A hundred years after Einstein predicted the existence of gravitational waves, the first direct detection was made from gravitational waves emitted by a binary black hole system. Other potential sources for an advanced gravitational-wave detector network include core-collapse supernovae. Due to complicated simulations of the physics involved in core-collapse supernovae, the exact waveform of a core-collapse supernova signal is unknown. A detection of a core-collapse supernova signal is challenging, as noise of non-astrophysical origin contaminates the science data taken by the advanced detectors. Noise transients in the detectors limit the false alarm rate of astrophysical detections, and could potentially mimic a core-collapse supernova signal. They can reduce the duty cycle of the detectors, which is particularly harmful for core-collapse supernovae detections due to their low event rate. Prompt characterization of instrumental and environmental noise transients will be critical for improving the sensitivity of the advanced detectors during observing runs. During the science runs of the initial gravitational-wave detectors, noise transients were manually classified by visually examining the time-frequency scan of each event. Here, we present a Bayesian model selection algorithm designed for the automatic classification of noise transients in advanced gravitational-wave detectors. The algorithm is tested on simulated data sets and real non-Gaussian, non-stationary Advanced LIGO noise, and we demonstrate the ability to automatically classify transients by frequency, SNR and waveform morphology. A classification of noise transients as data is taken can lead to an improvement in data quality during an observing run and determine their origin. In this thesis, we show how Bayesian model selection can be used to determine if a core-collapse supernova candidate gravitational-wave signal is a noise transient, a core-collapse supernova signal or other astrophysical transient. If the signal is a core-collapse supernova detection, we show how the core-collapse supernova explosion mechanism can be determined using a combination of principal component analysis and Bayesian model selection. We use the latest three-dimensional simulations of gravitational-wave signals from core-collapse supernovae exploding via neutrino-driven convection and rapidly-rotating core-collapse. We show that with an advanced detector network, we can determine if the core-collapse supernova explosion mechanism is neutrino-driven convection for sources in our Galaxy, and rapidly-rotating core collapse for sources out to the Large Magellanic Cloud.

The subject matter of this thesis is the formation of large-scale structure in the universe. Most of the study has dealt with the non-linear evolution of cosmological uctuations, focusing on the scalar sector of perturbation theory. The period of transition between the radiation era and the matter era has been largely examined, extending the already known linear results to a nonstandard matter model and to a non-linear analysis. The obtained second order solutions for the matter uctuations variables have been used to find the skewness of the density and velocity distributions, an important statistical estimator measuring the level of non-Gaussianity of a distribution. In the context of cosmological perturbations, a complete Post-Newtonian (1PN) treatment is presented with the aim of obtaining a set of equations suitable in particular for the intermediate scales. The final result agrees with both the non linear Newtonian theory of small scales and the linear general relativistic theory of large scales. Analyzing the limiting cases of our approach to 1PN cosmology, we have clarified the link between the Newtonian theory of gravity and General Relativity. This work is the result of the agreement signed by the Department of Physics, University of Roma Tor Vergata and the Institute of Cosmology and Gravitation, University of Portsmouth, United Kingdom in the formal context of the co-tutela project. The chapters 5, 6 and 7 are the themes of two articles in preparation, that will be shortly submitted: "How the universe got its skewness" - M. Bruni, I.Milillo, K.Koyama; "Post-Newtonian Cosmology" - I. Milillo, D.Bertacca, M. Bruni

