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Livingstone, Margaret Anne. "Timing young pulsars: challenges to standard pulsar spin-down models." Thesis, McGill University, 2010. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=94909.
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Pulsars are rapidly rotating neutron stars which are often noted for their very regular rotation rates. Young pulsars however, frequently exhibit two types of deviations from steady spin down, ``glitches'' - sudden jumps in spin frequency, which provide insight into pulsar interiors, and ``timing noise,'' a smooth stochastic wander of the pulse phase over long time periods. The youngest pulsars also offer a window into the physics that govern pulsar spin down via the measurement of the "braking index'' - a parameter that relates the observable spin frequency of the pulsar with the slowing down torque acting on the neutron star. This thesis discusses long-term timing observations of two young pulsars. First, we present observations of PSR J0205+6449, acquired with the Green Bank Telescope, the Jodrell Bank Observatory and the Rossi X-ray Timing Explorer. We present phase-coherent timing analyses showing timing noise and two spin-up glitches. We also present an X-ray pulse profile analysis showing that the pulsar is detected up to approximately 40 keV and does not vary appreciably over four years. We report the phase offset between the radio and X-ray pulse, showing that the radio pulse leads by 0.10+/-0.01 in phase. We compile measurements of phase offsets for this and other X-ray and gamma-ray pulsars and show that there is no relationship between pulse period and phase offset. Next, we present 10 years of monitoring of PSR J1846-0258 with the Rossi X-ray Timing Explorer. We report the first measurement of the braking index for this pulsar, n=2.65+/-0.01, only the sixth such measurement ever made, and show that the pulsar experienced a small glitch in 2001. In May 2006, PSR J1846-0258 was briefly transformed: it exhibited a series of X-ray bursts, a dramatic increase in the source flux, and significant softening of its X-ray spectrum - behaviours best explained in the context of the magnetar model. PSR J1846-0258 was thus identified as the first rotation-poLes pulsars, des étoiles à neutrons tournant rapidement sur elles-mêmes, sont reconnus pour leur vitesse de rotation très régulière. Les jeunes pulsars, par contre, présentent fréquemment des comportements qui dévient du ralentissement uniforme de leur vitesse de rotation: des glitchs, variations brutales de la fréquence de révolution qui nous aident à comprendre l'intérieur des plusars, et le bruit chronométrique, une variation stochastique de la phase de rotation sur une longue échelle de temps. Les pulsars les plus jeunes nous offrent aussi un aperçu de la physique qui gouverne le ralentissement de la vitesse de rotation par l'indice de freinage, un paramètre qui relie la fréquence de rotation d'un pulsar au torque qui agit sur lui, et dont la valeur diminue graduellement. Cette thèse discute du chronométrage à long terme de deux jeunes pulsars. Tout d'abord, nous présentons des observations de PSR J0205+6449 acquises avec l'Observatoire de Green Bank, l'Observatoire Jodrell Bank ainsi que le Rossi X-ray Timing Explorer. Nous présentons l'analyse du chronométrage à phase cohérente montrant du bruit chronométrique ainsi que deux glitchs. Nous présentons aussi une analyse du profil du pulse en rayons X montrant que le pulsar est détectable jusqu'à ~40 keV et ne varie pas significativement sur quatre ans. Nous rapportons une mesure de la différence de phase entre le pulse radio et le pulse en rayons X, montrant que le pulse radio précède le pulse en rayons X par 0.10+/-0.01. Une compilation des différences de phase pour ce pulsar et d'autres qui émettent en rayons X et en rayons gamma montre qu'il n'y a aucune relation entre la période de rotation et la différence de phase. Ensuite, nous présentons 10 années de suivi de PSR J1846-0258 avec le Rossi X-ray Timing Explorer. Nous rapportons la première mesure de l'indice de freinage pour ce pulsar, n=2.65+/-0.01, le sixième indice mesuré à ce jour, et montrons que ce pul
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Mingarelli, Chiara Maria Francesca. "Gravitational wave astrophysics with pulsar timing arrays." Thesis, University of Birmingham, 2014. http://etheses.bham.ac.uk//id/eprint/5117/.
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This thesis focuses on gravitational wave (GW) astrophysics with Pulsar Timing Arrays (PTAs). Firstly it is shown that anisotropy in the GW background may be present, and that its characterization at different angular scales carries important information. The standard analysis for isotropic backgrounds is then generalized by decomposing the angular distribution of the GW energy density into multipole moments. Generalized overlap reduction functions (ORFs) are computed for a generic level of anisotropy and PTA configuration. A rigorous analysis is then done of the assumptions made when calculating ORFs. It is shown that correlated phase changes introduce previously unmodeled effects for pulsars pairs separated by less than a radiation wavelength. The research then turns to the study of continuous GW sources from supermassive black hole binaries (SMBHBs). Here it shown that the detection of GWs from SMBHB systems can yield direct information about the masses and spins of the black holes, provided that the GW-induced timing fluctuations both at the pulsar and at Earth are detected. This in turn provides a map of the nonlinear dynamics of the gravitational field and a new avenue to tackle open problems in astrophysics connected to the formation and evolution of SMBHs.
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Hemberger, Daniel. "Improving Pulsar Timing through Interstellar Scatter Correction." Oberlin College Honors Theses / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1207521228.
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Van, Straten Willem Herman Bernadus, and straten@astron nl. "High-Precision timing and polarimeter of PSR JO437-4715." Swinburne University of Technology. School of Biophysical Sciences and electrical Engineering, 2003. http://adt.lib.swin.edu.au./public/adt-VSWT20040311.123754.
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This thesis reports on the recent results of a continuing, high-precision pulsar timing project, currently focused on the nearby, binary millisecond pulsar, PSR J0437_4715. Pulse arrival time analysis has yielded a remarkable series of constraints on the physical parameters of this system and evidence for the distortion of space-time as predicted by the General Theory of Relativity.
Owing to the proximity of the PSR J0437_4715 system, relative changes in the positions of the Earth and pulsar result in both annual and secular evolution of the line of sight to the pulsar. Although the changes are miniscule, the effects on the projected orbital parameters are detectable in our data at a high level of significance, necessitating the implementation of an improved timing model.
In addition to producing estimates of astrometric parameters with unparalleled precision, the study has also yielded the first three-dimensional orbital geometry of a binary pulsar. This achievement includes the first classical determination of the orbital inclination, thereby providing the unique opportunity to verify the shape of the Shapiro delay and independently confirm a general relativistic prediction.
With a current post-fit arrival time residual RMS of 130 ns over four years, the unrivaled quality of the timing data presented herein may eventually contribute to the most stringent limit on the energy density of the proposed stochastic gravitational wave background. Continuing the quest for even greater timing precision, a detailed study of the polarimetry of PSR J0437_4715 was undertaken. This effort culminated in the development of a new, phase-coherent technique for calibrating the instrumental response of the observing system.
Observations were conducted at the Parkes 64-m radio telescope in New South Wales, Australia, using baseband recorder technologies developed at York University, Toronto, and at the California Institute of Technology. Data were processed off-line at Swinburne University using a beowulf-style cluster of high-performance workstations and custom software developed by the candidate as part of this thesis.
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Sakai, Satoru. "The effect of Shapiro delay on pulsar timing." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/3020/.
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Light passing near a massive object (star) will take longer to arrive at the Earth than it would if the object was not present. This additional time is called the Shapiro delay. In globular clusters, where there are millions of stars, the cumulative effect of the Shapiro delay from these stars will affect pulsar timings by introducing an additional noise term. This effect has been previously assumed to be small, yet no definite investigation has been done to determine its magnitude. In this thesis a model of the globular cluster 47 Tucanae was created in order to determine the effect of the change in Shapiro delay (called the Shapiro noise) for an observed duration of 3600 days -- the current longest observation period for pulsar timing. This noise was then added to the pulsar time of arrival (TOA) as the only noise source in pulsar timing. A polynomial fit was then used to subtract the first two orders from the pulse arrival time (the f and \dot{f} terms) to determine the timing residuals. This model was then realised 100 times to obtain the average root mean square (RMS) timing residual for every pulsar. The model showed that the Shapiro noise has a significant, and observable effect on pulsar timing, especially for pulsars situated close to the core of the globular cluster. From the model the average RMS timing residuals were of the order of 10^{-5} to 10^{-7} seconds and the variance of the RMS timing residuals were significantly larger in magnitude, ranging from 10^{-4} to 10^{-7} seconds for every pulsar. The importance of this result motivated further investigation of the stellar distribution of the globular cluster. In addition an investigation on how the effect of gravitational acceleration (produced by stars situated close to the pulsar) affects pulsar timing residual was also done. While the acceleration has an effect, the effect is smaller than that of the Shapiro noise. From the timing residuals produced by the Shapiro noise, it was then discussed whether any star close to the LOS would have an affect on the pulsar timing residuals. From additional simulations it was determined that stars anywhere along the LOS will have an affect on pulsar timing, however the stellar density of such a region would have to be greater than \rho_{min} > 10^{5} M_{\sun} pc^{-3}. The implications of this result for other pulsars in (other) globular clusters is discussed.
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Keane, Evan. "The transient radio sky." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/the-transient-radio-sky(37c08735-cd96-4598-a8b9-2d24ef9e871d).html.
