Dissertations / Theses: 'Pulsar: generale'

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RIGOSELLI, MICHELA. "X-ray emission from the magnetic polar caps of old rotation-powered pulsars." Doctoral thesis, Università degli Studi di Milano-Bicocca, 2020. http://hdl.handle.net/10281/277373.

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Le stelle di neutroni sono il risultato dell'evoluzione di stelle massive dopo l'esplosione di supernova. Il progetto di questa Tesi di PhD consiste nello studio dell'emissione di raggi X da parte di stelle di neutroni isolate di età superiore a 100000 anni. Sono stati analizzati dati provenienti dal satellite XMM-Newton (ESA). Per estrarre la miglior informazione possibile dai dati, ho implementato un metodo di maximum likelihood (ML) e l'ho utilizzato per estrarre spettri e profili pulsati di pulsar vecchie in banda X, che poi sono stati analizzati con raffinati di emissione. La Tesi è strutturata come segue: nei primi tre capitoli illustro le proprietà principali delle stelle di neutroni, con particolare attenzione ai processi termici e non termici che producono raggi X. I raggi X non termici sono prodotti da particelle relativistiche accelerate da campi elettromagnetici; una frazione di queste particelle viene accelerata verso la superficie della stella, e riscalda le zone delle calotte polari magnetiche. La componente termica, che può essere prodotta dall'intera superficie o da una parte, viene solitamente descritta come un corpo nero; tuttavia, la presenza di intensi campi magnetici superficiali influenza le proprietà della materia, e la radiazione emessa è ampiamente anisotropa. Nel Capitolo 4 descrivo come ho generato spettri e profili pulsati sintetici, utilizzando modelli di emissione che considerano calotte polari ricoperte di un'atmosfera di idrogeno magnetizzata. Mi sono basata su un software esistente che, dato un certo set di parametri relativi alle proprietà fisiche della stella, stima l'intensità della radiazione prodotta. Successivamente, esso somma i contributi degli elementi di superficie che sono visibili all'osservatore alle differenti fasi di rotazione. Quindi, nel Capitolo 5 descrivo come ho implementato un software di analisi che si basa sul metodo di ML. Dato un certo modello, esso stima i parametri più probabili che ricostruiscono i dati osservati, nella fattispecie il numero di conteggi relativo alla sorgente e al background. Ho validato il metodo e dimostrato che esso è particolarmente efficace per sorgenti deboli, quali sono la maggior parte delle pulsar vecchie. Successivamente, ho applicato i metodi finora descritti ad alcune pulsar vecchie. Nel Capitolo 6 riporto l'analisi di PSR J0726-2612, una pulsar radio che ha alcune delle caratteristiche delle XDINSs: un periodo di rotazione lungo, un intenso campo magnetico, ed emissione X termica. Grazie ad un'analisi congiunta dello spettro e del profilo pulsato, ho mostrato che la presenza di impulsi radio in PSR J0726-2612, così come la loro assenza nelle XDINSs, potrebbe essere dovuta ad un'orientazione differente rispetto all'osservatore. Nel Capitolo 7 presento il caso di PSR B0943+10, una pulsar con emissione X sia termica sia non termica ma che, nonostante sia un rotatore allineato, ha una grande frazione pulsata. Sono riuscita a riappacificare i due diversi aspetti grazie ad un'attenta analisi di ML e all'intrinseca anisotropia dell'emissione termica prodotta da un'atmosfera magnetizzata. Nel Capitolo 8 ho invece applicato il metodo di ML su sette pulsar poco brillanti, delle quali quattro avevano diverse analisi già pubblicate in letteratura, ma con risultati discordanti, mentre le altre tre non erano ancora state rivelate in banda X. Ho trovato tracce evidenti di emissione termica solo in due oggetti, più un accenno nello spettro pulsato di un terzo oggetto. Infine, ho considerato tutte le pulsar vecchie che emettono raggi X termici e ho confrontato le misure di temperatura, raggio e luminosità alle aspettative dei modelli teorici. In particolare, ho scoperto che le aree di emissione sono generalmente in accordo con quelle previste dal modello di dipolo magnetico rotante, purché vengano considerati anche effetti di proiezione geometrica e modelli di emissione realistici, quali appunto i modelli di atmosfera magnetizzata.
Neutron stars are the remnants of massive stars whose cores collapse during the supernova explosions. The project of this PhD Thesis consisted in the study of the X-ray emission from isolated neutron stars older than about 100000 years. The work was based mainly on data obtained with the XMM-Newton satellite (ESA). To extract the best possible information from the data, I implemented a maximum likelihood (ML) technique and used it to derive the X-ray spectra and pulse profiles of several old pulsars, that were then studied with state-of-the-art models of X-ray emission. The Thesis is structured as follows: in the first three chapters I outline the main properties of neutron stars, with a major focus on the thermal and nonthermal processes that produce X-rays. The nonthermal X-rays are produced by relativistic particles accelerated by rotation-induced electric fields and moving along the magnetic field lines. A fraction of these particles is accelerated backward and returns on the stellar surface, heating the magnetic polar caps. The thermal component, that can be produced by the whole stellar surface or by small hot spots, can be described, in a first approximation, by a blackbody. However, the presence of intense surface magnetic fields strongly affects the properties of matter, and the emergent radiation is widely anisotropic. In Chapter 4, I describe how I generated synthetic spectra and pulse profiles using thermal emission models that consider polar caps covered by a magnetized hydrogen atmosphere or with a condensed iron surface. I relied on an existing software that, given a set of stellar parameters, evaluates the emerging intensity of the radiation. A second software, which I adapted on the sources I analyzed in the Thesis, collects the contribution of surface elements which are in view at different rotation phases from a stationary observer. Then, in Chapter 5, I describe how I implemented an analysis software that relies on the ML method. It estimates the most probable number of source and background counts by comparing the spatial distribution of the observed counts with the expected distribution for a point source plus an uniform background. I demonstrated that the ML method is particularly effective for dim sources, as most old pulsars are. Subsequently, I applied the methods described above to some old pulsars. In Chapter 6, I report the analysis of PSR J0726-2612, a radio pulsars that shares some properties with the radio-silent XDINSs, as the long period, the high magnetic field, and the thermal X-ray emission from the cooling surface. Thanks to an in-depth analysis of the combined spectrum and pulse profile, I showed that the presence of radio pulses from PSR J0726-2612, as well as the absence from the XDINSs, might simply be due to different viewing geometries. In Chapter 7, I present the case of PSR B0943+10, a pulsar with a nonthermal and thermal X-ray spectrum but that, despite being an aligned rotator, has a large pulsed fraction. I could reconcile the two opposite properties analyzing with the ML the spectrum and the pulse profile, and considering the magnetic beaming of a magnetized atmosphere model, that well fits the thermal component. In Chapter 8, I applied the ML method to seven old and dim pulsars, of which four had controversial published results, and three were so far undetected. I found convincing evidence of thermal emission only in the phase-averaged spectrum of two of them, plus a hint for a thermal pulsed spectrum in a third object. Finally, I considered all the old thermal emitters and I compared their observed temperatures, radii and luminosities to the expectations of the current theoretical models for these objects. In particular, I found that the emitting area are generally in agreement with the polar cap regions evaluated in a dipole approximation, if the combined effects of geometry projections plus realistic thermal models (as the magnetic atmosphere) are taken into account.

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Venter, Christo. "Millisecond pulsars and pulsar wind nebulae as sources of gamma rays and cosmic rays / C. Venter." Thesis, North-West University, 2008. http://hdl.handle.net/10394/2067.

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Venter, Christo. "The effect of general relativistic frame dragging on millisecond pulsar visibility for the H.E.S.S. telescope / C. Venter." Thesis, North-West University, 2004. http://hdl.handle.net/10394/215.

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It has been noted by several authors that General Relativistic frame dragging in rotating neutron stars is a first order effect which has to be included in a self-consistent model of pulsar magnetospheric structure and associated radiation and transport processes. To this end, I undertook the present study with the aim of investigating the effect of General Relativity (GR) on millisecond pulsar (MSP) visibility. I developed a numerical code for simulating a pulsar magnetosphere, incorporating the GR-corrected expressions for the electric potential and field. I included curvature radiation (CR) due to primary electrons accelerated above the stellar surface, as well as inverse Compton scattering (ICS) of thermal X-ray photons by these electrons. I then applied the model to PSR J0437-4715, a prime candidate for testing the GR-Electrodynamic theory, and examined its visibility for the H.E.S.S. telescope. I also considered the question of whether magnetic photon absorption would take place for this particular pulsar. In addition, I developed a classical model for comparison with the GR results. I found that the typical electron energies and associated CR photon energies are functions of position above the polar cap (PC). These energies are also quite smaller in the GR case than in the classical case due to the different functional forms of the GR and classical electric fields. I found the CR energy cut-off to be ~ 4 GeV compared to the well-known classical value of ~ 100 GeV. Since the H.E.S.S. energy threshold is ~ 100 GeV, it seems as though the CR component will not be visible, contrary to wide-held opinion. However, the ICS component seems to be well in excess of the H.E.S.S. energy threshold and is expected to be visible. I also found that no pair production will take place for PSR J0437-4715. Hopefully, forthcoming H.E.S.S. observations will provide validation of these results. KEY WORDS: General relativistic frame dragging, GR electrodynamics, millisecond pulsar visibility, non-thermal radiation processes, pair production, H.E.S.S., individual pulsars: PSR J0437-4715.
Thesis (M.Sc. (Physics))--North-West University, Potchefstroom Campus, 2004.

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Gralla, Samuel E., Alexandru Lupsasca, and Alexander Philippov. "PULSAR MAGNETOSPHERES: BEYOND THE FLAT SPACETIME DIPOLE." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622675.

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Most studies of the pulsar magnetosphere have assumed a pure magnetic dipole in flat spacetime. However, recent work suggests that the effects of general relativity are in fact of vital importance and that realistic pulsar magnetic fields will have a significant nondipolar component. We introduce a general analytical method for studying the axisymmetric force-free magnetosphere of a slowly rotating star of arbitrary magnetic field, mass, radius, and moment of inertia, including all the effects of general relativity. We confirm that spacelike current is generically present in the polar caps (suggesting a pair production region), irrespective of the stellar magnetic field. We show that general relativity introduces a similar to 60% correction to the formula for the dipolar component of the surface magnetic field inferred from spindown. Finally, we show that the location and shape of the polar caps can be modified dramatically by even modestly strong higher moments. This can affect emission processes occurring near the star and may help explain the modified beam characteristics of millisecond pulsars.

