Robust Experimental Method Research Articles

Spherical Indentation and Implementation of S3/P for yield stress determination of brittle materials

A mathematically transparent and robust experimental method has been developed to estimate the yield stress of brittle materials through the analysis of depth-sensing spherical indentation. Employing Hertzian contact mechanics, an elastically invariant ratio based on the simple equation S3/P=6REr2, (where S and P are contact stiffness and indentation load, respectively) has been derived that enables more accurate and confident determination of the transition from elastic to inelastic deformation; a transition that the yield stress dictates and represents. Using two diamond spheres with radii of 3.2 and 8.6 μm, the indentation test method and analyses are applied to two vitreous silicates: Corning's HPFS 7980® fused silica and Vitro's Starphire® soda-lime silicate. The estimated yield strengths are 8.15 GPa ± 2.5 % for the fused silica and 6.1 GPa ± 3.3 % for the soda-lime silicate, and both were independent of indenter radius. Verification of this new experimental method is demonstrated with an as-drawn titanium by showing equivalence of measured yield stress by its spherical indentation and that from uniaxial compression testing. This method will enable easier and more confident estimation of yield stress in brittle materials - a property that historically has been elusive to measure for these materials using common laboratory mechanical test methods.

Specific analysis of highly absorbing nanoporous powder by small-angle X-ray scattering.

The characterization of nanoporous powders of highly absorbing compounds by small-angle X-ray scattering (SAXS) involves overcoming several difficulties before quantitative information related to the porous texture, such as the specific surface and the porous volume, can be derived. In this article, first, the contribution of the grain facet reflectivity and scattering from the bulk of a grain with the density of ThO2, a highly absorbing material, were calculated. Microporous ThO2 powder having micrometric grain size was characterized, in which the scattering signal is predominant. A high-resolution synchrotron instrument was used in order to cover a wider q range and minimize the absorption effect, and the results were compared with those obtained using a laboratory X-ray source. Concerning the absorption problem existing with a laboratory X-ray source, a new and robust experimental method was proposed to correctly determine the scattering intensity of the highly absorbing granular samples on an absolute scale. This method allows one to calculate accurately the porous volume and the specific surface via Porod's law and the invariant using a laboratory SAXS instrument. This last result opens new perspectives for the characterization of the volume and the specific surface of highly absorbing actinide oxide powders.

Measuring representative volume elements from high‐resolution grain‐scale strain fields

AbstractMost crystalline materials present a highly heterogeneous response at the microscale, which can be affected by both internal factors (such as microstructural parameters) and external factors (such as loading). Relating microscale inhomogeneities to the macroscale response of a material requires the use of homogenisation techniques, usually based on the concept of a representative volume element (RVE)—the smallest volume of material that represents the global average response. In this work, we present a new and robust experimental method of measuring the size of a strain‐based RVE from high‐resolution grain‐scale strain fields obtained using digital image correlation (DIC). The proposed method is based on the statistical (stereological) nature of the RVE, which has been widely adopted in numerical studies, and involves dividing a strain field into randomly selected regions of varying sizes and statistically analysing the distributions of average strains within them. To validate the new method, we generate a large number of synthetic strain fields from a fractional Gaussian noise algorithm. The proposed stereological method is shown to be capable of producing reliable RVE measurements from a very large range of possible microscale strain fields while at the same time being robust in that it can produce RVE measurement results even in cases where other existing methods may be unable to do so. The proposed method has a low field‐of‐view requirement, only needing a field‐of‐view about 1.2 times as large as the RVE to produce reliable measurements. In addition, the stereological method offers significant flexibility since its statistical nature allows for control over how strict the RVE measurement should be in each case.

