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Inhomogeneity
Kinds of Inhomogeneity Terms modified by Inhomogeneity Selected AbstractsInhomogeneity of composition in near-stoichiometric LiNbO3 single crystal grown from Li rich meltCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4 2006L. Gao Abstract A near-stoichiometric LiNbO3 single crystal has been grown by the Czochralski technique from a melt of 58.5 mol% Li2O. Its composition homogeneity was assessed by measuring the UV absorption edge. It was found that the maximum composition difference is about 0.03 mol% in the radial direction and 0.05 mol% in the axial direction. Differential scanning calorimetry (DSC) analysis was performed on the powder from the synthesized raw material and the frozen melt after crystal growth. The analytical results indicate that, during crystal growth, the magnitude of lithium volatilization from the melt surface is more than the degree of segregation from the crystal. The volatilized lithium diffuses into the crystal to compensate for the lithium segregation in the LiNbO3 crystal. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Lateral Inhomogeneity in the Electronic Structure of a Conjugated Poly(3-hexylthiophene) Thin FilmADVANCED FUNCTIONAL MATERIALS, Issue 13 2010Kaname Kanai Abstract How annealing influences the morphology of a highly regioregular poly(3-hexylthiophene) (RR-P3HT) film at the substrate interface as well as the lateral inhomogeneity in the electronic structure of the film are elucidated. Whereas previous studies have reported that high-molecular-weight (MW) RR-P3HT films tend to show low crystallinity even after annealing, it is found that high-MW RR-P3HT does show high crystallinity after annealing at high temperature for a long time. Photoemission electron microscopy (PEEM), X-ray photoemission spectroscopy, and ultraviolet photoemission spectroscopy results clearly resolve a considerable lateral inhomogeneity in the morphology of RR-P3HT film, which results in a variation of the electronic structure depending on the local crystallinity. The PEEM results show how annealing facilitates crystal growth in a high-MW RR-P3HT film. [source] Lung Function Tests in Neonates and Infants with Chronic Lung Disease: Global and Regional Ventilation InhomogeneityPEDIATRIC PULMONOLOGY, Issue 2 2006J. Jane Pillow FRACP Abstract This review considers measurement of global and regional ventilation inhomogeneity (VI) in infants and young children with acute neonatal respiratory disorders and chronic lung disease of infancy (CLDI). We focus primarily on multiple-breath inert gas washout (MBW) and electrical impedance tomography (EIT). The literature is critically reviewed and the relevant methods, equipment, and studies are summarized, including the limitations and strengths of individual techniques, together with the availability and appropriateness of any reference data. There has been a recent resurgence of interest in using MBW to monitor lung function within individuals and between different groups. In the mechanically ventilated, sedated, and paralyzed patient, VI indices can identify serial changes occurring following exogenous surfactant. Similarly, global VI indices appear to be increased in infants with CLDI and to differentiate between infants without lung disease and those with mild, moderate, and severe lung disease following preterm birth. While EIT is a relatively new technique, recent studies suggest that it is feasible in newborn infants, and can quantitatively identify changes in regional lung ventilation following alterations to ventilator settings, positive end expiratory pressure (PEEP), and administration of treatments such as surfactant. As such, EIT represents one of the more exciting prospects for continuous bedside pulmonary monitoring. For both techniques, there is an urgent need to establish guidelines regarding data collection, analysis, and interpretation in infants both with and without CLDI. © 2005 Wiley-Liss, Inc. [source] Investigation of the InGaN Quantum Wells Compositional InhomogeneityPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2003A. Vivet Abstract The finite element modeling is used to improve the accuracy of In composition determination by taking into account the two limiting factors in high resolution microscopy: strain relaxation and projection. [source] Temperature Inhomogeneity during Multibubble Sonoluminescence,ANGEWANDTE CHEMIE, Issue 6 2010Hangxun Xu Leuchtende Blasen! Extrem helle Sonolumineszenz tritt in konzentrierter Phosphorsäure auf (siehe Bild). In der Multiblasen-Sonolumineszenz können zwei unabhängige emittierende Molekülarten beobachtet werden (angeregtes OH. und PO.), und beide dienen als spektroskopische Thermometer, um die Extrembedingungen während des Blasenkollapses zu untersuchen. [source] Nondipolar Content of T Wave Derived from a Myocardial Source Simulation with Increased Repolarization InhomogeneityANNALS OF NONINVASIVE ELECTROCARDIOLOGY, Issue 2 2009Milos Kesek M.D., Ph.D. Background: Several conditions with repolarization disturbances are associated with increased level of nondipolar components of the T wave. The nondipolar content has been proposed as a measure of repolarization inhomogeneity. This computer simulation study examines the link between increased nondipolar components and increased repolarization inhomogeneity in an established model. Methods: The simulation was performed with Ecgsim software that uses the equivalent double-layer source model. In the model, the shape of transmembrane potential is derived from biological recordings. Increased repolarization inhomogeneity was simulated globally by increasing the variance in action potential duration and locally by introducing changes mimicking acute myocardial infarction. We synthesized surface ECG recordings with 12, 18, and 300 leads. The T-wave residue was calculated by singular value decomposition. The study examined the effects of the number of ECG leads, changes in definition of end of T wave and random noise added to the signal. Results: Normal myocardial source gave a low level of nondipolar content. Increased nondipolar content was observed in the two types of increased repolarization inhomogeneity. Noise gave a large increase in the nondipolar content. The sensitivity of the result to noise increased when a higher number of principal components were used in the computation. Conclusions: The nondipolar content of the T wave was associated with repolarization inhomogeneity in the computer model. The measure was very sensitive to noise, especially when principal components of high order were included in the computations. Increased number of ECG leads resulted in an increased signal-to-noise ratio. [source] A new type of susceptibility-artefact-based magnetic resonance angiography: intra-arterial injection of superparamagnetic iron oxide particles (SPIO) A Resovist® in combination with TrueFisp imaging: a feasibility studyCONTRAST MEDIA & MOLECULAR IMAGING, Issue 5 2006Robbert M. Maes Abstract The goal of this study was to evaluate the use of super paramagnetic particles of iron oxide (SPIO) as a dark blood contrast agent, in combination with a bright blood steady-state free precession sequence for magnetic resonance angiography (MRA), in an animal model. The original concentration of the SPIO of 500,mmol Fe/l and dilutions to 250, 125, 60, 30, 10 and 5,mmol Fe/l were intra-arterially injected into the aorta of a pig. Then the dilution of 10,mmol Fe/l was chosen for repeated intra-arterial injections into two pigs. During these intra-arterial SPIO injections MR images were acquired with a 1.5,T scanner. Signal intensity measurements were performed in the aorta. The signal-to-noise ratio during SPIO bolus passage was significantly less than during baseline conditions (Fisher's F -ratio 159.8, p,<,0.005) or the recovery signal-to-noise ratio (Fisher's F -ratio 144.6, p,<,0.005). Also, confirmation of flow distal to the catheter-tip position was possible. The use of SPIO as a dark blood agent in combination with a bright blood MR imaging sequence is feasible. Temporary loss of intraluminal signal occurs due to local decrease of the signal because of induction of local inhomogeneities after mixture the present blood and SPIO solution. It provides immediate information about blood flow distal to the catheter and is a potentially useful to guide intravascular MR-interventional procedures. Copyright © 2006 John Wiley & Sons Ltd. [source] Dielectric properties of thallium gallium diselenide layered crystal in the incommensurate phaseCRYSTAL RESEARCH AND TECHNOLOGY, Issue 9 2005entürk Abstract The dielectric measurements of the layered crystal were studied in temperature range of successive phase transitions. The measurements revealed that the phase transition occurred in 242 K is an incommensurate phase transition. When the sample is annealed at a stabilized temperature in the incommensurate phase, a remarkable memory effect has been observed on cooling run. The mechanism of the memory effect in the incommensurate phase of the semiconducting ferroelectric TlGaSe2 can be interpreted in the frame of the theory of defect density waves. This theory claims that the memory effect is the result of pinning of the incommensurate structure by the lattice inhomogeneities. With decreasing the annealing temperature the phase transition temperature shifts to lower temperatures gradually. Moreover, the peak intensities also increase gradually. In addition to these effects, the phase transition temperature shifts to lower temperatures with increasing annealing time. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Chamber-specific effects of hypokalaemia on ventricular arrhythmogenicity in isolated, perfused guinea-pig heartEXPERIMENTAL PHYSIOLOGY, Issue 4 2009Oleg E. Osadchii Diuretic-induced hypokalaemia has been shown to promote cardiac arrhythmias in hypertensive patients. The present study was designed to determine whether hypokalaemia increases arrhythmic susceptibility of the left ventricle (LV) or the right ventricle (RV), or both. Proarrhythmic effects of hypokalaemic perfusion (2.5 mm K+ for 30 min) were assessed in isolated guinea-pig heart preparations using simultaneous recordings of volume-conducted electrocardiogram and monophasic action potentials from six ventricular epicardial sites. Effective refractory periods, ventricular fibrillation thresholds and inducibility of tachyarrhythmias by programmed electrical stimulation and tachypacing were determined at the LV and the RV epicardial stimulation sites. Hypokalaemia promoted spontaneous ventricular ectopic activity, an effect attributed to non-uniform prolongation of ventricular repolarization resulting in increased RV-to-LV transepicardial dispersion of refractoriness and action potential duration. Furthermore, hypokalaemic perfusion was associated with reduced ventricular fibrillation threshold and increased inducibility of tachyarrhythmias by programmed electrical stimulation and tachypacing as determined at the LV stimulation site. In contrast, the RV stimulation revealed no change in arrhythmic susceptibility of the RV chamber. Consistently, hypokalaemia reduced the LV effective refractory period but had no effect on the RV refractoriness. This change enabled generation of premature propagating responses by extrastimulus application at earlier time points during LV repolarization. Increased prematurity of extrastimulus-evoked propagating responses was associated with exaggerated local inhomogeneities in intraventricular conduction and action potential duration in hypokalaemic LV, thus creating a favourable stage for re-entrant tachyarrhythmias. Taken together, these findings suggest that proarrhythmic effects of hypokalaemia are mostly attributed to increased LV arrhythmogenicity in the guinea-pig heart. [source] A one-way wave equation for modelling seismic waveform variations due to elastic heterogeneityGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2005D. A. Angus SUMMARY The application of a new one-way narrow-angle elastic wave equation to isotropic