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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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Gralla, Samuel E., Alexandru Lupsasca, and Alexander Philippov. "Inclined Pulsar Magnetospheres in General Relativity: Polar Caps for the Dipole, Quadrudipole, and Beyond." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/626414.

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In the canonical model of a pulsar, rotational energy is transmitted through the surrounding plasma via two electrical circuits, each connecting to the star over a small region known as a "polar cap." For a dipole-magnetized star, the polar caps coincide with the magnetic poles (hence the name), but in general, they can occur at any place and take any shape. In light of their crucial importance to most models of pulsar emission (from radio to X-ray to wind), we develop a general technique for determining polar cap properties. We consider a perfectly conducting star surrounded by a force-free magnetosphere and include the effects of general relativity. Using a combined numerical-analytical technique that leverages the rotation rate as a small parameter, we derive a general analytic formula for the polar cap shape and charge-current distribution as a function of the stellar mass, radius, rotation rate, moment of inertia, and magnetic field. We present results for dipole and quadrudipole fields (superposed dipole and quadrupole) inclined relative to the axis of rotation. The inclined dipole polar cap results are the first to include general relativity, and they confirm its essential role in the pulsar problem. The quadrudipole pulsar illustrates the phenomenon of thin annular polar caps. More generally, our method lays a foundation for detailed modeling of pulsar emission with realistic magnetic fields.

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CUOFANO, Carmine. "Magnetic fields generated by r-modes in accreting millisecond pulsars." Doctoral thesis, Università degli studi di Ferrara, 2010. http://hdl.handle.net/11392/2389313.

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In rotating neutron stars the existence of the Coriolis force allows the presence of the so-called Rossby oscillations (r-modes) which are known to be unstable to emission of gravitational waves. In the Thesis, for the first time, we introduce the magnetic damping rate in the evolution equations of r-modes. We show that r-modes can generate very strong toroidal fields in the core of accreting millisecond pulsars by inducing differential rotation. We shortly discuss the instabilities of the generated magnetic field and its long time-scale evolution in order to clarify how the generated magnetic field can stabilize the star. Finally we discuss the possible astrophysical scenarios.

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Icdem, Burcin. "Viscous Time Scale In Accreting Powered Pulsars And Anomalous X-ray Pulsars." Master's thesis, METU, 2011. http://etd.lib.metu.edu.tr/upload/12613373/index.pdf.

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In this thesis we analyse X-ray data of accretion powered low mass and high mass X-ray binaries to understand the nature of their accretion mechanisms by searching for some clues of viscous time-scales of their accretion discs, if they have, in their low frequency power density spectra created from their long-term X-ray observations, or by doing pulse timing analysis with much shorter X-ray data to detect the effects of torque fluctuations caused by the accreting material on the pulsar. The low mass and high mass X-ray binaries we analysed have breaks in their power density spectra, which are attributed to the role of viscosity in the formation of accretion discs. Although, the time-scales corresponding to these break frequencies are smaller than the predictions of the Standard theory of accretion discs, the sources give consistent results among themselves by displaying the expected correlation between their break and orbital frequencies. The correlation curve of LMXBs implies thicker appearing accretion discs than those assumed by the theory. The dichotomy of the HMXBs on this curve points out the different origins of accretion that these sources may have, and offers a way to distinguish the stellar-wind fed systems from the Roche-lobe overflow systems. The timing and spectral analysis of Swift J1626.6-5156 reveal a correlation between the spin-up rate and the luminosity of the source implying that the pulsar is accretion-powered. This correlation together with the characteristics of the X-ray spectra enables us to estimate the magnetic field and the distance of the source. The AXP 1E 2259+586 does not display any signs of viscous time-scale in its low frequency power density spectra, and its pulse timing analysis gives a much smaller torque noise value than that expected from accretion powered pulsars. In addition, the analysis results presented in this thesis reveal magnetar-like glitches which differ than those of radio pulsars, due to the presence of the strong magnetic field of the pulsar. These results eliminate the possibility that the AXP is an accretion-powered pulsar.

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Yuen, Rai. "Pulsar Magnetosphere Revisited: Emission Geometry and the Synthesis of the Vacuum-Dipole and the Rotating-Magnetosphere Models." Thesis, The University of Sydney, 2013. http://hdl.handle.net/2123/10011.

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We reconsider the vacuum-dipole model (VDM) and the corotating-magnetosphere model (CMM) for pulsar electrodynamics. Both the VDM and the CMM are fatally flawed as stand-alone models. The former model is used for deriving certain pulsar parameters, such as the surface magnetic field strength and characteristic age, but it lacks the plasma required to emit the observed radiation. The latter model introduces important concepts, such as the Goldreich-Julian charge density and corotation electric field, which form the basis for more detailed models, but it neglects the inductive electric field. When this field is included, the model is unstable to growth of large-amplitude electric oscillations when subject to a temporal perturbation. Furthermore, the predicted highly-relativistic magnetospheric plasma given by the two models is inconsistent with results obtained from observations with the Double Pulsar system. We therefore propose a way of synthesizing the VDM and the CMM for obliquely rotating pulsars. We first modify the VDM to a "minimal" model by assuming that the parallel component of the inductive electric field is screened by charges. We define a class of synthesized models as a linear combination of a fraction y times the minimal model and 1 - y times the CMM. We suggest that the synthesized model provides a basis for understanding the abrupt changes in the magnetospheres of some pulsars, which can alter their slowing down rates. The synthesized model also implies that the velocity of the magnetospheric plasma depends on y and the position of the emission point, which is determined numerically based on the obliquity and viewing angles for emission heights close to stellar surface in dipolar magnetic field structure. We also explore the field structure by including higher order terms in the ratio of the radius to the light-cylinder radius in the magnetic field and explore the implications of these additional terms.

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Bernard, Franck. "Anesthesie generale pour cesarienne : comparaison, par oxymetrie pulsee, de deux methodes de preoxygenation." Rennes 1, 1992. http://www.theses.fr/1992REN1M051.

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Maines, Geoffrey C. "Underwater Pressure Pulses Generated by Mechanically Alloyed Intermolecular Composites." Thèse, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/30708.

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Recently, the use of thermite-based pressure waves for applications in cellular transfection and drug delivery have shown significant improvements over previous technologies. In the present study, a new technique for producing thermite-generated pressure pulses using fully-dense nano-scale thermite mixtures was evaluated. This was accomplished by evaluation of a stoichiometric mixture of aluminium (Al) and copper(II)-oxide (CuO) prepared by mechanical alloying. Flame propagation speeds, constant-volume pressure characteristics and underwater pressure characteristics of both a micron-scale and mechanically alloyed mixture were measured experimentally and compared with conventional nano-scale thermites. It was determined that mechanically alloyed mixtures are capable of attaining flame propagation speeds on the same order as nano-scale mixtures, with flame speeds reaching as high as approximately 100 m/s. Constant-volume pressure experiments indicated that mechanically alloyed mixtures result in lower pressurization rates compared with conventional nano-scale mixtures, however, an improvement by as much as an order of magnitude was achieved compared with micron-scale mixtures. Thermochemical equilibrium predictions for pressures observed in constant-volume reactions were found to capture relatively well the equilibrium pressure for both low and high values of relative density. Generally, the predictions over-estimated the measured pressures by approximately 60%. Results from underwater experiments indicated that the mechanically alloyed samples produced peak shock pressures and waveforms similar to those for a nano-scale Al-Bi2O3 mixture reported by Apperson et al. (2008). In an effort to model the pressure signal obtained from the underwater reaction, calculations were performed based on the rate of expansion of the high pressure gas sphere. Predicted pressures were found to agree fairly well in terms of both the peak pressure and pressurization rate. The present study has thus identified the ability for mechanically alloyed thermite mixtures to produce underwater pressure profiles that may be conducive for applications in cellular transfection and drug delivery. Récemment, l'utilisation d'ondes de pression produite par des mélanges de thermite pour des applications dans la transfection cellulaire et l'administration de médicaments ont démontré des améliorations importantes par rapport aux technologies précédentes. Dans l'étude ci jointe, une nouvelle technique pour produire des impulsions de pression générée par un mélange thermite, soumit a de l'alliage mécanique, a été évaluée. Ceci a été accompli par l'évaluation d'un mélange stoechiométrique d' aluminium (Al) et de l'oxyde de cuivre(II) (CuO), préparé par mécanosynthèse. Les vitesses de propagation de la flamme, les caractéristiques de pression pour la combustion à volume constant et les caractéristiques de pression pour la combustion sous l'eau ont été mesurées expérimentalement et comparés avec les thermites conventionnel à l'échelle nano. Nous avons déterminé que les mélanges alliés mécaniquement sont capables d'atteindre des vitesses de propagation de flamme du même ordre que les mélanges à l'échelle nanométrique, atteignant jusqu'à environ 100 m/s. Les expériences de combusition à volume constant, indique que les mélanges alliés mécaniquement induit des taux de pressurisation inférieures à celles des mélanges de nano-échelle conventionnel, cependant, une amélioration de près d'un ordre de grandeur a été atteint par rapport aux mélanges d'échelle micronique. Prédictions thermochimiques des pression de compbustion se sont révélés capable de relativement bien saisir les valeurs observées dans les expériences à volume constant. En règle générale, les prévisions sur-estimé les pressions mesurées par environ 60%. Les résultats des expériences sous-marines ont indiqué que les échantillons alliés mécaniquement ont produit des pressions et des profils d'onde similaires à celles produit par un mélange de Al-Bi2O3 de nano-échelle, comme indiqué par Apperson et al. (2008). Pour modéliser les pressions obtenues dans les expériences sous-marines, des calculs basés sur le taux d'expansion de la bulle de gaz à haute pression ont été obtenus. Les pressions prédites ont été trouvés d'être relativement en accord avec la pression maximale et le taux de pressurisation observé. Cette étude a ainsi identifié la possibilité pour l'utilisation des mélanges de thermites alliés mécaniquement pour produire des profils de pression sous l'eau propices pour des applications de transfection cellulaire et l'administration de médicaments.

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Crosbie, Ross Andrew. "Quantitative non-destructive evaluation using laser generated ultrasonic pulses." Thesis, University of Hull, 1987. http://hydra.hull.ac.uk/resources/hull:5393.

