Flood susceptibility mapping using a geomorphometric approach in South Australian basins

Natural Hazards - Watershed characteristics and their hydrological responses can have severe effects on the occurrence and extent of floods. Therefore, this study focuses on the integration of...     

An experimental study of Stewartson layer separation

Abstract

The separation of sidewall boundary layers in a rotating annulus of homogeneous fluid is studied experimentally. The flow is driven by a differentially rotating lid, and a very small uniform slope of the bottom causes a weak mountain vortex pair to form in the interior, away from the sidewalls. A necessary condition for aerodynamic separation of the sidewall boundary layers is derived and compared with the experimental results. The laboratory flow separates for parameters that are just slightly more inviscid than those required by the necessary condition for the existence of adverse pressure gradients at the wall. As the bottom friction is decreased further, the flow becomes unsteady and chaotic. The most interesting aspect of this problem is that chaotic interior behavior, associated with the separated boundary layer, is observed for parameter values for which the interior topographically forced flow is, by itself, essentially linear.     

Landsat data to evaluate urban expansion and determine land use/land cover changes in Penang Island,Malaysia

Land surface temperature (LST) plays an important role in local, regional and global climate studies. LST controls the distribution of the budget for radiation heat between the atmosphere and the earth’s surface. Therefore, it is important to evaluate abrupt changes in land use/land cover (LULC). Penang Island, Malaysia has been experiencing a rapid and drastic change in urban expansion over the past two decades due to growth in industrial and residential areas. The aim of this study was to investigate and evaluate the impact of LST with respect to land use changes in Penang Island, Malaysia. Three supervised classification techniques known as maximum likelihood, minimum distance-to-mean and parallelepiped were applied to the images to extract thematic information from the acquired scene by using PCI Geomatica 10.1 image processing software. These remote sensing classification techniques help to examine land-use changes in Penang Island using multi-temporal Landsat data for the period of 1999–2007. Training sites were selected within each scene and seven land cover classes were assigned to each classifier. The relative performance of each technique was evaluated. The accuracy of each classification map was assessed using a reference data set consisting of a large number of samples collected per category. Two Landsat satellite images captured in 1999 and 2007 were chosen to classify the LULC types using the maximum likelihood classification method, determined from visible and near-infrared bands. The study revealed that the maximum likelihood classifier produced superior results and achieved a high degree of accuracy. The LST and normalised difference vegetation index (NDVI) were computed based on changes in LULC. The results showed that the urban (highly built-up) area increased dramatically, and grassland area increased moderately. Inversely, barren land decreased obviously, and forest area decreased moderately. While urban (minimally built-up) area decreased slightly. These changes in LULC caused at significant difference in LST between urban and rural areas. Strong correlation values were observed between LST and NDVI for all LULC classes. The remote sensing technique used in this study was found to be efficient; it reduced the time for the analysis of the urban expansion, and it was found to be a useful tool to evaluate the impact of urbanisation with LST.     

Mineralogy, whole-rock and Sr-Nd isotope geochemistry of mafic microgranular enclaves in Cretaceous Dagbasi granitoids, Eastern Pontides, NE Turkey: Evidence of magma mixing, mingling and chemical equilibration

