Tile Boundaries Research Articles

Electron beam profile measurement using enhanced dual-techniques in high heat flux test facility at Institute for Plasma Research.

During operation of an ITER-like plasma fusion device, Plasma Facing Components (PFCs) of a divertor are subjected to steady-state and transient heat loads of up to 20 MW/m2. At High Heat Flux Test Facility (HHFTF) at Institute for Plasma Research, PFCs are subjected to such heat flux scenarios using 200 kW electron beam (EB). A heat flux distribution on PFCs is significantly influenced by the EB profile and scanning technique. A novel dual-technique approach is used to measure EB cross-sectional profiles in HHFTF. A single setup is designed, fabricated, and installed in HHFTF consisting of (1) the knife-edge technique involving graphite and tungsten rectangular tiles bonded on a copper block adjacent to each other to form a sharp edge and (2) the wire scanner technique wherein tungsten wires are placed at equal distances. Current collected by the setup is measured as EB is rastered across the wire and tile boundaries. Current measured as a function of EB position is used to calculate the EB profile using a customized LabVIEW software application. Experiments are conducted by varying EB power from 28 to 200 kW and correspondingly the full width at half maximum of the EB profile grows from 5.30 to 16.04mm, as observed by both these techniques. The COMSOL Multiphysics simulation of the wire scanner technique is performed to verify the experimental results. X-ray and infra-red imaging diagnostics of HHFTF are also used to measure the EB profile in a unique and first-of-its-kind way, and they are found to agree well with the dual-technique measurements.

Photometric Correction of Chang’E-1 Interference Imaging Spectrometer’s (IIM) Limited Observing Geometries Data with Hapke Model

The main objective of this study is to develop a Hapke photometric model that is suited for Chang’E-1 (CE-1) Interference Imaging Spectrometer (IIM) data. We first divided the moon into three areas including ‘maria’, ‘new highland’ and old ‘highland’ with similar photometry characteristic based on the Hapke parameters of the moon derived from Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) multispectral data. Then, we selected the sample data in the ‘maria’ area and obtained a new set of Hapke model’s parameters that can best fit these data. Result shows that photometric correction using Hapke model with these new derived parameters can eliminate the effect of variations in viewing and luminating geometry, especially ‘opposition surge’, more efficiently than the empirical model. The corrected mosaic shows no significant artifacts along the tile boundaries and more detailed information of the image can be exhibited due to a better correction of ‘opposition surge’ at small phase angle (g < 15°).

Dynamic load balancing algorithm based on HEVC tiles for just-in-time video encoding for heterogeneous architectures

ABSTRACTThis paper proposes a novel algorithm for dynamic tile partitioning to achieve the optimal workload balance for parallel processing architectures in just-in-time HEVC encoding. Tile boundaries are dynamically shifted depending on the tile cost, a value that denotes predicted computational complexity of a single tile in a frame. The overall cost of a tile is determined as a combination of costs of three computationally most expensive and resource-hungry operations in HEVC encoding: prediction, transformation, and entropy coding. The algorithm aims at exploiting different types of processing architectures, from homogeneous multicore CPU architectures to heterogeneous architectures in the actual conditions in which streaming servers operate. The experimental results show that the proposed algorithm outperforms uniform tiling, by up to 5.5% in processing time, while maintaining the same video quality and bitrate. Compared to the state-of-the-art algorithms, the proposed algorithm achieves up to 8.85% speedup depending on the number of videos that are being encoded concurrently on a video streaming server.

Adaptive Boundaries of Wang Tiles for Heterogeneous Material Modelling

This contribution deals with algorithms for the generation of modified Wang tiles as a tool for the heterogeneous materials modelling. The proposed approach considers material domains only with 2D hard discs of both equal and different radii distributed within a matrix. Previous works showed potential of the Wang tile principles for reconstruction of heterogeneous materials. The main advantage of the tiling theory for material modelling is to stack large/infinite areas with relative small set of tiles with emphasis on a periodicity reduction in comparison with the traditional Periodic Unit Cell (PUC) concept. The basic units of the Wang Tiling are tiles with codes (colors) on edges. The algorithm for distribution of hard discs is based on the molecular dynamics to avoid particles overlapping. Unfortunately the nature of the Wang tiling together with molecular dynamics algorithms cause periodicity artefacts especially in tile corners of a composed material domain. In this paper a new algorithm with adaptive tile boundaries is presented in order to avoid edge and corner periodicity.

