Construction of FASR subsystem testbed and application for solar burst trajectories and RFI study

The construction of the Frequency Agile Solar Radiotelescope (FASR) Subsystem Testbed (FST) and observational results are described. Three antennas of Owens Valley Solar Array (OVSA) have been upgraded with newly designed, state of art technology. The 1-9 GHz RF signal from the antenna feed is transmitted via broadband (45 MHz-9.5 GHz) optical fiber links to the control room. The RF is then downconverted to a 500 MHz, single-sideband signal that can be tuned across the 1-9 GHz RF band. The data are sampled with an 8-bit, 1 GHz sampling-rate digitizer, and further saved to a computer hard disk. The full-resolution time-domain data thus recorded are then correlated through offline software to provide phase and amplitude spectra. An important feature of this approach is that the data can be reanalyzed multiple times with different digital signal-processing techniques (e.g., different bit-sampling, windowing, and RFI excision methods) to test the effects of different designs. As a prototype of the FASR system, FST provides the opportunity to study the design, calibration and interference-avoidance requirements of FASR. In addition, FST provides, for the first time, the ability to perform broadband spectroscopy of the Sun with high spectral, temporal and moderate spatial resolution. With this three-element interferometer, one has the ability to determine the location of simple sources with spectrograph-like time and frequency resolution. The large solar flare of 2006 December 6 was detected by the newly constructed FASR Subsystem Testbed, which is operating on three antennas of Owens Valley Solar Array. This record-setting burst produced an especially fine set of fiber bursts--so-called intermediate-drift bursts that drift from high to low frequencies over 6-10 s. According to a leading theory (Kuijpers 1975), the fibers are generated by packets of whistler waves propagating along a magnetic loop, which coalesce with Langmuir waves to produce escaping electromagnetic radiation in the decimeter band. With this three element interferometer, for the first time fiber burst source locations can be determined relative to the background even though the absolute location is still unkown for the lack of phase calibration information. The radio information over a 500 MHz band (1.0-1.5 GHz) was used to determine the trajectories of the bursts. Since the digital data are recorded with full resolution and processed offline, a key advantage of it is that one can process the data in different ways in order to simulate and test hardware implementations. FST data provides a unique testbed for studying methods of RFI excision. RFI is observed to be present in every one of the 500 MHz bands, and the high time and frequency resolution provided by FST allows one to characterize it in great detail. The use of time-domain kurtosis, and a variant of the kurtosis method in the frequency domain were explored to identify the presence of RFI and flag bad channels in simulated real time (i.e., we play back the raw, full-resolution recorded data and flag the bad channels during play-back just as a real-time system would do). The ability to select alternate RFI excision algorithms during play-back allows one to compare algorithms on an equal basis. From the same data set, the two kurtosis (time domain and frequency domain) RFI excision algorithms were compared. The results are compared quantitatively to show that the spectral kurtosis is more effective than time domain kurtosis algorithm for detecting the RFI contamination, as expected from theoretical considerations

On-line signal analysis of partial discharges in medium-voltage power cables

Partial discharges are symptomatic of many degradation phenomena in power cables and may cause further deterioration of the insulation in many cases. Electrical im- pulses, generated by partial discharges, travel towards the cable ends, and can there be detected using appropriate sensors. Continuous monitoring of the insulation con- dition can be achieved by on-line detection and location of partial discharge (PD) signals. An important aspect of such a diagnostic is the analysis of on-line measure- ments. The research reported in this thesis is aimed at analysis of PD signals from on-line measurements and location of discharge sites. Signal analysis depends on knowledge of both signals and disturbances that are to be expected. To that end, characteristics of PD signals in medium voltage cables are studied in this thesis. The result of this study is a signal model of the propagation path between the discharge site and the sensors. The model accounts for cable sections with di®erent properties, and incorporates the propagation channel load impedances, i.e. the equipment to which a cable is terminated in an on-line situation. The exact propagation properties and load impedances depend on the speci¯c cable connection under test, and are unknown a priori. For this reason, research is conducted on meth- ods that enable experimental characterization of the parameters, by evaluating the response of the cable to applied transients. The presented methods rely on the ex- traction of pulses that are re°ected on impedance transitions within the cable system under test. On-line ¯eld measurements are corrupted by noise and interference, which impede PD signal detection and location. Generally, narrowband interferences resulting from radio broadcasts dominate the measurements, thus prohibiting data-acquisition trig- gered by PD signals. Broadband background noise is present within the entire PD signal bandwidth, and therefore poses a fundamental limit on PD signal analysis. Generally, existing extraction techniques for PD signals only partially exploit a priori knowledge of both signals and interference. In this thesis, matched ¯lters are ap- plied that are derived from the signal model, and are optimally adapted to the signals that can be expected. Besides signal extraction, matched ¯lters provide a means to estimate the PD magnitude and the signal arrival time. Likewise, discharge location methods based on the signal model are proposed, resulting in optimal location esti- mators. Computer simulations illustrate the e®ectiveness of the proposed algorithms and show that the attainable accuracy can be speci¯ed by theoretical bounds. Accurate PD location relies on estimation of the di®erence in arrival times of signals originating from the same discharge. In case of on-line detection, the cable is connected to the grid, and signals are not necessarily re°ected at the cable ends. Therefore signal detection at both sides is generally required for the purpose of dis- charge location. Synchronization of the measurement equipment is achieved using pulses that are injected into the cable connection. Finite-energy disturbances, such as PD signals that originate outside the cable connection under test, frequently occur in on-line situations. Since measurements are synchronously conducted at both cable ends, pulses originating within and outside the cable can be distinguished by examining the di®erence in time of arrival. Moreover, in many situations, the signal direction of arrival can be determined by detecting pulses in two di®erent current paths at a cable termination. This method is applied as an additional technique to discriminate PD signals and disturbances. Based on the results of research, a measurement system is proposed, which enables automated on-line PD detection and location in medium voltage cable connections. The conceptual design is validated by experiments, and the results demonstrate that the practical application is promising

