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Structural Index (structural + index)
Selected AbstractsInterpretation of regional aeromagnetic data by the scaling function method: the case of Southern Apennines (Italy)GEOPHYSICAL PROSPECTING, Issue 4 2009G. Florio ABSTRACT A complex aeromagnetic anomaly in Southern Apennines (Italy) is analysed and interpreted by a multiscale method based on the scaling function. We use multiscale methods allowing analysis of a potential field along ridges, which are lines defined by the position of the extrema of the field at the considered scales. The method developed and applied in this paper is based on the study of the scaling function of the total magnetic field. It allows recovering of source parameters such as depth and structural index. The studied area includes a Pleistocene volcanic structure (Mt. Vulture) whose intense dipolar anomaly is superimposed on a longer wavelength regional anomaly. The interpretation of ridges of the modulus of the analytic signal at different altitude ranges allows recognition of at least three distinct sources between about 5 km and 20 km depth. Their interpretation is discussed in light of borehole data and other geophysical constraints. A reasonable geological model for these sources indicates the presence of intrusions, probably linked to the past activity of Mt. Vulture. [source] An enhanced method for source parameter imaging of magnetic data collected for mineral explorationGEOPHYSICAL PROSPECTING, Issue 5 2005Richard S. Smith ABSTRACT We have developed a method for imaging magnetic data collected for mineral exploration to yield the following structural information: depth, model type (structural index) and susceptibility. The active nature of mineral exploration data requires we derive the structural information from a robust quantity: we propose that the first- or second-order analytic-signal amplitude is suitably stable. The procedure is to normalize the analytic-signal amplitude by the peak value and then use non-linear inversion to estimate the depth and the structural index for each anomaly. In our field example, different results are obtained depending on whether we inverted for the first- or second-order analytic-signal amplitude. This is probably because the two-dimensional contact, thin sheet or horizontal cylinder models we have assumed are not appropriate. In cases such as these, when our model assumptions are not correct, the results should not be interpreted quantitatively, but they might be useful for giving a qualitative indication of how the structure might vary. With a priori information, it is possible to assume a model type (i.e. set the structural index) and generate estimates of the depth and susceptibility. These data can then be gridded and imaged. If a contact is assumed, the susceptibility contrast is estimated; for the dike model, the susceptibility-thickness is estimated; for the horizontal cylinder, the susceptibility-area is estimated. To emphasize that the results are dependent on our assumed model, we advocate prefixing any derived quantity by the term ,apparent'. [source] Euler deconvolution of the analytic signal and its application to magnetic interpretationGEOPHYSICAL PROSPECTING, Issue 3 2004P. Keating ABSTRACT Euler deconvolution and the analytic signal are both used for semi-automatic interpretation of magnetic data. They are used mostly to delineate contacts and obtain rapid source depth estimates. For Euler deconvolution, the quality of the depth estimation depends mainly on the choice of the proper structural index, which is a function of the geometry of the causative bodies. Euler deconvolution applies only to functions that are homogeneous. This is the case for the magnetic field due to contacts, thin dikes and poles. Fortunately, many complex geological structures can be approximated by these simple geometries. In practice, the Euler equation is also solved for a background regional field. For the analytic signal, the model used is generally a contact, although other models, such as a thin dike, can be considered. It can be shown that if a function is homogeneous, its analytic signal is also homogeneous. Deconvolution of the analytic signal is then equivalent to Euler deconvolution of the magnetic field with a background field. However, computation of the analytic signal effectively removes the background field from the data. Consequently, it is possible to solve for both the source location and structural index. Once these parameters are determined, the local dip and the susceptibility contrast can be determined from relationships between the analytic signal and the orthogonal gradients of the magnetic field. The major advantage of this technique is that it allows the automatic identification of the type of source. Implementation of this approach is demonstrated for recent high-resolution survey data from an Archean granite-greenstone terrane in northern Ontario, Canada. [source] Imaging magnetic sources using Euler's equationGEOPHYSICAL PROSPECTING, Issue 1 2002Shu-Kun Hsu ABSTRACT The conventional Euler deconvolution method has the advantage of being independent