The safety of future spaceflight depends on space surveillance and space traffic management, as the density of objects in Earth orbit has reached a level that requires collision avoidance maneuvers to be performed on a regular basis to avoid a mission or, in the context of human space flight, life-endangering threat. Driven by enhanced sensor systems capable of detecting centimeter-sized debris, megaconstellations and satellite miniaturization, the space debris problem has revealed many parallels to the plastic waste in our oceans, however with much less visibility to the eye. Future catalog sizes are expected to increase drastically, making it even more important to detect potentially dangerous encounters as early as possible. Due to the limited number of monitoring sensors, continuous observation of all objects is impossible, resulting in the need to predict the orbital paths and their uncertainty via models to perform collision risk assessment and space object catalog maintenance. For many years the uncertainty models used for orbit determination neglected any uncertainty in the astrodynamic force models, thereby implicitly assuming them to be flawless descriptions of the true space environment. This assumption is known to result in overly optimistic uncertainty estimates, which in turn complicate collision risk analysis. The keynote of this doctoral thesis is to establish uncertainty realism for low Earth orbiting satellites via a physically connected quantification of the dominant force model uncertainties, particularly multiple sources of atmospheric density uncertainty and orbital gravity uncertainty. The resulting process noise models are subsequently integrated into classical and state of the art orbit determination algorithms. Their positive impact is demonstrated via numerical orbit determination simulations and a collision risk assessment study using all non-restricted objects in the official United States space catalogs. It is shown that the consideration of atmospheric density uncertainty and gravity uncertainty significantly improves the quality of the orbit determination and thus makes a contribution to future spaceflight safety by increasing the reliability of the uncertainty estimates used for collision risk assessment. / Die Sicherheit der künftigen Raumfahrt hängt von der Weltraumüberwachung und dem Weltraumobjektmanagement ab, da inzwischen die Dichte an Objekten im Erdorbit ein Niveau erreicht hat, welches regelmäßige Kollisionsvermeidungsmanöver erfordert um eine missions- oder, im Kontext der bemannten Raumfahrt, lebensgefährdende Situation zu vermeiden. Durch verbesserte Sensorsysteme, die in der Lage sind, zentimetergroße Objekte zu erkennen, Megakonstellationen und die Satellitenminiaturisierung hat das Weltraummüllproblem viele Parallelen zu den Plastikabfällen in unseren Weltmeeren offenbart, jedoch mit deutlich geringerer Sichtbarkeit für das Auge. Es ist zu erwarten, dass die Größe der Weltraumobjektkataloge in Zukunft drastisch ansteigen wird, was es umso wichtiger macht, potenziell gefährliche Begegnungen so früh wie möglich zu erkennen. Durch die begrenzte Anzahl an Überwachungssensoren ist eine kontinuierliche Beobachtung aller Objekte unmöglich, sodass die Umlaufbahnen und deren Unsicherheiten über Modelle vorausberechnet werden müssen, um die Bewertung von Kollisionsrisiken vorzunehmen und die Wartung der Objektkataloge sicherzustellen. Viele Jahre haben die zur Bahnbestimmung verwendeten Unsicherheitsmodelle jegliche Unsicherheit in den astrodynamischen Kräftemodellen vernachlässigt und somit implizit angenommen, dass diese fehlerfreie Beschreibungen der wahren Weltraumumgebung darstellen. Diese Annahme ist jedoch dafür bekannt, zu übermäßig optimistischen Unsicherheitsabschätzungen zu führen, was die Kollisionsrisikobewertung erschwert. Das Leitthema dieser Doktorarbeit ist die Berechnung realistischer Unsicherheiten von Objekten in einer niedrigen Erdumlaufbahn anhand einer Unsicherheitsquantifizierung mit physikalischem Bezug zu den Kräftemodellen, welche die größten Anteile an der Propagationsunsicherheit aufweisen. Dies sind insbesondere mehrere Quellen von atmosphärischer Dichteunsicherheit, sowie Gravitationsunsicherheit. Die resultierenden Prozessrauschmodelle werden anschließend in klassische und moderne Algorithmen zur Umlaufbahnbestimmung integriert. Die positiven Auswirkungen dieser Technik werden durch numerische Simulationen zur Orbitbestimmung, sowie durch eine Risikobewertungsstudie anhand aller nicht-sensitiven Objekte in den amerikanischen Weltraumkatalogen belegt. Es wird gezeigt, dass die Berücksichtigung von Unsicherheiten in der atmosphärischen Dichte und dem Gravitationsmodell die Qualität der Umlaufbahnbestimmung signifikant verbessert und somit durch zuverlässigere Unsicherheitsschätzungen bei der Kollisionsrisikobewertung einen Beitrag zur künftigen Sicherheit im Weltraum leistet.

Cosmological perturbation theory (CPT) is an important tool with which inhomogeneities that seed the observed structure of our universe can be studied. This thesis introduces the subject of CPT and discusses applications of this at both linear and second order. At linear order the evolution of the curvature perturbation around horizon crossing is examined. We study single field inflation models numerically, and compare the curvature perturbation at horizon crossing to that at the end of inflation. In addition, linear-order CPT is extended to the case of a multi-fluid system and an approximation for the velocities of the baryons and photons in the early universe as well as the strength of the electric field is found. We use second order CPT to study magnetogenesis. By using fully relativistic, non-linear CPT we show how magnetic fields are generated. This is done by presenting the first fully analytical calculation of the magnetic field at second order. Our results suggest that magnetic fields with strengths of the order of 10²⁷G and with scale dependence M ∝ k⁴ may be generated - findings which are largely in agreement with previous numerical results. We end by outlining possible extensions to this work, in particular related to the study of primordial magnetogenesis.

