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1
Forssén, Ulla. "Extremely low frequency magnetic fields and breast cancer /". Stockholm, 2003. http://diss.kib.ki.se/2003/91-7349-532-8/.
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2
Ker, Louise Moira. "Radio AGN evolution with low frequency radio surveys". Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7616.
Testo completoAbstract (sommario):
Supermassive black holes are leading candidates for the regulation of galaxy growth and evolution over cosmic time, via ‘feedback’ processes, whereby outflows from the Active Galactic Nuclei (AGN) halt star formation within the galaxy. AGN feedback is generally thought to occur in two modes, high-excitation (HERG, or ‘quasar-mode’) and low-excitation (LERG or ’radio-mode’) each having a different effect on the host galaxy. LERGs curtail the growth of the most massive galaxies, whereas HERGs are thought to be activated by mergers/interactions, switching off star formation at high redshift. A critical problem in current extragalactic astrophysics lies in understanding the precise physical mechanisms by which these feedback processes operate, and how they evolve over cosmic time. Radio-loud AGN are an essential tool for studying major feedback mechanisms, as they are found within the largest ellipticals, and hence are beacons for the most massive black holes across the bulk of cosmic time. In this thesis I develop and study existing complete radio samples with extensive new multi-wavelength data in the radio, optical and infrared, aiming to investigate the evolution of AGN feedback modes, and methods to locate and study such systems at the very highest redshifts. This will serve to inform further studies of radio-AGN planned with next generation radio instruments such as the LOw Frequency ARray (LOFAR). Very few radio-loud AGN systems are currently known at high redshifts, and the effectiveness of traditional high redshift selection techniques, such as selection based on steep spectral index, have not been well quantified. A purely evidence-based approach to determining the efficiency of various high redshift selection techniques is presented, using nine highly spectroscopically complete radio samples; although weak correlations are confirmed between spectral index and linear size and redshift, selection first of infrared-faint radio sources remains by far the most efficient method of selecting high-z radio galaxies from complete samples. Radio spectral curvature in four of the complete samples is analysed and the effect of radio spectral shape on the measurement of the radio luminosity function (RLF) of steep-spectrum radio sources is investigated. Below z=1, curvature has negligible effect on the measurement of the RLF, however at higher redshifts, where source numbers are low, the shape of the radio spectrum should be taken into account, as individual source luminosities can change up to 0.1-0.2 dex, and this can in some cases introduce errors in space density measurements of up to a factor of 2-3 where source numbers are low. Building upon these samples, the very first independent determinations of the separate RLFs for high and low excitation radio sources across the bulk of cosmic time are made, out to z=1. Here it is shown that HERGs show very clear signs of strong evolution, in line with theoretical predictions. LERGs also show some very weak evolution with redshift, showing increases in space density of typically around a factor of 2. These measurements are also used to estimate the contribution of LERGs, which typically show weak or no emission lines to the ‘missing redshift’ population, which are sources within the complete samples not identifiable spectroscopically. Complementary to this, a pilot study is presented in selecting ‘missing redshift’ sources which are classed as infra-red faint (IFRS), which show no optical or near-IR identification, and are compact in the radio. Follow up spectroscopy on these candidate high z sources detected no line emission. Finally, work carried out towards the testing and commissioning of the new LOFAR telescope is presented. The findings from this thesis will serve to both streamline and inform high redshift radio-AGN searches and studies planned to be carried out with LOFAR and other multi-wavelength complementary surveys in the near future, and help to open up an as yet unexplored epoch in radio-AGN formation and evolution.
3
Lazenby, Andrea Natalie. "Extremely low frequency magnetic field exposure in British railway environments". Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.555811.
Testo completoAbstract (sommario):
Exposure to extremely low frequency magnetic fields has been investigated in relation to various health effects. In the past, epidemiological studies have focused on residential and occupational exposures. The time spent commuting to work may not be insignificant, therefore any exposures acquired during those periods may have an effect on the strength of association. Given that millions of train journeys are made in Britain every year, extremely low frequency and static magnetic field measurements were made on six types of British trains and on five station platforms in order to characterise passenger exposure. Trains investigated included four elec- trical multiple units, one diesel-electrical multiple unit and one diesel locomotive. Power to the electric trains was supplied by either overhead cables (25 kV 50 Hz a.c.), the third rail (750 V d.c.) or from a four-rail system (630 V d.c.). The highest resultant a.c. magnetic field was measured on-board a diesel-electric multiple unit. The a.c. magnetic field was shown to vary with height above the carriage floor. The majority of resultant a.c. magnetic fields were higher closer to the floor, attributable to traction equipment mounted beneath the carriage. Average resultant a.c. magnetic fields at waist height across all train types were in the range 0.03-1.82 /-LT. The frequency component of the resultant a.c. magnetic field was shown to vary with increasing and decreasing speed on-board two different train types. The a.c. and d.c. magnetic field waveforms measured at different stations were dependent on the railway electrification and the types of train travelling on the line. Frequency spectra calculated from magnetic field waveforms taken on two station platforms showed component frequencies which were not multiples of the 50 Hz fundamental. Metrics such as the polarisation, total harmonic distortion and rate of change metric are considered, together with standard statistical measures of magnetic field.
4
Shepherd, Sebastian James. "The effects of extremely low frequency electromagnetic fields on insects". Thesis, University of Southampton, 2018. https://eprints.soton.ac.uk/422277/.
