Rich Clusters Research Articles

Star clusters in the Magellanic Clouds – I. Parametrization and classification of 1072 clusters in the LMC

We have introduced a semi-automated quantitative method to estimate the age and reddening of 1072 star clusters in the Large Magellanic Cloud (LMC) using the Optical Gravitational Lensing Experiment (OGLE) III survey data. This study brings out 308 newly parameterised clusters. In a first of its kind, the LMC clusters are classified into groups based on richness/mass as very poor, poor, moderate and rich clusters, similar to the classification scheme of open clusters in the Galaxy. A major cluster formation episode is found to happen at 125 +- 25 Myr in the inner LMC. The bar region of the LMC appears prominently in the age range 60 - 250 Myr and is found to have a relatively higher concentration of poor and moderate clusters. The eastern and the western ends of the bar are found to form clusters initially, which later propagates to the central part. We demonstrate that there is a significant difference in the distribution of clusters as a function of mass, using a movie based on the propagation (in space and time) of cluster formation in various groups. The importance of including the low mass clusters in the cluster formation history is demonstrated. The catalog with parameters, classification, and cleaned and isochrone fitted CMDs of 1072 clusters, which are available as online material, can be further used to understand the hierarchical formation of clusters in selected regions of the LMC.

RECENT GALAXY MERGERS AND RESIDUAL STAR FORMATION OF RED SEQUENCE GALAXIES IN GALAXY CLUSTERS

ABSTRACT This study explored the Galaxy Evolution Explorer ultraviolet (UV) properties of optical red sequence galaxies in four rich Abell clusters at . In particular, we tried to find a hint of merger-induced recent star formation (RSF) in red sequence galaxies. Using the NUV colors of the galaxies, RSF fractions were derived based on various criteria for post-merger galaxies and normal galaxies. Following k-correction, about 36% of the post-merger galaxies were classified as RSF galaxies with a conservative criterion (NUV ), and that number was doubled (∼72%) when using a generous criterion (NUV ). The trend was the same when we restricted the sample to galaxies within 0.5 × R 200. Post-merger galaxies with strong UV emission showed more violent, asymmetric features in the deep optical images. The RSF fractions did not show any trend along the clustocentric distance within R 200. We performed a Dressler–Shectman test to check whether the RSF galaxies had any correlation with the substructures in the galaxy clusters. Within R 200 of each cluster, the RSF galaxies did not appear to be preferentially related to the clusters’ substructures. Our results suggested that only 30% of RSF red sequence galaxies show morphological hints of recent galaxy mergers. This implies that internal processes (e.g., stellar mass loss or hot gas cooling) for the supply of cold gas to early-type galaxies may play a significant role in the residual star formation of early-type galaxies at a recent epoch.

The fundamental plane and other scaling relations for galaxy groups and clusters

In this paper we study the relations between the main characteristics of groups and clusters of galaxies using the archival data of the SDSS and 2MASX catalogs. We have developed and implemented a new method of determining the size of galaxy systems and their effective radius which contains half of the galaxies and not half the luminosity, since the luminosity of the brightest galaxy in a group can account for over 50% of the total luminosity of the group. The derived parameters (log L K , logR e , and log σ 200) for 94 systems of galaxies (0.0038 < z < 0.09) determine the Fundamental Plane (FP), which, with a scatter of 0.15, is similar in form to the FP of galaxy clusters obtained by Schaeffer et al. (1993) and D’Onofrio et al. (2013) with other methods and for different bands. We show that the FP in the near-infrared region (NIR) for 94 galaxy systems has the form of L K ∝ $$R_e^{0.70 \pm {{0.13}_\sigma }1.34 \pm 0.13}$$ , whereas in x-rays it has the form of—L X ∝ $$R_e^{1.15 \pm {{0.39}_\sigma }2.56 \pm 0.40}$$ . The form of the FP for groups and clusters is consistent with the FP for early-type galaxies determined in the same way. The form of the FP for galaxy systems deviates from the shape that one would expect from virial predictions. Adding the mass-to-light ratio as a fourth independent parameter has little effect on this deviation, but decreases the scatter of the FP for a sample of rich galaxy clusters by 12%.