heterogeneous media is described. This narrow-angle finite-difference propagator should provide an efficient and accurate method of simulating primary body wave(s) passing through smoothly varying heterogeneous media. Although computationally slower than ray theory, the narrow-angle propagator can model frequency-dependent forward diffraction and scattering as well as the averaging effects due to smooth variations in medium parameters that vary on the sub-Fresnel zone level. Example waveforms are presented for the propagation of body waves in deterministic as well as stochastic heterogeneous 3-D Earth models. Extrapolation within deterministic media will highlight various familiar wave-diffraction and pulse-distortion effects associated with large-scale inhomogeneities, such as geometrical spreading, wavefront folding and creeping-wave diffraction by a compact object. Simulation within stochastic media will examine the effects of varying the correlation lengths of random heterogeneities on wave propagation. In particular, wave phenomena such as frequency-dependent forward scattering, the appearance of random caustics and the generation of seismic coda will be shown. [source] Amplitude fluctuations due to diffraction and refraction in anisotropic random media: implications for seismic scattering attenuation estimatesGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2003T. M. Müller SUMMARY We calculate the variance of the log-amplitude within the Rytov approximation for plane waves propagating in weakly inhomogeneous and statistically anisotropic random media. Since there is a simple relation between the log-amplitude variance and the attenuation coefficient of seismic primaries in the weak wavefield fluctuation regime, we also obtain scattering attenuation estimates that additionally depend on the aspect ratio of longitudinal and transverse correlation scales of the inhomogeneities. These estimates can be useful for the statistical characterization of anisotropic, large-scale inhomogeneities (large compared with the wavelength of the probing pulse) in the Earth crust and mantle, such as fault zones. With the help of plane-wave-transmission numerical experiments using the finite-difference method we compute the log-amplitude variance as a function of the propagation distance and observe reasonable agreement with the analytical results. We discuss the implications of our results in the context of seismic scattering attenuation estimations. [source] On strike-slip faulting in layered mediaGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2002Maurizio Bonafede Summary We study the effects of structural inhomogeneities on the stress and displacement fields induced by strike-slip faults in layered media. An elastic medium is considered, made up of an upper layer bounded by a free surface and welded to a lower half-space characterized by different elastic parameters. Shear cracks with assigned stress drop are employed as mathematical models of strike-slip faults, which are assumed to be vertical and planar. If the crack is entirely embedded within the lower medium (case A), a Cauchy-kernel integral equation is obtained, which is solved by employing an expansion of the dislocation density in Chebyshev polynomials. If the crack is within the lower medium but it terminates at the interface (case B), a generalized Cauchy singularity appears in the integral kernel. This singularity affects the singular behaviour of the dislocation density at the crack tip touching the interface. Finally, the case of a crack crossing the interface is considered (case C). The crack is split into two interacting sections, each placed in a homogeneous medium and both open at the interface. Two coupled generalized Cauchy equations are obtained and solved for the dislocation density distribution of each crack section. An asymptotic study near the intersection between the crack and the interface shows that the dislocation densities for each crack section are bounded at the interface, where a jump discontinuity is present. As a corollary, the stress drop must be discontinuous at the interface, with a jump proportional to the rigidity contrast between the adjoining media. This finding is shown to have important implications for the development of geometrical complexities within transform fault zones: planar strike-slip faults cutting across layer discontinuities with arbitrary stress drop values are shown to be admissible only if the interface between different layers becomes unwelded during the earthquake at the crack/interface junction. Planar strike-slip faulting may take place only in mature transform zones, where a repetitive earthquake cycle has already developed, if the rheology is perfectly elastic. Otherwise, the fault cannot be planar: we infer that strike-slip faulting at depth is plausibly accompanied by en-echelon surface breaks in a shallow sedimentary layer (where the stress drop is lower than prescribed by the discontinuity condition), while ductile deformation (or steady sliding) at depth may be accommodated by multiple fault branching or by antithetic faulting in the upper brittle layer (endowed with lower rigidity but higher stress). [source] Scattering behaviour at Merapi volcano (Java) revealed from an active seismic experimentGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2001Ulrich Wegler SUMMARY The seismic structure of the stratovolcano Merapi (Java, Indonesia) was studied using an active seismic experiment. Three 3 km long seismic profiles each consisting of up to 30 three-component seismometers with an interstation distance of 100 m were built up in an altitude range between 1000 and 2000 m above sea level. The detailed study of the seismic properties of the propagation media in active volcanic regions is important to understand the natural seismic signals used for eruption forecasting. The seismic experiment at Merapi therefore concentrates on the heterogeneous structure within a radius of 5 km from the active dome, where the sources of most of the natural volcanic seismic events are