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Different Spatial Locations (different + spatial_locations)
Selected AbstractsAnalytical power series solutions to the two-dimensional advection,dispersion equation with distance-dependent dispersivitiesHYDROLOGICAL PROCESSES, Issue 24 2008Jui-Sheng Chen Abstract As is frequently cited, dispersivity increases with solute travel distance in the subsurface. This behaviour has been attributed to the inherent spatial variation of the pore water velocity in geological porous media. Analytically solving the advection,dispersion equation with distance-dependent dispersivity is extremely difficult because the governing equation coefficients are dependent upon the distance variable. This study presents an analytical technique to solve a two-dimensional (2D) advection,dispersion equation with linear distance-dependent longitudinal and transverse dispersivities for describing solute transport in a uniform flow field. The analytical approach is developed by applying the extended power series method coupled with the Laplace and finite Fourier cosine transforms. The developed solution is then compared to the corresponding numerical solution to assess its accuracy and robustness. The results demonstrate that the breakthrough curves at different spatial locations obtained from the power series solution show good agreement with those obtained from the numerical solution. However, owing to the limited numerical operation for large values of the power series functions, the developed analytical solution can only be numerically evaluated when the values of longitudinal dispersivity/distance ratio eL exceed 0·075. Moreover, breakthrough curves obtained from the distance-dependent solution are compared with those from the constant dispersivity solution to investigate the relationship between the transport parameters. Our numerical experiments demonstrate that a previously derived relationship is invalid for large eL values. The analytical power series solution derived in this study is efficient and can be a useful tool for future studies in the field of 2D and distance-dependent dispersive transport. Copyright © 2008 John Wiley & Sons, Ltd. [source] Repetition effect in visual recognition of letters1JAPANESE PSYCHOLOGICAL RESEARCH, Issue 2 2004TOSHINORI KUWANA Abstract:, This study examined the influence of the repetitive presentation of a letter on the recognition of two letters. In two experiments4, two letters, which were either identical or not, were presented successively for a short duration at different spatial locations, and the subjects were required to identify them. In Experiment 1, the presentation time of the first letter was varied, whereas that of the second letter was constant. The results revealed that a reduced performance in identifying a second letter was observed in the case that the first letter, which was identical to the second letter, could be identified correctly. Experiment 2 examined whether or not this reduction was due to the identity of the visual shape of two letters. The first letter was presented either in the usual vertical orientation or rotated orientation by 180 degrees and the second letter was constantly presented in the usual orientation. The results revealed that a reduced performance in identifying a repeated letter was observed, regardless of the orientation of the first letter. The findings from the two experiments suggested that the identity of the information in memory was a main cause of the interference effect by repetition. [source] The Ambiguous Veil: On Transparency, the Mashrabiy'ya, and ArchitectureJOURNAL OF ARCHITECTURAL EDUCATION, Issue 4 2003BECHIR KENZARI Transparency without a glazed medium can be found in the Middle Eastern device of the mashrabiy'ya. Promoted by Orientalism as a typical Eastern motif, it has slowly become a mark of subjugation and confinement. The logic of the mashrabiy'ya permits other interpretations, however. By trying to etymologically and historically link it to weaving and holiness, to the veil and its uplifting, to the gaze and its subtleties, an attempt is made here to liberate this device from excessive interpretations and to present it as an architectural motif that involves a motivated perception of different spatial locations, a viewpoint, a stand, and an intention. Thus, the mashrabiy'ya becomes closely linked to phenomenological transparency. [source] Prediction of Polymer Properties in LDPE ReactorsMACROMOLECULAR MATERIALS & ENGINEERING, Issue 4 2005Gary J. Wells Abstract Summary: A new analysis tool is presented that uses the governing kinetic scheme to predict properties of low-density polyethylene (LDPE) such as the detailed shape of the molecular weight distribution (MWD). A model that captures mixing details of autoclave reactor operation is used to provide a new criterion for the onset of MWD shouldering. Kinetic effects are shown to govern the existence of MWD shoulders in LDPE reactors, even when operation is far from perfectly-mixed. MWD shoulders occur when the mean reaction environment has a relatively high radical concentration and has a high polymer content, and is at a low temperature. Such conditions maximize long chain formation by polymer transfer and combination-termination, while limiting chain scission. For imperfectly-mixed reactors, the blending of polymer-distributions produced in different spatial locations has a small effect on the composite MWD. However, for adiabatic LDPE