Quasi-viscous accretion flow – I. Equilibrium conditions and asymptotic behaviour

In a novel approach to studying viscous accretion flows, viscosity has been introduced as a perturbative effect, involving a first-order correction in the α-viscosity parameter. This method reduces the problem of solving a second-order non-linear differential equation (Navier–Stokes equation) to that of an effective first-order equation. Viscosity breaks down the invariance of the equilibrium conditions for stationary inflow and outflow solutions, and distinguishes accretion from wind. Under a dynamical systems classification, the only feasible critical points of this 'quasi-viscous' flow are saddle points and spirals. On large spatial scales of the disc, where a linearized and radially propagating time-dependent perturbation is known to cause a secular instability, the velocity evolution equation of the quasi-viscous flow has been transformed to bear a formal closeness with Schrödinger's equation with a repulsive potential. Compatible with the transport of angular momentum to the outer regions of the disc, a viscosity-limited length-scale has been defined for the full spatial extent over which the accretion process would be viable.     

Chromothermal oscillations and collapse of strange stars to black holes: astrophysical implications

We study the effects of temperature on strange stars. It is found that the maximum mass of the star decreases with the increase of temperature, as at high temperatures the equations of state become softer. Moreover, if the temperature of a strange star increases, keeping its baryon number fixed, its gravitational mass increases and its radius decreases. This leads to a limiting temperature, where it turns into a black hole. These features are the result of a combined effect of the change of gluon mass and the quark distribution with temperature. We report on a new type of radial oscillation of strange stars, driven by what we call 'chromothermal' instability. We also discuss the relevance of our findings in the astrophysics of core collapse supernovae and gamma-ray bursts.     

Response of a Resilient Community to Natural Disasters: The Gorkha Earthquake in Nepal, 2015

The ability of a community to withstand and recover from adversities including natural and man-made disasters has emerged as a major policy issue in recent years. This research aims to assess the role of institutional initiatives in building resilient communities and their response to natural disasters like the Gorkha earthquake in Nepal in 2015. The work is based on data collected from primary and secondary sources along with field observations. It is evident that resilient communities are equipped with greater coping capacities in the face of natural disasters and have reduced vulnerability to future hazards. Institutional capacity building and resilient construction including the School Earthquake Safety Program ensured better disaster preparedness. The traditional open spaces and building designs added to the structural resilience. There is, however, a need to build back better and to communicate earthquake-resistant designs to the affected communities.     

Combining Geography,Math, and Science to Teach Climate Change and Sea Level Rise

This study examines the effectiveness of integrating geography into existing math and science curriculum to teach climate change and sea level rise. The desired outcome is to improve student performance in all three subjects. A sample of 120 fifth graders from three schools were taught the integrated curriculum over a period of two to three weeks. They were given a pretest and posttest comprised of questions measuring knowledge relevant to the lesson in terms of geography, math, science, and spatial skills. Paired-samples t-tests were conducted to determine significant differences in student performance. These t-tests indicate statistically significant improvements in all but one instance across all subjects, at all schools for both boys and girls. No statistically significant results were observed for a control group of an additional twenty-seven fifth graders. These results demonstrate the value of combining geography with math and science to improve student performance in STEM knowledge.     

Simultaneous X-ray and IR variability in the quasar 3C 273

From a combination of high-quality X-ray observations from the NASA Rossi X-ray Timing Explorer ( RXTE ) and IR observations from the UK Infrared Telescope (UKIRT) we show that the medium-energy X-ray (3–20 keV) and near-IR fluxes in the quasar 3C 273 are highly correlated. It is widely believed that the X-ray emission in quasars like 3C 273 arises from Compton scattering of low-energy seed photons, and our observations provide the first reliable detection of correlated variations in 3C 273 between the X-ray band and any lower energy band. For a realistic electron distribution we demonstrate that it is probable that each decade of the seed-photon distribution from the mm to IR wavebands contributes roughly equally to the medium-energy X-ray flux. However, the expected mm variations are too small to be detected above the noise, probably explaining the lack of success of previous searches for a correlation between X-ray and mm variations. In addition, we show that the IR leads the X-rays by  0.75±0.25 d  . These observations rule out the 'External Compton' emission process for the production of the X-rays.     