THE SPITZER-HETDEX EXPLORATORY LARGE-AREA SURVEY

ABSTRACT We present post-cryogenic Spitzer imaging at 3.6 and 4.5 μm with the Infrared Array Camera (IRAC) of the Spitzer/HETDEX Exploratory Large-Area (SHELA) survey. SHELA covers ≈24 deg2 of the Sloan Digital Sky Survey “Stripe 82” region, and falls within the footprints of the Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) and the Dark Energy Survey. The HETDEX blind R ∼ 800 spectroscopy will produce ∼200,000 redshifts from the Lyα emission for galaxies in the range 1.9 &lt; z &lt; 3.5, and an additional ∼200,000 redshifts from the [O ii] emission for galaxies at z &lt; 0.5. When combined with deep ugriz images from the Dark Energy Camera, K-band images from NEWFIRM, and other ancillary data, the IRAC photometry from Spitzer will enable a broad range of scientific studies of the relationship between structure formation, galaxy stellar mass, halo mass, the presence of active galactic nuclei, and environment over a co-moving volume of ∼0.5 Gpc3 at 1.9 &lt; z &lt; 3.5. Here, we discuss the properties of the SHELA IRAC data set, including the data acquisition, reduction, validation, and source catalogs. Our tests show that the images and catalogs are 80% (50%) complete to limiting magnitudes of 22.0 (22.6) AB mag in the detection image, which is constructed from the weighted sum of the IRAC 3.6 and 4.5 μm images. The catalogs reach limiting sensitivities of 1.1 μJy at both 3.6 and 4.5 μm (1σ, for R = 2″ circular apertures). As a demonstration of the science, we present IRAC number counts, examples of highly temporally variable sources, and galaxy surface density profiles of rich galaxy clusters. In the spirit of the Spitzer Exploratory programs, we provide all of the images and catalogs as part of the publication.

THE GLOBULAR CLUSTER SYSTEM OF THE COMA CD GALAXY NGC 4874 FROM HUBBLE SPACE TELESCOPE ACS AND WFC3/IR IMAGING*

ABSTRACT We present new Hubble Space Telescope (HST) optical and near-infrared (NIR) photometry of the rich globular cluster (GC) system NGC 4874, the cD galaxy in the core of the Coma cluster (Abell 1656). NGC 4874 was observed with the HST Advanced Camera for Surveys in the F475W (g 475) and F814W (I 814) passbands and with the Wide Field Camera 3 IR Channel in F160W (H 160). The GCs in this field exhibit a bimodal optical color distribution with more than half of the GCs falling on the red side at g 475−I 814 &gt; 1. Bimodality is also present, though less conspicuously, in the optical-NIR I 814−H 160 color. Consistent with past work, we find evidence for nonlinearity in the g 475−I 814 versus I 814−H 160 color–color relation. Our results thus underscore the need for understanding the detailed form of the color–metallicity relations in interpreting observational data on GC bimodality. We also find a very strong color–magnitude trend, or “blue tilt,” for the blue component of the optical color distribution of the NGC 4874 GC system. A similarly strong trend is present for the overall mean I 814−H 160 color as a function of magnitude; for M 814 &lt; −10 mag, these trends imply a steep mass–metallicity scaling with Z ∝ M GC 1.4 ± 0.4 , but the scaling is not a simple power law and becomes much weaker at lower masses. As in other similar systems, the spatial distribution of the blue GCs is more extended than that of the red GCs, partly because of blue GCs associated with surrounding cluster galaxies. In addition, the center of the GC system is displaced by 4 ± 1 kpc toward the southwest from the luminosity center of NGC 4874, in the direction of NGC 4872. Finally, we remark on a dwarf elliptical galaxy with a noticeably asymmetrical GC distribution. Interestingly, this dwarf has a velocity of nearly −3000 km s−1 with respect to NGC 4874; we suggest it is on its first infall into the cluster core and is undergoing stripping of its GC system by the cluster potential.

