Real-world Materials Research Articles

A novel approach for hybrid performance modelling and prediction of large-scale computing systems

We present a novel approach for hybrid performance modelling and prediction of large-scale parallel and distributed computing systems, which combines Mathematical Modelling (MathMod) and Discrete-Event Simulation (DES). We use MathMod to develop parameterised performance models for components of the system. Thereafter, we use DES to describe the structure of system and the interaction among its components. As a result we obtain a high-level performance model, which combines the evaluation speed of mathematical models with the structure awareness and fidelity of the simulation model. We evaluate empirically our approach with a real-world material science program that comprises more than 15,000 lines of code.

Simulation in Emergent Computational Systems.

Simulation in Emergent Computational Systems.

Preparing for Terrorism Involving Radioactive Materials: Three Lessons from Recent Experience and Research

Experts now see the risk of terrorism involving radioactive materials as significant and growing. Indeed, there have already been terrorist threats to use radioactive materials and suspected plots to launch attacks. As efforts are made to improve preparedness for this deve- loping challenge, it will be important to learn as much as possible from recent experience with real-world radioactive materials emergencies and from recent research on people's views, reactions, and concerns regarding potential radiological/nuclear terrorism situations. This article highlights three of the most important lessons that have emerged from the growing body of research and experience.

A photometric approach for estimating normals and tangents

This paper presents a technique for acquiring the shape of real-world objects with complex isotropic and anisotropic reflectance. Our method estimates the local normal and tangent vectors at each pixel in a reference view from a sequence of images taken under varying point lighting. We show that for many real-world materials and a restricted set of light positions, the 2D slice of the BRDF obtained by fixing the local view direction is symmetric under reflections of the halfway vector across the normal-tangent and normal-binormal planes. Based on this analysis, we develop an optimization that estimates the local surface frame by identifying these planes of symmetry in the measured BRDF. As with other photometric methods, a key benefit of our approach is that the input is easy to acquire and is less sensitive to calibration errors than stereo or multi-view techniques. Unlike prior work, our approach allows estimating the surface tangent in the case of anisotropic reflectance. We confirm the accuracy and reliability of our approach with analytic and measured data, present several normal and tangent fields acquired with our technique, and demonstrate applications to appearance editing.

Material-specific adaptation of color invariant features

For the modeling of materials, the mapping of image features onto a codebook of feature representatives receives extensive treatment. For reason of their generality and simplicity, filterbank outputs are commonly used as features. The MR8 filterbank of Varma and Zisserman is performing well in a recent evaluation. In this paper, we construct color invariant filter sets from the original MR8 filterbank. We evaluate several color invariant alternatives over more than 250 real-world materials recorded under a variety of imaging conditions including clutter. Our contribution is a material recognition framework that learns automatically for each material specifically the most discriminative filterbank combination and corresponding degree of color invariance. For a large set of materials each with different physical properties, we demonstrate the material-specific filterbank models to be preferred over models with fixed filterbanks.

Nonlinear refraction of hard x rays

We study the nonlinear refraction of x rays in highly ionized condensed matter by using a classical model of a cold electron plasma in a lattice of still ions coupled with Maxwell equations. By employing a group-theoretical technique, we reduce the governing equations of the system to an integrable set of nonlinear ordinary differential equations, discussing the existence and stability of nonlinear waves. This allows us to define the effective Kerr coefficient ${n}_{2}$ at x rays. With reference to real-world crystalline materials (B, C, Li, and Na), we consider beam self-defocusing and predict that nonlinear processes become comparable to the linear ones for focused beams with powers on the order of $m{c}^{3}/{r}_{0}$ $(\ensuremath{\approx}10\text{ }\text{GW})$, the classical electron power. As a consequence, nonlinear phenomena are expected to largely affect imaging experiments in currently exploited x-ray free-electron lasers and in their future developments.