Testo completoAbstract (sommario):
Flying insect species are currently in decline, including many species that provide important pollination ecosystem services. Combined exposure to various environmental stressors are associated with insect declines, including land-use change, pesticide use and climate change, but the potential biological and environmental effects of extremely low frequency electromagnetic fields (ELF EMFs) are poorly understood. ELF EMFs are pervasive in the environment, and anthropogenic ELF EMF pollution has increased greatly in recent years. Despite this, little has been done to consider the potential environmental impacts of ELF EMFs. Given that there is evidence that ELF EMFs can have biological effects, it is important to explore these biological stimuli and their potential to affect insects in the environment. Here the biological effects of ELF EMFs on important insect species were investigated, with two-fold aims of both increasing understanding of the biological effects of ELF EMFs, and determining whether field-realisitc levels of ELF EMFs have the potential to cause envrionemental stress to insects. ELF EMF impacts were investigated with the desert locust, as an economically important agricultural pest and a species that provides utility in understanding insect neurophysiology, and the honey bee, as a globally important pollinator and a well known study species for insect cognitive behaviour. Short-term exposure to high levels of ELF EMFs was found to affect neurophysiology, and reduce locomotory function in locusts, as well as increase stress protein levels in bees and locusts, and affect honey bee cognitive behaviour. Acute exposure to ELF EMFs at levels that can be encountered regularly in the environment around man-man sources for ELF EMFs reduced honey bee performance in olfactory learning assays, affected flight behaviour, and affected feeding and flight performance in a semi-field scenario. Further to this, some of these impacts of ELF EMFs on cognitive behaviour and flight were reduced when ELF EMFs were applied in combination with other well-known environmental stressors, neonicotinoid insecticides. These findings give a more detailed indication of some of the physiological effects that may underpin changes in insect locomotory behaviour that occur after short-term exposure. This is the first time that powerline simulating ELF EMFs have been directly measured and applied to insects in the context of considering the ecological effects (and thus using field-realistic exposure levels) of the ELF EMFs, rather than just the biological effects. This is the first indication that short-term and acute ELF EMF exposure can affect insect cognitive behaviour, and these effects have been shown to occur at levels which can be encountered in the field by a globally important pollinator species, the honey bee. This is also the first indication that acute field-realistic ELF EMF exposure can affect insect locomotory behaviour in the environement. This research describes new effects of ELF EMFs on insect biology and establishes that ELF EMFs have a potential to affect insect ecology, such that future ELF EMF understanding must be focused in further exploring mechanisms by with ELF EMFs cause biological effects, as well as the larger scale ecological risk assessment of ELF EMF impacts from powerlines.
5
Belcher, Robert W. "Extremely High Frequency (EHF) Low Probability of Intercept (LPI) communication applications". Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA226653.
Testo completoAbstract (sommario):
Thesis (M.S. in Telecommunications Systems Management)--Naval Postgraduate School, March 1990.Thesis Advisor(s): Schwendtner, Thomas A. Second Reader: Davidson, K. L. "March 1990." Description based on title screen as viewed on August 25, 2009. DTIC Descriptor(s): Interception probabilities, communication and radio systems, communications networks, spectra, command and control systems, extremely high frequency, naval operations, tactical warfare, low rate, theses, scenarios, line of sight, military applications. Author(s) subject terms: Millimeter wave, EHF, Extremely High Frequency, LPI, Low Probability of Intercept. Includes bibliographical references (p. 68-70). Also available print.
6
Deadman, Jan-Erik. "Estimation of exposures to extremely low frequency electric and magnetic fields". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp03/NQ29919.pdf.
Testo completo
7
Koyama, Shin. "Genotoxic effects of extremely low frequency electromagnetic fields and radiofrequency radiation". Kyoto University, 2007. http://hdl.handle.net/2433/136436.
Testo completoAbstract (sommario):
Kyoto University (京都大学)0048
新制・課程博士
博士(人間・環境学)
甲第13165号
人博第372号
新制||人||91(附属図書館)
18||D||173(吉田南総合図書館)
UT51-2007-H438
京都大学大学院人間・環境学研究科相関環境学
(主査)教授 小松 賢志, 助教授 倉橋 和義, 助教授 三浦 智行
学位規則第4条第1項該当
8
Murji, Rizwan Deen M. Jamal. "Low-power CMOS radio frequency integrated circuits for frequency synthesis /". *McMaster only, 2005.
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9
Stephens, P. W. "Low frequency mapping with MERLIN". Thesis, University of Manchester, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382763.
Testo completo
10
Spinks, M. J. "Low frequency long baseline interferometry". Thesis, University of Cambridge, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372284.
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11
Bhakta, Nitin. "Extremely low frequency electromagnetic properties in marine environments with non-parallel interfaces". Thesis, King's College London (University of London), 2001. https://kclpure.kcl.ac.uk/portal/en/theses/extremely-low-frequency-electromagnetic-properties-in-marine-environments-with-nonparallel-interfaces(b13ce673-453d-4aca-925a-a7adf547cb69).html.
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12
Kim, Tony C. "Interaction of Very Low Frequency (VLF) and Extremely Low Frequency (ELF) Waves in the Ionospheric Plasma and Parametric Antenna Concept". Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1486674973747427.
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13
Maguire, Sean Thomas George. "Attitude determination using low frequency radio polarisation measurements". Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.708927.
Testo completo
14
Feng, Yi. "Mapping soil moisture using low-frequency radio signals". Thesis, University of Bath, 2016. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687379.
Testo completoAbstract (sommario):
Sufficient knowledge of near-surface soil moisture and sea surface salinity is essential for environmental studies. In recent years, efforts worldwide have focused on the use of imaging sensors onboard remote sensing satellites to capture such information. This thesis investigates if low-frequency radio signals originating from ground-based stations are suitable for the remote sensing of soil moisture and sea surface salinity. It is found that the time delay variation of 100 kHz Loran-C pulses may be representative of electrical conductivity changes along the propagation path, which have a direct link with soil and sea surface properties. The validation studies using Loran-C signals recorded at Bath and Harwich clearly show that the proposed method is capable of producing an estimation of soil moisture and sea surface salinity. This will form the basis for further validation and studies.
15
Strange, Samuel J. "Removal of coherent extremely low frequency (ELF) background noise by adaptive noise cancelation". Thesis, Monterey, California. Naval Postgraduate School, 1993. http://hdl.handle.net/10945/26725.
Testo completoAbstract (sommario):
The use of the Sequential Regression Algorithm (SER) to coherently remove background noise from an ELF sensor is presented. The SER algorithm is described for a multi-channel application in order to cancel coherent portions of reference sensors from a primary sensor. The algorithm adaptively accounts for differences between two parallel array platforms for the purpose of coherent subtraction. A section on likelihood ratio detector schemes for detecting narrowband signals is also presented. This work is in support of a submerged ELF sensor array project run by the Johns Hopkins University Applied Physics Lab
16
Ainsbury, Elizabeth Ann. "The physics of extremely low frequency magnetic fields in relation to health effects". Thesis, University of Bristol, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.445814.
Testo completo
17
Wilson, James William. "The effects of extremely low-frequency magnetic fields on mutation induction in mice". Thesis, University of Leicester, 2016. http://hdl.handle.net/2381/37610.