A Study of Cold Gas and Star Formation in Low-Mass Blue-Sequence E/S0s

We present a study of cold gas and star formation in low-mass blue-sequence E/S0 galaxies — a population that is morphologically early-type, but resides on the blue sequence in color vs. stellar mass space alongside spirals. A subset of these blue-sequence E/S0s may provide an evolutionary link between traditional red and dead early-type galaxies and star-forming spirals via disk (re)growth. In this dissertation, we use data from the Green Bank Telescope (GBT), the Combined Array for Research in Millimeter-wave Astronomy (CARMA), the Spitzer Space Telescope, and the Galaxy Evolution Explorer (GALEX) to examine the potential for morphological transformation of low-mass blue-sequence E/S0s. In considering the HI content of these galaxies, we find that, normalized to stellar mass, the atomic gas masses for 12 of the 14 blue-sequence E/S0s range from 0.1 to ≥1.0. These gas-to-stellar mass ratios are comparable to those of spiral and irregular galaxies, and have a similar dependence on stellar mass. Assuming that the HI is accessible for star formation, we find that 9 of 14 blue-sequence E/S0s can increase in stellar mass by 10–60% in 3 Gyr with current HI reservoirs alone. We present evidence that star formation in these galaxies is bursty and likely involves externally triggered gas inflows. For a sub-sample of eight E/S0s (four blue-, two mid-, and two red-sequence) whose CARMA CO(1–0), Spitzer MIPS 24μm, and GALEX FUV emission distributions are spatially resolved on a 750pc scale, we find roughly linear relationships between molecular-gas and star-formation surface densities within all galaxies, with power law indices N = 0.6–1.9 (median 1.2). Adding 11 more blue-sequence E/S0s whose CO(1–0) emission is not as well resolved, we find that most of our E/S0s have 1–8 kpc aperture-averaged molecular-gas surface densities overlapping the range spanned by the disks and centers of spiral galaxies. While many of our E/S0s fall on the same Schmidt-Kennicutt relation as local spirals, ∼80% are offset towards apparently higher molecular-gas star formation efficiency. We discuss possible interpretations of the apparently elevated efficiencies. We examine star formation in blue- and red-sequence E/S0s as traced by the 8μm PAH emission. We find the 8μm PAH/3.6μm emission ratios for most of our blue-sequence E/S0s to be similar to those of local spirals. Ratio images of the two tracers reveal ring-like and non-axisymmetric structures in some of our E/S0s, suggestive of internally and/or externally triggered gas inflow and centrally concentrated star formation. Comparison between the CO(1–0) and 8μm PAH emission distributions shows good agreement globally, although the 8μm PAH/3.6μm emission ratio appears to better trace non-axisymmetric structures observed in CO. Similar to CO observations of spiral galaxies, we find detectable CO emission in our E/S0s to be centrally concentrated, ranging from 0.1&ndash0.6r25 (median 0.3r25). We also find that the aperture-averaged 8μm PAH to 3.6μm stellar emission ratio correlates with the atomic and molecular gas mass fractions

Gas Around Active Galactic Nuclei and New Phase Calibration Strategies for High-Frequency VLBI

