metodologia baseada no monitoramento dos tempos TT para inferir a distância de interferência modal D, e sua variabilidade temporal em relação a fenômenos atmosféricos e naturais. Para isso, utilizamos dados fornecidos pela rede SAVNET (South America VLF Network) durante o período 2007 - 2011. Os resultados mostraram que a metodologia é relevante para estudar a dinâmica da baixa ionosfera, através da obtenção de valores diários da altura noturna hN. Identificamos variabilidades de curto e longo período para hN, sendo estas últimas relacionadas ao ciclo de atividade solar. O método deverá ser aplicado à procura de efeitos sismo-eletromagnéticos utilizando caminhos com comprimento médios ou curtos. Foram realizadas simulações dos tempos TT, utilizando o código Long Wave Propagation Capability (LWPC), que mostraram boa concordância com as observações, sugerindo um valor de hN = 88 km para a altura noturna da baixa ionosfera. Os resultados apresentados neste trabalho contribuem para uma maior viabilização do uso da técnica de VLF, para o estudo da baixa ionosfera e os forçantes que agem sobre esta região da atmosfera terrestre.

The objective of this thesis is to use radio emissions from lightning, known as `radio atmospherics' or `sferics', to study the temporal and spatial variation of the lower ionosphere, a layer of ionized atmosphere beginning at $\sim$70 km altitude (D-region). Very Low Frequency (VLF, 3$-$30kHz) radio waves are a useful diagnostic for lower ionospheric monitoring due to their reflection from this region and global propagation. Traditionally, the lower ionosphere has been sensed using single-frequency VLF transmitters allowing for analysis of a single propagation path, as there are only a small number of transmitters. A lightning stroke, however, releases an intense amount of impulsive broadband VLF radio energy in the form of a sferic, which propagates through the Earth-ionosphere waveguide. Lightning is globally distributed and very frequent, so a sferic is therefore also a useful diagnostic of the D-region. This is true both for ambient or quiet conditions, and for ionospheric perturbations such as solar flare x-ray bursts. Lightning strokes effectively act as separate VLF transmitting sources. As such, they uniquely provide the ability to add a spatial component to ionospheric remote sensing, in addition to their broadband signature which cannot be achieved with man-made transmitters. We describe the methods of processing in detail. As an example, we analyze a solar flare during which time there is a significant change in magnitude and frequency content of sferics. This disturbance varies with distance from the source, as well as time. We describe the methods of processing in detail, and show results at Palmer Station, Antarctica for both a quiet and active solar day.

Measurement of lava effusion rates is a key objective for monitoring basaltic eruptions because it helps constrain geophysical models of magma dynamics, conduit geometry, and both deep and shallow volcano processes. During these eruptions, lava frequently travels through a single "master" lava tube. A new method and instrument for continuously monitoring the crosssectional area of lava streams in tubes and estimating the instantaneous effusion rate (IER) is described. The method uses 2 stationary very low frequency (VLF) radio receivers to measure an unperturbed VLF signal and the influence of highly conductive molten lava on that signal. The difference between these signals is a function of the cross-sectional area of molten lava and the IER. Data from a short test of the instrument are described. This methodology represents a breakthrough in the continuous monitoring of IER because it provides higher temporal resolution than competing methods at a fraction of the cost.

Made available in DSpace on 2016-03-15T19:38:53Z (GMT). No. of bitstreams: 1 ALBERTO FARES AKEL JUNIOR.pdf: 5112998 bytes, checksum: f18fc33d2f9508c3ec265c0efa016b43 (MD5) Previous issue date: 2015-08-21<br>Fundação de Amparo a Pesquisa do Estado de São Paulo<br>We study the behavior of the Earth-ionosphere waveguide through the modeling of the propagation of very low frequency radio waves (VLF). We use the computational model LWPC (Long Wave Propagation Capability) to estimate changes in amplitude and phase of the VLF signals detected by the SAVNET network (South America VLF NETwork), and thus try to understand the behavior of the lower ionosphere under different ionization conditions. The research was divided into two parts. The first part investigates the behavior of the VLF signals in quiescent regimes of ionization. Amplitude and phase simulations for the were carried out, modifying adapting polynomials for the &#946; and h parameters (or Wait s parameters) as a function of the zenithal angle. The second part of this research, uses these polynomials in the study of the lower ionosphere under transient ionization regimes in two distinct conditions: first during of solar flares and second during solar eclipse. For the simulations under solar flare conditions, we calculate the changes in &#946; and &#8462;&#8242; parameters during the 25/03/2008 solar explosion. With these values, we calculate the electronic density profile through an exponential model and we find that the electronic density at 75 km is &#8764; 104 cm&#8722;3, that is twenty times higher than during quiescent conditions. To evaluate our parameter estimates, we calculate the variation of the Wait s parameters for the case of twelve solar events of different classes. We note that the variations &#916;&#8462;&#8242; found in this work are larger than that in Muraoka, Murata e Sato (1977) because they consider the variations in the conductivity gradient. For the solar eclipse simulations on 11/07/2011, we investigate its effect on the VLF phase. For this, we use the obscuration coefficient to estimate the guide height variation along the whole path during the eclipse. The simulations reproduce the phase behavior during the eclipse. However, a delay of about twenty four minutes was observed between the simulated and observed measurements. The observed delay is a direct consequence of own estimates of the perturbed ionospheric height and it causal relation with the obscuration during the eclipse. lower ionosphere, VLF, modeling, ionospheric disturbances, solar flares, solar eclipse.<br>Neste trabalho realizamos o estudo do comportamento do guia de ondas terra-ionosfera através da modelagem da propagação ondas de rádio de frequência muito baixa (VLF). Para isto, utilizamos o modelo computacional LWPC (Long Wave Propagation Capability) para estimar as variações de amplitude e fase de sinais de VLF detectados nos trajetos da rede SAVNET (South America VLF NETwork) e assim compreender o comportamento da baixa ionosfera em diferentes regimes de ionização. A pesquisa foi dividida em duas partes. A primeira parte, investigou o comportamento do sinal VLF em regimes quiescente de ionização, assim realizou-se simulações de amplitude e fase adaptando polinômios que definem os parâmetros &#946; e &#8462;&#8242; (ou parâmetros de Wait) em função do ângulo zenital solar. Na segunda parte desta pesquisa, aplicou-se os polinômios no estudo da baixa ionosfera sob regimes transientes de ionização em duas condições distintas. A primeira para o caso de explosões solares e a segunda um para eclipse solar. Nas simulações relativas a explosões solares, calculamos as variações dos parâmetros &#946; e &#8462;&#8242; durante o evento do dia 25/03/2008. Com esses valores, calculamos o perfil de densidade eletrônica, através de um modelo exponencial e observamos que a densidade eletrônica em 75 km é &#8764; 104 cm&#8722;3, ou seja, vinte vezes maiores que antes da explosão. Para avaliar nossas estimativas, calculamos a variação dos parâmetros de Wait para doze eventos de diferentes classes. Observamos que as variações &#916;&#8462;&#8242; neste trabalho são sempre maiores do que as descritas em Muraoka, Murata e Sato (1977), devido elas considerarem as variações no gradiente de condutividade. Nas simulações relativa ao eclipse solar do dia 11/07/2011, investigamos seu efeito na fase observada. Para esse estudo, utilizou-se o coeficiente de obscurecimento para realizar as simulações, desta forma foi possível estimar a variação da altura do guia ao longo de todo o trajeto durante o eclipse. As simulações reproduziram o comportamento da fase durante o eclipse. Entretanto, foi observado um atraso entre as medidas calculadas e observadas de aproximadamente &#8764; vinte e quatro minutos. O atraso observado é diretamente decorrente da estimativa da altura de referência da ionosfera pertubada e de sua relação causal com o obscurecimento durante o eclipse.

