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Orthogonal
Terms modified by Orthogonal Selected AbstractsVisualization of anterior skull base defects with intraoperative cone-beam CTHEAD & NECK: JOURNAL FOR THE SCIENCES & SPECIALTIES OF THE HEAD AND NECK, Issue 4 2010Gideon Bachar MD Abstract Background The role of cone-beam CT (CBCT) in demonstrating anterior skull base defects (ASBDs), differing in size and location, was investigated. The study was designed to describe the potential advantage of CBCT in the setting of an intraoperative cerebrospinal fluid (CSF) leak. Methods In all, 120 ASBD were evaluated in 5 cadaver heads. Orthogonal and oblique slices were reconstructed. Observer studies assessed the visibility of ASBD in each location as a function of defect size. Results For 1-, 2-, and 4-mm defects, the percentage that were undetectable ranged from 20% to 33%, 0% to 14%, and 0% to 5%, respectively. Confident breach detection increased with defect size and was most challenging in the lateral lamella and cribriform. CBCT permitted confident detection of ASBD as small as about 2 mm in the fovea ethmoidalis and planum. Oblique views were found to be superior to orthogonal planes. Conclusions The ability to identify ASBD depended on the size and location of defect. Oblique viewing planes were optimal for ASBD visualization. © 2009 Wiley Periodicals, Inc. Head Neck, 2010 [source] Influence of Orthogonal Overload on Human Vertebral Trabecular Bone Mechanical Properties,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 11 2007Arash Badiei Abstract The aim of this study was to investigate the effects of overload in orthogonal directions on longitudinal and transverse mechanical integrity in human vertebral trabecular bone. Results suggest that the trabecular structure has properties that act to minimize the decrease of apparent toughness transverse to the primary loading direction. Introduction: The maintenance of mechanical integrity and function of trabecular structure after overload remains largely unexplored. Whereas a number of studies have focused on addressing the question by testing the principal anatomical loading direction, the mechanical anisotropy has been overlooked. The aim of this study was to investigate the effects of overload in orthogonal directions on longitudinal and transverse mechanical integrity in human vertebral trabecular bone. Materials and Methods: T12/L1 vertebral bodies from five cases and L4/L5 vertebral bodies from seven cases were retrieved at autopsy. A cube of trabecular bone was cut from the centrum of each vertebral body and imaged by ,CT. Cubes from each T12/L1 and L4/L5 pairs were assigned to either superoinferior (SI) or anteroposterior (AP) mechanical testing groups. All samples were mechanically tested to 10% apparent strain by uniaxial compression according to their SI or AP allocation. To elucidate the extent to which overload in orthogonal directions affects the mechanical integrity of the trabecular structure, samples were retested (after initial uniaxial compression) in their orthogonal direction. After mechanical testing in each direction, apparent ultimate failure stresses (UFS), apparent elastic moduli (E), and apparent toughness moduli (u) were computed. Results: Significant differences in mechanical properties were found between SI and AP directions in both first and second overload tests. Mechanical anisotropy far exceeded differences resulting from overloading the structure in the orthogonal direction. No significant differences were found in mean UFS and mean u for the first or second overload tests. A significant decrease of 35% was identified in mean E for cubes overloaded in the SI direction and then overloaded in the AP direction. Conclusions: Observed differences in the mechanics of trabecular structure after overload suggests that the trabecular structure has properties that act to minimize loss of apparent toughness, perhaps through energy dissipating sacrificial structures transverse to the primary loading direction. [source] ChemInform Abstract: Orthogonal, Convergent Syntheses of Dendrimers Based on Melamine with One or Two Unique Surface Sites for Manipulation.CHEMINFORM, Issue 3 2002Wen Zhang Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Generalized minimum-norm perspective shadow mapsCOMPUTER ANIMATION AND VIRTUAL WORLDS (PREV: JNL OF VISUALISATION & COMPUTER ANIMATION), Issue 5 2008Fan Zhang Abstract Shadow mapping has been extensively used for real-time shadow rendering in 3D computer games, though it suffers from the inherent aliasing problems due to its image-based nature. This paper presents an enhanced variant of light space perspective shadow maps to optimize perspective aliasing distribution in possible general cases where the light and view directions are not orthogonal. To be mathematically sound, the generalized representation of perspective aliasing errors has been derived in detail. Our experiments have shown the enhanced shadow quality using our algorithm in dynamic scenes. Copyright © 2008 John Wiley & Sons, Ltd. [source] A Fast Simulation Method Using Overlapping Grids for Interactions between Smoke and Rigid ObjectsCOMPUTER GRAPHICS