Statistical space velocity distributions, gravitation field strength and vertex deviation for nearby young stars, using density wave theory of galactic spirals

Three theoretical problems concerning the large scale structure of disk galaxies in general, and the Milky Way System, in particular, were proposed to study. They are, namely, modes of spiral density waves, evolutionary change of the abundance distribution of the gas in the Milky Way System and the motions of the cloud medium behind the large scale galactic shock.

Under the influence of a spiral gravitational field, there should be differences among the mean motions of different types of objects with different dispersion velocities in a sipral galaxy. The old stars with high dispersion velocity should have essentially no mean motion normal to the galactic rotation. On the other hand, young objects and interstellar gas may be moving relative to the old stars at a velocity of a few kilometer per second in both the radial (galacto-centric), and circular directions, depending on the spiral model adopted. Such a velocity is usually referred as the systematic motion or the streaming motion. The conventionally adopted local standard of rest is indeed co-moving with the young objects of the solar vicinity. Therefore, it has a net systematic motion with respect to the circular motion of an equilibrium ga...

Under the influence of a spiral gravitational field, there should be differences among the mean motions of different types of objects with different dispersion velocities in a spiral galaxy. The old stars with high dispersion velocity should have essentially no mean motion normal to the galactic rotation. On the other hand, young objects and interstellar gas may be moving relative to the old stars at a velocity of a few kilometer per second in both the radial (galacto-centric), and circular directions, depending on the spiral model adopted. Such a velocity is usually referred as the systematic motion or the streaming motion. The conventionally adopted local standard of rest is indeed co-moving with the young objects of the solar vicinity. Therefore, it has a net systematic motion with respect to the circular motion of an equilibrium ga...

The mechanism responsible for the massive rapidly expanding Galactic feature known as the 3-kpc arm (Rougoor and Oort, 1960) is investigated theoretically in the framework of a density-wave model of the Galaxy. The arm is attributed to outgoing waves excited at the outer Lindblad resonance (OLR) of a small rotating oval distortion near the Galactic center. Linear and nonlinear models are developed, and it is shown that a density crest at 3.5 kpc with expansion velocity 53 km/s can be generated by a distortion turning at 118 km/s kpc with a 10-percent perturbation of the main gravitational field at the OLR (located at 3 kpc). The wave character of the nonlinear solution is found to be the same as that of the linear solution and to give good agreement with the observations in terms of expansion velocity, size, shape, and mass; only the o...

Designing a fuselage involves many considerations such as strength and stability, fatigue, damage tolerance, fire and lightning resistance, thermal and acoustic insulation, production, inspection, maintenance and repair. In the background of the application of composite sandwich structures on the aircraft fuselage, the focus of the thesis is to investigate the vibration and acoustic behaviours of sandwich structures.
As a preliminary design of aircraft fuselages, a sizing work of sandwich cylinders was conducted with respect to the strength and stability. FE models for the buckling prediction of the sandwich cylinder were validated with the analytical expressions. Under a typical flight loading, the sizing results of a sandwich cylinder and a laminated cylinder were compared and it was found that the mechanical efficiency of the sandwi...

We give the helicity amplitudes for the process , and examine the validity of the equivalence theorem by comparing longitudinal W scattering with the corresponding unphysical Higgs scattering. We also study the production rates of fourth-generation heavy leptons and neutrinos in the effective W approximation.

This dissertation presents a new Bayesian rain rate retrieval algorithm for the TRMM Microwave Imager (TMI), along with associated error analysis of synthetic sensitivity tests and real-world applications. The Bayesian approach offers a rigorous way of optimally combining the actual multichannel observations with prior knowledge. It has been applied in many studies to retrieve instantaneous rain rates from microwave radiances. However, this is believed to be the first self-contained algorithm whose output is not just a single rain rate, but rather continuous posterior probability distributions of the rain rate. ^ The success of the Bayesian algorithm depends on the accuracy of both the conditional probability density function (pdf) of microwave observations and the prior pdf of rain rate, as well as on the interpretation of the poste...