Ultra-High Transmission Electrowetting Displays Enabled by Integrated Reflectors

A reflector technique for increasing the transmission performance of a back-lit electrowetting display is presented. The electrowetting display pixel structure consists of an opaque oil film that blocks light transmission. Electrowetting with 5-10 V breaks up the oil film and creates a transmissive area for the pixel. With real-world electrowetting materials and device constraints, the transmissive area typically reaches 60% to 80% of the pixel area. By integrating a simple thin-film reflector between the backlight and the remaining oil film area, the effective transmission can be boosted to >90%. This high efficiency is promising for battery-powered applications and for high-brightness sunlight-legible displays.

Evaluation of methods for approximating shapes used to synthesize 3D solid textures

In modern computer graphics applications, textures play an important role in conveying the appearance of real-world materials. But while surface appearance can often be effectively captured with a photograph, it is difficult to use example imagery to synthesize fully three-dimensional (3D) solid textures that are perceptually similar to their inputs. Specifically, this research focuses on human perception of 3D solid textures composed of aggregate particles in a binding matrix. Holding constant an established algorithm for approximating particle distributions , we examine the problem of estimating particle shape . We consider four methods for approximating plausible particle shapes—including two methods of our own contribution. We compare the performance of these methods under a variety of input conditions using automated, perceptually motivated metrics, as well as a psychophysical experiment. In the course of assessing the relative performance of the four algorithms, we also evaluate the reliability of the automated metrics in predicting the results of the experiment.

Acoustic scattering and propagation through spatially complex dispersive media via the direct numerical solution of the wave equation

Analytical approaches for modeling propagation and scattering in inhomogeneous media are difficult, and often require extremely simplifying approximations in order to achieve a solution. To avoid such approximations, the direct numerical solution of the wave equation via the method of finite differences offers the most direct tool, which takes into account diffraction and refraction. It also allows for detailed modeling of spatially complex media. In all cases, the correct inclusion of the dispersive properties of the medium can make the difference in the interpretation of the results. However, the inclusion of dispersion directly in the time domain proved until recently to be an elusive problem. In order to model the transient signal, a convolution operator that takes into account the dispersive characteristics of the medium is introduced to the linear wave equation. In this work, numerical modeling of scattering from a variety of different dispersive media with physical properties associated with real world material is presented. Where possible, the numerical solutions are compared with a known solution. It is shown that in those cases, the use of the convolutional propagation operator leads to the correct solution for the scattered field. [Work supported by ONR/NRL.]

Extreme Compression and Modeling of Bidirectional Texture Function

The recent advanced representation for realistic real-world materials in virtual reality applications is the Bidirectional Texture Function (BTF) which describes rough texture appearance for varying illumination and viewing conditions. Such a function can be represented by thousands of measurements (images) per material sample. The resulting BTF size excludes its direct rendering in graphical applications and some compression of these huge BTF data spaces is obviously inevitable. In this paper we present a novel, fast probabilistic model-based algorithm for realistic BTF modeling allowing an extreme compression with the possibility of a fast hardware implementation. Its ultimate aim is to create a visual impression of the same material without a pixel-wise correspondence to the original measurements. The analytical step of the algorithm starts with a BTF space segmentation and a range map estimation by photometric stereo of the BTF surface, followed by the spectral and spatial factorization of selected sub-space color texture images. Single mono-spectral band-limited factors are independently modeled by their dedicated spatial probabilistic model. During rendering, the sub-space images of arbitrary size are synthesized and both color (possibly multi-spectral) and range information is combined in a bump-mapping filter according to the view and illumination directions. The presented model offers a huge BTF compression ratio unattainable by any alternative sampling-based BTF synthesis method. Simultaneously this model can be used to reconstruct missing parts of the BTF measurement space.