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The high time-resolution radio sky represents unexplored astronomical territory where the discovery potential is high. In this thesis I have studied the transient radio sky, focusing on millisecond scales. As such, this work is concerned primarily with neutron stars, the most populous member of the radio transient parameter space. In particular, I have studied the well known radio pulsars and the recently identified group of neutron stars which show erratic radio emission, known as RRATs, which show radio bursts every few minutes to every few hours. When RRATs burst onto the scene in 2006, it was thought that they represented a previously unknown, distinct class of sporadically emitting sources. The difficulty in their identification implies a large underlying population, perhaps larger than the radio pulsars. The first question investigated in this thesis was whether the large projected population of RRATs posed a problem, i.e. could the observed supernova rate account for so many sources. In addition to pulsars and RRATs, the various other known neutron star manifestations were considered, leading to the conclusion that distinct populations would result in a 'birthrate problem'. Evolution between the classes could solve this problem - the RRATs are not a distinct population of neutron stars. Alternatively, perhaps the large projected population of RRATs is an overestimate. To obtain an improved estimate, the best approach is to find more sources. The Parkes Multi-beam Pulsar Survey, wherein the RRATs were initially identified, offered an opportunity to do just this. About half of the RRATs showing bursts during the survey were thought to have been missed, due to the deleterious effects of impulsive terrestrial interference signals. To remove these unwanted signals, so that we could identify the previously shrouded RRATs, we developed new interference mitigation software and processing techniques. Having done this, the survey was completely re-processed, resulting in the discovery of 19 new sources. Of these, 12 have been re-detected on multiple occasions, whereas the others have not been seen to re-emit since the initial discovery observations, and may be very low burst-rate RRATs, or, isolated burst events. These discoveries suggest that the initial population estimate was not over-estimated - RRATs, though not a distinct population, are indeed numerous. In addition to finding new sources, characterisation of their properties is vital. To this end, a campaign of regular radio observations of the newly discovered sources, was mounted, at the Parkes Observatory, in Australia. In addition, some of the initially identified RRATs were observed with the Lovell Telescope at Jodrell Bank. These have revealed glitches in J1819-1458, with anomalous post-glitch recovery of the spin-down rate. If such glitches were common, it would imply that the source was once a magnetar, neutron stars with the strongest known magnetic fields of up to 10¹⁵ gauss. The observations have also been used to perform 'timing' observations of RRATs, i.e. determination of their spin-down characteristics. At the beginning of this thesis, 3 of the original sources had 'timing solutions' determined. This has since risen to 7, and furthermore, 7 of the newly discovered sources now also have timing solutions. With this knowledge, we can see where RRATs lie in period-period derivative space. The Parkes RRATs seem to be roughly classifiable into three groupings, with high observed nulling fractions - normal pulsars, high magnetic field pulsars and old, 'dying' pulsars. It seems that RRATs and pulsars are one and the same. When a pulsar is more easily detected in searches for single bright pulses, as opposed to in periodicity searches, we label it a RRAT. Such searches impart a selection effect on the parameter space of possible sources, in both nulling fraction and rotation period. In this sense, an observational setup could be designed to make any pulsar appear as a RRAT. For realistic survey parameters however, this is not the case, and the groups mentioned above seem to be the most likely to appear as RRATs. In fact, we can utilise RRAT searches to identify neutron stars, difficult to find by other means, in particular high-magnetic field pulsars, and pulsars approaching the pulsar "death valley". Some of the RRATs are well explained as being distant/weak pulsars with a high modulation index, others seem to be nulling pulsars. This highlights the incomplete knowledge of nulling behaviour in the pulsar population. It seems that there may be a continuum of nulling durations, under a number of guises, from 'nulling pulsars' to 'RRATs' to 'intermittent pulsars'. In fact this nulling may fit into the emerging picture, whereby pulsar magnetospheres switch between stable configurations.
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Grandy, Victoria Rebecca. "Wideband timing of the double pulsar (PSR J0737-3039A)." Thesis, University of British Columbia, 2016. http://hdl.handle.net/2429/59959.
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Pulsars are neutron stars (NS) that produce beamed radio-frequency emission. Due to their rapid, steady rotation rate, this signal is detected as a series of pulses whose integrated profile is unusually stable over time. Pulsars in double neutron star (DNS) binary systems are a rare, but extremely useful, astronomical tool and have been used in tests of gravity theories in the strong-gravitational field limit. Rarer still are DNS systems in which both objects have been detected as pulsars; only one such system has been found thus far -- PSR J0737-3039A/B. Discovered over a decade ago, this system consists of one recycled pulsar, PSR J0737-3039A, and its companion, PSR J0737-3039B, which has since become undetectable.
In any pulsar-related research, precise timing is necessary to produce meaningful results. The pulse time of arrivals (TOAs) are greatly affected by the medium through which the electromagnetic (EM) signal travels in both frequency-dependent and -independent ways. Even after accounting for such effects, many pulse profiles still exhibit frequency-dependent shape changes, which can greatly affect the precision of the timing results. Traditionally, corrections are applied to the TOAs after calculation in an ad hoc manner. In contrast to this, we explored the wideband timing algorithm developed by Timothy T. Pennucci and collaborators which accounts for frequency-dependent profile changes through a two-dimensional Gaussian pulse portrait model implemented in the TOA calculations. It was found that the portrait model is well-representative of the pulse profile shape over a wide frequency range. This method is also able to produce a robust set of wideband TOAs. The subsequent timing model, determined with TEMPO timing software, was found to be comparable to those produced from subbanded TOAs derived though more traditional methods. Some inconsistencies between the timing model astrometric and spin parameters of the wideband and subbanded data of this well-studied pulsar imply potential difficulties in achieving precise timing results not only for this pulsar, but for others, such as those used in pulsar timing arrays aiming to detect gravitational waves.Science, Faculty of
Physics and Astronomy, Department of
Graduate
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Middleton, Hannah Rose. "Astrophysical inference from pulsar timing array searches for gravitational waves." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8044/.
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Gravitational waves (GWs) have been detected for the first time in 2015 by the LIGO-Virgo Scientific Collaboration. The source of the GWs was a binary black hole (BBH). The observation caught the final fraction of a second as the two black holes spiralled together and merged. This observation (and the others to follow) marked the beginnings of GW astronomy, ‘a new window on the dark universe’, providing a means to observe astronomical phenomena which may be completely inaccessible via other avenues as well as a new testing ground for Einstein’s theory of general relativity (GR). However, this is just the beginning – like electromagnetic astrophysics, there is a full spectrum of GW frequencies to explore. At very low frequencies, pulsar timing arrays (PTAs) are being used to search for the GW background from the merging population of massive black hole binaries (MBHBs). No detection has yet been made, but upper limits have been placed. Here we present results on what inference on the MBHB population can be learnt from present and possible future PTA results, and also compare current upper limits with astrophysical predictions, finding them to be fully consistent so far. We also present a generic method for testing the consistency of a theory against experimental evidence in the situation where there is no strong viable alternative (for example GR). We apply this to BBH observations, finding them to be fully consistent with GR and also to Newton’s constant of gravitation, where there is considerable inconsistency between measurements.
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NG, Wing Yan [Verfasser]. "Pulsar searching and timing with the Parkes telescope / Wing Yan NG." Bonn : Universitäts- und Landesbibliothek Bonn, 2014. http://d-nb.info/1077289022/34.
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Caballero, Pouroutidou Ricardo Nicolaos [Verfasser]. "Probing Gravity with High-Precision Pulsar Timing / Ricardo Nicolaos Caballero Pouroutidou." Bonn : Universitäts- und Landesbibliothek Bonn, 2016. http://d-nb.info/1124540318/34.
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Hartman, Jacob M. Ph D. Massachusetts Institute of Technology. "X-ray timing of the accreting millisecond pulsar SAX J1808.4-3658." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/45413.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2007.Includes bibliographical references (p. 105-114).
We present a 7 yr timing study of the 2.5 ms X-ray pulsar SAX J1808.4-3658, an X-ray transient with a recurrence time of =2 yr, using data from the Rossi X-ray Timing Explorer covering 4 transient outbursts (1998-2005). Substantial pulse shape variability, both stochastic and systematic, was observed during each outburst. Analysis of the systematic pulse shape changes suggests that, as an outburst dims, the X-ray "hot spot" on the pulsar surface drifts longitudinally and a second hot spot may appear. The overall pulse shape variability limits the ability to measure spin frequency evolution within a given X-ray outburst (and calls previous zi measurements of this source into question), with typical upper limits of Jil < 2.5 x 10-14 Hz s-1 (2a). However, combining data from all the outbursts shows with high (6 a) significance that the pulsar is undergoing long-term spin down at a rate /i = (-5.6 ± 2.0) x 10-16 Hz s-1, with most of the spin evolution occurring during X-ray quiescence. We discuss the possible contributions of magnetic propeller torques, magnetic dipole radiation, and gravitational radiation to the measured spin down, setting an upper limit of B < 1.5 x 108 G for the pulsar's surface dipole magnetic field and Q < 4.4 x 1036 g cm2 for the mass quadrupole moment. We also measured an orbital period derivative of Porb = (3.5 + 0.2) x 10-12 s s-1 We identify a strong anti-correlation between the fractional amplitude of the harmonic (r2) and the X-ray flux (fx) in the persistent pulsations of four sources: SAX J1808.4-3658, IGR J00291+5934, and XTE J1751-305, XTE J1807-294. These sources exhibit a powerlaw relationship r2 x( fx7 with slopes ranging from y = -0.47 to -0.70. The three other accreting millisecond pulsars that we analyzed, XTE J0929-314, XTE J1814-338, and HETE J1900.1-2455, do not as fully explore a wide range of fluxes, but they too seem to obey a similar relation. We argue that these trends may be evidence of the recession of the accretion disk as the outbursts dim. We examine the energy dependence of the persistent pulsations and thermonuclear burst oscillations from SAX J1808.4-3658.
We confirm the soft phase lags previously discovered from this source, and we discover that these phase lags increase as the source flux decays slowly following its peak flux. When the source decay becomes rapid and the outburst enters its flaring tail stage, this relationship reverses, and the phase lags diminish as the flux dims further. This result, along with the pulse profile changes observed at the beginning of the flairing tail stage, suggests an abrupt change in the geometry of the accretion disk and column at this time in the outburst. In contrast, the thermonuclear burst oscillation timing does not show appreciable lags, and the burst oscillation phases and fractional amplitudes appear to be relatively independent of energy.
by Jacob M. Hartman.
Ph.D.
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Octau, Franck. "Exploration d'un grand relevé à Nançay et diversité de la population de pulsars." Thesis, Orléans, 2017. http://www.theses.fr/2017ORLE2042/document.