Testo completoAbstract (sommario):
Extremely low-frequency magnetic fields (ELF-MF) are classified as possibly carcinogenic, despite inconsistent data and no plausible biological mechanism linking their universal exposure with childhood leukaemia and genotoxic effects. Given discrepancies in mutagenic data and widespread public concern over genotoxic effects, this study was designed to provide an in-depth analysis of potential molecular changes induced by ELF-MF exposure in vivo. Seven-week old, BALB/c x CBA/Ca hybrid F1 male mice were exposed to 50 Hz magnetic fields of 10, 100 and 300 μT for 2- or 15 hours. Blood and sperm DNA samples were collected 12 weeks post-exposure and mutation induction frequencies established at the Expanded Simple Tandem Repeat (ESTR) Ms6-hm loci using single-molecule PCR (SM-PCR). Likewise, Ms6-hm mutation induction frequencies were established in age-matched sham-treated hybrid males (control group) and those exposed to 1 Gy acute X-rays (positive controls). No significant increases in ESTR mutation frequencies were detected in either tissue at any ELF-MF exposure parameter compared to their sham-treated controls. Whilst a marginally significant increase was observed in the mutation induction frequency of pooled sperm data, these data should be regarded cautiously due to the lack of correlating dose-dependent responses. Conversely, germline and somatic ESTR mutation frequencies were significantly elevated in males exposed to acute 1 Gy X-rays. These data were validated in a high-throughput microarray pilot study, whereby no significant alterations in gene expression in kidney cells of hybrid males were detected following ELF-MF exposure. In contrast, five transcripts were significantly up-regulated in the irradiated males. Ultimately, these findings indicate that, within the analysed range of doses, the in vivo effects of ELF-MF exposure on mutation induction and gene expression are likely to be negligible. This study represents the first methodical attempt to determine mutation frequencies in vivo after continuous exposure to 50 Hz ELF-MFs up to 300 μT.
18
Alaiwi, Ayman Ahmed. "The design and investigation of an extremely low frequency (ELF) transmission data link". Thesis, University of Huddersfield, 2013. http://eprints.hud.ac.uk/id/eprint/19029/.
Testo completoAbstract (sommario):
The telecommunication engineering field is playing a big role in the technology revolution, with most new technologies, smart phones and computers etc requiring 3G internet connection to be constantly in communication worldwide. A high spectral efficiency spectrum and maximising the number of users and transmission rate within a frequency band are the most critical design objectives and challenge to improve the reliability and performance of wireless communications systems. The use of the Extremely Low Frequency (ELF) band has largely been confined to submerged submarine communications and its application to civilian data transmission has been neglected. ELF signals propagate through the ground itself using earth rods for long distances without regeneration compared to Radio Frequency (RF). There are two major noise sources in the ELF band, namely flicker noise (1/f) and 50Hz radiation of power feed cables underground. This thesis has described the theoretical aspects of adopting the ELF band and the ground itself as transmission medium in a communication link based on Orthogonal Frequency Division Multiplex (OFDM scheme. The use of 16-Quadrature Amplitude Modulation (16-QAM) and OFDM in ELF link enhances the transmission capacity at such low frequencies and reduces the multi-path interference. The link could handle at least 1000 bit/s (bps) and replace the complexity and reduces the power needed for RF link in some applications. This thesis investigated the practical implementations of Binary Amplitude Shift Keying(BASK), 8-Phase Shift Keying (8-PSK) and 16-QAM with 20 Hz carrier and a data rate of 4 symbols/s from context to practice using Field Programmable Gate Array (FPGA). The highly flexible nature of FPGAs allows the systems designers to integrate any signal processing function. FPGAs replace the use of Digital Signal Processing (DSP) processors in many applications. Very high speed circuit Hardware Description Language (VHDL) language, Matlab, Altera DSP Builder and Altera Quartus II were used to design the ELF link. A thorough literature review showed that demodulating phase data is generally performed using carrier recovery. The current technology generally incorporates a complex mathematics ‘tan’ function and Costas loop to detect the phase changes of the 8-PSK and 16-QAM signals. The 8-PSK and 16-QAM are widely used in Wide-band Code Division Multiple Access (WCDMA), High-Speed Download Packet Access (HSDPA), World wide Inter-operability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN) Broadband wireless access technologies. Alternative method has been proposed to use cross correlation to detect the phase modulated data. Patent literature review showed that there is no such patent or known prior art related to the proposed technique. This novel technique does not extract the carrier for demodulation purposes and offer improved phase detection performance as well as superior resistance to Additive-White-Gaussian-Noise (AWGN) compared to a carrier recovery scheme operating at low Signal-to-Noise Ratio (SNR). The proposed demodulation scheme significantly reduces the implementation resources to demodulate 8-PSK and 16-QAM. As a consequent, this technique will yield cost reduction in products using 8-PSK and 16-QAM demodulators, namely Broadband internet and Digital TV. Furthermore, the cross correlations would have potential impacts on the development of ELF link using OFDM scheme that would require significantly less resources compared to recent OFDM systems.
19
Park, Byeong-Ha. "A low-voltage, low-power, CMOS 900MHZ frequency synthesizer". Diss., Georgia Institute of Technology, 1997. http://hdl.handle.net/1853/16686.
Testo completo
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Li, Xiaoyong. "Low noise design techniques for radio frequency integrated circuits /". Thesis, Connect to this title online; UW restricted, 2004. http://hdl.handle.net/1773/6013.
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21
Cantwell, Therese. "Low frequency radio observations of galaxy clusters and groups". Thesis, University of Manchester, 2018. https://www.research.manchester.ac.uk/portal/en/theses/low-frequency-radio-observations-of-galaxy-clusters-and-groups(35ee5532-96b2-48c9-a064-3a86c4f33747).html.
