Remote Clusters Research Articles

Masses, Tidal Radii, and Escape Speeds in Dwarf Spheroidal Galaxies under MOND and Dark Halos Compared

We investigate the success and problems of MOdified Newtonian Dynamics (MOND) in explaining the structural parameters and dynamics of remote Galactic globular clusters (GCs) and dwarf spheroidal (dSph) galaxies. Using the MOND value for the mass of the Milky Way as inferred from the Galactic rotation curve, we derive the tidal radii of Galactic GCs, and compare to observed values. Except for Pal 14, the predicted tidal radii of GCs are systematically larger than the observed nominal values. However, the associated uncertainties are so large that tidal radii are consistent on the $1\sigma$ level. We have considered the importance of the Galactic tidal force on the survival of dSphs under MOND. Assuming mass-to-light ratios compatible with a naked stellar population, we found that the present Galactic dSphs preserve their integrity over one Hubble time, except Sextans which may survive the tidal interaction only for several Gyr. Mass-to-light ratios as inferred from the internal kinematics of dSph galaxies can be used, but they appear too large to be accounted for only by the stellar population in Willman 1, Coma Berenice, Ursa Minor, Draco, Ursa Major and possibly Bo\"{o}tes dwarves. Finally, the ability of the Sculptor dwarf to retain the observed population of low-mass X-ray binaries (LMXBs) is examined. Under the MOND paradigm, we find that the retention fraction in Sculptor is likely not larger than a few percent. Compared to the dark matter scenario, it turns out that MOND makes the retention problem worse. We propose that measurements of the radial velocities of the observed LMXBs in Sculptor could provide a way to distinguish between modified gravities or extended and massive dark matter halos.

Toxin production in a rare and genetically remote cluster of strains of the Bacillus cereus group

BackgroundThree enterotoxins are implicated in diarrhoeal food poisoning due to Bacillus cereus: Haemolysin BL (Hbl), Non-haemolytic enterotoxin (Nhe), and Cytotoxin K (CytK). Toxin gene profiling and assays for detection of toxin-producing stains have been used in attempts to evaluate the enterotoxic potential of B. cereus group strains. B. cereus strain NVH 391/98, isolated from a case of fatal enteritis, was genetically remote from other B. cereus group strains. This strain lacked the genes encoding Hbl and Nhe, but contains CytK-1. The high virulence of this strain is thought to be due to the greater cytotoxic activity of CytK-1 compared to CytK-2, and to a high level of cytK expression. To date, only three strains containing cytK-1 have been identified; B. cereus strains NVH 391/98, NVH 883/00, and INRA AF2.ResultsA novel gene variant encoding Nhe was identified in these three strains, which had an average of 80% identity in protein sequence with previously identified Nhe toxins. While culture supernatants containing CytK and Nhe from NVH 391/98 and INRA AF2 were highly cytotoxic, NVH 883/00 expressed little or no CytK and Nhe and was non-cytotoxic. Comparative sequence and expression studies indicated that neither the PlcR/PapR quorum sensing system, nor theYvrGH and YvfTU two-component systems, were responsible for the observed difference in toxin production. Additionally, phylogenetic analysis of 13 genes showed that NVH 391/98, NVH 883/00, and INRA AF2 comprise a novel cluster of strains genetically distant from other B. cereus group strains.ConclusionDue to its divergent sequence, the novel nhe operon had previously not been detected in NVH 391/98 using PCR and several monoclonal antibodies. Thus, toxigenic profiling based on the original nhe sequence will fail to detect the toxin in this group of strains. The observation that strain NVH 883/00 carries cytK-1 but is non-cytotoxic indicates that the detection of this gene variant is not a sufficient criterion for identification of highly cytotoxic strains. The presence of the novel nhe operon and the cytK-1 gene variant in this cluster of strains reflect their phylogenetically remote relationship towards other B. cereus group strains.

