A multiwavelength study of the remnant of nova GK Persei

We present new observations of the nebular remnant of the old nova GK Persei 1901, in the optical using the 2m HCT and at low radio frequencies using the GMRT. The evolution of the nova remnant indicates shock interaction with the ambient medium, especially in the southwest quadrant. Application of a simple model for the shock and its evolution to determine the time dependence of the radius of the shell in the southwest quadrant indicates that the shell is now expanding into an ambient medium that has a lower density compared to the density of the ambient medium ahead of the shock in 1987.There are indications of a recent interaction of the nova remnant with the ambient medium in the northeast quadrant also. The nova remnant of GK Per is detected at all the observed radio frequencies and is of similar extent as the optical remnant. Putting together our radio observations with VLA archival data on GK Per from 1997, we obtain three interesting results: 1. The spectrum above 1.4 GHz follows a power law with an index -0.7 and below 1.4 GHz follows a power law with an index ~ -0.85. This could be due to the presence of at least two populations of electrons dominating the global emission at different frequencies. 2. We record an annual secular decrease of 2.1% in the flux density of the nova remnant at 1.4 and 4.9 GHz between 1984 and 1997 which has left the spectral index unchanged at -0.7. No such decrease is observed in the flux densities below 1 GHz. 3. We record an increase in the flux density at 0.33 GHz compared to the previous estimate in 1987. We conclude that the remnant of nova GK Per is similar to supernova remnants and in particular, to the young supernova remnant Cas A.Comment: 10 pages; uses A&A style; figures 1, 2 & 6 are in JPEG format. Accepted for publication in Astronomy & Astrophysics. Full paper including Figures 1, 2 & 6 may be downloaded from http://www.iiap.res.in/personnel/gca/gca.htm

On the progenitor of V838 Monocerotis

We summarize and analyze the available observational data on the progenitor and the enviroment of V838 Mon. From the available photometric data for the progenitor of V838 Mon we exclude the possibility that the object before eruption was an evolved red giant star (AGB or RGB star). We find that most likely it was a main sequence or pre-main sequence star of ~ 5-10 M_sun. From the light echo structure and evolution we conclude that the reflecting dust is of interstellar nature rather than blown by V838 Mon in the past. We discuss the IRAS and CO data for interstellar medium observed near the position of V838 Mon. Several interstellar molecular regions have radial velocities similar to that of V838 Mon, so dust seen in the light echo might be related to one of them.Comment: 12 pages, 7 figures, accepted for publication in Astronomy & Astrophysic

Metacommunities, metaecosystems and the environmental fate of chemical contaminants

Although pollution is a major driver of ecosystem change, models predicting the environmental fate of contaminants suffer from critical uncertainties related to oversimplifying the dynamics of the biological compartment.It is increasingly recognized that contaminant processing is an outcome of ecosystem functioning, that ecosystem functioning is contingent on community structure and that community structure is influenced by organismal dispersal. We propose a conceptual organization of the contribution of organismal dispersal to local contaminant fate. Direct dispersal effects occur when the dispersing organism directly couples contaminant stocks in spatially separate ecosystems by transporting contaminants in its biomass. Indirect dispersal effects occur when the dispersing organism indirectly influences contaminant fate via community assembly. This can occur either when the dispersing organism is a contaminant processor or when the dispersing organism alters, via species interactions, the abundance of contaminant biotransporters or processors already established in the ecosystem. The magnitude of direct and indirect dispersal effects is modulated by many factors, including other contaminants. These will influence population growth rates of the dispersing species in the donor ecosystem, or the probability that a dispersing individual reaches the recipient ecosystem.We provide a review of pertinent literature demonstrating that these two mechanisms, and their chemical modulation, are well supported or likely to occur in many natural and human‐modified landscapes. The literature also demonstrates that they can operate in concert with each other.Synthesis and applications. Managed ecosystems thought to be important contaminant and nutrient sinks, such as artificial ponds and constructed wetlands, should be monitored and controlled for in‐and‐out animal movement if contaminant export is found to be relevant. Uncontaminated fishing grounds linked to contaminated sites via movement of dispersing species should be monitored and resident species evaluated for health consumption advisories. Assessing the success of contaminated site remediation can be improved by better matching the spatial extent of site remediation and the home range of monitored species. Finally, interagency research fund programmes should be developed that narrow the current gap between the fields of ecology and ecotoxicology.Managed ecosystems thought to be important contaminant and nutrient sinks, such as artificial ponds and constructed wetlands, should be monitored and controlled for in‐and‐out animal movement if contaminant export is found to be relevant. Uncontaminated fishing grounds linked to contaminated sites via movement of dispersing species should be monitored and resident species evaluated for health consumption advisories. Assessing the success of contaminated site remediation can be improved by better matching the spatial extent of site remediation and the home range of monitored species. Finally, interagency research fund programmes should be developed that narrow the current gap between the fields of ecology and ecotoxicology.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/143615/1/jpe13054.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/143615/2/jpe13054_am.pd