Testo completoAbstract (sommario):
The detection of Mpc scale diffuse radio emission in galaxy clusters provides evidence that cosmic ray electrons, as well as cluster scale magnetic fields are present in clusters. As such, radio observations of clusters provide a unique opportunity to study the non-thermal populations of the intra-cluster medium. Observations of Faraday rotation in sources embedded in cluster and group environments offers an additional method for probing the cluster/group magnetic field. In this thesis I present low frequency radio observations of multiple galaxy clusters in order to investigate the nature of diffuse radio emission present in many clusters. I also present observations of the giant radio galaxy NGC 6251 and discuss both the source properties as well as the host group environment. In Chapter 1 of this thesis I review the current understanding of galaxy clusters, groups and radio galaxies. I also describe some of the astrophysical processes important to this thesis. In Chapter 2 I discuss the interferometry and the process of calibrating interferometric data. I also describe some of the techniques used later in the thesis such as QUfitting and RM synthesis. In Chapter 3 I present my observations of the massive merging galaxy cluster MACSJ2243.3-0935. I report the discovery of a radio halo in MACSJ2243.3-0935, as well as a new radio relic candidate, using the Giant Meterwave Radio Telescope and the KAT-7 telescope. The radio halo is coincident with the cluster X-ray emission and has a largest linear scale of approximately 0.9 Mpc. I measure a flux density of $10.0\pm 2.0\, \rm mJy$ at 610 MHz for the radio halo. I discuss equipartition estimates of the cluster magnetic field and constrain the value to be of the order of $1\, \rm \mu G$. The relic candidate is detected at the cluster virial radius where a filament meets the cluster. The relic candidate has a flux density of $5.2\pm 0.8\, \rm mJy$ at 610 MHz. I discuss possible origins of the relic candidate emission and conclude that the candidate is consistent with an infall relic. In Chapter 4 I present my GMRT observations at 610 MHz of 3 disturbed galaxy clusters, A07, A1235 and A2055. No diffuse emision was observed any of the three clusters. In order to place upper limits on the radio halo power in these clusters I have injected simulated halos at difffent radio powers into the uvdata. A07 has a radio halo upper limit of $P_{\rm 610MHz}=1.5\times10^{24}$ W Hz$^{-1}$. A2055 has a radio halo upper limit of $P_{\rm 610MHz}=1.8\times10^{24}$ W Hz$^{-1}$. A1235 has a radio halo upper limit of $P_{\rm 610MHz}=5.8\times10^{23}$ W Hz$^{-1}$. These limits are below the $P_{610}-L_{\rm X}$ relation and rule out bright radio halo in these clusters. I have identified these clusters as potential hosts for Ultra Steep Spectrum Radio Halo (USSRH). Observations with LOFAR should be capable of confirming whether or not these clusters host USSRH. In Chapter 5 I present observations of the giant radio galaxy NGC 6251 with LOFAR HBA. NGC 6251 is a giant radio galaxy with a borderline FRI/FRII morphology located in a poor group. The images presented in this chapter are the highest sensitivity and resolution images of NGC 6251 at these frequencies to date. Analysis of the low frequencies spectral index did not reveal any change in the low frequency spectra when compared with the higher frequency spectral index. NGC 6251 is found to be either at equilibrium or slightly electron dominated, similar to FRII sources. I calculated the ages of the low surface brightness extension of the northern lobe and the backflow of the southern lobe, which are only clearly visible at these low frequencies, to be 205 Myr$.
22
Lazell, Matthew. "Investigating active galactic nuclei with low frequency radio observations". Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5976/.
Testo completoAbstract (sommario):
Low frequency radio astronomy allows us to observe the fainter and older synchrotron emission from the relativistic plasma associated with active galactic nuclei (AGN) in galaxies and clusters. In this thesis, we use the Giant Metrewave Radio Telescope to explore the impact that AGN have on their surroundings. We present deep, high quality, 150-610 MHz radio observations for a sample of fifteen predominantly cool-core galaxy clusters. For well-known clusters such as MS0735, our low noise images and multi-frequency data enable us to see in improved detail the radio lobes working against the intracluster medium, whilst deriving the energies and timescales of this event. Our excellent field of view allowed us to explore the point-source like radio AGN for a subsample of our clusters. We used additional optical and infra-red data to identify cluster members, remove radio contamination and investigate the energetics of the many cluster galaxies. We find that low mass radio-loud AGN can easily quench the star formation at their core and compare our observations with the results of cosmological hydrodynamical simulations, to explore the mechanical and binding energy levels over a large range of galaxy masses. Comparing our sample to published X-ray cavity powers, we find an improved relation from our integrated radio luminosities, allowing a more accurate estimation of jet powers when X-ray or radio observations are unavailable. Our deepest low-frequency radio observations of these well-known clusters will yield valuable information about the nature of feedback when combined with X-ray observations of comparable depth.
23
Wilson, Derek Edwin. "A Pilot Survey for Astronomical Low Frequency Radio Transients". Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/34715.
Testo completoAbstract (sommario):
Dispersed low-frequency radio astronomical pulses may result from exploding primordial
black holes, gamma ray bursts, supernovae, or mergers of exotic objects, but have not yet
been detected. Detection would be of great scientific significance because such events must
involve extreme physics. The transient nature of these events makes detection unlikely with
traditional instruments due to lack of sensitivity to single pulses and narrow field of view.
For this thesis, a low-frequency wide-bandwidth astronomical search instrument has been
developed as an alternative approach. This instrument consists of a single dipole which
yields all-sky field of view, albeit at reduced sensitivity. The spectrum from 37 - 55 MHz
is coherently digitized at 200 million samples per second, recorded, and analyzed off-line for
the presence of dispersed pulses. A preliminary survey has been made at a remote site in
western North Carolina. In a 20 minute observation, 9 detections greater than 6.5 occurred, corresponding to pulses of 20 ms duration and dispersion measures (DMs) ranging from 15 to 70 pc cm−3 . In addition, groups of pulses were detected ( 5) at DMs of 43.1, 52.1,
and 52.2 pc cm−3 . The possibility of association with known pulsars is considered; however,
it is also possible these are due simply to radio frequency interference. Improvements to this
instrument and survey technique are suggested.Master of Science
24
DeLong, Brock J. "Integration of Radio Frequency Harvesting with Low Power Sensors". The Ohio State University, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=osu152408949118599.
Testo completo
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Foster, Griffin. "Large-N correlator systems for low frequency radio astronomy". Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:2bca41ff-ec75-4a41-a634-c5bbbceae434.
Testo completoAbstract (sommario):
Low frequency radio astronomy has entered a second golden age driven by the development of a new class of large-N interferometric arrays. The low frequency array (LOFAR) and a number of redshifted HI Epoch of Reionization (EoR) arrays are currently undergoing commission and regularly observing. Future arrays of unprecedented sensitivity and resolutions at low frequencies, such as the square kilometer array (SKA) and the hydrogen epoch of reionization array (HERA), are in development. The combination of advancements in specialized field programmable gate array (FPGA) hardware for signal processing, computing and graphics processing unit (GPU) resources, and new imaging and calibration algorithms has opened up the oft underused radio band below 300 MHz. These interferometric arrays require efficient implementation of digital signal processing (DSP) hardware to compute the baseline correlations. FPGA technology provides an optimal platform to develop new correlators. The significant growth in data rates from these systems requires automated software to reduce the correlations in real time before storing the data products to disk. Low frequency, widefield observations introduce a number of unique calibration and imaging challenges. The efficient implementation of FX correlators using FPGA hardware is presented. Two correlators have been developed, one for the 32 element BEST-2 array at Medicina Observatory and the other for the 96 element LOFAR station at Chilbolton Observatory. In addition, calibration and imaging software has been developed for each system which makes use of the radio interferometry measurement equation (RIME) to derive calibrations. A process for generating sky maps from widefield LOFAR station observations is presented. Shapelets, a method of modelling extended structures such as resolved sources and beam patterns has been adapted for radio astronomy use to further improve system calibration. Scaling of computing technology allows for the development of larger correlator systems, which in turn allows for improvements in sensitivity and resolution. This requires new calibration techniques which account for a broad range of systematic effects. And, a deep integration between DSP hardware and software data reduction into a single backend.