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The work presented here utilises features of laser generated ultrasound for the detection of defects in solids. Ultrasound is generated noncontactively by this method and likewise many of the detection devices used do not require direct coupling to the test pieces, thus acoustic pulses with high frequency components are able to be produced and monitored on a range of samples. Steel samples coated with between 3 and 7mm of plasma-transferred arc depositions are examined for bond quality via measurements of attenuation caused by porosity in the coatings, found to be related to weld current. Surface breaking cracks, (of depth < 3mm), in such claddings are quantitatively detected by a method which utilises Rayleigh pulses. A two sided automated scanning system is described which examines samples for subsurface defects. Results from the examinations of a dural test piece, plasma sprayed steel bars and carbon fibre composite samples are presented. Resolution of defects is shown to be within 0.5mm for a 1mm thick section of the composite material. A second scanning technique, requiring access to only one sample face, is presented which employs an interferometer for detection and is thus a truly remote system. Laminar flaws are modelled using flat-bottomed holes, the dimensions of which are measured using the resonance of the bodies. A theoretical investigation using various boundary conditions suggests possible applications for quantitative NDE of structures with well defined natural vibration frequencies. The propagation of acoustic transients in plates is also examined. Possible future work concerning laser/ultrasonic NDE is discussed.

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Hill, Samuel Joseph. "Time-frequency localisation of defects using broadband pulsed arrays." Thesis, University of Warwick, 2014. http://wrap.warwick.ac.uk/63771/.

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The spatial periodicity of an array of emitters with an alternating polarity structure is utilised to generate a wavefront with a range of interesting properties. This wavefront is generated by simultaneously exciting the elements with a pulse with carefully selected broadband characteristics. The creation of these waves leads to a broadband interference effect that causes the wavefront to cover a large range of solid angles. More interestingly, however, is the continuous variation of the frequency of the wavefront as a function of angle. Whilst this pulsed array system demonstrates many interesting phenomena, it can also be applied to practical scenarios within the field of non-destructive testing. As the generated wavefront propagates through the sample, it will be scattered by discontinuities that may be present in the sample. This scattered wave will have a unique time of flight and frequency, and this information can be used to locate the position of defects. Due to the frequency variation of the wavefront, the angular position of the defect can be calculated from the frequency of the scattered wave. The radial position of the scatterer can be estimated using the time of flight of the wave. This approach has some advantages over the phased array techniques, which are currently utilised within the field of ultrasonic inspection. Whilst phased array techniques are versatile and can control the generated ultrasonic beam, they require complicated electronics and beam-forming algorithms to achieve this. This requirement is avoided with the pulsed array, as all of the array elements are activated simultaneously. Also, as the time-frequency characteristics of the scattered wave maps directly to the polar co-ordinates, only a single measurement is needed to locate a defect. This is in contrast to other ultrasonic methods that only utilise the time of flight information of the scattered wave, and hence multiple measurements are needed to localise a defect.

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Fitzsimons, Paul. "Selective ablation of thin films using ultra-short laser pulses." Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/10853/.

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The micro processing of materials using ultra short pulse (USP) lasers with durations in the low picosecond (ps) and femtosecond (fs) range allows for the possibility of precision material removal on both nanometre and micron scales. Precision material removal can be achieved due to the near diffraction limited focus spot size and ultra-short pulse durations, which provide extremely high peak intensities with minimal thermal impact on the surrounding area. The work presented in this thesis is primarily concerned with the selective ablation of thin films deposited on various surfaces, using lasers with picosecond temporal pulse lengths at 1064 nm. As a result, damage to the substrate is negated through exploitation of the difference in linear absorption coefficients between the thin film and substrate. To elucidate the mechanism of selective processing with USP lasers; absorption, single and multi-pulse ablation effects were investigated in both fixed and variable beam positions. A sample of white float glass vacuum coated with indium tin oxide (ITO) was chosen as the material for this study. Experimental results demonstrate that linear absorption (α (λ)) of the ITO and substrate plays a key role in achieving selective thin film ablation. As a direct consequence of the difference in absorption coefficients at 1064 nm, the single (ϕ_th^1 ) and multi (ϕ_th^n ) pulse ablation thresholds of both materials are altered during the high peak intensity exposure. Selective processing was achieved by exploiting the difference between the ablation thresholds of ITO and glass. When irradiated with multiple pulses the ablation threshold of the substrate was observed to decrease with increasing pulse number. This change in threshold fundamentally limits the selective processing window; therefore incubation (S) effects must be considered when determining the viability of selective processing. For the purpose of practical applications, a series of case studies are also presented which attempt to utilise selective materials processing. These investigations were split into industrial and conservation. Industrial case studies focused on successfully micro processing a small thin film ITO circuit using a Spatial Light Modulator and a new low cost solar cell (F doped SnO2); whilst in conservation, the restoration of a pair of Royal gloves and the removal of unwanted bronze gilding is presented. The application of USP lasers in conservation represents a relatively new field of study where little previous research has been carried out. These case studies not only showcase the wide range of USP applications in which selective processing can be applied but also highlight the limitations of this method.

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Inam, Sitki Cagdas. "X-ray Observations Of Accretion Powered Pulsars." Phd thesis, METU, 2004. http://etd.lib.metu.edu.tr/upload/12605552/index.pdf.

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In this thesis, X-ray observations of four accretion powered pulsars are presented. Using RXTE observations of 4U 1907+09, we found three new pulse periods of the source. We found that the source spun-down almost at a constant rate of $dot nu$ = (-3.54 $pm 0.02) times 10^{-14}$ Hz s$^{-1}$ for more than 15 years. Using RXTE observations, X-ray flux related spectral and timing features in 2S 1417-62 were, in general, interpreted as a sign of a disc accretion with a similar geometry with a varying mass accretion rate, whereas spectral and timing features of the low X-ray flux regions were interpreted as a sign of possible temporary accretion geometry change prior to the next periastron. Using XMM-Newton and RXTE observations of SAX J2103.5+4545, we discovered quasi periodic oscillations around 0.044 Hz (22.7 sec) while the source was spinning-up with a rate of $(7.4pm0.9)times10^{-13}$Hz s$^{-1}$. In the X-ray spectrum, we also found a soft component consistent with a blackbody emission with ${rm{kT}}sim1.9$keV. Using RXTE observations, we also studied spectral evolution of Her X-1

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Patel, Sunil. "A chirped, pulsed laser system and magneto-optical trap for rubidium." Thesis, University of Southampton, 2009. https://eprints.soton.ac.uk/66245/.

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This thesis covers the construction and characterisation of a magneto-optical trap (MOT) for 85Rb from the very beginning. It details both the optical and mechanical aspects from laser diode assembly, tuning and stabilisation to the preparation and assembly of the vacuum system. The MOT construction forms the first goal of the project, the second was to develop a laser system capable of producing custom programmable, amplitude modulated and frequency chirped pulses (on the tens of microseconds timescale) from a continuous wave source. This involved developing software and computer control for several arbitrary signal generators linked to drivers for acousto-optic and electro-optic modulators. This chirped, pulsed laser system will be used to perform state manipulations on the 85Rb MOT cloud using two-photon Raman transitions in an adiabatic rapid passage regime. The chirped pulse system was initially tested with a rubidium vapour cell in an attempt to perform atomic interferometry that would produce spatial interference fringes along the length of the cell. However, due to the beam power requirements, the beam diameter together with the large Doppler shift at room temperature meant these fringes were not seen and so the vapour cell was replaced with the cold atom cloud in the MOT. Two-photon experiments were attempted with the MOT cloud using the chirped pulse system, however despite greatly improved laser power and detection eficiency, the signal indicating ground state population transfer via a two-photon interaction was not seen. The results indicate that the hyperfine-ground state splitting frequency has been shifted due to the proximity of the ion pump magnet to the vacuum system. Presently, efforts are being directed towards searching for the correct frequency.

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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.

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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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18

Bannister, David A. "A pulsed NMR relaxation and diffusion study of water in treated and untreated waterlogged wood." Thesis, University of Nottingham, 1990. http://eprints.nottingham.ac.uk/11137/.

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Freezing curve, NMR relaxation data, and steady field gradient and pulsed field gradient experiments were conducted on samples of water-logged woods excavated from the Tudor warship, the Mary Rose and on similar samples impregnated with Polyethylene-Glycol solutions: the polymer used as a bulking agent to prevent decay. At least two distinguishable populations of water molecules are found in wood. Freezing curves indicate the presence of approximately 0.38 g/g of hydration water, close to that observed in fresh timbers. Relaxation measurements on pre-treated samples provides evidence of a very tightly bound fraction, present at water contents of below 0.14 g/g 0i hydration water, with a second population of hydration water being present up to 0.1.8 9/9. Above this value a third ‘free' population is observed. The relaxation decays in longitudinal and transverse direction have been analysed in terms of a sum of exponentials. These indicate the presence of two populations of water which do not correspond to populations observed in freezing curve analysis. Exchange mechanisms dominate the temperature dependency of the relaxation behaviour in pre-treated samples, which is similar to that observed in other fibrous materials such as meat. However, t he different components do not appear to correspond to the physical characteristics of the wood and the spin populations cannot be associated with a distribution between identifiable compartments within the system. In PEG impregnated samples the contribution to the signal from the polymer is not resolvable on the equipment used. Samples treated with PEGs for which the degree of polymerisation is greater than 1540 show a dependency of relaxation characteristics on the water content of the sample. At low water contents PEGs of low molecular weight impart a mobility to the "bound" water molecules which is not seen in untreated samples. . Belt diffusion coefficients for water molecules in wood are anisotropic, and are reduced from those observed in distilled water. This reduction is brought about because water molecules are both held in a hydration layer, and bounded by the cellular structure of the wood. In impregnated samples the diffusion rates are lowered by a factor of 10, though this is not reflected in the relaxation behaviour. The anisotropy is reduced, and proton exchange mechanisms are blocked.

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Cadot, Guillaume Bastien Jérémy. "Experimental and numerical investigations of diamond and related materials controlled-depth machining using pulsed laser ablation." Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/46409/.