of magnetization parameters in locating magnetic sources and estimating their corresponding depths. However, this method has the disadvantage that a suitable structural index must be chosen, which may cause spatial diffusion of the Euler solutions and bias in the estimation of depths to the magnetic sources. This problem becomes more serious when interfering anomalies exist. The interpretation of the Euler depth solutions is effectively related to the model adopted, and different models may have different structural indices. Therefore, I suggest a combined inversion for the structural index and the source location from the Euler deconvolution, by using only the derivatives of the magnetic anomalies. This approach considerably reduces the diffusion problem of the location and depth solutions. Consequently, by averaging the clustered solutions satisfying a given criterion for the solutions, we can image the depths and attributes (or types) of the causative magnetic sources. Magnetic anomalies acquired offshore northern Taiwan are used to test the applicability of the proposed method. [source] Short note: Source geometry identification by simultaneous use of structural index and shape factorGEOPHYSICAL PROSPECTING, Issue 1 2001Lopamudra Roy A cross-plot of the shape factors and the structural indices, determined from gravity anomalies over various idealized sources, namely horizontal/vertical lines and vertical ribbons with various strike lengths and depth extents, forms a closed loop. Different segments of this loop, termed the source geometry identification loop (SGIL), correspond to different source geometries. Combined use of the structural index and the shape factor determined from an isolated gravity anomaly reduces the ambiguity in characterizing the source geometry. A simulated example and three field examples, namely a Cuban chromite anomaly, an Indian example over manganese ore and a sulphide ore from Quebec, have been analysed by the proposed method in order to identify their respective source geometries. [source] A structural index to affect the operation life of steam turbine generatorsINTERNATIONAL JOURNAL OF CIRCUIT THEORY AND APPLICATIONS, Issue 8 2008Chi-Hshiung Lin Abstract Since there is a largest occurrence probability among power line faults, the single-phase-to-ground fault (1P-G fault) plays a non-negligible role on fatigue life of a turbine generator unit. It is found in this paper that the system frequency disturbance is the principal one to arouse torsional vibrations on turbine mechanism under a 1P-G fault, which is different from the unidirectional one for a three-phase-to-ground fault (3P-G fault). By analyzing the turbine-generator-exciter-blade model using the electromechanical analogy, it is further found that the structural index of KGEN-TURB/HGEN ratio governs the response sensitivity to such a disturbance. That means the larger the ratio is, the severer the torsional vibrations induced will be. According to this result, it can be deduced that the coming generation of turbine generator units would get more sensitive to the 3P-G fault because the tendency is toward reducing the inertia of generators. Copyright © 2008 John Wiley & Sons, Ltd. [source] Structural acclimation and radiation regime of silver fir (Abies alba Mill.) shoots along a light gradientPLANT CELL & ENVIRONMENT, Issue 3 2003A. CESCATTI ABSTRACT Shoot architecture has been investigated using the ratio of mean shoot silhouette area to total needle area ( ) as a structural index of needle clumping in shoot space, and as the effective extinction coefficient of needle area. Although can be used effectively for the prediction of canopy gap fraction, it does not provide information about the within-shoot radiative regime. For this purpose, the estimation of three architectural properties of the shoots is required: needle area density, angular distribution and spatial aggregation. To estimate these features, we developed a method based on the inversion of a Markov three-dimensional interception model. This approach is based on the turbid medium approximation for needle area in the shoot volume, and assumes an ellipsoidal angular distribution of the normals to the needle area. Observed shoot dimensions and silhouette areas for different vertical and azimuth angles (AS) are used as model inputs. The shape coefficient of the ellipsoidal distribution (c) and the Markov clumping index (,0) are estimated by a least square procedure, in order to minimize the differences between model prediction and measurements of AS. This methodology was applied to silver fir (Abies alba Mill.) shoots collected in a mixed fir,beech,spruce forest in the Italian Alps. The model worked effectively over the entire range of shoot morphologies: c ranged from 1 to 8 and ,0 from 0·3 to 1 moving from the top to the base of the canopy. Finally, the shoot model was applied to reconstruct the within-shoot light regime, and the potential of this technique in upscaling photosynthesis to the canopy level is discussed. [source] NMR of peptides and proteins in oriented membranesCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2002Francesca