located. The cone of Merapi volcano consists of different materials changing on a small scale due to the layering of eruptive material. Additionally, the topography of the erosion valleys leads to an irregular deposition, which cannot be described by a simple 1-D layering. These inhomogeneities have a strong influence on seismic signals. The direct P and S waves are attenuated quickly and show only small amplitudes on seismograms. The energy lost from the direct waves, however, is not changed into heat but scattered and can be observed as seismic coda following the direct waves. The observed seismograms show a spindle-like amplitude increase after the direct P phase. This shape of the envelope can be explained by the diffusion model. According to this model there are so many strong inhomogeneities that the direct wave can be neglected and all energy is concentrated in multiple scattered waves. Besides the envelope, the coherence and polarization properties of the wavefield also indicate strong scattering. Only the first onset shows coherence over a station spacing of 100 m, whereas the late phases carrying the major part of the energy are mainly incoherent. The horizontal components of the seismograms have larger amplitudes than the vertical component, but within the horizontal plane the polarization is almost arbitrary, corresponding to waves arriving from scatterers located arbitrarily in space. As a result of the inversion using the diffusion model we obtain values of the S -wave scattering attenuation coefficient, ,s, and the S -wave intrinsic absorption coefficient, ,i. In the frequency range of 4,20 Hz used in this study the scattering attenuation is at least one order of magnitude larger than the intrinsic absorption (,s,,i). The mean free path of S waves is as low as 100 m (,s,1,100 m). The scattering coefficient is independent of frequency (,s,f0.0), whereas the coefficient of intrinsic attenuation increases with increasing frequency (,i,f1.6). The natural seismic signals at Merapi volcano show similar characteristics to the artificial shots. The first onsets have only small amplitudes and the energy maximum arrives delayed compared to the direct waves. Therefore, these signals appear to be strongly affected by multiple scattering also. [source] Improved understanding of velocity,saturation relationships using 4D computer-tomography acoustic measurementsGEOPHYSICAL PROSPECTING, Issue 2 2005K. Monsen ABSTRACT A recently developed laboratory method allows for simultaneous imaging of fluid distribution and measurements of acoustic-wave velocities during flooding experiments. Using a specially developed acoustic sample holder that combines high pressure capacity with good transparency for X-rays, it becomes possible to investigate relationships between velocity and fluid saturation at reservoir stress levels. High-resolution 3D images can be constructed from thin slices of cross-sectional computer-tomography scans (CT scans) covering the entire rock-core volume, and from imaging the distribution of fluid at different saturation levels. The X-ray imaging clearly adds a new dimension to rock-physics measurements; it can be used in the explanation of variations in measured velocities from core-scale heterogeneities. Computer tomography gives a detailed visualization of density regimes in reservoir rocks within a core. This allows an examination of the interior of core samples, revealing inhomogeneities, porosity and fluid distribution. This mapping will not only lead to an explanation of acoustic-velocity measurements; it may also contribute to an increased understanding of the fluid-flow process and gas/liquid mixing mechanisms in rock. Immiscible and miscible flow in core plugs can be mapped simultaneously with acoustic measurements. The effects of core heterogeneity and experimentally introduced effects can be separated, to clarify the validity of measured velocity relationships. [source] Rafts in oligodendrocytes: Evidence and structure,function relationshipGLIA, Issue 6 2006Ellen Gielen Abstract The plasma membrane of eukaryotic cells exhibits lateral inhomogeneities, mainly containing cholesterol and sphingomyelin, which provide liquid-ordered microdomains (lipid "rafts") that segregate membrane components. Rafts are thought to modulate the biological functions of molecules that become associated with them, and as such, they appear to be involved in a variety of processes, including signal transduction, membrane sorting, cell adhesion and pathogen entry. Although still a matter of ongoing debate, evidence in favor of the presence of these microdomains is gradually accumulating but a consensus on issues like their size, lifetime, composition, and biological significance has yet to be reached. Here, we provide an overview of the evidence supporting the presence of rafts in oligodendrocytes, the myelin-producing cells of the central nervous system, and discuss their functional significance. The myelin membrane differs fundamentally from the plasma membrane, both in lipid and protein composition. Moreover, since myelin membranes are unusually enriched in glycosphingolipids, questions concerning the biogenesis and functional relevance of microdomains thus appear of special interest in oligodendrocytes. The current picture of rafts in oligodendrocytes is mainly based on detergent methods. The robustness of such data is discussed and alternative methods that may provide complementary data are indicated. © 2006 Wiley-Liss, Inc. [source] Influence of Small-Scale Heterogeneities on Contaminant Transport in Fractured Crystalline RockGROUND WATER, Issue 5 2006Ralph Mettier We present a sequence of purely advective transport models that demonstrate the influence of small-scale geometric inhomogeneities on contaminant transport in fractured crystalline rock. Special weight is placed on the role of statistically generated variable fracture apertures. The fracture network geometry and the aperture distribution are based on information from an in situ radionuclide retardation experiment performed