autoclaves, imperfect mixing broadens the stable range of mean reactor conditions, and thereby increases the possibility for MWD shouldering. Polymer MWD produced in an LDPE autoclave reactor by various kinetic mechanisms. [source] On the timing characteristics of the apparent diffusion coefficient contrast in fMRIMAGNETIC RESONANCE IN MEDICINE, Issue 2 2002Stacey L. Gangstead Abstract For the past 10 years, functional MRI (fMRI) has seen rapid progress in both clinical and basic science research. Most of the imaging techniques are based on the blood oxygenation level-dependent (BOLD) contrast which arises from the field perturbation of the paramagnetic deoxyhemoglobin due to the mismatch between the local oxygen demand and delivery. Because the changes of oxygenation level take place mostly in the veins, the dominant signal sources of the BOLD signal are intra- and extravascular proton pools of the veins. Perfusion imaging methods, developed parallel to the BOLD technique, seek to quantify the blood flow and perfusion. Recently, perfusion imaging using arterial spin tagging methods have been used to study brain function by investigating the changes of the blood flow and perfusion during brain activation, thereby generating an alternative contrast mechanism to the functional brain imaging. Since most of these methods require tagging pulse and wait time for blood to be delivered to the imaged slice, the temporal resolution may not be optimal. Dynamic intravoxel incoherent motion (IVIM) weighting schemes using apparent diffusion coefficient (ADC) contrast were suggested to image the relative changes of the in-plane blood flow during brain function. In this report, it was demonstrated that, in addition to the spatial discrepancies of the activated areas, the time course based on the ADC contrast consistently precedes that from the BOLD contrast with timing offset on the order of 1 sec. Since arterial networks would have different spatial locations and preceding temporal characters, the findings in this report are indicative that the ADC contrast is sensitive to the arterial blood flow changes. Magn Reson Med 48:385,388, 2002. © 2002 Wiley-Liss, Inc. [source] Use of resistance surfaces for landscape genetic studies: considerations for parameterization and analysisMOLECULAR ECOLOGY, Issue 17 2010STEPHEN F. SPEAR Abstract Measures of genetic structure among individuals or populations collected at different spatial locations across a landscape are commonly used as surrogate measures of functional (i.e. demographic or genetic) connectivity. In order to understand how landscape characteristics influence functional connectivity, resistance surfaces are typically created in a raster GIS environment. These resistance surfaces represent hypothesized relationships between landscape features and gene flow, and are based on underlying biological functions such as relative abundance or movement probabilities in different land cover types. The biggest challenge for calculating resistance surfaces is assignment of resistance values to different landscape features. Here, we first identify study objectives that are consistent with the use of resistance surfaces and critically review the various approaches that have been used to parameterize resistance surfaces and select optimal models in landscape genetics. We then discuss the biological assumptions and considerations that influence analyses using resistance surfaces, such as the relationship between gene flow and dispersal, how habitat suitability may influence animal movement, and how resistance surfaces can be translated into estimates of functional landscape connectivity. Finally, we outline novel approaches for creating optimal resistance surfaces using either simulation or computational methods, as well as alternatives to resistance surfaces (e.g. network and buffered paths). These approaches have the potential to improve landscape genetic analyses, but they also create new challenges. We conclude that no single way of using resistance surfaces is appropriate for every situation. We suggest that researchers carefully consider objectives, important biological assumptions and available parameterization and validation techniques when planning landscape genetic studies. [source] Feshbach shape resonance for high Tc superconductivity in superlattices of nanotubesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 11 2006Antonio Bianconi Abstract The case of a Feshbach shape resonance in the pairing mechanism for high Tc superconductivity in a crystalline lattice of doped metallic nanotubes is described. The superlattice of doped metallic nanotubes provides a superconductor with a strongly asymmetric gap. The disparity and different spatial locations of the wave functions of electrons in different subbands at the Fermi level should suppress the single electron impurity interband scattering giving multiband superconductivity in the clean limit. The Feshbach resonances will arise from the component single-particle wave functions out of which the electron pair wave function is constructed: pairs of wave functions which are time inverse of each other. The Feshbach shape resonance increases the critical temperature by tuning the chemical potential at the Lifshitz electronic topological transition (ETT) where the Fermi surface of one of the bands changes from the one dimensional (1D) to the two dimensional (2D) topology (1D/2D ETT). (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] | ||||||||||