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O'Connor, Rodney Philip. "Mitochondrial Ca²⁺ signalling and the effects of visible, radiofrequency and extremely low frequency electromagnetic fields". Thesis, University of Cambridge, 2010. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609010.
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Myoung, Suk Keun. "Low frequency feedforward and predistortion linearization of RF power amplifiers". Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1150416616.
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Rossitter, D. A. "The nature of faint radio sources in low frequency samples". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235304.
Testo completoAbstract (sommario):
The behaviour of the radio source population at high redshift has been a major area of research in extragalactic radio astronomy during the past decade. In particular, the question of at what redshift the co-moving number density of radio sources reaches a peak, has been of considerable interest. Radio surveys are particularly good for yielding large numbers of distant radio galaxies and quasars but at the price of having the edshift of the individual sources very difficult to obtain. This thesis has examined the behaviour of faint radio sources at large redshift, in particular those objects showing the classical double structure as is commonly found in samples selected at low frequency. The first part of this thesis identifies the need for at least approximate redshift information for complete flux limited samples to properly address the behaviour of these sources at large redshift; known redshift indicators are shown to be inadequate for this purpose. A new method of obtaining the intrinsic radio luminosity and hence redshift for classical double radio sources from the bright 3C sample from the radio data alone, is introduced. The same relationship is shown to be applicable to similar sources found at larger redshifts when selected from fainter samples. The middle part of this work is concerned with the construction of two new faint radio samples selected at 151 MHz. In addition to VLA and 5km telescope mapping, a review of existing optical data together with new CCD imaging and some spectroscopy is given. Finally, by taking these two new samples together with the intermediate sample of Eales and the bright sample of LRL, the new method of deriving radio luminosity has been used to explore the shape of the evolution function and degree of linear size evolution required for double radio sources at a much larger redshift than has been previously possible.
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Yang, Ta-I. "Low loss polymer nanoparticle composites for radio frequency (RF) applications". College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8767.
Testo completoAbstract (sommario):
Thesis (Ph. D.) -- University of Maryland, College Park, 2008.Thesis research directed by: Dept. of Chemical and Biomolecular Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Hu, Jingying Ph D. Massachusetts Institute of Technology. "Design of low-voltage, high-bandwidth radio frequency power converters". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/75637.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 158-166).
The mass and volume required for power electronics circuitry is a dominant obstacle to the miniaturization and integration of many systems. Likewise, power electronics with greater bandwidth and efficiency are becoming vital in many applications. To realize smaller and highly responsive power electronics at low voltages, this thesis explores devices, circuits, and passives capable of operating efficiently at very high frequencies (VHF, 30-300 MHz). Operation at these frequencies enables reduction of the numerical values and physical size of the passive components that dominate power converters, and enables increased bandwidth and transient performance which is valuable in a multitude of low-voltage and low-power applications. This thesis explores the scaling of magnetic component size with frequency, and it is shown that substantial miniaturization is possible with increased frequencies even considering material and heat transfer limitations. Moreover, the impact of frequency scaling of power converters on magnetic components is investigated for different design criteria. Quantitative examples of magnetics scaling are provided that clearly demonstrate the benefits and opportunities in VHF magnetics design. It is shown to utilize the advantages of frequency scaling on passive component size that system losses and other limitations must be considered. One such area that is examined is semiconductor device requirements, where through a combination of device layout optimization for cascode structures and integrated gate drive designs on a 0.35-um CMOS process, converter performance (i.e., loss and bandwidth) can be significantly improved in the VHF regime. In this thesis a dc-dc converter topology is developed that is suitable for low-voltage power conversion and employs synchronous rectification to improve efficiency. The converter is also comprised of a high-bandwidth and high-switching-frequency inverter topology that can dynamically adjust the output power from one-quarter to full power, while maintaining good efficiency. Furthermore, with its inherent capability of gate-width switching, the inverter can further reduce gating loss by one-half resulting in substantial performance improvements at light load operation. A major contribution of this thesis is the development of a synchronous rectifier operating in the VHF regime. VHF power conversion is especially challenging at low voltages due to poor efficiency resulting from rectification loss. To overcome diode rectification loss, the benefits of synchronous rectification are discussed in the context of a 100MHz class-E resonant rectifier, which results in a 2.5 x overall converter efficiency improvement. The culmination of the developed design techniques in passives, semiconductor devices, and circuit topologies is an experimental prototype of a miniaturized 100MHz, 1W power converter utilizing synchronous rectification.
by Jingying Hu.
Ph.D.
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Li, Pei Zhi. "Maternal occupational exposure to extremely low frequency magnetic fields and risk of brain tumors in offspring". Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=116091.
Testo completoAbstract (sommario):
Background: The causes of childhood brain tumors (CBT) are essentially unknown. Exposure to extremely low frequency magnetic fields (ELF-MF) (3-3000Hz) is an ubiquitous part of modern life. However, very few studies have investigated the possible effect of maternal occupational ELF-MF exposure on CBT and the available findings are inconsistent across studies.Methods: We examined the role of maternal occupational exposure to ELF-MF shortly before and during pregnancy on the incidence of childhood brain tumors. A total of 548 incident cases and 760 healthy controls recruited between 1980 and 2002 from two Canadian provinces (Quebec and Ontario) were included and their mothers were interviewed. Tumors were classified as astroglial tumors, primitive neuroectodermal tumors (PNET), and other gliomas. Quantitative occupational ELF-MF exposure in microtesla units was estimated using individual exposure estimations or a job exposure matrix. We used three metrics to analyze exposure: cumulative, average, and maximum level attained.
Results: Using the average exposure metric measured before conception, an increased risk was observed for astroglial tumors (OR=1.5, and 95% CI=1.0-2.4). During the entire pregnancy period, a significantly increased risk was observed for astroglial tumors as well as for all childhood brain tumors with the average metric (OR=1.6, 95% CI=1.1-2.5 and OR=1.5; 95% CI=1.1-2.2, respectively). Based on job titles, a two-fold risk increase was observed for astroglial tumors (OR=2.3, 95% CI=0.8-6.3) and for all childhood brain tumors (OR=2.3, 95% CI=1.0-5.4) among sewing machine operators.
Conclusion: Results are suggestive of a possible association between maternal occupational ELF-MF exposure and certain brain tumors in their offspring.
Keywords: brain tumors, occupational exposures, maternal exposures, magnetic fields, childhood cancer, job exposure matrix
32
Wiese, Michelle Kim. "Immune stimulation with short-term exposure to extremely low frequency electromagnetic fields in mice (Mus. musculus)". Thesis, Bloemfontein : Central University of Technology, Free State, 2013. http://hdl.handle.net/11462/209.
