52 research outputs found
Rapid methods of landslide hazard mapping : Fiji case study
A landslide hazard probability map can help planners (1) prepare for, and/or mitigate against,
the effects of landsliding on communities and infrastructure, and (2) avoid or minimise the
risks associated with new developments. The aims of the project were to establish, by means
of studies in a few test areas, a generic method by which remote sensing and data analysis
using a geographic information system (GIS) could provide a provisional landslide hazard
zonation map. The provision of basic hazard information is an underpinning theme of the
UNâs International Decade for Natural Disaster Reduction (IDNDR). It is an essential
requirement for disaster preparedness and mitigation planning. This report forms part of BGS
project 92/7 (R5554) âRapid assessment of landslip hazardsâ Carried out under the ODA/BGS
Technology Development and Research Programme as part of the British Governmentâs
provision of aid to developing countries. It provides a detailed technical account of work
undertaken in a test area in Viti Levu in collaboration with Fiji Mineral Resources
Department. The study represents a demonstration of a methodology that is applicable to
many developing countries.
The underlying principle is that relationships between past landsliding events, interpreted
from remote sensing, and factors such as the geology, relief, soils etc provide the basis for
modelling where future landslides are most likely to occur. This is achieved using a GIS by
âweightingâ each class of each variable (e.g. each lithology âclassâ of the variable âgeologyâ)
according to the proportion of landslides occurring within it compared to the regional
average. Combinations of variables, produced by summing the weights in individual classes,
provide âmodelsâ of landslide probability. The approach is empirical but has the advantage
of potentially being able to provide regional scale hazard maps over large areas quickly and
cheaply; this is unlikely to be achieved using conventional ground-based geotechnical
methods.
In Fiji, landslides are usually triggered by intense rain storms commonly associated with
tropical cyclones. However, the regional distribution of landslides has not been mapped nor
is it known how far geology and landscape influence the location and severity of landsliding
events. The report discusses the remote sensing and GIS methodology, and describes the
results of the pilot study over an area of 713 km2 in south east Viti Levu. The landslide
model uses geology, elevation, slope angle, slope aspect, soil type, and forest cover as
inputs. The resulting provisional landslide hazard zonation map, divided into high, medium
and low zones of landslide hazard probability, suggests that whilst rainfall is the immediate
cause, others controls do exert a significant influence. It is recommended that consideration
be given in Fiji to implementing the techniques as part of a national strategic plan for
landslide hazard zonation mapping
The first ultracompact Roche lobe-filling hot subdwarf binary
We report the discovery of the first short period binary in which a hot subdwarf star (sdOB) fills its Roche lobe and started mass transfer to its companion. The object was discovered as part of a dedicated high-cadence survey of the Galactic Plane named the Zwicky Transient Facility and exhibits a period of Porb=39.3401(1) min, making it the most compact hot subdwarf binary currently known. Spectroscopic observations are consistent with an intermediate He-sdOB star with an effective temperature of Teff=42,400±300 K and a surface gravity of log(g)=5.77±0.05. A high-signal-to noise GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the sdOB star and an eclipse of the sdOB by an accretion disk. We infer a low-mass hot subdwarf donor with a mass MsdOB=0.337±0.015 Mâ and a white dwarf accretor with a mass MWD=0.545±0.020 Mâ. Theoretical binary modeling indicates the hot subdwarf formed during a common envelope phase when a 2.5â2.8 Mâ star lost its envelope when crossing the Hertzsprung Gap. To match its current Porb, Teff, log(g), and masses, we estimate a post-common envelope period of Porbâ150 min, and find the sdOB star is currently undergoing hydrogen shell burning. We estimate that the hot subdwarf will become a white dwarf with a thick helium layer of â0.1 Mâ and will merge with its carbon/oxygen white dwarf companion after â17 Myr and presumably explode as a thermonuclear supernova or form an R CrB star
A dense 0.1-solar-mass star in a 51-minute-orbital-period eclipsing binary