FORUM, Issue 2 2008Yoshinori Dobashi Abstract Recently, many techniques using computational fluid dynamics have been proposed for the simulation of natural phenomena such as smoke and fire. Traditionally, a single grid is used for computing the motion of fluids. When an object interacts with a fluid, the resolution of the grid must be sufficiently high because the shape of the object is represented by a shape sampled at the grid points. This increases the number of grid points that are required, and hence the computational cost is increased. To address this problem, we propose a method using multiple grids that overlap with each other. In addition to a large single grid (a global grid) that covers the whole of the simulation space, separate grids (local grids) are generated that surround each object. The resolution of a local grid is higher than that of the global grid. The local grids move according to the motion of the objects. Therefore, the process of resampling the shape of the object is unnecessary when the object moves. To accelerate the computation, appropriate resolutions are adaptively-determined for the local grids according to their distance from the viewpoint. Furthermore, since we use regular (orthogonal) lattices for the grids, the method is suitable for GPU implementation. This realizes the real-time simulation of interactions between objects and smoke. [source] Effect of slice angle on inhomogeneity artifact and its correction in slice-selective MR imagingCONCEPTS IN MAGNETIC RESONANCE, Issue 4 2009Kwan-Jin Jung Abstract The inhomogeneity of a local magnetic field causes an image artifact of geometric distortion and intensity abnormality because of the slice offset and readout shift in slice-selective MR imaging. It has been found that this artifact can be corrected by the projection of the slice offset onto the readout axis at a certain oblique slice angle. The slice angle for the artifact correction is determined by the amplitude of slice selection and readout gradients, and is independent of the magnetic field inhomogeneity and the main magnetic field direction. In addition, the existing view-angle tilting technique is found to be valid only for the slice orientation orthogonal to the object axis. The slice angle effect on the inhomogeneity artifact was confirmed experimentally through phantom and volunteer's head imaging for both regular and view-angle tilted spin echo sequences at 3 T. © 2009 Wiley Periodicals, Inc.Concepts Magn Reson Part A 34A: 238,248, 2009. [source] Use of mutually inductive coupling in probe design,CONCEPTS IN MAGNETIC RESONANCE, Issue 4 2002D.I. Hoult Abstract An analysis is presented of mutually inductive coupling in probe design. It is assumed that near field couplings predominate and that lumped constants may therefore be employed. Using three published designs as examples, analytic techniques are presented for assessing B1 field strength, losses, and signal-to-noise ratio in increasingly complex situations. The perturbing effect of the B1 field from a matching coil is examined and it is shown that if the coil is too close to the sample there can be an asymmetry introduced in the rotating frame B1 field. It is then shown that such asymmetries are potentially a general feature of inductively coupled, loaded coils. The importance of suppressing unwanted resonances is highlighted if tuning and matching are to be orthogonal, a potential advantage of mutually inductive matching. Finally, a lumped-constant simulation is briefly described for those situations where an analytic approach becomes too cumbersome. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 262,285, 2002 [source] Some Notes on Institutions in Evolutionary Economic GeographyECONOMIC GEOGRAPHY, Issue 2 2009Ron Boschma abstract Within the evolutionary economic geography framework, the role of institutions deserves more explicit attention. We argue that territorial institutions are to be viewed as orthogonal to organizational routines since each territory is characterized by a variety of routines and a single firm can apply its routines in different territorial contexts. It is therefore meaningful to distinguish between institutional economic geography and evolutionary economic geography as their explanans is different. Yet the two approaches can be combined in a dynamic framework in which institutions coevolve with organizational routines, particularly in emerging industries. Furthermore, integrating the evolutionary and institutional approach allows one to analyze the spatial diffusion of organizational routines that mediate conflicts among social groups, in particular, those between employers and employees. An evolutionary economic geography advocates an empirical research program, both qualitative and quantitative, that can address the relative importance of organizational routines and territorial institutions for regional development. [source] Optimal separation times for electrical field flow fractionation with Couette flowsELECTROPHORESIS, Issue 20 2008Jennifer Pascal Abstract The prediction of optimal times of separation as a function of the applied electrical field and cation valence have been studied for the case of