Testo completoAbstract (sommario):
Thesis (M. Tech. (Biomedical Technology)) -- Central University of technology, Free State, 2013Electromagnetic fields are present wherever electricity is created. The frequency range of these electromagnetic fields is from extremely low to extremely high. The fields present in domestic areas fall within the extremely low frequency range. These fields are created by domestic electrical appliances and telecommunication. There has been much debate on the effect of exposure to these fields on human health. Research has not yet been able to prove adverse effect of these fields on human health. In fact, the benefits of magneto therapy has been recognized and used for several decades. Recently a specific electromagnetic signal has been under investigation for its ability to stimulate the immune response. This signal is produced by a patented generator, called Immunent Activator. Studies performed with the Immunent Activator signal on farm animals revealed increased feed conversion and decreased intestinal lesions of animals with intestinal infections. Most of the research was performed on fish and fowls and evidence of similar findings in mammals is lacking. In the current study, mice were exposed to the Immunent BV signal for seven days, after which immune cell counts were performed and compared to the immune cell counts of a control group of mice which received no electromagnetic exposure. It was found that the T-lymphocyte population of immune cells in the exposed group of mice was statistically significantly higher than that of the control group. The neutrophil count was statistically significantly lower in the exposed group compared to the control group. These findings revealed evidence of immune stimulation in the mice which were exposed to the Immunent Activator signal. Suggestions for further research could be made with regard to specific mechanisms of immune stimulation. The findings of this and other related studies hold benefits for the farming and health industry.
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Moustakidis, Iordanis Vlasios. "Detection of erosion/deposition depth using a low frequency passive radio frequency identification (rfid) technology". Thesis, University of Iowa, 2012. https://ir.uiowa.edu/etd/1490.
Testo completoAbstract (sommario):
This thesis presents an experimental study both in the laboratory and field to develop and test a method for continuously measuring and monitoring scour using an automated identification technology known as Radio Frequency Identification (RFID). RFID systems consist of three main components, namely (a) the reader which controls the system, (b) the transponder (derived from transmitter/responder) that transmits data to the reader and (c) the excitation antenna that allows the communication between the reader and the transponder.
The study provides an insight into the RFID technology and develops the framework for using this technology to eventually address two central themes in river mechanics and sediment transport; (a) the determination of the active layer thickness and (b) the scour/deposition depth around a hydraulic structure. In particular, this study develops the methodology for relating the signal strength of a radio frequency (RF) device with the distance between an excitation antenna and the RF device.
The experiments presented herein are classified into two main groups, (1) the laboratory and (2) the RF signal vs. the detection distance experiments (field experiments). The laboratory experiments were designed to understand the effect of key RFID parameters (e.g., transponder orientation with respect to the excitation antenna plane, maximum antenna-transponder detection distance), measured in terms of the transponder return RF signal strength for various antenna-transponder distances, transponder orientations with respect to the excitation antenna plane and different mediums in between the excitation antenna and the transponder, on the overall performance of the RFID system. On the other hand, the RF signal vs. the detection distance experiments were based on the results obtained during the laboratory experiments and focused on developing calibration curves by relating the transponder return RF signal strength with the distance between the excitation antenna and a transponder.
The laboratory results show that the dominant RFID parameters affecting the system performance are (a) the transponder orientation towards the excitation antenna plane and (b) the medium type in between the excitation antenna and the transponder. The differences in reading distances were attributed to the transponder inner antenna type, while the effect of the medium was related with the void ratio, where higher porosity materials have, less RF signal strength decay. The parameter that governs the RF signal strength decay was found to be the distance between the excitation antenna and the transponder (erosion process experiments). The RF signal strength decays almost linearly with distance, while the rate of the RF signal strength decay is controlled by the material type in between the excitation antenna and the transponder (deposition process experiments).
The RF signal vs. the detection distance experiments demonstrate that the reading distance of the RFID system can be significantly increased by using a custom made excitation antenna. The custom made excitation antenna not only increases the reading distance between the antenna and the transponder to nearly 20 ft., but also allows the user to manipulate the excitation antenna's shape and size to meet the specific landscape requirements at the monitoring site.
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Marshall, Robert Andrew. "Very low frequency radio signatures of transient luminous events above thunderstorms /". May be available electronically:, 2009. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Testo completo
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Senguttuvan, Rajarajan. "Low-cost test, diagnosis, and tuning for adaptive radio frequency systems". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22575.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Electrical and Computer Engineering, Georgia Institute of Technology, 2008.Committee Chair: Chatterjee, Abhijit; Committee Member: Anderson, David; Committee Member: Durgin, Gregory; Committee Member: Swaminathan, Madhavan; Committee Member: Zhou, Hao-Min.
36
Hickish, Jack. "Digital signal processing methods for large-N, low-frequency radio telescopes". Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:7d983fb3-9411-4906-92cd-70e2c1040b54.
Testo completoAbstract (sommario):
Current attempts to make precision measurements of the HI power spectrum at high redshifts have led to the construction of several low-frequency, large-N, interferometric arrays. The computational demands of digital correlators required by these arrays present a significant challenge. These demands stem from the treatment of radio telescopes as collections of two-element interferometers, which results in the need to multiply O(N2) pairs of antenna signals in an N-element array. Given the unparalleled flexibility offered by modern digital processing systems, it is apt to consider whether a different way of treating the signals from antennas in an array might be fruitful in current and future radio telescopes. Such methods potentially avoid the unfavourable N2 scaling of computation rate with array size. In this thesis I examine the prospect of using direct-imaging methods to map the sky without first generating correlation matrices. These methods potentially provide great computational savings by creating images using efficient, FFT-based algorithms. This thesis details the design and deployment of such a system for the Basic Element of SKA Training II (BEST-2) array in Medicina, Italy. Here the 32-antenna BEST-2 array is used as a test bed for comparison of FX correlation and direct-imaging systems, and to provide a frontend for a real-time transient event detection pipeline. Even in the case of traditional O(N2) correlation methods, signal processing algorithms can be significantly optimized to deliver large performance gains. In this thesis I present a new mechanism for optimizing the cross-correlation operation on Field Programmable Gate Array (FPGA) hardware. This implementation is shown to achieve a 75% reduction in multiplier usage, and has a variety of benefits over existing optimization strategies. Finally, this thesis turns its focus towards The Square Kilometre Array (SKA). When constructed, the SKA will be the world's largest radio telescope and will comprise a variety of arrays targeting different observing frequencies and science goals. The low-frequency component of the SKA (SKA-low) will feature ~250,000 individual antennas, sub-divided into a number of stations. This thesis explores the impact of the station size on the computational requirements of SKA-low, investigating the optimal array configuration and signal processing realizations.
