193 research outputs found
Orbital Decay and Tidal Disruption of a Star Cluster: Analytical Calculation
The orbital decay and tidal disruption of a star cluster in a galaxy is
studied in an analytical manner. Owing to dynamical friction, the star cluster
spirals in toward the center of the galaxy. Simultaneously, the galactic tidal
field strips stars from the outskirts of the star cluster. Under an assumption
that the star cluster undergoes a self-similar evolution, we obtain the
condition and timescale for the star cluster to reach the galaxy center before
its disruption. The result is used to discuss the fate of so-called
intermediate-mass black holes with >10^3 M(sun) found recently in young star
clusters of starburst galaxies and also the mass function of globular clusters
in galaxies.Comment: 12 pages, 1 PS file for 2 figures, to appear in The Astrophysical
Journa
Runaway Merging of Black Holes: Analytical Constraint on the Timescale
Following the discovery of a black hole (BH) with a mass of 10^3-10^6 M(sun)
in a starburst galaxy M82, we study formation of such a BH via successive
merging of stellar-mass BHs within a star cluster. The merging has a runaway
characteristic. This is because massive BHs sink into the cluster core and have
a high number density, and because the merging probability is higher for more
massive BHs. We use the Smoluchowski equation to study analytically the
evolution of the BH mass distribution. Under favorable conditions, which are
expected for some star clusters in starburst galaxies, the timescale of the
runaway merging is at most of order 10^7 yr. This is short enough to account
for the presence of a BH heavier than 10^3 M(sun) in an ongoing starburst
region.Comment: 10 pages, no figures, to appear in The Astrophysical Journal
(Letters
Grain Survival in Supernova Remnants and Herbig-Haro Objects
By using the flux ratio [FeII]8617/[OI]6300, we demonstrate that most of the
interstellar dust grains survive in shocks associated with supernova remnants
and Herbig-Haro objects. The [FeII]/[OI] flux ratio is sensitive to the
gas-phase Fe/O abundance ratio, but is insensitive to the ionization state,
temperature, and density of the gas. We calculate the [FeII]/[OI] flux ratio in
shocks, and compare the results with the observational data. When only 20% of
iron is in the gas phase, the models reproduce most successfully the
observations. This finding is in conflict with the current consensus that
shocks destroy almost all the grains and 100% of metals are in the gas phase.
We comment on previous works on grain destruction, and discuss why grains are
not destroyed in shocks.Comment: 8 pages (AASTex v5.0), 3 figures. To be published in ApJ Letters
(accepted 3/10/2000
Mass Segregation in Star Clusters: Analytic Estimation of the Timescale
Mass segregation in a star cluster is studied in an analytical manner. We
consider a two-component cluster, which consists of two types of stars with
different masses. Plummer's model is used for the initial condition. We trace
the overall behaviors of the probability distribution functions of the two
components and obtain the timescale of mass segregation as a simple function of
the cluster parameters. The result is used to discuss the origin of a black
hole with mass of > 1000 M(sun) found in the starburst galaxy M82.Comment: 12 pages, 1 ps file for 2 figures, to appear in The Astrophysical
Journa
Improvement and Evaluation of a Function for Tracing the Diffusion of Classified Information on KVM
The increasing amount of classified information currently being managed by personal computers has resulted in the leakage of such information to external computers, which is a major problem. To prevent such leakage, we previously proposed a function for tracing the diffusion of classified information in a guest operating system (OS) using a virtual machine monitor (VMM). The tracing function hooks a system call in the guest OS from the VMM, and acquiring the information. By analyzing the information on the VMM side, the tracing function makes it possible to notify the user of the diffusion of classified information. However, this function has a problem in that the administrator of the computer platform cannot grasp the transition of the diffusion of classified processes or file information. In this paper, we present the solution to this problem and report on its evaluation
Study on Application of Static Magnetic Field for Adjuvant Arthritis Rats
In order to examine the effectiveness of the application of static magnetic field (SMF) on pain relief, we performed a study on rats with adjuvant arthritis (AA). Sixty female Sprague–Dawley (SD) rats (age: 6 weeks, body weight: approximately 160 g) were divided into three groups [SMF-treated AA rats (Group I), non-SMF-treated AA rats (Group II) and control rats (Group III)]. The SD rats were injected in the left hind leg with 0.6 mg/0.05 ml Mycobacterium butyrium to induce AA. The rats were bred for 6 months as chronic pain model. Thereafter, the AA rats were or were not exposed to SMF for 12 weeks. We assessed the changes in the tail surface temperature, locomotor activity, serum inflammatory marker and bone mineral density (BMD) using thermography, a metabolism measuring system and the dual-energy X-ray absorptiometry (DEXA) method, respectively. The tail surface temperature, locomotor activity and femoral BMD of the SMF-exposed AA rats were significantly higher than those of the non-SMF-exposed AA rats, and the serum inflammatory marker was significantly lower. These findings suggest that the pain relief effects are primarily due to the increased blood circulation caused by the rise in the tail surface temperature. Moreover, the pain relief effects increased with activity and BMD of the AA rats
Solid-phase total synthesis and structural confirmation of antimicrobial longicatenamide A
Longicatenamides A–D are cyclic hexapeptides isolated from the combined culture of Streptomyces sp. KUSC_F05 and Tsukamurella pulmonis TP-B0596. Because these peptides are not detected in the monoculture broth of the actinomycete, they are key tools for understanding chemical communication in the microbial world. Herein, we report the solid-phase total synthesis and structural confirmation of longicatenamide A. First, commercially unavailable building blocks were chemically synthesized with stereocontrol. Second, the peptide chain was elongated via Fmoc-based solid-phase peptide synthesis. Third, the peptide chain was cyclized in the solution phase, followed by simultaneous cleavage of all protecting groups to afford longicatenamide A. Chromatographic analysis corroborated the chemical structure of longicatenamide A. Furthermore, the antimicrobial activity of synthesized longicatenamide A was confirmed. The developed solid-phase synthesis is expected to facilitate the rapid synthesis of diverse synthetic analogues
Analysis of variance for multivariate time series
Open House, ISM in Tachikawa, 2018.6.15統計数理研究所オープンハウス(立川)、H30.6.15ポスター発
Galaxy Interaction and Starburst-Seyfert Connection
Galaxy interactions are studied in terms of the starburst-Seyfert connection.
The starburst requires a high rate of gas supply. Since the efficiency for
supplying the gas is high in a galaxy interaction, although the companion is
not necessarily discernible, Seyfert galaxies with circumnuclear starbursts are
expected to be interacting. Since the large amounts of circumnuclear gas and
dust obscure the broad-line region, they are expected to be observed as Seyfert
2. The active galactic nucleus itself does not require a high rate of gas
supply. Seyfert galaxies without circumnuclear starbursts are not necessarily
expected to be interacting even at the highest luminosities. They are not
necessarily expected to evolve from Seyfert galaxies with circumnuclear
starbursts. We derive these and other theoretical expectations and confirm them
with statistics on observational data of magnitude-limited samples of Seyfert
galaxies.Comment: 28 pages, to appear in The Astrophysical Journa
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