A new experimental approach for small-scale dynamic tests on masonry arches aimed at seismic assessment

This paper considers the dynamics of stone or brick masonry modeled 'a la Heyman'. Current regulations prescribe for such structures to adopt response spectra based on the identification with a harmonic oscillator. Since 1963, Housner observed that the dynamic of structures behaving unilaterally is more correctly described by the rocking motion. This approach enabled lately other scientists to reconstruct response spectra for arches, portals, and more complex structures. In this light, the present paper focuses on response spectra for masonry arches obtained by performing laboratory tests on a shaking table of scale models produced through 3D printing formworks. The difficulty due to the scaling of friction is overcome by special indents at the interfaces of the blocks enforcing no-sliding conditions. The comparisons with numerical solutions represent the first results, being the final goal to obtain a robust experimental method to test scale models of complex masonry structures.

Cerium ion(III)-triggered aggregation-induced emission of copper nanoclusters for trace-level p-nitrophenol detection in water

Herein, we provide the first report on the effects of Ce3+ addition on the fluorescence of copper nanoclusters (CuNCs), which have excellent optical properties and lower toxicity as compared to AgNCs and AuNCs. We synthesized glutathione-encapsulated copper nanoclusters (GSH-CuNCs) using a simple one-pot chemical reduction approach. The excitation/emission wavelengths of the GSH-CuNCs were 350/650 nm. Introduction of Ce3+ triggered an aggregation-induced emission of GSH-CuNCs due to formation of GSH-CuNCs-Ce3+ complexes, resulting in a prominent fluorescence enhancement (~42-fold) of the mixed system. Fluorescent intensities (FIs) for the GSH-CuNCs-Ce3+ system were significantly quenched by introduction of p-nitrophenol (p-NP). The aforementioned quenching mechanism resulted from an inner-filter effect producing nearly unchanged fluorescence lifetime and overlap between UV–Vis absorption of Ce3+ and the excitation wavelength of GSH-CuNCs. Consequently, a GSH-CuNCs-Ce3+-based “ON-OFF” platform was constructed for fluorescent detection of p-NP in water matrices. Under optimized conditions (5-min incubation time, pH = 5.6, 20 mM Ce3+), the FIs of the GSH-CuNCs-Ce3+ system were linear for p-NP concentrations from 0.5 to 500 μM and achieved a low detection limit of 0.17 μM. Moreover, the as-constructed nanofluoroprobe demonstrated high stability and specificity to p-NP, thereby offering a simple, cheap and robust experimental method for conventional monitoring of p-NP at trace levels in real-world water samples.

Faraday waves in soft elastic solids.

Recent experiments have observed the emergence of standing waves at the free surface of elastic bodies attached to a rigid oscillating substrate and subjected to critical values of forcing frequency and amplitude. This phenomenon, known as Faraday instability, is now well understood for viscous fluids but surprisingly eluded any theoretical explanation for soft solids. Here, we characterize Faraday waves in soft incompressible slabs using the Floquet theory to study the onset of harmonic and subharmonic resonance eigenmodes. We consider a ground state corresponding to a finite homogeneous deformation of the elastic slab. We transform the incremental boundary value problem into an algebraic eigenvalue problem characterized by the three dimensionless parameters, that characterize the interplay of gravity, capillary and elastic waves. Remarkably, we found that Faraday instability in soft solids is characterized by a harmonic resonance in the physical range of the material parameters. This seminal result is in contrast to the subharmonic resonance that is known to characterize viscous fluids, and opens the path for using Faraday waves for a precise and robust experimental method that is able to distinguish solid-like from fluid-like responses of soft matter at different scales.

Optimization of compressive strength of MTV decoy flare pellets by Taguchi method

Magnesium/Teflon/Viton or MTV based pyrotechnic composition has been the most preferred composition for decoy flares against conventional heat-seeking missiles for more than four decades. MTV flares of standard configurations are available globally but the details of their manufacturing process including compacting pressure and compressive strength of the flare pellets have not been explicitly defined. The pellets are sub-assembly of the flares dispensed in flight and are critical for successful operations of the decoy flares. Hence, in the present paper, an attempt has been made to optimize the process parameters namely charge mass (A), applied load (B) and dwell time (C) which are responsible for performance variation of compacted standard configuration cylindrical pellets of 50 mm diameter. Each of the process parameters has been considered for three levels. L27 array has been selected to represent these parameters and their interactions. The Taguchi robust experimental method arrived at the optimal result as A1B3C3 (100 g of charge mass, 78.48 KN of applied load and 20 s of dwell time). Analysis of Variance (ANOVA) highlighted that applied load followed by charge mass significantly influenced the density of the pellets. Finally, general regression equation was derived with R 2 value of 0.936 and validated with experimental results.