field flow fractionation [Martin M., Giddings J. C., J. Phys. Chem. 1981, 85, 727] with charged solutes. These predictions can be very useful to a priori design or identify optimal operating conditions for a Couette-based device for field flow fractionation when the orthogonal field is an electrical field. Mathematically friendly relationships are obtained by applying the method of spatial averaging to the solute species continuity equation; this is accomplished after the role of the capillary geometrical dimensions on the applied electrical field equations has been assessed [Oyanader M. A., Arce P., Electrophoresis 2005; 26, 2857]. Moreover, explicit analytical expressions are derived for the effective parameters, i.e. diffusivity and convective velocity as functions of the applied (orthogonal) electrical field. These effective transport parameters are used to study the effect of the cation valence of the solutes and of the magnitude of the applied orthogonal electrical field on the values of the optimal time of separation. These parameters play a significant role in controlling the optimal separation time, leading to a family of minimum values, for particular magnitudes of the applied orthogonal electrical field. [source] Role of geometrical dimensions in electrophoresis applications with orthogonal fieldsELECTROPHORESIS, Issue 15 2005Mario A. Oyanader Abstract The role of geometrical dimensions in electrophoresis applications with axial and orthogonal (secondary) electric fields is investigated using a rectangular capillary channel. In particular, the role of the applied orthogonal electrical field in controlling key parameters involved in the effective diffusivity and effective (axial) velocity of the solute is identified. Such mathematically friendly relationships are obtained by applying the method of spatial averaging to the solute species continuity equation; this is accomplished after the role of the capillary geometrical dimensions on the applied electrical field equations has been studied. Moreover, explicit analytical expressions are derived for the effective parameters, i.e., diffusivity and convective velocity as functions of the applied (orthogonal) electric field. Previous attempts (see Sauer et al., 1995) have only led to equations for these parameters that require numerical solution and, therefore, limited the use of such results to practical applications. These may include, for example, the design of separation processes as well as environmental applications such as soil reclamation and wastewater treatment. An illustration of how a secondary electrical field can aid in reducing the optimal separation time is included. [source] Mother,Child Relationships in France: Balancing Autonomy and Affiliation in Everyday InteractionsETHOS, Issue 3 2004MARIE-ANNE SUIZZO French child-rearing beliefs share features of both individualist and collectivist cultural orientations and have appeared contradictory within this individualism,collectivism framework in previous research. For this study, 32 Parisian mothers of infants and young children were interviewed regarding four possible sources of variation in their relationships with their children: interpersonal distance, communicative accommodation, desirable and undesirable early behaviors, and long-term goals and values. Five themes are identified and a cultural model of Parisian parenting is elaborated, demonstrating how beliefs, practices, and goals are connected in mothers' minds. This study demonstrates that individualism and collectivism are orthogonal, multifaceted orientations, each containing dimensions, such as autonomy as separateness and group affiliation and belonging, that can coexist both harmoniously and in dynamic tension within individuals and within cultures. [source] Six independent factors of personality variation: a response to SaucierEUROPEAN JOURNAL OF PERSONALITY, Issue 1 2002Michael C. Ashton We address the concerns raised by Saucier about our proposed six-factor structure of personality. First, we dispute Saucier's new interpretation of the Negative Valence factor as a meaningful dimension of personality variation. We explain that Negative Valence terms may distort the structure of personality-descriptive terms, and that the substantive variance of Honesty is weakly correlated with Negative Valence. Also, we point out that our proposed six factors are (like the Big Five) roughly orthogonal, and that the occurrence of rotational variants within this six-dimensional space is not problematic. We argue that in terms of comprehensiveness, parsimony, independence of factors, and replicability across languages, our proposed six-factor model so far seems to be the optimal structure of personality characteristics. Copyright © 2002 John Wiley & Sons, Ltd. [source] Connecting Optimal Capital Investment and Equity ReturnsFINANCIAL MANAGEMENT, Issue 2 2005R. Burt Porter Economic theory predicts a contemporaneous correlation between equity returns and investment growth that is only weakly present in the data. By modifying the firm's production function to include a lag between investment decisions and expenditures, and after correcting for the temporal aggregation of