BTF modelling using BRDF texels

The highest fidelity representations of realistic real-world materials currently comprise Bidirectional Texture Functions (BTF). The BTF is a six-dimensional function depending on view and illumination directions as well as on planar texture coordinates. The huge size of such measurements, typically in the form of thousands of images covering all possible combinations of illumination and viewing angles, has prohibited their practical exploitation, and obviously some compression and modelling method of these enormous BTF data spaces is inevitable. The two proposed approaches combine BTF spatial clustering with cluster index modelling by means of efficient Markov random field models. The methods allow the generation of a seamless cluster index of arbitrary size to cover large virtual 3D object surfaces. Both methods represent original BTF data using a set of local spatially dependent Bidirectional Reflectance Distribution Function (BRDF) values which are combined according to the synthesized cluster index and illumination/viewing directions by means of two types of Markov random field models. BTF data compression using both methods is about 1:200 and their synthesis is very fast.

Time-varying BRDFs.

The properties of virtually all real-world materials change with time, causing their bidirectional reflectance distribution functions (BRDFs) to be time varying. However, none of the existing BRDF models and databases take time variation into consideration; they represent the appearance of a material at a single time instance. In this paper, we address the acquisition, analysis, modeling, and rendering of a wide range of time-varying BRDFs (TVBRDFs). We have developed an acquisition system that is capable of sampling a material's BRDF at multiple time instances, with each time sample acquired within 36 sec. We have used this acquisition system to measure the BRDFs of a wide range of time-varying phenomena, which include the drying of various types of paints (watercolor, spray, and oil), the drying of wet rough surfaces (cement, plaster, and fabrics), the accumulation of dusts (household and joint compound) on surfaces, and the melting of materials (chocolate). Analytic BRDF functions are fit to these measurements and the model parameters' variations with time are analyzed. Each category exhibits interesting and sometimes nonintuitive parameter trends. These parameter trends are then used to develop analytic TVBRDF models. The analytic TVBRDF models enable us to apply effects such as paint drying and dust accumulation to arbitrary surfaces and novel materials.

Adult Age Differences in Errand Planning: The Role of Task Familiarity and Cognitive Resources

This study examines the effects of age, cognitive resources, and task familiarity on planning performance. Fifty-two young and 52 old adults completed one of two errand-planning tasks. The tasks were matched for structure, difficulty, and format, but differed in content, such that one planning task required planning a real-world shopping tour whereas the other involved planning an unfamiliar space tour. In addition, the participants' memory capacity, speed of processing, inhibition, and memory for relevant versus irrelevant task features were assessed. Results revealed no age differences for the real-world planning material. In contrast, old adults performed worse than young adults in the artificial planning task. Data are discussed in the context of old adults possibly being able to compensate for cognitive deficits in speed and inhibition by selectively allocating resources to relevant task elements, but only if they perform a planning task containing elements that approximate their real-world experience with errand-planning problems.

Mixed DNA/oligo (ethylene glycol) functionalized gold surfaces improve DNA hybridization in complex media

