Redefining A in RGBA: Towards a Standard for Graphical 3D Printing

Advances in multimaterial 3D printing have the potential to reproduce various visual appearance attributes of an object in addition to its shape. Since many existing 3D file formats encode color and translucency by RGBA textures mapped to 3D shapes, RGBA information is particularly important for practical applications. In contrast to color (encoded by RGB), which is specified by the object's reflectance, selected viewing conditions and a standard observer, translucency (encoded by A) is neither linked to any measurable physical nor perceptual quantity. Thus, reproducing translucency encoded by A is open for interpretation. In this paper, we propose a rigorous definition for A suitable for use in graphical 3D printing, which is independent of the 3D printing hardware and software, and which links both optical material properties and perceptual uniformity for human observers. By deriving our definition from the absorption and scattering coefficients of virtual homogeneous reference materials with an isotropic phase function, we achieve two important properties. First, a simple adjustment of A is possible, which preserves the translucency appearance if an object is re-scaled for printing. Second, determining the value of A for a real (potentially non-homogeneous) material, can be achieved by minimizing a distance function between light transport measurements of this material and simulated measurements of the reference materials. Such measurements can be conducted by commercial spectrophotometers used in graphic arts. Finally, we conduct visual experiments employing the method of constant stimuli, and derive from them an embedding of A into a nearly perceptually uniform scale of translucency for the reference materials.Comment: 20 pages (incl. appendices), 20 figures. Version with higher quality images: https://cloud-ext.igd.fraunhofer.de/s/pAMH67XjstaNcrF (main article) and https://cloud-ext.igd.fraunhofer.de/s/4rR5bH3FMfNsS5q (appendix). Supplemental material including code: https://cloud-ext.igd.fraunhofer.de/s/9BrZaj5Uh5d0cOU/downloa

BSSRDF estimation from single images

We present a novel method to estimate an approximation of the reflectance characteristics of optically thick, homogeneous translucent materials using only a single photograph as input. First, we approximate the diffusion profile as a linear combination of piecewise constant functions, an approach that enables a linear system minimization and maximizes robustness in the presence of suboptimal input data inferred from the image. We then fit to a smoother monotonically decreasing model, ensuring continuity on its first derivative. We show the feasibility of our approach and validate it in controlled environments, comparing well against physical measurements from previous works. Next, we explore the performance of our method in uncontrolled scenarios, where neither lighting nor geometry are known. We show that these can be roughly approximated from the corresponding image by making two simple assumptions: that the object is lit by a distant light source and that it is globally convex, allowing us to capture the visual appearance of the photographed material. Compared with previous works, our technique offers an attractive balance between visual accuracy and ease of use, allowing its use in a wide range of scenarios including off-the-shelf, single images, thus extending the current repertoire of real-world data acquisition techniques

Point-Based Rendering for Homogeneous Participating Media with Refractive Boundaries

International audienceIllumination effects in translucent materials are a combination of several physical phenomena: refraction at the surface, absorption and scattering inside the material. Because refraction can focus light deep inside the material, where it will be scattered, practical illumination simulation inside translucent materials is difficult. In this paper, we present an a Point-Based Global Illumination method for light transport on homogeneous translucent materials with refractive boundaries. We start by placing light samples inside the translucent material and organizing them into a spatial hierarchy. At rendering, we gather light from these samples for each camera ray. We compute separately the sample contributions for single, double and multiple scattering, and add them. We present two implementations of our algorithm: an offline version for high-quality rendering and an interactive GPU implementation. The offline version provides significant speed-ups and reduced memory footprints compared to state-of-the-art algorithms, with no visible impact on quality. The GPU version yields interactive frame rates: 30 fps when moving the viewpoint, 25 fps when editing the light position or the material parameters

