The tidal force from a supermassive black hole can rip apart a star that passes close enough in what is known as a Tidal Disruption Event (TDE). Typically, half of the destroyed star remains bound to ...the black hole and falls back on highly eccentric orbits, forming an accretion flow that powers a luminous flare. In this paper, we use analytical and numerical calculations to explore the effect of stellar rotation on the fallback rate of material. We find that slowly spinning stars ( * 0.01 breakup) provide only a small perturbation to fallback rates found in the non-spinning case. However, when the star spins faster, there can be significant effects. If the star is spinning retrograde with respect to its orbit, the tidal force from the black hole has to spin down the star first before disrupting it, causing delayed and sometimes only partial disruption events. However, if the star is spinning prograde, this works with the tidal force and the material falls back sooner and with a higher peak rate. We examine the power-law index of the fallback curves, finding that in all cases the fallback rate overshoots the canonical t−5/3 rate briefly after the peak, with the depth of the overshoot dependent on the stellar spin. We also find that, in general, the late time evolution is slightly flatter than the canonical t−5/3 rate. We therefore conclude that considering the spin of the star may be important in modeling observed TDE light curves.
Titan's stratosphere exhibits significant seasonal changes, including breakup and formation of polar vortices. Here we present the first analysis of midinfrared mapping observations from Cassini's ...Composite InfraRed Spectrometer to cover the entire mission (Ls=293–93°, 2004–2017)—midnorthern winter to northern summer solstice. The north polar winter vortex persisted well after equinox, starting breakup around Ls∼60° and fully dissipating by Ls∼90°. Absence of enriched polar air spreading to lower latitudes suggests large‐scale circulation changes and photochemistry control chemical evolution during vortex breakup. South polar vortex formation commenced soon after equinox and by Ls∼60° was more enriched in trace gases than the northern middle‐winter vortex and had temperatures ∼20 K colder. This suggests that early‐winter and middle‐winter vortices are dominated by different processes—radiative cooling and subsidence‐induced adiabatic heating respectively. By the end of the mission (Ls=93°) south polar conditions were approaching those observed in the north at Ls=293°, implying seasonal symmetry in Titan's vortices.
Plain Language Summary
The Cassini spacecraft observed Saturn's largest moon, Titan, during its 13‐year tour of the Saturn system. This allowed temperature and gas composition to be measured for almost half a Titan year, which lasts 29.46 Earth years. Spectra measured by Cassini's infrared spectrometer show that Titan's winter poles are much colder and significantly more enriched in trace gas species than more equatorial latitudes. These observations can be explained by the presence of winter polar vortices, where sinking air enriches the composition of the lower atmosphere and isolation by strong vortex winds allows enhanced cooling in the winter darkness. The coldest temperatures and most extreme trace gas concentrations were seen at Titan's southern pole during early winter and vortex formation.
Key Points
Early‐ and middle‐winter polar vortices have distinct behaviors and different dominant processes
Large‐scale dynamics and photochemistry determine polar chemical evolution during vortex breakup
The northern winter vortex persisted until late spring, with breakup completed by midsummer
The aim of this comprehensive systematic review was to identify the most effective behavioural models and behaviour change strategies, underpinning preschool‐ and school‐based interventions aimed at ...preventing obesity in 4–6‐year‐olds. Searching was conducted from April 1995 to April 2010 using MEDLINE, EMBASE, CINAHL, PsycINFO and The Cochrane Library. Epidemiological studies relevant to the research question with controlled assignment of participants were included in the review, if they had follow‐up periods of 6 months or longer. Outcomes included markers of weight gain; markers of body composition; physical activity behaviour changes and dietary behaviour changes. Twelve studies were included in the review. The most commonly used model was social cognitive theory (SCT)/social learning theory (SLT) either as a single model or in combination with other behavioural models. Studies that used SCT/SLT in the development of the intervention had significant favourable changes in one, or more, outcome measures. In addition, interventions that (i) combined high levels of parental involvement and interactive school‐based learning; (ii) targeted physical activity and dietary change; and (iii) included long‐term follow‐up, appeared most effective. It is suggested that interventions should also be focused on developing children's (and parents') perceived competence at making dietary and physical changes.