M. Marassi Abstract Solid-state NMR spectroscopy is used to determine the structures of membrane peptides and proteins in lipid bilayers. The methodology for membrane protein structure determination using solid-state NMR of oriented lipid bilayer samples is outlined. Recent developments in recombinant bacterial expression systems for the preparation of isotopically labeled membrane proteins, pulse sequences for high-resolution spectroscopy, and structural indices that guide the structure assembly process greatly extend the capabilities of the technique. © 2002 Wiley Periodicals, Inc. Concepts in Magn Reson 14, 212,224, 2002. [source] Language lateralization in temporal lobe epilepsy using functional MRI and probabilistic tractographyEPILEPSIA, Issue 8 2008Sebastian Rodrigo Summary Purpose: Language functional magnetic resonance imaging (fMRI) is used to noninvasively assess hemispheric language specialization as part of the presurgical work-up in temporal lobe epilepsy (TLE). White matter asymmetries on diffusion tensor imaging (DTI) may be related to language specialization as shown in controls and TLE. To refine our understanding of the effect of epilepsy on the structure,function relationships, we focused on the arcuate fasciculus (ArcF) and the inferior occipitofrontal fasciculus (IOF) and tested the relationship between DTI- and fMRI-based lateralization indices in TLE. Methods: fMRI with three language tasks and DTI were obtained in 20 patients (12 right and 8 left TLE). The ArcF, a major language-related tract, and the IOF were segmented bilaterally using probabilistic tractography to obtain fractional anisotropy (FA) lateralization indices. These were correlated with fMRI-based lateralization indices computed in the inferior frontal gyrus (Pearson's correlation coefficient). Results: fMRI indices were left-lateralized in 16 patients and bilateral or right-lateralized in four. In the ArcF, FA was higher on the left than on the right side, reaching significance in right but not in left TLE. We found a positive correlation between ArcF anisotropy and fMRI-based lateralization indices in right TLE (p < 0.009), but not in left TLE patients. No correlation was observed for the IOF. Conclusions: Right TLE patients with more left-lateralized functional activations also showed a leftward-lateralized arcuate fasciculus. The decoupling between the functional and structural indices of the ArcF underlines the complexity of the language network in left TLE patients. [source] Imaging magnetic sources using Euler's equationGEOPHYSICAL PROSPECTING, Issue 1 2002Shu-Kun Hsu ABSTRACT The conventional Euler deconvolution method has the advantage of being independent of magnetization parameters in locating magnetic sources and estimating their corresponding depths. However, this method has the disadvantage that a suitable structural index must be chosen, which may cause spatial diffusion of the Euler solutions and bias in the estimation of depths to the magnetic sources. This problem becomes more serious when interfering anomalies exist. The interpretation of the Euler depth solutions is effectively related to the model adopted, and different models may have different structural indices. Therefore, I suggest a combined inversion for the structural index and the source location from the Euler deconvolution, by using only the derivatives of the magnetic anomalies. This approach considerably reduces the diffusion problem of the location and depth solutions. Consequently, by averaging the clustered solutions satisfying a given criterion for the solutions, we can image the depths and attributes (or types) of the causative magnetic sources. Magnetic anomalies acquired offshore northern Taiwan are used to test the applicability of the proposed method. [source] Short note: Source geometry identification by simultaneous use of structural index and shape factorGEOPHYSICAL PROSPECTING, Issue 1 2001Lopamudra Roy A cross-plot of the shape factors and the structural indices, determined from gravity anomalies over various idealized sources, namely horizontal/vertical lines and vertical ribbons with various strike lengths and depth extents, forms a closed loop. Different segments of this loop, termed the source geometry identification loop (SGIL), correspond to different source geometries. Combined use of the structural index and the shape factor determined from an isolated gravity anomaly reduces the ambiguity in characterizing the source geometry. A simulated example and three field examples, namely a Cuban chromite anomaly, an Indian example over manganese ore and a sulphide ore from Quebec, have been analysed by the proposed method in order to identify their respective source geometries. [source] Anticipating bipedalism: trabecular organization in the newborn iliumJOURNAL OF ANATOMY, Issue 6 2009Craig A. Cunningham Abstract Trabecular bone structural organization is considered to be predominantly influenced by localized temporal forces which act to maintain and remodel the trabecular architecture into a biomechanically optimal configuration. In the adult pelvis, the most significant remodelling forces are