investment, I find the predicted correlation to be present in the data. I estimate the model for 31 industries and find that investment returns are highly correlated with the industry portfolio equity returns. Further, the portion of investment returns orthogonal to equity returns is associated positively with changes in profitability and negatively with lagged differences between equity and investment returns. [source] Deformation during exhumation of medium- and high-grade metamorphic rocks in the Variscan chain in northern Sardinia (Italy)GEOLOGICAL JOURNAL, Issue 3 2009Rodolfo Carosi Abstract The Anglona and SW Gallura regions represent key places to investigate the tectonic evolution of medium- and high-grade metamorphic rocks cropping out in northern Sardinia (Italy). From south to north we distinguish two different metamorphic complexes recording similar deformation histories but different metamorphic evolution: the Medium Grade Metamorphic Complex (MGMC) and the High Grade Metamorphic Complex (HGMC). After the initial collisional stage (D1 deformation phase), both complexes were affected by three contractional deformational phases (D2, D3 and D4) followed by later extensional tectonics. The D2 deformation phase was the most significant event producing an important deformation partitioning that produced localized shearing and folding domains at the boundary between the two metamorphic complexes. We highlight the presence of two previously undocumented systems of shear belts with different kinematics but analogous orientation in the axial zone of Sardinia. They became active at the boundary between the MGMC and HGMC from the beginning of D2. They formed a transpressive regime responsible for the exhumation of the medium- and high-grade metamorphic rocks, and overall represent a change from orthogonal to orogen-parallel tectonic transport. Copyright © 2008 John Wiley & Sons, Ltd. [source] Processing, modelling and predicting time-lapse effects of overpressured fluid-injection in a fractured reservoirGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2002Erika Angerer Summary Time-lapse seismology is important for monitoring subsurface pressure changes and fluid movements in producing hydrocarbon reservoirs. We analyse two 4-D, 3C onshore surveys from Vacuum Field, New Mexico, USA, where the reservoir of interest is a fractured dolomite. In Phase VI, a time-lapse survey was acquired before and after a pilot tertiary-recovery programme of overpressured CO2 injection, which altered the fluid composition and the pore-fluid pressure. Phase VII was a similar time-lapse survey in the same location but with a different lower-pressure injection regime. Applying a processing sequence to the Phase VI data preserving normal-incidence shear-wave anisotropy (time-delays and polarization) and maximizing repeatability, interval-time analysis of the reservoir interval shows a significant 10 per cent change in shear-wave velocity anisotropy and 3 per cent decrease in the P -wave interval velocities. A 1-D model incorporating both saturation and pressure changes is matched to the data. The saturation changes have little effect on the seismic velocities. There are two main causes of the time-lapse changes. Any change in pore-fluid pressures modifies crack aspect ratios. Additionally, when there are overpressures, as there are in Phase VI, there is a 90° change in maximum impedance directions, and the leading faster split shear wave, instead of being parallel to the crack face as it is for low pore-fluid pressures, becomes orthogonal to the crack face. The anisotropic poro-elasticity (APE) model of the evolution of microcracked rock, calculates the evolution of cracked rock to changing conditions. APE modelling shows that at high overburden pressures only nearly vertical cracks, to which normal incidence P waves are less sensitive than S waves, remain open as the pore-fluid pressure increases. APE modelling matches the observed time-lapse effects almost exactly demonstrating that shear-wave anisotropy is a highly sensitive diagnostic of pore-fluid pressure changes in fractured reservoirs. In this comparatively limited analysis, APE modelling of fluid-injection at known pressure correctly predicted the changes in seismic response, particularly the shear-wave splitting, induced by the high-pressure CO2 injection. In the Phase VII survey, APE modelling also successfully predicted the response to the lower-pressure injection using the same Phase VI model of the cracked reservoir. The underlying reason for this remarkable predictability of fluid-saturated reservoir rocks is the critical nature and high crack density of the fluid-saturated cracks and microcracks in the reservoir rock, which makes cracked reservoirs critical systems. [source] Migration velocity analysis for tilted transversely isotropic mediaGEOPHYSICAL PROSPECTING, Issue 1 2009Laxmidhar Behera ABSTRACT Tilted transversely isotropic formations cause serious imaging distortions in active tectonic areas (e.g., fold-and-thrust belts) and in subsalt exploration. Here, we introduce a methodology for P-wave prestack depth imaging in tilted transversely isotropic media that properly accounts