Observational Constraints on the Progenitors of Core-Collapse Supernovae: The Case for Missing High-Mass Stars

Over the last 15 years, the supernova community has endeavoured to directly identify progenitor stars for core-collapse supernovae discovered in nearby galaxies. These precursors are often visible as resolved stars in high-resolution images from space-and ground-based telescopes. The discovery rate of progenitor stars is limited by the local supernova rate and the availability and depth of archive images of galaxies, with 18 detections of precursor objects and 27 upper limits. This review compiles these results (from 1999 to 2013) in a distance-limited sample and discusses the implications of the findings. The vast majority of the detections of progenitor stars are of type II-P, II-L, or IIb with one type Ib progenitor system detected and many more upper limits for progenitors of Ibc supernovae (14 in all). The data for these 45 supernovae progenitors illustrate a remarkable deficit of high-luminosity stars above an apparent limit of log L/L-circle dot similar or equal to 5.1 dex. For a typical Salpeter initial mass function, one would expect to have found 13 high-luminosity and high-mass progenitors by now. There is, possibly, only one object in this time-and volume-limited sample that is unambiguously high-mass (the progenitor of SN2009ip) although the nature of that supernovae is still debated. The possible biases due to the influence of circumstellar dust, the luminosity analysis, and sample selection methods are reviewed. It does not appear likely that these can explain the missing high-mass progenitor stars. This review concludes that the community's work to date shows that the observed populations of supernovae in the local Universe are not, on the whole, produced by high-mass (M greater than or similar to 18 M-circle dot) stars. Theoretical explosions of model stars also predict that black hole formation and failed supernovae tend to occur above an initial mass of M similar or equal to 18 M-circle dot. The models also suggest there is no simple single mass division for neutron star or black-hole formation and that there are islands of explodability for stars in the 8-120 M-circle dot range. The observational constraints are quite consistent with the bulk of stars above M similar or equal to 18 M-circle dot collapsing to form black holes with no visible supernovae.

A systematic review and meta-analysis of the survival of feldspathic porcelain veneers over 5 and 10 years

PURPOSE: This systematic review reports on the survival of feldspathic porcelain veneers.

MATERIALS AND METHODS: The Cochrane Library, MEDLINE (OVID), Embase, Web of Knowledge, selected journals, clinical trials registers, and conference proceedings were searched independently by two reviewers. Academic colleagues were also contacted to identify relevant research. Inclusion criteria were human cohort studies (prospective and retrospective) and controlled trials assessing outcomes of feldspathic porcelain veneers in more than 15 patients and with at least some of the veneers in situ for 5 years. Of 4,294 articles identified, 116 studies underwent full-text screenings and 69 were further reviewed for eligibility. Of these, 11 were included in the qualitative analysis and 6 (5 cohorts) were included in meta-analyses. Estimated cumulative survival and standard error for each study were assessed and used for meta-, sensitivity, and post hoc analyses. The I2 statistic and the Cochran Q test and its associated P value were used to evaluate statistical heterogeneity, with a random-effects meta-analysis used when the P value for heterogeneity was less than .1. Galbraith, forest, and funnel plots explored heterogeneity, publication patterns, and small study biases.

RESULTS: The estimated cumulative survival for feldspathic porcelain veneers was 95.7% (95% confidence interval [CI]: 92.9% to 98.4%) at 5 years and ranged from 64% to 95% at 10 years across three studies. A post hoc meta-analysis indicated that the 10-year best estimate may approach 95.6% (95% CI: 93.8% to 97.5%). High levels of statistical heterogeneity were found.

CONCLUSIONS: When bonded to enamel substrate, feldspathic porcelain veneers have a very high 10-year survival rate that may approach 95%. Clinical heterogeneity is associated with differences in reported survival rates. Use of clinically relevant survival definitions and careful reporting of tooth characteristics, censorship, clustering, and precise results in future research would improve metaanalytic estimates and aid treatment decisions.