Microplasma UV lamp as a new source for UV-induced water treatment: Protocols for characterization and kinetic study

The newly emerged microplasma UV radiating technology can be a viable alternative to conventional radiation sources for UV water treatment. The capability of the microplasma UV lamp to monochromatically irradiate various wavelengths with different pulsation frequencies in a flat form opens new pathways for the development of novel UV-based water purifiers. This study is the first to systematically examine the microplasma UV lamp and develop a robust experimental method and apparatus for its operation to study the kinetics of both microbial and chemical pollutant degradation. The microplasma UV lamp was characterized in terms of its radiation profile and the impact of operating parameters on the lamp radiant power output. It was shown to be an instant-on and fast stabilized source. The radiant power output was a linear function of the electrical current and was not influenced by the lamp operating temperature and intermittent on/off cycles. A protocol was developed for obtaining reliable kinetic data for UV-induced elimination of microorganisms and micropollutants. An experimental setup was proposed for the kinetic studies, where the characteristics of the incident irradiance of the lamp, including uniformity, collimation, and divergence, were quantitatively evaluated. In addition, the water factor (WF) for calculating the average fluence rate was redefined for both the transient and steady state conditions. This modification is essential to account for changes in the UV transmittance of the medium, which could be an important factor for kinetic study of chemical contaminants. Two studied cases of microbial direct inactivation and the chemical photo-initiated oxidation process in different setups, based on the developed protocol, confirmed the reproducibility of the fluence-based kinetic data independent of the reactor size. The proposed protocol can be applied to the kinetic study of the elimination of microbial and chemical contaminants using microplasma UV lamps of any size, power, and peak wavelength.

Neural Network-WPCA Based Method for Multi-Objective Optimal Redundancy Allocation

For systems with multiple redundancies, reliability evaluation in the redundancy allocation problem (RAP) constitutes a computational complexity. It has been demonstrated that neural network training provides an efficient approach to estimate the complex system reliability function. When executing the neural network algorithm, there are many parameters that need to be determined for improving the training performance. Therefore, robust experimental design method can be used to determine the neural network parameters. The traditional robust design methods are intended for a single response variable. However, the application of neural network method includes more than one measurement, such as estimation accuracy and time efficiency. In this paper, utility function is first estimated by neural network training, in which the algorithm parameters are determined by weighted principal component (WPCA)-based multi-response optimization which simultaneously optimizes more than one training performance measurements. Moreover, it is always desirable to simultaneously optimize several objectives in designing a system, such as reliability, cost, etc. Therefore, continuous WPCA-based multi-response design is then applied to obtain the best design of redundancies in RAP, which simultaneously optimize multiple objectives by taking into account the correlations between them.

P067 Evaluation of HLA class II peptide binding prediction models against a robust experimental method