for the tilt of the symmetry axis as well as for spatial velocity variations. For purposes of migration velocity analysis, the model is divided into blocks with constant values of the anisotropy parameters , and , and linearly varying symmetry-direction velocity VP0 controlled by the vertical (kz) and lateral (kx) gradients. Since determination of tilt from P-wave data is generally unstable, the symmetry axis is kept orthogonal to the reflectors in all trial velocity models. It is also assumed that the velocity VP0 is either known at the top of each block or remains continuous in the vertical direction. The velocity analysis algorithm estimates the velocity gradients kz and kx and the anisotropy parameters , and , in the layer-stripping mode using a generalized version of the method introduced by Sarkar and Tsvankin for factorized transverse isotropy with a vertical symmetry axis. Synthetic tests for several models typical in exploration (a syncline, uptilted shale layers near a salt dome and a bending shale layer) confirm that if the symmetry-axis direction is fixed and VP0 is known, the parameters kz, kx, , and , can be resolved from reflection data. It should be emphasized that estimation of , in tilted transversely isotropic media requires using nonhyperbolic moveout for long offsets reaching at least twice the reflector depth. We also demonstrate that application of processing algorithms designed for a vertical symmetry axis to data from tilted transversely isotropic media may lead to significant misfocusing of reflectors and errors in parameter estimation, even when the tilt is moderate (30°). The ability of our velocity analysis algorithm to separate the anisotropy parameters from the velocity gradients can be also used in lithology discrimination and geologic interpretation of seismic data in complex areas. [source] Adaptive subtraction of multiples using the L1 -normGEOPHYSICAL PROSPECTING, Issue 1 2004A. Guitton ABSTRACT A strategy for multiple removal consists of estimating a model of the multiples and then adaptively subtracting this model from the data by estimating shaping filters. A possible and efficient way of computing these filters is by minimizing the difference or misfit between the input data and the filtered multiples in a least-squares sense. Therefore, the signal is assumed to have minimum energy and to be orthogonal to the noise. Some problems arise when these conditions are not met. For instance, for strong primaries with weak multiples, we might fit the multiple model to the signal (primaries) and not to the noise (multiples). Consequently, when the signal does not exhibit minimum energy, we propose using the L1 -norm, as opposed to the L2 -norm, for the filter estimation step. This choice comes from the well-known fact that the L1 -norm is robust to ,large' amplitude differences when measuring data misfit. The L1 -norm is approximated by a hybrid L1/L2 -norm minimized with an iteratively reweighted least-squares (IRLS) method. The hybrid norm is obtained by applying a simple weight to the data residual. This technique is an excellent approximation to the L1 -norm. We illustrate our method with synthetic and field data where internal multiples are attenuated. We show that the L1 -norm leads to much improved attenuation of the multiples when the minimum energy assumption is violated. In particular, the multiple model is fitted to the multiples in the data only, while preserving the primaries. [source] Cationic Conjugated Polyelectrolytes with Molecular Spacers for Efficient Fluorescence Energy Transfer to Dye-Labeled DNA,ADVANCED FUNCTIONAL MATERIALS, Issue 2 2007Y. Woo Abstract Two water-soluble conjugated polyelectrolytes, poly(9,9,-bis(6- N,N,N -trimethylammoniumhexyl)fluorene- alt -1,4-(2,5-bis(6- N,N,N -trimethylammoniumhexyloxy))phenylene) tetrabromide (P1i) and poly((10,10,-bis(6- N,N,N -trimethylammoniumhexyl)-10H-spiro(anthracene-9,9,-fluorene))- alt -1,4-(2,5-bis(6- N,N,N -trimethylammoniumhexyloxy))phenylene) tetrabromide (P2i) are synthesized, characterized, and used in fluorescence resonance energy transfer (FRET) experiments with fluorescein-labeled single-stranded DNA (ssDNA-Fl). P1i and P2i have nearly identical ,-conjugated backbones, as determined by cyclic voltammetry and UV-vis spectroscopy. The main structural difference is the presence of an anthracenyl substituent, orthogonal to the main chain in each of the P2i repeat units, which increases the average interchain separation in aggregated phases. It is possible to observe emission from ssDNA-Fl via FRET upon excitation of P2i. Fluorescein is not emissive within the ssDNA-Fl/P1i electrostatic complex, suggesting Fl emission quenching through photoinduced charge transfer (PCT). We propose that the presence of the anthracenyl "molecular bumper" in P2i increases the distance between optical partners, which decreases PCT more acutely relative to FRET. [source] The Orthogonal (e,e,e)-Tris-Adduct of 9,10-Dimethylanthracene with C60 -Fullerene: A Hidden Cornerstone of Fullerene Chemistry.HELVETICA CHIMICA ACTA, Issue 8 2008Preliminary Communication Abstract Tris(9,,10,-dimethyl[9,10]ethanoanthracene[11,,12,:,1,9;11,,12,:,16,17;11,,,,12,,,:,30,31])[5,6]fullerene