The effect of Shapiro delay on pulsar timing

Light passing near a massive object (star) will take longer to arrive at the Earth than it would if the object was not present. This additional time is called the Shapiro delay. In globular clusters, where there are millions of stars, the cumulative effect of the Shapiro delay from these stars will affect pulsar timings by introducing an additional noise term. This effect has been previously assumed to be small, yet no definite investigation has been done to determine its magnitude. In this thesis a model of the globular cluster 47 Tucanae was created in order to determine the effect of the change in Shapiro delay (called the Shapiro noise) for an observed duration of 3600 days -- the current longest observation period for pulsar timing. This noise was then added to the pulsar time of arrival (TOA) as the only noise source in pulsar timing. A polynomial fit was then used to subtract the first two orders from the pulse arrival time (the f and \dot{f} terms) to determine the timing residuals. This model was then realised 100 times to obtain the average root mean square (RMS) timing residual for every pulsar. The model showed that the Shapiro noise has a significant, and observable effect on pulsar timing, especially for pulsars situated close to the core of the globular cluster. From the model the average RMS timing residuals were of the order of 10^{-5} to 10^{-7} seconds and the variance of the RMS timing residuals were significantly larger in magnitude, ranging from 10^{-4} to 10^{-7} seconds for every pulsar. The importance of this result motivated further investigation of the stellar distribution of the globular cluster. In addition an investigation on how the effect of gravitational acceleration (produced by stars situated close to the pulsar) affects pulsar timing residual was also done. While the acceleration has an effect, the effect is smaller than that of the Shapiro noise. From the timing residuals produced by the Shapiro noise, it was then discussed whether any star close to the LOS would have an affect on the pulsar timing residuals. From additional simulations it was determined that stars anywhere along the LOS will have an affect on pulsar timing, however the stellar density of such a region would have to be greater than \rho_{min} > 10^{5} M_{\sun} pc^{-3}. The implications of this result for other pulsars in (other) globular clusters is discussed

Visual Systems & Control on Polynomial Space and Its Application to Sloshing Problems

This paper proposes a novel approach for camera-based modeling and control for a large class of continuous systems and the validity is confirmed by liquid sloshing experiments. It is an unsolved problem to design a model-based control in nonplanar sloshing cases. This is because the whole shape of the liquid surface is a complex curve (a set of an infinite number of points) in coordinate spaces. This paper solves this problem. First, the whole shape of the liquid surface corresponding to the output measured by a camera is a single point in a polynomial space as well as the input and the state. Second, without any physical parameter identification, input-output modeling on polynomial space, unlike existing types of modeling, captures the whole dynamics even in nonplanar sloshing cases and is linked to design of implementable controllers. Finally, in the presence of occlusion, the nonplanar sloshing is controlled well by state estimation on polynomial space without adding any image processing technology.ArticleIEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY. 22(6):2176-2187 (2014)journal articl

Visualization of Hydraulic Cylinder Dynamics by a Structure Preserving Nondimensionalization

Date of Online Publication: 10 July 2018This paper reveals a new simplicity of nominal hydraulic cylinders whose original representation suffers from the many physical parameters. The 8-dimensional parameter space in the original representation is reduced to the 3-dimensional parameter space in the proposed nondimensional representation preserving the parametric structure. To clarify comprehensive relations between the nonlinear dynamics and the many physical parameters, an advanced direct search approach is suggested. More precisely, we can repeat the fast computations of the nonlinear dynamics and the updates of the only three parameters without verifying any new simulator. The efficient visualization of the numerical solutions presents the best possible result corresponding to the analytical solution.ArticleIEEE-ASME TRANSACTIONS ON MECHATRONICS. 23(5):2196-2206 (2018)journal articl

Passivity based force control of hydraulic robots

This paper gives a new nonlinear force control of hydraulic robots. Unlike the electrical robots, hydraulic robots are governed not only by the energy conservation but also by the mass conservation. First we propose a generalized continuity law and a canonical form of hydraulic robots. Second, we propose a new nonlinear robust force control based on passivity in order to achieve the desired force in the presence of unknown environment consisting of the energy storing elements and dissipative elements. Finally, we confirm the validity of our proposed methods by simulation and experiment

η′\eta^\prime meson under partial restoration of chiral symmetry in nuclear medium

In-medium modification of the eta' mass is discussed in the context of partial restoration of chiral symmetry in nuclear medium. We emphasize that the U_A(1) anomaly effects causes the eta'-eta mass difference necessarily through the chiral symmetry breaking. As a consequence, the eta' mass is expected to be reduced by order of 100 MeV in nuclear matter where about 30% reduction of chiral symmetry takes place. The strong attraction relating to the eta' mass generation eventually implies that there should be also a strong attractive interaction in the scalar channel of the eta'-N two-body system. We find that the attraction can be strong enough to form a bound state.Comment: 4 pages, 3 figures. Talk given at the XI International Conference on Hypernuclear and Strange Particle Physics (HYP2012), Oct. 1-5, 2012, Barcelona, Spain. Accepted version. Some typos were correcte

Visual Feedback Without Geometric Features Against Occlusion: A Walsh Basis

Date of Online Publication: 09 January 2018For a visual feedback without geometric features, this brief suggests to apply a basis made by the Walsh functions in order to reduce the off-line experimental cost. Depending on the resolution, the feedback is implementable and achieves the closed-loop stability of dynamical systems as long as the input-output linearity on matrix space exists. Remarkably, a part of the whole occlusion effects is rejected, and the remaining part is attenuated. The validity is confirmed by the experimental feedback for nonplanar sloshing