Aim Peptide binding to HLA molecules is a key event in T cell responses. Due to the highly polymorphic nature of HLA alleles in humans, it is desirable to predict peptides that are likely to bind specific alleles. Many bioinformatics models exist to predict peptide binding, but these have not been evaluated compared to experimental peptide binding. In this study, we evaluated commonly used prediction models against a high throughput peptide binding assay. Methods We tested binding of six peptides (collagen 258-272 , vimentin 66-78 , vimentin, Large T Antigen 313-327 , enolase 11-25 , hemagluttinin A 306-318 to Luminex class II HLA beads and compared the results to the predictions of models NN-align, Sturniolo, SMM-align and NetMHC 3.0. Experimental peptide binding was done by incubating biotinylated peptides with Luminex Class II HLA Beads from OneLambda. Peptide binding was detected with Streptavidin-PE and data acquired on the Luminex. Comparisons between experimental methods and prediction models included correlation statistics, calculations of sensitivity and specificity using the experimental model as the true value expected. Results Three of four methods we tested had excellent specificity (95.9%-99%). Sturniolo had both poor sensitivity (46.4%) and specificity (20.9%). Sensitivity of the remaining three methods was poor, at less than 50%. Using R square to measure correlation, we found NetMHC 3.0, NN and SMM align were significantly positively correlated with our experimental data. While the correlations were significant, they were lacking in accuracy, with R squared values of 0.09, 0.19 and 0.28). Sturniolo method had poor correlation values ( R squared 0.016, p = 0.24). Overall, while SMM and NN align performed better than NetMHC3.0, they lack the broad applicability of NetMHC 3.0, which was the only method with which we could compare all the HLA alleles tested. Conclusions Prediction models can consistently identify the common event (non-binding), but are much less capable of predicting positive binding. We recommend lowering the threshold of what is considered binding when using these models, which will eliminate this problem. We would additionally recommend that developers use non-competitive peptide binding data when editing models to obtain better positive predictive results.

Stability of a Transient Protein Complex in a Charged Aqueous Droplet with Variable pH.

Electrospray ionization mass spectrometry (ESI-MS) has the potential to become a high-throughput robust experimental method for the detection of protein-protein equilibrium constants. Poorly understood processes that affect the stability of weak noncovalent protein complexes in the intervening droplet environment are a significant factor that precludes the advancement of the method. We use molecular dynamics to study the stability of a ubiquitin and ubiquitin-associated domain complex (RCSB PDB code 2MRO ) in an aqueous droplet with changing size and charge concentration. We present evidence that a weak protein complex changes conformation and may dissociate in shrinking droplets. Then, the droplets containing these dissociated proteins divide. Our findings suggest that in some cases ESI-MS does not measure the correct association constants. The study intends to stimulate research for systematic development of experimental protocols that stabilize weakly bound protein interfaces in droplets.

Two-dimensional mapping of the asymmetric lateral coherence of thermal light.

We report in this work the first experimental verification of the asymmetric lateral coherence which is a measurement of the spatio-temporal coherence by using a wide-band Young interference experiment with a fixed off-axis slit. We demonstrate the coherence properties through the measurement of the real part of the coherence factor of thermal light. We extend our recent results obtained for betatron and undulator radiations providing a robust experimental method for the two-dimensional mapping of the two-point correlation function of broadband radiation preserving the phase information. The proposed method can be used as a high-sensitivity alternative to traditional interferometry with quasi-monochromatic radiation.

NMR technique for determining the depth of shallow nitrogen-vacancy centers in diamond

We demonstrate a robust experimental method for determining the depth of individual shallow Nitrogen-Vacancy (NV) centers in diamond with $\sim1$ nm uncertainty. We use a confocal microscope to observe single NV centers and detect the proton nuclear magnetic resonance (NMR) signal produced by objective immersion oil, which has well understood nuclear spin properties, on the diamond surface. We determine the NV center depth by analyzing the NV NMR data using a model that describes the interaction of a single NV center with the statistically-polarized proton spin bath. We repeat this procedure for a large number of individual, shallow NV centers and compare the resulting NV depths to the mean value expected from simulations of the ion implantation process used to create the NV centers, with reasonable agreement.

Strategies to realize decentralized manufacture through hybrid manufacturing platforms