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Pulsed laser ablation is a non-conventional machining technique that is used to machine complex parts in ultra-hard materials and for minute part geometry, which are otherwise not readily accessible with conventional tooling. The constant development of new materials with enhanced properties, as well as the demand for products with improved functionality have led to a renewed interest for alternative machining. Pulsed laser ablation is regarded as a promising technology with potential to machine a wide range of materials and shapes. The use of non-mechanical methods is advantageous due to the reduced tool-wear for ultra-hard materials and minute geometry. However, these advantages pose significant challenges since the removal rate of the material in term of shape and amount is controlled through a set of operating parameters. It is therefore necessary to have a comprehensive understanding of the process and the relation between such parameters and the effect of the laser on the surface. Furthermore, the process itself is hard to monitor online due to the short temporal and small spatial space it occurs within, and this makes it more complex to establish a detailed understanding of the process, and the optimum parameters to control the machining. The main objective of this thesis is to develop mathematical frameworks that have the capability to predict the removal rate of pulsed laser ablation for the main operating parameters (feed speed, power, position, etc.) and the physical processes occurring during pulsed laser ablation of diamond and related materials for nanosecond laser pulses at 1064 nm and 248 nm. This is addressed using two modelling approaches: a physical model that simulates the mass and heat conservation in the system coupled with a collisional radiative model for the plasma, and a simplified approach based on geometrical aspect built on the idea that trenches represent the simplest element of the machining method enabling quantification of the relation between the control parameters and the removal rate. In the physical approach, the system is modelled using the conservation of mass and energy with the capability to accurately predict the position of the interfaces (graphitisation front and surface), and the amount of material removed. The model is validated against boron doped diamond and is used to estimate the activation energy and rate of graphitisation for tetrahedral amorphous carbon. The framework developed provides accurate results for two different carbon allotropes with a high content of sp$^3$ bounds for a range of fluence. A geometrical approach for the prediction of the material removal during large pulsed laser ablation machining task has been developed. Since, the objective of this model is for it to be integrated into CAD/CAM packages, the model needs to be computationally efficient and should require as little empirical data as possible to be accurately calibrated. This framework has been validated against three materials, graphite POCO AF-5, a mechanical polycrystalline diamond CVD Mechanical, and a metal-matrix poly-crystalline diamond CMX850. The model enables the prediction of material removal for large machining tasks and is being used with an optimisation procedure for the machining parameters (power, feed speed, etc.) for CAD/CAM packages. Finally, the physical model is coupled with a collisional radiative model for the plasma, and it enables the prediction of the pressure over the crater. Experimental investigations have confirmed that melting of the graphite only occurs for a fluence over 30 J.cm$^{-2}$. TEM analysis and Raman spectroscopy also show an increase in the disorder of the graphite lattice with an increase of fluence which is coherent with thermal damage and constraint growth of the graphite crystal at the graphitisation front. The fluence threshold for the melting of the graphite lattice is in agreement with the prediction of the model. The work developed in this thesis contributes to the understanding of the ablation process and graphitisation process during pulsed laser ablation of diamond and related material, and demonstrates how a simplified modelling approach can be used to improve current capabilities of this technology for large micro-machining tasks.

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Sourie, Aurélien. "Modèles superfluides d'étoiles à neutrons en relativité générale : applications à la dynamique des pulsars." Thesis, Paris Sciences et Lettres (ComUE), 2017. http://www.theses.fr/2017PSLEO002/document.

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L'objectif de cette thèse est d'étudier différents aspects microscopiques et macroscopiques liés à la présence de superfluidité dans les étoiles à neutrons. Dans un premier temps, nous avons calculé des configurations stationnaires d'étoiles à neutrons superfluides en rotation, en relativité générale, basées sur l'utilisation d'équations d'état réalistes. A l'aide de ces configurations d'équilibre, nous avons ensuite développé un modèle simple de glitch, en relativité générale, vu comme un transfert de moment cinétique entre les neutrons superfluides et les particules chargées constituant l'étoile. Cela nous a permis d'obtenir des temps caractéristiques de montée qui pourront être comparés à de futures observations précises de glitches afin d'apporter de meilleures contraintes sur l'intérieur de ces étoiles. Enfin, nous nous sommes également intéressés à la dynamique des vortex superfluides, en présence de tubes de flux, dans le cas où les protons dans le coeur des étoiles formeraient un supraconducteur de type II
The aim of this thesis is to study different aspects, both microscopic and macroscopic, associated with the presence of a large amount of superfluid matter inside neutron stars. First, we computed stationary configurations of rotating superfluid neutron stars, in general relativity, using realistic equations of state. Based on these equilibrium configurations, we then developed a simple model of pulsar glitches, in general relativity, seen as angular momentum transfers between the superfluid neutrons and the charged particles composing the star. This enables us to infer spin-up time scales that could be compared with future accurate glitch observations, in order to get some constraints on the interior of neutron stars. Finally, we also focused on the dynamics of superfluid vortex lines, accounting for the presence of fluxtubes, if the protons are forming a type II superconductor in the core of neutron stars

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Pacella, Manuela. "Pulsed laser ablation (PLA) of ultra-hard structures : generation of damage-tolerant freeform surfaces for advanced machining applications." Thesis, University of Nottingham, 2014. http://eprints.nottingham.ac.uk/27730/.

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The current methods for manufacturing super-abrasive elements result in a stochastic geometry of abrasives with random three-dimensional abrasive spatial locations. This thesis covers the laser generation of novel micro-cutting arrays in ultra-hard super-abrasive composites (e.g. polycrystalline diamond, PCD and polycrystalline cubic boron nitride, PCBN). Pulsed laser ablation (PLA) has been used to manufacture repeatable patterns of micro cutting/abrasive edges onto micro structurally different PCD/PCBN composites. The analysis on the influence of microstructural factors of the composite materials in the use of laser ablation technology has been carried out via a novel technique (Focused Ion Beam/High Resolution Transmission Electron Microscopy/Electron Energy Loss Spectroscopy) to identify the allotropic changes occurring in the composite as a consequence of PLA allowing the laser ablated PCD/PCBN surfaces to be characterized and the nanometric changes evaluated. The wear/failure characteristics/progression of the ultra-hard laser generated micro cutting/abrasive arrays has been studied in wear tests of Silicon Dioxide workpiece shafts and the influence of the microstructural factors in the wear properties of the super-abrasive micro cutting edges has been found. Opposing to these highly-engineered microcutting/abrasive arrays, conventional electroplated abrasive pads containing diamond and CBN abrasives respectively have been chosen as benchmarks and tested under the same conditions. Contact profiling, Optical Microscopy and Environmental Scanning Electron Microscopy have been employed for the characterization of the abrasive arrays/electroplated tools before/during/after the wear/cutting tests. In the PCD abrasive micro-arrays, the type of grain and binder percentage proved to affect the wear performances due to the different extents of compressive stresses occurring at the grain boundaries. In this respect, the micro-arrays made of PCD with mixed diamond grains have shown slower wear progression when compared to the electroplated diamond pads confirming the combination of the high wear resistance typical of the fine grain and the good shock resistance typical of the coarse grain structures. While PCD laser manufactured arrays indicated edge break as typical wear mechanism, the abrasive pad confirmed flattening of grits as main wear mechanism. Mixed grained PCD arrays performed 25% better than fine grained arrays. The improved wear performances of laser manufactured arrays when compared to industrial benchmark is proved by the different wear failure mechanism in the array and in the electroplated pad: in the first one the edges break creating new sharp edges during testing, while in the latter grit flattening is the main wear mechanism. This increases up to 60% the life of the laser manufactured array when compared to the benchmarked pads. As for the PCBN abrasive micro-arrays, two are the main wear mechanisms experienced by the arrays: edge flattening for the high CBN content array and edge breaking for the medium CBN content array. The wear performance of the high content PCBN array is directly comparable to the electroplated boron nitride pad, because they both worn out with edge/grit flattening. The increase of metallic binder and the presence of metalloids in the medium content-CBN specimens have shown to produce higher contact pressure with the workpiece when compared to the electroplated specimen, causing fracturing as the main wear mechanism; while the PCBN micro-array with purely a metallic binder phase has shown better wear performances and lower contact pressure in comparison to the electroplated CBN specimen. In particular, the laser manufactured array proved to perform 50% better than the electroplated ones in terms of wear resistance. Among all of the tested arrays, the mixed grained PCD and the purely metallic binder phase PCBN micro-arrays have shown slower wear when benchmarked to the electroplated pads, giving a possible application of their use in the cutting tool industry.

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22

Patera, Giuseppe. "Quantum properties of ultra-short pulses generated by SPOPOs : multi-mode squeezing and entanglement." Paris 6, 2008. https://tel.archives-ouvertes.fr/tel-00404162.

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Ce mémoire présente une étudie théorique des propriétés dynamiques et quantiques d’un oscillateur paramétrique optique dégénéré de type I que est pompé de manière synchrone par un laser verrouillé en phase (SPOPO). Récemment, des SPOPO ont été exploité pour générer des impulsions optique de très bref durée et leurs propriétés temporelles ont été étudiées théoriquement. Ayant un très grand nombre de degrés de liberté, le champ sortant d’un SPOPO doit être caractérisé au moyen d’une analyse quantique multimodale. Par conséquent, nous développons d’abord un modèle multi-mode de ce système en déduisant des équations quantiques pour les opérateurs de champ intra-cavité. Ensuite, nous étudions les solutions stationnaires pour les champs générés. Celles-ci sont solution d’une équation aux valeurs propres dont le spectre donne des informations sur le nombre de modes « utiles » qui peuvent être extraits et qui condensent toutes les propriétés dynamiques et quantiques du champ intra-cavité et que nous appelons « super-modes ». En fait, nous montrons que non seulement le super-mode de seuil le plus bas a (idéalement) des fluctuations parfaitement comprimées au seuil, mais aussi tout les autres super-modes, dont les seuils sont suffisamment proches du première, ont un caractère non-classique important. Cette propriété démontre clairement le fait qu’un SPOPO est un système fortement multi-mode. La dernière partie est consacrée à l’étude du champ de sortie sous le point de vue de la génération d’états intriqué multi-modes et à l’optimisation de ces états au moyen de configurations expérimentales spécifiques.

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Özel, Feryal, Dimitrios Psaltis, Zaven Arzoumanian, Sharon Morsink, and Michi Bauböck. "MEASURING NEUTRON STAR RADII VIA PULSE PROFILE MODELING WITH NICER." IOP PUBLISHING LTD, 2016. http://hdl.handle.net/10150/622456.

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The Neutron-star Interior Composition Explorer is an X-ray astrophysics payload that will be placed on the International Space Station. Its primary science goal is to measure with high accuracy the pulse profiles that arise from the non-uniform thermal surface emission of rotation-powered pulsars. Modeling general relativistic effects on the profiles will lead to measuring the radii of these neutron stars and to constraining their equation of state. Achieving this goal will depend, among other things, on accurate knowledge of the source, sky, and instrument backgrounds. We use here simple analytic estimates to quantify the level at which these backgrounds need to be known in order for the upcoming measurements to provide significant constraints on the properties of neutron stars. We show that, even in the minimal-information scenario, knowledge of the background at a few percent level for a background-to-source countrate ratio of 0.2 allows for a measurement of the neutron star compactness to better than 10% uncertainty for most of the parameter space. These constraints improve further when more realistic assumptions are made about the neutron star emission and spin, and when additional information about the source itself, such as its mass or distance, are incorporated.

