Visible Boundaries Research Articles

Apparent diffusion coefficient (ADC) measurements may be more reliable and reproducible than lesion volume on diffusion-weighted images from patients with acute ischaemic stroke–implications for study design

Early ischemic change after stroke can be demonstrated with diffusion-weighted imaging (DWI) and quantified by measuring the apparent diffusion coefficient (ADC) and/or lesion volume. We examined the reliability and reproducibility of lesion volume and ADC measurement on DWI images, and discuss the implications for clinical studies. Using 38 DWI scans from 15 stroke patients, two observers (a physicist and a neuroscience graduate) blind to each other, recorded the lesion volume on DWI sequences, measured the ADC values in this volume and calculated the ratio of ischemic: control ADC (ADCr). One observer repeated his measurements blind to his first, and also examined the effect on lesion volume and ADC of deliberately varying by only one pixel, the outline of the visible boundary of the lesion. The inter and intra-rater reliability were worse for lesion volume than ADC or ADCr measurements: lesion volume, inter-rater coefficient of variation (CoV) 85 ± 130%, intra-rater CoV 20+/−SD80% ( p < 0.05); ADC inter-rater CoV 7.7 ± SD 19%, intra-rater CoV 0.2 ± SD 12% ( p = NS); and ADCr inter-rater CoV 8 ± SD27%, intra-rater CoV 0.8 ± SD73% ( p = NS). Altering the position of the outline tracing of the lesion boundary by one pixel altered the measured volumes by 22 ± SD25% ( p < 0.05), but ADC values were altered by only 2.9 ± SD4.9% and ADCr by 2.7 ± SD4.8% ( p = NS). ADC and ADCr values are more reliable and reproducible than DWI lesion size in acute ischemic stroke because altering where the lesion boundary is measured has a much greater impact on lesion volume than on the ADC or ADCr. This effect is greatest in large lesions.

Sequential extraction of iron, manganese and related elements in S1 sapropel sediments, eastern Mediterranean

A detailed sequential extraction scheme (MESEX) was developed to distinguish Fe and Mn phases in eastern Mediterranean sediments. After calibration and validation using single natural minerals and a mixed mineral standard, MESEX was applied to Holocene eastern Mediterranean sediments from (1) a former brine basin, and (2) a normal setting, including the organic-rich sapropel S1. In both sediments the Mn(II)/Mn(III,IV) redox boundary is clearly distinguished with carbonate-related Mn being enriched below, and Mn oxides occurring only above it. A clear Fe(II)/Fe(III) redox boundary is present in the normal eastern Mediterranean sediments and is located just below the Mn(II)/Mn(III,IV) redox boundary. The Fe(II)/Fe(III) boundary closely coincides with the visible boundary between the lower unoxidised and the upper oxidised (burned-down) part of the original sapropel S1 interval. Pyrite is only present within the unoxidised interval, whereas Fe oxides are abundant above it. The Fe(II)/Fe(III) redox boundary in the former brine sediments resides on top of the organic-enriched sediments, as deduced from the distribution of Fe oxides and pyrite. As a result of burn-down of the sapropel S1 unit in the normal sediments, a vanadium peak has been formed below the oxidation front, whereas no such V peak was observed in the former brine sediments. This, together with the location of the Mn(II)/Mn(III,IV) redox boundary well above the organic-enriched sediments, suggests that no burn-down has taken place into the sapropelic sediments of the former brine basin, resulting in the preservation of the relationships of trace metal to organic carbon or pyrite. In these latter sediments, Mn and Co appear to be associated with pyrite, whereas Ni, Cu and Zn, as well as V, are more related to organic matter. On the basis of MESEX, variations have also been detected in the terrigenous component, i.e. aluminosilicates. (Fe/Al) clay, (Mg/Al) clay, and several trace metal to Al ratios are higher in sapropelic than in non-sapropelic sediments. These results indicate that sources of terrestrial material have been different during sapropel times compared to the period immediately after it. On the other hand, the fairly constant K/Al clay ratio suggests that no major changes may have occurred in the relative illite contribution.

Mortuary behaviour on the Hay Plain: do cemeteries exist?

