Threshold between Spontaneous and Cloud-Collisional Star Formation

Based on simple physical and geometric assumptions, we have calculated the mean surface molecular density of spiral galaxies at the threshold between star formation induced by cloud-cloud collision and spontaneous gravitational collapse. The calculated threshold is approximately $\log \Sigma_\mathrm{crit} \sim 2.5$, where \Sigma \quad \mathrm{M_{\solar}}\cdot \mathrm{pc}^{-2} is the observed surface mass density of an assumed flat gas disk. Above this limit, the rate of molecular cloud collisions dominates over spontaneous molecular cloud collapse. This model may explain the apparent discontinuity in the Schmidt law found recently at $2 \lesssim \log \Sigma \lesssim 3$.Comment: Accepted for publication in PAS

Experimental study on vascular graft. I. Replacement of inferior vena cava with crimped woven Tetoron (polyester) grafts and those reinforced with stainless steel coil

Experimental replacement of inferior vena cava with crimped woven Tetoron arterial graft was performed in dogs. Bypass-graft to thoracic inferior vena cava was not successful in two animals. Total repacement of thoracic inferior vena cava was attempted in four animals, and thoracoabdominal long implantation to inferior vena cava through diaphragm behind liver, followed by excision of thoracic inferior vena cava between the anastomoses, was done in 12 animals. Of these 16 animals, the graft was patent or not occluded in nine at autopsy between the 30th and the 451st day after implantation. Similar thoracoabdminal implantation of a graft reinforced with a steel coil was made in seven animals. Two grafts were patent at autopsy after 37 and 251 days, respectively. Abdominal vena cava replacement with a graft reinforced with a coil was undertaken in three animals. Two grafts were patent at autopsy after 117 and 142 days, respectively. On the whole, long term survival without occlusion over 30 days was obtained in fifteen/twenty-eight animals. Aside from the instances of simple bypassgraft and obvious technical errors in early experiments, it was in fifteen/ eighteen, and the graft was completely patent in ten/eighteen animals. The failures within 30 days resulted mostly from either lung complications or technical errors, and the latter were remarkable in the thoracoabdominal group where the graft reinforced with coil was used, but the application of the coil was very effective in protecting the graft against the compression by the adjacent organs. Tissue reaction to Tetoron was not noticeable and to the silk thread it was very slight and seemed not to affect long term success. By the present method even the total replacement of theracic inferior vena cava can be performed safely under normothermia and thoracoabdominallong implantation to inferior vena cava is also possible with considerable success. In order to prepare a more suitable synthetic graft for vein, it requires further search for harder, lighter, more elastic and physicochemically more stable material. The fabric of venous graft should be preferably more porous and thinner than that of the arterial graft available at the present in order to make the organization within the shortest time possible.</p

Experimental study on vascular graft. II. Replacement of inferior vena cava and abdoninal aorta with the autogenous segment of small intestine submucosa

Replacement of abdominal vena cava with a fresh autogenous substitute, the segment of small intestinal submucosa, was attempted in 15 animals. Five segments were prepared from the intestine smeared with iodine tincture, and reinforced with a steel coil externally in the entire length and a steel or polyethylene ring at the anastomosis. Thoracoabdominal long implantation was done in three animals, of which one with the intestinal segment devoid of mucosa, and the other two with the submucosa. Replacement of abdominal vena cava with the submucosa taken out of the intestinal segment preserved for nine days in 1% mercurochrome solution, or 0.1 % acrinolum solution was done in one animal each. In these two a coil and two rings were also applied. Replacement of abdominal aorta with the double layer tube of a reconstructed submucosa and another very porous Tetoron gauze was done in two animals, each coupled with the abdominal vena cava replacement at the same time. Of these experiments, aorta replacements were nearly patent in both. The abdominal vena cava replacements made of the submucosa treated with iodine tincture were patent in three. The one that was preserved in acrinolum showed moderate constriction. Most of the others were also observed for a long period of time but these all occluded in spite of the initial patency which was revealed at three to seven days in cavograms, and the time of the occlusion was not determined. The internal surface of the segment of submucosa, being implanted, is covered in the first stage with the deposition of fibrin, which is subsequently organized into a fibrous layer, in the same manner as that of the synthetic graft. Another disadvantage of this substitute is its readily collapsible tendency. Infection is preventable in the experiment. The substitute seems to be useful for the replacement of aorta and for the short segment of vena cave.</p

