56 research outputs found
Optical Flares from the Tidal Disruption of Stars by Massive Black Holes
A star that wanders too close to a massive black hole (BH) is shredded by the
BH's tidal gravity. Stellar gas falls back to the BH, releasing a flare of
energy. In anticipation of upcoming transient surveys, we predict the light
curves and spectra of tidal flares as a function of time, highlighting the
unique signatures of tidal flares in the optical and near-IR. Some of the gas
initially bound to the BH is likely blown away when the fallback rate is
super-Eddington at early times. This outflow produces an optical luminosity
comparable to that of a supernova; such events have durations of ~10 days and
may have been missed in supernova searches that exclude the nuclear regions of
galaxies. When the fallback rate subsides below Eddington, the gas accretes
onto the BH via a thin disk whose emission peaks in the UV to soft X-rays. Some
of this emission is reprocessed by the unbound stellar debris, producing a
spectrum of very broad emission lines (with no corresponding narrow forbidden
lines). These lines are strongest for BHs with MBH ~ 10^5 - 10^6 Msun and thus
optical surveys are particularly sensitive to the lowest mass BHs in galactic
nuclei. Calibrating our models to ROSAT and GALEX observations, we predict
detection rates for Pan-STARRS, PTF, and LSST and highlight observational
challenges in the optical. Pan-STARRS should detect at least several events per
year--many more if current theoretical models of super-Eddington outflows are
correct. These surveys will significantly improve our knowledge of stellar
dynamics in galactic nuclei, the physics of super-Eddington accretion, the
demography of intermediate mass BHs, and the role of tidal disruption in the
growth of massive BHs.Comment: Accepted for publication in MNRA
Laparoscopic versus open colectomy for colon cancer in an older population: a cohort study
<p>Abstract</p> <p>Background</p> <p>Laparoscopic colectomy for colon cancer has been compared with open colectomy in randomized controlled trials, but these studies may not be generalizable because of strict enrollment and exclusion criteria which may explicitly or inadvertently exclude older individuals due to associated comorbidities. Previous studies of older patients undergoing laparoscopic colectomy have generally focused on short-term outcomes. The goals of this cohort study were to identify predictors of laparoscopic colectomy in an older population in the United States and to compare short-term and long-term outcomes.</p> <p>Methods</p> <p>Patients aged 65 years or older with incident colorectal cancer diagnosed 1996-2002 who underwent colectomy within 6 months of cancer diagnosis were identified from the linked Surveillance, Epidemiology, and End Results-Medicare database. Laparoscopic and open colectomy patients were compared with respect to length of stay, blood transfusion requirements, intensive care unit monitoring, complications, 30-day mortality, and long-term survival. We adjusted for potential selection bias in surgical approach with propensity score matching.</p> <p>Results</p> <p>Laparoscopic colectomy cases were associated with left-sided tumors; areas with higher population density, income, and education level; areas in the western United States; and National Cancer Institute-designated cancer centers. Laparoscopic colectomy cases had shorter length of stay and less intensive care unit monitoring. Although laparoscopic colectomy patients (n = 424) had fewer complications (21.5% versus 26.3%), lower 30-day mortality (3.3% versus 5.8%), and longer median survival (6.6 versus 4.8 years) compared with open colectomy patients (n = 27,012), after propensity score matching these differences disappeared.</p> <p>Conclusions</p> <p>In this older population, laparoscopic colectomy practice patterns were associated with factors which likely correlate with tertiary referral centers. Although short-term and long-term survival are comparable, laparoscopic colectomy offers shorter hospitalizations and less intensive care.</p
Genetic diversity Goals and Targets have improved, but remain insufficient for clear implementation of the post-2020 global biodiversity framework
Genetic diversity among and within populations of all species is necessary for people and nature to survive and thrive in a changing world. Over the past three years, commitments for conserving genetic diversity have become more ambitious and specific under the Convention on Biological Diversityâs (CBD) draft post-2020 global biodiversity framework (GBF). This Perspective article comments on how goals and targets of the GBF have evolved, the improvements that are still needed, lessons learned from this process, and connections between goals and targets and the actions and reporting that will be needed to maintain, protect, manage and monitor genetic diversity. It is possible and necessary that the GBF strives to maintain genetic diversity within and among populations of all species, to restore genetic connectivity, and to develop national genetic conservation strategies, and to report on these using proposed, feasible indicators
PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy
We present the discovery and characterisation of PTF10iya, a short-lived (dt
~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21
mag) transient source found by the Palomar Transient Factory. The
ultraviolet/optical spectral energy distribution is reasonably well fit by a
blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x
10^44 erg per s (depending on the details of the extinction correction). A
comparable amount of energy is radiated in the X-ray band that appears to
result from a distinct physical process. The location of PTF10iya is consistent
with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within
350 mas (99.7 per cent confidence radius), or a projected distance of less than
1.2 kpc. At first glance, these properties appear reminiscent of the
characteristic "big blue bump" seen in the near-ultraviolet spectra of many
active galactic nuclei (AGNs). However, emission-line diagnostics of the host