AbstractAboriginal burial practices on the Hay Plain are highly variable yet recurrent characteristics of density, exclusivity, boundedness and formalism of burials suggest specific preferences for, and maintenance of, locations for burials. However, these groupings of burials do not fit the criteria developed by Pardoe (1988) for cemeteries.This is demonstrated in the analysis of burials at two locations: Jeraly (76 burials) and Toogimbie (114 burials) where scattered and grouped burials are found in the same area as a single site described as a cemetery. Comparison of these finds to other burials on the Hay Plain indicates this is a recurrent pattern.It is argued that burials represent isolated single events (n=76) or multiple events (n=89), a small number (17) of which reflect deliberate maintenance of an area for burials. While cemeteries do exist on the Hay Plain they form a restricted category and making the term more inclusive would simply mask important differences between burial places, all of which form a patterned part of the entire burial repertoire on the Hay Plain.

G-fluxes and non-perturbative stabilisation of heterotic M-theory

We examine heterotic M-theory compactified on a Calabi–Yau manifold with an additional parallel M5-brane. The dominant non-perturbative effect stems from open membrane instantons connecting the M5 with the boundaries. We derive the four-dimensional low-energy supergravity potential for this situation including subleading contributions as it turns out that the leading term vanishes after minimisation. At the minimum of the potential the M5 gets stabilised at the middle of the orbifold interval while the vacuum energy is shown to be manifestly positive. Moreover, induced by the non-trivial running of the Calabi–Yau volume along the orbifold which is driven by the G-fluxes, we find that the orbifold-length and the Calabi–Yau volume modulus are stabilised at values which are related by the G-flux of the visible boundary. Finally we determine the supersymmetry-breaking scale and the gravitino mass for this open membrane vacuum.

Uncovering hierarchical structure in data using the growing hierarchical self-organizing map

Discovering the inherent structure in data has become one of the major challenges in data mining applications. It requires stable and adaptive models that are capable of handling the typically very high-dimensional feature spaces. In particular, the representation of hierarchical relations and intuitively visible cluster boundaries are essential for a wide range of data mining applications. Current approaches based on neural networks hardly fulfill these requirements within a single model. In this paper we present the growing hierarchical self-organizing map ( GHSOM), a neural network model based on the self-organizing map. The main feature of this novel architecture is its capability of growing both in terms of map size as well as in a three-dimensional tree-structure in order to represent the hierarchical structure present in a data collection during an unsupervised training process. This capability, combined with the stability of the self-organizing map for high-dimensional feature space representation, makes it an ideal tool for data analysis and exploration. We demonstrate the potential of the GHSOM with an application from the information retrieval domain, which is prototypical both of the high-dimensional feature spaces frequently encountered in today's applications as well as of the hierarchical nature of data.

Multiframe blocking-artifact reduction for transform-coded video

A major drawback of block-based still-image or video-compression methods at low rates is the visible block boundaries that are also known as blocking artifacts. Several methods have been proposed in the literature to reduce these artifacts. Most are single image methods, which do not distinguish between video and still images. However, video has a temporal dimension that can lead to better reconstruction if utilized effectively. We show how to combine information from multiple frames to reduce blocking artifacts. We derive constraint sets using motion between neighboring frames and quantization information that is available in the video bit stream. These multiframe constraint sets can be used to reduce blocking artifacts in an alternating-projections scheme. They can also be included in existing set-theoretic algorithms to improve their performance by narrowing down the feasibility set. Experimental results show the effectiveness of using these multiframe constraint sets.

Cold, Supersonic Evershed Downflows in a Sunspot

We report here on the discovery of supersonic Evershed downflows in the penumbra of a sunspot. These flows are shown to occur along spatially unresolved, very cold magnetic flux tubes whose downflowing footpoints are found from the middle penumbra outward. Evershed flows along magnetic field lines returning to the solar surface were discovered by Westendorp Plaza and coworkers, but only in the outer parts of the penumbra and beyond its visible boundary; on the other hand, no supersonic flows of any type have ever been reported in the photosphere of sunspots, except for the very different case of the delta spot analyzed by Martinez Pillet and coworkers. We present unequivocal evidence of such supersonic motions, already predicted theoretically by the siphon-flow model, from the interpretation of infrared spectropolarimetric observations of a sunspot with unprecedented spatial resolution.