ACS Photometry of Newly Discovered Globular Clusters in the Outer Halo of M31

We report the first results from deep ACS imaging of 10 classical globular clusters in the far outer regions (15 kpc Rp 100 kpc) of M31. Eight of the clusters, including two of the most remote M31 globular clusters presently known, are described for the first time. Our F606W, F814W color-magnitude diagrams extend ~3 mag below the horizontal branch and clearly demonstrate that the majority of these objects are old (10 Gyr), metal-poor clusters. Five have [Fe/H] ~ -2.1, while an additional four have -1.9 [Fe/H] -1.5. The remaining object is more metal-rich, with [Fe/H] ~ -0.70. Several clusters exhibit the second-parameter effect. Using aperture photometry, we estimate integrated luminosities and structural parameters for all clusters. Many, including all four clusters with projected radii greater than 45 kpc, are compact and very luminous, with -8.9 MV -8.3. These four outermost clusters are thus quite unlike their Milky Way counterparts, which are typically diffuse, subluminous (-6.0 MV -4.7), and more metal-rich (-1.8 [Fe/H] -1.3).

Communication and Computing Paradigm for Distributed Mobile Systems

The advancements in technology have enabled mobile devices to become information and service providers by complementing or replacing static hosts. This motivates the need for merging of mobile and grid technologies, leading to mobile grid paradigm. Computational mobile grid can also be viewed as a seamless integration of cluster of mobile clusters. Hence, as a first step in realizing a mobile grid, Anonymous Remote Mobile Cluster Computing (ARMCC) model is proposed. The main purpose of ARMCC is to utilize the idle computing power of both the static and mobile nodes, to provide parallel programming on a distributed mobile computing environment. The cluster model was extended to a mobile grid paradigm that integrates the computational, data and service grids. However, though the mobile grid is visualized as cluster of mobile clusters, the model of mobile cluster is not directly applicable to mobile grid. In addition to computational power other resources and services offered by the participating nodes are shared in case of mobile grid. Thus, all the participating mobile nodes in the mobile grid are represented using surrogate objects which reside on the static portion of the network. These surrogate objects are realized as a shared distributed object space. The constrained nature of the mobile devices participating in the mobile cluster requires an efficient communication primitive for exactly-once message delivery. Thus a novel communication paradigm, namely, Fault Tolerant Exactly Once Reliable Multicast Protocol (FTEORMP) for distributed mobile system is proposed.

A panoramic view of the Southern quadrant of the Andromeda galaxy outer halo

How clumpy are galactic halos? Recent observations around both the Milky Way and the Andromeda galaxy (M31) have revealed numerous faint stellar streams and dwarf galaxies, leading to the belief that more of these may yet remain undetected. In this contribution, we present the map produced from the Megacam/CFHT survey that our group has undertaken in the outer halo of M31 and that, for the first time, gives a deep panoramic view of a significant region of the outer halo of a spiral galaxy. This panoramic survey, which covers ∼ 60 sq. deg. of the southern quadrant of the M31 halo, extends the WFC/INT survey of the inner halo (Ferguson et al. 2002) from a projected distance of ∼ 50 to ∼ 150 kpc. It is deep enough to cover three magnitudes below the tip of the red giant branch of stellar populations at the distance of M31. The survey reveals: • Three faint dwarf galaxies with absolute magnitudes in the range −7.3 < MV < −6.4 and the most remote M31 globular cluster at a projected distance of ∼ 120 kpc from M31 (see Martin et al. 2006 for more details). • That the giant stream of Ibata et al. (2001) covers a much wider area than previously expected from shallower surveys, has an apocenter at 125 ± 25 kpc from M31 and is probably due to the accretion of a small disk galaxy. • A new stellar stream or shell approximately perpendicular to the minor axis of M31 at a projected distance of 120 kpc and with a metallicity of [Fe/H] ∼ −1.5 (assuming it is at the distance of M31). • A new stellar stream along the ma jor axis of M31 that extends to at least 100 kpc from M31 with [Fe/H] ∼ −1.3 (once again assuming it is at the distance of M31). • Regions void of any stellar structure brighter than 34− 35mag/arcsec at a distance of 100 to 130 kpc from M31. The survey shows that the outer halo of the Andromeda galaxy is very structured, in qualitative agreement with recent cosmological simulations (e.g. Bullock & Johnston, 2005).