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Macario, Giulia <1982>. "Low frequency study of diffuse radio emission in clusters of galaxies". Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amsdottorato.unibo.it/3764/.
Testo completo
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Bell, Martin. "The low frequency array and the transient and variable radio sky". Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/208253/.
Testo completoAbstract (sommario):
This thesis addresses the topic of exploring and characterising the transient and variable radio sky, using both existing radio telescopes, and the next generation of radio facilities such as the Low Frequency Array (LOFAR). Studies of well known variable radio sources are presented in conjunction with blind searches of parameter space for unknown sources. Firstly, a three year campaign to monitor the low luminosity Active Galactic Nucleus NGC 7213 in the radio and X-ray bands is presented. Cross-correlation functions are used to calculate a global time lag between inflow (X-ray) and outflow (radio) events. Through this work the previously established scaling relationship between core radio and X-ray luminosities and black hole mass, known as the ‘fundamental plane of black hole activity’ is also explored with respect to NGC 7213. Secondly, the technical and algorithmic procedures to search for transient and variable radio sources within radio images is presented. These algorithms are intended for deployment on the LOFAR telescope, however, they are heavily tested in a blind survey using data obtained from the VLA archive. Through this work an upper limit on the rate of transient events on the sky at GHz frequencies is placed and compared with those found from other dedicated transient surveys. Finally, the design, operation and data reduction procedure for the Low Frequency Array, which will revolutionise our understanding of low frequency time domain astrophysics is explored. LOFAR commissioning observations are reduced and searched for transient and variable radio sources. The current quality of the calibration limits accurate variability studies, however, two unique LOFAR transient candidates that are not present in known radio source catalogues are explored (including multi-wavelength followup observations). In the conclusion to this thesis the parameter space that future radio telescopes may probe - including the potential rates of such events - is presented. At the nano-Jansky level up to 107 transients deg−2 yr−1 are predicted, which will form an unprecedented torrent of data, followup and unique physics to classify
39
Pantazopoulou, Maria J. "Spectral characteristics of low-frequency variability in compact extragalactic radio sources". Diss., Virginia Tech, 1996. http://hdl.handle.net/10919/40238.
Testo completo
40
Tang, Jin Niu Guofu. "Modeling and scaling limitations of SiGe HBT low-frequency noise and oscillator phase noise". Auburn, Ala., 2006. http://repo.lib.auburn.edu/Send%208-7-07/TANG_JIN_32.pdf.
Testo completo
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Orr, Andrew McLean White. "Computational techniques for evaluating extremely low frequency electromagnetic fields produced by a horizontal electric dipole in seawater". Thesis, King's College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.326222.
Testo completo
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Harun, Mahmud. "Modification of Large Reflector Antennas for Low Frequency Operation". Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/29455.
Testo completoAbstract (sommario):
Modifications of large reflector antennas, such that their observing capabilities are enhanced in the range of about 10-500~MHz without affecting operation of the pre-existing higher-frequency systems, are addressed in this dissertation. The major contributions of this dissertation can be divided into two parts: 1) designing new low frequency feeds, and 2) developing new analysis methodologies which, as opposed to traditional techniques, are suitable for analyzing low frequency systems.
First, we consider the performance of existing schemes that provide low frequency capability. Then, a new class of dipole-based low frequency feeds - namely, the ``distributed feed array'' - is designed to cover the frequency range of interest without affecting operation at higher frequencies. As an example, distributed feed arrays are designed for the Expanded Very Large Array (EVLA) to cover the range of 50-250~MHz. A method of moments (MoM) model of an EVLA antenna is developed for this purpose. The new design shows performance comparable to the existing 4 m system on the EVLA in the range of 50-88~MHz, and introduces observing capabilities in the range of 110-250~MHz (currently not covered by the EVLA). Moreover, the blockage presented to the existing EVLA L-band system is reduced significantly when the existing 4 m system is replaced by the proposed system.
At low frequencies, external noise can be a significant or dominant contribution to the total noise of the system. This, combined with mutual coupling between the array elements of the distributed feed array, makes it difficult to predict the sensitivity of these systems. This dissertation describes a system model and procedure for estimating the system equivalent flux density (SEFD) - a useful and meaningful metric of the sensitivity of a radio telescope - that accounts for these issues.
We consider the efficiency of methods other than MoM - in particular, Physical Optics (PO), Uniform Geometrical Theory of Diffraction (UTD), and hybrid methods - for accelerated computation at low frequencies. A method for estimating the blockage presented by low frequency systems to the pre-existing higher-frequency systems is also described.Ph. D.
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Laycock, S. C. "Very steep spectrum radio sources and clusters of galaxies". Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.233300.
Testo completoAbstract (sommario):
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.
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Rafla, Ramez. "Integrated inductor modeling and CMOS low noise amplifiers for radio-frequency applications". Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=32971.
Testo completoAbstract (sommario):
A large demand for bandwidth, both for voice and data communication, has increased the need for high-speed systems. Specifically, a wireless revolution is establishing renewed standards and design requirements, such as higher operation frequencies and higher levels of integration.The improved performance of traditional technologies, such as CMOS, which used to be geared towards digital circuits running at lower frequencies, makes them now suitable for Radio-Frequency applications. The challenge is not only to design RF systems, but also to establish design methodologies for their building-blocks.
This thesis is concerned with one of those building blocks, namely the low noise amplifier, when implemented using modern submicron CMOS technologies. The design of this circuit, as well as that of many of the RF building blocks, requires accurate integrated inductor modeling tools. The challenge of modeling inductors implemented in silicon technologies lies in the complex electro-magnetic behavior of these devices. A powerful modeling engine, McGill Inductor Modeler (MIND), was implemented for this purpose, and proven to be accurate and precise.
The contribution of this work is twofold: First, proving that performant high-frequency CMOS RF LNA's could be achieved. Second, creating a powerful and versatile inductor modeling tool.
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Deshpande, Kshitija Bharat. "A Dedicated Search for Low Frequency Radio Transient Astrophysical Events using ETA". Thesis, Virginia Tech, 2009. http://hdl.handle.net/10919/35666.