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Depuis la découverte du premier pulsar en 1967, nous connaissons désormais plus de 2500 pulsars aujourd’hui. Les pulsars offrent un champ d’études considérable : depuis l’étude des propriétés du milieu interstellaire et l’étude de la magnétosphère des pulsars jusqu’aux tests de la gravité en champ fort et la caractérisation d’un fond d’ondes gravitationnelles d’origine cosmologique. Cela explique pourquoi nous continuons de chercher de nouveaux pulsars de nos jours. Après des découvertes de pulsars millisecondes dans les sources non identifiées du Fermi Large Area Telescope, un programme de recherche de nouveaux pulsars a été mené à partir de 2012 par G. Desvignes. Observant à 1.4 GHz avec une haute résolution temporelle et fréquentielle, le programme SPAN512 a été conçu pour la recherche de pulsars rapides et lointains situés dans le plan Galactique. Nous décrirons les méthodes d’analyse mises en place pour traiter les données afin de trouver de nouveaux pulsars, méthodes soit basées sur la stabilité de la période de rotation des pulsars soit sur leur émission d’impulsions individuelles. Nous présenterons aussi l’état actuel de l’analyse du programme SPAN512 et les découvertes effectuées, plus particulièrement du pulsar trouvé au cours de ce travail de thèse, PSR J2055+3829, un pulsar milliseconde de période de rotation de 2.08 ms appartenant à un système de type « Veuve Noire ». Ce sera l’occasion de présenter les études chronométriques réalisées pour trouver l’éphéméride de ce pulsar et, dans le même temps, j’en profiterai pour parler d’une analyse similaire faite sur le pulsar J1618-3921, un pulsar dans une orbite excentrique. Enfin, nous présenterons des études polarimétriques de pulsars réalisées à la lumière d’un nouveau modèle, le modèle du vecteur tournant décentré (DRVM). Nous montrerons qu’un champ magnétique hautement décentré peut expliquer les variations brusques de l’angle de polarisationSince the discovery of the first pulsar in 1967, we know over 2500 pulsars today. Pulsars offer a broad range of studies: from the study of the properties of interstellar medium and of pulsar magnetospheres up to test of gravity in the strong-field regime and the characterisation of the cosmological Gravitation Waves background. This explains why we keep searching pulsars nowadays. After successful detections of new millisecond pulsars in Fermi Large Area Telescope unassociated sources at Nançay, a blind pulsar survey was initiated in 2012 by G. Desvignes. Conducted at 1.4 GHz with short sampling time and narrow frequency channels, the SPAN512 was designed to find fast and distant pulsars within the Galactic plane. We describe the methods to analyse data in order to find new pulsars, thanks to their spin stability or tto their single pulses. We will also describe the current status of the survey and the discoveries, more especially the pulsar discovered during this thesis, PSR J2055+3829, a 2.08 ms pulsar in a black widow system. It will be the opportunity to present the radio timing analysis of this pulsar and, in the same time, we will describe similar studies conducted on the pulsar J1618-3921, a pulsar in an eccentric orbit. Finally, we present some polarisation studies of pulsars in light of a new model, the Decentred Rotating Vector Model (DRVM). We will show that a highly decentred dipole may explain abrupt variations of polarisation profiles
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Sanidas, Sotirios Asimaki. "Constraining the gravitational wave background of cosmic strings using pulsar timing arrays." Thesis, University of Manchester, 2012. https://www.research.manchester.ac.uk/portal/en/theses/constraining-the-gravitational-wave-background-of-cosmic-strings-using-pulsar-timing-arrays(76706320-607d-47c8-9e3d-6129482cc044).html.
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The existence of cosmic strings was proposed in the mid-seventies as a by-product of the various phase transitions that occured in the early Universe. Cosmic strings are one-dimensional topological defects; structures of extremely high energy density with infinitesimal widths and lengths of cosmological size. After they were proposed, cosmic strings with GUT energy scales became very popular as a potential source for galaxy formation, but after CMB observations ruled out this possibility, they stopped attracting much scientific attention. The whole field was revived as part of superstring theory, where the formation of cosmic (super)string networks is a very common characteristic of brane inflation models, allowing them to acquire energies over a much more extended range. Attempts to detect cosmic strings centers on the three most basic observational signatures they create: CMB anisotropies, gravitational lensing events and the stochastic gravitational wave background they are expected to have created. So far, no detection of cosmic strings has been achieved. Their non-detection has inevitably led to setting constraints on their most important characteristic; their lineal energy density (or tension) which describes their energy scale. The topic of this thesis is how to use pulsar timing arrays (PTAs) in order to set constraints on the string tension. The limits PTAs can set on the amplitude of the stochastic gravitational wave background at ~nHz frequencies can be used to set constraints on the string tension. Such an effort is much more complicated than CMB or gravitational lensing investigations due to the large number of unknown cosmic string model parameters which are involved and for which, not only we do not have any observational evidence for their value, but moreover, they can acquire values over very wide ranges. So far, previous investigations were based on assumptions about these parameters and on the specific gravitational wave emission mechanism from cosmic string loops. In this work we have constructed a new code to reproduce the gravitational wave background from a cosmic string network, based on the widely accepted one scale model. Using this, we have performed numerous simulations to study the effects on the gravitational wave spectrum for each cosmic string model parameter, covering the whole parameter space of interest for each of them. Moreover, we have also extended the application of our code in order to describe cosmic string networks which create loops on more than one scale, models of which have recently appeared in the literature. In particular, we have investigated cosmic string networks which create loops at two distinct scales and loops with scales described by a log-normal distribution After studying the properties of the gravitational wave spectrum from cosmic strings, we combined our simulations with the most stringent limit so far on the stochastic gravitational wave background imposed by the EPTA. This limit is provided as a function of the slope of the gravitational wave background and we have also used this information for the first time to acquire even more accurate results. In our approach, we did not make any assumption about the values of the cosmic string model parameters, investigating all possibilities and we managed to compute a conservative and completely general constraint on the cosmic string tension, G mu<5.3x10 -7, which is slightly weaker than the current constraints set by CMB and gravitational lensing. We concluded our work by estimating the projected constraints that are expected to be achieved by near future experiments like LEAP, and ultimately by the SKA, to find an improvement of at least two orders of magnitude, significantly outperforming the expected constraints by future CMB investigations.
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Lassus, Antoine. "Méthode de détection de sources individuelles d'ondes gravitationnelles par chronométrie d'un réseau de pulsars : application aux données de l'EPTA." Phd thesis, Université d'Orléans, 2013. http://tel.archives-ouvertes.fr/tel-01017215.
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L'existence des ondes gravitationnelles, fluctuations de l'espace-temps lui-même, a été prédite sans, pour l'instant, qu'une détection directe n'ait été encore possible. A l'heure actuelle, des méthodes consistant en des détecteurs interférométriques de plusieurs kilomètres de long sont à l'oeuvre pour permettre une première détection. Nous proposons, dans cette thèse, d'étudier une autre méthode : la chronométrie d'un réseau de pulsars milliseconde. Elle consiste en l'observation régulière et la datation précise des impulsions radio en provenance de pulsars ultrastables. L'onde gravitationnelle produisant retards ou avances des impulsions sur Terre, nous recherchons sa présence sous forme d'un signal corrélé entre les observations faites des différents pulsars du réseau. Dans un premier temps, nous détaillons les processus d'observation et de chronométrie des pulsars, pour nous pencher sur un cas particulier avec le pulsar J1614-2230. Puis, nous présentons les ondes gravitationnelles et leurs sources ainsi que les différentes méthodes de détection. Nous décrivons tout particulièrement la méthode de chronométrie d'un réseau de pulsars appliquée à la recherche d'un signal en provenance d'un système binaire de tous noirs supermassifs. Ensuite, après avoir détaillé les outils statistiques et numériques utilisés, nous appliquons notre méthode à l'injection d'un tel signal dans les observations réelles faites dans le cadre de l'EPTA. Enfin, nous présentons les limites supérieures sur l'amplitude d'un signal en provenance d'un système binaire obtenues sur ces données sans injection grâce à notre méthode en fonction de la fréquence et de la position de la source.
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Jussila, Adam P. "Simulating Pulsar Signal Scattering in the Interstellar Medium with Two Distinct Scattering Phenomena." Oberlin College Honors Theses / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1528814998720461.
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Sasmaz, Mus Sinem. "X-ray And Timing Properties Of Anomalous X-ray Pulsar 1e 2259+586." Master's thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608625/index.pdf.
Full textAbstract:
In this thesis, we present the spectral and timing variabilities of anomalous X-ray pulsar 1E 2259+586 observed with European Photon Imaging PN Camera (EPIC PN) on board X-ray Multi Mirror Mission (XMM), Proportional Counter Array (PCA) on board Rossi X-ray Timing Explorer (RXTE) and Advanced CCD Imaging Spectrometer (ACIS) on board Chandra X-ray Observatory.
We presented the results of spectral analysis of 2000 January 11 ACIS observation. Pulse phase spectroscopy was performed on two XMM observations before and after the outburst. Pulse profiles of two XMM observations before the outburst and three XMM observations after the outburst were studied. Results are consistent with the those presented by Patel et al. (2001) and Woods et al. (2004).
We searched for the spectral variations versus spin rate during the outburst. Long-term spectral, frequency and spin-down rate variations are presented between 1996 and 2006 including 98 RXTE and 4 XMM observations. However, except outburst region (Woods et al. 2004) no significant spectral and spin rate variabilities were seen. Around the outburst region we confirmed the spectral hardening with increasing spin rate and flux.
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Turner, Jacob E. "Improving the Sensitivity of a Pulsar Timing Array: Correcting for Interstellar Scattering Delays." Oberlin College Honors Theses / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=oberlin1495573098864359.
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Martinez, Jose Guadalupe [Verfasser]. "Pulsar Searching and Timing with the Arecibo and Effelsberg Radio Telescopes / Jose Guadalupe Martinez." Bonn : Universitäts- und Landesbibliothek Bonn, 2019. http://d-nb.info/1194464866/34.
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Purver, Mark Benedict. "High-precision pulsar timing : the stability of integrated pulse profiles and their representation by analytic templates." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/highprecision-pulsar-timing-the-stability-of-integrated-pulse-profiles-and-their-representation-by-analytic-templates(38efcea7-b3eb-4a6b-8376-ef192907ea4e).html.
Full textAbstract:
High-precision timing is an exciting field of pulsar research that holds the promise of direct gravitational wave detection. This goal is at the limit of current technology, and requires the near-seamless combination of data from multiple pulsars observed with multiple telescopes. Accuracy in the recording of pulse profiles and the measurement of their times of arrival (TOAs) is key. In order to time a pulsar, a template is needed that is as close as possible to an ideal version of the pulse profile. Four pulsars were timed using analytic, noise-free templates composed of Gaussian components, and their system parameters were measured to high accuracy. These templates were found to be usable at different telescopes and were adaptable across more than 100 MHz in observing frequency without loss of TOA alignment. The same approach was used to investigate profile variation in the pulsar PSR J1022+1001, which is a promising member of the arrays used to search for gravitational waves. Variation with time was found that is almost equal in magnitude to typical measurement noise. The timing of the pulsar could not be improved using adaptive templates which were allowed to vary with the profile to a limited extent. If the variation is due to instrumental error, then its removal would improve timing accuracy significantly for this pulsar. If it is intrinsic, then it is an interesting and unusual phenomenon. PSRJ1022+1001 was compared to two similar pulsars, one of which showed a lesser degree of variation and one of which did not exhibit significant change.Timing of PSR J1022+1001 was used to calculate upper limits on the amplitude of the stochastic gravitational wave background. A reasonable limit was estimated to be Amax = 1.7 x 10⁻¹⁴, which is stringent for a single pulsar timed alone. However, there was evidence that the timing residuals were somewhat correlated in time, which can produce an artificially low limit. Nevertheless, PSR J1022+1001 has the potential to make a valuable contribution to gravitational wave detection. Investigation into its variation highlights the fact that the timing of a number of pulsars may be crucially improved by the next generation of processing instruments.
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Sahiner, Seyda. "X-ray Spectral And Timing Studies Of The High Mass X-ray Binary Pulsar 4u 1907+09." Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/12610941/index.pdf.
