Disrupted asteroid P/2016 G1. II. Follow-up observations from the Hubble Space Telescope

After the early observations of the disrupted asteroid P/2016 G1 with the 10.4m Gran Telescopio Canarias (GTC), and the modeling of the dust ejecta, we have performed a follow-up observational campaign of this object using the Hubble Space Telescope (HST) during two epochs (June 28 and July 11, 2016). The analysis of these HST images with the same model inputs obtained from the GTC images revealed a good consistency with the predicted evolution from the GTC images, so that the model is applicable to the whole observational period from late April to early July 2016. This result confirms that the resulting dust ejecta was caused by a relatively short-duration event with onset about 350 days before perihelion, and spanning about 30 days (HWHM). For a size distribution of particles with a geometric albedo of 0.15, having radii limits of 1 $\mu$m and 1 cm, and following a power-law with index --3.0, the total dust mass ejected is $\sim$2$\times$10$^7$ kg. As was the case with the GTC observations, no condensations in the images that could be attributed to a nucleus or fragments released after the disruption event were found. However, the higher limiting magnitude reachable with the HST images in comparison with those from GTC allowed us to impose a more stringent upper limit to the observed fragments of $\sim$30 m.Comment: 10 pages, 2 figures Accepted by Astronomical Journal, Nov. 2, 201

Patterns of Dispersion, Movement and Feeding of the Sea Urchin Lytechinus variegatus, and the Potential Implications for Grazing Impact on Live Seagrass

The sea urchin Lytechinus variegatus is a known grazer of both living and dead tissue of turtlegrass, Thalassia testudinum, occasionally denuding large areas of seagrass. Field studies have attempted to assess effects of herbivory on seagrass by enclosing urchins at various densities. However, it is unclear how unrestricted urchins affect seagrass at lower densities more typically observed in the field. This study describes movement, feeding, and distribution of L. variegatus within beds of T. testudinum in St. Joseph Bay, Florida (USA) to quantify this urchin’s impact as a seagrass grazer. Urchins were absent from portions of seagrass beds closest to shore, present at low densities midway across the bed, and at highest densities (up to ~5 individuals/m2) at the offshore edge of the bed. Urchins tended not to aggregate, moved twice as rapidly where seagrass cover was reduced, and moved \u3e 20X faster when placed in areas of open sand. Dead seagrass tissue occurred 4—30X more frequently on oral surfaces than living seagrass tissue. Fecal pellets with dead seagrass tissue were \u3e 3X more common than pellets with live seagrass tissue. Injury to seagrass leaves was more common along dead leaf sections than live sections (\u3e 2—10X). Overall, spatial distributions, movement, and diet indicate that L. variegatus at densities observed in this study would tend to have minimal effects on living seagrass. Episodic periods of denuding grassbeds reported in the literature suggest L. variegatus switches to live seagrass tissue as dead tissue becomes scarce during times of high urchin density

Clinical Preceptors\u27 Perspectives on Clinical Education in Post-Professional Athletic Training Education Programs

Context: Clinical education is the interaction between a clinical preceptor and student within the clinical setting to help the student progress as a clinician. Post-professional athletic training clinical education is especially important to improve these students\u27 clinical knowledge and skills. However, little research has been conducted to assess the pedagogical principles for clinical education at this level or what factors are necessary to enhance the clinical skills and decision-making abilities of post-professional students. Therefore, exploring the perspectives of clinical preceptors involved in post-professional education will help educators understand what strategies are necessary to improve post-professional athletic training education programs (PPATEPs). Objective: To qualitatively investigate clinical preceptors\u27 perspectives and experiences regarding clinical education within PPATEPs. Design: Consensual qualitative research (CQR) with an emergent design. Setting: Telephone interviews were conducted with all participants. Patients or Other Participants: Eleven collegiate post-professional clinical preceptors (7 males, 4 females; average age = 38±7.3 years; average years as an athletic trainer = 15±6.6 years) who were affiliated with a PPATEP were interviewed, representing 11 out of 16 PPATEPs. Data Collection and Analysis: Interview transcripts were coded for themes and categories. Triangulation included a consensus process by the research team and member checking to verify the data. Results: Data analysis yielded four themes relating to clinical education in PPATEPs: importance of clinical education, clinical preceptor responsibilities, clinical preceptor qualities, and barriers to clinical education. Participants indicated that clinical education was important for students to develop clinical skills and give them opportunities to make patient care decisions, and that several fundamental responsibilities and qualities contribute to being an effective clinical preceptor at the post-professional level. Conclusions: Post-professional clinical preceptors recognized that an appropriate balance between autonomy and guided practice in clinical experiences fostered an effective learning environment which allowed post-professional students to improve their clinical and decision-making skills beyond their entry-level skill set. Preceptors should also demonstrate attributes of a clinician, educator, and communicator to be an effective mentor

Hubble Space Telescope Identification of the Optical Counterparts of Ultraluminous X-ray Sources in M51

We present the results of a search for optical identifications of ultraluminous X-ray sources (ULXs) in M51 by using mosaic images taken with the Hubble Space Telescope Advanced Camera for Surveys in filters F435W (B), F555W (V), F814W (I), and F658N (Halpha). Our sample consisting of nine ULXs is defined by analyzing the three Chandra observations of M51 performed in 2000 June, 2001 June, and 2003 Aug. We found four ULXs have one or two candidates for counterparts, while two have multiple stars within their error circles. The other three have no candidate counterparts. Four ULXs are located near or in a star cluster, while others have no association with a cluster. These results indicate that the companion star, environment, and origin of ULXs are probably heterogeneous.Comment: 10 pages, 5 figures, accepted for publication in Ap