Thesis (MScEng)--Stellenbosch University, 2011.<br>ENGLISH ABSTRACT: A well-known problem with FM-CW radar systems is the leakage of transmitter power into the receiver which leads to the making of close-in targets, and can severely limit the system dynamic range performance. This thesis considers two solutions to this radar system problem for a low frequency radar operating in the VHF band. The first method to suppress coupling is using separate transmit and receive antennas designed in such a way as to reduce coupling between them. The second is to design a negative feedback loop as part of the radar receiver where the feedback loop adaptively reduces the amount of transmitter leakage through to the receiver. This project details the realisation of these two solutions. A number of antenna designs are modelled in software and simulated to determine their characteristics of which the transmit-to-receive coupling is the key parameter. As no low coupling configuration could be found a simple configuration is chosen and practical measurements are taken. These antennas are then used in the radar system that is to be built. An FM-CW radar system is designed and simulated using software with a negative feedback loop being designed and implemented into the radar simulation. A practical radar system is then made inclusive of the feedback loop. Measurements are then taken to determine the efficacy of the feedback loop.<br>AFRIKAANSE OPSOMMING: ʼn Bekende probleem met FM-CW radar stelsels is die lekkasie van versender krag tot in die ontvanger wat lei tot die maak van nabye teikens en kan die stelsel se dinamiese sendbereik steng beperk. Hierdie tesis oorweeg twee oplossings tot hierdie probleem vir ʼn lae frekwensie radar wat in die VHF band werk. Die eerste metode wat na gekyk word om die koppeling te onderdruk is om die twee antennas van die radar stelsel so te ontwerp sodat die hoeveelheid koppeling tussen hulle verminder is. Die tweede is om ʼn negatiewe terugvoerlus as deel van die ontvanger te ontwerp. Hierdie terugvoerlus sal die versender lekkasie sein aanpassend in die ontvanger verminder. In hierdie projek word die realisering van bogenoemde oplossings uiteengeset. ʼn Paar verskillende antenna ontwerpe word gemodelleer in sagteware en word gesimuleer om hul karakteristieke te bepaal. Die belangrikste van hierdie faktore is die versender na ontvanger koppeling. Sienend dat geen ontwerp met ʼn lae genoeg koppeling gevind kon word nie, is ʼn eenvoudige ontwerp gekies en praktiese metings daarvan geneem. Hierdie antennas word dan gebruik in die radar stelsel wat gebou sal word. ʼn FM-CW radar stelsel word ontwerp en gesimuleer in sagteware. Die negatiewe terugvoerlus word ook ontwerp en geïmplementeer in die radar simulasie. ʼn Praktiese radar stelsel word dan gemaak insluitend die terugvoerlus. Metings word dan geneem om die effektiwiteit daarvan te bepaal.

The increased need for electric power combined with an aging underground cable infrastructure in a deregulated market environment have forced utilities to refocus their attention on reliability while at the same time reducing maintenance costs as much as possible. This has created a significant need for diagnostic methods and technologies to assess the condition of the underground cable systems. However, while several cable diagnostic technologies are available, they have not all yet been fully accepted in the United States. This is because the different technologies lead to different conclusions for the same cable system, and thus utilities do not completely trust the conclusions. A better understanding of the diagnostic technologies and their correct application is therefore required. The most widely used diagnostic technologies in the United States include dissipation factor (Tan-delta and partial discharge measurements; these tests are therefore, the main focus of this thesis; in particular, when applied to underground extruded cable systems. The purpose of this research is to advance the field of characterization of power cable defects by addressing a number of theoretical and practical diagnostic measurements and their interpretation issues. The discussion is based on data from laboratory experiments and field tests. This thesis consists of two major parts. The first part is devoted to the characterization by Tan-delta measurements in which the major contribution is a new approach for condition assessment using this technology. The second part is devoted to the work on characterization by partial discharge measurements, and the major contribution is a novel approach that is able to analyze, evaluate, and reduce the number of partial discharge diagnostic features.