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In this thesis, X-ray spectral and pulse timing analysis of the high mass X-ray binary pulsar 4U 1907+09, based on the observations with Rossi X-ray Timing Explorer (RXTE) and International Gamma-Ray Astrophysics Laboratory (INTEGRAL), are presented. INTEGRAL (October 2005 - November 2007) and RXTE (June 2007 - December 2008) observations confirm that the luminosity of the source is highly variable such that, flaring and dipping activities are observed.
The results of time-averaged energy spectra of RXTE and INTEGRAL observations are consistent with the previous studies. Orbital phase resolved spectroscopy with RXTE data, reveals that the Hydrogen column density varies through the orbit reaching to its maximum value just after periastron. This variation approves that the location of the absorbing material is the accretion flow. A slight spectral softening with increasing luminosity is aslo observed.
4U 1907+09 had been steadily spinning down for more than ~15 years with a rate of -3.54x10-14 Hz s-1. RXTE observations of the source in 2001 showed a ~60% decrease in the spin-down rate and INTEGRAL observations in 2003 showed a reversal to spin-up. The timing analysis presented in this thesis reveals a new spin-down episode with a rate of -3.59x10-14 Hz s-1, which is close to the previous steady spin-down rate. This result implies that a recent torque reversal before June 2007 has taken place. The reversal is a rare event for 4U 1907+09 and it indicates the variations in the mass accretion rate and/or geometry.
Using RXTE observations, 24 new pulse periods are measured to demonstrate the period evolution. Energy resolved pulse profiles confirm that the profile has a double peak sinusoidal shape at energies below 20 keV, whereas the leading peak significantly loses its intensity above 20 keV. This energy dependence indicates that the physical circumstances of the two polar caps are different.
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Chen, Siyuan. "What can we learn from pulsar timing arrays (or not) : constraining astrophysical parametric models with gravitational waves." Thesis, University of Birmingham, 2018. http://etheses.bham.ac.uk//id/eprint/8613/.
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Super massive black holes have been found in the centre of massive galaxies, which have also been observed to merge. Consequently, the central black holes should also form a binary and merge when their host galaxies collide. The galaxy merger rate can be calculated from astrophysical observables, such as the galaxy stellar mass function, pair fraction and merger time scale. Using galaxy - black hole relations it can be converted into a super massive black hole binary (SMBHB) merger rate, i.e. the population of SMBHBs in the Universe. Additionally, properties of individual SMBHBs, like their eccentricities and the densities of their stellar environment, also have an impact on the emission of gravitational waves (GWs). All the GWs emitted by the population of SMBHBs form a gravitational wave background (GWB), which is one of the prime targets for PTAs. Although, PTAs have not been able to detect such a background yet, stringent upper limits on the GWB have been produced. This thesis aims to investigate what we can learn from these upper limits as well as what could be learned from a detection.
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Guillemot, Lucas. "Détections de pulsars milliseconde avec le FERMI Large Area Telescope." Phd thesis, Bordeaux 1, 2009. http://tel.archives-ouvertes.fr/tel-00432706.
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Le satellite Fermi a été lancé le 11 juin 2008, avec à son bord le Large Area Telescope (LAT). Le LAT est un télescope sensible au rayonnement gamma de 20 MeV à plus de 300 GeV. Au début de l'activité de Fermi, neuf pulsars jeunes et énergétiques étaient connus dans le domaine gamma. Le nombre de détections de pulsars par le LAT prédit avant lancement était de plusieurs dizaines au moins. Le LAT permettait également l'étude des pulsars milliseconde (MSPs), jamais détectés avec certitude à très haute énergie jusqu'alors. Cette thèse aborde dans un premier temps la campagne de chronométrie des pulsars émetteurs radio et/ou X, candidats à la détection par le LAT, en collaboration avec les grands radiotélescopes et télescopes X. Cette campagne a permis la recherche de signaux gamma pulsés avec une grande sensibilité. En outre, la plupart des MSPs galactiques ont été suivis dans le cadre de cette campagne, sans biais de sélection a priori sur cette population d'étoiles. Pour la première fois, des pulsations ont été détectées pour huit MSPs galactiques au-dessus de 100 MeV. Quelques bons candidats à une détection prochaine apparaissent. Une recherche similaire a été conduite pour des MSPs d'amas globulaires, sans succès à présent. L'analyse des courbes de lumière et des propriétés spectrales des huit MSPs détectés révèle que leur rayonnement gamma est relativement similaire à celui des pulsars ordinaires, et est vraisemblablement produit dans la magnétosphère externe. Cette découverte suggère que certaines sources non identifiées sont des MSPs, pour l'instant inconnus.
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Gomez, Julio D. "Pulse timings for binary black hole-pulsar systems." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0024/MQ31349.pdf.
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Livingstone, Margaret Anne. "Long-term timing of two young, energetic pulsars." Thesis, McGill University, 2005. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=84054.
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We report on the long-term phase-coherent timing of two young, energetic pulsars, PSR B1509-58 and PSR B0540-69, using data from the Rossi X-ray Timing Explorer, the Parkes Radio Telescope and the Molonglo Observatory Synthesis Telescope. We present fully phase-coherent timing analyses of both sources, and show that contamination from timing noise can significantly affect measured timing parameters. As a result, we also present, a partially phase-coherent timing analysis which is less sensitive to timing noise.We present an updated measurement of n = 2.839 +/- 0.003 for PSR B1509-58, and we report a measurement of the second braking index, m = 18.3 +/- 2.9, in agreement with the prediction from the simple model of pulsar spin-down. We also examine changes in dispersion measure and present an analysis of the noise, measuring a low-resolution power spectrum corresponding to a spectral index of beta = -4.6 +/- 1.0. This implies that the noise cannot be explained by a pure random walk. We also show that no glitches have occurred in 21.3 yr, implying that this pulsar glitches less often than typical young pulsars.
We measure the braking index for PSR B0540-69, n = 2.140 +/- 0.009 and discuss our measurement in the context of other discordant values reported in the literature. In addition, we detect evidence for a glitch which has been previously reported but later disputed. The glitch occurred at MJD 51335 +/- 12 with Deltanu/nu = (1.4 +/- 0.2) x 10-9 and Delta n&d2;/n&d2; = (1.33 +/- 0.02) x 10-4. We present an improved source position from the phase-coherent timing of this pulsar, to our knowledge, the first of its kind from X-ray pulsar timing.
We discuss the physical implications of n < 3, the value predicted from the model of pulsar spin down. In addition, we discuss possible causes of timing noise in these two young pulsars. We also discuss the anomalously small glitch activity in very young pulsars which suggests that neutron stars of similar apparent ages, rotation properties and inferred dipolar B fields can have significantly different internal properties.
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Beklen, Elif. "Timing Observations From Rossi X-ray Timing Explorer (rxte)." Master's thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/1260199/index.pdf.
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In this thesis, RXTE observations of 4U 1907+09 are presented. Timing
analysis of these data sets have yielded quasi periodic oscillations
(QPOs) at orbital phases corresponding to the two flares in every orbital
period. Known continuous spin down trend and QPO behaviour at the
flares strongly suggest that a transient accretion disk occurs at the
flares. Our
findings strongly suggested that neutron star passes through the
equatorial wind of Be companion star. During these passages a
transient disk forms around Be neutron star.
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Ridolfi, Alessandro [Verfasser]. "Long-term timing of pulsars in globular clusters / Alessandro Ridolfi." Bonn : Universitäts- und Landesbibliothek Bonn, 2017. http://d-nb.info/1149744871/34.
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Shaifullah, Golam [Verfasser], and Joris [Akademischer Betreuer] Verbiest. "Timing and properties of recycled pulsars / Golam Shaifullah ; Betreuer: Joris Verbiest." Bielefeld : Universitätsbibliothek Bielefeld, 2017. http://d-nb.info/1139117661/34.
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Chakrabarty, Deepto Prince Thomas A. Prince Thomas A. "Hard X-ray detection and timing of accretion-powered pulsars with BATSE /." Diss., Pasadena, Calif. : California Institute of Technology, 1996. http://resolver.caltech.edu/CaltechETD:etd-09022008-132322.
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Serim, Muhammed Mirac. "Timing Properties Of Recently Discovered Soft Gamma Repeaters." Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12614803/index.pdf.
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In this thesis, the recently discovered Soft Gamma Ray Repeaters SGR
J1833-0832, SWIFT J1822.3-1606 and SWIFT J1834.9-0846 are analysed
using the archival Swift, RXTE, Chandra and XMM-Newton observations.
The period fluctuations and timing noise properties of these sources are
investigated. Spectral characteristics and long term frequency evolution
of these sources are presented. Investigation for timing noise structure of
these magnetars has shown a correlation between first frequency derivative
of the spin frequency and torque noise strength.
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Kurtti, S. (Sami). "Integrated receiver channel and timing discrimination circuits for a pulsed time-of-flight laser rangefinder." Doctoral thesis, Oulun yliopisto, 2013. http://urn.fi/urn:isbn:9789526200460.