Distributed mutual exclusion algorithms for grid applications: A hierarchical approach

The majority of current distributed mutual exclusion algorithms are not suited for parallel or distributed applications on a Grid as they do not consider the heterogeneity of latency on Grids. We propose two distributed mutual exclusion algorithms, based on Naimi–Trehel's token-based algorithm, which take into account latency gaps, especially those between local and remote clusters of machines. Our first algorithm exploits cluster locality by giving higher priority to critical section requests issued from nodes of the same cluster when compared to those from remote nodes. Our second algorithm adds a router layer to the first algorithm, bringing it closer to Grid network topology. Viewing each cluster as a single node, the Naimi–Trehel algorithm is applied to this router layer. Redirection of inter-cluster messages to cluster's nodes is then minimized.

Neural tube defects in India—time for action

In today's Lancet, Anil Cherian and colleagues 1 Cherian A Seena S Bullock RK Antony AC Incidence of neural tube defects in the least-developed area of India: a population-based study. Lancet. 2005; 366: 930-931 Summary Full Text Full Text PDF PubMed Scopus (82) Google Scholar report the incidence of neural tube defects in village clusters in one of the most underdeveloped areas in India. The investigators found an incidence of 6·57–8·21 per 1000 livebirths. This rate is one of the highest in the world. Several factors have been implicated as causes of neural tube defects. 2 Botto LD Moore CA Khoury MJ Erickson JD Neural-tube defects. N Engl J Med. 1999; 341: 1509-1519 Crossref PubMed Scopus (712) Google Scholar However, the role of folic acid deficiency in causing birth defects and the corollary that folic acid supplementation prevents them has now gained universal acceptance. Incidence of neural tube defects in the least-developed area of India: a population-based studyHospital-based records from major cities of India, where roughly a quarter of the population resides, identified the frequency of neural tube defects (NTDs) as ranging from 3·9 to 8·8 per 1000 births, but the incidence in rural areas is unknown. We did a population-based door-to-door survey of mothers living in remote clusters of villages in Balrampur District in Uttar Pradesh, a region ranked as the least-developed area in India. The data showed that the incidence of NTDs was 6·57–8·21 per 1000 livebirths, which is among the highest worldwide. Full-Text PDF

Incidence of neural tube defects in the least-developed area of India: a population-based study

Hospital-based records from major cities of India, where roughly a quarter of the population resides, identified the frequency of neural tube defects (NTDs) as ranging from 3.9 to 8.8 per 1000 births, but the incidence in rural areas is unknown. We did a population-based door-to-door survey of mothers living in remote clusters of villages in Balrampur District in Uttar Pradesh, a region ranked as the least-developed area in India. The data showed that the incidence of NTDs was 6.57-8.21 per 1000 livebirths, which is among the highest worldwide. India's Ministry of Health needs to produce a strategy to reduce the incidence of such defects.

Discovery of remote star clusters in the halo of the Irregular galaxy NGC 6822

We report the discovery of three new star clusters in the halo of the Local Group dwarf irregular galaxy NGC 6822. These clusters were found in the deep images taken with the MegaPrime at the CFHT covering a total field of 2 deg 2 deg. The most remote cluster is found to be located as far as 79 arcmin away from the center of NGC 6822. This distance is several times larger than the size of the region in NGC 6822 where star clusters were previously found. Morphological structures of the clusters and color-magnitude diagrams of the resolved stars in the clusters show that at least two of these clusters are proabably old globular clusters.

A Grid Service for the Interactive Use of a Parallel Non-rigid Registration Algorithm of Medical Images

The goal of this work is to improve the usability of a non-rigid registration software for medical images. We have built a registration grid service in order to use the interactivity of a visualization workstation and the computing power of a cluster. On the user side, the system is composed of a graphical interface that interacts in a complex and fluid manner with the registration software running on a remote cluster. Although the transmission of images back and forth between the computer running the user interface and the cluster running the registration service adds to the total registration time, it provides a user-friendly way of using the registration software without heavy infrastructure investments in hospitals. The system exhibits good performances even if the user is connected to the grid service through a low throughput network such as a wireless network interface or ADSL.