Reliable, direct "sample-to-answer" capture of nucleic acid targets from complex media would greatly improve existing capabilities of DNA microarrays and biosensors. This goal has proven elusive for many current nucleic acid detection technologies attempting to produce assay results directly from complex real-world samples, including food, tissue, and environmental materials. In this study, we have investigated mixed self-assembled thiolated single-strand DNA (ssDNA) monolayers containing a short thiolated oligo(ethylene glycol) (OEG) surface diluent on gold surfaces to improve the specific capture of DNA targets from complex media. Both surface composition and orientation of these mixed DNA monolayers were characterized with x-ray photoelectron spectroscopy (XPS) and near-edge x-ray absorption fine structure (NEXAFS). XPS results from sequentially adsorbed ssDNA/OEG monolayers on gold indicate that thiolated OEG diluent molecules first incorporate into the thiolated ssDNA monolayer and, upon longer OEG exposures, competitively displace adsorbed ssDNA molecules from the gold surface. NEXAFS polarization dependence results (followed by monitoring the N 1s-->pi(*) transition) indicate that adsorbed thiolated ssDNA nucleotide base-ring structures in the mixed ssDNA monolayers are oriented more parallel to the gold surface compared to DNA bases in pure ssDNA monolayers. This supports ssDNA oligomer reorientation towards a more upright position upon OEG mixed adlayer incorporation. DNA target hybridization on mixed ssDNA probe/OEG monolayers was monitored by surface plasmon resonance (SPR). Improvements in specific target capture for these ssDNA probe surfaces due to incorporation of the OEG diluent were demonstrated using two model biosensing assays, DNA target capture from complete bovine serum and from salmon genomic DNA mixtures. SPR results demonstrate that OEG incorporation into the ssDNA adlayer improves surface resistance to both nonspecific DNA and protein adsorption, facilitating detection of small DNA target sequences from these undiluted, unpurified complex biological mixtures unachievable with previously reported, analogous ssDNA/11-mercapto-1-undecanol monolayer surfaces [P. Gong, C.-Y. Lee, L. J. Gamble, D. G. Castner, and D. W. Grainger, Anal. Chem. 78, 3326 (2006)].

Surface-Initiated Atom Transfer Radical Polymerization of Oligo(ethylene glycol) Methyl Methacrylate from a Mixed Self-Assembled Monolayer on Gold

This paper describes the in-situ synthesis of an oligo(ethylene glycol)-functionalized polymer brush in which the oligo(ethylene glycol) chains are presented as side-chains from a methacrylate backbone that is anchored to the surface. These polymer “bottlebrushes” have been synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP) of oligo(ethylene glycol) methyl methacrylate (OEGMA) from a mixed self-assembled monolayer (SAM) of an ATRP initiator-functionalized alkanethiol and a diluent, methyl-terminated thiol. The systematic control of the ATRP initiator surface density afforded by the mixed SAM on gold and the polymerization time enables the polymer chain length and surface density to be independently controlled. Surface plasmon resonance (SPR) spectroscopy of fibronectin (Fn) adsorption on poly(OEGMA) grown from the surface of the mixed SAMs on gold shows that above a threshold solution molar ratio of the ATRP-initiator thiol to methyl-terminated thiol of 0.2, and a dry film thickness of ∼ 4 nm, Fn adsorption on the surface-initiated poly(OEGMA) coatings was below the detection limit of SPR. The relatively low surface density of the ATRP initiator required to confer protein resistance to the surface suggests that SI-ATRP may be a viable strategy to create protein resistant polymer brushes on real-world materials.

A cross-property relation between the tensile modulus and the thermal conductivity of porous materials

Elastic moduli and thermal conductivity are key properties determining a material's response to mechanical deformations and temperature gradients. Although in the case of heterogeneous materials the effective properties are uniquely determined by the material's microstructure, in the case of porous materials, due to the large difference in the phase properties, it is usually not possible to predict the porosity dependence of any of these properties based on volume fraction information alone. Thus, for real-world materials experimental measurement is often considered to be the only feasible way to obtain a reliable porosity dependence for the property in question. Here we show, however, that for isotropic materials either the relative tensile modulus E r or the relative thermal conductivity k r can be calculated from the other via the cross-property relation 3 ln E r = 4 ln k r , as soon as one of them has been measured.

Homogenization of balanced plain weave composites with imperfect microstructure: Part I––Theoretical formulation