Full textAbstract:
Abstract In this thesis integrated receiver channel techniques and circuit implementations for a pulsed time-of-flight (TOF) laser rangefinder are developed with the aim to achieve centimetre level accuracy within the dynamic range of > 1:10 000 of the input pulse amplitudes. The receiver channel converts the input current pulses produced by the photo detector to voltage pulses and produces a logic-level timing pulse for the time interval measurement. In addition to the minimization of noise, the main design challenge is the minimization of the timing walk error resulting from the varying amplitude of the received optical echo. In automotive perception laser radar application, which was the target application of this work, the input amplitude of the received echo varies in a range of 1:10 000 or even more due to changes in the measured distance and reflectivity and orientation of the target. Two receiver channel and timing discriminator architectures were developed and realized as integrated circuits in 0.35 μm BiCMOS technology, and finally verified by measurements. One of the receiver channels is based on the detection of the zero-crossing of the timing pulse produced with a unipolar-to-bipolar conversion at the input of the receiver. It achieved a timing walk error of ±8 mm in a dynamic range of 1:3000. Another receiver channel is based on the leading edge timing discrimination, in which the timing walk error is being compensated for in time domain by measuring the width of the timing pulse simultaneously with its leading edge time position. An important feature of this technique, suggested in this thesis, is that it is operative also beyond the linear range of the receiver channel, which is typically limited to < 1:100. The receiver channel with leading edge detection and pulse width compensation achieved a compensated walk error of ± 2–3 mm in a dynamic range of ~ 1:100 000. The bandwidth and input referred current noise of the channel were 230 MHz and <100 nArms, respectively. The single-shot timing precision was 120 ps (20 mm in distance) at the SNR of 10. The feasibility of the receiver electronics was verified by two laser radar prototypes. An accuracy of < ± 5 mm was measured in a measurement range from 1 to 55 m, which corresponds to the receiver dynamic range of > 1:10 000 taking into consideration the varying reflectivity of the target materials usedTiivistelmä Väitöskirjatyössä on suunniteltu integroituja vastaanotintekniikoita ja –piirejä valopulssin kulkuaikamittaustekniikkaan perustuvaan laseretäisyysmittaukseen. Tavoitteena on ollut saavuttaa senttimetriluokan tarkkuus laajalla tulopulssin amplitudin dynaamisella alueella > 1:10 000. Vastaanotinkanava muuntaa valoilmaisimelta saadun tulovirtapulssin jännitepulssiksi ja muodostaa siitä logiikkatasoisen ajoituspulssin aikavälimittauspiirille. Kohinan minimoimisen lisäksi toinen suuri suunnitteluhaaste on minimoida ajoitusvirhe, jota syntyy vastaanotetun optisen tulosignaalin amplitudin vaihdellessa laajalla alueella. Työssä kehitettyjen vastaanotinkanavien yksi sovelluskohdetavoitteista on ollut autoteollisuudessa käytettävät etäisyysmittarit. Näissä tulosignaalin taso vaihtelee erittäin laajalla dynaamisella alueella, joka voi olla > 1:10 000, johtuen laajasta etäisyysmittausalueesta sekä kohteen heijastavuuden ja orientaation vaihteluista. Väitöskirjatyössä kehitettiin ja valmistettiin kaksi vastaanotin- ja ajoitusilmaisurakennetta. Piirit valmistettiin 0,35 μm BiCMOS- teknologialla, ja niiden toiminta varmistettiin mittauksilla. Ensimmäinen vastaanotinkanava-arkkitehtuuri perustuu kanavan tulossa tapahtuvaan unipolaari-bipolaari muutokseen ja sen jälkeiseen nollaylityskohdan ilmaisuun. Piirillä saavutettiin ±8 mm ajoitusvirhe 1:3000 dynaamisella alueella. Toinen vastaanotinkanava-arkkitehtuuri perustuu etureunanilmaisuun, jossa ajoitusvirhe korjataan aikatasossa mittaamalla samanaikaisesti ajoituspulssin paikka ja leveys. Ajoitusvirheenkorjausmenetelmän tärkeä ominaisuus on, että se toimii laajemmalla kuin vastaanottimen lineaarisella alueella (< 1:100). Etureunanilmaisuun ja pulssinleveyden korjaukseen perustuvalla vastaanotinkanavalla saavutettiin korjattu ajoitusvirhe ± 2–3 mm 1:100 000 dynaamisella alueella. Kanavan kaistanleveys oli 230 MHz ja tulon redusoitu virtakohina < 100 nArms. Signaalikohinasuhteella 10 laseretäisyysmittauksen kertamittaustarkkuudeksi mitattiin 120 ps (20 mm etäisyydessä). Väitöskirjatyön yhteydessä valmistettiin lisäksi kaksi prototyyppilasertutkaa, joilla varmistettiin vastaanotinelektroniikan toiminta laajalla > 1:10 000 dynaamisella tulopulssin amplitudin vaihtelualueella. Lasertutkan ajoitusvirheeksi mitattiin < ± 5 mm 1–55 m:n mittausalueella
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Palojärvi, P. (Pasi). "Integrated electronic and optoelectronic circuits and devices for pulsed time-of-flight laser rangefinding." Doctoral thesis, University of Oulu, 2003. http://urn.fi/urn:isbn:9514269667.
Full textAbstract:
Abstract
The main focus of this work concerned with the development of integrated electronic and optoelectronic circuits and devices for pulsed time-of-flight laser rangefinding is on the construction of the receiver channel, system level integration aimed at realisation of the laser radar module and in integration of all the receiver functions of laser radar on one chip.
Since the timing discriminator is a very important part of a pulsed
time-of-flight laser rangefinder, two timing discrimination methods are presented and verified by means of circuit implementations, a leading edge discriminator and a high-pass timing discriminator. The walk error of the high-pass timing discriminator is ±4 mm in a dynamic range of 1:620 and the uncompensatable walk error of the leading edge discriminator is ±30 mm in a dynamic range of 1:4000. Additionally a new way of combining the timing discriminator with time interval measurement is presented which achieves a walk error of ±0.5 mm in a dynamic range of 1:21.
The usability of the receiver channel chip is verified by constructing three prototypes of pulsed TOF laser radar module. The laser
radar achieves mm-level accuracy in a measurement range from 4 m to 34 m with non-cooperative targets. This performance is similar to that of earlier realisations using discrete components or even better and has markedly reduced power consumption and size.
The integration level has been increased further by implementing a photodetector on the same chip as the rest of the receiver electronics. The responsivity of the photodetector is about 0.3 A/W at 850 nm wavelength and the noise of the receiver is reduced by a factor of about two relative to realisations using an external photodetector, because of the absence of parasitic capacitances and inductances caused by packages, PCB wiring, bond wires and ESD and I/O cell structures.
The functionality of a multi-channel pulsed TOF laser radar chip is demonstrated using the photodiode structure investigated here. The chip includes four photodetectors with receiver channels and a three-channel time-to-digital converter. The chip together with external optics and a laser pulse transmitter enables distances to be measured in three directions with a single optical pulse, thus showing the feasibility of implementing all the receiver functions of a pulsed time-of-flight imager on a single chip using a current semiconductor process.
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Gavriil, Fotis P. "Long-term monitoring of anomalous X-ray pulsars with the rossi x-ray timing explorer." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=33763.
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We report on the long-term monitoring of five anomalous X-ray Pulsars (AXPs) using the Rossi X-ray Timing Explorer (RXTE ). We present a phase-coherent timing ephemeris for 4U 0142+61, and show that it has rotated with high stability over 4.4 yr, with RMS phase deviation of 7% of the pulse period from a simple fit including only n and n&d2; . We show that 1E 1048.1-5937 shows significant deviations from simple spin-down such that phase-coherent timing has not been possible over time spans longer than a few months. We find that the deviations from simple spin down are not consistent with single "glitch" type events, nor are they consistent with radiative precession. We suggest that 1E 1048.1-5937 may be a transition object between the soft gamma-ray repeater and AXP populations, and the AXP most likely to one day undergo an outburst. We also report on the continued timing stability of 1E 2259.1+586, for which phase coherence has now been maintained over 4.5 yr, as well as on the detection of a significant n&d3; in RXS J170849.0-400910, consistent with recovery following a glitch. We note a possible correlation in which timing stability decreases with increasing n&d2; . We find no large variability in pulse morphology as a function of time. We present high signal-to-noise ratio average pulse profiles for each AXP, and consider them as a function of energy. We find a variety of different behaviors, and consider possible trends in the data. We also find no large variations in pulsed flux, and set la upper limits of ∼20--30% of the mean.
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Ruotsalainen, T. (Tarmo). "Integrated receiver channel circuits and structures for a pulsed time-of-flight laser radar." Doctoral thesis, University of Oulu, 1999. http://urn.fi/urn:isbn:9514252160.
Full textAbstract:
Abstract
This thesis describes the development of integrated structures and circuit implementations for the receiver channel of portable pulsed time-of-flight laser rangefinders for industrial measurement applications where the measurement range is from ∼1 m to ∼100 m to noncooperative targets and the required measurement accuracy is from a few millimetres to a few centimetres. The receiver channel is used to convert the current pulse from a photodetector to a voltage pulse, amplify it, discriminate the timing point and produce an accurately timed logic-level pulse for a time-to-digital converter.
Since the length of the laser pulse, typically 5 ns, is large compared to the required accuracy, a specific point in the pulses has to be discriminated. The amplitude of the input pulses varies widely as a function of measurement range and the reflectivity of the target, typically from 1 to 100 ... 1000, so that the gain of the amplifier channel needs to be controlled and the discrimination scheme should be insensitive to the amplitude variation of the input signal. Furthermore, the amplifier channel should have low noise in order to minimize timing jitter.
Alternative circuit structures are discussed, the treatment concentrating on the preamplifier, gain control circuitry and timing discriminator, which are the key circuit blocks from the performance point of view. New circuit techniques and structures, such as a fully differential transimpedance preamplifier and a current mode gain control scheme, have been developed. Several circuit implementations for different applications are presented together with experimental results, one of them being a differential BiCMOS receiver channel with a bandwidth of 170 MHz, input referred noise of 6 pA/√Hz
and maximum transimpedance of 260 kW. It has an accuracy of about +/- 7 mm (average of 10000 measurements), taking into account walk error with an input signal range of 1:624 and jitter (3s).
The achievable performance level using integrated circuit technology is comparable or superior to that of the previously developed commercially available discrete component implementations, and the significantly reduced size and power consumption open up new application areas.
34
Coburn, Wayne. "A study of magnetic fields of accreting x-ray pulsars with the Rossi x-ray timing explorer /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3015845.
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Kilpelä, A. (Ari). "Pulsed time-of-flight laser range finder techniques for fast, high precision measurement applications." Doctoral thesis, University of Oulu, 2004. http://urn.fi/urn:isbn:9514272625.
Full textAbstract:
Abstract
This thesis describes the development of high bandwidth (~1 GHz) TOF (time-of-flight) laser range finder techniques for industrial measurement applications in the measurement range of zero to a few dozen metres to diffusely reflecting targets. The main goal has been to improve single-shot precision to mm-level in order to shorten the measurement result acquisition time.
A TOF laser range finder consists of a laser transmitter, one or two receivers and timing discriminators, and a time measuring unit. In order to improve single-shot precision the slew-rate of the measurement pulse should be increased, so the optical pulse of the laser transmitter should be narrower and more powerful and the bandwidth of the receiver should be higher without increasing the noise level too much.
In the transmitter usually avalanche transistors are used for generating the short (3–10 ns) and powerful (20–100 A) current pulses for the semiconductor laser. Several avalanche transistor types were compared and the optimization of the switching circuit was studied. It was shown that as high as 130 A current pulses are achievable using commercially available surface mount avalanche transistors.
The timing discriminator was noticed to give the minimum walk error, when high slew rate measurement pulses and a high bandwidth comparator were used. A walk error of less than +/- 1 mm in an input amplitude dynamic range higher than 1:10 can be achieved with a high bandwidth receiver channel. Adding an external offset voltage between the input nodes of the comparator additionally minimized the walk error.
A prototype ~1 GHz laser range finder constructed in the thesis consists of a laser pulser and two integrated ASIC receiver channels with silicon APDs (avalanche photodiodes), crossover timing discriminators and Gilbert cell attenuators. The laser pulser utilizes an internal Q-switching mode of a commercially available SH-laser and produces optical pulses with a pulse peak power and FWHM (full-width-at-half-maximum) of 44 W and 74 ps, respectively. Using single-axis optics and 1 m long multimode fibres between the optics and receivers a total accuracy of +/-2 mm in the measurement range of 0.5–34.5 m was measured. The single-shot precision (σ-value) was 14 ps–34 ps (2–5 mm) in the measurement range. The single-shot precision agrees well with the simulations and is better with a factor of about 3-5 as compared to earlier published pulsed TOF laser radars in comparable measuring conditions.