The use of RAPD markers for differentiation of grapevine varieties registered in the Czech Republic

Fifty-one grapevine cultivars registered in the Czech Republic were a subject of RAPD analysis. Nine grapevine varieties which were supposed to be genetically distant, were analysed by means of 120 Operon primers during the initial screening of RAPD method. Sixteen primers producing reproducible and polymorphic bands were then used for amplification of all registered varieties. A dendrogram of genetic relationships and a methodology of identification of each variety were created. The resultant dendrogram mostly corresponds with known information about the origin and genetic relationships of the varieties. It is necessary to use the combination of RAPD markers for identification of each variety. It was possible to identify 26 out of 51 varieties registered in the Czech Republic by RAPD markers without any problems. Nine varieties were identifiable only on the basis of present and absent markers. Some varieties were very close relatives &amp;ndash; they formed remote clusters. It was not possible to distinguish between them by RAPD method. Two varieties were not identifiable by the designed key. &amp;nbsp;

On the determination of age and mass functions of stars in young open star clusters from the analysis of their luminosity functions

Based on the CCD observations of remote young open clusters NGC 2383, NGC 2384, NGC 4103, NGC 4755, NGC 7510 and Hogg 15, we constructed their observed luminosity functions (LFs). The observed LFs are corrected for field star contamination determined with the help of galactic star count model. In the case of Hogg 15 and NGC 2383 we also considered the additional contamination from neighbouring clusters NGC 4609 and NGC 2384 respectively. These corrections provided the realistic pattern of cluster LF in the vicinity of the MS turn on point and at fainter magnitudes, revealed the so called H-feature arising due to transition of the Pre-MS phase to MS, which is dependent on the cluster age. The theoretical LFs were constructed representing a cluster population model with continuous star formation for a short time scale and a power law Initial Mass Function (IMF) and these were fitted to the observed LF. As a result we are able to determine for each cluster a set of parameters, describing cluster population (the age, duration of star formation, IMF slope and percentage of field star contamination). It was found that in spite of the non-monotonic behaviour of observed LFs, cluster IMFs can be described as the power law functions with slopes similar to Salpeter's value. The present MS turn on cluster ages are several times lower than those derived from the fitting of theoretical isochrones to the turn off region of the upper Main Sequences.

Tidal radii of globular clusters and the mass of the Milky Way

Tidal radii of remote globular clusters (R_{GC}>= 35 kpc) are used to provide constraints of the mass profile of the Milky Way galaxy that are independent of kinematic data. The available data are consistent with the profile of an isothermal sphere with circular velocity V_c = 220 +/- 40 km/s in the radial range 35 kpc < R_{GC} < 100 kpc, in good agreement with all recent estimates. The more robust constraint at large distances from the galactic center is provided by NGC 2419, yelding an enclosed mass of ~ 1.3 (+2.9/-1.0) * 10**12 M_{sun} at R_{GC}= 90 kpc.

Wide-Field Stellar Distributions around the Remote Young Galactic Globular Clusters Palomar 3 and Palomar 4