A scalable approach for tree segmentation within small-footprint airborne LiDAR data

This paper presents a distributed approach that scales up to segment tree crowns within a LiDAR point cloud representing an arbitrarily large forested area. The approach uses a single-processor tree segmentation algorithm as a building block in order to process the data delivered in the shape of tiles in parallel. The distributed processing is performed in a master-slave manner, in which the master maintains the global map of the tiles and coordinates the slaves that segment tree crowns within and across the boundaries of the tiles. A minimal bias was introduced to the number of detected trees because of trees lying across the tile boundaries, which was quantified and adjusted for. Theoretical and experimental analyses of the runtime of the approach revealed a near linear speedup. The estimated number of trees categorized by crown class and the associated error margins as well as the height distribution of the detected trees aligned well with field estimations, verifying that the distributed approach works correctly. The approach enables providing information of individual tree locations and point cloud segments for a forest-level area in a timely manner, which can be used to create detailed remotely sensed forest inventories. Although the approach was presented for tree segmentation within LiDAR point clouds, the idea can also be generalized to scale up processing other big spatial datasets.

Improve load balancing and coding efficiency of tiles in high efficiency video coding by adaptive tile boundary

High efficiency video coding (HEVC) not only improves the coding efficiency drastically compared to the well-known H.264/AVC but also introduces coding tools for parallel processing, one of which is tiles. Tile partitioning is allowed to be arbitrary in HEVC, but how to decide tile boundaries remains an open issue. An adaptive tile boundary (ATB) method is proposed to select a better tile partitioning to improve load balancing (ATB-LoadB) and coding efficiency (ATB-Gain) with a unified scheme. Experimental results show that, compared to ordinary uniform-space partitioning, the proposed ATB can save up to 17.65% of encoding times in parallel encoding scenarios and can reduce up to 0.8% of total bit rates for coding efficiency.

Evaluation of ALOS PALSAR Data for High-Resolution Mapping of Vegetated Wetlands in Alaska

As the largest natural source of methane, wetlands play an important role in the carbon cycle. High-resolution maps of wetland type and extent are required to quantify wetland responses to climate change. Mapping northern wetlands is particularly important because of a disproportionate increase in temperatures at higher latitudes. Synthetic aperture radar data from a spaceborne platform can be used to map wetland types and dynamics over large areas. Following from earlier work by Whitcomb et al. (2009) using Japanese Earth Resources Satellite (JERS-1) data, we applied the “random forests” classification algorithm to variables from L-band ALOS PALSAR data for 2007, topographic data (e.g., slope, elevation) and locational information (latitude, longitude) to derive a map of vegetated wetlands in Alaska, with a spatial resolution of 50 m. We used the National Wetlands Inventory and National Land Cover Database (for upland areas) to select training and validation data and further validated classification results with an independent dataset that we created. A number of improvements were made to the method of Whitcomb et al. (2009): (1) more consistent training data in upland areas; (2) better distribution of training data across all classes by taking a stratified random sample of all available training pixels; and (3) a more efficient implementation, which allowed classification of the entire state as a single entity (rather than in separate tiles), which eliminated discontinuities at tile boundaries. The overall accuracy for discriminating wetland from upland was 95%, and the accuracy at the level of wetland classes was 85%. The total area of wetlands mapped was 0.59 million km2, or 36% of the total land area of the state of Alaska. The map will be made available to download from NASA’s wetland monitoring website.

Efficient In-Loop Filtering Across Tile Boundaries for Multi-Core HEVC Hardware Decoders With 4 K/8 K-UHD Video Applications

HEVC is a next generation video coding standard designed with modern coding techniques to be especially efficient for coding high-resolution video such as 4 K/8 K-ultra high- definition (UHD) video. Among the advanced coding tools of HEVC, tiles and wavefront parallel processing (WPP) have been newly adopted for parallel processing of such high-resolution (4 K/8 K-UHD) video. To realize UHD video services over portable devices with limited battery power, it is essential to implement multi-core-based and dedicated HEVC hardware decoders that support the tile- and wavefront-based parallel processing. By doing so, each frame is divided into a multiple number of picture partitions which can then be processed by multiple hardware decoder cores in parallel. However, in-loop filtering (ILF) at tile boundaries cannot be easily parallelized by a multi-core HEVC hardware decoder because of the data dependency between samples in different tiles. In this paper, an efficient control method for ILF across tile boundaries is proposed for multi-core HEVC hardware decoders. The proposed method does not require additional in-loop filters for ILF across the tile boundaries and it allows a decoder core to continue to process the next coding tree unit (CTU) without waiting for other decoders until they finish their ILF processing for the neighboring CTUs in other tiles. From experiments, we show the effectiveness of our ILF control method via a quad-core HEVC decoder for 4 K-UHD video implemented on a prototyping FPGA board.

Seamless stitching of tile scan microscope images.