A mathematically sound computational framework is presented for the determination of a representative volume element (RVE) of plain weave fabric composites with reinforcement imperfections. Although treated as periodic two-phase composites the imperfect geometry of such material systems often precludes a straightforward representation of the RVE in terms of a simple periodic unit cell (PUC). To circumvent various limitations of simple unit cells when applied to real material systems the present contribution suggests a rigorous theoretical approach for the derivation of a reliable PUC exploiting the knowledge of the real geometry of a composite supplied by the manufacturer. It is expected that sufficient geometrical information about the real microstucture can be obtained from digitized micrographs of plain weave cross-sections that reveal the most critical imperfections caused by manufacturing processes. No attempt is therefore made to address a specific type of imperfection but rather treat them all in the combined manner. It has been demonstrated that the morphology of imperfect material systems is well-described by an appropriate set of statistical descriptors. Introducing these descriptors into a suitable optimization environment then provides a tool for the derivation of a PUC that statistically resembles the actual composite system as close as possible. In particular the parameters of the idealized unit cells follow from minimization of the objective function defined as the least square difference of the statistical descriptor related to the original microstructure and to the idealized unit cell, respectively. Once the desired geometrical parameters are determined, the finite element model of a woven composite is formulated and used to predict the overall response of the composite by the numerical homogenization method. The quality of the resulting unit cells is addressed from the point of view of effective elastic properties to examine the applicability and limitations of this procedure and to provide modeling strategy for the analysis of real-world material systems. Although applied to plain weave fabric composites the theoretical formulation presented in this paper is rather general and can be applied to any material systems with disordered or imperfect microstructures.

Finite Element Approach to Model and Analyze Piezoelectric Actuators.

The basic research into the area of the behavior of piezoelectrics under static loading condition in far behind the effort put forth in the study of the vibrational behavior of piezoelectrics. Also, the application of the vibrational characteristics of piezoelectrics has been widespread, but the application of the static characteristics has been relatively left untapped. The piezoelectric based actuators are gaining more pupularity in many areas ranging from micro-motion control as positioners to macro-motion in space applications. So, it is very vital to understand the behavior of practical piezoelectric micro actuator under arbitrarily applied external voltage. The solution for moderately complex piezoelectric model using analytical methodology is very challenging. So, a numerical solution scheme based on the method of finite elements has been developed to analyze the deformations of and potentials within piezoelectric materials subjected to external static voltage loading. The formulation of the finite element equations developed and used for computer implementation is also dealt with. Computer software has been created to model piezoelectric three-dimensional geometries, based on the equations developed. The case studies chosen for evaluation of this numerical scheme are representative of real-world piezoceramic materials. The results are found to be in excellent agreement with published product data. This work carried out would be a foundation for the development of a powerful analysis tool, capable of testing multiple conceptual designs of piezoelectric actuators.

Mapping the rule table of a 2-D probabilistic cellular automaton to the chemical physics of etching and deposition

Molecules undergo only a finite number of possible chemical reactions. They can therefore be modeled as finite state machines and an array of them, in a cellular automaton, can be used to study molecular dynamics and self organization at the nanotechnology scale. The cellular automaton rule table is, in essence, a map to the molecular dynamics. We would like to use heuristic programming to design new molecules and structures in the space of cellular automata. To that end we have been investigating mapping relations between a cellular automata rule table and the chemical physics of real-world materials. We demonstrate our ideas in the domain of crystal growth and dissolution.

ON THE RADIATION EFFICIENCY OF INFINITE PLATES SUBJECT TO A POINT LOAD IN WATER

This paper describes an approach to calculate the radiation efficiency of infinite plates subject to a point load for any frequency. The results obtained by this approach are valid for the radiation efficiency of point-driven finite plates in water with real world material properties for frequencies near and above coincidence. This approach can be used to guide experimental measurements and numerical calculations of radiation efficiency as the excitation frequency is increased for infinite plates in water. The radiation efficiency calculation for an infinite plate for all frequencies is derived for the first time. The limitation of thin plate theory in this application is also assessed by comparing it with the thick plate theory used in this work. An important distinct behavior above the coincidence frequency in a heavy fluid is revealed through the calculation of the radiation efficiency and explained by the dispersion relation of an infinite plate fully coupled with a fluid. In contrast to the case of light fluid (e.g., air), the radiation efficiency in a heavy fluid (e.g., water) does not approach unity in the neighbourhood of the coincidence frequency but at a significantly higher frequency.