at Grimsel test site (Swiss Alps). The obtained breakthrough curves are fitted with the advection dispersion equation and continuous-time random walks (CTRW). CTRW is found to provide superior fits to the late-arrival tailing and is also found to show a good correlation with the velocity distributions obtained from the hydraulic models. The impact of small-scale heterogeneities, both in fracture geometry and aperture, on transport is shown to be considerable. [source] Quantitative evaluation of automated skull-stripping methods applied to contemporary and legacy images: Effects of diagnosis, bias correction, and slice locationHUMAN BRAIN MAPPING, Issue 2 2006Christine Fennema-Notestine Abstract Performance of automated methods to isolate brain from nonbrain tissues in magnetic resonance (MR) structural images may be influenced by MR signal inhomogeneities, type of MR image set, regional anatomy, and age and diagnosis of subjects studied. The present study compared the performance of four methods: Brain Extraction Tool (BET; Smith [2002]: Hum Brain Mapp 17:143,155); 3dIntracranial (Ward [1999] Milwaukee: Biophysics Research Institute, Medical College of Wisconsin; in AFNI); a Hybrid Watershed algorithm (HWA, Segonne et al. [2004] Neuroimage 22:1060,1075; in FreeSurfer); and Brain Surface Extractor (BSE, Sandor and Leahy [1997] IEEE Trans Med Imag 16:41,54; Shattuck et al. [2001] Neuroimage 13:856,876) to manually stripped images. The methods were applied to uncorrected and bias-corrected datasets; Legacy and Contemporary T1 -weighted image sets; and four diagnostic groups (depressed, Alzheimer's, young and elderly control). To provide a criterion for outcome assessment, two experts manually stripped six sagittal sections for each dataset in locations where brain and nonbrain tissue are difficult to distinguish. Methods were compared on Jaccard similarity coefficients, Hausdorff distances, and an Expectation-Maximization algorithm. Methods tended to perform better on contemporary datasets; bias correction did not significantly improve method performance. Mesial sections were most difficult for all methods. Although AD image sets were most difficult to strip, HWA and BSE were more robust across diagnostic groups compared with 3dIntracranial and BET. With respect to specificity, BSE tended to perform best across all groups, whereas HWA was more sensitive than other methods. The results of this study may direct users towards a method appropriate to their T1 -weighted datasets and improve the efficiency of processing for large, multisite neuroimaging studies. Hum. Brain Mapping, 2005. © 2005 Wiley-Liss, Inc. [source] EEG-fMRI of focal epileptic spikes: Analysis with multiple haemodynamic functions and comparison with gadolinium-enhanced MR angiogramsHUMAN BRAIN MAPPING, Issue 3 2004Andrew P. Bagshaw Abstract Combined EEG-fMRI has recently been used to explore the BOLD responses to interictal epileptiform discharges. This study examines whether misspecification of the form of the haemodynamic response function (HRF) results in significant fMRI responses being missed in the statistical analysis. EEG-fMRI data from 31 patients with focal epilepsy were analysed with four HRFs peaking from 3 to 9 sec after each interictal event, in addition to a standard HRF that peaked after 5.4 sec. In four patients, fMRI responses were correlated with gadolinium-enhanced MR angiograms and with EEG data from intracranial electrodes. In an attempt to understand the absence of BOLD responses in a significant group of patients, the degree of signal loss occurring as a result of magnetic field inhomogeneities was compared with the detected fMRI responses in ten patients with temporal lobe spikes. Using multiple HRFs resulted in an increased percentage of data sets with significant fMRI activations, from 45% when using the standard HRF alone, to 62.5%. The standard HRF was good at detecting positive BOLD responses, but less appropriate for negative BOLD responses, the majority of which were more accurately modelled by an HRF that peaked later than the standard. Co-registration of statistical maps with gadolinium-enhanced MRIs suggested that the detected fMRI responses were not in general related to large veins. Signal loss in the temporal lobes seemed to be an important factor in 7 of 12 patients who did not show fMRI activations with any of the HRFs. Hum. Brain Mapp. 22:179,192, 2004. © 2004 Wiley-Liss, Inc. [source] Homogeneity analysis of Turkish meteorological data setHYDROLOGICAL PROCESSES, Issue 8 2010Sinan Sahin Abstract The missing value interpolation and homogeneity analysis were performed on the meteorological data of Turkey. The data set has the observations of six variables: the maximum air temperature, the minimum air temperature, the mean air temperature, the total precipitation, the relative humidity and the local pressure of 232 stations for the period 1974,2002. The missing values on the monthly data set were estimated using two methods: the linear regression (LR) and the expectation maximization (EM) algorithm. Because of higher correlations between test and reference series, EM algorithm results were preferred. The homogeneity analysis was performed on the annual data using a relative test and four absolute homogeneity tests were used for the stations where non-testable series were found due to the low correlation coefficients between the test and the reference series. A comparison was accomplished by the graphics where relative and absolute tests provided different outcomes. Absolute tests failed to detect the inhomogeneities in the precipitation series at the significance level 1%. Interestingly, most of the inhomogeneities detected on the temperature variables existed in the Aegean region of Turkey. It is considered that theseinhomogeneities were mostly caused by non-natural effects such as relocation. Because of changes at topography at short distance in this region intensify non-random characteristics of the temperature series when relocation occurs even in small distances. The marine effect, which