Investigation of the thermo-mechanical behavior of neutron-irradiated Fe-Cr alloys by self-consistent plasticity theory

The thermo-mechanical behavior of non-irradiated (at 223 K, 302 K and 573 K) and neutron irradiated (at 573 K) Fe-2.5Cr, Fe-5Cr and Fe-9Cr alloys is studied by a self-consistent plasticity theory, which consists of constitutive equations describing the contribution of radiation defects at grain level, and the elastic-viscoplastic self-consistent method to obtain polycrystalline behaviors. Attention is paid to two types of radiation-induced defects: interstitial dislocation loops and solute rich clusters, which are believed to be the main sources of hardening in Fe-Cr alloys at medium irradiation doses. Both the hardening mechanism and microstructural evolution are investigated by using available experimental data on microstructures, and implementing hardening rules derived from atomistic data. Good agreement with experimental data is achieved for both the yield stress and strain hardening of non-irradiated and irradiated Fe-Cr alloys by treating dislocation loops as strong thermally activated obstacles and solute rich clusters as weak shearable ones.

The WSRT ZoA Perseus-Pisces filament wide-field H i imaging survey – I. H i catalogue and atlas

We present results of a blind 21cm HI-line imaging survey of a galaxy overdensity located behind the Milky Way at $\ell,b$ $\approx$ 160 deg, 0.5 deg. The overdensity corresponds to a Zone-of-Avoidance crossing of the Perseus-Pisces Supercluster filament. Although it is known that this filament contains an X-ray galaxy cluster (3C129) hosting two strong radio galaxies, little is known about galaxies associated with this potentially rich cluster because of the high Galactic dust extinction. We mapped a sky area of $\sim$9.6 sq.deg using the Westerbork Synthesis Radio Telescope in a hexagonal mosaic of 35 pointings observed for 12 hours each, in the radial velocity range $cz = 2400 - 16600$ km/s. The survey has a sensitivity of 0.36 mJy/beam rms at a velocity resolution of 16.5 km/s. We detected 211 galaxies, 62% of which have a near-infrared counterpart in the UKIDSS Galactic Plane Survey. We present a catalogue of the HI properties and an HI atlas containing total intensity maps, position-velocity diagrams, global HI profiles and UKIDSS counterpart images. For the resolved galaxies we also present HI velocity fields and radial HI surface density profiles. A brief analysis of the structures outlined by these galaxies finds that 87 of them lie at the distance of the Perseus-Pisces Supercluster ($cz \sim 4000 - 8000$ km/s) and seem to form part of the 3C129 cluster. Further 72 detections trace an overdensity at a velocity of $cz \approx$ 10000 km/s and seem to coincide with a structure predicted from mass density reconstructions in the first 2MASS Redshift Survey.

A 17-billion-solar-mass black hole in a group galaxy with a diffuse core.

Quasars are associated with and powered by the accretion of material onto massive black holes; the detection of highly luminous quasars with redshifts greater than z = 6 suggests that black holes of up to ten billion solar masses already existed 13 billion years ago. Two possible present-day 'dormant' descendants of this population of 'active' black holes have been found in the galaxies NGC 3842 and NGC 4889 at the centres of the Leo and Coma galaxy clusters, which together form the central region of the Great Wall--the largest local structure of galaxies. The most luminous quasars, however, are not confined to such high-density regions of the early Universe; yet dormant black holes of this high mass have not yet been found outside of modern-day rich clusters. Here we report observations of the stellar velocity distribution in the galaxy NGC 1600--a relatively isolated elliptical galaxy near the centre of a galaxy group at a distance of 64 megaparsecs from Earth. We use orbit superposition models to determine that the black hole at the centre of NGC 1600 has a mass of 17 billion solar masses. The spatial distribution of stars near the centre of NGC 1600 is rather diffuse. We find that the region of depleted stellar density in the cores of massive elliptical galaxies extends over the same radius as the gravitational sphere of influence of the central black holes, and interpret this as the dynamical imprint of the black holes.

