Schnyder Decompositions for Regular Plane Graphs and Application to Drawing

Schnyder woods are decompositions of simple triangulations into three edge-disjoint spanning trees crossing each other in a specific way. In this article, we generalize the definition of Schnyder woods to d-angulations (plane graphs with faces of degree d) for all d≥3. A Schnyder decomposition is a set of d spanning forests crossing each other in a specific way, and such that each internal edge is part of exactly d?2 of the spanning forests. We show that a Schnyder decomposition exists if and only if the girth of the d-angulation is d. As in the case of Schnyder woods (d=3), there are alternative formulations in terms of orientations (“fractional” orientations when d≥5) and in terms of corner-labellings. Moreover, the set of Schnyder decompositions of a fixed d-angulation of girth d has a natural structure of distributive lattice. We also study the dual of Schnyder decompositions which are defined on d-regular plane graphs of mincut d with a distinguished vertex v ^?: these are sets of d spanning trees rooted at v ^? crossing each other in a specific way and such that each edge not incident to v ^? is used by two trees in opposite directions. Additionally, for even values of d, we show that a subclass of Schnyder decompositions, which are called even, enjoy additional properties that yield a reduced formulation; in the case d=4, these correspond to well-studied structures on simple quadrangulations (2-orientations and partitions into 2 spanning trees). In the case d=4, we obtain straight-line and orthogonal planar drawing algorithms by using the dual of even Schnyder decompositions. For a 4-regular plane graph G of mincut 4 with a distinguished vertex v ^? and n?1 other vertices, our algorithms places the vertices of Gv ^? on a (n?2)×(n?2) grid according to a permutation pattern, and in the orthogonal drawing each of the 2n?4 edges of Gv ^? has exactly one bend. The vertex v ^? can be embedded at the cost of 3 additional rows and columns, and 8 additional bends. We also describe a further compaction step for the drawing algorithms and show that the obtained grid-size is strongly concentrated around 25n/32×25n/32 for a uniformly random instance with n vertices.     

Automated quality control of printed flasks and bottles

The paper faces the quality control problem for printed flasks, bottles and cans, used as containers for drugs and beverages. The control is mainly aimed at identifying ink spots and faded prints produced by a serigraphic process, but the approach is generically applicable to any kind of printing and printed cylindrical surface. Differently from the existing systems, based on the acquisition of good printed samples, the automatic control is based on the original digital image feeded to the printing system. Therefore, the control takes place directly between the ideal model and the result of a complex printing process including a number of distortion and noise sources. Problems related to image acquisition, reconstruction and alignment are investigated; a novel technique for image-model verification, based on adaptive local deformation, is also proposed and tested over a significant set of samples. A complete prototype system designed for such quality control is finally described and its operating capability on the field is discussed.     

An efficient multi-resolution framework for high quality interactive rendering of massive point clouds using multi-way kd-trees

We present an efficient technique for out-of-core multi-resolution construction and high quality interactive visualization of massive point clouds. Our approach introduces a novel hierarchical level of detail (LOD) organization based on multi-way kd-trees, which simplifies memory management and allows control over the LOD-tree height. The LOD tree, constructed bottom up using a fast high-quality point simplification method, is fully balanced and contains all uniformly sized nodes. To this end, we introduce and analyze three efficient point simplification approaches that yield a desired number of high-quality output points. For constant rendering performance, we propose an efficient rendering-on-a-budget method with asynchronous data loading, which delivers fully continuous high quality rendering through LOD geo-morphing and deferred blending. Our algorithm is incorporated in a full end-to-end rendering system, which supports both local rendering and cluster-parallel distributed rendering. The method is evaluated on complex models made of hundreds of millions of point samples.     

Calcium silicate cements obtained from rice hull ash: A comparative study

This work describes the utilization of rice hull as raw-material for the preparation of two calcium silicates namely, β-Ca_1.91Ba_0.04SiO₄ and β-Ca_1.96Ba_0.04SiO₄. The synthesis was completed at 800°C. Hydration rate and compressive strength of mortars prepared with the two calcium silicates were studied and compared to mortars prepared with commercial Portland cement. Hydration rates for both silicates, studied by thermogravimetric and FTIR analysis are very similar; after 60 days the hydration rates are around 42–43% and reaches 75% after 270 days. Compressive strength experiments were performed using test specimen prepared with commercial Portland cement as reference, and blends of Portland cement and the two calcium silicates, at replacement levels of 10 and 20%. Results have shown that after a 90 days curing period, the compressive strength of the reference and the blends containing 10% of each of the calcium silicates show the same behavior. Using a replacement level of 20% there is a small decrease in compressive strength. This behavior is attributed to the lower hydration rate of these calcium silicates.     

A prototype of very high resolution small animal PET scanner using silicon pad detectors

A very high-resolution small animal positron emission tomograph (PET), which can achieve sub-millimeter spatial resolution, is being developed using silicon pad detectors. The prototype PET for a single slice instrument consists of two 1 mm thick silicon pad detectors, each containing a 32×16 array of 1.4×1.4 mm pads readout with four VATAGP3 chips which have 128 channels low-noise self-triggering ASIC in each chip, coincidence units, a source turntable and tungsten slice collimator. The silicon detectors were located edgewise on opposite sides of a 4 cm field-of-view to maximize efficiency. Energy resolution is dominated by electronic noise, which is 0.98% (1.38 keV) FWHM at 140.5 keV. Coincidence timing resolution is 82.1 ns FWHM and coincidence efficiency was measured to be 1.04×10⁻³% from two silicon detectors with annihilation photons of ¹⁸F source. Image data were acquired and reconstructed using conventional 2-D filtered-back projection (FBP) and a maximum likelihood expectation maximization (ML-EM) method. Image resolution of approximately 1.45 mm FWHM is obtained from 1-D profile of 1.1 mm diameter ¹⁸F line source image. Even better resolution can be obtained with smaller detector element sizes. While many challenges remain in scaling up the instrument to useful efficiency including densely packed detectors and significantly improved timing resolution, performance of the test setup in terms of easily achieving sub-millimeter resolution is compelling.     

Business Group Affiliation and R&D

This paper analyzes whether belonging to a business group enhances firms' propensity for and intensity of R&D based on the greater opportunities to finance and co-ordinate R&D strategies and internalize knowledge spillovers. Compared with the existing literature, this paper has the following novelties: (a) it examines how the organization and diversification of business groups influence the R&D investment of affiliated firms; (b) it analyzes the role of R&D spillovers among affiliated firms; and (c) it distinguishes between propensity for and intensity of R&D. We find that less diversified groups are more likely to centralize R&D, while in more diversified groups firms are more likely to be autonomous. We find that controlled companies are more likely to benefit from knowledge spillovers than firms at the head of the group. Finally, we find that R&D autonomy is significantly associated with both a higher propensity for and intensity of R&D in controlled companies.