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Pre-low-mass X-ray binaries containing a black hole: investigating a detection mechanism

100%
Bleach J.
Open Physics
|
2007
|
vol. 5
|
issue 1
1-10
EN
This work investigates the feasibility of detecting close, detached, black hole-red dwarf binaries, which are expected to be evolutionary precursors of low-mass X-ray binaries (LMXBs). Although this pre-low-mass X-ray binary (pre-LMXB) phase of evolution is predicted theoretically, as yet no such systems have been identified observationally. The calculations presented here suggest that the X-ray luminosity of black hole wind accretion in a pre-LMXB system could exceed the intrinsic X-ray luminosity of the red dwarf secondary star, thereby providing a detection mechanism. However, there is significant uncertainty regarding the efficiency of the conversion of gravitational potential energy to X-ray luminosity resulting from accretion onto a black hole, for example energy may be lost via advection across the event horizon. Still, sources with X-ray luminosities greater than that expected for a red dwarf star, but whose positions coincide with that of a red dwarf would represent candidate pre-LMXB systems. These candidates should be surveyed for the radial velocity shifts that would occur as a result of the orbital motion of a red dwarf star within a close binary system containing a black hole.
2
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Analysis of Shoreline Changes in the Coastal Area of Kuala Terengganu, Malaysia

88%
Subiyanto S., Ahmad A., Mamat M., Ihsan Y. N., Afrianto E., Hidayat Y., Supian S.
World News of Natural Sciences
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2020
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vol. 28
24-33
EN
The analysis of shoreline change trends is fundamental to a broad range of investigations undertaken by coastal scientists, coastal engineers, and coastal managers, as well as the government, in this case, the coastal development policy-maker. In order to know the changing of shoreline position around the coastal area of Kuala Terengganu, an analysis and then simulation of shoreline change was performed over, respectively, 2 years, 3 years and 4 years. In this simulation, the longshore distance was divided into 87 cells of length 34 m. Shoreline positions from satellite imagery in 2010 were used in this simulation as the initial condition. Based on the numerical result, both erosion (north side) and accretion (south side) occurred around the Sultan Mahmud Airport, Kuala Terengganu. The average erosion and accretion during the 4 year period is 42.93 m and 40.89 m, respectively.
3
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Spatial Modeling of Coastline Change for Two Decades (1994-2014) in Pangandaran, West Java - Indonesia

75%
Harahap S. A., Nurruhwati I., Purba N. P., Gamma M.
World News of Natural Sciences
|
2022
|
vol. 41
1078-122
EN
Coastal areas are very vulnerable to various pressures, developments, and changes. In the last three decades, due to the process of abrasion and accretion, there have been changes in coastlines in various coastal areas in Indonesia. Coastal abrasion and accretion are major concerns in coastal management. Morphological changes have had a major impact on land use and the socio-economic development of communities in coastal areas. In connection with this issue, it is necessary to conduct a study that aims to determine the rate and location of coastline changes in Pangandaran Regency. Considering that Pangandaran Regency is one of the southern regions of Java which is directly facing the Indian Ocean it has high coastal dynamics. In addition, Pangandaran beach is a beach tourism destination that is quite well known and has the potential to be developed, but in some locations, there are indications of a significant decline in the coastline. In this study, Landsat satellite images in time series (1994-2014) were analyzed using remote sensing technology and GIS approaches. Analysis of coastline change was carried out using the DSAS program. The results of the study show that the coastline change in Pangandran is dominated by abrasion at a rate of about -2.5 to -0.1 meters/year. The rate of change of the Pangandaran coastline which experienced the highest abrasion was -4.7 meters/year and the lowest was -0.1 meters/year, while the highest accretion rate was 40.1 meters/year and the lowest was 0.1 meters/year. Maximum abrasion is located at Sukaresik village (Sidamulih Sub-district) at the mouth of the Karang Tirta River. The minimum abrasion is located at Pananjung village. Meanwhile, accretion occurred in several villages such as Pananjung Village, Wonoharjo Village (Pangandaran Sub-district), Balogo Village (Kalipucang Sub-district), Kerta Mukti Village (Cimerak Sub-district), and Cikambulan Village (Sidamulih Sub-district). Minimum accretion is located at Pananjung village and maximum accretion is located at Bagolo village near the estuary of Citanduy River.
4
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A remark about possible unity of the neutron star and black hole high frequency QPOs

75%
Török G., Stuchlík Z., Bakala P.
Open Physics
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2007
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vol. 5
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issue 4
457-462
EN
In a series of papers it was discussed,on the basis of phenomenological arguments, whether the high frequency quasiperiodic oscillations (kHz QPOs)observed in the neutron-star and black-hole X-ray sources originate in the same physical mechanism. Recently it was suggested that a general trend seen in neutron star kHz QPOs instead excludes such a uniform origin. Using the example of the atoll source 4U 1636-53 we illustrate that this is not neccesarily true.
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