Spatial Distribution of Faint Fuzzy Star Clusters in NGC 5195

We present a study of a faint fuzzy star cluster system in the nearby SB0 galaxy NGC 5195 interacting with the famous spiral galaxy NGC 5194 (M51), based on HST ACS BVI mosaic images taken by the Hubble Heritage Team. We have found about 50 faint fuzzy star clusters around NGC 5195 which are larger than typical globular clusters with effective radii r_eff > 7 pc and red with (V-I) > 1.0. They are mostly fainter than M_V ~ 8.3 mag. From the comparison of BVI photometry of these clusters with the simple stellar population models, we find that they are as massive as ~ 10^5 M_sun and older than 1 Gyr. Strikingly, most of these clusters are found to be scattered in an elongated region almost perpendicular to the northern spiral arm of NGC 5194, and the center of the region is slightly north of the NGC 5195 center, while normal compact red clusters of NGC 5195 are located around the bright optical body of the host galaxy. This is in contrast against the cases of NGC 1023 and NGC 3384 where spatial distribution of faint fuzzy clusters shows a ring structure around the host galaxy. We suggest that at least some faint fuzzy clusters are experiencing tidal interactions with the companion galaxy NGC 5194 and must be associated with the tidal debris in the western halo of NGC 5195.Comment: 12 pages, 3 figures, accepted for publication in ApJ Letters (Only a few typos are corrected in the revised version

The LTHE LUMINOSITY, MASS, AND AGE DISTRIBUTIONS OF COMPACT STAR CLUSTERS IN M83 BASED ON HUBBLE SPACE TELESCOPE/WIDE FIELD CAMERA 3 OBSERVATIONS

The newly installed Wide Field Camera 3 (WFC3) on the Hubble Space Telescope has been used to obtain multi-band images of the nearby spiral galaxy M83. These new observations are the deepest and highest resolution images ever taken of a grand-design spiral, particularly in the near-ultraviolet, and allow us to better differentiate compact star clusters from individual stars and to measure the luminosities of even faint clusters in the U band. We find that the luminosity function (LF) for clusters outside of the very crowded starburst nucleus can be approximated by a power law, dN/dL vprop L α, with α = –2.04 ± 0.08, down to MV ≈ –5.5. We test the sensitivity of the LF to different selection techniques, filters, binning, and aperture correction determinations, and find that none of these contribute significantly to uncertainties in α. We estimate ages and masses for the clusters by comparing their measured UBVI, Hα colors with predictions from single stellar population models. The age distribution of the clusters can be approximated by a power law, dN/dτ vprop τγ, with γ = –0.9 ± 0.2, for M gsim few × 103 M sun and τ lsim 4 × 108 yr. This indicates that clusters are disrupted quickly, with ≈80%-90% disrupted each decade in age over this time. The mass function of clusters over the same M-τ range is a power law, dN/dM vprop M β, with β = –1.94 ± 0.16, and does not have bends or show curvature at either high or low masses. Therefore, we do not find evidence for a physical upper mass limit, MC , or for the earlier disruption of lower mass clusters when compared with higher mass clusters, i.e., mass-dependent disruption. We briefly discuss these implications for the formation and disruption of the clusters

Alpha(1)-adrenergic-mediated eNOS phosphorylation in intact arteries

Activation of arterial smooth muscle alpha(1)-adrenergic receptors results in vasoconstriction, as well as a secondary release of nitric oxide and slow vasodilation, presumably through gap junction communication from smooth muscle to endothelium. We hypothesized that this slow vasodilation is due to activation of eNOS through phosphorylation at Ser1179 and dephosphorylation at Thr495. Phosphorylation was measured by western blot using mouse mesenteric arteries that were cannulated and pressurized (75 mm Hg) and treated either by 1) 5 mm of phenylephrine superfusion (10(-5) M) (PE5), 2) 15 min of phenylephrine (PE15), 3) 15 min phenylephrine followed by acetylcholine (10(-4) M) (PE + ACh), or 4) 20 min time control with no treatment (NT) [4-5 arteries pooled per treatment per blot; 5 blots performed]. These treatments allowed correlation between vasomotor changes, namely maximal constriction (PE5), slow vasodilation (PE15), and maximal dilation (PE + ACh), and relative phosphorylation changes. Phosphorylation of eNOS at Ser1179 was increased relative to NT by more than 2-fold at PE5 and remained similarly increased at PE15 and PE + ACh. Phosphotylation of eNOS at Thr495 was less in all treatments relative to NT, but not significantly. Treatment with L-NAME (10(-4) M) or endothelial denudation indicated that the slow dilation in response to phenylephrine was completely due to nitric oxide synthase and was endothelial dependent. These results indicate that eNOS phosphorylation at Ser1179 occurs before the slow dilation and is not actively involved in this vasodilation or dilation to acetylcholine, but may play a permissive role in eNOS activation by other mechanisms. It is not yet known what mechanism is responsible for Ser1179 phosphorylation with phenylephrine stimulation. (C) 2012 Elsevier Inc. All rights reserved