Circumstellar features in hot DA white dwarfs

We present a phenomenological study of highly ionised, non-photospheric absorption features in high spectral resolution vacuum ultraviolet spectra of 23 hot DA white dwarfs. Prior to this study, four of the survey objects (Feige 24, REJ 0457-281, G191-B2B and REJ 1614-085) were known to possess these features. We find four new objects with multiple components in one or more of the principal resonance lines: REJ 1738+665, Ton 021, REJ 0558-373 and WD 2218+706. A fifth object, REJ 2156-546 also shows some evidence of multiple components, though further observations are required to confirm the detection. We discuss possible origins for these features including ionisation of the local interstellar environment, the presence of material inside the gravitational well of the white dwarf, mass loss in a stellar wind, and the existence of material in an ancient planetary nebula around the star. We propose ionisation of the local interstellar medium as the origin of these features in G191-B2B and REJ 1738+665, and demonstrate the need for higher resolution spectroscopy of the sample, to detect multiple ISM velocity components and to identify circumstellar features which may lie close to the photospheric velocity.Comment: 20 figures, 21 page

Biomechanical analyses of the performance of Paralympians: From foundation to elite level

Biomechanical analysis of sport performance provides an objective method of determining performance of a particular sporting technique. In particular, it aims to add to the understanding of the mechanisms influencing performance, characterization of athletes, and provide insights into injury predisposition. Whilst the performance in sport of able-bodied athletes is well recognised in the literature, less information and understanding is known on the complexity, constraints and demands placed on the body of an individual with a disability. This paper provides a dialogue that outlines scientific issues of performance analysis of multi-level athletes with a disability, including Paralympians. Four integrated themes are explored the first of which focuses on how biomechanics can contribute to the understanding of sport performance in athletes with a disability and how it may be used as an evidence-based tool. This latter point questions the potential for a possible cultural shift led by emergence of user-friendly instruments. The second theme briefly discusses the role of reliability of sport performance and addresses the debate of two-dimensional and three-dimensional analysis. The third theme address key biomechanical parameters and provides guidance to clinicians, and coaches on the approaches adopted using biomechanical/sport performance analysis for an athlete with a disability starting out, to the emerging and elite Paralympian. For completeness of this discourse, the final theme is based on the controversial issues on the role of assisted devices and the inclusion of Paralympians into able-bodied sport is also presented. All combined, this dialogue highlights the intricate relationship between biomechanics and training of individuals with a disability. Furthermore, it illustrates the complexity of modern training of athletes which can only lead to a better appreciation of the performances to be delivered in the London 2012 Paralympic Games

Aerobic fitness is a potential crucial factor in protecting paralympic athletes with locomotor impairments from atherosclerotic cardiovascular risk

PurposeTo test the hypothesis that aerobic fitness is inversely related to the risk of atherosclerotic cardiovascular disease (ACVD) in athletes with locomotor impairments deriving from health conditions, such as spinal cord injury (SCI), lower limb amputation, cerebral palsy, poliomyelitis, and other health conditions different from the previous ones.MethodsA total of 68 male athletes who competed in either summer or winter Paralympic games were divided in two health conditions groups (35 with SCI, mean age 37.28.0 years, and 33 with different health conditions, mean age 37.89.9 years) and in four sport type groups (skill, power, intermittent-mixed metabolism-and endurance). They were evaluated through anthropometric and blood pressure measurements, laboratory blood tests, and graded cardiopulmonary maximal arm cranking exercise test, with oxygen uptake peak (VO2peak) measurement. Cardiovascular risk profile was assessed in each athlete.ResultsThe prevalence of ACVD-risk factors in the overall population was 20.6% for hypertension; 47% and 55.9% for high values of total and LDL cholesterol, respectively; 22.1% for reduce glucose tolerance; and 8.8% for obesity. No difference was found between athletes with and without SCI, while the prevalence of obesity was significantly higher in those practicing skill sports (22.7%, p=0.035), which was the sport type group with Paralympic athletes with the lowest VO2peak (22.5 +/- 5.70 ml kg(-1) min(-1)). VO2peak was lower in athletes with SCI than those with different health conditions (28.6 +/- 10.0 vs 33.6 +/- 8.9 ml kg(-1) min(-1)p=0.03), and in those with 3-4 risk factors (19.09 +/- 5.34 ml kg(-1) min(-1)) than those with 2 risk factors (27.1 +/- 5.50 ml kg(-1) min(-1)), 1 risk factor (31.6 +/- 8.55 ml kg(-1) min(-1)), or none (36.4 +/- 8.76 ml kg(-1) min(-1)) (p<0.001).ConclusionsThe present study suggests that having higher VO2peak seems to offer greater protection against ACVD in individuals with a locomotor impairment. Prescribing physical exercise at an intensity similar to that of endurance and intermittent sports should become a fundamental tool to promote health among people with a locomotor impairment.Open access funding provided by Universita degli Studi dell'Aquila within the CRUI-CARE Agreement