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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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Smithbauer, David Paul. "Analysis and Application of Automated Methods for Detecting Pulsars in the Green Bank Telescope 350MHz Drift-Scan Survey." Thesis, West Virginia University, 2013. http://pqdtopen.proquest.com/#viewpdf?dispub=1523624.

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A significant portion of the process of detecting pulsars from radio sky surveys remains a largely manual task. The visual inspection of data in order to detect and validate potential pulsar candidates is by far the most time consuming portion of the overall process. Coupled with the fact that well over a Petabyte of pulsar survey data has been archived, the task of identifying these valuable phenomena is tedious and time consuming.

Using data from a survey performed with the National Radio Astronomy Observatory’s (NRAO’s) Green Bank Telescope (GBT) in 2007, this thesis explores the application of machine learning techniques to mitigate the manual efforts involved in pulsar candidate detection. The performance of three different classifiers is explored - Naive Bayes, C4.5 (J48) Decision Tree, and Support Vector Machine. Preprocessing and feature extraction methods are described and a framework for applying the classifiers to the survey data is presented. Multiple features were extracted from the survey data and used to train the classifiers. Cross-validation results of the various feature sets and classifiers are documented. Experiments suggest the potential of the proposed framework in rapidly detecting pulsars from large amounts of survey data.

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Dexter, J., A. Deller, G. C. Bower, P. Demorest, M. Kramer, B. W. Stappers, A. G. Lyne, et al. "Locating the intense interstellar scattering towards the inner Galaxy." OXFORD UNIV PRESS, 2017. http://hdl.handle.net/10150/625730.

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We use VLBA+VLA observations to measure the sizes of the scatter-broadened images of six of the most heavily scattered known pulsars: three within the Galactic Centre (GC) and three elsewhere in the inner Galactic plane (Delta l < 20 degrees). By combining the measured sizes with temporal pulse broadening data from the literature and using the thin-screen approximation, we locate the scattering medium along the line of sight to these six pulsars. At least two scattering screens are needed to explain the observations of the GC sample. We show that the screen inferred by previous observations of SGR J1745-2900 and Sgr A*, which must be located far from the GC, falls off in strength on scales less than or similar to 0 degrees.2. A second scattering component closer to (Delta < 2 kpc) or even (tentatively) within (Delta < 700 pc) the GC produces most or all of the temporal broadening observed in the other GC pulsars. Outside the GC, the scattering locations for all three pulsars are similar or equal to 2 kpc from Earth, consistent with the distance of the Carina-Sagittarius or Scutum spiral arm. For each object the 3D scattering origin coincides with a known H II region (and in one case also a supernova remnant), suggesting that such objects preferentially cause the intense interstellar scattering seen towards the Galactic plane. We show that the H II regions should contribute greater than or similar to 25 per cent of the total dispersion measure (DM) towards these pulsars, and calculate reduced DM distances. Those distances for other pulsars lying behind H II regions may be similarly overestimated.

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Natarajan, Madhan. "Characterisation of pulpal responses to bacterial challenge and novel antimicrobials for management of bacterial contamination of infected pulps." Thesis, Cardiff University, 2018. http://orca.cf.ac.uk/116535/.

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Dental pain from pulpal infection and inflammation are the common cause of dental emergencies. Therefore, evaluation of modalities to treat them would be beneficial. This work aims to characterise and validate the previously developed ex vivo pulp infection model and make it reliable and reproducible in terms of quantifying cell viability, area of bacterial colonisation and expression of inflammatory markers. The method developed and used in this work demonstrated that SAG infection reduced cell viability and IL-10 levels. SAG infection also Increased area of SAG colonisation of pulp,expression of IL-β, TNF-a and IL-18 in a time depended manner compared to uninfected control pulp. These findings were consistent with clinical observations, making it a reliable model for the observed characteristics. There were differences in the response to two SAG strains, with similar overall trends, but with greater response to S. constellatus. Differences in response to the two strains was confirmed by evaluating the effect of the SAG supernatants using the model. The response observed confirmed the deleterious effects of the supernatant on cell viability, and increase in expression of inflammatory markers, with a greater response of pulp observed to S. constellatus. Analysing the supernatants of SAG strains revealed the difference could be due to hyaluronidase produced by S. constellatus. Triclosan’s anti-microbial and anti-inflammatory effect in the treatment of pulpal infection was demonstrated using the SAG model through increased cell viability, reduced area of colonisation and inflammatory marker expression levels form triclosan treatment. Triclosan showed no anti-hyaluronisase activity. A poly-microbial infection model was developed with E. faecalis and S. anginosus on tooth slices. It was observed that E. faecalis perpetuated S. anginosus growth in mixed culture and caused greater cell-death compared to S. anginosus mono-infection. The proportion of E.faecalis and its affinity to blood vessels could influence the response of the model.

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Giraud, Quentin. "Corrections général-relativistes à l’émission radio et haute énergie des pulsars." Thesis, Strasbourg, 2020. http://www.theses.fr/2020STRAE024.

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Les étoiles à neutrons sont des astres extrêmement denses, plus denses qu’un noyau atomique, formés au cours d’une supernova. Un étoile à neutrons typique concentre ainsi une masse supérieure à celle du Soleil dans son diamètre d’une vingtaine de kilomètres. D’après la théorie de la relativité générale, qui décrit la gravité comme une déformation de l’espace-temps, le champ gravitationnel de ces étoiles devrait affecter de manière non négligeable les rayonnements électromagnétiques à proximité de celles-ci. Au cours de ma thèse, j’ai simulé les émissions radio et haute énergie provenant de l’accélération de particules le long des lignes de champ magnétique d’une étoile à neutrons dans la métrique de Schwarzschild pour savoir comment le rayonnement ainsi produit allait être affecté par les déformations de l’espace-temps au voisinage de l’étoile à neutrons
Neutron stars are very dense objects, denser than an atomic nucleus, formed during a supernova. A typical neutron star concentrates a mass superior to the one of the Sun in its diameter of around twenty kilometers. According to general relativity, which describes gravity as a space-time distorsion, the gravitational field of those stars should have a non-negligible impact on electromagnetic radiations close to them. During my thesis, I have simulated radio and high-energy emission originating from particules accelerated along the magnetic field lines of the neutron star inside the Schwarzschild metric to have an insight of how this kind of radiations would be affected by space-time distorsions in the vicinity of the neutron star

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Yukita, M., A. Ptak, A. E. Hornschemeier, D. Wik, T. J. Maccarone, K. Pottschmidt, A. Zezas, et al. "Identification of the Hard X-Ray Source Dominating the E > 25 keV Emission of the Nearby Galaxy M31." IOP PUBLISHING LTD, 2017. http://hdl.handle.net/10150/623858.

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We report the identification of a bright hard X-ray source dominating the M31 bulge above 25 keV from a simultaneous NuSTAR-Swift observation. We find that this source is the counterpart to Swift J0042.6+4112, which was previously detected in the Swift BAT All-sky Hard X-ray Survey. This Swift BAT source had been suggested to be the combined emission from a number of point sources; our new observations have identified a single X-ray source from 0.5 to 50 keV as the counterpart for the first time. In the 0.5-10 keV band, the source had been classified as an X-ray Binary candidate in various Chandra and XMM-Newton studies; however, since it was not clearly associated with Swift J0042.6+4112, the previous E < 10 keV observations did not generate much attention. This source has a spectrum with a soft X-ray excess (kT similar to 0.2 keV) plus a hard spectrum with a power law of Gamma similar to 1 and a cutoff around 15-20 keV, typical of the spectral characteristics of accreting pulsars. Unfortunately, any potential pulsation was undetected in the NuSTAR data, possibly due to insufficient photon statistics. The existing deep HST images exclude high-mass (> 3 M-circle dot) donors at the location of this source. The best interpretation for the nature of this source is an X-ray pulsar with an intermediate-mass (< 3 M-circle dot) companion or a symbiotic X-ray binary. We discuss other possibilities in more detail.

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Abdel-Rahman, Mohamed A. "Numerical Reconstruction and Applications of Acoustic and Electromagnetic Ultra-Wideband Localized Pulses Generated by Dynamic Aperture Antennas." Diss., Virginia Tech, 1997. http://hdl.handle.net/10919/26335.

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A study is undertaken of the numerical reconstruction of acoustic and electromagnetic (EM) localized waves (LWs). The latter are carrier-free ultra-wideband pulses characterized by large focusing depths and extended ranges of localization. Special emphasis is placed on finite energy LWs that can be generated by dynamic aperture antennas with independently addressable elements. The reconstruction techniques are based on Huygens and Rayleigh-Sommerfeld integral I and II representations, both in the time and frequency domains. In contradistinction to the Weyl representation,they lend themselves to the physical realization of space-time aperture sources capable of generating localized wave solutions propagating away from the aperture plane. A detailed comparison of the three reconstruction techniques has been carried out in connection with LW solutions to the scalar wave equation, especially with respect to their handling of acausal components incorporated in the aperture excitation fields. In addition, a study is presented of the characteristic properties of LWs propagating through dispersive media modeled by the Klein-Gordon equation. It is demonstrated that contrary to expectation, the depletion of the spectral components of the LW Klein-Gordon field may be slower than that associated with the free space scalar field. Previous work by Power et al. [73] is extended by studying the acoustic bistatic scattering of a modified power spectrum (MPS) pulse from rigid and compressible spheres. The analysis allows the extraction of the radius of a sphere from the backscattered data. Finally, a special class of electromagnetic (EM) LWs, referred to as azimuthally polarized X waves (APXWs), is derived and their reconstruction is addressed, both in the time and frequency domains.
Ph. D.

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Sophian, Ali. "Characterisation of surface and sub-surface discontinuities in metals using pulsed eddy current sensors." Thesis, University of Huddersfield, 2003. http://eprints.hud.ac.uk/id/eprint/6916/.