Of more than a thousand known cataclysmic variables (CVs), where a white dwarf is accreting from a hydrogen-rich star, only a dozen have orbital periods below 75 minutes1,2,3,4,5,6,7,8,9. One way to achieve these short periods requires the donor star to have undergone substantial nuclear evolution before interacting with the white dwarf10,11,12,13,14, and it is expected that these objects will transition to helium accretion. These transitional CVs have been proposed as progenitors of helium CVs13,14,15,16,17,18. However, no known transitional CV is expected to reach an orbital period short enough to account for most of the helium CV population, leaving the role of this evolutionary pathway unclear. Here we report observations of ZTFâJ1813+4251, a 51-minute-orbital-period, fully eclipsing binary system consisting of a star with a temperature comparable to that of the Sun but a density 100 times greater owing to its helium-rich composition, accreting onto a white dwarf. Phase-resolved spectra, multi-band light curves and the broadband spectral energy distribution allow us to obtain precise and robust constraints on the masses, radii and temperatures of both components. Evolutionary modelling shows that ZTFâJ1813+4251 is destined to become a helium CV binary, reaching an orbital period under 20 minutes, rendering ZTFâJ1813+4251 a previously missing link between helium CV binaries and hydrogen-rich CVs
A new class of Roche lobeâfilling hot subdwarf binaries
We present the discovery of the second binary with a Roche lobeâfilling hot subdwarf transferring mass to a white dwarf (WD) companion. This 56 minute binary was discovered using data from the Zwicky Transient Facility. Spectroscopic observations reveal an He-sdOB star with an effective temperature of T eff = 33,700 ± 1000 K and a surface gravity of log(g) = 5.54 ± 0.11. The GTC+HiPERCAM light curve is dominated by the ellipsoidal deformation of the He-sdOB star and shows an eclipse of the He-sdOB by an accretion disk as well as a weak eclipse of the WD. We infer a He-sdOB mass of M sdOB = 0.41 ± 0.04 M â and a WD mass of M WD = 0.68 ± 0.05 M â. The weak eclipses imply a WD blackbody temperature of 63,000 ± 10,000 K and a radius R WD = 0.0148 ± 0.0020 R â as expected for a WD of such high temperature. The He-sdOB star is likely undergoing hydrogen shell burning and will continue transferring mass for â1 Myr at a rate of 10â9 M â yrâ1, which is consistent with the high WD temperature. The hot subdwarf will then turn into a WD and the system will merge in â30 Myr. We suggest that Galactic reddening could bias discoveries toward preferentially finding Roche lobeâfilling systems during the short-lived shell-burning phase. Studies using reddening-corrected samples should reveal a large population of helium coreâburning hot subdwarfs with T eff â 25,000 K in binaries of 60â90 minutes with WDs. Though not yet in contact, these binaries would eventually come into contact through gravitational-wave emission and explode as a subluminous thermonuclear supernova or evolve into a massive single WD
A 62-minute orbital period black widow binary in a wide hierarchical triple
Over a dozen millisecond pulsars are ablating low-mass companions in close binary systems. In the original âblack widowâ, the eight-hour orbital period eclipsing pulsar PSR J1959+2048 (PSR B1957+20)1, high-energy emission originating from the pulsar2 is irradiating and may eventually destroy3 a low-mass companion. These systems are not only physical laboratories that reveal the interesting results of exposing a close companion star to the relativistic energy output of a pulsar, but are also believed to harbour some of the most massive neutron stars4, allowing for robust tests of the neutron star equation of state. Here we report observations of ZTF J1406+1222, a wide hierarchical triple hosting a 62-minute orbital period black widow candidate, the optical flux of which varies by a factor of more than ten. ZTF J1406+1222 pushes the boundaries of evolutionary models5, falling below the 80-minute minimum orbital period of hydrogen-rich systems. The wide tertiary companion is a rare low-metallicity cool subdwarf star, and the system has a Galactic halo orbit consistent with passing near the Galactic Centre, making it a probe of formation channels, neutron star kick physics6 and binary evolution
Representational predicaments for employees: Their impact on perceptions of supervisors\u27 individualized consideration and on employee job satisfaction
A representational predicament for a subordinate vis-à -vis his or her immediate superior involves perceptual incongruence with the superior about the subordinate\u27s work or work context, with unfavourable implications for the employee. An instrument to measure the incidence of two types of representational predicament, being neglected and negative slanting, was developed and then validated through an initial survey of 327 employees. A subsequent substantive survey with a fresh sample of 330 employees largely supported a conceptual model linking being neglected and negative slanting to perceptions of low individualized consideration by superiors and to low overall job satisfaction. The respondents in both surveys were all Hong Kong Chinese. Two case examples drawn from qualitative interviews illustrate and support the conceptual model. Based on the research findings, we recommend some practical exercises to use in training interventions with leaders and subordinates. © 2013 Copyright Taylor and Francis Group, LLC
Bio-analytical Assay Methods used in Therapeutic Drug Monitoring of Antiretroviral Drugs-A Review