High voltage testing of the stator winding insulation is one of the most recognized methods used to determine the state of degradation in the insulation. HV tests performed at 0.1 Hz do have potential advantages compared to more traditional 50 Hz tests. This thesis therefore aims to perform and compare tan delta, capacitance and partial discharge measurements on stator windings when using a 0.1 Hz voltage source and a more traditional 50 Hz voltage supply. Several associated test parameters with considerable influence on the test results were varied during the tests. An associated data analysis followed that was focused on the differences and similarities of the analyzed parameters and the results due to the differences in frequency. The results show that there are substantial levels of noise present in the partial discharge measurements when utilizing the VLF voltage source. There are also more numerous partial discharges for VLF measurements than for regular power frequency measurements if the same amount of voltage cycles is considered. The generated patterns show similarities with those generated at 50 Hz, but a larger sample base is probably needed for more thorough conclusions. The tan delta/capacitance part of the test do indicate potential advantages compared to power frequency measurements regarding the sensitivity in the measurements.

Abstract Polymetallic (Pb-Zn-Cu-Ag-Au-Sb-As-Bi-Cd-Te-Se-Ge…) quartz veins occur in an area from Eidsvoll in southeastern Norway to west of LakeVänern in southwestern Sweden. They most likely formed during the waning stage of the c. 1 Ga Sveconorwegian orogeny. In Värmskog parish, Värmland county, several mineralized quartz veins of different types are known. Of these, three of the larger vein deposits, Vegerbol, Karlsbol and Södra Gärdsjön, have been investigated. Despite a history of mining activities (mostly for silver) and exploration from the mid-1800s up until the present day, details about their ore mineralogy have remained essentially unknown. In order to classify and characterize them better, the present study was undertaken. The main ore minerals in the veins are galena, sphalerite, chalcopyrite, tetrahedrite sensu lato and pyrite. Additionally, this investigation showed the occurrence of an array of silver-bearing phases such as argentian tetrahedrite to freibergite, native silver, polybasite, pyrargyrite, jalpaite, aguilarite, cervelleite, hessite and matildite. These are the main and accessory silver carriers in the studied deposits. Gold (argentiferous) was also found, as well as the nickel-cobalt sulphide siegenite.    The silver contents of the tetrahedrites may vary within one deposit, ranging from tetrahedrite sensu stricto to freibergite. A weak positive correlation occurs between silver and iron in the tetrahedrites. Cadmium was found both in the tetrahedrites and in the sphalerites. Many sphalerites, however, are very pure ZnS. The complex accessory ore mineralogy, including native gold as well as tellurium and selenium-bearing phases (Vegerbol), makes these vein deposits comparable to mineralized veins to the west and southwest of the Värmskog area.    Combining mineralogical and textural observations with previous studies, the vein mineralizations most likely formed during a change in tectonic regime, in recurrently active brittle structures, at temperatures ranging from c. 350 down to below 100°C. The occurrence of pyrite and hematite and the lack of pyrrhotite and magnetite points to an oxidizing ore-forming environment with relatively high sulphur activity.    Finally, in order to assess the possibility of connecting two of the mined vein systems, VLF (Very Low Frequency) electromagnetic measurements were performed across the strike of a possible continuation between the Vegerbol and Karlsbol deposits. The VLF survey showed a significant anomaly where such a continuation was to be expected, thus indicating an overall strike length of at least 1 km for that vein system.<br>Sammanfattning Polymetalliska (Pb-Zn-Cu-Ag-Au-Sb-As-Bi-Cd-Te-Se-Ge…) kvartsgångar förekom­mer inom ett område från Eidsvoll, Norge i norr, till sydväst om Vänern i Sverige. De tros ha bildats under den svekonorvegiska orogenesens (ca 1 Ga) slutskede. I Värmskogs socken, Värmland, förekommer mineraliserade kvartsgångar av flera olika typer. Bland dessa har tre undersökts med avseende på malmmineralogi. Dessa kallas för Vegerbol, Karlsbol och Södra Gärdsjön, och de har brutits i huvudsak på silver. Trots att brytning och prospekteringsarbeten pågått från 1800-talet fram till i dag har det saknats detaljerade mineralogiska beskrivningar över fyndigheterna. Denna studie har genomförts för att bättre kunna karakterisera och klassificera dessa mineralis­eringar. Huvudmalmmineral vid dessa förekomster är blyglans, zinkblände, koppar­kis, pyrit och för Södra Gärdsjön även tetraedrit. Denna undersökning har påvisat förekomsten av silverförande faser som silverhaltig tetraedrit till freibergit, gediget silver, polybasit, jalpait, aguilarit, cervelleit, hessit och matildit, vilka utgör både huvudsakliga och accessoriska silverbärare i de undersökta förekomsterna. Guld (silverhaltigt) har också hittats, samt ett Ni-Co-förande mineral, siegenit.    Silverinnehållet i tetraedriterna varierar inom en och samma förekomst, några analyser har givit freibergitsammansättningar. En svag positiv korrelation finns mellan silver och järnhalt i tetraedrit. Kadmium förekommer både i tetraedrit och i zinkblände. Många zinkbländen består dock av rent ZnS. Förekomsten av relativt komplexa accessoriska mineral inklusive guld och Se-Te-faser (Vegerbol) visar att dessa gångar är jämförbara med liknande förekomster väster och sydväst om Värmskogs­området.    Genom att sammanföra data från denna undersökning med sådana från tidigare studier gjorda på gångarna kan man anta att de bildats vid vid en förändring av den tektoniska miljön, i upprepat aktiva spröda strukturer och vid temperaturer mellan ungefär 350 till under 100 °C. Förekomsten av pyrit och hematit samt avsaknad av magnetkis och magnetit tyder på att malmbildningen skett under oxiderade förhållan­den och relativt hög svavelaktivitet.      Elektromagnetiska mätningar i VLF-bandet (Very Low Frequency) utfördes tvärs över den förmodade strykningsriktningen för en möjlig fortsättning av gången mellan Karlsbol och Vegerbol. Mätningarna gav en tydlig anomali där en sådan fortsättning kan förväntas vilket skulle kunna betyda att det finns en sammanhängande mineralisering med ca 1 kilometers längd.

