The Globular Cluster System of the Coma cD Galaxy NGC 4874 from Hubble Space Telescope ACS and WFC3/IR Imaging

We present new HST optical and near-infrared (NIR) photometry of the rich globular cluster (GC) system of 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) and F814W (I) passbands and the Wide Field Camera 3 IR Channel in F160W (H). 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-I > 1. Bimodality is also present, though less conspicuously, in the optical-NIR I-H color. Consistent with past work, we find evidence for nonlinearity in the g-I versus I-H 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-H color as a function of magnitude; for M_814 < -10 mag, these trends imply a steep mass-metallicity scaling with $Z\propto M_{\rm GC}^{1.4\pm0.4}$, 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 towards 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 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.Comment: 24 pages, 20 figures, accepted for publication in Ap

Robust Tensioned Kevlar Suspension Design

One common but challenging problem in cryogenic engineering is to produce a mount that has excellent thermal isolation but is also rigid. Such mounts can be achieved by suspending the load from a network of fibers or strings held in tension. Kevlar fibers are often used for this purpose owing to their high strength and low thermal conductivity. A suite of compact design elements has been developed to improve the reliability of suspension systems made of Kevlar

The role of Cra in regulating acetate excretion and osmotic tolerance in E. coli K-12 and E. coli B at high density growth

<p>Abstract</p> <p>Background</p> <p><it>E. coli </it>B (BL21), unlike <it>E.coli </it>K-12 (JM109) is insensitive to glucose concentration and, therefore, grows faster and produces less acetate than <it>E. coli </it>K-12, especially when growing to high cell densities at high glucose concentration. By performing genomic analysis, it was demonstrated that the cause of this difference in sensitivity to the glucose concentration is the result of the differences in the central carbon metabolism activity. We hypothesized that the global transcription regulator Cra (FruR) is constitutively expressed in <it>E. coli </it>B and may be responsible for the different behaviour of the two strains. To investigate this possibility and better understand the function of Cra in the two strains, <it>cra </it>- negative <it>E. coli </it>B (BL21) and <it>E. coli </it>K-12 (JM109) were prepared and their growth behaviour and gene expression at high glucose were evaluated using microarray and real-time PCR.</p> <p>Results</p> <p>The deletion of the <it>cra </it>gene in <it>E. coli </it>B (BL21) minimally affected the growth and maximal acetate accumulation, while the deletion of the same gene in <it>E.coli </it>K-12 (JM109) caused the cells to stop growing as soon as acetate concentration reached 6.6 g/L and the media conductivity reached 21 mS/cm. <it>ppsA </it>(gluconeogenesis gene), <it>aceBA </it>(the glyoxylate shunt genes) and <it>poxB </it>(the acetate producing gene) were down-regulated in both strains, while <it>acs </it>(acetate uptake gene) was down-regulated only in <it>E.coli </it>B (BL21). These transcriptional differences had little effect on acetate and pyruvate production. Additionally, it was found that the lower growth of <it>E. coli </it>K-12 (JM109) strain was the result of transcription inhibition of the osmoprotectant producing <it>bet </it>operon (<it>betABT</it>).</p> <p>Conclusions</p> <p>The transcriptional changes caused by the deletion of <it>cra </it>gene did not affect the activity of the central carbon metabolism, suggesting that Cra does not act alone; rather it interacts with other pleiotropic regulators to create a network of metabolic effects. An unexpected outcome of this work is the finding that <it>cra </it>deletion caused transcription inhibition of the <it>bet </it>operon in <it>E. coli </it>K-12 (JM109) but did not affect this operon transcription in <it>E. coli </it>B (BL21). This property, together with the insensitivity to high glucose concentrations, makes this the <it>E. coli </it>B (BL21) strain more resistant to environmental changes.</p

Systematic Review of the Predictors of Recurrent Hemorrhage After Endoscopic Hemostatic Therapy for Bleeding Peptic Ulcers

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73351/1/j.1572-0241.2008.02070.x.pd