Cory S. Myers. / Originally presented as author's thesis (Ph. D.--Massachusetts Institute of Technology), 1986. / Bibliography: leaves 232-235. / Supported in part by the Advanced Research Projects Agency monitored by ONR under contract no. N00014-81-K-0742 Supported in part by the National Science Foundation under grant ECS-8407285 Supported in part by Sanders Associates, Inc and an Amoco Foundation Fellowship.

No description available.

Gravitational waves are considered as ripples in the curvature of space-time and were predicted by Einstein in his general theory of relativity. Gravitational waves interact very weakly with matter which makes them very difficult to detect. However, research groups around the world are engaged in building a network of ultra sensitive ground and space based interferometers for the first detection of these signals. Their detection will open a new window in the field of astronomy and astrophysics. The nature of gravitational waves is such that when incident on a particle, they stretch and squeeze the particle orthogonally thus producing a tidal strain. The strain amplitude expected for gravitational waves which may be detected on earth are of the order of hrms ~10-22 to 10-23 (over a frequency range from few Hz to a few kHz). A network of instruments based on the Michelson interferometer design currently exists around the world. These detectors are undergoing a major upgrade and once online by 2015-16 the improved sensitivity and increased sky coverage may lead to the first detection of the gravitational waves signals. The Institute for Gravitational Research in the University of Glasgow in collaboration with the Albert Einstein Institute in Hannover, Golm and the University of Cardiff has been actively involved in the research for the development of instruments and data analysis techniques to detect gravitational waves. This includes construction of a long ground based interferometer in Germany called GEO 600 (upgraded to GEO-HF) having an arm length 600 m and strong involvement in the larger detectors of the LIGO (Laser interferometer gravitational wave observatory) project in USA having arm lengths of 4 km (Operated by MIT, Boston and CALTECH, Pasadena). An upgrade to LIGO called Advanced LIGO (aLIGO) is currently under construction with significant input from the University of Glasgow. Thermal noise is one of the most significant noise sources affecting the sensitivity of the detector at a range of frequencies. Thermal noise arises due to the random fluctuations of atoms and molecules in the materials of the test mass mirrors and suspension elements, and is related to mechanical loss in these materials. The work presented in chapter 3 of this thesis is devoted to the analysis of aspects of mechanical loss and thermal noise in the final stages of the GEO suspension. GEO-600 is currently undergoing an upgrade to GEO-HF targeting sensitivity improvements in the kiloHertz region. However, the planned upgrade requires access to the vacuum tanks enclosing the fused silica suspension system. There is a risk of damaging the suspension, which has led to a repair scenario being developed in Glasgow, to reduce the downtime of the detector. An optimised design of the fused silica fibre has been proposed. A study of mechanical loss has been undertaken through Finite Element Analysis (FEA) modeling techniques. The mechanical loss of the optimised fibre is estimated to be lower than the original GEO fibre by a factor of ~4. In terms of thermal noise performance the optimised fibre gives an improvement of ~1.8. The repair scenario of the monolithic suspension has led to the development of tools and welding procedures. Three prototype suspensions involving metal masses were successfully built, before fabricating the monolithic fused silica suspension in Glasgow. The work in chapter 4 focuses on the theory of photoelasticty and birefringence techniques. The production and use of various forms of polarised light has been discussed. A setup of plane and a circular polariscope using two polarisers and two-quarter wave plates has been shown. The retardation of light due to the birefringence in the sample can be measured using the Tardy method of compensation and a Babinet-Soleil compensator. Finally a discussion on the stress-optic law has shown that the relative stress in a sample can be measured once the retardance is known. The silica fibres in the aLIGO detector would be laser welded using a 100 W CO2 laser. The laser welding would lead to high temperature and development of thermal gradients. This could result in residual thermal stress in fused silica, which could lead to an additional mechanical loss. A study of mechanical and thermal stress induced in fused silica has been discussed in chapter 5 of this thesis. To understand the working of photoelastic techniques learned in chapter 4, a study of mechanical stress was undertaken by applying a load on the sample to induce temporary birefringence. The estimated values of stress showed a good agreement when compared with the theoretical predictions and FEA modelling. Thermal stress was induced in fused silica by applying a 25 W CO2 laser beam for 10 seconds and the relative stress was measured using photoelastic birefringence techniques. Thermal modelling of the stressed sample was performed using the techniques developed in FEA. The experimental values show a good agreement with the estimated 1st principal stress (FEA model) and equivalent stress. A study of thermal stress in fused silica welds has also been presented in chapter 5. Two fused silica samples were welded using CO2 laser welding and the relative stress at different points were measured. The stress in the weld region was measured to be relatively lower than other areas. At a distance of 3 mm away from the weld line the maximum stress was measured which was greater than the stress in the weld region by a factor of ~5. The work discussed in chapter 6 focuses on the study of the suspension thermal noise in aLIGO detector for applying incremental upgrades. To further enhance the sensitivity of the aLIGO detector, incremental upgrades could be applied to the suspension system to improve the thermal noise. The incremental upgrades focused on two aspects: improving the dissipation dilution factor, and obtaining a lower mechanical loss than the aLIGO baseline. Based on the results from FEA, two designs were compared, each having a suspension of length 100 cm but different stock diameter - 3mm and 5 mm. A comparison with the aLIGO baseline showed that these two models obtained a lower mechanical loss by a factor of 3.4 to 6.8. In terms of suspension thermal noise there was an improvement by factor of 2.5 to 3.7, which could lead to rise in the sensitivity of the detector by a factor of 2.5.