Abstract Brain activity fluctuations occur in multiple spatial and temporal scales. Functional magnetic resonance imaging (fMRI) has shown that infra slow fluctuations (ISF) of blood oxygen level-dependent signal (BOLD) are organized into well-defined areas called resting state networks (RSN). ISFs have also been detected in full-band EEG (fbEEG) data and in recent years, many have combined these two modalities to enable more accurate measurements of brain fluctuations. In simultaneous EEG-fMRI measurements the ISFs of BOLD signal have been found to be correlated with amplitude envelopes of faster electrophysiological data, suggesting the same underlying neuronal dynamics. Also direct correlations have been found in task related studies but not previously in resting state studies. Understanding the relation between EEG and BOLD signal in resting state might prove beneficial in the research of baseline activity fluctuations of the brain. Functional connectivity (FC) of the RSNs has been found to vary in different tasks and in some diseases, but also in resting state in healthy people. Despite numerous studies, no clear cause for these variations has yet been found. To research these open questions we performed simultaneous fbEEG-fMRI studies. The measurements from both modalities were analyzed with independent component analysis to improve the comparability of these results. Correlation analysis revealed that the EEG ISFs correlate with BOLD signal both temporally and spatially. These correlations showed spatiotemporal variability that was related to the strength of RSN functional connectivity. These results indicate that the ISFs of EEG and BOLD reflect a common source of fluctuations. The understanding of the correlations between ISFs in EEG and fMRI BOLD signals gives basic information of brain dynamics and of the variables that affect it. A better understanding of the background of brain activity helps in the development of more effective treatments for various neurological diseases as the knowledge of the mechanisms behind them grows. The ability to measure RSN activity with EEG more accurately can help in the development of new methods for early diagnosis of diseases<br>Tiivistelmä Aivojen toiminta vaihtelee monissa avaruudellisissa ja ajallisissa mittakaavoissa. Toiminnallisissa magneettikuvauksissa (TMK) on havaittu, että veren happipitoisuudesta riippuvan (engl. BOLD) signaalin erittäin hitaat vaihtelut ovat järjestäytyneet hyvin määriteltyihin alueisiin, joita kutsutaan lepotilahermoverkostoiksi. Erittäin hitaita vaihteluita on havaittu myös täysikaistaisesta aivosähkökäyrästä (fbEEG). Viime vuosina nämä kaksi menetelmää on usein yhdistetty tarkemman mittaustuloksen aikaansaamiseksi. Samanaikaisissa EEG-TMK-mittauksissa BOLD signaalin erittäin hitaiden vaihteluiden on huomattu korreloivan nopeampien elektrofysiologisten värähtelyjen amplitudien verhokäyrien kanssa, mikä viittaa samaan perustana olevaan neuraaliseen dynamiikkaan. Myös suoria korrelaatioita on löydetty tehtäviin liittyvissä tutkimuksissa, mutta ei aiemmin lepotilatutkimuksissa. Lepotilan EEG:n ja BOLD-signaalin suhteen ymmärrys voi osoittautua hyödylliseksi aivojen perustilan aktiivisuuden vaihteluiden tutkimisessa. Hermoverkostojen toiminnallisen liittyvyyden on todettu huojuvan tietyissä tehtävissä ja joissain sairauksissa, mutta myös lepotilassa terveillä henkilöillä. Runsaasta tutkimuksesta huolimatta ei liittyvyyden huojunnalle ole vielä löytynyt selkeää aiheuttajaa. Näiden avoimien kysymysten tutkimiseksi suoritimme yhdenaikaisia fbEEG-TMK-mittauksia. Kummankin modaliteetin mittaustuloksia analysoitiin itsenäisten komponenttien analyysillä tulosten vertailtavuuden parantamiseksi. Korrelaatioanalyysit osoittivat, että EEG:n erittäin hitaat vaihtelut korreloivat ajallisesti ja avaruudellisesti TMK:n BOLD-signaalin kanssa. Näissä korrelaatioissa esiintyi sekä paikkaan että aikaan liittyvää huojuntaa, joka oli yhteydessä lepotilahermoverkostojen toiminnallisen liittyvyyden vahvuuteen. Nämä tulokset viittaavat siihen, että samat tekijät tuottavat EEG:n ja TMK:n BOLD-signaalien hitaat vaihtelut. EEG:n ja TMK:n signaalien erittäin hitaiden vaihteluiden välisen korrelaation ymmärtäminen antaa perustason tietoa aivojen toiminnan dynamiikasta sekä siihen vaikuttavista tekijöistä. Parempi ymmärrys aivotoiminnan taustoista auttaa kehittämään tehokkaampia hoitoja neurologisiin sairauksiin, kun tieto mekanismeista niiden takana tarkentuu. Mahdollisuus mitata lepotilahermoverkostojen toimintaa EEG:llä aiempaa tarkemmin voi auttaa kehittämään uusia menetelmiä sairauksien varhaiseen diagnostiikkaan

Observation supposee effectuee en un point fixe de l'espace. Cette observation consiste en la mesure simultanee d'au moins trois composantes du champ electromagnetique. Discussion des estimateurs du degre de polarisation proposes par samson. Simulation numerique. Identification experimentale des modes d'une onde multiple en propagation dans ce magnetoplasma (ou deux modes peuvent coexister), obtenue a partir des caracteristiques de polarisation des ondes. Application aux emissions tres basse frequence observees par satellite aureol-3