Centralized factory dominance has led to optimization and set-up for manufacture of a sole product or product-range. In-house efficacy of such systems has been greatly improved due to lean six-sigma methodologies; however, wider scale distribution and supply has undergone little to no transformation over the past century. Research pertaining to distributed manufacture, cloud-manufacture and reconfigurable systems have provided several decentralized models using traditional manufacturing capabilities. Due to practical limitations they have not been fully realized to date. This paper outlines the emerging concept and scope for hybrid manufacturing platforms – systems using a plurality of processes on a single motion platform, to manufacture products in a decentralized network. Necessity of on-machine inspection is highlighted, outlining the potential of generic artifact machine calibration and verification of parts made. A robust experimental method using a novel hybrid manufacturing approach is used to realize the post-process adaptation of subsequent parts and demonstrates significant improvement with adapted features being cut within 15 μm of nominal position, compared to the original 300 μm error. Social, economic and environmental ramifications of adopting such a system are highlighted. The combination of several key processes will allow users to manufacture parts with minimal intervention. A move to personal fabrication would allow greater customization and convenience for the end user; however, the issues of copyright and loss of economy of scale would inhibit mass uptake in the near-future. Growing interest by enthusiasts and early adopters will continue to make an impact on the way the populace views manufacture.

Thermomagnetic and magnetocaloric properties of metamagnetic Ni-Mn-In-Co Heusler alloy in magnetic fields up to 140 kOe

High cooling power of magnetocaloric refrigeration can be achieved only at large amounts of heat, which can be transferred in one cycle from cold end hot end at quasi-isothermal conditions. The simple and robust experimental method of direct measuring of the transferred heat of materials with magnetocaloric effect (MCE) in thermal contact with massive copper block with definite heat capacity in quasi-isothermal regime was proposed. The vacuum calorimeter for the specific transferred heat ∆Q and adiabatic temperature change ∆T measurements of MCE materials in the fields of Bitter coil magnet up to H = 140 kOe was designed and tested on samples of Ni43Mn37.9In12.1Co7 Heusler alloy with inverse MCE in the vicinity of meta-magneto- structural phase transition (PT). It was found, that the magnetic field H = 80 kOe produces complete PT from martensite to austenite with ∆Q = - 1600 J/kg at initial temperature 273 K.

Using instrumented small-scale models to study structural load paths in wood-framed buildings

A large 1/3-scale model of a light-framed wood structure was constructed in order to study the structural reactions to wind loads in a three-dimensional model of a residential building. Thirty load cells measuring structural reactions at roof-to-wall and wall-to-foundation connections were used to determine influence functions in response to surface pressures generated by extreme winds. The influence functions are used in a database-assisted design (DAD) methodology to estimate failure loads in structures subjected to spatio-temporally varying wind loads. Current numerical methods based on 2D component models alone can lead to underestimated failure loads and inadequate designs. This paper describes the approach to develop the physical models and to validate their applicability to full-scale houses. Non-dimensional modeling techniques are explained, and scale model material properties for sheathing, wood-framing members, nails and truss-plate connections are provided. The need for a robust experimental method for determining influence functions is critical as load distributions are unpredictable in these structurally indeterminate systems. Further, the 1/3-scale physical models provide an economical approach to generate a large dataset of empirically-based models needed to cover a wide variety of geometrically complex houses and to calibrate non-linear numerical analysis programs for further DAD studies. The approach introduced in this study can be applied to more complex roof geometries and also to study the combined effects of horizontal and vertical wind load distributions in wood buildings.

Cytoadherence of erythrocytes invaded by Plasmodium falciparum: Quantitative contact-probing of a human malaria receptor

Cytoadherence of red blood cells (RBCs) invaded by Plasmodium falciparum parasites is an important contributor to the sequestration of RBCs, causing reduced microcirculatory flow associated with fatal malaria syndromes. The phenomenon involves a parasite-derived variant antigen, the P. falciparum erythrocyte membrane protein 1 (PfEMP1), and several human host receptors, such as chondroitin sulfate A (CSA), which has been explicitly implicated in placental malaria. Elucidating the molecular mechanisms of cytoadherence requires quantitative evaluation, under physiologically relevant conditions, of the specific receptor–ligand interactions associated with pathological states of cell–cell adhesion. Such quantitative studies have not been reported thus far for P. falciparum malaria under conditions of febrile temperatures that accompany malarial infections. In this study, single RBCs infected with P. falciparum parasites (CSA binding phenotype) in the trophozoite stage were engaged in mechanical contact with the surface of surrogate cells specifically expressing CSA, so as to quantify cytoadherence to human syncytiotrophoblasts in a controlled manner. From these measurements, a mean rupture force of 43pN was estimated for the CSA–PfEMP1 complex at 37°C. Experiments carried out at febrile temperature showed a noticeable decrease in CSA–PfEMP1 rupture force (by about 23% at 41°C and about 20% after a 40°C heat treatment), in association with an increased binding frequency. The decrease in rupture force points to a weakened receptor–ligand complex after exposure to febrile temperature, while the rise in binding frequency suggests an additional display of nonspecific binding molecules on the RBC surface. The present work establishes a robust experimental method for the quantitative assessment of cytoadherence of diseased cells with specific molecule-mediated binding.