The tidal disruption of stars by supermassive black holes (SMBHs) can be used to probe the SMBH mass function, the properties of individual stars, and stellar dynamics in galactic nuclei. Upcoming ...missions will detect thousands of tidal disruption events (TDEs), and accurate theoretical modeling is required to interpret the data with precision. Here we analyze the influence of more realistic stellar structure on the outcome of TDEs; in particular, we compare the fallback rates-being the rate at which tidally disrupted debris returns to the black hole-from progenitors generated with the stellar evolution code mesa to and γ = 5/3 polytropes. We find that mesa-generated density profiles yield qualitatively different fallback rates as compared to polytropic approximations, and that only the fallback curves from low-mass (1 M or less), zero-age main-sequence stars are well fit by either a or 5/3 polytrope. Stellar age has a strong affect on the shape of the fallback curve, and can produce characteristic timescales (e.g., the time to the peak of the fallback rate) that greatly differ from the polytropic values. We use these differences to assess the degree to which the inferred black hole mass from the observed light curve can deviate from the true value, and find that the discrepancy can be at the order of magnitude level. Accurate stellar structure also leads to a substantial variation in the critical impact parameter at which the star is fully disrupted, and can increase the susceptibility of the debris stream to fragmentation under its own self-gravity. These results suggest that detailed modeling is required to accurately interpret observed light curves of TDEs.
The radiant energy budget and internal heat are fundamental properties of giant planets, but precise determination of these properties remains a challenge. Here, we report measurements of Jupiter's ...radiant energy budget and internal heat based on Cassini multi-instrument observations. Our findings reveal that Jupiter's Bond albedo and internal heat, 0.503 ± 0.012 and 7.485 ± 0.160 W m
respectively, are significantly larger than 0.343 ± 0.032 and 5.444 ± 0.425 Wm
, the previous best estimates. The new results help constrain and improve the current evolutionary theories and models for Jupiter. Furthermore, the significant wavelength dependency of Jupiter's albedo implies that the radiant energy budgets and internal heat of the other giant planets in our solar system should be re-examined. Finally, the data sets of Jupiter's characteristics of reflective solar spectral irradiance provide an observational basis for the models of giant exoplanets.
Frailty is independently associated with worse health-related quality of life (HRQOL) in chronic kidney disease (CKD). However, the relationship between frailty and symptom experience is not well ...described in people living with CKD. This study's aim was to evaluate the relationship between frailty and symptom-burden in CKD.
This study is a secondary analysis of a cross-sectional observational study, the QCKD study (ISRCTN87066351), in which participants completed physical activity, cardiopulmonary fitness, symptom-burden and HRQOL questionnaires. A modified version of the Frailty Phenotype, comprising 3 self-report components, was created to assess frailty status. Multiple linear regression was performed to assess the association between symptom-burden/HRQOL and frailty. Logistic regression was performed to assess the association between experiencing symptoms frequently and frailty. Principal Component Analysis was used to assess the experienced symptom clusters.
A total of 353 patients with CKD were recruited with 225 (64%) participants categorised as frail. Frail participants reported more symptoms, had higher symptom scores and worse HRQOL scores. Frailty was independently associated with higher total symptom score and lower HRQOL scores. Frailty was also independently associated with higher odds of frequently experiencing 9 out of 12 reported symptoms. Finally, frail participants experienced an additional symptom cluster that included loss of appetite, tiredness, feeling cold and poor concentration.
Frailty is independently associated with high symptom-burden and poor HRQOL in CKD. Moreover, people living with frailty and CKD have a distinctive symptom experience. Proactive interventions are needed that can effectively identify and address problematic symptoms to mitigate their impact on HRQOL.
Peroxisome Proliferator-Activated Receptor Gamma (PPARG) is one of the three members of the PPAR family of transcription factors. Besides its roles in adipocyte differentiation and lipid metabolism, ...we recently demonstrated an association between PPARG and metastasis in prostate cancer. In this study a functional effect of PPARG on AKT serine/threonine kinase 3 (AKT3), which ultimately results in a more aggressive disease phenotype was identified. AKT3 has previously been shown to regulate PPARG co-activator 1 alpha (PGC1α) localisation and function through its action on chromosome maintenance region 1 (CRM1). AKT3 promotes PGC1α localisation to the nucleus through its inhibitory effects on CRM1, a known nuclear export protein. Collectively our results demonstrate how PPARG over-expression drives an increase in AKT3 levels, which in turn has the downstream effect of increasing PGC1α localisation within the nucleus, driving mitochondrial biogenesis. Furthermore, this increase in mitochondrial mass provides higher energetic output in the form of elevated ATP levels which may fuel the progression of the tumour cell through epithelial to mesenchymal transition (EMT) and ultimately metastasis.