C60, the orthogonal (e,e,e)-tris-adduct of C60 and 9,10-dimethylanthracene, was obtained from [4+2]-cycloaddition (Diels,Alder reaction) at room temperature. The thermally unstable orange red (e,e,e)-tris-adduct was purified by chromatography and was isolated in the form of red monoclinic crystals. Its C3 -symmetric addition pattern was established spectroscopically. Its structure could be further investigated by single crystal X-ray diffraction. The (e,e,e)-tris-adduct of C60 and 9,10-dimethylanthracene has earlier been suggested as intermediate and reversibly formed critical component in ,template directed' addition reactions of C60. This previously elusive compound has now been isolated and structurally characterized. [source] Effective elastic properties of the double-periodically cracked platesINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2005G. S. Wang Abstract In this paper, the interaction of double-periodical cracks is accurately solved based on the isolating analysis procedure, superposition principle, pseudo-traction method, Chebyshev polynomial expansion and crack-surface collocation technique. The jump displacement crossing crack faces, the average additional strain and therefore the effective compliance of the double-periodically cracked plate are directly determined. The numerical results for axial-symmetrically distributed double-periodical cracks, general double-periodical cracks with one collinear direction as well as two sets of double-periodical cracks with same size and square distribution are given in this paper. And the partial typical numerical results are compared with the previous works. The analysis shows that the anisotropy induced by the general double-periodical cracks is generally not orthogonal anisotropy. Only when the double-periodical cracks are axial-symmetrically distributed, is the anisotropy orthogonal. In this special cases, the effective engineering constants (consist of effective elastic modulus, the effective Poisson's ratio, the effective shear modulus) of cracked plate versus crack spacing, in the plane stress and plane strain conditions, respectively, are analysed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Numerical study of lid-driven flow in orthogonal and skewed porous cavityINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 10 2008D. Jaya Krishna Abstract Effects of Reynolds number, Darcy number, porosity, aspect ratio and skewness are studied in detail for lid-driven cavity flows filled with fluid-saturated porous medium. A generalized non-Darcy approach has been considered to account for linear and non-linear drag forces. The governing equations are solved by using finite volume method. A quadrilateral cell in a semi-staggered arrangement has been employed and is transformed into a standard square element using local body-fitting co-ordinates by co-ordinate transformation. Details of the flow physics reveal that by the reduction of Darcy number, the primary vortex becomes weaker and tends to move towards the lid. As a measure of volume flow rate maximum stream function value is considered. It is found that, with the reduction in Darcy number and with the increase in Reynolds number and skewness the maximum stream function value reduces. Copyright © 2007 John Wiley & Sons, Ltd. [source] Accurate eight-node hexahedral elementINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 6 2007Magnus Fredriksson Abstract Based on the assumed strain method, an eight-node hexahedral element is proposed. Consistent choice of the fundamental element stiffness guarantees convergence and fulfillment of the patch test a priori. In conjunction with a ,-projection operator, the higher order strain field becomes orthogonal to rigid body and linear displacement fields. The higher order strain field in question is carefully selected to preserve correct rank for the element stiffness matrix, also for distorted elements. Volumetric locking is also removed effectively. By considerations of the bending energy, improved accuracy is obtained even for coarse element meshes. The choice of local co-ordinate system aligned with the principal axes of inertia makes it possible to improve the performance even for distorted elements. The strain-driven format obtained is well suited for materials with non-linear stress,strain relations. Several numerical examples are presented where the excellent performance of the proposed eight-node hexahedral is verified. Copyright © 2007 John Wiley & Sons, Ltd. [source] Enrichment of enhanced assumed strain approximations for representing strong discontinuities: addressing volumetric incompressibility and the discontinuous patch testINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2004J. E. Dolbow Abstract We present a geometrically non-linear assumed strain method that allows for the presence of arbitrary, intra-finite element discontinuities in the deformation map. Special attention is placed on the coarse-mesh accuracy of these methods and their ability to avoid mesh locking in the incompressible limit. Given an underlying mesh and an arbitrary failure surface, we first construct an enriched approximation for the deformation map