Incorporation of support vector machines in the LIBS toolbox for sensitive and robust classification amidst unexpected sample and system variability

Despite the intrinsic elemental analysis capability and lack of sample preparation requirements, laser-induced breakdown spectroscopy (LIBS) has not been extensively used for real-world applications, e.g., quality assurance and process monitoring. Specifically, variability in sample, system, and experimental parameters in LIBS studies present a substantive hurdle for robust classification, even when standard multivariate chemometric techniques are used for analysis. Considering pharmaceutical sample investigation as an example, we propose the use of support vector machines (SVM) as a nonlinear classification method over conventional linear techniques such as soft independent modeling of class analogy (SIMCA) and partial least-squares discriminant analysis (PLS-DA) for discrimination based on LIBS measurements. Using over-the-counter pharmaceutical samples, we demonstrate that the application of SVM enables statistically significant improvements in prospective classification accuracy (sensitivity), because of its ability to address variability in LIBS sample ablation and plasma self-absorption behavior. Furthermore, our results reveal that SVM provides nearly 10% improvement in correct allocation rate and a concomitant reduction in misclassification rates of 75% (cf. PLS-DA) and 80% (cf. SIMCA)-when measurements from samples not included in the training set are incorporated in the test data-highlighting its robustness. While further studies on a wider matrix of sample types performed using different LIBS systems is needed to fully characterize the capability of SVM to provide superior predictions, we anticipate that the improved sensitivity and robustness observed here will facilitate application of the proposed LIBS-SVM toolbox for screening drugs and detecting counterfeit samples, as well as in related areas of forensic and biological sample analysis.     

Cellular Mechanics of Modulated Osteoblasts Functions in Graphene Oxide Reinforced Elastomers

We describe here favorable modulation of osteoblasts functions and cell–substrate interactions in hybrid silicone elastomers consisting of biocompatible graphene oxide. Pressure induced curing was used to synthesize the hybrid silicone elastomer with high strength–high elongation combination. It was intriguing that the cell–substrate interactions in the hybrid silicone elastomer were observed to be significantly different from those observed in stand alone silicone. The origin of differences in cell–substrate interactions in terms of cell attachment, viability, and proliferation and assessment of proteins actin, vinculin, and fibronectin are addressed and attributed to physico‐chemical properties (topography and hydrophilicity) and to the presence of graphene oxide. The end outcome of the study is a new family of nanostructured polymer composite with desired (enhanced cell functions) and bulk properties (long term stability—high strength‐at‐break). The integration of cellular and molecular biology with material science and engineering described here provides an insight into the ability to modulate cellular and molecular reactions in promoting osteoinductive signaling of surface adherent cells, in the present case, osteoblasts for joint reconstruction.     

Validation of a reduced combustion mechanism for light hydrocarbons

Due to the tremendous costs and difficulties associated with flare measurements, computational fluid dynamics (CFD) simulation could be a viable approach to predict the combustion efficiency as well as VOC/NO _x emissions from industrial flaring activities. However, consisting of a large number of reactions and species, most of the detailed kinetic mechanisms for the speciation study of flaring events are too complicated to use in the CFD simulation of industrial-scale flares. A reduced combustion mechanism will lead to improved computational efficiency; however, its fidelity must be validated. This study uses 2D CFD simulations and 1D Chemkin simulations to validate a reduced mechanism developed for the combustion of light hydrocarbons up to C₁–C₃. This mechanism, consisting of 50 species and 337 reactions, is applicable to C₁–C₃ hydrocarbons and can be used to predict the combustion efficiency and fate of pollutants released from industrial flares composed of C₁–C₃ waste gases. In this article, experimental data reported in the literatures have been used to validate the reduced mechanism. The key performance indicators used for comparison are laminar burner-stabilized flames, laminar flame speeds, adiabatic flame temperatures, ignition delay tests, and temperature and concentration profiles of the critical species. The software package CHEMKIN 4.1.1 was used to verify the computational results of laminar flame speeds, adiabatic flame temperatures, and ignition delays. The axial profiles of various critical species are simulated using the commercial CFD software package FLUENT. It is demonstrated that simulation results using this reduced mechanism are in good agreement with reported experimental results.     