causes artifical cooling effect due to sea breezes has important impact on temperature series and the orograhpy allows this impact go through the inner parts in this region. Copyright © 2010 John Wiley & Sons, Ltd. [source] Transient heat conduction in a medium with multiple circular cavities and inhomogeneitiesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2009Elizaveta Gordeliy Abstract A two-dimensional transient heat conduction problem of multiple interacting circular inhomogeneities, cavities and point sources is considered. In general, a non-perfect contact at the matrix/inhomogeneity interfaces is assumed, with the heat flux through the interface proportional to the temperature jump. The approach is based on the use of the general solutions to the problems of a single cavity and an inhomogeneity and superposition. Application of the Laplace transform and the so-called addition theorem results in an analytical transformed solution. The solution in the time domain is obtained by performing a numerical inversion of the Laplace transform. Several numerical examples are given to demonstrate the accuracy and the efficiency of the method. The approximation error decreases exponentially with the number of the degrees of freedom in the problem. A comparison of the companion two- and three-dimensional problems demonstrates the effect of the dimensionality. Copyright © 2009 John Wiley & Sons, Ltd. [source] A framework for fracture modelling based on the material forces concept with XFEM kinematicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 13 2005Ragnar Larsson Abstract A theoretical and computational framework which covers both linear and non-linear fracture behaviour is presented. As a basis for the formulation, we use the material forces concept due to the close relation between on one hand the Eshelby energy,momentum tensor and on the other hand material defects like cracks and material inhomogeneities. By separating the discontinuous displacement from the continuous counterpart in line with the eXtended finite element method (XFEM), we are able to formulate the weak equilibrium in two coupled problems representing the total deformation. However, in contrast to standard XFEM, where the direct motion discontinuity is used to model the crack, we rather formulate an inverse motion discontinuity to model crack development. The resulting formulation thus couples the continuous direct motion to the inverse discontinuous motion, which may be used to simulate linear as well as non-linear fracture in one and the same formulation. In fact, the linear fracture formulation can be retrieved from the non-linear cohesive zone formulation simply by confining the cohesive zone to the crack tip. These features are clarified in the two numerical examples which conclude the paper. Copyright © 2005 John Wiley & Sons, Ltd. [source] Finite element and sensitivity analysis of thermally induced flow instabilitiesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2010Jean-Serge Giguère Abstract This paper presents a finite element algorithm for the simulation of thermo-hydrodynamic instabilities causing manufacturing defects in injection molding of plastic and metal powder. Mold-filling parameters determine the flow pattern during filling, which in turn influences the quality of the final part. Insufficiently, well-controlled operating conditions may generate inhomogeneities, empty spaces or unusable parts. An understanding of the flow behavior will enable manufacturers to reduce or even eliminate defects and improve their competitiveness. This work presents a rigorous study using numerical simulation and sensitivity analysis. The problem is modeled by the Navier,Stokes equations, the energy equation and a generalized Newtonian viscosity model. The solution algorithm is applied to a simple flow in a symmetrical gate geometry. This problem exhibits both symmetrical and non-symmetrical solutions depending on the values taken by flow parameters. Under particular combinations of operating conditions, the flow was stable and symmetric, while some other combinations leading to large thermally induced viscosity gradients produce unstable and asymmetric flow. Based on the numerical results, a stability chart of the flow was established, identifying the boundaries between regions of stable and unstable flow in terms of the Graetz number (ratio of thermal conduction time to the convection time scale) and B, a dimensionless ratio indicating the sensitivity of viscosity to temperature changes. Sensitivities with respect to flow parameters are then computed using the continuous sensitivity equations method. We demonstrate that sensitivities are able to detect the transition between the stable and unstable flow regimes and correctly indicate how parameters should change in order to increase the stability of the flow. Copyright © 2009 John Wiley & Sons, Ltd. [source] Instabilities during batch sedimentation in geometries containing obstacles: A numerical and experimental study,INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2007Rekha R. Rao Abstract Batch sedimentation of non-colloidal particle suspensions is studied with nuclear magnetic resonance flow visualization and continuum-level numerical modelling of particle migration. The experimental method gives particle volume fraction as a function of time and position, which then provides validation data for the numerical model. A finite element method is used to discretize the equations of motion, including an evolution equation for the particle volume fraction and a generalized Newtonian viscosity dependent on local particle concentration. The diffusive-flux equation is based on the Phillips model (Phys. Fluids A 1992; 4:30,40) and includes sedimentation terms described by Zhang and Acrivos (Int. J. Multiphase Flow 1994; 20:579,591). The model and experiments are utilized in three distinct geometries with particles that are heavier and lighter than the suspending fluid, depending on the experiment: (1) sedimentation in a cylinder with a