The VLT-FLAMES Tarantula Survey XXII. Multiplicity properties of the B-type stars

We investigate the multiplicity properties of 408 B-type stars observed in the 30 Doradus region of the Large Magellanic Cloud with multi-epoch spectroscopy from the VLT-FLAMES Tarantula Survey (VFTS). We use a cross-correlation method to estimate relative radial velocities from the helium and metal absorption lines for each of our targets. Objects with significant radial-velocity variations (and with an amplitude larger than 16 km s^-1) are classified as spectroscopic binaries. We find an observed spectroscopic binary fraction (defined by periods of <10^3.5 d and mass ratios >0.1) for the B-type stars, f<inf>B</inf>(obs) = 0.25 ± 0.02, which appears constant across the field of view, except for the two older clusters (Hodge 301 and SL 639). These two clusters have significantly lower binary fractions of 0.08 ± 0.08 and 0.10 ± 0.09, respectively. Using synthetic populations and a model of our observed epochs and their potential biases, we constrain the intrinsic multiplicity properties of the dwarf and giant (i.e. relatively unevolved) B-type stars in 30 Dor. We obtain a present-day binary fraction f<inf>B</inf>(true) = 0.58 ± 0.11, with a flat period distribution. Within the uncertainties, the multiplicity properties of the B-type stars agree with those for the O stars in 30 Dor from the VFTS.

Metformin use and survival after colorectal cancer: A population-based cohort study.

Preclinical evidence suggests that metformin could delay cancer progression. Previous epidemiological studies however have been limited by small sample sizes and certain time-related biases. This study aimed to investigate whether colorectal cancer patients with type 2 diabetes who were exposed to metformin had reduced cancer-specific mortality. We conducted a retrospective cohort study of 1,197 colorectal cancer patients newly diagnosed from 1998 to 2009 (identified from English cancer registries) with type 2 diabetes (based upon Clinical Practice Research Datalink, CPRD, prescription and diagnosis records). In this cohort 382 colorectal cancer-specific deaths occurred up to 2012 from the Office of National Statistics (ONS) mortality data. Metformin use was identified from CPRD prescription records. Using time-dependent Cox regression models, unadjusted and adjusted hazard ratios (HR) and 95% CIs were calculated for the association between post-diagnostic exposure to metformin and colorectal cancer-specific mortality. Overall, there was no evidence of an association between metformin use and cancer-specific death before or after adjustment for potential confounders (adjusted HR 1.06, 95% CI 0.80, 1.40). In addition, after adjustment for confounders, there was also no evidence of associations between other diabetic medications and cancer-specific mortality including sulfonylureas (HR 1.14, 95% CI 0.86, 1.51), insulin use (HR 1.35, 95% CI 0.95, 1.93) or other anti-diabetic medications including thiazolidinediones (HR 0.73, 95% CI 0.46, 1.14). Similar associations were observed by duration of use and for all-cause mortality. This population-based study, the largest to date, does not support a protective association between metformin and survival in colorectal cancer patients.

Obsessive-compulsive symptoms and attentional bias: An eye-tracking methodology

Background and objectives: Cognitive models suggest that attentional biases are integral in the maintenance of obsessive-compulsive symptoms (OCS). Such biases have been established experimentally in anxiety disorders; however, the evidence is unclear in Obsessive Compulsive disorder (OCD). In the present study, an eye-tracking methodology was employed to explore attentional biases in relation to OCS.
Methods: A convenience sample of 85 community volunteers was assessed on OCS using the Yale-Brown Obsessive Compulsive Scale-self report. Participants completed an eye-tracking paradigm where they were exposed to OCD, Aversive and Neutral visual stimuli. Indices of attentional bias were derived from the eye-tracking data.
Results: Simple linear regressions were performed with OCS severity as the predictor and eye-tracking measures of the different attentional biases for each of the three stimuli types were the criterion variables. Findings revealed that OCS severity moderately predicted greater frequency and duration of fixations on OCD stimuli, which reflect the maintenance attentional bias. No significant results were found in support of other biases.
Limitations: Interpretations based on a non-clinical sample limit the generalisability of the conclusions, although use of such samples in OCD research has been found to be comparable to clinical populations. Future research would include both clinical and sub-clinical participants.
Conclusions: Results provide some support for the theory of maintained attention in OCD attentional biases, as opposed to vigilance theory. Individuals with greater OCS do not orient to OCD stimuli any faster than individuals with lower OCS, but once a threat is identified, these individuals allocate more attention to OCS-relevant stimuli.

LD Score regression distinguishes confounding from polygenicity in genome-wide association studies

Both polygenicity (many small genetic effects) and confounding biases, such as cryptic relatedness and population stratification, can yield an inflated distribution of test statistics in genome-wide association studies (GWAS). However, current methods cannot distinguish between inflation from a true polygenic signal and bias. We have developed an approach, LD Score regression, that quantifies the contribution of each by examining the relationship between test statistics and linkage disequilibrium (LD). The LD Score regression intercept can be used to estimate a more powerful and accurate correction factor than genomic control. We find strong evidence that polygenicity accounts for the majority of the inflation in test statistics in many GWAS of large sample size.