In a search for tidal extension features and/or streams of the probable parent satellite galaxies around the remote young globular clusters Pal 3 and Pal 4, we used wide-field VI photometry of an area a ~ 13 × 13 around Pal 3 and an area a ~ 13 × 09 around Pal 4, obtained with the CFH12K mosaic CCD. Applying the CMD-mask algorithm to stars in the vicinity of the clusters, we selected member star candidates that were used to examine the characteristics of the spatial distribution of stars around Pal 3 and Pal 4. The isodensity contours in the Gaussian-smoothed spatial stellar density maps around the clusters, and the Kolmogorov-Smirnov test applied to the corresponding luminosity functions, indicate tidal halos around Pal 3 at distances of up to ~4rt, and around Pal 4 of up to ~6rt. The stellar distribution around Pal 3 suggests north-south elongations along the directions of the Galactic center and anticenter, and a northeast extension in the direction of the cluster's proper motion. In the vicinity of Pal 4 an extension of a tail around the cluster in the opposite direction to the Galactic center and a possible extension of stars toward the Galactic center have also been detected in the isodensity maps and in the angular luminosity functions. We discuss the relevance of the spatial distribution of stars in possible streams around Pal 3 and Pal 4 to these spatial correlations and to the space orbits of the possible parent satellite galaxies.

1208 股関節手術計画システムの遠隔化と医師のノウハウの定量化

The purpose of our research is to formulate 'the Automated CT-based 3D remote surgical planning system for total hip replacement'. Recent advanced planning systems evaluate quantitatively the fitness and stability of each individual implant (e.g. femoral stem) to provide some objective measure for surgeons on a local machine. However, calculation of those parameters and visualization of the 3D models occupy much throughput of the computer. Nowadays, broadband has become popular and computers can access to remote PC clusters easily. So even on low spec computers, doctors can distribute required processings and receive the results sooner than ever.

Kinematic Study of the Disrupting Globular Cluster Palomar 5 Using VLT Spectra

Wide-field photometric data from the Sloan Digital Sky Survey have recently revealed that the Galactic globular cluster Palomar 5 is in the process of being tidally disrupted. Here we investigate the kinematics of this sparse remote star cluster using high-resolution spectra from the Very Large Telescope (VLT). Twenty candidate cluster giants located within 6' of the cluster center have been observed with the UV-Visual Echelle Spectrograph on VLT-UT2. The spectra provide radial velocities with a typical accuracy of 0.15 km s-1. We find that the sample contains 17 certain cluster members with very coherent kinematics, two unrelated field dwarfs, and one giant with a deviant velocity, which is most likely a cluster binary showing fast orbital motion. From the confirmed members we determine the heliocentric velocity of the cluster as -58.7 ± 0.2 km s-1. The total line-of-sight velocity dispersion of the cluster stars is 1.1 ± 0.2 km s-1 (all members) or 0.9 ± 0.2 km s-1 (stars on the red giant branch only). This is the lowest velocity dispersion that has so far been measured for a stellar system classified as a globular cluster. The shape of the velocity distribution suggests that there is a significant contribution from orbital motions of binaries and that the dynamical part of the velocity dispersion is therefore still substantially smaller than the total dispersion. Comparing the observations with the results of Monte Carlo simulations of binaries we find that the frequency of binaries in Pal 5 is most likely between 24% and 63% and that the dynamical line-of-sight velocity dispersion of the cluster must be smaller than 0.7 km s-1 (90% confidence upper limit). The most probable values of the dynamical dispersion lie in the range 0.12 ≤ σ/km s-1 ≤ 0.41 (68% confidence). Pal 5 thus turns out to be a dynamically very cold system. Our results are compatible with an equilibrium system. We find that the luminosity of the cluster implies a total mass of only 4.5 to 6.0 × 103 M⊙. We further show that a dynamical line-of-sight velocity dispersion of 0.32 to 0.37 km s-1 admits a King model that fits the observed surface density profile of Pal 5 (with W0 = 2.9 and rt = 161) and its mass.

