Complex Surface Geometry Research Articles

Individual IOL Surface Topography Analysis by the WaveMaster Reflex UV

Purpose. In order to establish inspection routines for individual intraocular lenses (IOLs), their surfaces have to be measured separately. Currently available measurement devices lack this functionality. The purpose of this study is to evaluate a new topography measurement device based on wavefront analysis for measuring individual regular and freeform IOL surfaces, the “WaveMaster Reflex UV” (Trioptics, Wedel, Germany). Methods. Measurements were performed on IOLs with increasingly complex surface geometries: spherical surfaces, surfaces modelled by higher-order Zernike terms, and freeform surfaces from biometrical patient data. Two independent parameters were measured: the sample's radius of curvature (ROC) and its residual (difference of sample topography and its best-fit sphere). We used a quantitative analysis method by calculating the residuals' root-mean-square (RMS) and peak-to-Valley (P2V) values. Results. The sample's best-fit ROC differences increased with the sample's complexity. The sample's differences of RMS values were 80 nm for spherical surfaces, 97 nm for higher-order samples, and 21 nm for freeform surfaces. Graphical representations of both measurement and design topographies were recorded and compared. Conclusion. The measurements of spherical surfaces expectedly resulted in better values than those of freeform surfaces. Overall, the wavefront analysing method proves to be an effective method for evaluating individual IOL surfaces.

Mapping the distribution of ferric iron minerals on a vertical mine face using derivative analysis of hyperspectral imagery (430–970 nm)

Hyperspectral imagery is used to map the distribution of iron and separate iron ore from shale (a waste product) on a vertical mine face in an open-pit mine in the Pilbara, Western Australia. Vertical mine faces have complex surface geometries which cause large spatial variations in the amount of incident and reflected light. Methods used to analyse imagery must minimise these effects whilst preserving any spectral variations between rock types and minerals. Derivative analysis of spectra to the 1st-, 2nd- and 4th-order is used to do this. To quantify the relative amounts and distribution of iron, the derivative spectrum is integrated across the visible and near infrared spectral range (430–970nm) and over those wavelength regions containing individual peaks and troughs associated with specific iron absorption features. As a test of this methodology, results from laboratory spectra acquired from representative rock samples were compared with total amounts of iron minerals from X-ray diffraction (XRD) analysis. Relationships between derivatives integrated over the visible near-infrared range and total amounts (% weight) of iron minerals were strongest for the 4th- and 2nd-derivative (R2=0.77 and 0.74, respectively) and weakest for the 1st-derivative (R2=0.56). Integrated values of individual peaks and troughs showed moderate to strong relationships in 2nd- (R2=0.68–0.78) and 4th-derivative (R2=0.49–0.78) spectra. The weakest relationships were found for peaks or troughs towards longer wavelengths.The same derivative methods were then applied to imagery to quantify relative amounts of iron minerals on a mine face. Before analyses, predictions were made about the relative abundances of iron in the different geological zones on the mine face, as mapped from field surveys. Integration of the whole spectral curve (430–970nm) from the 2nd- and 4th-derivative gave results which were entirely consistent with predictions. Conversely, integration of the 1st-derivative gave results that did not fit with predictions nor distinguish between zones with very large and small amounts of iron oxide.Classified maps of ore and shale were created using a simple level-slice of the 1st-derivative reflectance at 702, 765 and 809nm. Pixels classified as shale showed a similar distribution to kaolinite (an indicator of shales in the region), as mapped by the depth of the diagnostic kaolinite absorption feature at 2196nm. Standard statistical measures of classification performance (accuracy, precision, recall and the Kappa coefficient of agreement) indicated that nearly all of the pixels were classified correctly using 1st-derivative reflectance at 765 and 809nm. These results indicate that data from the VNIR (430–970nm) can be used to quantify, without a priori knowledge, the total amount of iron minerals and to distinguish ore from shale on vertical mine faces.

Freeform surface filtering using the lifting wavelet transform

Texture measurement for simple geometric surfaces is well established. Many surface filtration techniques using Fourier, Gaussian, wavelets, etc., have been proposed over the past decades. These filtration techniques cannot be applied to today's complex freeform surfaces, which have non-Euclidean geometries in nature, without distortion of the results. Introducing the lifting scheme opens the opportunity to extend the wavelet analysis to include irregular complex surface geometries. In this paper, a method of filtering those complex freeform surfaces presented by triangular meshes based on the lifting wavelet has been proposed. The proposed algorithm generalises the traditional lifting scheme to any freeform surface represented by any type of triangular mesh; regular, semi-regular or irregular mesh. This technique consists of five major stages; split, predict, update, simplify (down-sampling) and merge (up-sampling). All of these techniques are discussed and explained in the paper. Results and discussion of the application of this method to simulated and measured data are presented.