Experiments and numerical investigations on trapped electron plasmas and traveling electron bunches are discussed. A Thomson backscattering diagnostics set up was installed in the ELTRAP (Electron TRAP) device, a Penning-Malmberg trap operating at the Department of Physics of the University of Milano since 2001. Here, an infrared (IR) laser pulse collides with nanosecond electron bunches with an energy of 1-20 keV traveling through a longitudinal magnetic field in a dynamical regime where space-charge effects play a significant role. The backscattered radiation is optically filtered and detected by means of a photomultiplier tube. The minimum sensitivity of the backscattering diagnostics has been estimated for the present set-up configuration. Constraints on the number of photons and thus on the information one can obtain with the Thomson backscattering technique are determined by the relatively low density of the electron beam as well as by noise issues. Solutions to increase the signal level and to reduce the noise are briefly discussed. The generation of an electron plasma by stochastic heating was realized in ELTRAP under ultra-high vacuum conditions by means of the application of low power RF (1-20 MHz) drives on one of the azimuthally sectored electrodes of the trap. The relevant experimental results are reviewed. The electron heating mechanism has been studied by means of a two-dimensional (2D) particle-in-cell (PIC) code, starting with a very low electron density, and applying RF drives of various amplitudes in the range 1-15 MHz on different electrodes. The axial kinetic energy of the electrons is in general increasing for all considered cases. Of course, higher temperature increments are obtained by increasing the amplitude of the RF excitation. The simulation results indicate in particular that the heating is initially higher close to the cylindrical wall of the device. These results on the electron heating point in the same direction of the experimental findings, where the plasma formation due to the ionization of the residual gas is found to be localized close to the trap wall. The simulations indicate also major heating effects when the RF drive is applied close to one end of the trap. Similar results are obtained for an electron plasma at higher densities, simulating a situation in which the RF is applied to an already formed plasma. With the aim to extend these RF studies to the microwave range, a bench test analysis has been performed of the transmission efficiency of a microwave injection system up to a few GHz. The test was based on the use of a prototype circular waveguide with the same diameter and length of the ELTRAP electrode stack and of a coupled rectangular waveguide with dimensions suitable for a future installation in the device. Electromagnetic PIC simulations have also been performed of the electron heating effect, again both at very low and relatively high electron densities, applying a microwave drive with a frequency of approximately 3 GHz close to the center and close to one end of the trap. Both the bench test of the injection system and the numerical simulations indicate that the new microwave heating system will allow the extension of the previous RF studies to the GHz range. In particular, the electron cyclotron resonance heating of the electrons will be aimed to increasing the electron temperature, and possibly its density as a consequence of a higher ionization rate of the residual gas. The installation of the new RF system will open up the possibility to study, e.g., the interaction between the confined plasma and traveling electron bunches.

Le long des littoraux sableux tels que la côte Aquitaine, les vagues et principalement les courants moyens induits par celles-ci jouent un rôle majeur dans l’évolution morphologique des plages. Que ce soit d’un point de vue socio-économique (aménagement des plages, protection de l’environnement) ou sécuritaire (noyade), comprendre la dynamique de tels environnements est devenu un réel enjeu scienti?que ces dernières années. Le développement d’une plateforme de modélisation morphodynamique opérationnelle a été menée au cours de cette thèse. Ce modèle est basé sur le couplage du modèle spectral de houle SWAN (Delft University of Technology) avec le modèle MARS 2DH (Ifremer), initialement conçu pour calculer les courants induits par la marée et les vents. Après avoir ajouté les phénomènes liés à la houle, un modèle sédimentaire a été développé pour estimer les évolutions morphodynamiques. La campagne de mesures Biscarrosse-PréECORS menée en juin 2007 sur la plage de Biscarrosse a permis de valider le modèle pour une large gamme d’état de mer. Le modèle a montré son e?cacité et sa robustesse pour décrire les courants et des circulations induites par les vagues au dessus de fortes hétérogénéités bathymétriques. Nous avons mis en évidence la forte modulation tidale des courants sagittaux qui sont intenses même pour de faibles conditions de vagues. La plateforme de modélisation morphodynamique a permis d’analyser la formation et le développement de morphologies tridimensionnelles rythmiques pour des systèmes simple et double barre. Pour les environnements à double barre comme la côte Aquitaine, l’intense couplage morphologique entre la barre externe et la barre interne a été étudié en réponse aux conditions de forçages. Nous avons mis en évidence l’in?uence de la marée sur la croissance des barres et révélé la corrélation existant entre croissance des barres et dissipation d’énergie des vagues sur les barres. Cette thèse a abouti au développement d’un modèle complet permettant d’appréhender la dynamique des environnements littoraux sableux<br>Along many sandy environments as the Aquitanian Coast, waves and wave-induced currents play a key role on the beach morphodynamics. Within a socio-economic (human interventions, natural environment protection) and touristic (human safety) framework, understand the complex dynamics of these systems is a real scienti?c challenge these last decades. The development of an operational morphodynamical modeling platform was performed during this PhD thesis. The modeling strategy consists in coupling the spectral wave model SWAN (Delft Univer- sity of Technology) with the non-linear shallow water model MARS 2DH (Ifremer). The MARS model was initially designed to compute tide- and wind-induced currents. Thus, the wave processes and a sed- imentary unit were implemented inside MARS to compute morphological evolutions of wave-dominated sandy beached. The Biscarrosse-PréECORS ?eld experiment carried out in June 2007 at Biscarrosse Beach was used to validate our modeling platform for a large range of o?shore wave conditions. Results have proved the e?ciency and the robustness of our model to calculate wave-induced currents and circulations over alongshore non-uniformities. The strong tidal modulation of currents and the intense rip currents for low-energy conditions were highlighted. The morphodynamical modeling platform was also used to analyze the generation and the development of rhythmic three-dimensional morphologies for one- and double-barred systems. For double-barred en- vironments, the intense morphological coupling between the inner and outer bar was studied in the response of wave and tide forcing. We have highlighted the in?uence of the tide on the bar growth and showed the correlation between the growth and the wave dissipation over the bar. This thesis has succeeded in the development of a complete model for understanding the dynamics of sandy coastal environments

Le frottement interne et le module d'young a basse frequence d'aerogels de silice de faible densite sont mesures par la methode de la lame vibrante encastree entre 100 mk et 80 k. Les resultats sont proches de ceux de la silicice vitreuse, en l'absence d'helium adsorbe, et sont interpretes en termes de systeme a deux niveaux. L'adsorption d'helium modidie notablement les resultats

