Bar dissolution in non-spherical halos

Dynamical evolution of N-body bars embedded in spherical and prolate dark matter halos is investigated. In particular, the configuration such that galactic disks are placed in the plane perpendicular to the equatorial plane of the prolate halos is considered. Such a configuration is frequently found in cosmological simulations. N-body disks embedded in a fixed external halo potential were simulated, so that the barred structure was formed via dynamical instability in initially cool disks. In the subsequent evolution, bars in prolate halos dissolved gradually with time, while the bar pattern in spherical halos remained almost unchanged until the end of simulations. The e-folding time of bars suggest that they could be destroyed in a time smaller than a Hubble time. This revised version was published online in August 2006 with corrections to the Cover Date.     

CS,C34S,and CH3OH observations of the molecular cloud associated with NGC 7538

CS(J=1–0), C³⁴S(J=1–0), and CH₃OH(1₀–0₀A and E) emission lines in the core region of molecular cloud associated with NGC 7538 have been surveyed at angular resolution of 33. Distribution of CS column density shows two prominent peaks. Both blue and red wings in CS line are most prominent at 30 northwest of IRS 11.Paper presented at the IAU Third Asian-Pacific Regional Meeting, held in Kyoto, Japan, between 30 September–6 October, 1984.This work was carried out under the common use observation program at the Nobeyama Radio Observatory (NRO). NRO, a branch of the Tokyo Astronomical Observatory, University of Tokyo, is a cosmic radio observing facility open to outside users.     

Seasonal and Spatial Variations of Total Mass Flux around Coral Reefs in the Southern Ryukyus,Japan

Total mass flux, size distribution of sediment particles and some chemical components such as total carbon (TC), total nitrogen (TN) and calcium carbonate (CaCO₃) were monitored monthly using a multi-cup sediment traps at seven coral reef sites (6 reef flat and 1 reef slope) of the Marine Protected Areas around Ishigaki, Kohama, Kuroshima and Iriomote Islands in the southern Ryukyus, Japan from September 2000 to September 2001. The size distribution of trapped sediments revealed mostly uni-modal fine sand to mud in the reef flat and gravelly to coarse sand in the reef slope. The total mass flux ranged between 0.54 to 872 gm⁻²d⁻¹, and showed a pronounced seasonality (high in summer-autumn and low in spring) at each site, which was consistent with the rainfall and typhoon regime. Exceptionally high values were observed on the reef slope (Iriomote) in February–March 2001 (1533 gm⁻²d⁻¹) owing to a large amount of bottom sediment re-suspension. On the reef flat (Todoroki South and North; Ishigaki), values obtained in July–August 2001 (872 gm⁻²d⁻¹) and August–September 2001 (800 gm^{− 2}d⁻¹) indicate the high terrestrial discharge from Todoroki River. Trapped sediment particles consist of CaCO₃ (1.2–27.1%) and a non-carbonate fraction (98.8–72.9%), which contains total carbon (4.9–26%), carbonate carbon (CO₂-C) (0.2–3.1%) and non-carbonate carbon (NC-C) (7.9–25.6%). Total nitrogen content was in the range 0.02–0.48%. TN is contained mainly in the carbonate fraction and NC-C may be contained in the non-carbonate fraction. The low TN/OC ratio of the trapped sediments suggests that they were mostly of terrestrial origin and that both fractions migrated. The high total mass flux derived from Todoroki River exceeded the threshold at which a lethal effect on coral community is caused. The results stress the importance of conducting seasonal studies of sedimentation over more than one year and at more than one location in south Japan coral reef ecosystems to gain an understanding of the processes controlling the total mass fluxes and their nutrients content, also to develop an awareness of how to prevent the damage of coral reef ecosystems and, if it does occur, to allow mitigation measures to be undertaken.     

Total Lipid and Fatty Acid Classes in Decomposing Mangrove Leaves of <Emphasis Type="Italic">Bruguiera gymnorrhiza</Emphasis> and <Emphasis Type="Italic">Kandelia candel</Emphasis>: Significance with respect to Lipid Input

Changes in the concentration of total lipid and fatty acids (FAs) during the decomposition of mangrove leaves were investigated by field experiments using yellow leaves of Bruguiera gymnorrhiza (L.) Lamk. and Kandelia candel (L.) Druce, in order to quantify mangrove contribution to lipid and fatty acid inputs to marine sediments. Total lipid and total FA in the fresh (green and yellow) and decomposing leaves of both species were significantly higher during winter than summer. During decomposition, total lipid content and FA concentration, in particular branched chain fatty acids (BrFAs) and bacterial fatty acids (BFAs), increased to a maximum concentration in 45 days during winter and in 17 days during summer. Lipids were lost faster in K. candel leaf detritus than in B. gymnorrhiza leaf detritus in which >90% of the total lipid original weight was lost during the summer experiment and <60% during the winter experiment. The changes in the concentrations of total lipids and FAs in the decomposing leaves also indicate that mangrove leaves are significant sources of fatty acids and probably other lipid compounds to estuarine ecosystems and that tidal waters transport the lipids and FAs adsorbed to particulate matter from mangroves to adjacent estuarine sediments and the ocean.     

