The inner structure and kinematics of the Sagittarius dwarf galaxy as a product of tidal stirring

The tidal stirring model envisions the formation of dwarf spheroidal (dSph) galaxies in the Local Group via the tidal interaction of disky dwarf systems with a larger host galaxy like the Milky Way. These progenitor disks are embedded in extended dark halos and during the evolution both components suffer strong mass loss. In addition, the disks undergo the morphological transformation into spheroids and the transition from ordered to random motion of their stars. Using collisionless N-body simulations we construct a model for the nearby and highly elongated Sagittarius (Sgr) dSph galaxy within the framework of the tidal stirring scenario. Constrained by the present known orbit of the dwarf, the model suggests that in order to produce the majority of tidal debris observed as the Sgr stream, but not yet transform the core of the dwarf into a spherical shape, Sgr must have just passed the second pericenter of its current orbit around the Milky Way. In the model, the stellar component of Sgr is still very elongated after the second pericenter and morphologically intermediate between the strong bar formed at the first pericenter and the almost spherical shape existing after the third pericenter. This is thus the first model of the evolution of the Sgr dwarf that accounts for its observed very elliptical shape. At the present time there is very little intrinsic rotation left and the velocity gradient detected along the major axis is almost entirely of tidal origin. We model the recently measured velocity dispersion profile for Sgr assuming that mass traces light and estimate its current total mass within 5 kpc to be 5.2 x 10^8 M_sun. To have this mass at present, the model requires that the initial virial mass of Sgr must have been as high as 1.6 x 10^10 M_sun, comparable to that of the Large Magellanic Cloud, which may serve as a suitable analog for the pre-interaction, Sgr progenitor.Comment: 14 pages, 14 figures, minor changes to match the version published in Ap

Spin coefficients for four-dimensional neutral metrics, and null geometry

Notation for spin coefficients for metrics of neutral signature in four dimensions is introduced. The utility and interpretation of spin coefficients is explored through themes in null geometry familiar from (complex) general relativity. Four-dimensional Walker geometry is exploited to provide examples and the generalization of the real neutral version of Pleba\~nski's (1975) second heavenly equation to certain Walker geometries given in Law and Matsushita [16] is extended further.Comment: 50 pages; minor typos corrected in v

Exploring Halo Substructure with Giant Stars: Spectroscopy of Stars in the Galactic Anticenter Stellar Structure

To determine the nature of the recently discovered, ring-like stellar structure at the Galactic anticenter, we have collected spectra of a set of presumed constituent M giants selected from the 2MASS point source catalog. Radial velocities have been obtained for stars spanning ~100 degrees, exhibiting a trend in velocity with Galactic longitude and an estimated dispersion of 20 +/- 4 km/sec. A mean metallicity [Fe/H] = -0.4 +/- 0.3 measured for these stars combines with previous evidence from the literature to suggest a population with a significant metallicity spread. In addition, a curious alignment of at least four globular clusters of lower mean metallicity is noted to be spatially and kinematically consistent with this stellar distribution. We interpret the M giant sample position and velocity variation with Galactic longitude as suggestive of a satellite galaxy currently undergoing tidal disruption in a non-circular, prograde orbit about the Milky Way.Comment: (1) University of Virginia, 4 pages, 3 figures, accepted for publication in The Astrophysical Journal Letter

Testing ‘Proportion of Females Calving’ as an indicator for population-level reproductive performance for black rhinoceros (Diceros bicornis)

The proportion of females calving (PFC) each year has been employed as an indicator of population reproductive performance in ungulates, especially for species that breed annually, because it requires less detailed population data than inter-birthing intervals and age at first reproduction. For asynchronous breeders with inter-birthing intervals longer than a year such as megaherbivores, however, it is unclear how much annual variation in PFC is expected and whether false signals of density feedback or environmental influence might result from analyzing PFC data. We used census data from a well studied, closed, expanding population of black rhinoceros (Diceros bicornis) to study annual variation in PFC over 22 years. Our analysis of PFC data yielded no false signals of density feedback but weak evidence for an unexpected influence of rainfall. The PFC data exhibited considerable variation, which we attribute to autocorrelation in the time series of PFC data, ‘demographic-founding effects’, changes in stage structure, and demographic stochasticity, some of which the modelling of PFC appears to confuse with an influence of rainfall. We expect such variation to be common in introduced populations and to persist for some years, complicating the interpretation of PFC, though moving averages of PFC can help if employed cautiously. While our analysis does not undermine the possible utility of PFC, the analysis and interpretation of PFC values require care

Interventions for central serous chorioretinopathy: a network meta-analysis.