The ToyBox intervention was developed using an evidence‐based approach, using the findings of four reviews. These reviews included three critical and narrative reviews of educational strategies and ...psychological approaches explaining young children's acquisition and formation of energy‐balance related behaviours, and the management of these behaviours, and also a systematic review of behavioural models underpinning school‐based interventions in preschool and school settings for the prevention of obesity in children aged 4–6 years. This paper summarises and translates the findings from these reviews into practical evidence based recommendations for researchers and policy‐makers to consider when developing and implementing interventions for the prevention of overweight and obesity in young (aged 4–6 years) children. The recommendations focus on two behaviours, physical activity and sedentary behaviour, and healthy eating, and include general recommendations, intervention approaches, interventions content, and simple messages. The review also briefly examines the role that the commercial sector plays in hindering or facilitating attempts to create healthy food environments for children. This paper also recognises that childhood obesity is not an issue for the education sector alone; it needs to be tackled at a multi sectoral level, recognizing the particularly important role of local governments, nongovernment organizations and the media.
The existence of methane in Titan's atmosphere (~6% level at the surface) presents a unique enigma, as photochemical models predict that the current inventory will be entirely depleted by ...photochemistry in a timescale of ~20 Myr. In this paper, we examine the clues available from isotopic ratios ( super(12)C/ super(13)C and D/H) in Titan's methane as to the past atmosphere history of this species. We first analyze recent infrared spectra of CH sub(4) collected by the Cassini Composite Infrared Spectrometer, measuring simultaneously for the first time the abundances of all three detected minor isotopologues: super(13)CH sub(4), super(12)CH sub(3)D, and super(13)CH sub(3)D. From these we compute estimates of super(12)C/ super(13)C = 86.5 + or - 8.2 and D/H = (1.59 + or - 0.33) x 10 super(-4), in agreement with recent results from the Huygens GCMS and Cassini INMS instruments. We also use the transition state theory to estimate the fractionation that occurs in carbon and hydrogen during a critical reaction that plays a key role in the chemical depletion of Titan's methane: CH sub(4) + C sub(2)H arrow right CH sub(3) + C sub(2)H sub(2). Using these new measurements and predictions we proceed to model the time evolution of super(12)C/ super(13)C and D/H in Titan's methane under several prototypical replenishment scenarios. In our Model 1 (no resupply of CH sub(4)), we find that the present-day super(12)C/ super(13)C implies that the CH sub(4) entered the atmosphere 60-1600 Myr ago if methane is depleted by chemistry and photolysis alone, but much more recently-most likely less than 10 Myr ago-if hydrodynamic escape is also occurring. On the other hand, if methane has been continuously supplied at the replenishment rate then the isotopic ratios provide no constraints, and likewise for the case where atmospheric methane is increasing. We conclude by discussing how these findings may be combined with other evidence to constrain the overall history of the atmospheric methane.
In this Letter, we report the monitoring of seasonal evolution near Titan's poles. We find Titan's south pole to exhibit since 2010 a strong temperature decrease and a dramatic enhancement of several ...trace species such as complex hydrocarbons and nitriles (HC3N and C6H6 in particular) previously only observed at high northern latitudes. This results from the seasonal change on Titan going from winter (2002) to summer (2017) in the north and, at the same time, the onset of winter in the south pole. During this transition period atmospheric components with longer chemical lifetimes linger in the north, undergoing slow photochemical destruction, while those with shorter lifetimes decrease and reappear in the south. An opposite effect was expected in the north, but not observed with certainty until now. We present here an analysis of high-resolution nadir spectra acquired by Cassini/Cassini Composite Infrared Spectrometer in the past years and describe the temperature and composition variations near Titan's poles. From 2013 until 2016, the northern polar region has shown a temperature increase of 10 K, while the south has shown a more significant decrease (up to 25 K) in a similar period of time. While the south polar region has been continuously enhanced since about 2012, the chemical content in the north is finally showing a clear depletion for most molecules only since 2015. This is indicative of a non-symmetrical response to the seasons in Titan's stratosphere that can set constraints on photochemical and GCM models.
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