Statistical process monitoring approach for high-density point clouds

Statistical process control (SPC) methods have been extensively applied to monitor the quality performance of manufacturing processes to quickly detect and correct out-of-control conditions. As sensor and measurement technologies advance, there is a continual need to adapt and refine SPC methods to effectively and efficiently use these new data-sets. One of the most state-of-the-art dimensional measurement technologies currently being implemented in industry is the 3D laser scanner, which rapidly provides millions of data points to represent an entire manufactured part's surface. Consequently, this data has a great potential to detect unexpected faults, i.e., faults that are not captured by measuring a small number of predefined dimensions. However, in order for this potential to be realized, SPC methods capable of handling these large data-sets need to be developed. This paper presents an approach to performing SPC using point clouds obtained through a 3D laser scanner. The proposed approach transforms high-dimensional point clouds into linear profiles through the use of Q---Q plots, which can be monitored by well established profile monitoring techniques. In this paper point clouds are simulated to determine the performance of the proposed approach under varying fault scenarios. In addition, experimental studies were performed to determine the effectiveness of the proposed approach using actual point cloud data. The results of these experiments show that the proposed approach can significantly improve the monitoring capabilities for manufacturing parts that are characterized by complex surface geometries.

Creating Superhydrophobic Polycarbonate Fiber Network from Hydrophilic Polycarbonate through Electrospinning

ABSTRACTConsiderable research has focused on the formation of superhydrophobic surfaces utilizing both the chemical composition of surfaces and geometric effects. In this study, a superhydrophobic polycarbonate (PC) network surface was produced from hydrophilic polycarbonate through electrospinning process. Complex surface geometries often related to material roughness is used to evaluate the wetting behavior of electrospun polycarbonate fiber network. The surface properties of electrospun polycarbonate fibers are therefore examined with the potential to exploit the fibers through enhancing hydrophobic behavior. Characterization and analysis of PC electrospun fiber and PC film surfaces were carried out to compare surface roughness with wetting contact angle. Analytical models are used to describe hydrophobicity in terms of roughness.

(Invited) ALD of Thin Films for Lithium-Ion Batteries

Atomic layer deposition (ALD) technique is a thin film deposition method that provides highly conformal films on 3D structured supports, including powder materials. The technique relies on sequential self-limiting gas-to-surface reactions which enable control of thin film depositions even down to the atomic level on complex surface geometries. Even if ALD technique has been used in the semiconductor industry in production scale for several years now, there are rather few reports on ALD of battery materials. However, the recent development in processes for lithium containing films clearly opens up new possibilities. Promising applications of ALD include 3D structured all-solid-state batteries and surface modification of electrode powders. The present paper presents an overview of the present status in application of ALD in the field of lithium ion batteries.

Mechanical properties of thermally sprayed Fe based coatings

An additional coating against wear or corrosion on component parts is required for many applications. These coatings protect the substrate material against external influences, thus increasing the economic lifetime of the component. Coating processes such as build-up welding and thermal spraying are well established and commonly used. The thermal spray process, in particular, permits deposition of metals, ceramics, or cermets materials to produce near net shape coatings on complex surface geometries. However, commonly used coating materials suffer from high raw material costs, thus decreasing the cost effectiveness of the coating process. Fe based materials are low priced and possess noteworthy mechanical properties; they thus provide the possibility of substituting the expensive Ni and Co based materials commonly used for thermal spray processes. In this work, 2 mm thick high velocity oxyfuel sprayed Fe based coatings in the as sprayed and thermally sprayed and hot isostatic pressed condition were investigated with respect to their mechanical and wear properties. Additionally, the fracture surface was investigated by scanning electron microscopy to characterise the fracture behaviour. It could be demonstrated that the substrate and the heat treatment have the greatest impact on the shear strength of thermally sprayed cold work tool steel. It is shown that the substrate materials as well as the heat treatment are promoting diffusion processes across the interface between the coating and the substrate. Hence, a material integrated bond is formed. The microstructures of the thermally sprayed coatings become more important regarding the mechanisms of failure of the four point bending tests. The material strength is influenced by quenching and tempering and the specimen deflection is influenced by diffusion reactions induced by hot isostatic pressing treatment. The thermally sprayed coatings in the as sprayed condition feature the highest wear resistance due to their hardness.