The Schmidt Law at High Molecular Densities

We have combined Halpha and recent high resolution CO(J=1-0) data to consider the quantitative relation between gas mass and star formation rate, or the so-called Schmidt law in nearby spiral galaxies at regions of high molecular density. The relation between gas quantity and star formation rate has not been previously studied for high density regions, but using high resolution CO data obtained at the NMA(Nobeyama Millimeter Array), we have found that the Schmidt law is valid at densities as high as $10^3 \mathrm{M_\odot} \mathrm{pc}^{-2}$ for the sample spiral galaxies, which is an order of magnitude denser than what has been known to be the maximum density at which the empirical law holds for non-starburst galaxies. Furthermore, we obtain a Schmidt law index of $N=1.33\pm0.09$ and roughly constant star formation efficiency over the entire disk, even within the several hundred parsecs of the nucleus. These results imply that the physics of star formation does not change in the central regions of spiral galaxies. Comparisons with starburst galaxies are also given. We find a possible discontinuity in the Schmidt law between normal and starburst galaxies

Molecular Gas Evolution across a Spiral Arm in M 51

We present sensitive and high angular resolution CO(1-0) data obtained by the Combined Array for Research in Millimeter-wave Astronomy (CARMA) observations toward the nearby grand-design spiral galaxy M 51. The angular resolution of 0.7" corresponds to 30 pc, which is similar to the typical size of Giant Molecular Clouds (GMCs), and the sensitivity is also high enough to detect typical GMCs. Within the 1' field of view centered on a spiral arm, a number of GMC-scale structures are detected as clumps. However, only a few clumps are found to be associated with each Giant Molecular Association (GMA), and more than 90% of the total flux is resolved out in our data. Considering the high sensitivity and resolution of our data, these results indicate that GMAs are not mere confusion of GMCs but plausibly smooth structures. In addition, we have found that the most massive clumps are located downstream of the spiral arm, which suggests that they are at a later stage of molecular cloud evolution across the arm and plausibly are cores of GMAs. By comparing with H-alpha and Pa-alpha images, most of these cores are found to have nearby star forming regions. We thus propose an evolutionary scenario for the interstellar medium, in which smaller molecular clouds collide to form smooth GMAs at spiral arm regions and then star formation is triggered in the GMA cores. Our new CO data have revealed the internal structure of GMAs at GMC scales, finding the most massive substructures on the downstream side of the arm in close association with the brightest H II regions.Comment: accepted for publication in Ap

Efficacy of interferon retreatment on interferon-resistant patients with chronic hepatitis C.

Chronic Hepatitis C can progress to end-stage liver cirrhosis or hepatocellular carcinoma. Interferon (IFN) therapy is effective in clearing the hepatitis C virus and in improving liver histology, however, few patients maintain a sustained response (SR) after IFN withdrawal. Immediate retreatment with IFN is therefore considered to be both effective and necessary, especially for patients who do not respond to the initial course of IFN therapy. All 145 patients included in the present study underwent liver biopsy, followed by a first treatment course with various IFNs (alpha2a, alpha2b, alpha, OIF or beta). If hepatitis C virus (HCV) RNA was positive after the first treatment, the patient was assigned to one of 3 groups, depending on whether his or her alanine transaminase (ALT)level was normalized (incomplete response, IR), partially responsive(PR), or non-responsive (NR). After an observational interval of 6 to 76 months, a second IFN treatment was initiated with a higher dose or the same dose of the same IFN for the IR group, and with a different IFN for the PR and NR groups. At 6 months after retreatment with IFN, the overall efficacy of the retreatment was 29.7.% In the case of the IR group, who received the same IFN, the overall efficacy was 45.2%. In patients identified as non-SR after the first treatment, who received a different type of IFN for retreatment, the overall efficacy was 18.6%. Anti-IFN antibody was not detected in most of the breakthrough cases. For some IR patients, retreatment with the same IFN was effective. Anti-IFN antibody was mostly negative, indicating that the same IFN can be used in both the first treatment and retreatment to obtain an SR. Switching to a different IFN was effective for some PR and NR patients, suggesting that changing IFN for such cases is a good therapeutic choice.</p