An engineering perspective of ceramics applied in dental reconstructions

The demands for dental materials continue to grow, driven by the desire to reach a better performance than currently achieved by the available materials. In the dental restorative ceramic field, the structures evolved from the metal-ceramic systems to highly translucent multilayered zirconia, aiming not only for tailored mechanical properties but also for the aesthetics to mimic natural teeth. Ceramics are widely used in prosthetic dentistry due to their attractive clinical properties, including high strength, biocompatibility, chemical stability, and a good combination of optical properties. Metal-ceramics type has always been the golden standard of dental reconstruction. However, this system lacks aesthetic aspects. For this reason, efforts are made to develop materials that met both the mechanical features necessary for the safe performance of the restoration as well as the aesthetic aspects, aiming for a beautiful smile. In this field, glass and high-strength core ceramics have been highly investigated for applications in dental restoration due to their excellent combination of mechanical properties and translucency. However, since these are recent materials when compared with the metal-ceramic system, many studies are still required to guarantee the quality and longevity of these systems. Therefore, a background on available dental materials properties is a starting point to provoke a discussion on the development of potential alternatives to rehabilitate lost hard and soft tissue structures with ceramic-based tooth and implant-supported reconstructions. This review aims to bring the most recent materials research of the two major categories of ceramic restorations: ceramic-metal system and all-ceramic restorations. The practical aspects are herein presented regarding the evolution and development of materials, technologies applications, strength, color, and aesthetics. A trend was observed to use high-strength core ceramics type due to their ability to be manufactured by CAD/CAM technology. In addition, the impacts of COVID-19 on the market of dental restorative ceramics are presented

Coral Disease and Health Workshop: Coral Histopathology II

The health and continued existence of coral reef ecosystems are threatened by an increasing array of environmental and anthropogenic impacts. Coral disease is one of the prominent causes of increased mortality among reefs globally, particularly in the Caribbean. Although over 40 different coral diseases and syndromes have been reported worldwide, only a few etiological agents have been confirmed; most pathogens remain unknown and the dynamics of disease transmission, pathogenicity and mortality are not understood. Causal relationships have been documented for only a few of the coral diseases, while new syndromes continue to emerge. Extensive field observations by coral biologists have provided substantial documentation of a plethora of new pathologies, but our understanding, however, has been limited to descriptions of gross lesions with names reflecting these observations (e.g., black band, white band, dark spot). To determine etiology, we must equip coral diseases scientists with basic biomedical knowledge and specialized training in areas such as histology, cell biology and pathology. Only through combining descriptive science with mechanistic science and employing the synthesis epizootiology provides will we be able to gain insight into causation and become equipped to handle the pending crisis. One of the critical challenges faced by coral disease researchers is to establish a framework to systematically study coral pathologies drawing from the field of diagnostic medicine and pathology and using generally accepted nomenclature. This process began in April 2004, with a workshop titled Coral Disease and Health Workshop: Developing Diagnostic Criteria co-convened by the Coral Disease and Health Consortium (CDHC), a working group organized under the auspices of the U.S. Coral Reef Task Force, and the International Registry for Coral Pathology (IRCP). The workshop was hosted by the U.S. Geological Survey, National Wildlife Health Center (NWHC) in Madison, Wisconsin and was focused on gross morphology and disease signs observed in the field. A resounding recommendation from the histopathologists participating in the workshop was the urgent need to develop diagnostic criteria that are suitable to move from gross observations to morphological diagnoses based on evaluation of microscopic anatomy. (PDF contains 92 pages

Trauma: How World War II Changed Cinematic Form

In the same way Paisà captured the Italian war experience by exploring a variety of vantage points, this essay analyses how the Second World War transformed film form by investigating the way three prominent directors changed how they made films. Directors Fred Zinnemann, Roberto Rossellini and Akira Kurosawa were confronted by the war in different ways. The most blatant distinction between them is the nation they film from, but even this holds multiplicity in its resonance. Not only did America, Italy and Japan have different relationships to the war, but they also had distinct approaches to cinema before the war. In the post-war narrative they represent the ‘liberators,’ ‘the liberated’ and ‘the conquered,’ but grapple directly and indirectly with the fallacies of these titles, as well as their consequences

Fracture Resistance of Compromised Endodontically Treated Teeth Restored with Bonded Post and Cores: An in Vitro Study

