Fine Surface Details Research Articles

Accuracy of the implant impression obtained from different impression materials and techniques: review

With the predictable integration of implants, the emphasis is shifted towards precise prosthesis. Reproducing the intraoral relationship of implants through impression procedures is the first step in achieving an accurate, passively fitting prosthesis. The critical aspect is to record the three dimensional orientation of the implant as it is present intraorally, other than reproducing fine surface detail for successful implant prosthodontic treatment. The development of impression techniques to accurately record implant position has become more complicated and challenging. During the prosthetic phase of implant therapy there are numerous options available to the implantologist in relation to different impression techniques and materials available for impression making. It is critical to ensure that implant – prosthesis interface have passive fit and original position of the implant maintained in the master cast. There is no evidence supporting that one impression technique or material is better than the other. In the present article the various parameters affecting the accuracy of implant impression along with impression material and technique pertaining to different clinical situations is reviewed.

Perispore Morphology of Bolbitidoid Ferns (Dryopteridaceae) in Relation to Phylogeny

The perispores of 48 species of bolbitidoid ferns (Mickelia, Arthrobotrya, Bolbitis, Elaphoglossum, Lomagramma, and Teratophyllum) were studied with an SEM. The species studied were those used in a published phylogenetic analysis. For each species, five perispore characters were scored and optimized onto a published molecular tree. A loose, nonappressed perispore with broad folds optimizes as ancestral for the bolbitidoids. The only exception is Lomagramma, for which the perispore adheres tightly to the exospore—a character state that optimizes as a synapomorphy for that genus. In the bolbitidoids, thin crests evolved from broad folds seven times. The presence of thin crests in Mickelia optimizes as a synapomorphy for that genus. The presence of fine surface detail, here termed “microstructure,” was present in nearly all bolbitidoids and optimized as ancestral. Microstructure consisted of spicules, minute crests, and verrucae. The presence of verrucae optimizes as a synapomorphy for Lomagramma. The perispore of Bolbitis appendiculata is visually striking because it is highly reticulate throughout, a character that is autapomorphic in this analysis. No correspondence was observed between perispore characters and the transition series going from terrestrial (Bolbitis) to hemiepiphytic (Mickelia, Arthrobotrya, Lomagramma, and Teratophyllum) to epiphytic (Elaphoglossum) genera. The spore images of all species studied are publicly available at http://www.plantsystematics.org.

Accurate, Dense, and Robust Multiview Stereopsis

This paper proposes a novel algorithm for multiview stereopsis that outputs a dense set of small rectangular patches covering the surfaces visible in the images. Stereopsis is implemented as a match, expand, and filter procedure, starting from a sparse set of matched keypoints, and repeatedly expanding these before using visibility constraints to filter away false matches. The keys to the performance of the proposed algorithm are effective techniques for enforcing local photometric consistency and global visibility constraints. Simple but effective methods are also proposed to turn the resulting patch model into a mesh which can be further refined by an algorithm that enforces both photometric consistency and regularization constraints. The proposed approach automatically detects and discards outliers and obstacles and does not require any initialization in the form of a visual hull, a bounding box, or valid depth ranges. We have tested our algorithm on various data sets including objects with fine surface details, deep concavities, and thin structures, outdoor scenes observed from a restricted set of viewpoints, and "crowded" scenes where moving obstacles appear in front of a static structure of interest. A quantitative evaluation on the Middlebury benchmark shows that the proposed method outperforms all others submitted so far for four out of the six data sets.

Physics-inspired topology changes for thin fluid features

We propose a mesh-based surface tracking method for fluid animation that both preserves fine surface details and robustly adjusts the topology of the surface in the presence of arbitrarily thin features like sheets and strands. We replace traditional re-sampling methods with a convex hull method for connecting surface features during topological changes. This technique permits arbitrarily thin fluid features with minimal re-sampling errors by reusing points from the original surface. We further reduce re-sampling artifacts with a subdivision-based mesh-stitching algorithm, and we use a higher order interpolating subdivision scheme to determine the location of any newly-created vertices. The resulting algorithm efficiently produces detailed fluid surfaces with arbitrarily thin features while maintaining a consistent topology with the underlying fluid simulation.