Measurements in an Outdoor Facility and Numerical Simulation of the Radar Cross Section of Targets at 10 GHz

This paper presents preliminary data from an ongoing study on the radar cross section (RCS) of targets with simple and complex surface geometries (a flat square plate, a 90° dihedral corner reflector and a retired air-to-air missile). Measurements and computer simulations of these metallic targets were carried out at 10 GHz and also when the surfaces of the targets were completely coated with a radar absorbing material (RAM), consisting of flexible sheets of carbonyl iron dispersed in a silicone rubber matrix. Experimental measurements were obtained in an outdoor facility, and computer simulations were performed using a commercial software package. The main objective of this study was to compare results in order to highlight some of the issues related to the determination of the RCS of an actual target. Additionally, a Brazilian research institute has demonstrated the capability to produce and characterize materials related to the main aspects of RCS research, namely, measurement, simulation, and production of RAM. This paper introduces the reader to the research being carried out in this area at the Materials Division in the Instituto de Aeronautica e Espaco.

Creating biomimetic polymeric surfaces by photochemical attachment and patterning of dextran.

In this work, we report the preparation of photoactive dextran and demonstrate its utility by photochemically attaching it onto various polymeric substrates. The attachment of homogeneous and patterned dextran films was performed on polyurethane and polystyrene, with detailed analysis of surface morphology, swelling behavior, and the protein resistance of these substrates. The described photoactive dextran and attachment procedure is applicable to a wide variety of substrates while accommodating surfaces with complex surface geometries. Dextran with azide content between 22 and 0.3 wt % was produced by esterification with p-azidobenzoic acid. Dextran (1.2 wt % azide) was photografted onto plasma oxidized polyurethane and polystyrene and displayed thicknesses of 5 +/- 3 and 7 +/- 3 nm, respectively. The patterned dextran on oxidized polyurethane was patchy with a nominal height difference between dextranized and nondextranized regions. The azidated dextran on oxidized polystyrene exhibited a distinct step in height. In the presence of phosphate buffered saline (PBS), the dextranized regions became smoother and more uniform without affecting the height difference at the oxidized polyurethane boundary. However, the dextranized regions on oxidized polyurethane were observed to swell by a factor of 3 relative to the dried thickness. These dissimilarities were attributed to hydrogen bonding between the dextran and oxidized polyurethane and were confirmed by the photoimmobiliization in the presence of LiCl. The resulting surface was the smoothest of all the azidated dextran samples (R(rms) = 1 +/- 0.3 nm) and swelled up to 2 times its dried thickness in PBS. The antifouling properties of dextran functionalized surfaces were verified by the selective adsorption of FITC-labeled human albumin only on the nondextranized regions of the patterned polyurethane and polystyrene substrates.

Evaluating shallow water assumptions in dam-break flows

It has become common practice to model dam-break floods with shallow water equations. Shocks in the flow can be reproduced in the form of discontinuities in the weak solution. Strictly speaking, the underlying assumptions behind the shallow water equations, such as gradual variation, small vertical velocity component and hydrostatic pressure distribution, are invalid close to the shocks. In an attempt to examine the accuracies/inaccuracies of the shallow water equations in modelling fast-varying flows, solutions to the shallow water equations are compared with laboratory measurements and solutions to the Navier–Stokes equations. The shallow water equations' predictions are made by using an extensively verified total variation diminishing-MacCormack scheme, while the Navier–Stokes equations are solved by using a smoothed particle hydrodynamics model. The propagations of the flood wave due to the entire and partial dam-breaks are simulated. The smoothed particle hydrodynamics model has shown the capability of reproducing complex flows involving highly distorted free surfaces. Apart from being unable to simulate the complex water surface geometry, the shallow water equations model tends to overestimate the propagation speed and steepness of waves when the water column is slender or when multiple waves interfere with each other.

Capture and fusion of 3d surface texture

Image fusion is a process that multiple images of a scene are combined to form a single image. The aim of image fusion is to preserve the full content and retain important features of each original image. In this paper, we propose a novel approach based on wavelet transform to capture and fusion of real-world rough surface textures, which are commonly used in multimedia applications and referred to as3D surface texture. These textures are different from 2D textures as their appearances can vary dramatically with different illumination conditions due to complex surface geometry and reflectance properties. In our approach, we first extract gradient/height and albedo maps from sample 3D surface texture images as their representation. Then we measure saliency of wavelet coefficients of these 3D surface texture representations. The saliency values reflect the meaningful content of the wavelet coefficients and are consistent with human visual perception. Finally we fuse the gradient/height and albedo maps based on the measured saliency values. This novel scheme aims to preserve the original texture patterns together with geometry and reflectance characteristics from input images. Experimental results show that the proposed approach can not only capture and fuse 3D surface texture under arbitrary illumination directions, but also has the ability to retain the surface geometry properties and preserve perceptual features in the original images.

