Research Outputs
Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2
Browse
6 results
Search Results
Publication Metadata only Constraining scalar-tensor theories using neutron star mass and radius measurements(American Physical Society (APS), 2022) Tuna, Semih; N/A; Department of Physics; Ünlütürk, Kıvanç İbrahim; Ramazanoğlu, Fethi Mübin; PhD Student; Faculty Member; Department of Physics; Graduate School of Sciences and Engineering; College of Sciences; N/A; 254225We use neutron star mass and radius measurements to constrain the spontaneous scalarization phenomenon in scalar-tensor theories using Bayesian analysis. Neutron star structures in this scenario can be significantly different from the case of general relativity, which can be used to constrain the theory parameters. We utilize this idea to obtain lower bounds on the coupling parameter ?? for the case of massless scalars. These constraints are currently weaker than the ones coming from binary observations, and they have relatively low precision due to the approximations in our method. Nevertheless, our results clearly demonstrate the power of the mass-radius data in testing gravity, and can be further improved with future observations. The picture is different for massive scalars, for which the same data is considerably less effective in constraining the theory parameters in an unexpected manner. We identify the main reason for this to be a large high-likelihood region in the parameter space where deviations from general relativity are relatively small. We hope this initial study to be an invitation to use neutron star structure measurements more commonly to test alternative theories in general.Publication Metadata only Electric propulsion optimization of microsatellite moon missions preliminary design application on CubeSats and Turkish small satellite field(International Astronautical Federation (IAF), 2014) N/A; N/A; Department of Mechanical Engineering; Kara, Ozan; Karabeyoğlu, Mustafa Arif; PhD Student; Faculty Member; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; N/A; 114595Subsystems miniaturization of spacecraft is making scientific microsatellite missions feasible. Specifically interplanetary space exploration mission can be provided by onboard micro propulsion systems. Due to the low requirements, Moon is a feasible destination for a preliminary space mission that universities, companies and governments can perform. This paper addresses the optimization of an electric propulsion system for a potential microsatellite lunar mission. Optimization takes the thrust level as a free variable to find the minimum initial mass along with the associated total burn time. The initial thrust range is chosen between 0.5-6mN. For a given thrust value, corresponding specific impulse, thruster power and thruster mass are determined based on curve fittings. As the next step, the input thrust level is extended up to 42mN to observe optimization over a broader thruster size. A feasible low thrust continuous orbit transfer to the Moon requires a high ΔV which is over 7,000 m/s. Edelbaum's analysis with optimal control theory is utilized to estimate the ΔV value. Edelbaum presents an approach for two non-coplanar circular orbits without any perturbations and shadowing effects. Furthermore, the optimization approach is applied for the preliminary design of a CubeSat Moon Mission. The spacecraft is determined to have an initial mass of 12 kg and requires a total power up to 100W. The particular mission selected for the study starts at 700km LEO and finishes at 200 km LLO. In addition, preliminary mission design presents (1) mass and power budgets, (2) thermal analysis, (3) ADCS selection, (4) structure and array mechanisms, and (5) cost estimation. In this paper, previous and planned small satellite researches in Turkey have also been reviewed. Small satellite projects which are performed by government, universities and industries show that Turkey has a small but growing small satellite activity.Publication Metadata only Findings from IAC 2013 Young Professional Workshop: tools and project organization methodologies that can be implemented into the space sector from other industries(International Astronautical Federation (IAF), 2014) Stube, Kevin; Wood, Danielle; Svoboda, Jan; Li, Rui; Fuse, Tetsuhito; Kukhta, Andrii; N/A; Kara, Ozan; PhD Student; Graduate School of Sciences and Engineering; N/AApplied technologies in space sector are performing complicated and challenging projects in comparison other industries. This complexity in the space sector requires new alternatives for business management and project development. Therefore, management strategies in an organization directly affect the project achievements. Project applications, improvement of economic earnings, relations among people in an organization, mentorships, motivation factors and international activities are other significant issues which are really crucial for space sector. To discuss these important issues, we were one of five groups at International Astronautical Congress, Young Professional Workshop in Beijing, 20th September 2013. Our relevant group topic was "What tools and project organization methodologies have been and can be implemented into the space sector from other industries and the YPs' experience (e.g. software, automotive)?". As a group we have met several times prior to the workshop. Many ideas are emerged in consequence of meetings. Pre-meeting report helped us to prepare individual materials as members