L'augmentation des transits de puissance dans les réseaux d'énergie électrique ainsi que les contraintes environnementales ont conduit à l'introduction des dispositifs FACTS (Flexible AC Transmission Systems) pour l'amélioration de l'exploitation des réseaux. Ces dispositifs sont capables de remplir diverses fonctions comme le maintien de la tension, le contrôle des flux de puissance, l'amélioration de la stabilité du réseau, l'augmentation de la puissance transmissible maximale, etc. De plus, grâce à leur temps de réponse rapide, ils sont apparus comme des outils efficaces pour l'amortissement des oscillations électromécaniques très basses fréquences. Cette nouvelle fonction des dispositifs FACTS est d'autant plus importante que les réseaux mondiaux sont de plus en plus interconnectés, donc sensibles aux oscillations électromécaniques inter-régions. Cependant, le recours à de nombreux dispositifs FACTS dans un réseau nécessite d'étudier attentivement les éventuels problèmes d'interaction de régulation des dispositifs FACTS entre eux, mais aussi avec les autres éléments du réseau. Le travail réalisé dans le cadre de cette thèse traite des phénomènes dynamiques liés aux problèmes d'interaction résultant de l'insertion d'un ou plusieurs dispositifs FACTS shunt. Des indices de sensibilité et d'influence sont définis depuis les concepts de commandabilité et d'observabilité respectivement afin de prévoir l'importance des phénomènes d'interaction liés à l'insertion d'un dispositif FACTS et d'identifier les zones d'influence du dispositif FACTS. Ces indices sont appliqués à un réseau test 2 zones 4 machines et à un réseau réel simplifié 29 machines. Deux méthodes de coordination (méthode de type " minimax " et méthode linéaire quadratique décentralisée) sont mises en œuvre pour coordonner les dispositifs FACTS entre eux et avec les stabilisateurs de puissance (PSS - Power System Stabilizer) dans le réseau test 2 zones 4 machines<br>Power fiow increase and environmental constraints in power Systems hâve led to FACTS (Flexible AC Transmission Systems) devices insertion in order to improve the power System exploitation. Thèse devices are able to cany out some funétions such as the voltage support, the power transfer control and the increase of power transfer capability. Moreover, due to their fast response time, they are an efficient tool for damping low frequency oscillations. This new FACTS devices application is important as power Systems are more and more interconnected and thereby more sensitive to inter-area eîectromechanical oscillations. However, the recourse to several FACTS devices in a power System requires the careful study of the possible controller interaction phenomena between FACTS devices and with others system éléments. This thesis deals with the analysis and resolution of dynamic phenomena due to interaction problems resulting from the insertion of one or several shunt FACTS devices. Sensitivity and influence indices are defined from the controllability and observability notions, respectively, in order to preview the interaction phenomena importance due to a FACTS device insertions and to identify the influence areas of a FACTS device. Thèse indices are applied to a two-area four-machine test system and to a simplified real 29-machine power system. Two coordination methods (" minimax " method and decentralized linear quadratic method) are used to coordinate the FACTS devices themselves and a FACTS device and PSS (Power System Stabilizer) in the two-area four-machine test system

abstract: The U.S. Navy is interested in evaluating the dielectric performance of SF6 at 30 kHz in order to develop optimal bushing designs and to ensure reliable operation for the Very Low Frequency/ Low Frequency (VLF/LF) transmitting stations. The breakdown experiments of compressed SF6 at 30 kHz in the pressure range of 1-5 atm were conducted in both the uniform field (plane-plane gap) and the non-uniform field (rod-plane gap). To understand the impact of pressure on the breakdown voltage of SF6 at VLF/LF, empirical models of the dielectric strength of SF6 were derived based on the experimental data and regression analysis. The pressure correction factors that present the correlation between the breakdown voltage of SF6 at VLF/LF and that of air at 50/60 Hz were calculated. These empirical models provide an effective way to use the extensively documented breakdown voltage data of air at 60 Hz to evaluate the dielectric performance of SF6 for the design of VLF/LF high voltage equipment. In addition, several breakdown experiments and similar regression analysis of air at 30 kHz were conducted as well. A ratio of the breakdown voltage of SF6 to that of air at VLF/LF was calculated, from which a significant difference between the uniform gap and the non-uniform gap was observed. All the models and values provide useful information to evaluate and predict the performance of the bushings in practice.<br>Dissertation/Thesis<br>M.S. Electrical Engineering 2010

abstract: Electric field imaging allows for a low cost, compact, non-invasive, non-ionizing alternative to other methods of imaging. It has many promising industrial applications including security, safely imaging power lines at construction sites, finding sources of electromagnetic interference, geo-prospecting, and medical imaging. The work presented in this dissertation concerns low frequency electric field imaging: the physics, hardware, and various methods of achieving it. Electric fields have historically been notoriously difficult to work with due to how intrinsically noisy the data is in electric field sensors. As a first contribution, an in-depth study demonstrates just how prevalent electric field noise is. In field tests, various cables were placed underneath power lines. Despite being shielded, the 60 Hz power line signal readily penetrated several types of cables. The challenges of high noise levels were largely addressed by connecting the output of an electric field sensor to a lock-in amplifier. Using the more accurate means of collecting electric field data, D-dot sensors were arrayed in a compact grid to resolve electric field images as a second contribution. This imager has successfully captured electric field images of live concealed wires and electromagnetic interference. An active method was developed as a third contribution. In this method, distortions created by objects when placed in a known electric field are read. This expands the domain of what can be imaged because the object does not need to be a time-varying electric field source. Images of dielectrics (e.g. bodies of water) and DC wires were captured using this new method. The final contribution uses a collection of one-dimensional electric field images, i.e. projections, to reconstruct a two-dimensional image. This was achieved using algorithms based in computed tomography such as filtered backprojection. An algebraic approach was also used to enforce sparsity regularization with the L1 norm, further improving the quality of some images.<br>Dissertation/Thesis<br>Doctoral Dissertation Electrical Engineering 2017