Particulate peptidoglycan in seawater determined by the silkworm larvae plasma (SLP) assay

Peptidoglycan (PG) is a biopolymer found exclusively in the cell wall of bacteria. Recent chemical analysis of particulate organic matter suggests that a major amount of the muramic acid, an amino sugar present only in PG, could not be accounted for in terms of bacterial cells (Benner and Kaiser, 2003); however, data on particulate PG is quite sparse. In the present study, conducted in 1996, the PG was examined at 5 sampling sites in the northwestern Pacific Ocean, and in natural seawater cultures. Particulate PG, which was concentrated using a 96-well filtration plate equipped with Durapore filters (pore size, 0.22 μm), was measured by the silkworm larvae plasma (SLP) assay. The PG concentration generally decreased with depth and correlated significantly with bacterial abundance throughout the entire water column. However, the ratio of particulate PG to bacterial abundance varied with depth. The average ratio was 0.61 ± 0.53 (average ± SD, n = 40) between 50 and 2000 m, which agreed with the bacterial cellular PG content from 0.63 to 1.1 fg cell⁻¹ obtained in seawater cultures. On the other hand, the ratios of PG to bacteria from the surface to 50 m (3.7 ± 2.6, n = 29) and below 2,000 m (2.1 ± 1.7, n = 7) were significantly higher than that between 50 and 2,000 m. These results may suggest that, in the surface and deep layers, a significant fraction of particulate PG was present in bacterial detritus, whereas this fraction was reduced in the middle layer.     

The concept of tidal exchange and the tidal exchange ratio

The principal character of the tidal exchange process is neither diffusion nor advection, but a third category of transport, “Massenaustausch”, which appears in the space/time averaged transport. The exchange process can be divided into four fluxes: the flux of standing eddies, the flux of tidal exchange, the flux of tidal eddies and the flux of local eddies. The results of observations at the entrance channel of Kumihama-Bay show a typical example of transport dominated by tidal exchange. The tidal exchange ratio defined by Parkeret al. (1972) applies to the process of exchange between the outflowing watermass and the surrounding watermass outside of the bay mouth, but this should also be considered as being coupled with the ratio for the process of exchange between the inflowing watermass and the surrounding watermass inside of the bay mouth. These two exchange ratios can be combined into a single exchange ratio which describes the exchange process between the outer watermass and the bay water.     

Thermostads and circulation in the upper layer of the Atlantic Ocean

There are three major permanent thermostads with roughly the same potential densities in the upper layer of the Atlantic Ocean. One is the thermostad of the 13°C Water in the equatorial Atlantic. The original type of the 13°C Water is formed in the thermocline in the eastern sector of the South Atlantic subtropical gyre by vertical mixing of dense, low-salinity water from the winter outcrop farther south and overlying less dense, high-salinity water. There might also be a lateral contribution of relatively high-salinity water from the Indian Ocean. The original 13°C Water thus formed is transported northwestward along the northern edge of the subtropical gyre and fed into the North Brazilian Current, which flows equatorward along the coast of Brazil. In the region of the equator, the Equatorial Undercurrent and the subsurface North and South Equatorial countercurrents branch off from the North Brazilian Current and carry the 13°C Water eastward to the thermostad region. Vertical mixing does not explain the development of the thermostad, but is found to be essential in determining the ultimate characteristics of the 13°C Water. The other two thermostads are those of the 18°C Water in the Sargasso Sea and the Subantarctic Mode Water in the western South Atlantic. Unlike the 13°C Water, both of these mode waters are formed as thermostads in the surface layer by winter convection, but vertical mixing in the subtropical gyres may play a role in determining their characteristics. All the three thermostads appear to be required to balance the system of flows in opposing directions.     

Tidal residual circulation produced by a tidal vortex

“TIDAL VORTEX” is a term for a kind of starting vortex formed as a pair of vortices at the head of a tidal jet emanating from a narrow entrance into a bay. In this study, its formation and movement have been investigated by means of a hydraulic experiment and an analytical model. A tidal vortex is formed as a result of flow separation at the abrupt widening of a channel entrance followed by rolling up of the discontinuity surface around its free end. The vortex shows three types of life-history (type I, II and III), which are characterized by the Strouhal number and the aspect ratio of the horizontal shape of the entrance channel. In the case of type-I, the tidal vortex proceeds toward the inner region of the bay and there amalgamates with successive vortex cores into a core of tidal residual circulation. In the case of type-II, the tidal vortex core flows out into the entrance channel on the ebb but returns back into the bay on the subsequent flood. And, in the case of type-III, the tidal vortex core which was formed on the bay-side opening of the entrance channel flows out to the open sea and never comes back, whereas the core which was formed on the open-sea side of the entrance flows into the bay and never flows out. The circulation of a tidal vortex core is proportional to the reciprocal of the Strouhal number. The movement of the core near the bay entrance is determined by interaction between the cores and transportation due to the irrotational component of the tidal current. There are three types of tidal residual circulation, corresponding to three life-history types of tidal vortices. In the case of type-I, a strong tidal residual circulation is formed, but in type-II a small and weak circulation is formed. While, in type-III, the circulation having an inverse sense of rotation to that of type-I is formed.