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Nissinen, J. (Jan). "Integrated CMOS circuits for laser radar transceivers." Doctoral thesis, Oulun yliopisto, 2011. http://urn.fi/urn:isbn:9789514295454.
Full textAbstract:
Abstract The main aim of this work was to design CMOS receiver channels for the integrated receiver chip of a pulsed time-of-flight (TOF) laser rangefinder. The chip includes both the receiver channel and the time-to-digital converter (TDC) in a single die, thus increasing the level of integration of the system, with the corresponding advantages of a cheaper price and lower power consumption, for example. Receiver channels with both linear and leading edge timing discriminator schemes were investigated. In general the receiver channel consists of a preamplifier, a postamplifier and a timing comparator. Since a large systematic timing error may occur due to high variation in the amplitude of the received echo, a leading edge timing discriminator scheme with time domain walk error compensation is proposed here, making use of the TDC already available in the chip to measure the slew rate of the pulse and using that information to evaluate the timing error. This compensation scheme benefits from the fact that compensation can be continued even though the signal is clipped in the amplitude domain, because the slew rate continues to increase even then. The receiver channel with leading edge detection and time domain walk error compensation achieved a compensated timing walk error of ±4.5 mm within a dynamic range of more than 1:10000. The standard deviation in single shot precision was less than 25 mm with an SNR of more than 20. The usability of the receiver channel in pulsed TOF laser rangefinders was verified by making actual time-of-flight measurements on a calibrated measurement track. The linearity of the receiver chip was better than ±5 mm in a measurement range from 3 m to 21 m, with the dynamic range of the receiver channel reaching more than 1:2000. An integrated CMOS laser diode pulser was also demonstrated to prove its functionality for generating ampere-scale peak current pulses through a low ohmic load and a laser diode. The CMOS pulser achieved a peak current pulse with the amplitude of ~1 A, an optical pulse width of ~2.5 ns and a rise time of ~1 ns with a 5 V power supplyTiivistelmä Työn ensisijaisena tavoitteena oli suunnitella CMOS-vastaanottimia valopulssin kulkuajan mittaukseen perustuvan lasertutkan integroituun vastaanotinpiiriin. Vastaanotinpiiri sisältää sekä vastaanotinkanavan että aika-digitaalimuuntimen yhdellä integroidulla sirulla. Tällöin systeemin integrointiastetta saadaan kasvatettua, mikä merkitsee esimerkiksi halvempaa hintaa ja pienempää tehon kulutusta. Työssä on tutkittu vastaanotinkanavia, jotka käyttävät joko lineaariseen ilmaisuun tai etureunailmaisuun perustuvaa ajoitusilmaisutekniikkaa. Yleisesti vastaanotinkanava sisältää esivahvistimen, jälkivahvistimen ja ajoituskomparaattorin. Vastaanotetun signaalin tason voimakas vaihtelu saattaa aiheuttaa suuren systemaattisen virheen etureunailmaisuun perustuvassa ajoitusilmaisussa. Tässä työssä on esitetty etureunailmaisua käyttävä ajoitusilmaisin, jossa syntyvää ajoitusvirhettä voidaan korjata mittaamalla pulssin nousunopeutta aika-digitaalimuuntimella, joka on integroitu samalle sirulle. Aikatasossa tapahtuvan virheenkorjauksen etuna on mahdollisuus jatkaa virheenkorjausta amplituditasossa tapahtuvan signaalin leikkautumisen jälkeenkin, koska signaalin nousunopeus kasvaa leikkaantumisesta huolimatta. Etureunailmaisua käyttävällä vastaanotinkanavalla, jossa ajoitusvirhettä korjattiin pulssin nousunopeutta mittaamalla, saavutettiin ±4,5 mm ajoitusvirhe 1:10000 dynaamisella alueella. Kertamittaustarkkuuden keskihajonta oli vähemmän kuin 25 mm, kun signaalikohinasuhde oli enemmän kuin 20. Vastaanotinkanavan käytettävyys osana lasertutkaa todettiin tekemällä tutkamittauksia kalibroidulla mittaradalla. Mittauksissa saavutettu lineaarisuus oli ±5 mm mittausalueen vaihdellessa 3 metristä 21 metriin ja signaalin dynamiikan ollessa enemmän kuin 1:2000. Lisäksi työssä esitellään integroitu CMOS-pulssitin, joka pystyy tuottamaan ampeeri-luokan virtapulsseja laserdiodiin. CMOS-pulssittimella voitiin tuottaa 5 V käyttöjännitteellä ~1 A virtapulsseja optisen pulssin leveyden ja nousuajan ollessa ~2,5 ns ja ~1 ns
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Bolar, Divya Sanam. "Accuracy of pulsed arterial spin labeling magnetic resonance imaging in the human brain : tag width and timing effects." Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38673.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 28-29).
Arterial spin labeling (ASL) is the only non-invasive magnetic resonance imaging (MRI) technique that allows absolute quantification of cerebral blood flow (CBF). It involves using radiofrequency pulses designed to invert the spins of water in arterial blood, effectively creating a magnetic bolus. This inverted blood can be considered an endogenous contrast agent; imaging as it traverses the vascular tree allows CBF measurements. Such types of experiments are especially useful for functional neuro-activation studies and in settings of neuropathology. Two flavors of ASL exist: continuous ASL and pulsed ASL. Pulsed ASL has the advantage of not requiring specialized imaging hardware, and can be performed using standard clinical scanners found in most hospitals. Pulsed ASL techniques, however, may yield inaccurate perfusion values and diminished perfusion sensitivity if appropriate labeling parameters are not chosen, particularly during global challenges such as hypercapnia. In this study, the accuracy of QUIPSS II (Quantitative Imaging of Perfusion using a Single Subtraction - second version) ASL for measuring flow changes during a global flow perturbation (hypercapnia) was assessed.
(Cont.) Multiple inversion time ASL experiments were performed to examine bolus delivery dynamics under conditions of normocapnia and hypercapnia and at variable inversion band thicknesses. Tag delivery (inflow) curves revealed that typical published parameter values can cause substantial perfusion error during global challenges and render perfusion increases nearly undetectable. Theoretical criteria for choosing optimal QUIPSS II ASL parameter values are explored, and a multiple inversion time method for empirical determination of tag characteristics presented. Single inversion time functional experiments were subsequently performed to show that by using larger inversion band thicknesses and optimized timing parameters, perfusion accuracy and sensitivity can be substantially improved. Activation maps from block design visual cortex activation experiments and normocapnia-hypercapnia experiments support this conclusion.
by Divya Sanam Bolar.
S.M.
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Hallman, L. (Lauri). "Single photon detection based devices and techniques for pulsed time-of-flight applications." Doctoral thesis, Oulun yliopisto, 2015. http://urn.fi/urn:isbn:9789526210445.
Full textAbstract:
Abstract In this thesis, a new type of laser diode transmitter using enhanced gain-switching suitable for use with a single photon avalanche diode (SPAD) detector was developed and tested in the pulsed time-of-flight laser range finding (lidar) application. Several laser diode versions were tested and the driving electronics were developed. The driving electronics improvements enabled a pulsing frequency of up to 1 MHz, while the maximum laser output power was about 5–40 W depending on the laser diode dimensions. The large output power is advantageous especially in conditions of strong photon noise emerging from ambient light outdoors. The length of the laser pulse matches the jitter of a typical SPAD detector providing several advantages. The new laser pulser structure enables a compact rangefinder for 50 m distance measurement outdoors in sunny conditions with sub-centimeter precision (σ-value) at a valid distance measurement rate of more than 10 kHz, for example. Single photon range finding techniques were also shown to enable a char bed level measurement of a recovery boiler containing highly attenuating and dispersing flue gas. In addition, gated single photon detector techniques were shown to provide a rejection of fluorescent photons in a Raman spectroscope leading to a greatly improved signal-to-noise ratio. Photonic effects were also studied in the case of a pulsed time-of-flight laser rangefinder utilizing a linear photodetector. It was shown that signal photon noise has an effect on the optimum detector configuration, and that pulse detection jitter can be minimized with an appropriate timing discriminatorTiivistelmä Tässä työssä kehitettiin uudentyyppinen, tehostettua "gain-switchingiä" hyödyntävä laserdiodilähetin käytettäväksi yksittäisten fotonien avalanche-ilmaisimien (SPAD) kanssa, ja sitä testattiin pulssin lentoaikaan perustuvassa laseretäisyysmittaussovelluksessa. Useita laserdiodiversioita testattiin ja ohjauselektroniikkaa kehitettiin. Ohjauselektroniikan parannukset mahdollistivat jopa 1 MHz pulssitustaajuuden, kun taas laserin maksimiteho oli noin 5–40 W riippuen laserdiodin dimensioista. Suuri lähtöteho on edullinen varsinkin vahvoissa taustafotoniolosuhteissa ulkona. Laserpulssin pituus vastaa tyypillisen SPAD-ilmaisimen jitteriä tarjoten useita etuja. Uusi laserpulssitinrakenne mahdollistaa esimerkiksi kompaktin etäisyysmittarin 50 m mittausetäisyydelle ulkona aurinkoisessa olosuhteessa mm–cm -mittaustarkkuudella (σ-arvo) yli 10 kHz mittaustahdilla. Yksittäisten fotonien lentoaikamittaustekniikan osoitettiin myös mahdollistavan soodakattilan keon korkeuden mittauksen, jossa on voimakkaasti vaimentavaa ja dispersoivaa savukaasua. Lisäksi portitetun yksittäisten fotonien ilmaisutekniikan osoitettiin hylkäävän fluoresenssin synnyttämiä fotoneita Raman-spektroskoopissa, joka johtaa selvästi parempaan signaali-kohinasuhteeseen. Fotoni-ilmiöitä tutkittiin myös lineaarista valoilmaisinta hyödyntävän pulssin kulkuaikamittaukseen perustuvan lasertutkan tapauksessa. Osoitettiin, että signaalin fotonikohina vaikuttaa optimaaliseen ilmaisinkonfiguraatioon, ja että pulssin ilmaisujitteri voidaan minimoida sopivalla ajoitusdiskriminaattorilla
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Beklen, Elif. "X-ray And Optical Observations Of High Mass X-ray Binaries." Phd thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612636/index.pdf.
Full textAbstract:
In this thesis, X-ray and optical observations of accretion powered pulsars are presented.
By using archival RXTE observations we work on the X-ray spectral and pulse timing
analysis of 4U 1538-52, 4U 1907+09, SMC X-1 to have more detailed information about their orbital and spin parameters.