Noise prediction for industrial facilities.

The methodologies used to predict the noise caused by industrial facilities are presented and ranked. There are a lot more scientifically based methods that use certain approximations to solve or apply the wave equation in a layered atmosphere. These methods are usable to predict even meteorological influences with long distance propagation but can hardly be used with complex source and surface geometries for receivers nearby. This latter case is the preferred application of engineering models using simple geometric ray approximations. The techniques to use it with complex and extended sources are presented. This includes the use of parametrized source description for technical sources such as motors, gears, pipes, and cooling towers and numerical aspects such as projection or angle scanning. It is shown how an intelligent software technique like the “object tree” supports the generation of variants of a plant including different steps of noise reduction measures.

Continuous spectrum analysis of roughness-induced transient growth

Continuous spectrum amplitude distributions are calculated for transiently growing roughness-induced perturbations in a flat-plate boundary layer. A direct method is employed when the complete flow is known via direct numerical simulation. A new method using regularizing functionals is developed for calculating the distributions when only partial experimental data are available. These amplitude distributions provide a way of rigorously characterizing the boundary layer receptivity to surface roughness. Contrasting the present results to optimal theory results conclusively demonstrates that roughness-induced disturbances cannot be described by optimal disturbance calculations. The continuous spectrum analysis demonstrates the linearity of the perturbations by correctly reproducing the flow evolution over the measurement domain. Extracting the continuous spectrum amplitudes using the partial data technique reveals the underlying vortex behavior that creates transient growth. The method described is amenable to future work with realistic distributed roughness and complex surface geometries.

HWCVD of polymers: Commercialization and scale-up

GVD Corporation specializes in process development and equipment design for the production of ultra-thin polymer coatings using hot wire chemical vapor deposition (HWCVD, also known as initiated chemical vapor deposition, iCVD). HWCVD allows many coating compositions to be produced, including fluorocarbon and silicone polymers, copolymers, and vinyl hydrocarbon polymers. It is especially valuable for creating ultra-thin layers of insoluble, infusible polymers which are hard to process by conventional means, such as polytetrafluoroethylene (PTFE, Teflon ®). HWCVD PTFE coatings are chemically robust, comprised of essentially 100% CF 2, resistant to solvents, conformal to complex surface geometry, and have excellent adhesion to a wide range of substrates. Since the part to be coated remains at room temperature, fragile materials like plastics and fabrics can be coated with ease. GVD has focused on scale-up of the process equipment and has developed several standard coating systems, which will be discussed in this paper. These include laboratory-scale batch coating systems, a medium sized production batch coating system, a large scale custom batch coater, and a pilot scale roll-to-roll web coater. All of GVD's systems are complete with fully automated, computer based control systems and include options for effluent monitors and an exhaust scrubber.

A variational principle for dynamic contact with large deformation

Dynamic contact between a deformable body with either large or small deformation and a rigid obstacle can be modeled with Signorini contact condition stated in terms of the normal component of the displacement – as long as the relative positions are clearly defined. The geometrical relation, however, is unpredictable when large motion or large deformation and complex surface geometry are involved. The use of normal velocity is more suitable. A variational inequality is proposed for the dynamic contact problem. The penalty method is introduced and implemented in explicit finite element software. Numerical examples are presented to demonstrate the robustness of the algorithm.

Wetting and Dewetting of Complex Surface Geometries

Surfaces exhibiting complex topographies, such as those encountered in biology, give rise to an enormously rich variety of interfacial morphologies of a liquid to which they are exposed. In the present article, we elaborate on some basic mechanisms involved in the statics and dynamics of such morphologies, focusing on a few simple paradigm topographies. We demonstrate that different liquid interface morphologies on the same sample frequently coexist. To exemplify the impact of the dynamics on the final droplet morphology, we discuss the shape instability of filamentous liquid structures in wedge geometries. We finally show that some side effects that may dominate on a larger scale, such as contact line pinning and contact angle hysteresis, seem to play a minor role on the microscopic scale under study. This establishes the validity of simple theoretical concepts of wetting as a starting point for describing liquids at substrate surfaces of high complexity.