Physics-inspired topology changes for thin fluid features

We propose a mesh-based surface tracking method for fluid animation that both preserves fine surface details and robustly adjusts the topology of the surface in the presence of arbitrarily thin features like sheets and strands. We replace traditional re-sampling methods with a convex hull method for connecting surface features during topological changes. This technique permits arbitrarily thin fluid features with minimal re-sampling errors by reusing points from the original surface. We further reduce re-sampling artifacts with a subdivision-based mesh-stitching algorithm, and we use a higher order interpolating subdivision scheme to determine the location of any newly-created vertices. The resulting algorithm efficiently produces detailed fluid surfaces with arbitrarily thin features while maintaining a consistent topology with the underlying fluid simulation.

Deforming meshes that split and merge

We present a method for accurately tracking the moving surface of deformable materials in a manner that gracefully handles topological changes. We employ a Lagrangian surface tracking method, and we use a triangle mesh for our surface representation so that fine features can be retained. We make topological changes to the mesh by first identifying merging or splitting events at a particular grid resolution, and then locally creating new pieces of the mesh in the affected cells using a standard isosurface creation method. We stitch the new, topologically simplified portion of the mesh to the rest of the mesh at the cell boundaries. Our method detects and treats topological events with an emphasis on the preservation of detailed features, while simultaneously simplifying those portions of the material that are not visible. Our surface tracker is not tied to a particular method for simulating deformable materials. In particular, we show results from two significantly different simulators: a Lagrangian FEM simulator with tetrahedral elements, and an Eulerian grid-based fluid simulator. Although our surface tracking method is generic, it is particularly well-suited for simulations that exhibit fine surface details and numerous topological events. Highlights of our results include merging of viscoplastic materials with complex geometry, a taffy-pulling animation with many fold and merge events, and stretching and slicing of stiff plastic material.

NBS: A new representation for point surfaces based on genetic clustering algorithm

In this paper, we propose a novel method that represents the highly complex point sets by clustering and reconstructing the points to normal-mapped B-spline surfaces (NBSs). The main idea is to construct elaborate normal maps on simple surfaces for the realistic rendering of complex point-set models. Based on this observation, we developed the coarse, NBSs to approximate the original point datasets with fine surface details. In our algorithm, a genetic clustering algorithm is proposed to automatically segment the point samples into several clusters according to their statistical properties, and a network of B-spline patches with normal maps are constructed according to the clustering results. In respect to signal processing, our algorithm decouples the original data into two collections: coarse geometry information and fine surface details. The multi-level B-spline surfaces are employed to describe the coarse geometry information, and the normal maps are constructed to capture the fine surface details. Our experimental results show that this representation facilitates the modeling and rendering of complex point sets without losing the visual qualities.

Carved Visual Hulls for Image-Based Modeling

This article presents a novel method for acquiring high-quality solid models of complex 3D shapes from multiple calibrated photographs. After the purely geometric constraints associated with the silhouettes found in each image have been used to construct a coarse surface approximation in the form of a visual hull, photoconsistency constraints are enforced in three consecutive steps: (1) the rims where the surface grazes the visual hull are first identified through dynamic programming; (2) with the rims now fixed, the visual hull is carved using graph cuts to globally optimize the photoconsistency of the surface and recover its main features; (3) an iterative (local) refinement step is finally used to recover fine surface details. The proposed approach has been implemented, and experiments with seven real data sets are presented, along with qualitative and quantitative comparisons with several state-of-the-art image-based-modeling algorithms.