A robust experimental design method to optimize formulations of retinol solid lipid nanoparticles

A robust experimental design method was developed using a response surface methodology and models to facilitate the development process of retinol solid lipid nanoparticles (SLNs). The SLNs were evaluated to determine how different parameters including lipid and surfactant affect size and encapsulation efficiency. This was conducted using factorial analysis and a robust design (RD) method was used to achieve optimal formulations. Two models were developed based on the RD principle and both mean and variance of the response characteristics were estimated functionally using the least squares method. They proved useful in formulation studies aiming to develop optimum by allowing a systematic and reliable design method. A model for maximizing the overall desirability represented by the geometric mean of all objectives was found to provide a better solution. The newly designed method provides useful information to characterize significant factors and obtain optimum formulations, thereby allowing a systematic and reliable design method.

Application of a robust experimental method to study soil warming effects on oilseed rape

Climate change is expected to cause a mean annual temperature increase in Germany of up to 4°C by 2100. Hence, field manipulation experiments for the assessment of the impact of global warming on agricultural production are needed to supplement existing modeling approaches. Here, we present a soil warming facility adapted for field crops, enabling common agronomic practices, including soil tillage, to be carried out while simulating natural warming scenarios. The experimental setup consists of buried heating cables and a fully computerized temperature control and data logging system. Treatments reflected medium- (up to 2050) and long-term (up to 2100) climate warming scenarios compared to the unheated (ambient) control. In a year-round experiment, there were no technical problems and the programmed temperature offset was kept stable at two levels, +1.6°C (±0.17°C) or +3.2°C (±0.27°C) above ambient throughout the experiment. We assessed warming effects on the plot microclimate as well as on biological parameters in a winter oilseed rape crop (Brassica napus L.). Growth stages were advanced in October and April, and plant length before flowering was significantly higher in the warmest treatment compared to the unheated control plots. Overall, our method proved stable and reliable under field conditions enabling common agronomic practices to be carried out while observing the effects of increased soil temperatures.

A new experimental design method to optimize formulations focusing on a lubricant for hydrophilic matrix tablets

A robust experimental design method was developed with the well-established response surface methodology and time series modeling to facilitate the formulation development process with magnesium stearate incorporated into hydrophilic matrix tablets. Two directional analyses and a time-oriented model were utilized to optimize the experimental responses. Evaluations of tablet gelation and drug release were conducted with two factors x1 and x2: one was a formulation factor (the amount of magnesium stearate) and the other was a processing factor (mixing time), respectively. Moreover, different batch sizes (100 and 500 tablet batches) were also evaluated to investigate an effect of batch size. The selected input control factors were arranged in a mixture simplex lattice design with 13 experimental runs. The obtained optimal settings of magnesium stearate for gelation were 0.46 g, 2.76 min (mixing time) for a 100 tablet batch and 1.54 g, 6.51 min for a 500 tablet batch. The optimal settings for drug release were 0.33 g, 7.99 min for a 100 tablet batch and 1.54 g, 6.51 min for a 500 tablet batch. The exact ratio and mixing time of magnesium stearate could be formulated according to the resulting hydrophilic matrix tablet properties. The newly designed experimental method provided very useful information for characterizing significant factors and hence to obtain optimum formulations allowing for a systematic and reliable experimental design method.