Finite element modelling of steelpan acoustics

In this paper the finite element method is used to model acoustic vibrations of steelpan shells. The steelpan surface is characterized as a three-dimensional compound shell, comprising notes (surfaces with reverse curvature) on a concave ellipsoidal surface attached to a cylindrical shell (the skirt). In this model note and inter-note surfaces are defined by geometric parameters which can be varied to define complex surface geometries. The geometric mesh model is used develop tenor, cello and bass steelpans instruments and a 3D finite element shell vibration algorithm is used to demonstrate their vibration characteristics. Modes shapes and frequencies of the composite shell structures are computed for typical configurations of note and skirt geometry. The model demonstrates that there exist many composite natural modes of a playing surface involving the interaction between two or more notes. In addition, it is found that the frequency range of mode shapes associated primarily within skirt vibration overlaps with the musical range of the notes underscoring the potential for “skirt-note” coupling. The degree of frequency overlap was found to be largely dependent on skirt length and configuration.

Numerical modeling of stress-permeability coupling in rough fractures

A numerical model is described for coupled flow and mechanical deformation in fractured rock. The mechanical response of rock joints to changes in hydraulic pressure is strongly influenced by the geometric characteristics of the joint surfaces. The concept of this work is to combine straightforward finite element solutions with complex and realistic fracture surface geometry in order to reproduce the non-linear stress-deformation-permeability coupling that is commonly observed in fractures. Building on the numerous studies that have expanded the understanding of the key parameters needed to describe natural rough-walled fractures, new methods have been developed to generate a finite element mesh representing discrete fractures with realistic rough surface geometries embedded in a rock matrix. The finite element code GeoSys/Rockflow was then used to simulate the coupled effects of hydraulic stress, mechanical stress, and surface geometry on the evolving permeability of a single discrete fracture. The modeling concept was experimentally verified against examples from the literature. Modeling results were also compared to a simple interpenetration model.

Healing of surgically created circumferential gap around Nano‐coating surface dental implants in dogs

AbstractThe development and expanded use of dental implants has been remarkably increased. The implant stability and osseointegration are important factors in the success of treatment. Commercially pure titanium and its alloys are the most commonly used materials for endosseous dental implants. Hydroxyapatite (HA), one of the calcium phosphate, has been studied for biomedical applications since it has similarity in chemistry with inorganic components of human bone and its biocompatibility. But the use of HA coated dental implants remain still controversial, because some reports suggest that the HA coating may separate from the substructure, undergo dissolution in tissue fluids, and contribute to rapid breakdown around the implants. HA coating can be applied on metal implants by numerous methods. Of several coating methods, ion beam‐assisted deposition (IBAD) has shown to promise. This study was to compare the healing response of various nano‐coating surface implants (by IBAD) placed in surgically created circumferential gaps 12 weeks postplacement.In six mongrel dogs, all mandible premolars and the first molar were extracted and after an 8‐week healing period, four kinds of implants were placed. 2 mm circumferential coronal defects around the implants were performed surgically with a customized step drill. Groups were divided according to the fixture surfaces. The dogs were sacrificed following a 12 week healing period. Specimens were analyzed histologically and histomorphometrically.During the healing period, healing was uneventful and implants were well maintained. The bone‐to‐implant contact (BIC) for experimental groups —calcium phosphate coating implants with or without heat treatment‐ were much higher than the control group. The defect fill were also higher in the experimental groups. In the control group, the coronal part showed minimal bone fill and osseointegration.Within the scope of this study, calcium phosphate coating using IBAD may improve the bone response and the calcium phosphate coating may therefore be suitable in implant design with complex surface geometries. Copyright © 2008 John Wiley & Sons, Ltd.

Reducing Photon-Mapping Bandwidth by Query Reordering

Photon mapping places an enormous burden on the memory hierarchy. Rendering a 512 x 512 image of a simple scene can require more than 196 Gbytes of raw bandwidth to the photon map data structure. This bandwidth is a major obstacle to real time photon mapping. This paper investigates two approaches for reducing the required bandwidth: 1) reordering the kNN searches and 2) cache conscious data structures. Using a Hilbert curve reordering, we demonstrate an experimental lower bound of 15 Mbytes of bandwidth for the same scene. Unfortunately, this improvement of four orders of magnitude requires a prohibitive amount of intermediate storage. We introduce two novel cost-effective algorithms that reduce the bandwidth by one order of magnitude. Scenes of different complexities are shown to exhibit similar reductions in bandwidth. We explain why the choice of data structure does not achieve similar reductions. We also examine the interaction of query reordering with two photon map acceleration techniques, importance sampling and the irradiance cache. Query reordering exploits the additional coherence that arises from the use of importance sampling in scenes with glossy surfaces. Irradiance caching also benefits from query reordering, even when complex surface geometry reduces the effectiveness of the irradiance cache.