Ultrastructural analysis of egg membrane abnormalities in post-ovulatory aged eggs

Microscopic analyses of mammalian gamete ultrastructure have provided among the most seminal insights into fertilization. Here we present a summary of ultrastructural studies of mammalian fertilization, together with a review of the effects of post-ovulatory aging in eggs, and our own results using scanning electron microscopy to examine the effects of post-ovulatory aging on the egg membrane topography. Our previous work detected two abnormalities in egg membrane function in aged eggs: aged eggs appeared to be less able to support sperm-egg membrane interaction, thus rendering the eggs less fertilizable, and aged eggs appear to have a reduced ability to prevent polyspermy at the level of the egg membrane, i.e., to establish a membrane block to polyspermy. In the work presented here, we tested the suitability of both environmental (ESEM) and low-vacuum (LVSEM) modes of the FEI Quanta 200 Environmental Scanning Electron Microscope to study mammalian gametes. While ESEM mode was not sufficient under the conditions we used to observe fine cell surface details, the LVSEM mode proved to be an excellent way to view egg membrane topography. Unfertilized aged eggs have an abnormally distended amicrovillar region over the meiotic spindle, and fertilized aged eggs had three different abnormalities detected, from reduced sperm-induced membrane remodeling to abnormal sperm-induced membrane remodeling and membrane blebbing. Combining these insights of egg membrane function and topography with others in the field of post-ovulatory aging, we have expanded insights into why fertilization at increased times after ovulation is associated with poor reproductive outcomes.

Guest Editors' Introduction: Special Section on Virtual Reality

IN this special section, we are pleased to present extended versions of four outstanding papers that were originally presented at the IEEE Virtual Reality 2006 Conference (VR 2006). IEEE Virtual Reality is the premier international conference on all aspects of virtual, augmented, and mixed reality. The conference program at VR 2006 consisted of nine sessions on the following topics: perception, simulation and visualization, applications of VR, distributed and collaborative systems, evaluation and user studies, augmented reality, tracking and projection displays, 3D interaction, and haptic and olfactory displays. For this special section, the international program committee selected four excellent papers from the 28 accepted research papers. As always, the choice was difficult since many of the other papers were also excellent candidates. The first paper, by Sean D. Young, Bernard D. Adelstein, and Stephen R. Ellis, received the best paper award at the VR 2006 for its high relevance to the field of virtual reality and simulation. The authors asked the question, “Does taking a motion sickness questionnaire make you motion sick?” Surprisingly, their research indicates that the answer is “yes!” The paper demonstrates that the administration of the questionnaire itself makes the participant aware that the virtual environment may produce motion sickness. The study shows that reports of motion sickness after immersion are much greater when both pre and posttest questionnaires are given than when only a posttest questionnaire is used. Since pretest questionnaires cannot simply be dropped in most cases, the authors suggest a number of ways to reduce this effect and discuss the implications of their observations. Augmented reality (AR) systems, which combine realworld and virtual imagery, present a unique set of perceptual issues for the user. The paper by J. Edward Swan II, Adam Jones, Eric Kolstad, Mark A. Livingston, and Harvey S. Smallman addresses such a problem: the accuracy of depth judgments made by users of optical see-through AR displays. These displays allow users to view the physical world directly, while overlaying virtual objects on the real scene. In many applications, it is critical that the user perceives the virtual objects to be in the correct position relative to the real world, but differences in depth perception between the virtual and real imagery may prevent this. Moreover, measuring the accuracy of users’ depth judgments is not trivial. The authors review previous work and methods used to address this problem, and then present two experiments of their own. The experiments use a perceptual matching technique and a blind walking technique to measure depth judgments, and reveal some interesting and surprising results. An emerging area of research in the VR community focuses on virtual humans. In the past, virtual human research has mainly addressed technical issues—making the virtual characters realistic in appearance, movements, emotions, behaviors, etc. With many of these problems at least partially solved, however, researchers can now begin to evaluate the social aspects of virtual humans; that is, how real users interact with virtual characters. Andrew B. Raij, Kyle Johnsen, Robert F. Dickerson, Benjamin C. Lok, Marc S. Cohen, Margaret Duerson, Rebecca Rainer Pauly, Amy O. Stevens, Peggy Wagner, and D. Scott Lint present a paper along these lines, describing two studies in which medical students interacted with a simulated patient. The simulated patient was either a real person acting the part of a patient, or a virtual human playing this role. The studies show that while the interpersonal interactions with the virtual human were similar to interactions with the real human in many ways, there were also subtle differences in the participants’ nonverbal behavior and attitude toward the virtual human. Such studies are critical for improving our understanding of how to use virtual characters in real-world VR applications. Believable haptic interaction with complex virtual objects is still a challenging research topic. Michael Ortega, Stephane Redon, and Sabine Coquillart have generalized the god-object method to enable high quality haptic interaction with rigid bodies consisting of tens of thousands of triangles. They suggest separating the computation of the motion of the six-degree-of-freedom god-object from the computation of the force applied to the user. The constraintbased force felt by the user can be computed within a few microseconds, which is necessary for the tactile simulation of fine surface details. The force is computed using a novel constraint-based quasistatic approach, which allows the suppression of force artifacts typically found in previous methods. The update of the pose of the rigid god-object is performed within a few milliseconds, which allows visual display at appropriate frame rates. 420 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS, VOL. 13, NO. 3, MAY/JUNE 2007