Rocks of the Late Cretaceous Dagbasi Pluton (88-83 Ma), located in the eastern Pontides, include mafic microgranular enclaves (MMEs) ranging from a few centimetres to metres in size, and from ellipsoidal to ovoid in shape. The MMEs are composed of gabbroic diorite, diorite and tonalite, whereas the felsic host rocks comprise mainly tonalite, granodiorite and monzogranite based on both mineralogical and chemical compositions. MMEs are characterized by a fine-grained, equigranular and hypidiomorphic texture. The common texture of felsic host rocks is equigranular and also reveals some special types of microscopic textures, e.g., oscillatory-zoned plagioclase, poikilitic K-feldspar, small lath-shaped plagioclase in large plagioclase, blade-shaped biotite, acicular apatite, spike zones in plagioclase and spongy-cellular plagioclase textures and rounded plagioclase megacrysts in MMEs. Compositions of plagioclases (An₃₃-An₆₀), hornblendes (Mg#=0.77-1.0) and biotites (Mg#=0.61-0.63) of MMEs are slightly distinct or similar to those of host rocks (An_12-57; hbl Mg#=0.63-1.0; Bi Mg#=0.50-0.69), which suggest partial to complete equilibration during mafic-felsic magma interactions.The felsic host rocks have SiO₂ between 60 and 76 wt% and display low to slightly medium-K tholeiitic to calc-alkaline and peraluminous to slightly metaluminous characteristics. Chondrite-normalized rare-earth element (REE) patterns are fractionated (La_cn/Lu_cn=1.5-7.3) with pronounced negative Eu anomalies (Eu/Eu*=0.46-1.1). Initial ε_Nd(i) values vary between −3.1 and 1.6, initial ⁸⁷Sr/⁸⁶Sr values between 0.7056 and 0.7067.Compared with the host rocks, the MMEs are characterized by relatively high Mg-number of 22-52, low contents of SiO₂ (53-63 wt%), low ASI (0.7-1.1) and low to medium-K tholeiitic to calc-alkaline, metaluminous to peraluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)_cn=1.4-3.9; (Tb/Yb)_cn=0.9-1.5] and show small negative Eu anomalies (Eu/Eu*=0.63-1.01). Isotope signatures of these rocks (⁸⁷Sr/⁸⁶Sr_(i)=0.7054-0.7055; ε_Nd(i)=-1.0 to 1.9) are largely similar to the host rocks. Gabbroic diorite enclaves have relatively low contents of SiO₂, ASI; high Mg#, CaO, Al₂O₃, TiO₂, P₂O₅, Sr and Nb concentrations compared to dioritic and tonalitic enclaves.The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, interacted with a crustal melt that originated from dehydration melting of the mafic lower crust at deep crustal levels. The existence of compositional and textural disequilibrium and the nature of chemical and isotopic variation in these rock types indicate that magma mixing/mingling between an evolved mafic and a granitic magma was involved in their genesis. Microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched lithospheric mantle source. Al-in-amphibole estimates the pluton emplacement at ca. 0.3-3.8 kbar, and therefore, magma mixing and mingling must have occurred at 3.8 kbar or below this level.     

Motion of artificial satellites in the set of Eulerian redundant parameters (III)

In this paper, the classical and generalized Sundman time transformations are used to establish new generating set of differential equations of motion in terms of the Eulerian redundant parameters. The implementation of this set on digital computers for the commonly used independent variables is developed once and for all. Motion prediction algorithms based on these equations are developed in a recursive manner for the motions in the Earth's gravitational field with axial symmetry whatever the number of the zonal harmonic terms may be. Applications for the two types of short and long term predictions are considered for the perturbed motion in the Earth's gravitational field with axial symmetry with zonal harmonic terms up to J ₃₆ . Numerical results proved the very high efficiency and flexibility of the developed equations.     

Placement of sensors/actuators on civil structures using genetic algorithms

The optimal design and placement of controllers at discrete locations is an important problem that will have impact on the control of civil engineering structures. Though algorithms exist for the placement of sensor/actuator systems on continuous structures, the placement of controllers on discrete civil structures is a very difficult problem. Because of the nature of civil structures, it is not possible to place sensors and actuators at any location in the structure. This usually creates a non‐linear constrained mixed integer problem that can be very difficult to solve. Using genetic algorithms in conjunction with gradient‐based optimization techniques will allow for the simultaneous placement and design of an effective structural control system. The introduction of algorithms based on genetic search procedures should increase the rate of convergence and thus reduce the computational time for solving the difficult control problem. The newly proposed method of simultaneously placing sensors/actuators will be compared to a commonly used method of sensors/actuators placement where sensors/actuators are placed sequentially. The savings in terms of energy requirements and cost will be discussed. Copyright © 2001 John Wiley & Sons, Ltd.     

Effects of ionospheric horizontal gradients on differential GPS

This paper outlines the effect of horizontal ionospheric gradients on transionospheric path propagation such as for the case of GPS signals. The total electron content (TEC) is a function of time of day, and is much influenced by solar activity and also the receiving station location. To make the model applicable for long baselines, for which the ionosphere is not generally well correlated between receiving stations, the ionospheric gradients should be taken into account. In this work the signal path is determined using a modified ray-tracing technique together with a homing-in method. Results show that horizontal gradients can have a significant effect on GPS positioning for both single station positioning and differential GPS. For differential GPS, the ionospheric delay can, however, be either increased or decreased compared with the case of no gradient, depending on the gradient direction.