Experimental Analysis about Heat Treatment Distortion in Bearing Race

It’s well known that the vehicle fuel economy is improved by reducing the weight of their structural and mechanical components. Therefore, there is a demand of bearing race with thin thickness for weight reduction. But, this thickness reduction also causes a large oval distortion in bearings after Heat Treatment (HT). The factors affecting the HT distortion are extremely complicated, which makes it difficult to do rectification only by experimental analysis. There is also a limitation in numerical analysis due to the lack of workable model for HT distortion. Therefore, the aim of this study is to identify the effective factors of HT distortion by experimental approach in order to build suitable numerical simulation model that can estimate HT distortion. The material used in this study is a conventional case-hardened steel (Fe-0.4mass%C-Cr-Mn). The ring with the diameter of 100mm is heat treated and quenched. The resulting HT distortion is evaluated by measurement of maximum and minimum diameter of the race. A jig was developed to correct the ring shape during heat treatment, which helped in identifying that the quenching affects more than 50% of HT distortion. From these results, we developed a cooling equipment to reproduce inhomogeneous cooling rate by controlling oil flow toward the exterior of the ring. The quenching with this equipment reveals that inhomogeneous flow with opposite side (0 degree and 180 degree) reproduces a large oval distortion. The data obtained from the experimental analysis is suitable for developing the numerical model for HT distortion.

Gas Dynamics and Active Phenomena in Galactic Nuclei: M100 and M94

Since molecular gas fuels AGNs and molecular clouds form stars, understanding of molecular gas dynamics is a key to the understanding of active phenomena (such as starbursts and AGNs) in galactic nuclei. To study gas dynamics in weakly barred galaxies, we made CO interferometry (to trace gas) and NIR imaging (to trace stars) toward two nearby SAB galaxies M100 and M94. Each galaxy has a small stellar nuclear bar and also has an outer bar or oval distortion, thus suitable for the study of gas dynamics in a barred gravitational potential. Observations were made using Nobeyama Millimeter Array (NMA) and the IRcamera PICNIC installed at the ISAS 1.3 m telescope.

O/H Abundances in the Ringed Galaxy NGC 4736: Mixing Processes in the Interstellar Medium

Imaging spectrophotometry in the main nebular lines has been performed on 65 H ɪɪ regions in the ringed galaxy NGC 4736. O/H abundances were derived using the line ratios [O ɪɪɪ]/Hβ and [N ɪɪ]/[O ɪɪɪ] calibrated by Edmunds & Pagel (1984). We show that the O/H scatter in the resonance ring of star forming regions is small, no greater than normally expected in the well-mixed ISM of disks of gas-rich galaxies. The global O/H gradient (−0.046 dex/kpc) in the disk of NGC 4736 is shallower than gradients of normal spirals but comparable to gradients observed in weakly barred spirals. This last result could indicate that radial mixing is or was present in NGC 4736. The oval distortion in the central regions can be responsible for this homogenization but it is also possible that a strong bar was present in the past.

A Possible Evolutionary Scenario for NGC 7217

NGC 7217 is an ordinary spiral galaxy with three rings whose size ratios are such that they can be associated with resonances, as for barred spirals. From 21-cm HI line data and BVRI CCD-images of this galaxy we find (cf. Verdes-Montenegro et al. 1995) : 1) a nuclear ring strong in Hα, 2) an inner ring seen clearly in a B - I colour map, and 3) an outer ring, with blue colours and strong HI-emission. After deprojection the disk has a mean ellipticity of 0.04 ± 0.01, while the position angle of the deprojected galaxy changes suddenly at 65″ radius, where the minor axis becomes major axis. Thus a very mild oval distortion could exist, with the outer ring perpendicular to the oval. Merrifield and Kuijken (1994) find from the stellar kinematics that about 20 – 30 % of the stars are in retrograde orbits.

On the 3-Kpc arm: waves excited at the resonance by an oval distortion in the central region

A relatively minor oval distortion in the central region of the Galaxy, turning at a representative angular pattern speed, can excite outgoing waves at the outer Lindblad resonance of that pattern speed. Associated with the density crest of these waves is fast-expanding gas flow. The physical basis of this phenomenon can be understood through a linear analysis. However, to explain the observed expanding velocity in the “3-kpc arm”, the non-linear theory must be used. In our calculations an oval distortion turning at 118 km s-1 kpc-1 with a perturbation of 10% of the mean gravitational field at the outer Lindblad resonance (located at 3 kpc in the present case) can generate an outgoing velocity of 53 km s-1 at the first density crest of the wave (located at 3.6 kpc).