Microstructure and Microcrack Formation at Phase Boundaries in Na3PO4-Doped Hydroxyapatite.

Hydroxyapatite, Ca10(PO4)6(OH)2, doped with 0.3 to 5.0mass% Na3PO4 as external sintering aid was studied by transmission electron microscopy. Densification of the powder blend was performed by hot-pressing at 1200°C for 30min. The overall microstructure of the material was composed of homogenous, equiaxed hydroxyapatite grains with an average size of about 1.5μm. Apart from the matrix grains, a sodium-plus calcium-containing secondary phase, β-NaCaPO4, precipitated at triple pockets of few hundred nanometer scale. The occurrence of this precipitated phase was typically accompanied by microcrack formation. Microcrack opening typically occurred at one edge of the three or four visible phase boundaries. It should be emphasized that nearly all of the secondary phase pockets revealed such a microcrack. The microcrack formation process is likely to be governed by two interacting material characteristics the thermal expansion mismatch of the adjacent phases and the interface bonding strength.

Photodoping of 60K and 90 K YBaCuO grain bounadry Josephson junctions

We have illuminated with UV or visible light YBaCuO grain boundary Josephson junctions (GBJJ) of different critical temperatures of the banks (90K and 60K). These GBJJ show both dc Josephson properties (Fraunhofer pattern) and ac Josephson properties (Fiske resonance). From the decrease of the normal state resistance we can estimate the oxygen content of the barrier which is lower in the 60 K junctions. The relative increase of the critical current by illumination is higher in the 60 K than in the 90K junctions.

Gradient match vector quantizers for images

We propose a new class of finite-state vector quantizers (FSVQs), called gradient match vector quantizers (GMVQs), in the im- age coding framework. GMVQs can be considered more general than previously proposed side match vector quantizers (SMVQs) since more border pixels between two neighboring blocks are considered in the state codebook design. Moreover, the concept of gradient matching used in GMVQs can be adjoined to another previously proposed overlap match vector quantizers (OMVQs). Thus another new class of FSVQs are pro- posed and named as gradient and overlap match vector quantizers (GOMVQs). GMVQs and GOMVQs utilize the 2-D spatial continuity of the pixel gradient as well as the high spatial correlation of pixels in typical grayscale images. Both minimize the gradient errors of the border pixels between blocks in ordinary vector quantization of images. In addition to reducing the granular noise that causes the annoying effect of visible pixel block boundaries, the proposed GMVQs and GOMVQs also can preserve the global gradient among the block boundaries and reduces more step noise than SMVQs and OMVQs in the area of high contrast edges. Experiments with the ''Lena'' image show that the proposed GMVQ can achieve the performance superior to those of SMVQ maxi- mum more than 1 dB peak signal-to-noise ratio (PSNR) under the same bit rate. On the other hand, GOMVQs can achieve further bit rate reduc- tion (about 0.14 to 0.3 bit/pixel) than OMVQ using the variable length noiseless code for the channel symbols. © 2000 Society of Photo-Optical Instru- mentation Engineers. (S0091-3286(00)00108-2)

Impurity segregation in horizontal bridgman grown cadmium zinc telluride

Segregation of impurities that cause low infrared (IR) transmission in horizontal Bridgman (HB) grown cadmium zinc telluride (CdZnTe) has been investigated. This segregation was characterized using IR transmission, glow discharge mass spectrometry (GDMS), and IR microscopy measurements. In the studied HB CdZnTe ingots, impurity segregation causes the formation of a small volume in the last-to-freeze portion of the ingot that has high impurity concentration and low IR transmission. Outside this region the concentration of impurities is low and the material shows high IR transmission. The region is visibly observable on CdZnTe slices and appears as a dark area with a sharp boundary. Free carrier absorption within the region causes a decrease in IR transmission with an increase in wavelength and correlates with the concentration of lithium and sodium impurities. Impurity segregation in HB ingots is described and explains the location of the high impurity region. The location of the visible boundary correlates with the first measurable change in IR transmission as compared to the high IR transmission of the surrounding material and supports the hypothesis that the darkening of the region is due to a reduction of the reflectivity due to free carrier absorption. With a properly controlled cool-down recipe, the impurities segregated in the last-to-freeze section of the ingots can remain localized, thereby improving the purity of the remaining bulk of the material.