Statement of problem: It is unclear which post and core system performs best when bonded to severely compromised endodontically treated teeth. Purpose: The purpose of this study was to investigate the fracture resistance and mode of failure of severely compromised teeth restored with 3 different adhesively bonded post and core systems. Material and methods: Thirty extracted endodontically treated maxillary anterior teeth were randomly divided into 3 groups, CPC, gold cast post and core; TPC, titanium prefabricated post/composite resin core; and FPC, quartz fiber reinforced post/composite resin core. All posts were adhesively cemented. All cores resembled a central incisor preparation with no remaining tooth structure above the finish line. Cast gold crowns were fabricated and cemented adhesively. The specimens were aged with thermocycling and cyclic loading. Two specimens per group were randomly selected for micro-computed tomographic imaging before and after aging. Failure was induced with a universal testing machine. The mode of failure was characterized by the interface separation. Data were analyzed with 1-way ANOVA (α=.05) followed by post hoc tests (Bonferroni). Results: A statistically significant difference was found among the 3 groups (P=.002). CPC was significantly different than TPC (P=.008) or FPC (P=.003). The primary mode of failure for CPC and TPC was root fracture, and for FPC post debonding. Conclusions: Severely compromised endodontically treated teeth restored with bonded gold cast post and cores showed significantly higher fracture resistance

E-topia: Utopia after the Mediated Body

open access journalA custom-made media installation, diplorasis, will be used to explore the body in digital media. This mediated body attempts to re-think how the Deleuzian time-image is translated from its cinematic confinement to the space of new media. In diplorasis the digitized time-image becomes more directly incorporated with-in the bodily schema. Consequently, the thinking of the virtual and actual space of the body in diplorasis enables a questioning of bodily space-time, and particularly the relation between self and digitized self-image. It is thus crucial to re-frame how this digitized mediated body is distinct from a conventional notion of a metric and habitual space—one that is reinforced by, for example, the medium of linear perspective. The articulation of the mediated body will be used to in-form and extend Elizabeth Grosz’s paradoxical reading of embodiment and utopia, by revisiting the notions of utopia as eu-topic/ou-topic. The spatio-temporality of the topos must be re-considered before utopia. Foucault’s analogy of the mirror will then serve to superimpose the dual and slippery relations between utopia and the heterotopic. The digitized mediated body will thus seek to explore emerging ways by which to consider the utopic by conflating embodiment, time and space within an electronic topos. It is argued that as the sensing and cognitive body becomes increasingly pliable in relation to technological mediations, our very understanding of space-time is changing

Electrokinetic generation of iron-rich barriers in soils:realising the potential for nuclear site management and decommissioning

Following earlier field-scale pilot work on nuclear site materials in the late 2000s, there has recently been renewed research and industry interest in the application of electrokinetic technologies for nuclear site management and remediation in the UK. One relatively novel application of electrokinetics is the use of sacrificial steel electrodes (coupled with an in situ generated pH-Eh gradient in the treated material) to precipitate sub-surface iron-rich barriers for groundwater and/or leachate containment, which could be used to grout or contain contaminated fluids in the sub-surface on working nuclear sites or sites undergoing decommissioning. Here, we report previously unpublished data from two work programmes exploring the higher Technology Readiness Level (TRL) application of this electrokinetic iron-barrier approach to materials typical of those found in the subsurface of the Sellafield nuclear licensed site, UK. The first programme, funded by the UK National Nuclear Laboratory (NNL), assessed the electrokinetic generation of iron-rich barriers at metre + scale in simulated Sellafield materials, while the second programme, funded under the current UK TRANSCEND consortium project, examined electrokinetic iron-barrier formation at smaller (&lt;1 m) scale, but in real site materials. Both programmes indicate that iron-rich barriers can be conveniently and electrokinetically grown in different geometries over reasonable timescales (months) in realistic site subsurface materials (sands), in electrolytes similar to natural waters found in the environment. Voltage requirements are low (&lt;1 V cm−1) with energy and consumables costs of no more than single-digit or tens of US dollars at the metre-plus scale. Further work is needed however to assess the longevity of the iron precipitates forming the subsurface barrier, and to explore barrier generation at the geometries and scales required for (site specific) field application.</p