E-Type Delayed Fluorescence of a Phosphine-Supported Cu_2(μ-NAr_2)_2 Diamond Core: Harvesting Singlet and Triplet Excitons in OLEDs

A highly emissive bis(phosphine)diarylamido dinuclear copper(I) complex (quantum yield = 57%) was shown to exhibit E-type delayed fluorescence by variable temperature emission spectroscopy and photoluminescence decay measurement of doped vapor-deposited films. The lowest energy singlet and triplet excited states were assigned as charge transfer states on the basis of theoretical calculations and the small observed S_1−T_1 energy gap. Vapor-deposited OLEDs doped with the complex in the emissive layer gave a maximum external quantum efficiency of 16.1%, demonstrating that triplet excitons can be harvested very efficiently through the delayed fluorescence channel. The function of the emissive dopant in OLEDs was further probed by several physical methods, including electrically detected EPR, cyclic voltammetry, and photoluminescence in the presence of applied current

Lost in the App Store: The Political Economy of the Canadian Game App Economy

This commentary discusses the political economy of apps. The authors found that Canadian-made game apps are notably absent in the Canadian App Store. This should be both worrying and surprising, as Canada has a relatively sizable game industry. While policy conversations on digital transformation focus on emerging technology, the authors point toward the power and politics of digital platforms as one of the key issues preventing growth in the Canadian digital economy

The Role of Light and Soil Moisture in Plant Community Resistance to Invasion by Yellow Starthistle (\u3ci\u3eCentaurea solstitialis\u3c/i\u3e)

To resist establishment by an invasive plant, a community may require one or more species functionally similar to the invader in their resource acquisition pattern. In this study, communities consisting of native winter annual forbs, non-native annual grasses, native perennials, or a combination of the two native communities were established with and without Centaurea solstitialis to determine the effect of soil moisture and light availability on plant community invasion resistance. The annual plant communities were unable to resist invasion by C. solstitialis. In the native winter annual forb community, senescence in late spring increased light penetration (\u3e75%) to the soil surface, allowing seeded C. solstitialis to quickly establish and dominate the plots. In addition, native annual forbs utilized only shallow soil moisture, whereas C. solstitialis used shallow and deep soil moisture. In communities containing native perennials, only Elymus glaucus established well and eventually dominated the plots. During the first 2 years of establishment, water use pattern of perennial communities was similar to native annual forbs and resistance to invasion was associated with reduced light availability during the critical stages of C. solstitialis establishment. In later years, however, water use pattern of perennial grass communities was similar or greater than C. solstitialis-dominated plots. These results show that Central Valley grasslands that include E. glaucus resist C. solstitialis invasion by a combination of light suppression and soil water competition. Spatiotemporal resource utilization patterns, and not just functional similarity, should be considered when developing restoration strategies to resist invasion by many non-native species

Molecular Dynamics Simulations of Cyanine Dimers Attached to DNA Holliday Junctions

Dye aggregates and their excitonic properties are of interest for their applications to organic photovoltaics, non-linear optics, and quantum information systems. DNA scaffolding has been shown to be effective at promoting the aggregation of dyes in a controllable manner. Specifically, isolated DNA Holliday junctions have been used to achieve strongly coupled cyanine dye dimers. However, the structural properties of the dimers and the DNA, as well as the role of Holliday junction isomerization are not fully understood. To study the dynamics of cyanine dimers in DNA, molecular dynamics simulations were carried out for adjacent and transverse dimers attached to Holliday junctions in two different isomers. It was found that dyes attached to adjacent strands in the junction exhibit stronger dye-DNA interactions and larger inter-dye separations compared to transversely attached dimers, as well as end-to-end arrangements. Transverse dimers exhibit lower inter-dye separations and more stacked configurations. Furthermore, differences in Holliday junction isomer are analyzed and compared to dye orientations. For transverse dyes exhibiting the smaller inter-dye separations, excitonic couplings were calculated and shown to be in agreement with experiment. Our results suggested that dye attachment locations on DNA Holliday junctions affect dye-DNA interactions, dye dynamics, and resultant dye orientations which can guide the design of DNA-templated cyanine dimers with desired properties