galaxy, along with a historical light curve extending back to 2007, show no
evidence for AGN-like activity. We therefore consider whether the tidal
disruption of a star by an otherwise quiescent supermassive black hole may
account for our observations. Though with limited temporal information,
PTF10iya appears broadly consistent with the predictions for the early
"super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black
hole. Regardless of the precise physical origin of the accreting material, the
large luminosity and short duration suggest that otherwise quiescent galaxies
can transition extremely rapidly to radiate near the Eddington limit; many such
outbursts may have been missed by previous surveys lacking sufficient cadence.Comment: 18 pages, 8 figures; revised following referee's comment
A pragmatic approach for integrating molecular tools into biodiversity conservation
DATA AVAILABILITY STATEMENT : The data availability statement does not apply for this article.SUPPLEMENTARY MATERIAL : TABLE S1. Case studies in which genetic data are being used to inform conservation.Molecular tools are increasingly applied for assessing and monitoring biodiversity and informing conservation action. While recent developments in genetic and genomic methods provide greater sensitivity in analysis and the capacity to address new questions, they are not equally available to all practitioners: There is considerable bias across institutions and countries in access to technologies, funding, and training. Consequently, in many cases, more accessible traditional genetic data (e.g., microsatellites) are still utilized for making conservation decisions. Conservation approaches need to be pragmatic by tackling clearly defined management questions and using the most appropriate methods available, while maximizing the use of limited resources. Here we present some key questions to consider when applying the molecular toolbox for accessible and actionable conservation management. Finally, we highlight a number of important steps to be addressed in a collaborative way, which can facilitate the broad integration of molecular data into conservation.Open Access funding enabled and organized by Projekt DEAL.http://wileyonlinelibrary.com/journal/csp2hj2024BiochemistryGeneticsMicrobiology and Plant PathologySDG-15:Life on lan
A pragmatic approach for integrating molecular tools into biodiversity conservation
Molecular tools are increasingly applied for assessing and monitoring biodiversity and informing conservation action. While recent developments in genetic and genomic methods provide greater sensitivity in analysis and the capacity to address new questions, they are not equally available to all practitioners: There is considerable bias across institutions and countries in access to technologies, funding, and training. Consequently, in many cases, more accessible traditional genetic data (e.g., microsatellites) are still utilized for making conservation decisions. Conservation approaches need to be pragmatic by tackling clearly defined management questions and using the most appropriate methods available, while maximizing the use of limited resources. Here we present some key questions to consider when applying the molecular toolbox for accessible and actionable conservation management. Finally, we highlight a number of important steps to be addressed in a collaborative way, which can facilitate the broad integration of molecular data into conservation
An exploration of the relationship between educational background and the coaching behaviours and practice activities of professional youth soccer coaches
This paper is closed access until 12 December 2019.Background and purpose: Despite the proliferation in recent years of higher education establishments offering tertiary-level study in the field of sports coaching, there is a lack of research into the impact of such courses on coaching practice. The behaviours employed and activities used by coaches during practice sessions is an area where one might expect to see such impact, indeed certain studies have tentatively noted the educational qualifications of coaches and suggested that this may play a role in the application of behaviours more aligned with player learning. The purpose of this study was therefore to compare youth soccer coaches with and without tertiary-level qualifications, examining their coaching behaviours and practice activities. Method: The participants were 10 male professional youth soccer coaches aged 24â55 with an average of 13 years coaching experience. Five of the coaches had completed undergraduate degree courses related to sport coaching. All of the coaches worked with players aged under 9 to under 18 in the youth academy of an English professional soccer club. Systematic observation of coach behaviour and practice activities was carried out using the Coach Analysis and Intervention System (Cushion et al. 2012), while follow-up interviews were used to elicit the coachesâ perceptions of, and rationale for, their behaviour. Findings: The observation data showed that graduate coaches used significantly more divergent questioning than non-graduate coaches, while the interview data revealed a general trend for graduate coaches to show greater self-awareness of behaviours and changes in behaviour between practice types. Graduate coaches also provided more comprehensive rationales, for example, seeing silence as a means of facilitating player decision-making as well as for observation. In contrast to previous research, sessions featured a higher proportion of playing form than training form activities and at over 20% of session duration, the âotherâ practice state was a prominent feature of contact time with players. While some coaches saw âotherâ as wasted time, graduate coaches identified this as an opportunity for group discussion and social interaction. The study adds to existing data about coach behaviours and practice activities, providing evidence that education background may indeed influence coaching practice
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