Local responses to changed circumstances: Coalmining in the market economy in Upper Silesia, Poland

It is argued that the emphasis of much recent research into coalmining has been placed on international and national scale influences which affect coalfields as a whole; change at the intra-coalfield scale has received less attention. After providing a background to events in Poland during communism, attention focuses on developments since 1989, commencing with coalfield-wide influences. There follows an examination of the work of the state body Państwowa Agencja Węgla Kamiennego, which executes government policy at the local level, and whose membership is drawn from the coalfield region. This agency recommends the closure and amalgamation of mines, but otherwise rationalisation measures are left to the seven mining companies and the colliery managers. The restructuring which has been carried out is considered under five heads: organisational change within the collieries, employment, production and technical change, and ecological adjustment. While recognising the importance of the socioeconomic and political environment and geology, there is much evidence to suggest that intra-coalfield patterns are strongly determined by local decision-makers. This revised version was published online in July 2006 with corrections to the Cover Date.     

A Global Synthesis of Managing Groundwater Dependent Ecosystems Under Sustainable Groundwater Policy

Groundwater is a vital water supply worldwide for people and nature. However, species and ecosystems that depend on groundwater for some or all of their water needs, known as groundwater dependent ecosystems (GDEs), are increasingly becoming threatened worldwide due to growing human water demands. Over the past two decades, the protection and management of GDEs have been incorporated into several water management policy initiatives worldwide including jurisdictions within Australia, the European Union, South Africa, and the United States. Among these, Australia has implemented the most comprehensive framework to manage and protect GDEs through its water policy initiatives. Using a science‐based approach, Australia has made good progress at reducing uncertainty when selecting management thresholds for GDEs in their water management plans. This has been achieved by incorporating appropriate metrics for GDEs into water monitoring programs so that information gathered over time can inform management decisions. This adaptive management approach is also accompanied by the application of the “Precautionary Principle” in cases where insufficient information on GDEs exist. Additionally, the integration of risk assessment into Australia's approach has enabled water managers to prioritize the most valuable and vulnerable ecologic assets necessary to manage GDEs under Australia's national sustainable water management legislation. The purpose of this paper is to: (1) compare existing global policy initiatives for the protection and management of GDEs; (2) synthesize Australia's adaptive management approach of GDEs in their state water plans; and (3) highlight opportunities and challenges of applying Australia's approach for managing GDEs under other water management policies worldwide.     

Flow resistance and hydraulic geometry in bedrock rivers with multiple roughness length scales

Many models of incision by bedrock rivers predict water depth and shear stress from discharge; conversely, palaeoflood discharge is sometimes reconstructed from flow depth markers in rock gorges. In both cases, assumptions are made about flow resistance. The depth–discharge relation in a bedrock river must depend on at least two roughness length scales (exposed rock and sediment cover) and possibly a third (sidewalls). A conceptually attractive way to model the depth–discharge relation in such situations is to partition the total shear stress and friction factor, but it is not obvious how to quantify the friction factor for rough walls in a way that can be used in incision process models. We show that a single flow resistance calculation using a spatially averaged roughness length scale closely approximates the partitioning of stress between sediment and rock, and between bed and walls, in idealized scenarios. Both approaches give closer fits to the measured depth–discharge relations in two small bedrock reaches than can be achieved using a fixed value of Manning's n or the Chézy friction factor. Sidewalls that are substantially rougher or smoother than the bed have a significant effect on the partitioning of shear stress between bed and sidewalls. More research is needed on how best to estimate roughness length scales from observable or measurable channel characteristics. © 2019 John Wiley & Sons, Ltd.