contraction; (2) particle flotation in a horizontal cylinder with a horizontal rod; and (3) flotation around a rectangular inclusion. Secondary flows appear in both the experiments and the simulations when a region of higher density fluid is above a lower density fluid. The secondary flows result in particle inhomogeneities, Rayleigh,Taylor-like instabilities, and remixing, though the effect in the simulations is more pronounced than in the experiments. Published in 2007 by John Wiley & Sons, Ltd. [source] Progress in Nanoengineered Microstructures for Tunable High-Current, High-Temperature Superconducting Wires,ADVANCED MATERIALS, Issue 3 2008G. Holesinger Abstract High critical current densities (Jc) in thick films of the Y1Ba2Cu3O7,, (YBCO, Tc , 92 K) superconductor directly depend upon the types of nanoscale defects and their densities within the films. A major challenge for developing a viable wire technology is to introduce nanoscale defect structures into the YBCO grains of the thick film suitable for flux pinning and the tailoring of the superconducting properties to specific, application-dependent, temperature and magnetic field conditions. Concurrently, the YBCO film needs to be integrated into a macroscopically defect-free conductor in which the grain-to-grain connectivity maintains levels of inter-grain Jc that are comparable to the intra-grain Jc. That is, high critical current (Ic) YBCO coated conductors must contain engineered inhomogeneities on the nanoscale, while being homogeneous on the macroscale. An analysis is presented of the advances in high-performance YBCO coated-conductors using chemical solution deposition (CSD) based on metal trifluoroacetates and the subsequent processing to nano-engineer the microstructure for tuneable superconducting wires. Multi-scale structural, chemical, and electrical investigations of the CSD film processes, thick film development, key microstructural features, and wire properties are presented. Prospects for further development of much higher Ic wires for large-scale, commercial application are discussed within the context of these recent advances. [source] Climate variability and change in the Greater Alpine Region over the last two centuries based on multi-variable analysisINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2009Michele Brunetti Abstract An extensive analysis of the HISTALP database is presented with the aim of giving a comprehensive picture of secular climate variability and change in the Greater Alpine Region (GAR, 4,19 E, 43,49 N). The HISTALP database encompasses 242 sites and concerns temperature, pressure, precipitation, cloudiness, sunshine duration, vapour pressure and relative humidity. The analyses are based on four regional mean records representing different GAR low-level areas and on an additional mean record representing high-level locations. The first goal of the paper is to give an overview of the seasonal and annual records for the different variables, aiming to highlight both variability on decadal time scale and long-term evolution. Then it focuses on trend and correlation analysis. Trends are presented both for the period of common data availability for all regional average series and for moving windows that permit studying the trends over a wide range of timescales. Correlations among the different variables are presented both for the regional average series and for their high-pass-filtered versions. The analyses, beside highlighting a warming that is about twice as large as the global trend, also show that the different variables have responded in different ways to this warming and that the mutual interactions linking the different variables are often present only at specific temporal scales and only in parts of the GAR and in defined seasons. In spite of this complex behaviour, which may also be due to some residual inhomogeneities still affecting the data, the analyses give evidence that the HISTALP database has an excellent internal consistency and show that the availability of a multi-variable database turns out to be very useful in order to evaluate the reliability of the reconstruction of each variable and to better understand the behaviour and the mutual interactions of the different variables. Copyright © 2009 Royal Meteorological Society [source] HISTALP,historical instrumental climatological surface time series of the Greater Alpine RegionINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 1 2007Ingeborg Auer This paper describes the HISTALP database, consisting of monthly homogenised records of temperature, pressure, precipitation, sunshine and cloudiness for the ,Greater Alpine Region' (GAR, 4,19°E, 43,49°N, 0,3500m asl). The longest temperature and air pressure series extend back to 1760, precipitation to 1800, cloudiness to the 1840s and sunshine to the 1880s. A systematic QC procedure has been applied to the series and a high number of inhomogeneities (more than 2500) and outliers (more than 5000) have been detected and removed. The 557 HISTALP series are kept in different data modes: original and homogenised, gap-filled and outlier corrected station mode series, grid-1 series (anomaly fields at 1° × 1°, lat × long) and Coarse Resolution Subregional (CRS) mean series according to an EOF-based regionalisation. The leading climate variability features within the GAR are discussed through selected examples and a concluding linear trend analysis for 100, 50 and 25-year subperiods for the four horizontal and two altitudinal CRSs. Among the key findings of the trend analysis is the parallel centennial decrease/increase of both temperature and air pressure in the 19th/20th century. The 20th century increase (+1.2 °C/+ 1.1 hPa for annual GAR-means) evolved stepwise with a first peak near 1950 and the second increase (1.3 °C/0.6hPa per 25 years) starting in the 1970s. Centennial and decadal scale temperature trends were identical for all subregions. Air pressure, sunshine and cloudiness show significant differences between low versus high elevations. A long-term increase of the high-elevation