with the non-linear analogue of the extended finite element method (X-FEM). With regard to the richer space of functions spanned by the gradient of the enriched approximation, we then adopt a broader interpretation of variational consistency for the construction of the enhanced strain. In particular, in those elements intersected by the failure surface, we construct enhanced strain approximations which are orthogonal to piecewise-constant stress fields. Contrast is drawn with existing strong discontinuity approaches where the enhanced strain variations in localized elements were constructed to be orthogonal to constant nominal stress fields. Importantly, the present formulation gives rise to a symmetric tangent stiffness matrix, even in localized elements. The present modification also allows for the satisfaction of a discontinuous patch test, wherein two different constant stress fields (on each side of the failure surface) lie in the solution space. We demonstrate how the proposed modifications eliminate spurious stress oscillations along the failure surface, particularly for nearly incompressible material response. Additional numerical examples are provided to illustrate the efficacy of the modified method for problems in hyperelastic fracture mechanics. Copyright © 2003 John Wiley & Sons, Ltd. [source] Orthogonal grids around convex bodies using foliationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2003B. Herrera Abstract A new technique for the construction of orthogonal grids around convex bodies is presented. The method, which is analytical or numerical depending on how the body boundary is expressed, is based on the development of geometric foliations that follow a prescribed direction (for instance, the prevailing direction of flow) around convex bodies of arbitrary shape. The construction of these foliations is straightforward and does not require the solution of any system of algebraic or differential equations, nor the use of iterative procedures. The method is applicable both to two- and three-dimensional domains since it is based solely on the concept of local curvature. The lines or surfaces given by the foliations of first and second order, together with the complementary orthogonal lines, respectively, define the orthogonal two- or three-dimensional grids. Copyright © 2002 John Wiley & Sons, Ltd. [source] Elastoplastic dynamic analysis with hybrid stress elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2002J. A. Teixeira de Freitas Abstract The stress model of the hybrid finite element formulation is applied to the solution of dynamic elastoplastic structural problems. The stress field is approximated in the domain of the elements and the displacements on its boundary. The displacement, velocity and acceleration approximations in the domain of the element are implicit, in the sense that they result from a combination of the stress estimate with the time integration procedure that ensures that the equilibrium condition is locally satisfied. The finite elements are subdivided in plastic cells where a gradient dependent model is implemented using a hybrid formulation based on the approximation of the plastic parameter and the plastic radiation fields in the domain and on the boundary of the plastic cells, respectively. Generalized variables associated with orthogonal and naturally hierarchical bases are used. The resulting solving systems are symmetric, sparse, p -adaptive and well suited to parallel processing. The performance of the element is assessed using a representative set of testing problems. Copyright © 2001 John Wiley & Sons, Ltd. [source] Effects of Fiber Architecture on Matrix Cracking for Melt-Infiltrated SiC/SiC CompositesINTERNATIONAL JOURNAL OF APPLIED CERAMIC TECHNOLOGY, Issue 3 2010Gregory N. Morscher The matrix cracking behavior of slurry cast melt-infiltrated SiC matrix composites consisting of Sylramic-iBN fibers with a wide variety of fiber architectures were compared. The fiber architectures included 2D woven, braided, 3D orthogonal, and angle interlock architectures. Acoustic emission was used to monitor in-plane matrix cracking during unload,reload tensile tests. Two key parameters were found to control matrix-cracking behavior: the fiber volume fraction in the loading direction and the area of the weakest portion of the structure, that is, the largest tow in the architecture perpendicular to the loading direction. Empirical models that support these results are presented and discussed. [source] The spatial and temporal behaviour of the lower stratospheric temperature over the Southern Hemisphere: the MSU view.INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 4 2001Part I: data, methodology, temporal behaviour Abstract The lower stratosphere monthly temperature anomalies over the Southern Hemisphere derived from soundings made by the Microwave Sounding Unit (MSU) between 1979 and 1997 are analysed. Specifically MSU channel 4 temperature retrievals are considered. Principal component (PC) analysis with the S-mode approach is used in order to isolate grid points that covary in a similar manner and to determine the main features of their temporal behaviour. The first six PCs