For 4U 1538-52 and SMC X-1, we determined new orbital epochs.
By using long term pulse history of 4U 1907+09, we were able to work spin-down trend of the system and also calculate the change in the spin-down rate.
Using Fermi/GBM observations we can monitor bright accreting pulsar systems. We are producing long term
histories of pulse frequency and
flux of 20 continuosly monitoring systems.
Adding Swift/BAT observations to GBM observations, for 4U 1626-67, we did reveal the characteristics belong to spin-down trend before and
spin-up behaviour after torque reversal seen in 2008 February.
Two newly discovered IGRJ06074+2205 and IGRJ01583+6713 sources are identified as X-ray binary systems and we found
parameters of them like distance, magnitudes, by using both optical photometric and spectroscopic observations.
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Farrell, Sean Adam Physical Environmental & Mathematical Sciences Australian Defence Force Academy UNSW. "The multi-coloured universe of 2S 0114+650." Awarded by:University of New South Wales - Australian Defence Force Academy. School of Physical, Environmental and Mathematical Sciences, 2007. http://handle.unsw.edu.au/1959.4/38692.
Full textAbstract:
This thesis presents the results of a comprehensive multi-wavelength study of the high mass X-ray binary 2S 0114+650. This enigmatic source has previously been proposed to be the first in a new class of super-slow X-ray pulsars, containing a neutron star revolving once every 2.7 h. The 11.6 d orbital period of this system has been well established in both X-ray and optical wavelengths. During the initial stages of the research presented in this thesis we discovered an additional 30.7 d ???super-orbital??? modulation in the X-ray emission from this source. While similar periodicities seen in other X-ray binaries are commonly attributed to the precession of a warped accretion disc, the observational evidence suggests the absence of such a disc in 2S 0114+650. The purpose of this project is thus to determine the nature of the super-orbital modulation and to better constrain the astrophysical parameters of this system. To investigate the long-term variability we analysed ~8.5 yr of archived data from the Rossi X-ray Timing Explorer space telescope. The problem of the spurious ~24 h periods in this data was solved as a by-product of these studies. Follow-up pointed observations were obtained with this satellite in order to examine the spectral and temporal behaviour over the spin, orbital and super-orbital timescales. Independent confirmation of the super-orbital modulation was performed using ~2 yr of data from the INTEGRAL satellite obtained during a long-term monitoring campaign of the Cassiopeia region. The evolution of the spin, orbital and super-orbital periods over ~10 yr was examined using archived data from the Rossi X-ray Timing Explorer satellite. Radio observations were performed with the Giant Meterwave Radio Telescope to search for any radio emission associated with this source and to determine whether it is variable over the known periodicities. Near infrared observations were performed with the Mt Abu telescope to determine whether a Be star nature can be ruled out for the optical component. Finally, a statistical analysis of the properties of the confirmed super-orbital X-ray binaries was performed in order to search for commonalities between these systems.
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Li, Shengyun. "Neuropeptide signalling systems involved in the timing of puberty onset and regulation of the gonadotrophin-releasing hormone pulse generator in the rat." Thesis, King's College London (University of London), 2016. http://kclpure.kcl.ac.uk/portal/en/theses/neuropeptide-signalling-systems-involved-in-the-timing-of-puberty-onset-and-regulation-of-the-gonadotrophinreleasing-hormone-pulse-generator-in-the-rat(a0a177b9-0690-451d-9ae3-d0771eeb94f4).html.
Full textAbstract:
The pulsatile release of luteinising hormone (LH) induced by intermittent release of the gonadotrophin-releasing hormone (GnRH) is essential for initiating puberty and maintaining normal reproductive functions. Many neuropeptides including neurokinin B (NKB), substance P, kisspeptin (Kiss1) and gonadotrophin-inhibiting hormone (GnIH) have been implicated in regulating the secretion of LH. However, few studies have demonstrated the effects of those neuropeptides on pulsatile LH release and the dynamic changes of LH secretion in different gonadal hormone conditions. Studies outlined in this thesis have shown that antagonism of NKB receptor inhibits the pulsatile release of LH and delays the timing of puberty onset in female rats. Furthermore, NKB receptor agonism suppresses pulsatile LH release in ovariectomised (OVX) adult rats, but stimulates LH secretion in OVX rats replaced with 17β-oestradiol (E2). Likewise, intra-arcuate nucleus (ARC) administration of substance P, a neuropeptide belonging to the same family of NKB, suppresses pulsatile LH release in OVX rats, but stimulates LH secretion in OVX rats replaced with E2. Kiss1, a potent stimulator of the hypothalamo-pituitary-gonadal (HPG) axis, has been studied extensively within the hypothalamus, but little is known about its extra-hypothalamic effects. Current studies have shown that administration of Kiss1 into the medial amygdala (MeA), a key limbic brain structure involved in reproduction, stimulates LH secretion in OVX rats. Furthermore, intra-MeA administration of Kiss1 receptor antagonist inhibits the pulsatile LH release in OVX rats and spontaneous LH surges in intact female rats. Unlike Kiss1, GnIH is a major inhibitor of the reproductive axis. Central administration of RFamide-related peptides-3 (RFRP-3), the mammalian orthologue of GnIH, suppresses the pulsatile LH release in OVX rats. This effect is partially mediated through the endogenous opioid peptides. RFRP-3 is also implicated in stress-induced suppression of pulsatile LH secretion. Furthermore, antagonism of RFRP-3 receptor in the ARC and the medial preoptic area (mPOA) stimulates LH secretion in OVX rats with E2 replacement, indicating that RFRP-3 may also regulate the E2-induced negative feedback control of LH release. Taken together, the present study has demonstrated that various neuropeptides signaling systems including NKB, substance P, Kiss1 and RFRP-3 regulate pulsatile LH secretion in female rats.
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El, bassri Farid. "Sources lasers déclenchées nanosecondes : Applications à la spectroscopie Raman cohérente sous champ électrique." Thesis, Limoges, 2014. http://www.theses.fr/2014LIMO0060/document.
Full textAbstract:
Du fait de leur compacité, leur robustesse et leur faible coût, les microlasers impulsionnels nanosecondes constituent des sources particulièrement attractives pour de nombreux systèmes de détection et d'analyse, en particulier les cytomètres en flux ou les dispositifs pour la spectroscopie CARS (Coherent Raman Anti Stokes Scattering). Cependant, ces applications nécessitent des performances améliorées en ce qui concerne la gigue temporelle et la cadence de répétition accessible. Dans sa première partie, cette thèse propose des solutions originales pour atteindre les performances requises à partir de microlasers passivement déclenchés, grâce à la mise en oeuvre d'une cavité hybride couplée, pompée par une onde modulée en intensité. Une cadence de répétition supérieure à 30 kHz avec une gigue demeurant inférieure à 200 ns est atteinte. Le potentiel de microlasers à fibres déclenchés par modulation du gain pour monter en cadence est aussi évalué, montrant que des impulsions à faible gigue, à une cadence de plus de 2 MHz peuvent être produites. Enfin, la dernière partie est consacrée à la mise au point et à l'exploitation d'un nouveau système de spectroscopie CARS assisté par une excitation électrique haute tension. Ce dispositif, réalisé à partir d'un microlaser amplifié, permet de s'affranchir du bruit de fond non résonnant des mesures et de réaliser une analyse spectroscopique fine de la réponse de différents milieux d'intérêt sous champ continu ou impulsionnel, pouvant conduire à une nouvelle méthode de microdosimétrie de champ. Diverses applications, dont la granulométrie à l'échelle micro ou nanométrique ou l'identification de marqueurs pour la biologie, sont démontréesThanks to their compactness, robustness and low cost, pulsed nanosecond microlasers are particularly attractive sources for different detection and analysis systems, particularly flow cytometers or devices for CARS (Coherent Anti Raman Stokes Scattering) spectroscopy. However, these applications require reduced time jitter and increased repetition rate. The first part of this thesis proposes novel solutions to achieve the required performance from passively Q-switched microlasers, which are based on an hybrid coupled-cavity and intensitymodulated pump wave. A repetition rate greater than 30 kHz with jitter remaining lower than 200 ns is reached. Pulsed fiber microlasers operating by gain switching are also studied, showing that pulses with low timing jitter, at a repetition rate of more than 2 MHz can be obtained. The last part is devoted to the development and the implementation of a new system of CARS spectroscopy assisted by a high-voltage electrical stimulation. This device, based on an amplified microlaser, allows to substract the non-resonant background noise in the measurements. Thus, a fine spectroscopic analysis of the response of different environments of interest in continuous or pulsed field can be achieved. It may lead to a new method for field microdosimetry. Various applications, including granulometry at the micro or nanometric scale and the identification of markers for biology, are shown
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Huang, Hsueh-Wei, and 黃學位. "Pulsar Timing and Equivalence Principle Tests." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/02137480092694631431.
Full text
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Navarro, Jose. "A wide bandwidth pulsar timing machine." Thesis, 1994. https://thesis.library.caltech.edu/3435/1/Navarro_j_1994.pdf.
Full textAbstract:
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Pulsar timing has turned millisecond pulsars into powerful tools for the study of neutron star physics, time-keeping, astrometry, the interstellar medium and binary systems. It uses millisecond pulsars as probes of the gravitational fields of their companions, of globular clusters and of the Galaxy, and provides information on the dynamics of the solar system. It has also confirmed predictions of general relativity, for which Joe Taylor and Russell Hulse received the 1993 Nobel Prize in Physics. Vasts amounts of information are expected as the current searches continue to discover new millisecond pulsars.
This thesis describes the design and construction of the Caltech Fast Pulsar Timing Machine and some preliminary results at the Parkes Observatory. The FPTM is a wide band timing machine built around a digital correlator for long-term timing stability and has a large observing bandwidth to time millisecond pulsars at high radio frequencies, where propagation effects are minimized.
It is the combination of the 128 MHz bandwidth. the 512 lag digital correlator and the 1024 period phase bins with a minimum size of 2.7 [...] that gives the FPTM its power. The large bandwidth makes new observations of faint pulsars possible above 1 GHz, where current receivers easily provide radio signals with more than 100 MHz of bandwidth. The large number of channels reduces the dispersion smearing of distant millisecond pulsars, which often defines the timing floor in timing systems, and the 1024 phase bins of 2.7 [...] or more ensure that the pulsar profile is adequately sampled.
The FPTM is currently at Parkes Observatory, in Australia, where we are undertaking a long-term precision timing program for millisecond pulsars. We frequently observe the bright binary millisecond pulsar J0437-4715 with sub-microsecond times-of-arrival, and have already found interesting features in the pulse profile that could not be resolved with previous timing systems. Nevertheless, we still find drifts in the timing residuals of as much as a few [...] over several hours which we do not yet understand (even though they are also seen by the other timing system at Parkes!). We are confident that we will solve these residuals and consistently time PSR J0437-4715 at the level of 100 ns or better.