Effect of Pd overlayer and mixed gases on hydrogen permeation of Pd/Nb30Hf35Co35/Pd composite membranes

Effect of Pd overlayer and mixed gases on hydrogen permeation of Pd/Nb₃₀Hf₃₅Co₃₅/Pd composite membranes was investigated. The diameter of Pd particle increases with increasing sputtering power. With this change, the membrane shows a signification reduction in hydrogen permeability/or flux, but its durability and stability increases significantly, which can be mainly attributed to a decrease in hydrogen solubility coefficient. In addition, H₂S impurity in mixed gases can greatly degrade membrane performance, especially the hydrogen permeability, whereas the Ar impurity content has less effect in the temperature range of 523–673 K. Lowering of permeability caused by the change of gas purity can be attributed to a decrease in hydrogen solubility, which is closely related to the stronger adsorption of H₂S molecules to the Pd overlayer of the membrane. Thus, it is concluded that aside from the optimum design for composition of Nb-based hydrogen permeable alloy to improve their permeability, the control of Pd overlayer film on membrane surface and gas purity in the feed gas is important.     

Continuous cooling transformation behavior and impact toughness in heat-affected zone of Nb-containing fire-resistant steel

Simulated heat-affected zone continuous cooling transformation diagram was developed for advanced fireresistant steel. Over a wide range of cooling rates, corresponding to t_8/5 from 6 s to 150 s, granular bainite was the dominant transformation constituent, while the morphology of less dominant martensite-austenite (M-A) constituent changed from film-like to block-type constituent; but the hardness remained similar to the average value of 190-205 HV (0.2). The start and finish transformation temperature was high at 700 °C and 500 °C, and is different from the conventional high strength low alloy steels. It is believed that the high-content (0.09 wt%) of Nb may promote bainite transformation at relatively high temperatures. Martenistic matrix was not observed at high cooling rate and the film-like M-A constituent and blocky M-A constituent with thin film of retained austenite and lath martensite were observed on slow cooling. Excellent impact toughness was obtained in the heat-affected zone with 15-75 kJ/cm welding heat input.     

Cellular Mechanisms of Enhanced Osteoblasts Functions via Phase‐Reversion Induced Nano/Submicron‐Grained Structure in a Low‐Ni Austenitic Stainless Steel

We elucidate here the fundamental principles underlying the modulation of osteoblasts functions in stainless steel biomedical devices achieved by nanoscale/submicron grain structure obtained through the novel concept of phase reversion in a low Ni bearing 15Cr–9Mn–1.7Cu steel. Interestingly, a comparative investigation of nano/submicron (N‐SM) and coarse‐grained (CG) structure under identical conditions indicated that cell attachment, proliferation, and viability are favorably enhanced in N‐SM grained structure and significantly different from the CG structure. These observations were further confirmed by expression levels of vinculin and associated actin cytoskeleton. Computational analysis of immunofluorescence micrographs suggested increased vinculin concentration associated with actin stress fibers in the outer regions of the cells and cellular extensions, implying enhanced cell–substrate interactions on the N‐SM grained substrate. The favorable enhancement of osteoblasts functions and cellular attachment on N‐SM grained surface is attributed to ultrafine grain size, i.e., the availability of greater open lattice in the position of high angle grain boundaries, and high hydrophilicity. The integration of cellular and molecular biology with material science and engineering as described here provides a route to modulate cellular and molecular reactions in promoting osteoinductive signaling of surface adherent cells. The end outcome of the study is that stainless steels with low Ni contents in comparison to the conventionally used bioimplant with 10–13 wt%Ni, as specially processed, exhibit desired, enhanced cell functions, and bulk properties.     

Enhanced Fibroblasts Functions in a New Family of Hierarchically Organized Nanohybrid Elastomers

Fibroblasts functions in a new family of nanohybrid network elastomers with high strength‐at‐break involving pressure‐induced curing and short chain cross‐links of inorganic nanostructures have been investigated. The concept of chemical design and synthesis involves covalently linking nanometer‐sized titania with a bi‐functional agent, acrylic acid, which has a carboxylic group to coordinate with titania and a vinyl group to form short chain cross‐links as an integral part of the silicone network structure elastomer. Interestingly, the cell–substrate interactions in the hybrid network structure elastomer are significantly different from those observed in stand alone silicone. The origin of intriguing differences in cell–substrate interactions in terms of cell attachment, viability, and proliferation and assessment of proteins actin, vinculin, and fibronectin are addressed and attributed to physico‐chemical properties (topography and hydrophilicity) and to the presence of nanocrystalline titania. The end outcome of the study is a new family of soft tissue implants with desired (enhanced cell functions) and bulk properties (long term stability–high strength‐at‐break). The integration of cellular and molecular biology with material science and engineering described here provides an insight into the ability to modulate cellular and molecular reactions in promoting osteoinductive signaling of surface adherent cells, in the present case, fibroblasts for soft tissue reconstruction.