ABSTRACT
This research presented the ability of the Hilbert transformation of The Very Low Frequency-Electromagnetic (VLF-EM) data to investigate the presence of faults. VLF-EM data was collected in the Pinggirsari village area, Arjasari District, Bandung Regency, West Java, Indonesia. Through the Hilbert transformation, the VLF-EM data was converted into apparent resistivity data and then inverted into a resistivity cross-section. For comparison, qualitative interpretation was also conducted using both the Fraser and the Karous-Hjelt filters. Interpretation results using both the Fraser and Karous-Hjelt filters indicate the presence of faults through tilt-angle curve peaks and apparent current density anomalies. The resistivity cross-section resulting from the Occam inversion of the apparent resistivity data, derived from the Hilbert transformation, accurately delineated fault positions. Resistivity changes around 700-800 m indicated fault proximity to a depth of approximately 150 m, with a good match to the geological map. Within a distance of 0-700 m, low resistivity values were associated with the Malabar tuff, while >700 m, higher resistivity values were associated with the Waringin-Bedil andesite. The Hilbert transform helps in clarifying VLF data interpretation for precise fault detection through resistivity parameters.
ABSTRACT
PURPOSE: To revisit the concept of retinectomy and the theory of mechanical forces on the retina occurring in rhegmatogenous retinal detachment (RRD) and to describe the potential application of radial retinectomy in RRD with advanced proliferative vitreoretinopathy (PVR). METHODS: A literature search was performed to identify all English language articles reporting the use of retinectomy for the management of RRD with PVR. We reviewed the theoretical background of mechanical forces occurring in RRD. RESULTS: Detachment of the retina from the retinal pigment epithelium (RPE)/choroid is influenced by disequilibrium of several physical forces: tangential forces on the epiretinal membrane T 1 and radial traction on the retina F R exceeding the retinal adhesion force to the RPE T 1 + F R > F A . PVR may exaggerate the amounts of tangential and radial forces ( T 1 and F R ) that pull the retina off. Relaxing radial retinectomy, by the nature of its cutting pattern, may theoretically decrease the amounts of both forces, therefore restoring the equilibrium between tensile and adhesive forces on the retinal surface T 1 + F R = F A . CONCLUSION: Relaxing radial retinectomy may potentially be applied in RRD with advanced PVR but has rarely been reported to date. Future studies are needed to evaluate its outcomes and long-term complications.
ABSTRACT
Leachate sludge samples were taken from two municipal solid waste sites of Jelekong and Sarimukti in Bandung, Indonesia. Their magnetic mineralogy and granulometry were analyzed to discriminate the sources of magnetic minerals using X-ray diffraction (XRD), scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy (SEM-EDX) and rock magnetism. SEM-EDX analyses infer that the main magnetic minerals in the leachate sludge are iron oxides. In terms of their morphology, the grains from Jelekong are mostly octahedral and angular, which are similar to the general shapes of magnetic grains from the local soils. The grains from Sarimukti, on the other hand, are dominated by imperfect spherule shapes suggesting the product of combustion processes. Hysteresis parameters verify that the predominant magnetic mineral in leachate sludge is low coercivity ferrimagnetic mineral such as magnetite (Fe(3)O(4)). Furthermore, comparisons of rock magnetic parameters show that the magnetic minerals of soil samples from Jelekong have higher degree of magnetic pedogenesis indicating higher proportion of superparamagnetic/ultrafine particles than those of soil samples from Sarimukti. The plot of susceptibilities ratio versus coercive force has a great potential to be used as a discriminating tool for determining the source of magnetic minerals.