Star formation and black hole accretion activity in rich local clusters of galaxies

We present a study of the star formation and central black hole accretion activity of the galaxies hosted in the two nearby (z$\sim$0.2) rich galaxy clusters Abell 983 and 1731. Aims: We are able to quantify both the obscured and unobscured star formation rates, as well as the presence of active galactic nuclei (AGN) as a function of the environment in which the galaxy is located. Methods: We targeted the clusters with unprecedented deep infrared Spitzer observations (0.2 mJy @ 24 micron), near-IR Palomar imaging and optical WIYN spectroscopy. The extent of our observations ($\sim$ 3 virial radii) covers the vast range of possible environments, from the very dense cluster centre to the very rarefied cluster outskirts and accretion regions. Results: The star forming members of the two clusters present star formation rates comparable with those measured in coeval field galaxies. The analysis of the spatial arrangement of the spectroscopically confirmed members reveals an elongated distribution for A1731 with respect to the more uniform distribution of A983. The emerging picture is compatible with A983 being a fully evolved cluster, in contrast with the still actively accreting A1731. Conclusions: The analysis of the specific star formation rate reveals evidence of on-going galaxy pre-processing along A1731's filament-like structure. Furthermore, the decrease in the number of star forming galaxies and AGN towards the cluster cores suggests that the cluster environment is accelerating the ageing process of galaxies and blocking further accretion of the cold gas that fuels both star formation and black hole accretion activity.

Patterns of climber distribution in temperate forests of the Americas

We propose a standard protocol at the landscape to continental scale for examining to what extent the range of ecological conditions found in temperate latitudes explains the variations in climber species richness and traits. The protocol was tested in forests of the two Americas. The data set included 151 climber species. We selected four categorical traits and grouped these species into six clusters with regard to these traits. Floristic records of American forests were first gathered into alliances, second combined with bioclimatic indices (rainfall, temperature, continentality). We obtained a total of 59 vegetational units in which we calculated values of climber species richness and proportion of clusters. Vegetational units were ultimately gathered into five forest formations (characterized by leaf longevity). Wetlands and uplands were considered separately. Our results emphasize clear trends in large-scale patterns of climber distribution, independently of taxonomy. Climber species richness (in particular woody climbers) peaks in moist and warm upland forests with oceanic climates, and where conifers are rare. In flooded areas, climber richness is also very high and peaks in seasonally flooded large floodplains. In ecological conditions of frost, dryness or lack of nutrients, climber species richness, abundance and trait diversity decline, resulting in the dominance of small, twining and deciduous life traits.

AN ULTRAMASSIVE 1.28 M⊙ WHITE DWARF IN NGC 2099*

ABSTRACT With the Keck I Low-Resolution Imaging Spectrometer we have observed nine white dwarf candidates in the very rich open cluster NGC 2099 (M37). The spectroscopy shows seven to be DA white dwarfs, one to be a DB white dwarf, and one to be a DZ white dwarf. Three of these DA white dwarfs are consistent with singly evolved cluster membership: an ultramassive (1.28 &minus; 0.08 &plus; 0.05 ?> M &CircleDot; ?> ) and two intermediate-mass (0.70 and 0.75 M &CircleDot; ?> ) white dwarfs. Analysis of their cooling ages allows us to calculate their progenitor masses and establish new constraints on the initial–final mass relation. The intermediate-mass white dwarfs are in strong agreement with previous work over this mass regime. The ultramassive white dwarf has V = 24.5, ∼2 mag fainter than the other two remnants. The spectrum of this star has lower quality, so the derived stellar properties (e.g., T eff ?> , log g) have uncertainties that are several times higher than the brighter counterparts. We measure these uncertainties and establish the star’s final mass as the highest-mass white dwarf discovered thus far in a cluster, but we are unable to calculate its progenitor mass because at this high mass and cooler T eff ?> its inferred cooling age is highly sensitive to its mass. At the highest temperatures, however, this sensitivity of cooling age to an ultramassive white dwarf’s mass is only moderate. This demonstrates that future investigations of the upper-mass end of the initial–final mass relation must identify massive, newly formed white dwarfs (i.e., in young clusters with ages 50–150 Myr).

