Partial Evaluation of Views

Many database applications and environments, such as mediation over heterogeneous database sources and data warehousing for decision support, lead to complex queries. Queries are often nested, defined over previously defined views, and may involve unions. There are good reasons why one might want to remove pieces (sub-queries or sub-views) from such queries: some sub-views of a query may be effectively cached from previous queries, or may be materialized views; some may be known to evaluate empty, by reasoning over the integrity constraints; and some may match protected queries, which for security cannot be evaluated for all users.In this paper, we present a new evaluation strategy with respect to queries defined over views, which we call tuple-tagging, that allows for an efficient removal of sub-views from the query. Other approaches to this are to rewrite the query so the sub-views to be removed are effectively gone, then to evaluate the rewritten query. With the tuple tagging evaluation, no rewrite of the original query is necessary.We describe formally a discounted query (a query with sub-views marked that are to be considered as removed), present the tuple tagging algorithm for evaluating discounted queries, provide an analysis of the algorithm's performance, and present some experimental results. These results strongly support the tuple-tagging algorithm both as an efficient means to effectively remove sub-views from a view query during evaluation, and as a viable optimization strategy for certain applications. The experiments also suggest that rewrite techniques for this may perform worse than the evaluation of the original query, and much worse than the tuple tagging approach.     

ScrewBender: smoothing piecewise helical motions.

Although a piecewise helical (polyscrew) motion is continuous, velocities are typically discontinuous at control poses when the motion switches between screws. We obtain a smooth motion through polyscrew 4-point, B-spline, or Jarek subdivision, which are trivial to implement and can be animated in real time. To overcome this problem, we use screw, or helical, motions to interpolate between poses. A screw is fully defined by the initial and final control poses. It combines a minimum-angle linear rotation around a fixed axis of direction S with a minimum-distance linear translation along S.     

Topologically exact evaluation of polyhedra defined in CSG with loose primitives

Floating point round-off causes erroneous and inconsistent decisions in geometric modelling algorithms. These errors lead to the generation of topologically invalid boundary models for CSG objects and significantly reduce the reliability of CAD applications. Previously known methods that guarantee topological consistency by relying on arbitrary precision rational arithmetic or on symbol-manipulation techniques are too expensive for practical purposes. This paper presents a new solution which takes as input a “fixed precision” regularized Boolean combination of linear half-spaces and produces a polyhedral boundary model that has the exact topology of the corresponding solid. Each half-space is represented by four homogeneous coefficients infixed precision format (L_a bits for the three direction cosines and L_d bits for the constant term, i.e. the distance from the origin). Exact answers to all topological and ordering questions are computed using a fixed length, 3 L_a+ L_d+ 2 bits, integer format. This new guaranteed tight limit on the number of bits necessary for performing intermediate calculations is achieved by expressing all of the topological decisions based on geometric computations in terms of the signs of 4 by 4 determinants of the input coefficients. The coordinates of intersection vertices are not required for making the correct topological decisions and hence vertices and lines are represented implicitly in terms of planes.     

GridLab—a grid application toolkit and testbed

In this paper we present the new project called GridLab which is funded by the European Commission under the Fifth Framework Programme. The GridLab project, made up of computer scientists, astrophysicists and other scientists from various application areas, will develop and implement the grid application toolkit (GAT) together with a set of services to enable easy and efficient use of Grid resources in a real and production grid environment. GAT will provide core, easy to use functionality through a carefully constructed set of generic higher level grid APIs through which an application will be able to call the grid services laying beneath in order to perform efficiently in the Grid environment using various, dramatically wild application scenarios.     

Particle Image Velocimetry (PIV) application in the measurement of indoor air distribution by an active chilled beam

We study the turbulent air flow behaviours of the attached plane jet discharged from an active chilled beam in a room using Particle Image Velocimetry (PIV). PIV is an innovative technology to study indoor air flow which began in the eighties of the last century for the measurement of whole air flow fields in fractions of a second. Here an experimental PIV system was built to reveal the structure of a turbulent attached plane jet in the entrainment process of the ambient air downstream from the jet slot. For the particle seeding in the PIV experiments, a few different particles were tested with the attached jet PIV application in a room. The results presented in this paper show the clear structure of the turbulent attached plane jet in the entrainment process after issuing from the chilled beam slot. The PIV visualisation results proved that the jet will attach to the ceiling and become fully turbulent a short distance downstream from the slot. The jet velocity vector fields show that the volume flow rate of the attached plane jet increases because of the large vortex mixing mechanism in the outer region of the jet. In three measurement cases, the air jet grows faster at a Reynolds number of 960 than at Reynolds numbers of 1320 and 1680. The calculated spreading angles in the cases with lower Reynolds numbers have similar values compared with the visualisation results.     