Background: Large-scale expansion of myogenic progenitors is necessary to support the development of high-throughput cellular assays in vitro and to advance genetic engineering approaches necessary to develop cellular therapies for rare muscle diseases. However, optimization has not been performed in order to maintain the differentiation capacity of myogenic cells undergoing long-term cell culture. Multiple extracellular matrices have been utilized for myogenic cell studies, but it remains unclear how different matrices influence long-term myogenic activity in culture. To address this challenge, we have evaluated multiple extracellular matrices in myogenic studies over long-term expansion. Methods: We evaluated the consequence of propagating mouse and human myogenic stem cell progenitors on various extracellular matrices to determine if they could enhance long-term myogenic potential. For the first time reported, we comprehensively examine the effect of physiologically relevant laminins, laminin 211 and laminin 521, compared to traditionally utilized ECMs (e.g., laminin 111, gelatin, and Matrigel) to assess their capacity to preserve myogenic differentiation potential. Results: Laminin 521 supported increased proliferation in early phases of expansion and was the only substrate facilitating high-level fusion following eight passages in mouse myoblast cell cultures. In human myoblast cell cultures, laminin 521 supported increased proliferation during expansion and superior differentiation with myotube hypertrophy. Counterintuitively however, laminin 211, the native laminin isoform in resting skeletal muscle, resulted in low proliferation and poor differentiation in mouse and human cultures. Matrigel performed excellent in short-term mouse studies but showed high amounts of variability following long-term expansion. Conclusions: These results demonstrate laminin 521 is a superior substrate for both short-term and long-term myogenic cell culture applications compared to other commonly utilized substrates. Since Matrigel cannot be used for clinical applications, we propose that laminin 521 could possibly be employed in the future to provide myoblasts for cellular therapy directed clinical studies.

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Αντικείμενο της παρούσης διπλωματικής εργασίας αποτελεί το Φωτοβαρυτικό Πρόβλημα των Τριών Σωμάτων, ένα άλυτο πρόβλημα που απασχόλησε και εξακολουθεί να απασχολεί τον τομέα των Εφαρμοσμένων Μαθηματικών και της Κλασικής Αστροφυσικής τουλάχιστον τους τελευταίους δύο αιώνες. Διεξάγεται μελέτη των σημείων ισορροπίας του συστήματος και προσδιορίζονται οικογένειες περιοδικών λύσεων, οι οποίες στην περίπτωσή μας διακρίνονται σε δύο κατηγορίες που χαρακτηρίζονται από το μέγεθος της περιόδου τους. / The topic of this thesis deals with the Restricted Photogravitational Three Body Problem, which is an unsolved problem in Astrophysics and Celestial Mechanics. Research is carried out concerning the equilibrium points, around which families of periodic solutions can be identified.