The Observational and Theoretical Tidal Radii of Globular Clusters in M87

Globular clusters have linear sizes (tidal radii) which theory tells us are determined by their masses and by the gravitational potential of their host galaxy. To explore the relationship between observed and expected radii, we utilize the globular cluster population of the Virgo giant M87. Unusually deep, high signal-to-noise images of M87 are used to measure the effective and limiting radii of approximately 2000 globular clusters. To compare with these observations, we simulate a globular cluster population that has the same characteristics as the observed M87 cluster population. Placing these simulated clusters in the well-studied tidal field of M87, the orbit of each cluster is solved and the theoretical tidal radius of each cluster is determined. We compare the predicted relationship between cluster size and projected galactocentric distance to observations. We find that for an isotropic distribution of cluster velocities, theoretical tidal radii are approximately equal to observed limiting radii for Rgc < 10 kpc. However, the isotropic simulation predicts a steep increase in cluster size at larger radii, which is not observed in large galaxies beyond the Milky Way. To minimize the discrepancy between theory and observations, we explore the effects of orbital anisotropy on cluster sizes, and suggest a possible orbital anisotropy profile for M87 which yields a better match between theory and observations. Finally, we suggest future studies which will establish a stronger link between theoretical tidal radii and observed radii.Comment: 8 pages, 8 figures, Accepted for publication in Ap

Radiocarbon dating of a multi-phase passage tomb on Baltinglass Hill, Co. Wicklow, Ireland

Baltinglass is a multi-chamber Neolithic passage tomb in Co. Wicklow, Ireland, excavated in the 1930s. This paper presents the results of a radiocarbon dating programme on charred wheat grains and hazelnut shell found underlying the cairn, and on cremated human bone found within and near two of the monument’s five chambers. The results are surprising, in that three of the six determinations on calcined bone pre-date by one or two centuries the charred cereals and hazelnut shells sealed under the cairn, dating to c. 3600–3400 cal bc. Of the remaining three bone results, one is coeval with the charred plant remains, while the final two can be placed in the period 3300/3200–2900 cal bc, that is more traditionally associated with developed passage tombs. A suggested sequence of construction is presented beginning with a simple tomb lacking a cairn, followed by a burning event – perhaps a ritual preparation of the ground – involving the deposition of cereal grains and other materials, very rapidly and intentionally sealed under a layer of clay, in turn followed by at least two phases involving the construction of more substantial chambers and associated cairns. What was already a complex funerary monument has proven to be even more complex, with a history spanning at least six centuries

Propionibacterium acnes and acne vulgaris: new insights from the integration of population genetic, multi-omic, biochemical and host-microbe studies.

The anaerobic bacterium Propionibacterium acnes is believed to play an important role in the pathophysiology of the common skin disease acne vulgaris. Over the last 10 years our understanding of the taxonomic and intraspecies diversity of this bacterium has increased tremendously, and with it the realisation that particular strains are associated with skin health while others appear related to disease. This extensive review will cover our current knowledge regarding the association of P. acnes phylogroups, clonal complexes and sequence types with acne vulgaris based on multilocus sequence typing of isolates, and direct ribotyping of the P. acnes strain population in skin microbiome samples based on 16S rDNA metagenomic data. We will also consider how multi-omic and biochemical studies have facilitated our understanding of P. acnes pathogenicity and interactions with the host, thus providing insights into why certain lineages appear to have a heightened capacity to contribute to acne vulgaris development, while others are positively associated with skin health. We conclude with a discussion of new therapeutic strategies that are currently under investigation for acne vulgaris, including vaccination, and consider the potential of these treatments to also perturb beneficial lineages of P. acnes on the skin

Dissecting the Colour-Magnitude Diagram: A Homogeneous Catalogue of Stellar Populations in Globular Clusters

We present a homogeneous catalogue for blue straggler, red giant branch, horizontal branch and main-sequence turn-off stars in a sample of 35 clusters taken from the ACS Survey for Globular Clusters. As a result of the superior photometry and relatively large field of view offered by the ACS data, this new catalogue is a significant improvement upon the one presented in Leigh, Sills & knigge (2007). Using our catalogue, we study and compare the radial distributions of the different stellar populations. We have confirmed our previous result (Knigge, Leigh & Sills 2009) that there is a clear, but sub-linear, correlation between the number of blue stragglers found in the cluster core and the total stellar mass contained within it. By considering a larger spatial extent than just the core, our results suggest that mass segregation is not the dominant effect contributing to the observed sub-linearity. We also investigate the radial distributions of the different stellar populations in our sample of clusters. Our results are consistent with a linear relationship between the number of stars in these populations and the total mass enclosed within the same radius. Therefore, we conclude that the cluster dynamics does not significantly affect the relative distributions of these populations in our sample.Comment: 14 pages, 5 figures, accepted for publication in MNRA