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Due primarily to today's rigorous safety standards the focus of non-destructive testing (NDT) has shifted from flaw detection to quantitative NIDT, where characterisation of flaws is the objective. This means information such as the type of flaw and its size is desired. The Pulsed Eddy Current (PEC) technique has been acknowledged as one of the potential contenders for providing this additional functionality, due to the potential richness of the information that it provides. The parameters mainly used to obtain information about the detected flaws are the signal's peak height and arrival time. However, it has been recognised that these features are not sufficient for defect classification. In this research, based on a comprehensive literature survey, the design of PEC systems and the interpretation of PEC signals, mainly for flaw classification, are studied. A PEC system consisting of both hardware and software components has been designed and constructed to facilitate the research work on PEC signal interpretation. After a comparative study of several magnetic sensing devices, probes using Hall device magnetic sensors have also been constructed. Some aspects related to probe design, such as coil dimensions and the use of ferrite core and shielding have also been studied. A new interpretation technique that uses the whole part of PEC responses and is able to produce more features has been proposed. The technique uses Principal Component Analysis (PCA) and Wavelet Transforms, and attempts to find the best features for discrimination from extracted time and frequency domain data. The simultaneous use of both temporal and spectral data is a logically promising extension to the use of time domain only with the signal-peak-based technique. Experiments show that the new 1 technique is promising as it performs significantly better than the conventional technique using peak value and peak time of PEC signals in the classification of flaws. A hierarchical structure for defect classification and quantification has been presented. Experiments in the project have also shown that the signal-peak-based technique cannot be used for flaw detection and characterisation in steels, both with and without magnetisation. The new proposed technique has shown to have potential for this purpose when magnetisation is used. The new technique proposed in the report has been successfully used for ferromagnetic and non-ferromagnetic materials. It has also been demonstrated that the new proposed technique performs better in dynamic behaviour tests, which shows its better potential for on-line dynamic NDT inspection which is required in many industrial applications. In addition to testing calibrated samples with different discontinuities, a study case using an aircraft lap joint sample from industry has further supported the statement regarding the potential of the new technique.

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32

Fani-Pakdel, Farzad. "Microsecond pulsed Grimm glow discharge time-of-flight mass spectrometry study of aerosols generated by nebulization and laser ablation." [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0024978.

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33

Taskin, Ozgur Mustafa. "Analysis Of The Physical Properties Of Different Types Of Neutron Stars." Phd thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606665/index.pdf.

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This thesis is composed of three published articles. Each chapter is devoted to an article. In the first part the origin of some of the single radio pulsars with relatively low magnetic fields (B <
1e12 G) and with characteristic ages (tau) less than 1e7 years is questioned. We proposed that such pulsars might occur as a result of the disruption of high-mass X-ray binary systems after a second supernova explosion. In these binaries, mass accretion on to the surface of X-ray pulsars may lead to the decrease in the magnetic field from its value at birth (B similar to 1e12 &ndash
1e13 G) down to B <
1e12 G similar to the processes in low-mass X-ray binaries. In the second part we put together many observational data of SGRs and AXPs and analyzed them with the main purpose of the removal of contradiction between the real age (t) of these objects and their characteristic times of period change (tau). SGRs and AXPs are neutron stars that undergo star-quakes. Magnetic activity increases from time to time. We suggest that as a result of these processes plasma is ejected from the NS and propeller mechanism starts to work. Due to propeller effect dP/dt increases, tau decreases. Indeed, high dP/dt values are observed in SGRs and in half of the AXPs. Then, for a long time NS looses its activity, its dP/dt decreases, tau increases and rapid cooling begins. It seems that there is a possible transition between each NS stage (AXP,SGR,dim). This transient cycle may be repeated once or several times until the spin period of the neutron star becomes P >
10 - 12 s. Observational data and mainly the data of AXP 1E 1048-5937 and DRQNS RX J1308.8+2127 support this idea. In the third part dependence of the X-ray luminosity (Lx) of young single pulsars, due to ejection of relativistic particles, on electric field intensity, rate of rotational energy loss (dE/dt), magnetic field, period and some other parameters of neutron stars are discussed. Influence of the magnetic field and effects of some other parameters of neutron stars on the Lx - dE/dt and the Lx - tau(characteristic time) relations are considered. Evolutionary factors also play an important role in our considerations. Only the pulsars whose X-ray luminosity in the 2 &ndash
10 keV energy band is greater than 1033 erg/s have pulsar wind nebula around them. The pulsars from which gamma-ray radiation has been observed have low X-ray luminosity in general.

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34

Yuksel, Yuksel. "Thermoelectric Cooling Of A Pulsed Mode 1064 Nm Diode Pumped Nd:yag Laser." Master's thesis, METU, 2010. http://etd.lib.metu.edu.tr/upload/12612550/index.pdf.

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Since most of the energy input is converted to thermal energy in laser applications, the proper thermal management of laser systems is an important issue. Maintaining the laser diode and crystal temperature distributions in a narrow range during the operation is the most crucial requirement for the cooling of a laser system. In the present study, thermoelectric cooling (TEC) of a 1064 nm wavelength diode pumped laser source is investigated both experimentally and numerically. During the heat removal process, the thermal resistance through and between the materials, the proper integration of the TEC assembly, and the heat sink efficiency become important. For the aim of evaluating and further improving the system performance, various assembly configurations, highly conductive components, efficient interface materials and heat sink alternatives are considered. Several experiments are conducted during the system development stage, and parallel numerical simulations are performed both for comparison and also for providing valuable input for the system design. Results of the experiments and the simulations agree well with each other. As the laser device works in the transient regime, the experiments and the simulations are also implemented in this regime. In the final part of the study, the experiments are performed under the actual device working conditions. It is proved that with the designed TEC module and the copper heat sink system, the laser device can operate longer than the required operational time successfully.

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35

Banaschik, Robert [Verfasser]. "Potential of Pulsed Corona Discharges Generated in Water for the Degradation of Recalcitrant Pharmaceutical Residues and for Water Disinfection / Robert Banaschik." Greifswald : Universitätsbibliothek Greifswald, 2017. http://d-nb.info/1147900051/34.

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36

Pentlehner, Dominik [Verfasser], and Alkwin [Akademischer Betreuer] Slenczka. "Perturbations of electronic transitions of organic molecules in helium droplets generated with a new pulsed droplet source / Dominik Pentlehner. Betreuer: Alkwin Slenczka." Regensburg : Universitätsbibliothek Regensburg, 2010. http://d-nb.info/1022872168/34.

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37

Sutherland, Julia Robin Miller. "Phase-Matching Optimization of Laser High-Order Harmonics Generated in a Gas Cell." Diss., CLICK HERE for online access, 2005. http://contentdm.lib.byu.edu/ETD/image/etd880.pdf.

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38

Akhmadaliev, Chavkat. "Investigation of acoustic waves generated in an elastic solid by a pulsed ion beam and their application in a FIB based scanning ion acoustic microscope." Forschungszentrum Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:d120-qucosa-28813.

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The rapid growth of the microelectronics industry in the last decades made it possible to produce structures in the sub-micrometer scale on silicon chips and to reach an integration scale under 100 nm. Decreasing the size and increasing the complexity of these structures make a control of quality and defects investigation more difficult. During a long time ultrasound devices are being used for nondestructive investigation of materials, like ultrasound microscopes, scanning photo-acoustic microscopes or scanning electron-acoustic microscopes, where acoustic waves are generated by acoustic transducers, focused laser or electron beams, respectively. The aim of this work is to investigate more precisely the acoustic wave generation by pulsed and periodically modulated ion beams in different solid materials depending on the beam parameters and to demonstrate the possibility to apply an intensity modulated focused ion beam (FIB) for acoustic emission and for nondestructive investigation of the internal structure of materials on a microscopic scale. The combination of a FIB and an ultrasound microscope in one device can provide the opportunity of nondestructive investigation, production and modification of micro- and nanostructures simultaneously. The FIB spot size in modern systems is comparable with that of a focused electron beam and the penetration depth of ions with energy of 20-60 keV is lower than 100 nm. This makes it possible to reach a sub-micrometer resolution of a scanning ion acoustic microscope. On the other hand side a FIB with energy of 20-60 keV is a good tool which can be used for the fabrication of nanostructures using ion milling, implantation or ion beam assisted deposition techniques. The bulk ultrasound emission in a solid was investigated using a pulsed high energy ion beam focused on aluminum, copper, iron and silicon samples. Oxygen, silicon and gold ion beams were applied in charge states from 1+ to 4+ with the pulse duration of 0.5 - 4 µs and an energy of 1.5 - 10 MeV. Intensity of the detected acoustic waves shows a linear dependence on the energy of the incident ions, on the ion flux as well as on the pulse duration. No influence of the ion charge and ion mass to the emission of acoustic waves was observed. The ion acoustic effect was applied for a nondestructive material inspection using intensity modulated FIB providing by the IMSA-100 FIB system with an accelerating potential of 30-35 kV. The achieved lateral resolution of this scanning ion acoustic microscope is in the micrometer range depending on the sample material and the beam modulation frequency. The resolution can be improved by increasing the frequency. The maximal modulation frequency which was obtained at IMSA-100 is about 2 MHz corresponding to lateral resolution of 4-5 µm on silicon. Using this microscope, some images of integrated microstructures on a silicon chip were obtained using the lock-in technique for filtering of the signal from the noise and increasing of the total imaging time. The possibility to visualize near sub-surface structure was demonstrated. Due to the strong sputtering effect and the long time of irradiation the imaged structures were significantly damaged. Si2+, Ge2+, Ga+ and Au+ ions were used. All these ions are quite heavy and have high sputtering coefficients. Long-time imaging improves the quality of acoustic images, i. e. the signal-to-noise ratio is reduced with the square root from the pixel time, but leads to significant erosion of the imaged structure.

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39

Akhmadaliev, Chavkat. "Investigation of acoustic waves generated in an elastic solid by a pulsed ion beam and their application in a FIB based scanning ion acoustic microscope." Forschungszentrum Rossendorf, 2004. https://hzdr.qucosa.de/id/qucosa%3A21708.