Education and selfâregulation of learning for gifted pupils: systemic design and development
Remote thermal IR surveying to detect abandoned mineshafts in former mining areas
In former mining areas it is critical to locate unknown, abandoned mineshafts prior to the development of a site. Abandoned mineshafts are ground disturbances that have very localized effects on the morphology and the physical, chemical, drainage and moisture properties of the surface geological materials and thus thermo-physical properties. Remotely sensed thermal IR surveys provide the potential for a rapid, inexpensive and non-intrusive technique for mineshaft detection. The key parameters of thermal IR radiation and the application of remote thermal IR surveys to planning are described, using case histories from former mining areas in Lancashire, Yorkshire and Nottinghamshire. Field-measured IR temperature differences correlated well with different ground conditions caused by changes in vegetation, disturbance, compaction and moisture-drainage regimes. A thermal anomaly over an area of c. 6 m2 above a known mineshaft was characterized by traces of methane and temperatures higher by 0.5â1 °C than those of the adjacent ground surface. Using thermal IR images, collected with the Daedalus 1260 Airborne Thematic Mapper, a scheme was developed to classify and map mineshafts with and without any observed visual characteristics. When applied using thermal imagery obtained from commercial flights the scheme identified several potential sites of abandoned mineshafts in an area designated for the redevelopment of the Nottingham Business Park, East Midlands. The thermal anomalies were associated with minor topographic features such as mounds, depressions and dereliction, as well as compositional features caused by coal enrichment and Coal Measures mudstone infill. These features had very little surface expression and were confirmed only using soil stripping
Rapid methods of landslide hazard mapping : Papua New Guinea case study
A landslide hazard probability map can help planners (1) prepare for, and/or mitigate against,
the effects of landsliding on communities and infrastructure, and (2) avoid or minimise the
risks associated with new developments. The aims of the project were to establish, by means
of studies in a few test areas, a generic method by which remote sensing and data analysis
using a geographic information system (GIS) could provide a provisional landslide hazard
zonation map. The provision of basic hazard information is an underpinning theme of the
United Nations International Decade for Natural Disaster Reduction (IDNDR). It is an
essential requirement for disaster preparedness and mitigation planning. This report forms
part of BGS project 92/7 (R5554) âRapid assessment of landslip hazardsâ carried out under
the ODA/BGS Technology Development and Research Programme as part of the British
Governmentâs provision of aid to developing countries. It provides a detailed technical
account of work undertaken in a test area in the highlands of Papua New Guinea (PNG) in
collaboration with the Geological Survey Division. The study represents a demonstration of
a methodology that is applicable to many developing countries.
The underlying principle is that relationships between past landsliding events, interpreted
from remote sensing, and factors such as the geology, relief, soils etc. provide the basis for
modelling where future landslides are most likely to occur. This is achieved using a GIS by
âweightingâ each class of each variable (e.g. each lithology âclassâ of the variable âgeologyâ)
according to the proportion of landslides occurring within it compared to the regional
average. Combinations of variables, produced by summing the weights in individual classes,
provide âmodelsâ of landslide probability. The approach is empirical but has the advantage
of potentially being able to provide regional scale hazard maps over large areas quickly and
cheaply; this cannot be achieved using conventional ground-based geotechnical methods.
In PNG, landslides are usually triggered by earthquakes or intense rain storms. Tectonic
instability and the extreme ruggedness of the terrain make the highlands very susceptible to
landsliding, but the extent to which regional factors influence the distribution and severity
of landsliding is uncertain. The report discusses the remote sensing and GIS methodology,
and describes the results of the pilot study over an area of approximately 4 500 km2 in the
Kaiapit/Saidor districts of the Finisterre mountain range. The landslide model uses geology,
elevation, slope angle, lineaments and catchments as inputs. The resulting provisional
landslide hazard zonation map, divided into 5 zones of landslide hazard probability, suggests
that regional controls on landslide occurrence do exist and are significant. It is recommended
that consideration be given in PNG to implementing the techniques as part of a national
strategic plan for landslide hazard zonation mapping
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