Agile manufacturing of a micro-embossed case by a two-step electromagnetic forming process

A very agile method, that relies solely on simple single-sided tooling, to form open-box-like enclosures with surface detail such as highly embossed surface features is demonstrated and analyzed. For example, this method may be used to fabricate personal electronics cases. The technique uses electromagnetic forces in a two-step process. In the first step a newly developed uniform pressure electromagnetic actuator is used to make a micro-embossed pre-form that can contain very fine surface detail in the part by micro-embossing features in the forming die. This blank is then trimmed. In the second major step electromagnetic flanging is used to give greater depth and steeper walls to the case. Both electromagnetic operations use one-sided tooling and very light equipment. In principle the tooling needed for this type of process can be put to use within days or hours of finalizing the component design and precise tooling tolerances or precise alignment are not required. This work shows the essential feasibility of this approach to manufacturing either small or large lots of components.

GPU-Based Multiresolution Deformation using Approximate Normal Field Reconstruction

Multiresolution shape editing performs global deformations while preserving fine surface details by modifying a smooth base surface and reconstructing the modified detailed surface as a normal disp...

Radar stereo- and interferometry-derived digital elevation models: comparison and combination using Radarsat and ERS-2 imagery

In this experiment, we derive and compare radar stereo and interferometric digital elevation models (DEMs) of a study site in Djibouti, East Africa. A Radarsat stereo pair, as well as Radarsat and ERS-2 interferometric data, comprise the test images. The primary objective of the study was to analyse and compare the results obtained by the two techniques and explore possible synergisms between them. We find that in regions of high coherence, the DEMs produced by interferometry are of much better quality than the stereo result. However, the corresponding error histograms also show some pronounced errors due to decorrelation and phase-unwrapping problems on forested mountain slopes. On the other hand, the more robust stereo reconstruction, with an error standard deviation of 45 m, is able to capture the general terrain shape, although finer surface details are lost. In the second part of our experiment, we demonstrate that merging the stereoscopic and interferometric DEMs by applying a user-defined weighting function to a filtered coherence map can significantly improve the accuracy of the computed elevation maps.

Fast Normal Map Generation for Simplified Meshes

Approximating detailed models with coarse, normal mapped meshes is a very efficient method for real-time rendering of complex objects with fine surface detail. In this paper, we present a new and fast normal map construction algorithm. We scan-convert each triangle of the simplified model, which results in a regularly spaced point set on the surface of each triangle. The original model and all these point samples of the simplified model are rendered from uniformly distributed camera positions. The actual normal map is created by computing the corresponding normals for the point sets. For each point, the normal of the closest point from the high resolution mesh over the set of all camera positions is chosen. Our approach works for general triangle meshes and exploits fully common graphics rendering hardware. Normal map construction times are generally in the range of only a few seconds even for large models. We render our normal-mapped meshes in real-time with a slightly modified version of the standard bump-mapping algorithm. In order to evaluate the approximation error, we investigate the distance and normal errors for normal-mapped meshes. Our investigation of the approximation errors shows that using more than 12 viewpoints does not result in a further improvement in the normal maps for our test cases.