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The rapid growth of the microelectronics industry in the last decades made it possible to produce structures in the sub-micrometer scale on silicon chips and to reach an integration scale under 100 nm. Decreasing the size and increasing the complexity of these structures make a control of quality and defects investigation more difficult. During a long time ultrasound devices are being used for nondestructive investigation of materials, like ultrasound microscopes, scanning photo-acoustic microscopes or scanning electron-acoustic microscopes, where acoustic waves are generated by acoustic transducers, focused laser or electron beams, respectively. The aim of this work is to investigate more precisely the acoustic wave generation by pulsed and periodically modulated ion beams in different solid materials depending on the beam parameters and to demonstrate the possibility to apply an intensity modulated focused ion beam (FIB) for acoustic emission and for nondestructive investigation of the internal structure of materials on a microscopic scale. The combination of a FIB and an ultrasound microscope in one device can provide the opportunity of nondestructive investigation, production and modification of micro- and nanostructures simultaneously. The FIB spot size in modern systems is comparable with that of a focused electron beam and the penetration depth of ions with energy of 20-60 keV is lower than 100 nm. This makes it possible to reach a sub-micrometer resolution of a scanning ion acoustic microscope. On the other hand side a FIB with energy of 20-60 keV is a good tool which can be used for the fabrication of nanostructures using ion milling, implantation or ion beam assisted deposition techniques. The bulk ultrasound emission in a solid was investigated using a pulsed high energy ion beam focused on aluminum, copper, iron and silicon samples. Oxygen, silicon and gold ion beams were applied in charge states from 1+ to 4+ with the pulse duration of 0.5 - 4 µs and an energy of 1.5 - 10 MeV. Intensity of the detected acoustic waves shows a linear dependence on the energy of the incident ions, on the ion flux as well as on the pulse duration. No influence of the ion charge and ion mass to the emission of acoustic waves was observed. The ion acoustic effect was applied for a nondestructive material inspection using intensity modulated FIB providing by the IMSA-100 FIB system with an accelerating potential of 30-35 kV. The achieved lateral resolution of this scanning ion acoustic microscope is in the micrometer range depending on the sample material and the beam modulation frequency. The resolution can be improved by increasing the frequency. The maximal modulation frequency which was obtained at IMSA-100 is about 2 MHz corresponding to lateral resolution of 4-5 µm on silicon. Using this microscope, some images of integrated microstructures on a silicon chip were obtained using the lock-in technique for filtering of the signal from the noise and increasing of the total imaging time. The possibility to visualize near sub-surface structure was demonstrated. Due to the strong sputtering effect and the long time of irradiation the imaged structures were significantly damaged. Si2+, Ge2+, Ga+ and Au+ ions were used. All these ions are quite heavy and have high sputtering coefficients. Long-time imaging improves the quality of acoustic images, i. e. the signal-to-noise ratio is reduced with the square root from the pixel time, but leads to significant erosion of the imaged structure.

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40

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.

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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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41

Mckechnie, Alasdair John. "In vitro and in vivo effects of human dendritic cells generated using a novel combination of cytokines and pulsed with nonapeptides of human telomerase reverse transcriptase." Thesis, University of Nottingham, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.441009.

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42

Johari, Dalina. "Features of the Electric Fields Generated by Lightning with Special Attention to Positive Ground Flashes." Doctoral thesis, Uppsala universitet, Elektricitetslära, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-331885.

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This thesis focuses on the main processes in positive ground flashes and the distant lightning environment for both positive and negative ground flashes. It presents the characteristics of the preliminary breakdown pulses (PBPs), the characteristics of the electric field pulses observed during leader propagation, and the characteristics of the electric fields produced by the first and the subsequent return strokes. It also features the observations of distant positive and negative ground flashes at distances up to 1000 km. The results were based on electric field measurements conducted remotely during summer thunderstorms in Sweden in 2014. We found that the majority of the positive ground flashes were preceded by PBPs. Some were preceded by more than one PBP train, and the parameter values for the subsequent PBP trains were found to be smaller than the values for the first PBP train. Three types of PBPs were also identified. The results suggest that the PBPs in positive ground flashes during summer thunderstorms in Sweden are weak, and the inverted dipole charge cloud configuration is consistent with our observation. A small percentage of these positive ground flashes were observed to be preceded by pronounced leader pulses. The presence of these pulses suggests that the leaders propagate in a stepped manner. We inferred that these pulses were due to the upward-connecting negative leader since their characteristics were similar to those of a negative stepped leader. On the basis of the leader pulses’ time of initiation and the average speed of the leader, we estimated the distance travelled by the leader. One case of positive return stroke preceded by negative leader pulses was also observed, and the occurrence of these pulses was the first in positive ground flashes to be reported. The majority of these positive ground flashes were found to be single-stroke. Comparison between the first and the subsequent return strokes showed that the average durations of the subsequent stroke parameters were smaller than that of the first strokes. The distances reported by the lightning location system suggest that the subsequent strokes probably created new terminations to ground. Two possible reasons were given to explain the reason for the shorter duration of the subsequent return strokes parameters compared to the first strokes. Finally, observations of distant positive and negative ground flashes showed that the electric field waveforms have a typical shape, like a distorted ‘W’ (or distorted ‘M’ for negative ground flashes) followed by small oscillations. These small oscillations were more pronounced in negative ground flashes, especially at a greater distance. The heights of the ionospheric reflections estimated for both ground flashes were found to likely correspond to a D-layer of the ionosphere. Two possible reasons were suggested for the small oscillations observed in the waveforms.

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43

Pele, Winnie Kasoma. "Income and bean consumption patterns in Zambia." Thesis, Kansas State University, 2015. http://hdl.handle.net/2097/19751.

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Master of Agribusiness
Department of Agricultural Economics
Vincent Amanor-Boadu
The literature shows that increases in incomes lead to changes in the allocation of income or expenditure shares to different food products. The purpose of this thesis is to identify the effect of income on expenditure share allocations among different food groups. The study was particularly interested in beans and how changes in incomes affect the share of bean expenditures. We used data from the 2010 Zambia Living Conditions Monitoring Survey (LCMS). The LCMS covers the whole country and provides segmentation of the respondents, across the region and rural versus urban. It also provides detailed information on the income and expenditure distributions of respondent households. This allowed for the achievement of the overall objective of this thesis: understanding how beans and other food products responded to income changes as well as other demographic and socio-economic variables. The food share is the proportion of total household income that was allocated to food. The results show that food averages about 40% of income but varied significantly across the four income groups. It was 92% for those earning less than ZMW300 per month and 37% for those earning between ZMW300 and ZMW750 per month. It was down to 22.6% for those earning between ZMW750 and ZMW2.1 million per month had a food share of total income of only 10.8%, similar to the average U.S. consumer. These averages were found to be statistically different across the income groups. We found that Zambians allocated about 40% of their food expenditure to cereals compared to 5% to pulses and 3.5% to beans. They allocated a higher proportion of their food expenditure to fruits and vegetables than to beans and/or to pulses. This shows that legumes are very low on the food hierarchy in Zambia. However, across income categories, it was found that consumers in the second income group (ZMW300 and ZMW750 per month) allocated the most of their food expenditure to beans, about 3.9%, while those in the highest income group (ZMW750 and ZMW2.1 million per month ) allocated the least, about 3%. The biggest influencing demographic factor for pulses and beans’ shares of food expenditure was locale, with urban consumers having about 1.1 and 0.8 percentage points higher share of food expenditures allocated to beans than rural consumers. The respective t-values were 15.58 and 16.96. All the demographic and socio-economic variables were statistically significant at or below the 5% level. There was no difference between the allocation of people in the highest income group and those in the lowest income group. The results suggest that if the long-term objective is to reap the nutritional benefits of beans, there may be value in focusing on two principal policy variables: education and income enhancement. However, because education is correlated with income, the benefits of undertaking this policy initiative would more than benefit the bean consumption. It should unleash across the economy a more productive workforce that understands the health benefits of its food choices.

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44

Jacquet, Maxime J. "Negative frequency at the horizon : scattering of light at a refractive index front." Thesis, University of St Andrews, 2017. http://hdl.handle.net/10023/11780.

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This thesis considers the problem of calculating and observing the mixing of modes of positive and negative frequency in inhomogeneous, dispersive media. Scattering of vacuum modes of the electromagnetic field at a moving interface in the refractive index of a dielectric medium is discussed. Kinematics arguments are used to demonstrate that this interface may, in a regime of linear dispersion, act as the analogue of the event horizon of a black hole to modes of the field. Furthermore, a study of the dispersion of the dielectric shows that five distinct configurations of modes of the inhomogeneous medium at the interface exist as a function of frequency. Thus it is shown that the interface is simultaneously a black- and white-hole horizon-like and horizonless emitter. The role, and importance, of negative-frequency modes of the field in mode conversion at the horizon is established and yields a calculation of the spontaneous photonic flux at the interface. An algorithm to calculate the scattering of vacuum modes at the interface is introduced. Spectra of the photonic flux in the moving and laboratory frame, for all modes and all realisable increase in the refractive index at the interface are computed. As a result of the various mode configurations, the spectra are highly structured in intervals with black-hole, white-hole and no horizon. The spectra are dominated by a negative-frequency mode, which is the partner in any Hawking-type emission. An experiment in which an incoming positive-frequency wave is populated with photons is assembled to observe the transfer of energy to outgoing waves of positive and negative frequency at the horizon. The effect of mode conversion at the interface is clearly shown to be a feature of horizon physics. This is a classical version of the quantum experiment that aims at validating the mechanism of Hawking radiation.

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45

Lodewijks, Marten Barend. "Probing general relativity through simulations of the Shapiro time delay of light in binary pulsar systems." Thesis, 2008. http://hdl.handle.net/10210/554.

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The theory of General Relativity has been in existence for 90 years and has stood up to all tests it has been subjected to in that time. The PPN parameter is a measure of the accuracy of theories of gravity and assumes different values in different theories. By measuring the Shapiro time delay of light it is possible to constrain and thereby constrain gravitational theories. This Shapiro time delay can be measured in our solar system but it is only in the vicinity of extremely compact objects such as pulsars and black holes that it can be tested under the immense gravitational fields that can only be found there. A pulsar in a binary orbit about another compact object is the ideal system in which to test this effect. In this work we have gone from Kepler’s laws of simple planetary motion to deriving the equations that explain binary orbits to incorporating General Relativity into these equations in order to obtain the equations for relativistic particle orbits. We then evolved this theory even further so as to be able to explain relativistic light ray orbits and then used this knowledge to model the Shapiro delay in a binary system. With a working model it became possible to simulate the Shapiro delay in a wide range of possible systems and then to use these simulations to say something about what type of system should be focussed on in future so as to measure the Shapiro delay and thereby constrain more tightly the parameter
Dr. C.A. Engelbrecht Dr. F.A.M. Frescura

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46

"Tunable multiwavelength picosecond pulses generated from a fabry-perot laser diode." 1998. http://library.cuhk.edu.hk/record=b5889738.