博士<br>國立臺灣師範大學<br>地球科學系<br>98<br>This dissertation presents a study using the very low frequency electromagnetic (VLF-EM) method with a new data processing technique, ensemble empirical mode decomposition (EEMD), and the 2D regularized inversion to investigate the subsurface structure of a mud volcanic site. The EEMD technique was served as a filter bank to enhance the signal-to-noise (S/N) ratio of the data. After the data were processed by the EEMD, a regularized inversion with finite-element forward modeling scheme was utilized to calculate the subsurface resistivity model of a single profile. Inversion results were confirmed by surface 2D contour analysis. The results indicate that the EEMD technique is critical in improving the model accuracy of the inversion. To demonstrate the effectiveness of this new data processing scheme in studying mud volcanoes, secular data collection and analysis in the Wu-Shan-Ding (WSD) mud volcano nature reserve in southwest Taiwan were conducted sporadically over the period 2005 to 2008. This study successfully predicted the evolving of a gryphon, and proposed a model for the shallow structure of the eruption site. Examining the inversion results, fluid content of the mud, distribution of gryphons and mud pools, and erupting events of the study area, an active Chi-shan fault model is also suggested in this study.

碩士<br>國立中山大學<br>應用數學研究所<br>86<br>This thesis studies the spectrum of EKG of a heart-diseased patient after he undergoes the surgery so as to explore these changes that come along with the patient''s recovery. We gather the EKG of the patient in the six day after the surgery is done and focus on the PR interval, RT interval and heart rate to do the spectrum analysis. The past analysis merely deals with the spectrum of heart rate; therefore, in this thesis, the analysis of the spectrum of RT and PR intervals is included.Fisrt of all, we do spline function of the PR｛nd RT intervals and heart rate and then calculate the ultra-low frequency through analy of variance. We find that the spectrum of the RT interval explains in a better way the situation of the patient as he recovers.

碩士<br>國立雲林科技大學<br>電機工程系<br>104<br>High voltage XLPE power cable is often used for power transmission and distribu-tion system in Taiwan. DC voltage insulation testing is commonly applied as withstand test or leakage current measurement technique to analyze the insulation of power cables. DC voltage insulation testing devices are portable and cost-effective, but it is a destruc-tive test. It is recommended to assess the insulation of high voltage XLPE power cable by simple withstand and tangent delta test with very low frequency (VLF: 0.01~0.1 Hz) sine wave voltage sources to overcome the weak point of the DC voltage insulation test-ing, and assess the insulation precisely. So far, the assessment criteria reported in the journal literature and IEEE standard are established by the cable system database in the North American region. In this research, we introduced a convenient cable insulation diagnostic system with VLF instrument in our field testing. Until now we have accumu-lated a lot of experience in the diagnostic system, and we established a new suitable as-sessment criterion by a cable system database in Taiwan. Thus, we can deduce possible causes of a defect in cable insulation from the condition assessment. In this way, the cost of resetting defective power cable systems can be reduced and the safety and quali-ty of electrical equipment can be improved.

The Very Low Frequency Electromagnetic (VLF-EM) method, which enables surveying without contact with the ground, is suitable for ground surveys in a wide area and has been used in mapping geology for decades. The technique makes use of signal radiation from military navigation radio transmitters operating in the frequency range of 15-30 kHz. When the electromagnetic wave impinges on the surface it is both reflected back into the air and refracted into the earth. By measuring the shifted reflected magnetic field relative to the primary field, subsurface structures can be constrained. Although the VLF method has been widely used to map geology in the last several decades, few modeling studies have been published. Particularly the effect of topography on VLF measurements is poorly characterized. The objective of my research is to study and simulate the VLF topographic responses, and therefore to distinguish between such responses and actual subsurface resistivity anomalies in VLF-EM data. A few basic models (homogenous half-space, horizontal contact and vertical contact) were first created using the finite-elements modeling software Comsol Multiphysics and verified with theoretical solutions. Subsequently, features such as hills and lakes were incorporated into these basic models and further analyzed. When modeling topographic effects, two relationships between max inphase / max slope and max Quad / max slope versus skin depth / hill width are found, which can be used to predict topographic effects when the slope of a hill and resistivity of the ground are known. Two different sets of field data acquired at Saskatoon’s Diefenbaker Hill and at Cameco’s Cree Extension are compared with the modeling results.

The ability to extract frequent pairs from a set of transactions is one of the fundamental building blocks of data mining. When the number of items in a given transaction is relatively small the problem is trivial. Even when dealing with millions of transactions it is still trivial if the number of unique items in the transaction set is small. The problem becomes much more challenging when we deal with millions of transactions, each containing hundreds of items that are part of a set of millions of potential items. Especially when we are looking for highly correlated results at extremely low support levels. For 25 years the Direct Hashing and Pruning Park Chen Yu (PCY) algorithm has been the principal technique used when there are billions of potential pairs that need to be counted. In this paper we propose a new approach that allows us to take full advantage of both multi-core and multi-CPU availability which works in cases where PCY fails, with excellent performance scaling that continues even when the number of processors, unique items and items per transaction are at their highest. We believe that our approach has much broader applicability in the field of co-occurrence counting, and can be used to generate much more interesting results when mining very large data sets.<br>Graduate