Atomic force microscopy (AFM) study of poly(ethylene terephthalate‐co‐4,4′‐bibenzoate): A polymer of intermediate structure

AbstractAn atomic force microscope (AFM) operating in both tapping and contact modes was used to study the surface topography and the molecular organization of a molded flexural test bar prepared from a poly(ethylene terephthalate‐co‐4,4'‐bibenzoate) copolymer containing a terephthalate:4,4′‐bibenzoate molar ratio of 45:55 (PETBB‐55). Micrometer‐scale (15 × 15 μm) contact‐mode AFM images revealed that the PETBB surface contains a deep indentation that forms trenches that extend over the entire surface examined. In addition, the surface may appear as an overlay of fibrils having different orientation. At greater magnification (1 × 1 μm), it is possible to observe the existence of micropores. These results were also observed in images obtained while operating the AFM in the tapping mode. The side of the part is more homogeneous and ordered than is its top surface. It has the appearance of a stacked lamellar structure in which missing fibrils can originate cracks ∼0.5‐μm wide. Fine surface details were observed in nanometer‐scale images, showing the presence of chains of white spots that could represent molecules or a cluster of molecules. These chains can form domains in which they are almost parallel to each other and have a preferred orientation; this structural organization was generated without any orientation other than that produced during a mold flow. Alternatively, chain lengths are interrupted and white spots form, distorted by easily recognizable hexagonal arrangements. The degree of lamellar order observed in the side of the bar, the area of greatest flow orientation in the part, was not been observed for the PET homopolymer in the past and bears some resemblance to previously imaged liquid crystalline polyester (LCP) structures. Combined with some previously reported LCP‐like mechanical properties, we propose that this PETBB copolymer is, in fact, a “frustrated LCP,” one that with some driving force could be converted to liquid crystallinity. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 2616–2623, 2001

In situ production of iron based surface composite

To make paper from wood raw materials, wood chips must be processed to turn them into individual fibers or fiber bundles. In mechanical pulping this is accomplished by introducing energy into the wood chip or fiber bundles as the wood chips are passed between a set of counter-rotating plates; these are up to 1.5 m in diameter and operate with a plate clearance on the order of 0.1 mm and plate peripheral velocity of 130 m s−1. The working life of refiner plates is sufficient for the paper industry; however, the deterioration of the fine surface detail of the plates reduces refining efficiency. This research was focused on the behavior of the plate materials in the refining environment, with the emphasis on understanding the deterioration behavior of the refiner plates. It combined wear analysis of normally used plates obtained from the paper mills, of plates used in designed trials in paper mills, and evaluation of plate materials in a broad range of laboratory tests. The laboratory tests were selected and suitably modified to reproduce phenomena observed on worn plates. The laboratory tests included cavitation erosion, dry-sand-rubber-wheel abrasion, and particulate erosion with high pressure water or steam as carrier fluids. Plate materials tested included 25Cr and 20Cr2Mo1Cu (both wt.%) high chromium white cast irons, Ni-hard white cast irons, and 440C and 17-4 PH stainless steels. Plate failure analysis revealed a variety of wear processes which varied with plate location and plate running time in the refiner. Cavitation erosion was clearly identified in the center of the plates where water was definitely present. Damage patterns with the same appearance as cavitation erosion were observed along plate bar edges near the periphery of the refiner plates where water is not thought to exist in a liquid form. Cavitation erosion tests in the laboratory duplicated the observed phenomena on the bar edges. Abrasion tests and erosion tests lacked such a close correlation to the observed phenomena. For all observed wear phenomena the role of the microstructure appears to be more important than the bulk hardness and for pitting-type damage such as that produced by cavitation erosion, the microstructure has a major influence on the wear process.