believed to be those generated during bipedal locomotion. However, during the fetal and neonatal period the pelvic complex is non-weight bearing and, as such, structural organization of iliac trabecular bone cannot reflect direct stance-related forces. In this study, micro-computed tomography scans from 28 neonatal ilia were analysed, using a whole bone approach, to investigate the trabecular characteristics present within specific volumes of interest relevant to density gradients highlighted in a previous radiographic study. Analysis of the structural indices bone volume fraction, trabecular thickness, trabecular spacing and trabecular number was carried out to quantitatively investigate structural composition. Quantification of the neonatal trabecular structure reinforced radiographic observations by highlighting regions of significant architectural form which grossly parallel architectural differences in the adult pattern but which have previously been attributed to stance-related forces. It is suggested that the seemingly organized rudimentary scaffold observed in the neonatal ilium may be attributable to other non-weight bearing anatomical interactions or even to a predetermined genetic blueprint. It must also be postulated that whilst the observed patterning may be indicative of a predetermined inherent template, early non-weight bearing and late stance-related locomotive influences may subsequently be superimposed upon this scaffolding and perhaps reinforced and likely remodelled at a later age. Ultimately, the analysis of this fundamental primary pattern has core implications for understanding the earliest changes in pelvic trabecular architecture and provides a baseline insight into future ontogenetic development and bipedal capabilities. [source] An appraisal of the Serra da Cangalha impact structure using the Euler deconvolution methodMETEORITICS & PLANETARY SCIENCE, Issue 8 2005A. Adekunle ADEPELUMI The efficacy of the method has been evaluated using the aeromagnetic data obtained over the Serra da Cangalha impact crater, northeastern Brazil. The analyses of the data have provided characteristic Euler deconvolution signatures and structural indices associated with impact craters. Also, through the interpretation of the computed Euler solutions, our understanding of the structural features present around the impact structure has been enhanced. The Euler solutions obtained indicate shallow magnetic sources that are interpreted as possibly post-impact faults and a circular structure. The depth of these magnetic sources varies between 0.8 and 2.5 km, while the Precambrian basement depth was found at ,1.5 km. This is in good agreement with the estimates of the Precambrian basement depth of about 1.1 km, calculated using aeromagnetic data. The reliability of the depth solutions obtained through the implementation of the Euler method was confirmed through the use of the existing information available in the area and the result of previous studies. We find that the Euler depth solutions obtained in this study are consistent with the results obtained using other methods. [source] Quantifying habitat structure: surface convolution and living space for species in complex environmentsOIKOS, Issue 12 2008D. M. Warfe Habitat complexity is often used to explain the distribution of species in environments, yet the ability to predict outcomes of structural differences between habitats remains elusive. This stems from the difficulty and lack of consistency in measuring and quantifying habitat structure, making comparison between different habitats and systems problematic. For any measure of habitat structure to be useful it needs to be applicable to a range of habitats and have relevance to their associated fauna. We measured three differently-shaped macrophyte analogues with nine indices of habitat structure to determine which would best distinguish between their shape and relate to the abundance and rarefied species richness of their associated macroinvertebrate assemblages. These indices included the physical, whole-plant attributes of surface area (SA) and plant volume (PV), the interstitial space attributes of average space size and frequency (ISI), average refuge space from predation (Sp/Pr), and total refuge space (FFV), and the degree of surface convolution at a range of scales (i.e. the fractal dimension at four spatial scales: 7.5×, 5×, 2.5× and 1× magnification). We found a high degree of inter-correlation between the structural indices such that they could be organised into two suites: one group describing interstitial space and surface convolution at coarse scales, the other describing whole-plant attributes and surface convolution at fine scales. Two of these indices fell into both suites: the average refuge space from predation (Sp/Pr) and the fractal dimension at 5× magnification. These two measures were also strongly related to macroinvertebrate abundance and rarefied species richness, which points to their usefulness in quantifying habitat structure and illustrates that habitat structure depends not just on shape, but on the space associated with shape. [source] | |||||||||||||