Dual-camera system for high-speed imaging in particle image velocimetry

Particle image velocimetry is an important technique in experimental fluid mechanics, for which it has been essential to use a specialized high-speed camera. However, the high speed is at the expense of other performances of the camera, i.e., sensitivity and image resolution. Here, we demonstrate that the high-speed imaging is also possible with a pair of still cameras.Comment: 4 pages, accepted by Journal of Visualization (see http://www.springerlink.com

Vortex tubes in velocity fields of laboratory isotropic turbulence: dependence on the Reynolds number

The streamwise and transverse velocities are measured simultaneously in isotropic grid turbulence at relatively high Reynolds numbers, Re(lambda) = 110-330. Using a conditional averaging technique, we extract typical intermittency patterns, which are consistent with velocity profiles of a model for a vortex tube, i.e., Burgers vortex. The radii of the vortex tubes are several of the Kolmogorov length regardless of the Reynolds number. Using the distribution of an interval between successive enhancements of a small-scale velocity increment, we study the spatial distribution of vortex tubes. The vortex tubes tend to cluster together. This tendency is increasingly significant with the Reynolds number. Using statistics of velocity increments, we also study the energetical importance of vortex tubes as a function of the scale. The vortex tubes are important over the background flow at small scales especially below the Taylor microscale. At a fixed scale, the importance is increasingly significant with the Reynolds number.Comment: 8 pages, 3 PS files for 8 figures, to appear in Physical Review

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

High stability design for new centrifugal compressor

It is essential that high-performance centrifugal compressors be free of subsynchronous vibrations. A new high-performance centrifugal compressor has been developed by applying the latest rotordynamics knowledge and design techniques: (1) To improve the system damping, a specially designed oil film seal was developed. This seal attained a damping ratio three times that of the conventional design. The oil film seal contains a special damper ring in the seal cartridge. (2) To reduce the destabilizing effect of the labyrinth seal, a special swirl canceler (anti-swirl nozzle) was applied to the balance piston seal. (3) To confirm the system damping margin, the dynamic simulation rotor model test and the full load test applied the vibration exciting test in actual load conditions

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

Molecular Hydrogen and [FeII] in Active Galactic Nuclei

(Abridge) Near-infrared spectroscopy is used to study the kinematics and excitation mechanisms of the H2 and [FeII] gas in a sample of AGN. The H2 lines are unresolved in all objects in which they were detected while the [FeII] lines have widths implying gas velocities of up to 650 km/s. This suggests that, very likely, the H2 and [FeII] emission does not originate from the same parcel of gas. Molecular H2 were detected in 90% of the sample, including PG objects, indicating detectavel amounts of molecular material even in objects with low levels of circumnuclear starburst activity. The data favors thermal excitation for the H2 lines. Indeed, in NGC3227, Mrk766, NGC4051 and NGC4151, the molecular emission is found to be purely thermal. This result is also confirmed by the rather similar vibrational and rotational temperatures in the objects for which they were derived. [FeII] lines are detected in all of the AGN. The [FeII] 1.254mu/Pa-beta ratio is compatible with excitation of the [FeII] by the active nucleus, but in Mrk 766 it implies a stellar origin. A correlation between H2/Br-gamma and [FeII]/Pa-beta is found. We confirm that it is a useful diagnostic tool in the NIR to separate emitting line objects by their level of nuclear activity. X-ray excitation models are able to explain the observed H2 and part of the [FeII] emission. Most likely, a combination of X-ray heating, shocks driven by the radio jet, and circumnuclear star formation contributes, in different proportions, to the H2 and [FeII] emission. In most of our spectra, the [FeII] 1.257mu/1.644mu ratio is found to be 30% lower than the intrinsic value based on current atomic data. This implies either than the extinction towards the [FeII] emitting clouds is very similar in most objects or there are possible inaccuracies in the A-values in the [FeII] transitions.Comment: 18 pages, 6 figures, Accepted for publication in Astronomy & Astrophysic

Sundarban mangroves: diversity, ecosystem services and climate change impacts

The Bengal delta coast harboring the famous Sundarban mangroves is extremely vulnerable to climate change. Already, salinity intrusion, increasing cyclones and anomalies in rainfall, and temperature, are causing many social and livelihood problems. However, our knowledge on the diversified climate change impacts on Sundarban ecosystems services, providing immense benefits, including foods, shelters, livelihood, and health amenities, is very limited. Therefore, this article has systematically reviewed the major functional aspects, and highlights on biodiversity, ecosystem dynamics, and services of the Sunderban mangroves, with respect to variations in climatic factors. The mangrove ecosystems are highly productive in terms of forest biomass, and nutrient contribution, especially through detritus-based food webs, to support rich biodiversity in the wetlands and adjacent estuaries. Sundarban mangroves also play vital role in atmospheric CO2 sequestration, sediment trapping and nutrient recycling. Sea level rise will engulf a huge portion of the mangroves, while the associated salinity increase is posing immense threats to biodiversity and economic losses. Climate-mediated changes in riverine discharge, tides, temperature, rainfall and evaporation will determine the wetland nutrient variations, influencing the physiological and ecological processes, thus biodiversity and productivity of Sundarban mangroves. Hydrological changes in wetland ecosystems through increased salinity and cyclones will lower the food security, and also induce human vulnerabilities to waterborne diseases. Scientific investigations producing high resolution data to identify Sundarban‟s multidimensional vulnerabilities to various climatic regimes are essential. Sustainable plans and actions are required integrating conservation and climate change adaptation strategies, including promotion of alternative livelihoods. Thus, interdisciplinary approaches are required to address the future climatic disasters, and better protection of invaluable ecosystem services of the Sunderban mangroves.Fil: Neogi, Sucharit Basu. Coastal Development Partnership; Bangladesh. Osaka Prefecture University; Japón. Leibniz Center for Tropical Marine Ecology GmbH; AlemaniaFil: Dey, Mouri. University of Chittagong; BangladeshFil: Lutful Kabir, S. M.. Bangladesh Agricultural University; BangladeshFil: Masum, Syed Jahangir H.. Coastal Development Partnership; BangladeshFil: Kopprio, Germán Adolfo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. Leibniz Center for Tropical Marine Ecology GmbH; AlemaniaFil: Yamasaki, Shinji. Osaka Prefecture University; JapónFil: Lara, Ruben Jose. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentin

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

Effects of high-energy ionizing particles on the Si:As mid-infrared detector array on board the AKARI satellite

We evaluate the effects of high-energy ionizing particles on the Si:As impurity band conduction (IBC) mid-infrared detector on board AKARI, the Japanese infrared astronomical satellite. IBC-type detectors are known to be little influenced by ionizing radiation. However we find that the detector is significantly affected by in-orbit ionizing radiation even after spikes induced by ionizing particles are removed. The effects are described as changes mostly in the offset of detector output, but not in the gain. We conclude that the changes in the offset are caused mainly by increase in dark current. We establish a method to correct these ionizing radiation effects. The method is essential to improve the quality and to increase the sky coverage of the AKARI mid-infrared all-sky-survey map.Comment: 16 pages, 8 figures, 1 table, accepted for publication in PAS