Advantages of stereo imaging of metallic surfaces with low voltage backscattered electrons in a field emission scanning electron microscope

High emission current backscattered electron (HC-BSE) stereo imaging at low accelerating voltages (</= 5 keV) using a field emission scanning electron microscope was used to display surface structure detail. Samples of titanium with high degrees of surface roughness, for potential medical implant applications, were imaged using the HC-BSE technique at two stage tilts of + 3 degrees and - 3 degrees out of the initial position. A digital stereo image was produced and qualitative height, depth and orientation information on the surface structures was observed. HC-BSE and secondary electron (SE) images were collected over a range of accelerating voltages. The low voltage SE and HC-BSE stereo images exhibited enhanced surface detail and contrast in comparison to high voltage (> 10 keV) BSE or SE stereo images. The low voltage HC-BSE stereo images displayed similar surface detail to the low voltage SE images, although they showed more contrast and directional sensitivity on surface structures. At or below 5 keV, only structures a very short distance into the metallic surface were observed. At higher accelerating voltages a greater appearance of depth could be seen but there was less information on the fine surface detail and its angular orientation. The combined technique of HC-BSE imaging and stereo imaging should be useful for detailed studies on material surfaces and for biological samples with greater contrast and directional sensitivity than can be obtained with current SE or BSE detection modes.

Tests of laser cleaning on archeological metal artefacts

Previously reported experiences on laser cleaning of metal surfaces of artworks such as statues and decorations altered by atmospheric pollution demonstrated the potential advantages of this technique. Here we present a study on the use of laser cleaning on excavated metal objects that typically show alterations and corrosion processes quite different with respect to exposed metal artefacts. Tests were performed on a selection of archaeological samples, such as coins, plates, clamps and ornaments collected from Italian sites. Metals considered in this study are bronze, copper, silver and lead. Different laser systems and different irradiation conditions were employed and compared. The results, evaluated by metallurgic diagnostics and objective observations, indicated that the laser cleaning process was selective and highly precise, allowing the preservation of fine surface details.

Three-dimensional vision based on a combination of gray-code and phase-shift light projection: analysis and compensation of the systematic errors

A combination of phase-shift with gray-code light projection into a three-dimensional vision system based on the projection of structured light is presented. The gray-code method is exploited to detect without ambiguity even marked surface discontinuities, whereas the phase-shift technique allows the measurement of fine surface details. The system shows excellent linearity. An overall mean value of the measurement error equal to 40 microm, with a variability of approximately +/-35 microm, corresponding to 0.06% of full scale, has been estimated. The implementation of the technique is discussed, the analysis of the systematic errors is presented in detail, and the calibration procedure designed to determine the optimal setting of the measurement parameters is illustrated.

Deterioration behavior of thermomechanical refiner plates

To make paper from wood raw materials, wood chips must be processed to turn them into individual fibers or fiber bundles. In mechanical pulping this is accomplished by introducing energy into the wood chip or fiber bundles as the wood chips are passed between a set of counter-rotating plates; these are up to 1.5 m in diameter and operate with a plate clearance on the order of 0.1 mm and plate peripheral velocity of 130 m s −1. The working life of refiner plates is sufficient for the paper industry; however, the deterioration of the fine surface detail of the plates reduces refining efficiency. This research was focused on the behavior of the plate materials in the refining environment, with the emphasis on understanding the deterioration behavior of the refiner plates. It combined wear analysis of normally used plates obtained from the paper mills, of plates used in designed trials in paper mills, and evaluation of plate materials in a broad range of laboratory tests. The laboratory tests were selected and suitably modified to reproduce phenomena observed on worn plates. The laboratory tests included cavitation erosion, dry-sand-rubber-wheel abrasion, and particulate erosion with high pressure water or steam as carrier fluids. Plate materials tested included 25Cr and 20Cr2Mo1Cu (both wt.%) high chromium white cast irons, Ni-hard white cast irons, and 440C and 17-4 PH stainless steels. Plate failure analysis revealed a variety of wear processes which varied with plate location and plate running time in the refiner. Cavitation erosion was clearly identified in the center of the plates where water was definitely present. Damage patterns with the same appearance as cavitation erosion were observed along plate bar edges near the periphery of the refiner plates where water is not thought to exist in a liquid form. Cavitation erosion tests in the laboratory duplicated the observed phenomena on the bar edges. Abrasion tests and erosion tests lacked such a close correlation to the observed phenomena. For all observed wear phenomena the role of the microstructure appears to be more important than the bulk hardness and for pitting-type damage such as that produced by cavitation erosion, the microstructure has a major influence on the wear process.