Richness-based masses of rich and famous galaxy clusters

We present a catalog of galaxy cluster masses derived by exploiting the tight correlation between mass and richness, i.e., a properly computed number of bright cluster galaxies. The richness definition adopted in this work is properly calibrated, shows a small scatter with mass, and has a known evolution, which means that we can estimate accurate ($0.16$ dex) masses more precisely than by adopting any other richness estimates or X-ray or SZ-based proxies based on survey data. We measured a few hundred galaxy clusters at $0.05<z<0.22$ in the low-extinction part of the Sloan Digital Sky Survey footprint that are in the 2015 catalog of Planck-detected clusters, that have a known X-ray emission, that are in the Abell catalog, or that are among the most most cited in the literature. Diagnostic plots and direct images of clusters are individually inspected and we improved cluster centers and, when needed, we revised redshifts. Whenever possible, we also checked for indications of contamination from other clusters on the line of sight, and found ten such cases. All this information, with the derived cluster mass values, are included in the distributed value-added cluster catalog of the 275 clusters with a derived mass larger than $10^{14}$ M$_{\odot}$. A web front-end is available at http://www.brera.mi.astro.it/$\sim$andreon/famous.html . Finally, in a technical appendix we illustrate with Planck clusters how to minimize the sensitivity of comparisons between masses listed in different catalogs to the specific overlapping of the considered subsamples, a problem recognized

Shell-like structures in our cosmic neighbourhood

Signatures of the processes in the early Universe are imprinted in the cosmic web. Some of them may define shell-like structures characterised by typical scales. We search for shell-like structures in the distribution of nearby rich clusters of galaxies drawn from the SDSS DR8. We calculate the distance distributions between rich clusters of galaxies, and groups and clusters of various richness, look for the maxima in the distance distributions, and select candidates of shell-like structures. We analyse the space distribution of groups and clusters forming shell walls. We find six possible candidates of shell-like structures, in which galaxy clusters have maxima in the distance distribution to other galaxy groups and clusters at the distance of about 120 Mpc/h. The rich galaxy cluster A1795, the central cluster of the Bootes supercluster, has the highest maximum in the distance distribution of other groups and clusters around them at the distance of about 120 Mpc/h among our rich cluster sample, and another maximum at the distance of about 240 Mpc/h. The structures of galaxy systems causing the maxima at 120 Mpc/h form an almost complete shell of galaxy groups, clusters and superclusters. The richest systems in the nearby universe, the Sloan Great Wall, the Corona Borealis supercluster and the Ursa Major supercluster are among them. The probability that we obtain maxima like this from random distributions is lower than 0.001. Our results confirm that shell-like structures can be found in the distribution of nearby galaxies and their systems. The radii of the possible shells are larger than expected for a BAO shell (approximately 109 Mpc/h versus approximately 120 Mpc/h), and they are determined by very rich galaxy clusters and superclusters with high density contrast while BAO shells are barely seen in the galaxy distribution. We discuss possible consequences of these differences.

An extensive radial velocity survey towards NGC 6253

The old and metal rich open cluster NGC 6253 was observed with the FLAMES multi-object spectrograph during an extensive radial velocity campaign monitoring 317 stars with a median of 15 epochs per object. All the targeted stars are located along the upper main sequence of the cluster between 14.8 $<$ V $<$ 16.5. Fifty nine stars are confirmed cluster members both by radial velocities and proper motions and do not show evidence of variability. We detected 45 variable stars among which 25 belong to NGC 6253. We were able to derive an orbital solution for 4 cluster members (and for 2 field stars) yielding minimum masses in between $\sim$90 M$\rm_J$ and $\sim$460 M$\rm_J$ and periods between 3 and 220 days. Simulations demonstrated that this survey was sensitive to objects down to 30 M$\rm_J$ at 10 days orbital periods with a detection efficiency equal to 50%. On the basis of these results we concluded that the observed frequency of binaries down to the hydrogen burning limit and up to 20 days orbital period is around (1.5$\pm$1.3)% in NGC 6253. The overall observed frequency of binaries around the sample of cluster stars is (13$\pm$3)%. The median radial velocity precision achieved by the GIRAFFE spectrograph in this magnitude range was around $\sim$240m$\rm\,s^{-1}$ ($\sim$180 m$\rm\,s^{-1}$ for UVES). Based on a limited follow-up analysis of 7 stars in our sample with the HARPS spectrograph we determined that a precision of 35 m $\rm s^{-1}$ can be reached in this magnitude range, offering the possibility to further extend the variability analysis into the substellar domain. Prospects are even more favourable once considering the upcoming ESPRESSO spectrograph at VLT.