Abdominal Aortic Aneurysm Genetic Associations: Mostly False? A Systematic Review and Meta-analysis

OBJECTIVE/BACKGROUND: Many associations between abdominal aortic aneurysm (AAA) and genetic polymorphisms have been reported. It is unclear which are genuine and which may be caused by type 1 errors, biases, and flexible study design. The objectives of the study were to identify associations supported by current evidence and to investigate the effect of study design on reporting associations.

METHODS: Data sources were MEDLINE, Embase, and Web of Science. Reports were dual-reviewed for relevance and inclusion against predefined criteria (studies of genetic polymorphisms and AAA risk). Study characteristics and data were extracted using an agreed tool and reports assessed for quality. Heterogeneity was assessed using I(2) and fixed- and random-effects meta-analyses were conducted for variants that were reported at least twice, if any had reported an association. Strength of evidence was assessed using a standard guideline.

RESULTS: Searches identified 467 unique articles, of which 97 were included. Of 97 studies, 63 reported at least one association. Of 92 studies that conducted multiple tests, only 27% corrected their analyses. In total, 263 genes were investigated, and associations were reported in polymorphisms in 87 genes. Associations in CDKN2BAS, SORT1, LRP1, IL6R, MMP3, AGTR1, ACE, and APOA1 were supported by meta-analyses.

CONCLUSION: Uncorrected multiple testing and flexible study design (particularly testing many inheritance models and subgroups, and failure to check for Hardy-Weinberg equilibrium) contributed to apparently false associations being reported. Heterogeneity, possibly due to the case mix, geographical, temporal, and environmental variation between different studies, was evident. Polymorphisms in nine genes had strong or moderate support on the basis of the literature at this time. Suggestions are made for improving AAA genetics study design and conduct.

The Rossiter-McLaughlin effect reloaded: Probing the 3D spin-orbit geometry, differential stellar rotation, and the spatially-resolved stellar spectrum of star-planet systems

When a planet transits its host star, it blocks regions of the stellar surface from view; this causes a distortion of the spectral lines and a change in the line-of-sight (LOS) velocities, known as the Rossiter-McLaughlin (RM) effect. Since the LOS velocities depend, in part, on the stellar rotation, the RM waveform is sensitive to the star-planet alignment (which provides information on the system’s dynamical history). We present a new RM modelling technique that directly measures the spatially-resolved stellar spectrum behind the planet. This is done by scaling the continuum flux of the (HARPS) spectra by the transit light curve, and then subtracting the infrom the out-of-transit spectra to isolate the starlight behind the planet. This technique does not assume any shape for the intrinsic local profiles. In it, we also allow for differential stellar rotation and centre-to-limb variations in the convective blueshift. We apply this technique to HD 189733 and compare to 3D magnetohydrodynamic (MHD) simulations. We reject rigid body rotation with high confidence (>99% probability), which allows us to determine the occulted stellar latitudes and measure the stellar inclination. In turn, we determine both the sky-projected (λ ≈ −0.4 ± 0.2◦) and true 3D obliquity (ψ ≈ 7+12 −4 ◦ ). We also find good agreement with the MHD simulations, with no significant centre-to-limb variations detectable in the local profiles. Hence, this technique provides a new powerful tool that can probe stellar photospheres, differential rotation, determine 3D obliquities, and remove sky-projection biases in planet migration theories. This technique can be implemented with existing instrumentation, but will become even more powerful with the next generation of high-precision radial velocity spectrographs.

Language Experience Affects Grouping of Musical Instrument Sounds

Language experience clearly affects the perception of speech, but little is known about whether these differences in perception extend to non-speech sounds. In this study, we investigated rhythmic perception of non-linguistic sounds in speakers of French and German using a grouping task, in which complexity (variability in sounds, presence of pauses) was manipulated. In this task, participants grouped sequences of auditory chimeras formed from musical instruments. These chimeras mimic the complexity of speech without being speech. We found that, while showing the same overall grouping preferences, the German speakers showed stronger biases than the French speakers in grouping complex sequences. Sound variability reduced all participants' biases, resulting in the French group showing no grouping preference for the most variable sequences, though this reduction was attenuated by musical experience. In sum, this study demonstrates that linguistic experience, musical experience, and complexity affect rhythmic grouping of non-linguistic sounds and suggests that experience with acoustic cues in a meaningful context (language or music) is necessary for developing a robust grouping preference that survives acoustic variability.