Observational evidence for stellar mass black holes

I review the evidence for stellar mass black holes in the Galaxy. The unique properties of the soft X-ray transient (SXTs) have provided the first opportunity for detailed studies of the mass-losing star in low-mass X-ray binaries. The large mass functions of these systems imply that the compact object has a mass greater than the maximum mass of a neutron star, strengthening the case that they contain black holes. The results and techniques used are discussed. I also review the recent study of a comparison of the luminosities of black hole and neutron star systems which has yielded compelling evidence for the existence of event horizons.     

Relative Sea Level Changes in Maldives and Vulnerability of Land Due to Abnormal Coastal Inundation

Oceanic Islands in the Pacific and Indian Oceans have extremely small land areas, usually less than 500 km2, with maximum height about 4 m above sea level. The Republic of Maldives is an independent island nation in the Indian Ocean south of Sri Lanka which stretches vertically in the Indian Ocean from 07° 06'N - 0° 42'S. The land area of this island country is about 300 km2, and none of Maldives' 1190 islands has an elevation more than 3 m above sea level. In fact the Maldives has the distinction of being the flattest country on earth, making it extremely vulnerable to the effects of global warming. Of the south Asian countries, the Maldives is the most vulnerable nation, facing severe consequences as a result of global warming and sea level rise (SLR). Because of their obvious vulnerability to SLR, the Government of Maldives is very much concerned about climate change. As global warming and the related SLR is an important integrated environmental issue, the need of the hour is to monitor and assess these changes. The present article deals mainly with the analysis of the tidal and Sea Surface Temperature (SST) data observed at Male and Gan stations along the Maldives coast in the northern and southern hemispheres, respectively. The objective of the analysis is to study the trends of these parameters. Trend analysis is also performed on the corresponding air temperature data of both stations. The results show that Maldives coastal sea level is rising in the same way (rising trend) as the global sea level. The mean tidal level at Male has shown an increasing trend of about 4.1 mm/year.Similarly at Gan, near the equator,it has registered a positive trend of about 3.9 mm/year.Sea level variations are the manifestations of various changes that are taking place in the Ocean-Atmosphere system. Therefore, the variations in SST and air temperature are intimately linked to sea level rise. It is found that SST and air temperature have also registered an increasing trend at both stations. The evidence of rising trends suggest that careful future monitoring of these parameters is very much required. Tropical cyclones normally do not affect the Maldives coast. However, due to its isolated location, the long fetches in association with swells generated by storms, that originated in the far south have resulted in flooding. Thus the rising rate of sea level with high waves and flat topography have increased the risk of flooding and increased the rate of erosion and alteration of beaches.     

Application of the topographic datuming operator to a data setfrom the Eastern Arabian Peninsula

We apply a redatuming methodology, designed to handle rugged topography and the presence of high‐velocity layers near the acquisition surface, to a 2D land seismic data set acquired in Saudi Arabia. This methodology is based on a recently developed prestack operator, which we call the topographic datuming operator (TDO). The TDO, unlike static corrections, allows for the movement of reflections laterally with respect to their true locations, corresponding to the new datum level. Thus, it mitigates mispositioning of events and velocity bias introduced by the assumption of surface consistency and the time‐invariant time shifts brought about by static corrections. Using the shallow velocities estimated from refracted events, the TDO provides a superior continuity of reflections and better focusing than that obtained from conventional static corrections in most parts of the processed 2D line. The computational cost of applying the TDO is only slightly higher than static corrections. The marginal additional computational cost and the possibility of estimating, after TDO redatuming, stacking velocities that are not affected by a spurious positive bias, as in the case of static corrections, are further advantages of the proposed methodology. The likelihood of strong heterogeneities in the most complex part of the line limits the applicability of any approach based upon geometrical optics; however, the TDO produces results that are slightly better than those obtained from static corrections because of its ability to partially collapse diffractions generated in the near surface.     

The world is sound? Geography, musicology and British-Asian soundscapes

This paper contributes to recent geographical engagements with sound and music by exploring the benefits of a geographical approach conversant with musicological and ethnomusicological tools and agendas within a specific political and empirical context: British-Asian cultural politics and contemporary dance music. Doing so, it suggests, sheds new light on an existing body of anthropological and cultural studies literature that critically highlights the commodification of exotica in this type of dance music. The paper shows how analysing the spatial politics of British-Asian musicality evokes the dynamic complexities around identity, belonging and the geographies of British popular culture and British-ness generated through this mode of cultural production.     