TWO MASSIVE WHITE DWARFS FROM NGC 2323 AND THE INITIAL–FINAL MASS RELATION FOR PROGENITORS OF 4–6.5 M⊙*

ABSTRACT We observed a sample of 10 white dwarf candidates in the rich open cluster NGC 2323 (M50) with the Keck Low-Resolution Imaging Spectrometer. The spectroscopy shows eight to be DA white dwarfs, with six of these having high signal-to-noise ratio appropriate for our analysis. Two of these white dwarfs are consistent with singly evolved cluster membership, and both are high mass ∼1.07 M ⊙, and give equivalent progenitor masses of 4.69 M ⊙. To supplement these new high-mass white dwarfs and analyze the initial–final mass relation (IFMR), we also looked at 30 white dwarfs from publicly available data that are mostly all high-mass ( &gsim; 0.9 ?> M ⊙). These original published data exhibited significant scatter, and to test if this scatter is true or simply the result of systematics, we have uniformly analyzed the white dwarf spectra and have adopted thorough photometric techniques to derive uniform cluster parameters for their parent clusters. The resulting IFMR scatter is significantly reduced, arguing that mass-loss rates are not stochastic in nature and that within the ranges of metallicity and mass analyzed in this work mass loss is not highly sensitive to variations in metallicity. Lastly, when adopting cluster ages based on Y2 isochrones, the slope of the high-mass IFMR remains steep and consistent with that found from intermediate-mass white dwarfs, giving a linear IFMR from progenitor masses between 3 and 6.5 M ⊙. In contrast, when adopting the slightly younger cluster ages based on PARSEC isochrones, the high-mass IFMR has a moderate turnover near an initial mass of 4 M ⊙.

The new world of inorganic polyphosphates.

Post-translational modifications (PTMs) add regulatory features to proteins that help establish the complex functional networks that make up higher organisms. Advances in analytical detection methods have led to the identification of more than 200 typesof PTMs. However, some modifications are unstable under the present detection methods, anticipating the existence of further modifications and a much more complex map of PTMs. An example is the recently discovered protein modification polyphosphorylation. Polyphosphorylation is mediated by inorganic polyphosphate (polyP) and represents the covalent attachment of this linear polymer of orthophosphate to lysine residues in target proteins. This modification has eluded MS analysis as both polyP itself and the phosphoramidate bonds created upon its reaction with lysine residues are highly unstable in acidic conditions. Polyphosphorylation detection was only possible through extensive biochemical characterization. Two targets have been identified: nuclear signal recognition 1 (Nsr1) and its interacting partner, topoisomerase 1 (Top1). Polyphosphorylation occurs within a conserved N-terminal polyacidic serine (S) and lysine (K) rich (PASK) cluster. It negatively regulates Nsr1-Top1 interaction and impairs Top1 enzymatic activity, namely relaxing supercoiled DNA. Modulation of cellular levels of polyP regulates Top1 activity by modifying its polyphosphorylation status. Here we discuss the significance of the recently identified new role of inorganic polyP.

Ionization of Phosphatidylinositol (3,4,5)-Trisphosphate in Mixed Lipid Membranes