Orbits of Globular Clusters in the Outer Galaxy: NGC 7006

We present a proper motion study of the distant globular cluster NGC 7006 based on the measurement of 25 photographic plates spanning a 40-year interval. The absolute proper motion determined with respect to extragalactic objects is (-0.96, -1.14) +- (0.35, 0.40) mas/yr. The total space velocity of NGC 7006 in a Galactocentric rest frame is 279 km/s, placing the cluster on one of the most energetic orbits (Ra =102 kpc) known to date for clusters within 40-kpc from the Galactic center. We compare the orbits of four clusters that have apocentric radii larger than 80 kpc (NGC 5466, NGC 6934, NGC 7006 and Pal 13) with those of Galactic satellites with well-measured proper motions. These clusters have orbits that are highly eccentric and of various inclinations with respect to the Galactic plane. In contrast, the orbits of the Galactic satellites are of low to moderate eccentricity and highly inclined. Based on orbit types, chemical abundances and cluster parameters, we discuss the properties of the hypothetical host systems of the remote globular clusters in the Searle-Zinn paradigm. It is apparent that clusters such as NGC 5466, NGC 6934 and NGC 7006 formed in systems that more likely resemble the Fornax dSph, rather than the Sagittarius dSph. We also discuss plausible causes for the difference found so far between the orbit type of outer halo clusters and that of Galactic satellites and for the tentative, yet suggestive phase-space scatter found among outer halo clusters.

Modeling Mid‐Ultraviolet Spectra. I. Temperatures of Metal‐poor Stars

Determining the properties of remote globular clusters and elliptical galaxies using evolutionary population synthesis requires a library of reliable model stellar fluxes. Empirical libraries are limited to spectra of stars in the solar neighborhood, with nearly solar abundances and abundance ratios. We report here a rst step towards providing a flux library that includes nonsolar abundances, based on calculations from rst principles that are calibrated empirically. Because the mid-ultraviolet spectrum of an old stellar system is dominated by the contribution from its main-sequence turno stars, we have started by modeling these. We have calculated mid-ultraviolet spectra for the Sun and nine nearby, near-main-sequence stars spanning metallicities from less than 1/100 solar to greater than solar, encompassing a range of light-element abundance enhancements. We rst determined temperatures of eight of the stars by analyzing optical echelle spectra together with the mid-ultraviolet. Both could be matched at the same time only when models with no convective overshoot were adopted, and only when an approximate chromosphere was incorporated near the surface of relatively metal-rich models. Extensive modications to mid-UV line parameters were also required, notably the manual assignment of approximate identications for mid-UV lines missing from laboratory linelists. Without recourse to additional missing opacity, these measures suce to reproduce in detail almost the entire mid-UV spectrum of solar-temperature stars up to one-tenth solar metallicity, and the region from 2900 A to 3100 A throughout the entire metallicity range. Ramications for abundance determinations in individual metal-poor stars and for age-metallicity determinations of old stellar systems are briefly discussed, with emphasis on the predictive power of the calculations. 1 Based on observations obtained with the Hubble Space Telescope of Space Telescope Science Institute, under contract with the National Aeronautics and Space Administration (NASA). 2 Based on observations obtained with the Shane Telescope at Mt. Hamilton, UCO/Lick Observatory.

A Highly Reddened Star Cluster Embedded in the Galactic Plane

We found a cluster of early-type star candidates embedded in the Galactic plane by using optical to near-infrared broadband imaging. The observed region is around the 10 highly reddened stars found as a possible new and very remote open cluster by Stephenson. The 10 stars are identified as red supergiants, and several similar stars are newly found in our images. Furthermore, 25 early-type star candidates suffering visual extinction of AV ~ 11.2 have been identified from various color-magnitude and color-color diagrams. These stars are likely to make a star cluster, and we estimate its age and distance to be ~107.7 yr and ~1.5 kpc, respectively.

Detection of Massive Tidal Tails around the Globular Cluster Palomar 5 with Sloan Digital Sky Survey Commissioning Data

We report the discovery of two well-defined tidal tails emerging from the sparse remote globular cluster Palomar 5. These tails stretch out symmetrically to both sides of the cluster in the direction of constant Galactic latitude and subtend an angle of 26 on the sky. The tails have been detected in commissioning data of the Sloan Digital Sky Survey, providing deep five-color photometry in a 25-wide band along the equator. The stars in the tails make up a substantial part (~) of the current total population of cluster stars in the magnitude interval 19.5 ≤ i* ≤ 22.0. This reveals that the cluster is subject to heavy mass loss. The orientation of the tails provides an important key for the determination of the cluster's Galactic orbit.