We also present the discovery of J0218+4232, a very luminous binary field millisecond pulsar. Its 2.3 ms pulsations were only detected after an exhaustive search that involved building new hardware.
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Tsai, Chao-Yang, and 蔡兆陽. "Long-term monitoring for timing properties of the accretion-powered millisecond pulsar SAX J1808.4-3658." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/3p899f.
Full textAbstract:
碩士國立中央大學
天文研究所
94
We present our analysis results of the spin and orbital properties of the first discovered accretion-powered millisecond pulsar SAX J1808.4-3658 observed by Rossi X-ray Timing Explorer (RXTE) during its 1998 and 2002 outbursts. The event arrival times are initially folded with an ephemeris consist of the neutron star spin frequency evolution plus the effect from the circular orbital motion and the parameters are then further refined according to the variation of the pulse phase. We obtain the binary barycenter neutron star spin frequency of ν=400.975210324(2)Hz , the orbital period of Porb = 7249.158(1)s and the project radius asini = 62.811(2)lt-ms from 2002 data. For the 1998 outburst, we get consistent project radius of asini = 62.814(2)lt-ms but significantly different orbital period (Porb = 7249.1558(9)s ), which indicates that the orbital period derivative is ~ (7 ± 4) × 10-8 1/yr. No pulsation is able to significant detect for 2000 and 2005 outbursts due to their low fluxes. In addition, the pulse phase variation of 1998 outburst shows a large spin-down rate of -3.15(1) × 10^-12 Hz s^-1, about a factor of 100 larger than the theoretical expectation value (~10^-14 Hz s^-1), whereas no clear spin frequency derivative during 2002 outburst.
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Sandhu, Jagmit S. "High precision dual frequency timing of millisecond pulsars." Thesis, 2001. https://thesis.library.caltech.edu/3590/1/Sandhu_js_2001.pdf.
Full textAbstract:
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
The science of precision millisecond pulsar timing can yield the most precise astrometric measurements ever made. This potential can only be realized through an extraordinary amount of investment in the experimental apparatus, the effort of many observers, and the close attention to details required to avoid the many pitfalls along the way. This thesis describes the work and results from a precision timing project aimed at monitoring the brightest millisecond pulsar, PSR J0437-4715. This pulsar is a very suitable target for such a study because of its small period (5.75 ms), low DM (2.69 pc cm[...]), and high flux density (~ 90 mJy at 1.4 GHz). The initial work for this thesis involved completion and installation of the Fast Pulsar Timing Machine (FPTM) at Parkes observatory, Australia. With a bandwidth of 128 MHz and time resolution of 4 [...], this machine made a quantum jump in the time of arrival precision for PSR J0437-4715. The precision improved from ~ 2 [...] to ~ 0.2 [...]. In order to further enhance the signal-to-noise ratio achievable with this pulsar and probe the limits of precision pulsar timing, we have subsequently improved the FPTM significantly by doubling its bandwidth, so that it can record the pulsar radio emission over a 256 MHz bandwidth. This required us to double the IF processing hardware in the FPTM and implement numerous software modifications to control the observing apparatus, interface the FPTM with the observatory control computers, as well as process the data to produce final times of arrival.
Integration of just a few minutes with the 64 m Parkes radio telescope yield times of arrival for PSR J0437-4715 with a precision of 100 nanoseconds. The longer term residuals (3 years) show root-mean-square deviations of 500 nanoseconds. This excessively large scatter in the residuals has been traced to inaccurate polarization calibration, and a systematic quadratic trend of ~ 5 [...] in the times of arrival as a function of baseband frequency. The latter phenomenon has been simulated in software and shown to arise from the large dynamic range in the baseband spectrum. Despite the systematic errors, our measurement of the pulsar's astrometric and binary parameters match the best obtained so far with other millisecond pulsars. This has allowed us to measure the pulsar's parallax, and the secular change in the binary's projected semi-major axis due to the system's proper motion. The latter effect restricts the inclination angle of the binary, [...] < 43[...]. The parallax, along with the period derivative and orbital period derivative, enable us to constrain the distance of the pulsar, 162 < d < 205 pc. A stability analysis of the pulsar's time of arrival residuals demonstrates that it matches the long term stability of the best studied millisecond pulsars, PSRs B1937+21 and B1855+09, at least on the time scale of the data available so far, 3 years. The precision in the pulsar position now matches the amplitude of the modulation of position expected from the pulsar's binary motion. Detection of this effect will require reduction of the calibration and spectral shape errors, as well as further refinements in the timing software used. Along with radio interferornetric observations of the pulsar and optical detection of the white-dwarf companion, the pulsar timing position will provide the best contraints for frame tie between the ecliptic and extragalactic reference frames.
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Chakrabarty, Deepto. "Hard X-ray Detection and Timing of Accretion-Powered Pulsars with BATSE." Thesis, 1996. https://thesis.library.caltech.edu/3313/3/Chakrabarty-Deepto-1996.pdf.
Full textAbstract:
The BATSE all-sky monitor on the Compton Gamma Ray Observatory is a superb tool for the study of accretion-powered pulsars. In the first part of this thesis, I describe its capabilities for hard X-ray observations above 20 keV, present techniques for timing analysis of the BATSE data, and discuss general statistical issues for the detection of pulsed periodic signals in both the time and frequency domains. BATSE's 1-day pulsed sensitivity in the 20-60 keV range is ≈ 15 mCrab for pulse periods 2s≲Ppulse≲400s, covering most of the known accreting pulsars. Its sensitivity degrades substantially outside of this range.
In the second part of this thesis, I present the results of several science investigations applying these techniques. Half the 42 known accreting pulsars have been detected with BATSE and are monitored whenever they are active. Except for a few which lie outside of BATSE's sensitivity range, the rest are all transient sources which may eventually be detected in outburst. The detected systems include four new transients discovered by BATSE, one of which is discussed in detail. A new technique used to localize this source, GRO J1948+32, is described.
Observations of the 38-s pulsar OAO 1657-415 discovered that it is in a 10.4-d eccentric orbit and undergoes regular X-ray eclipses by its massive companion, making it only the seventh known eclipsing X-ray pulsar. Constraints placed by the pulsar mass function and the eclipse duration indicate that the undetected binary companion must be an OB supergiant. If the companion can be identified and its orbital velocity measured, the neutron star mass can be determined.
The 7.7-s pulsar 4U 1626-67 was found to be in an extended spin-down state, ending over a decade of rapid, steady spin-up. It is only the second steady-state disk accreter known to have undergone a torque reversal. The other, the 2-min pulsar GX 1+4, underwent two torque reversals during our observations and is detected up to 160 keV. During spin-down, we find that pulsed flux and torque in GX 1+4 are anticorrelated, the opposite of what is predicted by the usual theories of magnetic accretion torques.
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Zong-HanYang and 楊宗翰. "Timing-Aware Clock Gating of Pulsed-Latch Circuits for Low Power Design." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/78599450369133032917.
Full textAbstract:
碩士國立成功大學
資訊工程學系碩博士班
100
Low power design is a crucial issue in modern circuit design. Several techniques have been developed to save power consumption. Of those techniques, the pulsed-latch technologies replace flip-flops with pulsed latches due to smaller capacitance of the latter. Additionally, the clock gating of pulsed-latch circuit, which is called pulser gating, has been developed recently to further reduce power consumption. However, pulser gating may incur a timing violation in the clock gating cell, making it impossible to operate the pulser gating correctly, and ultimately causing a fatal error in the circuits. Therefore, this work propose an algorithm to resolve the problem of pulser gating and timing constraints simultaneously. We use a line-search algorithm to determine gate location to satisfy the timing constraint and apply the minimum-cost maximum-flow network to globally determine the clock-tree topology of pulsed-latch circuits. Experimental results indicate that the proposed algorithm can reduce power consumption with timing constraint e ectively compared to state-of-the-art proposed.
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Liu, Jinn-Yann, and 劉晉硯. "A Programmable Wide-range Phase Shifter for the Timing Control of Pulsed Radar SoC." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/16714213414080674753.
Full textAbstract:
碩士國立清華大學
電機工程學系
102
Abstract With the progress of technology and CMOS process, radar system is widely used in many of today’s electronic devices. A pulsed radar would transmit continuous pulse signals periodically, and detect the object by receiving the echo signals. By the transmit time of the echo signal it takes, radar system yield the position information of the object. Therefore, a timing control unit is very important part for a pulsed radar SoC, since it would directly affect the measurement accuracy including direction and distance. In this work, we would introduce a wide-range Programmable Phase Shifter. This circuit can create a programmable phase shift (i.e. timing delay in other words) to a given 10MHz clock signal. The circuit is designed with following features: (1) The tunable range of phase shift as wide as 100ns. (2) All Digital design and almost implemented by digital standard cells, easy to transport to another process. (3) A calibration scheme using frequency multiplier/divider to get a fine shifted phase.
50
Liao, Yun-Jia, and 廖允嘉. "A Programmable Wide-Range Phase Shifter with Temperature Tracking for the Timing Control of Pulsed Radar SoC." Thesis, 2015. http://ndltd.ncl.edu.tw/handle/71811837340896666772.
Full textAbstract:
碩士國立清華大學
電機工程學系
103
This thesis presents a circuit named wide tuning range programmable phase shifter with temperature tracking. It is divided to 3 blocks which are calibration block, coarse-tuning block and fine-tuning block, and it uses four procedures which are (1) calibration (2) coarse-tuning (3) fine-tuning (4) normal-mode to produce the phase shift amount. This circuit is cell-based, which means that it can be easily replaced to next generation of process, it not only has ability to produce output signal with designated and controllable phase shift to input clock signal, but it has very wide tuning range from 0 to 100ns. In general, temperature will gravely impact this kind of timing control circuit; in circuit without temperature tracking, the more the temperature changes, the more the phase error happens. As a result, the function of temperature tracking is considered necessary in this kind of circuits.. To achieve this function, the generic DLL(delay lock loop) which is different from conventional DLL is presented; with the help of TDC(time to digital converter) as a feedback monitoring two ends of delay line, whole circuit is not operated in open loop in order to track the temperature. According to Nanosim simulation result in TT corner, the phase error without temperature tracking function will be 96ps from 25o c rising to 125o c and this phase error will be reduced from -7ps to 12ps during the temperature changing period when added function of temperature tracking. At last, in same Nanosim simulation in TT corner, this circuit successfully produces from 38ps to 100,036ps with simulating 400 input patterns from whole 10,000 input patterns; although there is offset error of 38ps, the local DNL/INL analysis verify this decent results.