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by Sui-Pan Yam.
Thesis (M.Phil.)--Chinese University of Hong Kong, 1998.
Includes bibliographical references.
Abstract also in Chinese.
Acknowledgements --- p.V
Abstract --- p.VI
Chapter Chapter 1 --- Introduction --- p.1-1
Chapter 1.1) --- Tunable Multi-Wavelength Optical Sources --- p.1 -1
Chapter 1.2) --- All-Optical Switching --- p.1 -3
Chapter 1.2.1) --- Nonlinear Effect
Chapter 1.2.2) --- Special Design of the Laser Structure
Chapter 1.2.3) --- Self-Injection Seeding of Fabry-Perot Laser Diode
Chapter 1.3) --- About This Project --- p.1-6
Chapter Chapter 2 --- Basic Theory --- p.2-1
Chapter 2.1) --- Mechanism of Gain-Switching --- p.2-1
Chapter 2.1.1) --- General Description
Chapter 2.1.2) --- "Optical Pulsewidth, Spectra, and Frequency Chirping of Gain-Switched Pulses"
Chapter 2.2) --- Mechanism of Self-Injection Seeding --- p.2-8
Chapter 2.2.1) --- General Description
Chapter 2.2.2) --- Dynamics of Single-Mode Formation
Chapter 2.2.3) --- Frequency Evolution of the Laser Diode for Cavity Mode Selection
Chapter 2.2.4) --- Turn-On Delay Time Jitter (TOJ)
Chapter 2.3) --- Mechanism of Injection Seeding --- p.2-17
Chapter 2.3.1) --- General Description
Chapter 2.3.2) --- The Model of Weak Injection
Chapter 2.3.3) --- The Model of Strong Injection
Chapter Chapter 3 --- Single- and Multi-wavelength Optical Pulses Generated by a Diffraction Grating --- p.3-1
Chapter 3.1) --- Introduction --- p.3-1
Chapter 3.2) --- Basic Principle --- p.3-2
Chapter 3.3) --- Experimental Setup --- p.3-5
Chapter 3.4) --- Results and Discussion --- p.3-7
Chapter 3.4.1) --- Spectral Characteristics Analysis
Chapter 3.4.2) --- Individually Access of the Four-Wavelength Output
Chapter 3.4.3) --- The Optical Pulsewidth Characteristics
Chapter 3.4.4) --- Discussion
Chapter 3.5) --- Summary --- p.3-14
Chapter Chapter 4 --- Using a Highly Dispersive Fiber for Tunable Multi-Wavelength Pulse Generation --- p.4-1
Chapter 4.1) --- Introduction --- p.4-1
Chapter 4.2) --- Basic Principle --- p.4-2
Chapter 4.3) --- Experimental Setup --- p.4-5
Chapter 4.4) --- Experimental Results --- p.4-7
Chapter 4.4.1) --- Spectral and Temporal Characteristics
Chapter 4.4.2) --- Wavelength Tuning
Chapter 4.4.3) --- Individually Access of Two Wavelength Channels
Chapter 4.4.4) --- Multi-Wavelength Generation
Chapter 4.5) --- Summary --- p.4-13
Chapter Chapter 5 --- Comparison of Two Self-Seeding Configurations --- p.5-1
Chapter 5.1) --- Introduction --- p.5-1
Chapter 5.2) --- Polarization Sensitivity --- p.5-1
Chapter 5.3) --- Stability --- p.5-2
Chapter 5.4) --- Tunability --- p.5-2
Chapter 5.5) --- Simplification --- p.5-3
Chapter 5.6) --- Summary of the advantages and disadvantages of Two Configurations --- p.5-4
Chapter Chapter 6 --- All-Optical Wavelength Switching achieved by Self-Seeding and External Injection-Seeding --- p.6-1
Chapter 6.1) --- Introduction --- p.6-1
Chapter 6.2) --- Experimental Setup --- p.6-2
Chapter 6.3) --- Results and Discussion --- p.6-4
Chapter 6.3.1) --- Spectral Characteristics
Chapter 6.3.2) --- The Optical Pulsewidth
Chapter 6.3.3) --- The Optical Switching Behaviors
Chapter 6.3.4) --- The Detail Information of Switching
Chapter 6.3.5) --- Optical Power
Chapter 6.4) --- Summary --- p.6-10
Chapter Chapter 7 --- A Novel Self-Injection Seeding Scheme --- p.7-1
Chapter 7.1) --- Introduction --- p.7-1
Chapter 7.2) --- Basic Principle --- p.7-2
Chapter 7.3) --- Experimental Setup --- p.7-9
Chapter 7.4) --- Results and Discussion --- p.7-11
Chapter 7.4.1) --- Spectral and Temporal Characterizations of Two-Wavelength Switching
Chapter 7.4.2) --- Different Wavelength Selection
Chapter 7.4.3) --- Operation Frequency Against the Fiber Length
Chapter 7.4.4) --- Multi-Wavelength Generation
Chapter 7.5) --- Discussion --- p.7-20
Chapter 7.6) --- Summary --- p.7-22
Chapter Chapter 8 --- Comparison of Switching Methods --- p.8-1
Chapter 8.1) --- Introduction --- p.8-1
Chapter 8.2) --- Switching between Self-Seeding and Injection-Seeding --- p.8-1
Chapter 8.3) --- Switching by Self-Seeding of a F-P Laser Diode --- p.8-2
Chapter 8.4) --- Summary --- p.8-3
Chapter Chapter 9 --- Conclusion --- p.9-1
References
Figure Captions
Appendix 一 Equipment Descriptions
List of Accepted and Submitted Publications

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47

"Wavelength selection and switching in short pulses generated from semiconductor lasers." 2000. http://library.cuhk.edu.hk/record=b5890470.

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Abstract:

by Chow Kin Kee.
Thesis (M.Phil.)--Chinese University of Hong Kong, 2000.
Includes bibliographical references.
Abstracts in English and Chinese.
Abstract --- p.ii
Acknowledgment --- p.v
Table of Contents --- p.vi
Chapter 1. --- Introduction --- p.1
Chapter 1.1 --- Ultra-short Pulse Generation in Semiconductor Lasers --- p.2
Chapter 1.2 --- Wavelength Selection and Switching in Short Pulses Generated from Semiconductor Laser --- p.4
Chapter 1.3 --- Structure of the Thesis --- p.6
Reference --- p.8
Chapter 2. --- Principles and Theories --- p.10
Chapter 2.1 --- Principle of Wavelength Switching in Self-Seeded Laser --- p.11
Chapter 2.2 --- Principle of Synchronous Injection Seeding of two Lasers --- p.15
Chapter 2.3 --- Principle of Fast Spectral Improvement in DFB Laser with Optical Feedback --- p.17
Chapter 2.4 --- Principle of Spectrally Resolved Analysis --- p.19
Reference --- p.24
Chapter 3. --- Switching Dynamics between Single-Mode and Dual-Mode Pulse Emissions from a Self-Seeded Laser Diode --- p.25
Chapter 3.1 --- Introduction --- p.26
Chapter 3.2 --- Experimental Details and Discussion --- p.28
Chapter 3.3 --- Summary --- p.37
Reference --- p.38
Chapter 4. --- Spectrally Resolved Analysis of Fast Tuning in Single-Mode Pulses Generated from Mutually Injection-Seeded Fabry- Perot Laser Diodes --- p.40
Chapter 4.1 --- Introduction --- p.41
Chapter 4.2 --- Experimental Details and Discussion --- p.42
Chapter 4.3 --- Summary --- p.51
Reference --- p.52
Chapter 5. --- Fast Spectral Improvement in Gain-Switched Pulses Generated from a Distributed Feedback Laser with Weak Optical Feedback --- p.54
Chapter 5.1 --- Introduction --- p.55
Chapter 5.2 --- Experimental Details and Discussion --- p.57
Chapter 5.3 --- Summary --- p.65
Reference --- p.66
Chapter 6. --- Conclusion and Future Work --- p.67
Chapter 6.1 --- Conclusion --- p.67
Chapter 6.2 --- Future Works --- p.69
Reference --- p.71
Appendices --- p.A-l
Appendix A. List of Publications --- p.A-l
Appendix B. Modeling of Self-Seeded Fabry-Perot Laser --- p.A-2
Appendix C. List of Figures --- p.A-4

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48

Liou, Jhe-Wei, and 劉哲瑋. "Characteristic of defect generated on graphene through pulsed scanning probe lithography." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/2jt2r6.

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碩士
國立中央大學
物理學系
105
Graphene has attracted attention in recent years because of low dimensional and high electron mobility. However, the gap-less feature is the main obstacle to further electronic application. Defect generation is one way to manipulate the band gap of graphene. To create defect on graphene, Scanning probe lithography (SPL) is a well-developed nano-meter scale technique. In our previous work, we formed graphene oxidation through negative bias SPL. However, the mechanism of the oxidation processing with SPL is still unveiled. To understand this, we set up a pulsed SPL system with precise pulse width, pulse treatment position control and the output impedance control. After point-like arrays are generated by pulsed SPL, both Raman and atomic force microscopy (AFM) measurements conclude that those defects are holes in average diameter 160 nm on graphene. In the limit of maximum current, ring-like patterns are generated. It indicates that the point-like holes are created by large charging current and that the ring patterns are caused by electrolysis which is driven by voltage. In summary, the point-like and ring-like patterns represent current dominant and voltage dominant phase in the charging process.

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49

Qi, Zhangfen. "Generation and characterization of femtosecond vacuum ultraviolet pulses." Thesis, 1994. http://hdl.handle.net/1911/13882.

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High power femtosecond VUV/XUV pulses covering new spectral regions have been generated through nonlinear interaction of a femtosecond KrF laser with xenon and argon. Conversion efficiencies as high as 10$\sp{-3}$ have been observed. A six-wave mixing process and several four-wave mixing processes under intense light field have been experimentally studied. The temporal duration of the femtosecond VUV pulse has been experimentally measured for the first time based on the defocusing caused by a femtosecond laser produced plasma.

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50

Sousa, Rui da Silva Pinto de. "Storage System for Pulsed Energy generated by a Pavement Energy Harvesting Solution." Master's thesis, 2020. https://hdl.handle.net/10216/132884.

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With the constant technological developments, there are nowadays (2020) the possibility of developing a Pavement Energy Harvesting solution that can harvest kinetic energy from vehicles and convert it into electricity. Harvesting kinetic energy from vehicles might be increasing road safety by reducing the vehicle´s speed without any driver action. When vehicles move across the module, an electro-mechanical system converts its surface motion into pulsed electric energy. The electric energy produced requires a storage system so it can be used in multiple electric applications locally installed. This project focus on the modelling of the electric generation behaviour of the Pavement Energy Harvesting generation module, the AC/DC energy conversion system, and its storage. At first, a comparative analysis of the different technologies for energy storage has been performed, leading to the selection of supercapacitors and ultracapacitors (LiC supercapacitors) as the strongest candidates to store pulsed energy from the generation module. Then a model of the generation module is created based on MATLAB/Simulink to test different conversion circuits and to analyse the performance of the storage system to achieve an effective and efficient combination.

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Dissertations / Theses on the topic 'Pulsar: generale'

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