The evolution of Kerr discs and late-time tidal disruption event light curves

An encounter between a passing star and a massive black hole at the centre of a galaxy, a so-called tidal disruption event or TDE, may leave a debris disc that subsequently accretes onto the hole. We solve for the time evolution of such a TDE disc, making use of an evolutionary equation valid for both the Newtonian and Kerr regimes. The late time luminosity emergent from such a disc is of interest as a model diagnostic, as it tends to follow a power law decline. The original simple ballistic fallback model, with equal mass in equal energy intervals, produces a -5/3 power law, while standard viscous disc descriptions yield a somewhat more shallow decline, with an index closer to -1.2. Of four recent, well-observed tidal disruption event candidates however, all had fall-off power law indices smaller than 1 in magnitude. In this work, we revisit the problem of thin disc evolution, solving this reduced problem in full general relativity. Our solutions produce power law indices that are in much better accord with observations. The late time observational data from many TDEs are generally supportive, not only of disc accretion models, but of finite stress persisting down to the innermost stable circular orbit.Comment: 9 pages, 4 figures. Accepted for publication in MNRA

Evolution of relativistic thin discs with a finite ISCO stress: II. Late time behaviour

We present solutions to the relativistic thin disc evolutionary equation using a modified description of the mean fluid flow within the disc. The model takes into account the effects of sub-circular velocities in the innermost disc regions, and resolves otherwise unsustainable behaviour present in simple finite ISCO stress disc models. We show that the behaviour of a relativistic thin disc evolving with a finite ISCO stress is comprised of three distinct stages which join the ordinarily distinct finite and vanishing ISCO stress solutions into a fully continuous model parameterisation. The most important prediction of our model is the existence of an intermediate stage of "stalled accretion", controlled by a single dimensionless parameter. The hallmarks of this evolutionary phase appear to have been seen in GRMHD simulations as well as in the late time X-ray observations of tidal disruption events, but dedicated simulations and extended observations are needed for a deeper understanding.Comment: 10 pages, 8 figures. Accepted for publication in MNRA

Three-dimensional in situ XCT characterisation and FE modelling of cracking in concrete

Three-dimensional (3D) characterisation and modelling of cracking in concrete have been always of great importance and interest in civil engineering. In this study, an in situ microscale X-ray computed tomography (XCT) test was carried out to characterise the 3D microscale structure and cracking behaviour under progressive uniaxial compressive loading. The 3D cracking and fracture behaviour including internal crack opening, closing, and bridging were observed through both 2D tomography slices and 3D CT images. Spatial distributions of voids and cracks were obtained to understand the overall cracking process within the specimen. Furthermore, the XCT images of the original configuration of the specimen were processed and used to build microscale realistic 3D finite element (FE) models. Cohesive interface elements were inserted into the FE mesh to capture complicated discrete crack initiation and propagation. An FE simulation of uniaxial compression was conducted and validated by the in situ XCT compression test results, followed by a tension simulation using the same image-based model to investigate the cracking behaviour. The quantitative agreement between the FE simulation and experiment demonstrates that it is a very promising and effective technique to investigate the internal damage and fracture behaviour in multiphasic composites by combining the in situ micro XCT experiment and image-based FE modelling

The spectral evolution of disc dominated tidal disruption events

We perform a detailed numerical and analytical study of the properties of observed light curves from relativistic thin discs, focussing on observational bands most appropriate for comparison with tidal disruption events (TDEs). We make use of asymptotic expansion techniques applied to the spectral emission integral, using time dependent disc temperature profiles appropriate for solutions of the relativistic thin disc equation. Rather than a power law associated with bolometric disc emission $L \sim t^{-n}$, the observed X-ray flux from disc-dominated TDEs will typically have the form of a power law multiplied by an exponential (see eq. 91). While precise details are somewhat dependent on the nature of the ISCO stress and disc-observer orientational angle, the general form of the time-dependent flux is robust and insensitive to the exact disc temperature profile. We present numerical fits to the UV and X-ray light curves of ASASSN-14li, a particularly well observed TDE. This modelling incorporates strong gravity optics. The full 900 days of ASASSN-14li X-ray observations are very well fit by a simple relativistic disc model, significantly improving upon previous work. The same underlying model also fits the final 1000 days of ASASSN-14li observations in three different UV bandpasses. Finally, we demonstrate that the analytic formulae reproduce the properties of full numerical modelling at both UV and X-ray wavelengths with great fidelity.Comment: 20 pages, 19 figures. Accepted for publication in MNRAS. Comments welcom

Transplantation of cells for cardiac repair

AbstractThe inability of adult cardiomyocytes to divide to a significant extent and regenerate the myocardium after injury leads to permanent deficits in the number of functional cells, which can contribute to the development and progression of heart failure. The transplantation of skeletal myoblasts or stem cells or cardiomyocytes derived from them into the injured myocardium is a novel and promising approach in the treatment of cardiac disease and the restoration of myocardial function. In this article, skeletal myoblasts and embryonic and bone marrow stem cells are discussed in the context of their potential therapeutic use in cardiac failure. The state of the art in both laboratory and clinic is presented. We discuss current and intrinsic limitations of cardiac cellular transplantation and suggest directions for future research

Late time HST UV and optical observations of AT~2018cow: extracting a cow from its background