Variations of Surface Air Temperature Over the Land Areas in and Around the Bay of Bengal

The inter-annual variation and linear trends of the surface air temperature in the regions in and around the Bay of Bengal have been studied using the time series data of monthly and annual mean temperature for 20–40 years period within 1951–1990. The study area extends from Pusma Camp of Nepal in the north and Kuala Lumpur of Malaysia in the south and between 80--100 ° E. The annual variation of temperature has also been studied using the mean monthly temperature for the variable time frames 1961–1975, 1976–1990 and 1961–1990. The trend of temperature has been analyzed using linear regression technique with the data from 1961–1990, which showed that the warming trend is dominant over the study areas except for a few stations. It has been found that Nepal shows predominant warming trends. Bangladesh and the adjacent areas of India and the northern part of Bay of Bengal adjacent to the Bangladesh coast have shown strong warming trends of the annual temperature with maximum at Dhaka (0.037 °C/year). The near equatorial zone, i.e., southern India, Sri Lanka and part of Thailand and Malaysia (Kuala Lumpur) shows warming trends in the annual mean temperature with strong warming at Pamban and Anuradhapura (around 0.04 °C/year). The cooling trends have been observed at a few stations including Port Blair, Yangoon and Cuttack. Further analysis shows the presence of prominent ENSO scale of variations with time period 4–7 years and 2–3 years for almost all the stations. The decadal mode with T >7 years is present in some data series. The results of the variations of temperature with respect to the Southern Oscillation Index (SOI) show that SOI has some negative correlation with temperature for most of the stations except those in the extreme northeast. It has been found that positive anomaly of temperature has been observed for El Niño events and negative anomaly for the La Nina events.     

Azimuth moveout correction for transversely isotropic media

The azimuth moveout (AMO) operator in homogeneous transversely isotropic media with a vertical symmetry axis (VTI), as in isotropic media, has an overall skewed saddle shape. However, the AMO operator in anisotropic media is complicated; it includes, among other things, triplications at low angles. Even in weaker anisotropies, with the anisotropy parameter η= 0.1 (10% anisotropy), the AMO operator is considerably different from the isotropic operator, although free of triplications. The structure of the operator in VTI media (positive η) is stretched (has a wider aperture) compared with operators in isotropic media, with the amount of stretch being dependent on the strength of anisotropy. If the medium is both vertically inhomogeneous, i.e. the vertical velocity is a function of depth (v(z)), and anisotropic, which is a common combination in practical problems, the shape of the operator again differs from that for isotropic media. However, the difference in the AMO operator between the homogeneous and the v(z) cases, even for anisotropic media, is small. Stated simply, anisotropy influences the shape and aperture of the AMO operator far more than vertical inhomogeneity does.     

Modeling the impact of groundwater harvesting on the hydro-salinity of a saline catchment in southeastern Australia

Recharge to a saline, unconfined shallow-water-table aquifer is normally considered as an irrecoverable loss of water, but such thinking could be reviewed empirically. The use of an appropriate groundwater harvesting system does not only provide an opportunity to recover this lost water, but can also help in catchment salinity management and improvement. Agricultural-based land-drainage systems such as those that use serial biological concentration (SBC) of salts, provide examples of such harvesting methods. The impact of groundwater harvesting has been assessed on the hydro-salinity of a saline catchment in southeastern Australia through modeling. For both the below average rainfall and very wet years, the “do nothing” scenario resulted in increasing salinization in the catchment. However, after introducing a SBC system, groundwater salinity showed a decreasing trend while hydraulic heads tended to stabilize around the depth of subsurface collector wells. However, for a successful groundwater harvesting system, proper understanding of the groundwater flows and salt mobilization associated with a catchment is necessary. The outcomes of this modelling study have the potential to address similar issues (salinization) and/or needs (water harvesting) existing elsewhere in the world, particularly in semi-arid regions.

An efficient wave extrapolation method for anisotropic media with tilt

Wavefield extrapolation operators for elliptically anisotropic media offer significant cost reduction compared with that for the transversely isotropic case, particularly when the axis of symmetry exhibits tilt (from the vertical). However, elliptical anisotropy does not provide accurate wavefield representation or imaging for transversely isotropic media. Therefore, we propose effective elliptically anisotropic models that correctly capture the kinematic behaviour of wavefields for transversely isotropic media. Specifically, we compute source‐dependent effective velocities for the elliptic medium using kinematic high‐frequency representation of the transversely isotropic wavefield. The effective model allows us to use cheaper elliptic wave extrapolation operators. Despite the fact that the effective models are obtained by matching kinematics using high‐frequency asymptotic, the resulting wavefield contains most of the critical wavefield components, including frequency dependency and caustics, if present, with reasonable accuracy. The methodology developed here offers a much better cost versus accuracy trade‐off for wavefield computations in transversely isotropic media, particularly for media of low to moderate complexity. In addition, the wavefield solution is free from shear‐wave artefacts as opposed to the conventional finite‐difference‐based transversely isotropic wave extrapolation scheme. We demonstrate these assertions through numerical tests on synthetic tilted transversely isotropic models.