For diagnostic purposes, optical imaging techniques need to obtain high-resolution images of extended biological specimens in reasonable time. The field of view of an objective lens, however, is often smaller than the sample size. To image the whole sample, laser scanning microscopes acquire tile scans that are stitched into larger mosaics. The appearance of such image mosaics is affected by visible edge artefacts that arise from various optical aberrations which manifest in grey level jumps across tile boundaries. In this contribution, a technique for stitching tiles into a seamless mosaic is presented. The stitching algorithm operates by equilibrating neighbouring edges and forcing the brightness at corners to a common value. The corrected image mosaics appear to be free from stitching artefacts and are, therefore, suited for further image analysis procedures. The contribution presents a novel method to seamlessly stitch tiles captured by a laser scanning microscope into a large mosaic. The motivation for the work is the failure of currently existing methods for stitching nonlinear, multimodal images captured by our microscopic setups. Our method eliminates the visible edge artefacts that appear between neighbouring tiles by taking into account the overall illumination differences among tiles in such mosaics. The algorithm first corrects the nonuniform brightness that exists within each of the tiles. It then compensates for grey level differences across tile boundaries by equilibrating neighbouring edges and forcing the brightness at the corners to a common value. After these artefacts have been removed further image analysis procedures can be applied on the microscopic images. Even though the solution presented here is tailored for the aforementioned specific case, it could be easily adapted to other contexts where image tiles are assembled into mosaics such as in astronomical or satellite photos.

Resolved Hapke parameter maps of the Moon

We derived spatially resolved near-global Hapke photometric parameter maps of the Moon from 21 months of Lunar Reconnaissance Orbiter Camera (LROC) Wide Angle Camera (WAC) multispectral observations using a novel “tile-by-tile method” (1° latitude by 1° longitude bins). The derived six parameters (w,b,c,BS0,hS, andθp) for each tile were used to normalize the observed reflectance (standard angles i = g = 60°, e = 0° instead of the traditional angles i = g = 30°, e = 0°) within each tile, resulting in accurate normalization optimized for the local photometric response. Each pixel in the seven-color near-global mosaic (70°S to 70°N and 0°E to 360°E) was computed by the median of normalized reflectance from large numbers of repeated observations (UV: ∼50 and visible: ∼126 on average). The derived mosaic exhibits no significant artifacts with latitude or along the tile boundaries, demonstrating the quality of the normalization procedure. The derived Hapke parameter maps reveal regional photometric response variations across the lunar surface. The b, c (Henyey-Greenstein double-lobed phase function parameters) maps demonstrate decreased backscattering in the maria relative to the highlands (except 321 nm band), probably due to the higher content of both SMFe (submicron iron) and ilmenite in the interiors of back scattering agglutinates in the maria. The hS (angular width of shadow hiding opposition effect) map exhibits relatively lower values in the maria than the highlands and slightly higher values for immature highland crater ejecta, possibly related to the variation in a grain size distribution of regolith.

Spatial structure of plasma potential oscillation and ion saturation current in VHF multi-tile electrode plasma source

Increasing RF frequency in the VHF range in the PECVD of Silicon for photovoltaic applications enables a higher rate of deposition while maintaining film quality. However, plasma uniformity on large substrates is compromised as wavelength effects are encountered at high frequencies. Using a segmented electrode consisting an array of individual tiles each 180° out of phase with adjacent tiles, a scalable VHF source that is not affected by wavelength effects is achieved. Due to the 180° phase shift between tiles, a spatial structure is imposed on the plasma. In this paper the spatial structure of the plasma potential oscillation and the ion saturation current density are examined. A capacitive probe measures the oscillation of the plasma potential. Spatial profiles of the plasma potential oscillation exhibit peaks on tile centers at odd harmonics (1F and 3F). The measured even harmonic (2F) is small in amplitude, as expected for the differential power feed, and peaks at tile boundaries. Spatial profiles of ion saturation current show peaks in plasma density over the tile-to-tile boundaries, with non-uniformity increasing with RF power. A discussion of the measured profiles at a variety of powers and pressures is presented.

Optimal semi-oblique tiling

For 2D iteration space tiling, we address the problem of determining the tile parameters that minimize the total execution time on a parallel machine. We consider uniform dependency computations tiled so that (at least) one of the tile boundaries is parallel to the domain boundaries. We determine the optimal tile size as a closed form solution. In addition, we determine the optimal number of processors and also the optimal slope of the oblique tile boundary. Our results are based on the BSP model, which assures the portability of the results. Our predictions are justified on a sequence global alignment problem specialized to similar sequences using Fickett's k-band algorithm, for which our optimal semi-oblique tiling yields an improvement of a factor of 2.5 over orthogonal tiling. Our optimal solution requires a block-cyclic distribution of tiles to processors. The best one can obtain with only block distribution (as many authors require) is three times slower. Furthermore, our best running time is within 10 percent of the "predicted theoretical peak" performance of the machine!.