BACKGROUND: Central serous chorioretinopathy (CSC) is characterized by serous detachment of the neural retina with dysfunction of the choroid and retinal pigment epithelium (RPE). The effects on the retina are usually self limited, although some people are left with irreversible vision loss due to progressive and permanent photoreceptor damage or RPE atrophy. There have been a variety of interventions used in CSC, including, but not limited to, laser treatment, photodynamic therapy (PDT), and intravitreal injection of anti-vascular endothelial growth factor (anti-VEGF) agents. However, it is not known whether these or other treatments offer significant advantages over observation or other interventions. At present there is no evidence-based consensus on the management of CSC. Due in large part to the propensity for CSC to resolve spontaneously or to follow a waxing and waning course, the most common initial approach to treatment is observation. It remains unclear whether this is the best approach with regard to safety and efficacy. OBJECTIVES: To compare the relative effectiveness of interventions for central serous chorioretinopathy. SEARCH METHODS: We searched CENTRAL (which contains the Cochrane Eyes and Vision Trials Register) (2015, Issue 9), Ovid MEDLINE, Ovid MEDLINE In-Process and Other Non-Indexed Citations, Ovid MEDLINE Daily, Ovid OLDMEDLINE (January 1946 to February 2014), EMBASE (January 1980 to October 2015), the ISRCTN registry (www.isrctn.com/editAdvancedSearch), ClinicalTrials.gov (www.clinicaltrials.gov) and the World Health Organization (WHO) International Clinical Trials Registry Platform (ICTRP) (www.who.int/ictrp/search/en). We did not use any date or language restrictions in the electronic searches for trials. We last searched the electronic databases on 5 October 2015. SELECTION CRITERIA: Randomized controlled trials (RCTs) that compared any intervention for CSC with any other intervention for CSC or control. DATA COLLECTION AND ANALYSIS: Two review authors independently selected studies and extracted data. We pooled data from all studies using a fixed-effect model. For interventions applied to the eye (i.e. not systemic interventions), we synthesized direct and indirect evidence in a network meta-analysis model. MAIN RESULTS: We included 25 studies with 1098 participants (1098 eyes) and follow-up from 16 weeks to 12 years. Studies were conducted in Europe, North and South America, Middle East, and Asia. The trials were small (most trials enrolled fewer than 50 participants) and poorly reported; often it was unclear whether key aspects of the trial, such as allocation concealment, had been done. A substantial proportion of the trials were not masked.The studies considered a variety of treatments: anti-VEGF (ranibizumab, bevacizumab), PDT (full-dose, half-dose, 30%, low-fluence), laser treatment (argon, krypton and micropulse laser), beta-blockers, carbonic anhydrase inhibitors, Helicobactor pylori treatment, and nutritional supplements (Icaps, lutein); there were only one or two trials contributing data for each comparison. We downgraded for risk of bias and imprecision for most analyses, reflecting study limitations and imprecise estimates. Network meta-analysis (as planned in our protocol) did not help to resolve this uncertainty due to a lack of trials, and problems with intransitivity, particularly with respect to acute or chronic CSC.Low quality evidence from two trials suggested little difference in the effect of anti-VEGF (ranibizumab or bevacizumab) or observation on change in visual acuity at six months in acute CSC (mean difference (MD) 0.01 LogMAR (logarithm of the minimal angle of resolution), 95% confidence interval (CI) -0.02 to 0.03; 64 participants). CSC had resolved in all participants by six months. There were no significant adverse effects noted.Low quality evidence from one study (58 participants) suggested that half-dose PDT treatment of acute CSC probably results in a small improvement in vision (MD -0.10 logMAR, 95% CI -0.18 to -0.02), less recurrence (risk ratio (RR) 0.10, 95% CI 0.01 to 0.81) and less persistent CSC (RR 0.12, 95% CI 0.01 to 1.02) at 12 months compared to sham treatment. There were no significant adverse events noted.Low quality evidence from two trials (56 participants) comparing anti-VEGF to low-fluence PDT in chronic CSC found little evidence for any difference in visual acuity at 12 months (MD 0.03 logMAR, 95% CI -0.08 to 0.15). There was some evidence that more people in the anti-VEGF group had recurrent CSC compared to people treated with PDT but, due to inconsistency between trials, it was difficult to estimate an effect. More people in the anti-VEGF group had persistent CSC at 12 months (RR 6.19, 95% CI 1.61 to 23.81; 34 participants).Two small trials of micropulse laser, one in people with acute CSC and one in people with chronic CSC, provided low quality evidence that laser treatment may lead to better visual acuity (MD -0.20 logMAR, 95% CI -0.30 to -0.11; 45 participants). There were no significant adverse effects noted.Other comparisons were largely inconclusive.We identified 12 ongoing trials covering the following interventions: aflibercept and eplerenone in acute CSC; spironolactone, eplerenone, lutein, PDT, and micropulse laser in chronic CSC; and micropulse laser and oral mifepristone in two trials where type of CSC not clearly specified. AUTHORS' CONCLUSIONS: CSC remains an enigmatic condition in large part due to a natural history of spontaneous improvement in a high proportion of people and also because no single treatment has provided overwhelming evidence of efficacy in published RCTs. While a number of interventions have been proposed as potentially efficacious, the quality of study design, execution of the study and the relatively small number of participants enrolled and followed to revealing endpoints limits the utility of existing data. It is not clear whether there is a clinically important benefit to treating acute CSC which often resolves spontaneously as part of its natural history. RCTs comparing individual treatments to the natural history would be valuable in identifying potential treatment groups for head-to-head comparison. Of the interventions studied to date, PDT or micropulse laser treatment appear the most promising for study in future trials

Real AlphaBeta-Geometries

By a real alphabeta-geometry we mean a four-dimensional manifold M equipped with a neutral metric h such that (M,h) admits both an integrable distribution of alpha-planes and an integrable distribution of beta-planes. We obtain a local characterization of the metric when at least one of the distributions is parallel (i.e., is a Walker geometry) and the three-dimensional distribution spanned by the alpha- and beta-distributions is integrable. The case when both distributions are parallel, which has been called two-sided Walker geometry, is obtained as a special case. We also consider real \alpha\beta-geometries for which the corresponding spinors are both multiple Weyl principal spinors.Comment: 14 page