The bright, blue, rapidly evolving AT2018cow is a well-studied peculiar extragalactic transient. Despite an abundance of multi-wavelength data, there still is no consensus on the nature of the event. We present our analysis of three epochs of Hubble Space Telescope (HST) observations spanning the period from 713-1474 days post burst, paying particular attention to uncertainties of the transient photometry introduced by the complex background in which AT2018cow resides. Photometric measurements show evident fading in the UV and more subtle but significant fading in the optical. During the last HST observation, the transient's optical/UV colours were still bluer than those of the substantial population of compact, young, star-forming regions in the host of AT2018cow, suggesting some continued transient contribution to the light. However, a compact source underlying the transient would substantially modify the resulting spectral energy distribution, depending on its contribution in the various bands. In particular, in the optical filters, the complex, diffuse background poses a problem for precise photometry. An underlying cluster is expected for a supernova occurring within a young stellar environment or a tidal-disruption event (TDE) within a dense older one. While many recent works have focused on the supernova interpretation, we note the substantial similarity in UV light-curve morphology between AT2018cow and several tidal disruption events around supermassive black holes. Assuming AT2018cow arises from a TDE-like event, we fit the late-time emission with a disc model and find $M_{BH} = 10^{3.2{\pm}0.8}$ M$_{\odot}$. Further observations are necessary to determine the late-time evolution of the transient and its immediate environment.Comment: 16 pages, 10 figures. Accepted for publication in MNRA

Investigating self-reported efficacy of lifestyle medicine approaches to tackle erectile dysfunction: a cross-sectional eSurvey based study

Background: Erectile dysfunction (ED) is the most common sexual dysfunction in men. Some types of ED are amenable to treatment using lifestyle medicine approaches with or without pharmacotherapy. Aim: Investigate self-reported efficacy of lifestyle medicine approaches to tackle ED. Methods: A cross-sectional online survey of 1177 community dwelling adults explored the prevalence and methods used to tackle ED in the community setting. We examined differences between participants with and without ED. Variables associated with ED in univariable analyses were included in a multivariable logistic regression to identify variables independently associated with the condition. Outcomes: Self-reported measure: perceived effectiveness of lifestyle medicine interventions to tackle ED. Results: Most respondents (76.5%) had experienced ED, and this was associated with having a long-term condition, taking anti-hypertensive medication, hypercholesterolaemia and obesity. Medication was the most common management strategy overall (65.9%), followed by stress management (43.5%) and weight loss (40.4%). Over half (53.9%) did not use any lifestyle modification strategies to tackle ED. Only 7.0% of ED sufferers received a mental health assessment and 29.2% received other tests (e.g., blood test, medical imaging) by GPs. Cardiovascular training was identified as the best rated strategy by its users (37.8%). Supplements (35.1%) and weight training/physical activity (32.6%) were also positively rated. Clinical implications Structured education to general practitioners and community dwelling adults about the impact of lifestyle behaviour modification and how this could influence the appearance or trajectory of ED could help improve personal choice when tackling ED. Strengths and limitations: To our knowledge, this is the first study to collect eSurvey responses from community dwelling adults to gauge their reliance and perceived effectiveness of lifestyle medicine approaches to tackle ED. The principal limitation was the lack of follow-up, and not recording other information including lifestyle factors such as nutrition, smoking, and the use of alcohol and recreational drugs, which may have enabled a fuller exploration of the factors that could influence the primary outcome measures examined. Conclusion: Despite the high prevalence of ED, there is not enough awareness in the community setting about effective and low-cost lifestyle medicine strategies, including cardiovascular training and the use of supplements and weight training, to help tackle this common condition

Associations between daily sitting time and the combinations of lifestyle risk factors in men

Background: Understanding the reciprocal role that multiple problematic behaviours play in men's health is important for intervention delivery and for reducing the healthcare burden. Data regarding the concurrence of problematic health behaviours is currently limited but offers insights into risk profiles, and should now include total time spent sitting/day. Methods: Self-reported data on lifestyle health behaviours was collected from 232 men aged ≥18 years who engaged in a men's health promotion programme delivered by 16 English Premier League Clubs. Results: Men at risk due to high sitting display multiple concurrent lifestyle risk factors, 88.6% displayed at least two ancillary risk factors and were three times more likely to report ≥2 lifestyle risk factors (OR. =3.13, 95% confidence interval (CI). =1.52-6.42) than those with low sitting risk. Significant differences in the mean number of risk factors reported between those participants in the higher risk (2.43. ±. 0.90) and lower risk (2.13. ±. 0.96) sitting categories were also found (P=0.015). Conclusions: Hard-to-reach men displayed multiple problematic concurrent behaviours, strongly linked to total sitting time. © 2012 WPMH GmbH

AT2023fhn (the Finch): a Luminous Fast Blue Optical Transient at a large offset from its host galaxy

Luminous Fast Blue Optical Transients (LFBOTs) - the prototypical example being AT 2018cow - are a rare class of events whose origins are poorly understood. They are characterised by rapid evolution, featureless blue spectra at early times, and luminous X-ray and radio emission. LFBOTs thus far have been found exclusively at small projected offsets from star-forming host galaxies. We present Hubble Space Telescope, Gemini, Chandra and Very Large Array observations of a new LFBOT, AT2023fhn. The Hubble Space Telescope data reveal a large offset (greater than 3.5 half-light radii) from the two closest galaxies, both at a redshift of 0.24. The isolated environment of AT 2023fhn is in stark contrast with previous events, is challenging to explain with most LFBOT progenitor models, and calls into question the homogeneity of LFBOTs as a class.Comment: Submitted to MNRASL. 7 pages, 4 figures, 2 table