Randomized Controlled Trial of the Use of an Educational Cancer Website to Increase Cancer Patient’s Participation into a Research Study

[[abstract]]The present randomized controlled trial was conducted to determine if providing access to an educational colorectal cancer Website for patients with colorectal cancer might increase their subsequent participation in a population-based cancer study. A total of 384 potential participants recruited from colorectal cancer cases identified from the Ontario Cancer Registry and the Mount Sinai Hospital in Toronto, Ontario, Canada were randomly divided into two groups. The control group was mailed an invitation package containing a brochure describing a population-based cancer registry (the Ontario Familial Colorectal Cancer Registry, OFCCR), a family history questionnaire, and a colorectal cancer educational pamphlet. The intervention group was mailed the information for access to a colorectal cancer educational Website in addition to the materials sent to the control group. Results indicated that providing access information to an educational Website about colorectal cancer did not increase the participation of colorectal cancer patients in a population-based cancer study. The participation for the intervention group (66%) was not significantly different (p=0.38) from the control group (62%). The additional provision of a Website with colorectal cancer information to patients appears not to be an effective strategy to improve subsequent participation in a population-based cancer study

Chronic testicular Chlamydia muridarum infection impairs mouse fertility and offspring development

With approximately 131 million new genital tract infections occurring each year, Chlamydia is the most common sexually transmitted bacterial pathogen worldwide. Male and female infections occur at similar rates and both cause serious pathological sequelae. Despite this, the impact of chlamydial infection on male fertility has long been debated, and the effects of paternal chlamydial infection on offspring development are unknown. Using a male mouse chronic infection model, we show that chlamydial infection persists in the testes, adversely affecting the testicular environment. Infection increased leukocyte infiltration, disrupted the blood:testis barrier and reduced spermiogenic cell numbers and seminiferous tubule volume. Sperm from infected mice had decreased motility, increased abnormal morphology, decreased zona-binding capacity, and increased DNA damage. Serum anti-sperm antibodies were also increased. When both acutely and chronically infected male mice were bred with healthy female mice, 16.7% of pups displayed developmental abnormalities. Female offspring of chronically infected sires had smaller reproductive tracts than offspring of noninfected sires. The male pups of infected sires displayed delayed testicular development, with abnormalities in sperm vitality, motility, and sperm-oocyte binding evident at sexual maturity. These data suggest that chronic testicular Chlamydia infection can contribute to male infertility, which may have an intergenerational impact on sperm quality

An Analytic Model for Blue Straggler Formation in Globular Clusters

We present an analytic model for blue straggler formation in globular clusters. We assume that blue stragglers are formed only through stellar collisions and binary star evolution, and compare our predictions to observed blue straggler numbers taken from the catalogue of Leigh, Sills & Knigge (2011). We can summarize our key results as follows: (1) Binary star evolution consistently dominates blue straggler production in all our best-fitting models. (2) In order to account for the observed sub-linear dependence of blue straggler numbers on the core masses (Knigge, Leigh & Sills 2009), the core binary fraction must be inversely proportional to the total cluster luminosity and should always exceed at least a few percent. (3) In at least some clusters, blue straggler formation must be enhanced by dynamical encounters (either via direct collisions or by stimulating mass-transfer to occur by altering the distribution of binary orbital parameters) relative to what is expected by assuming a simple population of binaries evolving in isolation. (4) The agreement between the predictions of our model and the observations can be improved by including blue stragglers that form outside the core but later migrate in due to dynamical friction. (5) Longer blue straggler lifetimes are preferred in models that include blue stragglers formed outside the core since this increases the fraction that will have sufficient time to migrate in via dynamical friction.Comment: 11 pages, 4 figures, accepted for publication in MNRA

Macrophage-induced blood vessels guide Schwann cell-mediated regeneration of peripheral nerves

The peripheral nervous system has remarkable regenerative capacities in that it can repair a fully cut nerve. This requires Schwann cells to migrate collectively to guide regrowing axons across a 'bridge' of new tissue, which forms to reconnect a severed nerve. Here we show that blood vessels direct the migrating cords of Schwann cells. This multicellular process is initiated by hypoxia, selectively sensed by macrophages within the bridge, which via VEGF-A secretion induce a polarized vasculature that relieves the hypoxia. Schwann cells then use the blood vessels as "tracks" to cross the bridge taking regrowing axons with them. Importantly, disrupting the organization of the newly formed blood vessels in vivo, either by inhibiting the angiogenic signal or by re-orienting them, compromises Schwann cell directionality resulting in defective nerve repair. This study provides important insights into how the choreography of multiple cell-types is required for the regeneration of an adult tissue