Using narratives to inform the development of a digital health intervention related to COVID-19 vaccination in Black young adults in Georgia, North Carolina and Alabama

Interactive stories are a relatively newer form of storytelling with great potential to correct misinformation while increasing self-efficacy, which is crucial to vaccine acceptance. To address COVID-19 vaccine hesitancy and medical mistrust in young Black adults (BYA), we sought to adapt a pre-existing application (“app”; Tough Talks) designed to address HIV disclosure decision-making through choose-your-own adventure (CYOA) narratives and other activities. The adapted app (Tough Talks – COVID) uses a similar approach to situate COVID-19 vaccination decision-making within social contexts and to encourage greater deliberation about decisions. To inform content for the CYOA narratives, we conducted an online survey that was used to elicit the behavioral, cognitive, and environmental determinants influencing COVID-19 vaccine hesitancy among 150 BYA (ages 18–29) in Georgia, Alabama, and North Carolina. The survey included scenario questions that were developed with input from a youth advisory board to understand responses to peer and family influences. In two scenarios that involved discussions with family and friends about vaccination status, most respondents chose to be honest about their vaccination status. However, vaccinated individuals perceived more social pressure and stigma about not being vaccinated than unvaccinated respondents who were not as motivated by social pressure. Personal choice/agency in the face of perceived vaccine risks was a more common theme for unvaccinated respondents. Results suggest that relying on changing social norms alone may not impact barriers to vaccination in unvaccinated young adults without also addressing other barriers to vaccination such as concerns about autonomy and vaccine safety. Based on these findings, CYOA narratives in the app were adapted to include discussions with family and friends but also to touch on themes of personal choice as well as other topics that influence behaviors besides norms such as safety, side effects, and risk of COVID-19 in an evolving pandemic

Purinergic signalling links mechanical breath profile and alveolar mechanics with the pro-inflammatory innate immune response causing ventilation-induced lung injury

Severe pulmonary infection or vigorous cyclic deformation of the alveolar epithelial type I (AT I) cells by mechanical ventilation leads to massive extracellular ATP release. High levels of extracellular ATP saturate the ATP hydrolysis enzymes CD39 and CD73 resulting in persistent high ATP levels despite the conversion to adenosine. Above a certain level, extracellular ATP molecules act as danger-associated molecular patterns (DAMPs) and activate the pro-inflammatory response of the innate immunity through purinergic receptors on the surface of the immune cells. This results in lung tissue inflammation, capillary leakage, interstitial and alveolar oedema and lung injury reducing the production of surfactant by the damaged AT II cells and deactivating the surfactant function by the concomitant extravasated serum proteins through capillary leakage followed by a substantial increase in alveolar surface tension and alveolar collapse. The resulting inhomogeneous ventilation of the lungs is an important mechanism in the development of ventilation-induced lung injury. The high levels of extracellular ATP and the upregulation of ecto-enzymes and soluble enzymes that hydrolyse ATP to adenosine (CD39 and CD73) increase the extracellular adenosine levels that inhibit the innate and adaptive immune responses rendering the host susceptible to infection by invading microorganisms. Moreover, high levels of extracellular adenosine increase the expression, the production and the activation of pro-fibrotic proteins (such as TGF-β, α-SMA, etc.) followed by the establishment of lung fibrosis

Persistent and polarised global actin flow is essential for directionality during cell migration

Cell migration is hypothesized to involve a cycle of behaviours beginning with leading edge extension. However, recent evidence suggests that the leading edge may be dispensable for migration, raising the question of what actually controls cell directionality. Here, we exploit the embryonic migration of Drosophila macrophages to bridge the different temporal scales of the behaviours controlling motility. This approach reveals that edge fluctuations during random motility are not persistent and are weakly correlated with motion. In contrast, flow of the actin network behind the leading edge is highly persistent. Quantification of actin flow structure during migration reveals a stable organization and asymmetry in the cell-wide flowfield that strongly correlates with cell directionality. This organization is regulated by a gradient of actin network compression and destruction, which is controlled by myosin contraction and cofilin-mediated disassembly. It is this stable actin-flow polarity, which integrates rapid fluctuations of the leading edge, that controls inherent cellular persistence

Polyamory: Intimate practice, identity or sexual orientation?

Polyamory means different things to different people. While some consider polyamory to be nothing more than a convenient label for their current relationship constellations or a handy tool for communicating their willingness to enter more than one relationship at a time, others claim it as one of their core identities. Essentialist identity narratives have sustained recent arguments that polyamory is best understood as a sexual orientation and is as such comparable with homosexuality, heterosexuality or bisexuality. Such a move would render polyamory intelligible within dominant political and legal frameworks of sexual diversity. The article surveys academic and activist discussions on sexual orientation and traces contradictory voices in current debates on polyamory. The author draws on poststructuralist ideas to show the shortcomings of sexual orientation discourses and highlights the losses which are likely to follow from pragmatic definitions of polyamory as sexual orientation