explain 81.3% of the variance and represent the different time variability patterns observed over the Southern Hemisphere for the ten area clusters determined by the method. The most important feature is common to all the PC score pattern,time series and corresponds to a negative linear trend present in almost all the Southern Hemisphere except over New Zealand and surrounding areas. The negative trend is largest over Antarctica. The remaining features of the temporal variability are different for each PC score and therefore for each cluster region over the Southern Hemisphere. The first PC score pattern shows the impact of the Chichón and Mt Pinatubo eruptions that each produced a 2-year warming over the tropical and sub-tropical lower stratosphere. This variability is orthogonal with the behaviour present over Antarctica. There are different anomalies between 1987 (El Niño) and 1988 (La Niña). This second PC does not show any evidence whatsoever of the volcanic eruptions. The semi-annual wave is present in the anomaly recurrence at mid to high latitudes. Over very low latitudes, close to the Equator, the Quasi-Biennial Oscillation (QBO) band of frequency is also present. Copyright © 2001 Royal Meteorological Society [source] Properties and performance of orthogonal neural network in function approximationINTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 12 2001Chieh F. Sher Backpropagation neural network has been applied successfully to solving uncertain problems in many fields. However, unsolved drawbacks still exist such as the problems of local minimum, slow convergence speed, and the determination of initial weights and the number of processing elements. In this paper, we introduce a single-layer orthogonal neural network (ONN) that is developed based on orthogonal functions. Since the processing elements are orthogonal to one another and there is no local minimum of the error function, the orthogonal neural network is able to avoid the above problems. Among the five existing orthogonal functions, Legendre polynomials and Chebyshev polynomials of the first kind have the properties of recursion and completeness. They are the most suitable to generate the neural network. Some typical examples are given to show their performance in function approximation. The results show that ONN has excellent convergence performance. Moreover, ONN is capable of approximating the mathematic model of backpropagation neural network. Therefore, it should be able to be applied to various applications that backpropagation neural network is suitable to solve. © 2001 John Wiley & Sons, Inc. [source] Multiscalet basis in Galerkin's method for solving three-dimensional electromagnetic integral equationsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 4 2008M. S. Tong Abstract Multiscalets in the multiwavelet family are used as the basis and testing functions in Galerkin's method. Since the multiscalets are orthogonal to their translations under the Sobolev inner product, the resulting Galerkin's method behaves like a collocation method but possesses the ability of derivative tracking for unknown functions in solving integral equations. The former makes the method simple in implementation and the latter allows to use coarse meshes in discretization. These robust features have been demonstrated in solving two-dimensional (2D) electromagnetic (EM) problems, but have not been exploited in three-dimensional (3D) scenarios. For 3D problems, the unknown functions in the integral equations are dependent on two coordinate variables. In order to preserve the use of coarse meshes for 3D cases, we realize the omnidirectional derivative tracking by tracking the directional derivatives along two orthogonal directions, or equivalently tracking the gradient. This process yields a nonsquare matrix equation and we use the least-squares method (LSM) to solve it. Numerical examples show that the multiscalet-based Galerkin's method is also robust in solving for 3D EM integral equations with a minor cost increase from LSM. Copyright © 2007 John Wiley & Sons, Ltd. [source] A direct conversion receiver for satellite communication systemsINTERNATIONAL JOURNAL OF SATELLITE COMMUNICATIONS AND NETWORKING, Issue 2 2005Xinping Huang Abstract A direct receiver is an alternative to the well-established super-heterodyne receiver. It is especially attractive to highly integrated low-cost terminals since it eliminates the need for components at intermediate frequencies. There is increasingly more interest in using it in various ground/space-based systems. This article presents a new direct quadrature receiver that uses three channels with different phase shifts and a novel technique to derive the in-phase and quadrature baseband signals independent of the actual gains and phases in the receiver chains. The new technique relies on the property that the in-phase and quadrature signals are orthogonal, and its implementation involves the signal subspace decomposition and projection. Computer simulations and a 90 Mbps Ka-band prototype receiver have demonstrated that the performance of the receiver closely matches the theory. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||||||||