A pipelined schedule to minimize completion time for loop tiling with computation and communication overlapping

This paper proposes a new method for the problem of minimizing the execution time of nested for-loops using a tiling transformation. In our approach, we are interested not only in tile size and shape according to the required communication to computation ratio, but also in overall completion time. We select a time hyperplane to execute different tiles much more efficiently by exploiting the inherent overlapping between communication and computation phases among successive, atomic tile executions. We assign tiles to processors according to the tile space boundaries, thus considering the iteration space bounds. Our schedule considerably reduces overall completion time under the assumption that some part from every communication phase can be efficiently overlapped with atomic, pure tile computations. The overall schedule resembles a pipelined datapath where computations are not anymore interleaved with sends and receives to nonlocal processors. We survey the application of our schedule to modern communication architectures. We performed two sets of experimental results, one using MPI primitives over FastEthernet and one using the SISCI API over an SCI network. In both cases, the total completion time is significantly reduced.

A wavelet transform with point-symmetric extension at tile boundaries

This paper presents a low-complexity wavelet transform that utilizes point-symmetric extension at the image tile boundaries. The proposed approach is considered as an alternative to the well-known symmetric signal extension in dealing with the boundary artifacts that manifest when tiles of images are lossy compressed. The new solution developed for odd-length filters preserves the perfect reconstruction property of the filter banks and deals efficiently with blocking artifacts without requiring any post processing technique or additional information from the neighboring tiles. It is shown that point-symmetric extension at the tile boundaries does not need to be applied explicitly, but instead the equivalent boundary filters can be derived. The lifting-based implementation of the filters provides a very simple way of changing filter parameters at the boundaries that suits both hardware and software platforms.

A procedure to average 3D anatomical structures

Creating a feature-preserving average of three dimensional anatomical surfaces extracted from volume image data is a complex task. Unlike individual images, averages present right-left symmetry and smooth surfaces which give insight into typical proportions. Averaging multiple biological surface images requires careful superimposition and sampling of homologous regions. Our approach to biological surface image averaging grows out of a wireframe surface tessellation approach by Cutting et al. (1993). The surface delineating wires represent high curvature crestlines. By adding tile boundaries in flatter areas the 3D image surface is parametrized into anatomically labeled (homology mapped) grids. We extend the Cutting et al. wireframe approach by encoding the entire surface as a series of B-spline space curves. The crestline averaging algorithm developed by Cutting et al. may then be used for the entire surface. Shape preserving averaging of multiple surfaces requires careful positioning of homologous surface regions such as these B-spline space curves. We test the precision of this new procedure and its ability to appropriately position groups of surfaces in order to produce a shape-preserving average. Our result provides an average that well represents the source images and may be useful clinically as a deformable model or for animation.

TEM Cross-Section Investigations of Epitaxial Ba2Bi4Ti5O18 Thin Films on LaNiO3 Bottom Electrodes on CeO2/YSZ-Buffered Si(100)

Epitaxial, ferroelectric Ba2Bi4Ti5O18 films grown on LaNiO3/CeO2/ZrO2:Y2O3 epi-taxial layers on Si(100) are investigated by plan-view and cross-section transmission elec-tron microscopy. The films consist of well-developed grains of rectangular shape, in the following called tiles. The boundaries between the tiles are strained and contain many defects. A new, specific type of lattice defect is found in the tile boundaries. This defect is de-scribed as a staircase formed by repeated lattice shifts of Delta ~ ct/12 ~ 4.2 Å in the [001] direction, which result in seemingly bent ribbons of stacked Bi2O2 planes. The individual Bi2O2 planes remain, however, strongly parallel to the (001) plane. Each step of the staircase being formed by short sections of two or more Bi2O2 layers in direct con-tact, the defects carry a bismuth excess. Accordingly, the tile bounda-ries are bismuth-rich. A model to explain this bismuth excess of the tile boundaries is proposed.

Dynamics of self-similar tilings

This paper investigates dynamical systems arising from the action by translations on the orbit closures of self-similar and self-affine tilings of ${\Bbb R}^d$. The main focus is on spectral properties of such systems which are shown to be uniquely ergodic. We establish criteria for weak mixing and pure discrete spectrum for wide classes of such systems. They are applied to a number of examples which include tilings with polygonal and fractal tile boundaries; systems with pure discrete, continuous and mixed spectrum.

Singularities of convex-polygonally generated shape-densities

AbstractIn earlier papers Kendall and Le[3,4] made a geometrical study of the structure and singularities of a convex-polygonally generated shape-density for any convex polygon K. The present work describes the singular tessellation T(K) in algebraic terms, and obtains explicit formulae for the ‘jump functions’ of m̃ across every edge of the tessellation. These results, combined with earlier work by Le[5] on the basic tile, make it possible to find m̃ explicitly in every tile by what we have called the ‘stepping-stone’ method. In a closing section the exact order of the differential singularity is found at the tile boundaries.