Tracking visible boundary of objects using occlusion adaptive motion snake

We propose a novel technique for tracking the visible boundary of a video object in the presence of occlusion. Starting with an initial contour that is interactively specified by the user and may be automatically refined by using intra-energy terms, the proposed technique employs piecewise contour prediction using local motion and color information on both sides of the contour segment, and contour snapping using scale-invariant intra-frame and inter-frame energy terms. The piecewise (segmented) nature of the contour prediction scheme and modeling of the motion on both sides of each contour segment enable accurate determination of whether and where the tracked boundary is occluded by another object. The proposed snake energy terms are associated with contour segments (as opposed to node points) and they are scale/resolution independent to allow multi-resolution contour tracking without the need to retune the weights of the energy terms at each resolution level. This facilitates contour prediction at coarse resolution and snapping at fine resolution with high accuracy. Experimental results are provided to illustrate the performance of the proposed occlusion detection algorithm and the novel snake energy terms that enable visible boundary tracking in the presence of occlusion.

The properties of velocity oscillations in vicinities of sunspot penumbra

It is suggested that the problem of the extent of the outer penumbra could be considered by investigating the range over which the influence of the penumbra on the oscillation regime of the surrounding medium extends. In summer 1998, velocity oscillations were observed in the vicinities of the penumbra of the NOAA 8263 sunspot. The observations were carried out in the Hβ line (chromosphere) and in the far wing of Ni i 4857.2 A (lower photosphere) simultaneously. The oscillation regime typical for sunspot penumbrae is observed within distances of about 15′′ from the visible outer boundary of the penumbra.

Modeling the coronal magnetic field, with a new method for obtaining boundary conditions on the farside of the Sun

A novel technique is presented that aids the reconstruction of solar coronal magnetic fields by augmenting the visible solar surface boundary conditions with an estimate of the simultaneous conditions on the far side of the Sun. In converting from line‐of‐sight measurements, two alternative assumptions are considered: (1) ignore the plasma beta differences between corona and photosphere and so find a radial field component that is consistent with an overlying potential (or force free) field corona; and (2) characterize the change in beta by a boundary layer, matching the coronal field to the photosphere where the field, seen in projection, is taken to be wholly radial. The radial magnetic field (or radial field component) over the unseen hemisphere of the Sun is deduced from information held within a time series of the Solar and Heliospheric Observatory Michelson Doppler imager photospheric magnetograms centered on the time of interest and combined with a full disc of visible data for that time. Comparison is made with the more usual synoptic map boundary conditions to test the time sensitivity of the problem. Several methods of extrapolation to the far side are assessed using data centered on an observation at the end of August 1996, when a large equatorial coronal hole was present on one side of the Sun. The corresponding magnetic field equilibrium in the corona is found, assuming a simple potential approximation, which employs an outer “source surface” in addition to the derived inner boundary condition. Together with the inherent assumption that the evolution of the global field is slow, the validity of the technique is confirmed by the self‐consistency of the results.

Structure investigations of SOFC anode cermets. Part I: Porosity investigations

The number of electrolyte/metal/pore three-phase boundaries in the SOFC anode cermet was determined in a cross-section photo according to the intercepted-segment method and given as the volume concentration of the electrochemically active phase boundary. The apparent geometrical exchange current density of hydrogen oxidation served as a relativizing measure of electrochemical activity. A direct correlation was found between the number of optically visible three-phase boundaries of ‘electrolyte/nickel agglomerates/gas pores’ in the unit volume of the electrode and the apparent electrochemical exchange current density. The electrode was also analysed porosimetrically by a standard porosimetry method (MSP) and the porosimetric curves were compared with the optical/electrochemical measurements of the same electrode. This comparison revealed that the sum of the integrated volume of nickel agglomerates and the single nickel particles in contact with the electrolyte give the total amount of the active nickel volume whose surface is directly proportional to the amount of optically visible three-phase boundaries in the unit volume.