Esta tese estuda o projecto e o comportamento de filtros em tempo contínuo de muito-alta-frequência. A motivação deste trabalho foi a investigação de soluções de filtragem para canais de leitura em sistemas de gravação e reprodução de dados em suporte magnético, com custos e consumo (tamanho total inferior a 1 mm2 e consumo inferior a 1mW/polo), inferiores aos circuitos existentes. Nesse sentido, tal como foi feito neste trabalho, o rápido desenvolvimento das tecnologias de microelectrónica suscitou esforços muito significativos a nível mundial com o objectivo de se investigarem novas técnicas de realização de filtros em circuito integrado monolítico, especialmente em tecnologia CMOS (Complementary Metal Oxide Semiconductor). Apresenta-se um estudo comparativo a diversos níveis hierárquicos do projecto, que conduziu à realização e caracterização de soluções com as características desejadas. Num primeiro nível, este estudo aborda a questão conceptual da gravação e transmissão de sinal bem como a escolha de bons modelos matemáticos para o tratamento da informação e a minimização de erro inerente às aproximações na conformidade aos princípios físicos dos dispositivos caracterizados. O trabalho principal da tese é focado nos níveis hierárquicos da arquitectura do canal de leitura e da realização em circuito integrado do seu bloco principal – o bloco de filtragem. Ao nível da arquitectura do canal de leitura, apresenta-se um estudo alargado sobre as metodologias existentes de adaptação de sinal e recuperação de dados em suporte magnético. Este desígnio aparece no âmbito da proposta de uma solução de baixo custo, baixo consumo, baixa tensão de alimentação e baixa complexidade, alicerçada em tecnologia digital CMOS, para a realização de um sistema DFE (Decision Feedback Equalization) com base na igualização de sinal utilizando filtros integrados analógicos em tempo contínuo. Ao nível do projecto de realização do bloco de filtragem e das técnicas de implementação de filtros e dos seus blocos constituintes em circuito integrado, concluiu-se que a técnica baseada em circuitos de transcondutância e condensadores, também conhecida como filtros gm-C (ou transcondutância-C), é a mais adequada para a realização de filtros adaptativos em muito-alta-frequência. Definiram-se neste nível hierárquico mais baixo, dois subníveis de aprofundamento do estudo no âmbito desta tese, nomeadamente: a pesquisa e análise de estruturas ideais no projecto de filtros recorrendo a representações no espaço de estados; e, o estudo de técnicas de realização em tecnologia digital CMOS de circuitos de transcondutância para a implementação de filtros integrados analógicos em tempo contínuo. Na sequência deste estudo, apresentam-se e comparam-se duas estruturas de filtros no espaço de estados, correspondentes a duas soluções alternativas para a realização de um igualador adaptativo realizado por um filtro contínuo passa-tudo de terceira ordem, para utilização num canal de leitura de dados em suporte magnético. Como parte constituinte destes filtros, apresenta-se uma técnica de realização de circuitos de transcondutância, e de realização de condensadores lineares usando matrizes de transístores MOSFET para processamento de sinal em muito-alta-frequência realizada em circuito integrado usando tecnologia digital CMOS submicrométrica. Apresentam-se métodos de adaptação automática capazes de compensar os erros face aos valores nominais dos componentes, devidos às tolerâncias inerentes ao processo de fabrico, para os quais apresentamos os resultados de simulação e de medição experimental obtidos. Na sequência deste estudo, resultou igualmente a apresentação de um circuito passível de constituir uma solução para o controlo de posicionamento da cabeça de leitura em sistemas de gravação/reprodução de dados em suporte magnético. O bloco proposto é um filtro adaptativo de primeira ordem, com base nos mesmos circuitos de transcondutância e técnicas de igualação propostos e utilizados na implementação do filtro adaptativo de igualação do canal de leitura. Este bloco de filtragem foi projectado e incluído num circuito integrado (Jaguar) de controlo de posicionamento da cabeça de leitura realizado para a empresa ATMEL em Colorado Springs, e incluído num produto comercial em parceria com uma empresa escocesa utilizado em discos rígidos amovíveis.<br>This thesis studies the design and behavior of continuous-time very-high-frequency filters. The motivation of this work was the search for filtering solutions for the readchannel in recording and reproduction of data on magnetic media systems, with costs and consumption (total size less than 1 mm2 and consumption under 1mW/pole), lower than the available circuits. Accordingly, as was done in this work, the rapid development of microelectronics technology raised very significant efforts worldwide in order to investigate new techniques for implementing such filters in monolithic integrated circuit, especially in CMOS technology (Complementary Metal Oxide Semiconductor). We present a comparative study on different hierarchical levels of the project, which led to the realization and characterization of solutions with the desired characteristics. In the first level, this study addresses the conceptual question of recording and transmission of signal and the choice of good mathematical models for the processing of information and minimization of error inherent in the approaches and in accordance with the principles of the characterized physical devices. The main work of this thesis is focused on the hierarchical levels of the architecture of the read channel and the integrated circuit implementation of its main block - the filtering block. At the architecture level of the read channel this work presents a comprehensive study on existing methodologies of adaptation and signal recovery of data on magnetic media. This project appears in the sequence of the proposed solution for a lowcost, low consumption, low voltage, low complexity, using CMOS digital technology for the performance of a DFE (Decision Feedback Equalization) based on the equalization of the signal using integrated analog filters in continuous time. At the project level of implementation of the filtering block and techniques for implementing filters and its building components, it was concluded that the technique based on transconductance circuits and capacitors, also known as gm-C filters is the most appropriate for the implementation of very-high-frequency adaptive filters. We defined in this lower level, two sub-levels of depth study for this thesis, namely: research and analysis of optimal structures for the design of state-space filters, and the study of techniques for the design of transconductance cells in digital CMOS circuits for the implementation of continuous time integrated analog filters. Following this study, we present and compare two filtering structures operating in the space of states, corresponding to two alternatives for achieving a realization of an adaptive equalizer by the use of a continuous-time third order allpass filter, as part of a read-channel for magnetic media devices. As a constituent part of these filters, we present a technique for the realization of transconductance circuits and for the implementation of linear capacitors using arrays of MOSFET transistors for signal processing in very-high-frequency integrated circuits using sub-micrometric CMOS technology. We present methods capable of automatic adjustment and compensation for deviation errors in respect to the nominal values of the components inherent to the tolerances of the fabrication process, for which we present the simulation and experimental measurement results obtained. Also as a result of this study, is the presentation of a circuit that provides a solution for the control of the head positioning on recording/playback systems of data on magnetic media. The proposed block is an adaptive first-order filter, based on the same transconductance circuits and equalization techniques proposed and used in the implementation of the adaptive filter for the equalization of the read channel. This filter was designed and included in an integrated circuit (Jaguar) used to control the positioning of the read-head done for ATMEL company in Colorado Springs, and part of a commercial product used in removable hard drives fabricated in partnership with a Scottish company.