Simplifying interactive design of solid models: A hypertext approach

Conceptual design and editing parameterized models of 3D solids often requires user interactions with many types of entities and relations. In this paper, we present a concept for simplifying the design process. The simplification is based on three paradigms; integration of data structures and control structures, multiple view interface, and use of hypertext techniques for fast traversal and selective display of data. Data structures and control structures are integrated into uniform building blocks called cells. Cells define assemblies of CSG solids and can be grouped bottom-up into more complex cells or, alternatively, can be refined top-down during the design process. Efficient specification of complex cells and patterns is made possible through the use of automatic default values, multiple instantiation, built-in repetition, and recursion. A multiple-view interface enables the designer to view and edit both the cell parameters and the hierarchical structure of the model. The interface provides integrated textual, 2D graphical, and 3D direct-manipulation techniques for specifying primitive dimensions and relative transformations.     

Ordered Boolean List (OBL): reducing the footprint for evaluating Boolean expressions

An Expanded Boolean Expression (EBE) does not contain any XOR or EQUAL operators. The occurrence of each variable is a different literal. We provide a linear time algorithm that converts an EBE of n literals into a logically equivalent Ordered Boolean List (OBL) and show how to use the OBL to evaluate the EBE in n steps and O(log log n) space, if the values of the literals are each read once in the order prescribed by the OBL. (An evaluation workspace of 5 bits suffices for all EBEs of up to six billion literals.) The primary application is the SIMD architecture, where the same EBE is evaluated in parallel for different input vectors when rendering solid models on the GPU directly from their Constructive Solid Geometry (CSG) representation. We compare OBL to the Reduced Ordered Binary Decision Diagram (ROBDD) and suggest possible applications of OBL to logic verification and to circuit design.     

Sharpen&Bend: recovering curved sharp edges in triangle meshes produced by feature-insensitive sampling

Various acquisition, analysis, visualization, and compression approaches sample surfaces of 3D shapes in a uniform fashion without any attempt to align the samples with sharp edges or to adapt the sampling density to the surface curvature. Consequently, triangle meshes that interpolate these samples usually chamfer sharp features and exhibit a relatively large error in their vicinity. We present two new filters that improve the quality of these resampled models. EdgeSharpener restores the sharp edges by splitting the chamfer edges and forcing the new vertices to lie on intersections of planes extending the smooth surfaces incident upon these chamfers. Bender refines the resulting triangle mesh using an interpolating subdivision scheme that preserves the sharpness of the recovered sharp edges while bending their polyline approximations into smooth curves. A combined Sharpen&Bend postprocessing significantly reduces the error produced by feature-insensitive sampling processes. For example, we have observed that the mean-squared distortion introduced by the SwingWrapper remeshing-based compressor can often be reduced by 80 percent executing EdgeSharpener alone after decompression. For models with curved regions, this error may be further reduced by an additional 60 percent if we follow the EdgeSharpening phase by Bender.     

The mycobiomes and bacteriomes of sputum,saliva, and home dust

Respiratory microbiome is an understudied area of research compared to other microbiomes of the human body. The respiratory tract is exposed to an array of environmental pollutants, including microbes. Yet, we know very little about the relationship between environmental and respiratory microbiome. The primary aim of our study was to compare the mycobiomes and bacteriomes between three sample types from the same participants, including home dust, saliva, and sputum. Samples were collected from 40 adolescents in a longitudinal cohort. We analyzed the samples using 16s bacterial rDNA and ITS fungal rDNA gene sequencing, as well as quantitative PCR with universal fungal and bacterial primers. Results showed that home dust had the greatest alpha diversity between the three sample types for both bacteria and fungi. Dust had the highest total fungal load and the lowest total bacterial load. Sputum had greater bacterial diversity than saliva, but saliva had greater fungal diversity than sputum. The distribution of major bacterial phyla differed between all sample types. However, the distribution of major fungal classes differed only between sputum and saliva. Future research should examine the biological significance of the taxa found in each sample type based on microbial ecology and associations with health effects.