thru the workshop. These different reflections were: (1) agile software and engineering issues, (2) process improvement techniques and learning from manufacturing by multiple copies of the same space platform, (3) social activities of organizations for the internal motivation, (4) TRL improvement, (5) project management and system engineering certification the examples from NASA APPEL and Aerospace Corporation, (6) technology transfer among sectors just as military-space and biology-space, (7) Experience assessment of JAXA, (8) software tools that are being used across industries. During the workshop, we simplified these findings and made the final presentation. In addition, preliminary survey questions are listed and determined after the workshop. Finally, common grounds in our final report are summarized as (1) Software development tools, (2) Process improvement techniques, (3) Project management, system engineering education and certification, (4) Company organization structures and (5) Social Activities to improve sector interest. In the final report, group recommendations are given for the each topic and presented to the IAF YP Committee.Publication Metadata only Inducing gravity from connections and scalar fields(Iop Publishing Ltd, 2019) N/A; Azri, Hemza; Resarcher; Graduate School of Sciences and Engineering; N/AWe propose an approach to induced gravity, or Sakharov's 'metrical elasticity', which requires only an affine spacetime that accommodates scalar fields. The setup provides the induction of metric gravity from a pure (One action, and it is established in two possible ways: (i) at the classical level, the Einstein-Hilbert action arises with both, metric and Newton's constant, from the nonzero potential energy of the background field (ii) at the quantum level (quantized matter), gravity scale is induced from the one-loop effective action by integrating out the scalar degrees of freedom. In the former, the cosmological constant is absorbed leading to the gravitational sector, however, the fact remains that quantum corrections induce a large cosmological constant. This new approach adds a crucial feature to induced gravity which is the fact that the metric structure is not imposed from the scratch, but it is an outcome of the primary theory.Publication Metadata only Supersymmetry of PT-symmetric tridiagonal hamiltonians(World Scientific Publ Co Pte Ltd, 2021) N/A; Almasri, Mohammad Walid; PhD Student; Graduate School of Sciences and Engineering; N/AWe extend the study of supersymmetric tridiagonal Hamiltonians to the case of non-Hermitian Hamiltonians with real or complex conjugate eigenvalues. We find the relation between matrix elements of the non-Hermitian Hamiltonian H and its supersymmetric partner H+ in a given basis. Moreover, the orthogonal polynomials in the eigenstate expansion problem attached to H+ can be recovered from those polynomials arising from the same problem for H with the help of kernel polynomials. Besides its generality, the developed formalism in this work is a natural home for using the numerically powerful Gauss quadrature techniques in probing the nature of some physical quantities such as the energy spectrum of PT-symmetric complex potentials. Finally, we solve the shifted PT-symmetric Morse oscillator exactly in the tridiagonal representation.Publication Metadata only Systems advantages of electric pump fed upper stage hybrid rocket(International Astronautical Federation (IAF), 2018) N/A; Department of Mechanical Engineering; N/A; Gegeoğlu, Kaan; Karabeyoğlu, Mustafa Arif; Kara, Ozan; Master Student; Faculty Member; PhD Student; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; College of Engineering; Graduate School of Sciences and Engineering; N/A; 114595; N/APropellant feed systems in liquid rocket engines deliver fuel and oxidizer from tanks to the combustion chamber at required flow rate and pressure. In hybrid rockets, only the liquid propellant is fed into the combustion chamber where solid propellant resides. The feed system has also a critical role for performance especially at upper stages of launch vehicles. There are two conventional feed system architectures that are mostly used. One employs a turbo pump while the other uses tank pressure to feed propellants. Briefly, propellant pumps are used in high pressure and high performance applications; however using turbo pumps makes design more complex and heavy. In contrast, the pressure fed system has simpler design although it is limited to low chamber pressures since high-pressure requirements make propellant tanks heavy. In addition there is a constant need for making elements such as tanks, valves, feed lines and pressurization devices lighter, simpler and more efficient. With advancing technologies in electric motor and batteries, electric pump feed system as an alternative to conventional feed system types has started to emerge. Most of the hybrid rocket applications evade turbo pumps since it requires carrying at least one another liquid propellant to drive turbines. Therefore, the performance of electric pump fed system over traditional pressure fed system is analyzed in this research on an upper stage of hybrid rocket engine. For this purpose, an optimization procedure has been applied on both systems and ∆V values as performance parameter are compared. on missions utilizing electric pump fed system, a noticeable improve of ∆V by 6.6% is reported. Optimization showed that longer burn times are also in the favor of electric pump fed systems.