Testo completoAbstract (sommario):
Astrophysical phenomena such as self-annihilation of primordial black holes (PBHs), gamma ray bursts (GRBs), and supernovae are expected to produce single dispersed pulses detectable in the low end of the radio spectrum. Analysis of these pulses could provide valuable information about the sources, and the surrounding and intervening medium. The Eight-meter-wavelength Transient Array (ETA) is a radio telescope dedicated to the search for these pulses in an 18 MHz bandwidth centered at 38 MHz. ETA consists of 10 dual-polarized active dipoles providing an all-sky field of view. This thesis describes the results of a search campaign using ETA, namely, a Crab giant pulse (CGP) search. CGPs are already known to exist, and thus provide an excellent diagnostic for system performance. We found 11 CGP candidates in 14 hours of data. Although there has not been a single compelling detection (signal-to-noise ratio > 6), our analysis shows that at least a few of these candidates may be CGPs. We also explain the analysis preparation for PBH and GRB searches. Additionally, we describe the instrument and a software "toolchain" developed for the analysis of data that includes calibration, radio frequency interference (RFI) mitigation, and incoherent dedispersion. A dispersed pulse simulation code was developed and used to test the toolchain. Finally, improvements are suggested.Master of Science
46
Smith, Brette. "The biological effects of radiofrequency (mobile phone) and extremely low frequency (power-line) electromagnetic fields on model systems". Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430647.
Testo completo
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Xiong, Zhijie. "Radio Frequency Low Noise and High Q Integrated Filters in Digital CMOS Processes". Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5043.
Testo completoAbstract (sommario):
Radio Frequency Low Noise and High Q
Integrated Filters in Digital CMOS Processes
Zhijie Xiong
149 pages
Directed by Dr. Phillip E. Allen
Presented in this work is a novel design technique for CMOS integration of RF high Q integrated filters using positive feedback and current mode approach. Two circuits are designed in this work: a 100MHz low-noise and high Q bandpass filter suited for an FM radio front-end, and a 2.4GHz low-noise and high-Q bandpass filter suited for a Bluetooth front-end. Current-mode approach and positive feedback design techniques are successfully used in the design of both circuits. Both circuits are fabricated through a 0.18um CMOS process provided by National Semiconductor Corp.
The 100MHz circuit achieves 3.15uV RF sensitivity with 26dB SNR, and the total current consumption is 12mA. The center frequency of the filter is tunable from 80MHz to 110MHz, and the Q value is tunable from 0.5 to 28.9. 1 dB compression point is measured as -34.0dBm, combined with noise measurement results, a dynamic range of 54.1 dB results. Silicon area of the core circuit is 0.4 square millimeters.
The center frequency of the 2.4GHz circuit is tunable from 2.4GHz to 2.5GHz, and the Q value is tunable from 20 to 120. The 1 dB compression dynamic range of the circuit is 50dB. Integrated spiral inductors are developed for this design. Patterned ground shields are laid out to reduce inductor loss through substrate, especially eddy current loss when the circuit is fabricated on epi wafers. Accumulation mode MOS varactors are designed to tune the frequency response. Silicon area of the core circuit is 1 square millimeter.
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Leung, Lydia Lap Wai. "Low-loss on-chip interconnects for silicon integrated radio-frequency and microwave systems /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?ELEC%202005%20LEUNG.
Testo completo
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Tan, Lizhe. "Feasibility of Novel Low-cost Deca-Nanometer Vertical MOSFETs for Radio Frequency Application". Thesis, University of Liverpool, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.507498.
Testo completo
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Knapp, Mary (Mary E. ). "Toward detection and characterization of exoplanetary magnetic fields via low frequency radio observation". Thesis, Massachusetts Institute of Technology, 2018. http://hdl.handle.net/1721.1/115642.
Testo completoAbstract (sommario):
Thesis: Ph. D. in Planetary Sciences, Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences, 2018.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 225-256).
Low frequency radio emission from planets is produced by the interaction of energetic charged particles from the planet's ionosphere and/or the solar wind with the planet's magnetic field. The temporal and spectral characteristics and variability of planetary radio emission encode information about a planet's magnetic field strength and morphology, rotation, and interior. This thesis describes three distinct approaches to detecting radio emission from extrasolar planets ( exoplanets). The first is a novel approach using 'big data' and computer aided discovery tools to mine radio survey images for faint radio emission from the location of nearby stars. The flexible approach described in this thesis produced upper limits of rv lOOx Jovian radio flux for a large sample of nearby stars and known exoplanet systems. The sensitivity is sufficient that large radio bursts from nearby stars or planets could have been detected if they took place during the survey observation(s). The framework developed here can be used for automated exoplanet radio emission searches in future radio survey data. The second approach described herein is a blind survey of the nearest Northern hemisphere stars across a broad range of frequencies in order to detect as-yet unknown planets or set tight constraints on radio emission from the stars and possible substellar companions. The survey approach used here is novel because it makes no assumptions about which stars are most likely to host radio emitting planets and it covers frequencies from 30 MHz to 4 GHz. This survey produced a detection of multiple rv50% circularly polarized flares from the M dwarf binary system Ross 614 as well as limits at the lOx Jovian flux level for the remaining stars observed. The limits attained from this survey are the first published at 1-4 GHz for these objects and the only available radio limits for a newly discovered cool (T9) brown dwarf. The limits from this survey place a preliminary constraint on the magnetic field of the brown dwarf at <350 G. The third approach focuses on known exoplanet systems and targets key orbital phases where intense radio emission is predicted. In the case of eccentric hot Jupiter HD 80606 b, radio flux from the planet is expected to increase by a factor of up to 3000 compared to the quiescent flux as the planet passes within 6 Rof its host at periastron due to high density stellar wind impinging on HD 80606 b's putative magnetosphere. Data obtained from LOFAR LBA is used to set the lowest limits to date on radio flux from HD 80606 b near planetary periastron. The same concept of orbital phase targeting is used to optimize an observing strategy for recently-discovered multiple planet host TRAPPIST-I. In the case of TRAPPIST-1, the quadrature phases of planets TRAPPIST-1 b and TRAPPIST-1 c are targeted to maximize the chance of observing Io-Jupiter like planetary modulation of stellar radio emission. The quadrature phase targeting approach is new to this field. The thesis concludes with a discussion of the benefits of space-based observation for exoplanetary radio searches. Ground-based observations are limited by the plasma frequency of the ionosphere, so planets with Earth-like magnetic fields cannot be observed. Telescopes on the ground also suffer from ionospheric phase errors that are difficult to fully calibrate. Space-based observation does not suffer from the effects of the ionosphere and can therefore support lower frequency observations than ground-based instruments. A novel instrument, the vector sensor, optimized for space-based radio interferometry is introduced. New algorithms for all-sky vector sensor imaging have been developed and tested in simulation and on sky data with encouraging results. Finally, the prospects for detecting Earth- or Jupiter-analogs in the solar neighborhood, either from the ground or from space, are assessed. Very large space-based arrays are required to detect either Jupiter or the Earth at 10 pc; at least 105 -106 antennas are needed for sufficient sensitivity.
by Mary Knapp.
Ph. D. in Planetary Sciences