Sur une Allemagne intérieure

On an inner Germany States and empires have visible boundaries, cultures have invisible ones in ourselves. The former will not be crossed if the latter are not transcended. A French sociologist tries to relate how the political conflicts opposing France and Germany can convert into a cultural exchange.

Three-Dimensional Shortest Path Planning in the Presence of Polyhedral Obstacles

A new algorithm is presented for solving the three-dimensional shortest path planning (3DSP) problem for a point object moving among convex polyhedral obstacles. It is the first non-approximate three-dimensional path planing algorithm that can deal with more than two polyhedral obstacles. The algorithm extends the visibility graph concept from two dimensions to three dimensions. The two main problems with 3DSP are identifying the edge sequence the shortest path passes through and the turning points of the shortest path. A technique based on projective relationships is presented for identifying the set of visible boundary edges (VBE) corresponding to a given view point over which the shortest path, from the view point to the goal, will pass. VBE are used to construct an initial reduced visibility graph (RVG). Optimization is used to revise the position of the turning points and hence the three-dimensional RVG (3DRVG) and the global shortest path is then selected from the 3DRVG. The algorithm is of computational complexity O(n3vk), where n is the number of verticles, v is the maximum number of vertices on any one obstacle and k is the number of obstacles. The algorithm is applicable only with polyhedral obstacles, as the theorems developed for searching for the turning points of the three-dimensional shortest path are based on straight edges of the obstacles. It needs to be further developed for dealing with arbitrary-shaped obstacles and this would increase the computational complexity. The algorithm is tested using computer simulations and some results are presented.

4-month-old infants' use of a visible boundary line as a cue in an object segregation task

4-month-old infants' use of a visible boundary line as a cue in an object segregation task

Structural Origins of the Surface Depressions at Alkanethiolate Monolayers on Au(111): A Scanning Tunneling and Atomic Force Microscopic Investigation

Scanning tunneling (STM) and atomic force (AFM) microscopies have been used to examine structural features of monolayers formed from the spontaneous adsorption of alkanethiols at Au(111) surfaces. In addition to the atomic scale spacings of the adlayer, the depressional features found in both large (50-250 nm) and atomic scale images have been characterized for monolayers formed from several alkyl chain lengths. These depressions, which are more predominant at monolayers from long chain alkanethiols, appear as 2-4 nm diameter, 0.24 nm deep depressions in STM images and as 2-5 nm diameter, low frictional features in lateral force images. The lateral force images of these depressions, along with an explanation of the imaging mechanism, are presented for the first time. Atomic scale STM images reveal the presence of the adlayer lattice within the depressions. In addition, atomic scale images show that these depressions occur along visible domain boundaries. Together, our results indicate that these depressions originate in the topmost layer of the Au(111) surface and are not a consequence of structural inhomogeneities in the monolayer or of imaging artifacts. Based on these findings, a mechanism for the origin of the depressions is proposed. 37 refs., 6 figs., 1 tab.

Robot navigation in unknown generalized polygonal terrains using vision sensors

This paper considers the problem of navigating a point robot in an unknown two-dimensional terrain populated by disjoint generalized polygonal obstacles. A generalized polygon consists of a connected sequence of circular arcs and straight-line segments. The terrain model is not known a priori, but the robot is equipped with a vision sensor. A discrete vision sensor detects all visible (from a single position) portions of the obstacle boundaries in a single scan operation. The navigation problem deals with moving the robot through the terrain from a source position to a destination position, and the terrain model acquisition problem deals with autonomously building a model of the terrain. A complete solution to either problem is shown to require an infinite number of scan operations in cusp regions formed by a pair of convex and concave obstacle edges. Either problem is considered solved with a precision /spl epsiv/ if the points that have not been scanned are those in a cusp region with a clearance less than /spl epsiv/ from two obstacle edges. Three methods are proposed to solve both problems with a precision /spl epsiv/ based on extensions of the generalized visibility graph, the generalized Voronoi diagram, and the trapezoidal decomposition. Then simplified versions of these structures are proposed to exactly solve the navigation and terrain model acquisition problems using a continuous vision sensor that detects all visible obstacle boundaries as the robot navigates along a path. >