We have a project to measure magnetic fields in the obscuring tori of AGNs. We observed five free-free absorbed jets in radio galaxies with polarimetric VLBI at 15 GHz to determine Faraday rotation measures. Surprisingly, all sources are unpolarized, putting severe constraints on the degree of magnetic field turbulence and the gas distribution in these objects. We have further carried out multi-frequency VLBI monitoring of the Seyfert 2 galaxy NGC 3079 and find unusually steep and inverted spectra in the radio components, and derive general properties of Seyfert galaxies using published VLBI observations of Seyfert galaxies. We have developed a new phase-referencing technique for high frequency VLBI observations with the VLBA. Instead of inserting short scans on a calibrator into the target source observations, the target source is continuously observed while rapidly switching between the target frequency and a lower reference frequency. We demonstrate that the technique allows phase calibration almost reaching the thermal noise limit and present the first detection of the AGN in NGC 4261 at 86 GHz. This is the weakest source ever detected with VLBI at that frequency.Comment: PhD thesis, 188 page

Application Of Digital Signal Analysis, Mass Data Acquisition and Processing Techniques, and Automated Experiment Protocols to the Study of Cardiac Cell Membrane Electrophysiology, with Mathematical Modeling

Traditional methods of collecting, analyzing and storing data from cardiac cell membrane electrophysiology experiments have become increasingly cumbersome and unwieldy as experimental protocols have become more sophisticated and complex. A global approach to collecting, analyzing, refining and storing electrophysiologic data, as well as a new approach to mathematical modeling of cell membrane single ion channel kinetics, was developed. This utilizes a comprehensive microcomputer based system of software with specialized analog and digital electronics for data acquisition, analysis and archiving. Unique discrete signal processing techniques for characterizing the electronic recording system, including specialized hardware and software adapted for minimizing distortions in biosignal recordings, are discussed in detail

Millimeter and sub-millimeter wave radiometers for atmospheric remote sensing from CubeSat platforms

2018 Fall.Includes bibliographical references.To view the abstract, please see the full text of the document

Test Facilities Capability Handbook: Volume 1 - Stennis Space Center (SSC); Volume 2 - Marshall Space Flight Center (MSFC)

The John C. Stennis Space Center (SSC) is located in Southern Mississippi near the Mississippi-Louisiana state line. SSC is chartered as the National Aeronautics and Space Administration (NASA) Center of Excellence for large space transportation propulsion system testing. This charter has led to many unique test facilities, capabilities and advanced technologies provided through the supporting infrastructure. SSC has conducted projects in support of such diverse activities as liquid, and hybrid rocket testing and development; material development; non-intrusive plume diagnostics; plume tracking; commercial remote sensing; test technology and more. On May 30, 1996 NASA designated SSC the lead center for rocket propulsion testing, giving the center total responsibility for conducting and/or managing all NASA rocket engine testing. Test services are now available not only for NASA but also for the Department of Defense, other government agencies, academia, and industry. This handbook was developed to provide a summary of the capabilities that exist within SSC. It is intended as a primary resource document, which will provide the reader with the top-level capabilities and characteristics of the numerous test facilities, test support facilities, laboratories, and services. Due to the nature of continually evolving programs and test technologies, descriptions of the Center's current capabilities are provided. Periodic updates and revisions of this document will be made to maintain its completeness and accuracy

Partial discharges studied by dielectric response method

The increasing demand of integrating various renewable energy recourses in power system requires extensive use of power electronic solutions, which allows energy conversion between different frequencies and stabilizes the system. Consequently, other than the traditional 50/60 Hz sinusoidal voltage stresses act on the high voltage insulation systems. Therefore a need for elaborating fast and accurate characterization methods arises for facilitating studies of the different types of voltage waveforms on the behaviour of insulation materials and systems. Two commonly applied non-destructive insulation characterization techniques, dielectric response and partial discharge (PD) measurements, are addressed in the project. Several methods based on the so called Arbitrary Waveform Impedance Spectroscopy (AWIS) technique have been developed to enable fast and accurate characterization of dielectric material frequency response. This approach was further adopted to study the behaviour of PDs in various types of test objects, including needle-plate electrode arrangement, twisted pair enamel wires and dielectrically insulated cavities, by simultaneously applying the dielectric response measurements and the stochastic PD detection. Various experiments, involving occasionally changing voltage level, circulating air around a specimen, and modifying conductivity of cavity walls, were performed and allowed identifying additional PD current components in the total current response, which are in the following named as excess currents. It is shown among others, by comparing the excess currents with simultaneously detected PD pulses, that contributions from weak discharges lying below the conventional PD detection threshold as well as slow contributions to the current caused by charge movements within the partial discharge area can be identified and evaluated. An important component of the excess current is a non-PD excess current that repeatedly appears in all studied types of objects and causes a decay or even disappearance of PD activity with time. At longer exposures of the dielectrically isolated cavities, it also yields oscillating interchanges between PD activity and the excess current