series relative to the low-elevation series is given for sunshine and air pressure. Of special interest is the exceptional high correlation near 0.9 between the series on mean temperature and air pressure difference (high-minus low-elevation). This, further developed via some atmospheric statics and thermodynamics, allows the creation of ,barometric temperature series' without use of the measures of temperature. They support the measured temperature trends in the region. Precipitation shows the most significant regional and seasonal differences with, e.g., remarkable opposite 20th century evolution for NW (9% increase) versus SE (9% decrease). Other long- and short-term features are discussed and indicate the promising potential of the new database for further analyses and applications. Copyright © 2006 Royal Meteorological Society. [source] Trends in storminess over the Netherlands, 1962,2002INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 10 2005A. Smits Abstract Trends in the annual number of independent wind events over the Netherlands are studied for the period 1962,2002. The events are selected out of 13 hourly 10 m wind speed records that are part of a high quality dataset of near-surface wind observations at Dutch meteorological stations. Comparisons are made with trends in independent wind events selected from geostrophic wind speed records and reanalysis data. The results for moderate wind events (that occur on average 10 times per year) and strong wind events (that occur on average twice a year) indicate a decrease in storminess over the Netherlands between 5 and 10%/decade. This result is inconsistent with National Centers for Environmental Prediction,National Center for Atmospheric Research or European Centre for Medium-Range Weather Forecasts reanalysis data, which suggest increased storminess during the same 41 year period. Possible explanations are given for the discrepancy between the trends in storminess based on station data and the trends in storminess based on reanalysis data. Evaluation of trends in geostrophic wind, both from station data and reanalysis data, and evaluation of trends in vector-averaged (upscaled) 10 m wind over the Netherlands point towards inhomogeneities in the reanalysis data as the main cause of the discrepancy. We conclude that it is likely that the decrease in storminess observed in Dutch station records of near-surface wind in the past four decades is closer to reality than the increase suggested by the reanalysis data. Copyright © 2005 Royal Meteorological Society. [source] An improved method of constructing a database of monthly climate observations and associated high-resolution gridsINTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 6 2005Timothy D. Mitchell Abstract A database of monthly climate observations from meteorological stations is constructed. The database includes six climate elements and extends over the global land surface. The database is checked for inhomogeneities in the station records using an automated method that refines previous methods by using incomplete and partially overlapping records and by detecting inhomogeneities with opposite signs in different seasons. The method includes the development of reference series using neighbouring stations. Information from different sources about a single station may be combined, even without an overlapping period, using a reference series. Thus, a longer station record may be obtained and fragmentation of records reduced. The reference series also enables 1961,90 normals to be calculated for a larger proportion of stations. The station anomalies are interpolated onto a 0.5° grid covering the global land surface (excluding Antarctica) and combined with a published normal from 1961,90. Thus, climate grids are constructed for nine climate variables (temperature, diurnal temperature range, daily minimum and maximum temperatures, precipitation, wet-day frequency, frost-day frequency, vapour pressure, and cloud cover) for the period 1901,2002. This dataset is known as CRU TS 2.1 and is publicly available (http://www.cru.uea.ac.uk/). Copyright © 2005 Royal Meteorological Society [source] Reflections on the optimal currency area (OCA) criteria in the light of EMUINTERNATIONAL JOURNAL OF FINANCE & ECONOMICS, Issue 4 2003M.J. Artis Abstract Optimal Currency Area (OCA) theory offers criteria for evaluating the optimality of monetary union arrangements. This paper reviews the use that has been made of these criteria in the specific context of European Monetary Union. It reviews the use of business cycle synchronization data and the data produced by SVAR analyses, which led to the ,core,periphery' distinction. It also reviews extensions of the criteria that have been proposed or generated in this context: in particular, the proposition that the criteria may be ,endogenous'. It presents Taylor rule estimates to check for inhomogeneities in Euro Area performance. The paper concludes that OCA criteria provide a useful starting point for evaluating monetary union options. Copyright © 2003 John Wiley & Sons, Ltd. [source] A CFL-like constraint for the fast marching method in inhomogeneous chemical kineticsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2008Ramón Escobedo Abstract Level sets and fast marching methods are a widely used technique for problems with moving interfaces. Chemical kinetics has been recently added to this family, for the description of reaction paths and chemical waves in homogeneous media, in which the velocity of the interface is described by a given field. A more general framework must consider variable velocities due to inhomogeneities induced by chemical changes. In this case, a constraint must be satisfied for the correct use of fast marching method. We deduce an analytical expression of this constraint when the Godunov scheme is used to solve the Eikonal equation, and we present numerical simulations of a case which must be enforced to obey the constraint. © 2007 Wiley Periodicals, Inc. 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