Ionization of Phosphatidylinositol (3,4,5)-trisphosphate in mixed lipid membranes Phosphatidylinositides are phospholipids that play many crucial roles in cells including stress and growth signaling. Phosphatidylinositol (3,4,5)-trisphosphate (PIP3) is synthesized from phosphatidylinositol (4,5)-bisphosphate (PIP2) by the PI3K enzyme and can alternately be converted back to PIP2 via the tumor suppressor PTEN. PIP3 is present in small amounts in the cell membrane, but is known to target specific proteins containing PH domains, including the AKT/PKB, PDK1, and BTK1 pathways. It has been shown that the ionization state of PIP3 can play a role in its interaction with other molecules, specifically proteins at the plasma membrane. In this study, nuclear magnetic resonance was used to analyze the ionization of PIP3 in mixed lipid membranes. We have previously observed that PI can interact with PIP2, altering the ionization of PIP2 and triggering the formation of PIP2 rich clusters within the membrane. Here we determine the effect of PI on the ionization of PIP3. PIP3 has a highly complex titration behavior due to the presence of intramolecular hydrogen bonds between the phosphate groups. This complex PIP3 ionization behavior was modeled in order to determine pKa values for each individual ionization step of the phosphate groups. In the presence of PI we observe a distinct shift in the pKa values of PIP3, suggesting a possible electrostatic hydrogen bond switch occurring between the PI and PIP3 headgroups. The interaction between PI and PIP3 may have important implications for PIP3-mediated signaling pathways leading to altered ionization of PIP3 and potentially altered lateral organization within the membrane.

Myosin-dependent remodeling of adherens junctions protects junctions from Snail-dependent disassembly.

Although Snail is essential for disassembly of adherens junctions during epithelial-mesenchymal transitions (EMTs), loss of adherens junctions in Drosophila melanogaster gastrula is delayed until mesoderm is internalized, despite the early expression of Snail in that primordium. By combining live imaging and quantitative image analysis, we track the behavior of E-cadherin-rich junction clusters, demonstrating that in the early stages of gastrulation most subapical clusters in mesoderm not only persist, but move apically and enhance in density and total intensity. All three phenomena depend on myosin II and are temporally correlated with the pulses of actomyosin accumulation that drive initial cell shape changes during gastrulation. When contractile myosin is absent, the normal Snail expression in mesoderm, or ectopic Snail expression in ectoderm, is sufficient to drive early disassembly of junctions. In both cases, junctional disassembly can be blocked by simultaneous induction of myosin contractility. Our findings provide in vivo evidence for mechanosensitivity of cell-cell junctions and imply that myosin-mediated tension can prevent Snail-driven EMT.

Exploiting Document Level Semantics in Document Clustering

Document clustering is an unsupervised machine learning method that separates a large subject heterogeneous collection (Corpus) into smaller, more manageable, subject homogeneous collections (clusters). Traditional method of document clustering works around extracting textual features like: terms, sequences, and phrases from documents. These features are independent of each other and do not cater meaning behind these word in the clustering process. In order to perform semantic viable clustering, we believe that the problem of document clustering has two main components: (1) to represent the document in such a form that it inherently captures semantics of the text. This may also help to reduce dimensionality of the document and (2) to define a similarity measure based on the lexical, syntactic and semantic features such that it assigns higher numerical values to document pairs which have higher syntactic and semantic relationship. In this paper, we propose a representation of document by extracting three different types of features from a given document. These are lexical , syntactic and semantic features. A meta-descriptor for each document is proposed using these three features: first lexical, then syntactic and in the last semantic. A document to document similarity matrix is produced where each entry of this matrix contains a three value vector for each lexical , syntactic and semantic . The main contributions from this research are (i) A document level descriptor using three different features for text like: lexical, syntactic and semantics. (ii) we propose a similarity function using these three, and (iii) we define a new candidate clustering algorithm using three component of similarity measure to guide the clustering process in a direction that produce more semantic rich clusters. We performed an extensive series of experiments on standard text mining data sets with external clustering evaluations like: FMeasure and Purity, and have obtained encouraging results.

Structural and optical study of Ce segregation in Ce-doped SiO1.5 thin films

Cerium doped SiO1.5 thin films fabricated by evaporation and containing silicon nanocrystals were investigated by atom probe tomography. The effect of post-growth annealing treatment has been systematically studied to correlate the structural properties obtained by atom probe tomography to the optical properties measured by photoluminescence spectroscopy. The atom probe results demonstrated the formation of Ce-Si rich clusters upon annealing at 900 °C which leads to a drastic decrease of the Ce-related luminescence. At 1100 °C, pure Si nanocrystals and optically active cerium silicate compounds are formed. Consequently, the Ce-related luminescence is found to re-appear at this temperature while no Si-nanocrystal related luminescence is observed for films containing more than 3% Ce.