An implementation of a fast, robust, and effective algorithm is inevitable in modern multivariate data analysis (MVDA). The principal component analysis (PCA) algorithm is becoming popular not only ...in the spectroscopic community because it complies with the qualities mentioned above. PCA is, therefore, often used for the processing of detected multivariate signal (characteristic spectra). Over the past decade, PCA has been adopted by the Laser-Induced Breakdown Spectroscopy (LIBS) community and the number of scientific articles referring to PCA steadily increases. The interest in PCA is not caused only by the basic need to obtain a fast data visualization on a lower dimensional scale and to inspect the most prominent variables. Most recently, PCA has also been applied to yield unconventional data analyses, i.e. processing of large scale LIBS maps. However, a rapid development of LIBS-related instrumentation and applications has led to some non-uniform methodologies in the implementation and utilization of MVDA, including PCA. Thus, in this work, we critically assess and elaborate on the approaches to utilize PCA in LIBS data processing. The aim of this article is also to derive some implications and to suggest advice in data preprocessing, visualization, dimensionality reduction, model building, classification, quantification and non-conventional multivariate mapping. This review reflects also other MVDA algorithms than PCA and consequently, presented conclusions and recommendations can be generalized.
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•Implementation of principal component analysis to processing of laser-induced breakdown spectroscopy data•Thorough review of articles on pattern recognition, classification and regression•Advices on data preprocessing and understanding of PCA outputs
This paper deals with the analysis of polymer materials of various composition and molecular structure using Laser-Induced Breakdown Spectroscopy (LIBS). To make the discussion more transparent, we ...studied structurally different polymer samples using LIBS in various atmospheres (air, He, Ar) and examined their influence on signal response. We chose aliphatic (PP, PA 66, POM) and aromatic (PS, ABS) polymers with/without heterogeneous atoms (N, O) in their backbone structure. The emission spectra of all examined polymers are exceedingly similar; they exhibit a characteristic atomic/ionic emission line from four biogenic elements (C, H, N, O) and specific molecular emission bands. We focused on intensities of spectral molecular bands such as carbon dimer (C2 Swan system at 516.5 nm) and cyano (CN band at 338.3 nm) bands as a response to various atmospheres. Sources of molecular bands are native bonds and bonds created from an interaction of plasma with buffers gas molecules. Here, we present a correlation between the polymer structure and signal responses. Finally, Principal Component Analysis was used to further assess the influence of ambient atmospheres on the clustering of LIBS data originating from various polymer samples.
•Explaining the formation of molecules bands (CN or C2) in polymer plasma under three different atmospheric conditions.•Using principal component analysis to study the formation of molecular bands relating to the polymer structure.•CN and C2 bands in LIBS spectra have decisive influence on the potential clustering of polymers.
This paper deals with various selective laser melting (SLM) processing strategies for aluminum 2618 powder in order to get material densities and properties close to conventionally-produced, ...high-strength 2618 alloy. To evaluate the influence of laser scanning strategies on the resulting porosity and mechanical properties a row of experiments was done. Three types of samples were used: single-track welds, bulk samples and samples for tensile testing. Single-track welds were used to find the appropriate processing parameters for achieving continuous and well-shaped welds. The bulk samples were built with different scanning strategies with the aim of reaching a low relative porosity of the material. The combination of the chessboard strategy with a 2 × 2 mm field size fabricated with an out-in spiral order was found to eliminate a major lack of fusion defects. However, small cracks in the material structure were found over the complete range of tested parameters. The decisive criteria was the elimination of small cracks that drastically reduced mechanical properties. Reduction of the thermal gradient using support structures or fabrication under elevated temperatures shows a promising approach to eliminating the cracks. Mechanical properties of samples produced by SLM were compared with the properties of extruded material. The results showed that the SLM-processed 2618 alloy could only reach one half of the yield strength and tensile strength of extruded material. This is mainly due to the occurrence of small cracks in the structure of the built material.
Phase contrast imaging (PCI) is used to extend X-ray computed nanotomography (nCT) technique for analyzing samples with a low X-ray contrast, such as polymeric structures or soft tissues. Although ...this technique is used in many variations at synchrotrons, along with the development of X-ray tubes and X-ray detectors, a PCI becomes available also for laboratory systems. This paper is focused on determining the conditions for propagation-based PCI in laboratory nCT systems based on three criteria. It is mostly employed in near-field imaging regime, which is quantified via the Fresnel number. X-rays must reach a certain degree of coherence to form edge enhancement. Finally, the setup of every computed tomography (CT) measurement has to avoid geometrical unsharpness due to the finite focal spot size. These conditions are evaluated and discussed in terms of different properties and settings of the CT machine. Propagation-based PCI is tested on a sample of carbon fibers reinforced polyethylene and the implementation of the Paganin phase retrieval algorithm on the CT data is shown.
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•Scaffolds with an open intrastrand pore network endured an order of magnitude more fatigue cycles than scaffolds with compact strands.•This unexpected behaviour is in contrast to ...traditional expectations in the field of metal fatigue.•Crack deflection and branching due to interactions with pores and small grains were responsible for fatigue life improvement.•Scaffolds produced by direct ink writing are competitive with those produced by other additive manufacturing methods.
Metallic porous structures (scaffolds) produced by additive manufacturing represent an important class of personalised implants used in load-bearing orthopaedic applications. As such, their fatigue performance must be excellent to prevent the need for revision surgery. This paper provides insight into the high-cycle fatigue behaviour of novel titanium scaffolds with hierarchical porosity and properties comparable to those of human bone that were produced by direct ink writing (DIW) and tested under cyclic loading typical for bone implants. Opposite to traditional expectations in the field of metal fatigue, scaffolds produced with an open intrastrand pore network (14.3%) endured nearly an order of magnitude more cycles than those with relatively compact strands (5.9%) and their normalized fatigue strength (62% of their yield strength in 106 cycles) was competitive with many current titanium scaffolds produced by other additive manufacturing technologies. Improved fatigue performance was related to fatigue crack growth shielding effects that reduced the crack growth rate, prolonged the crack path, and increased energy absorption. Consequently, these novel hierarchically porous titanium structures prepared by DIW can serve safely under cyclic loading conditions, and at the same time can provide multiple open porosity-related functionalities in advanced biomedicine and other industrial sectors.
Contamination of the environment with toxic metals such as cadmium or lead is a worldwide issue. The accumulator of metals Cannabis sativa L. has potential to be utilized in phytoremediation, which ...is an environmentally friendly way of soil decontamination. Novel non-thermal plasma-based technologies may be a helpful tool in this process. Plasma activated water (PAW), prepared by contact of gaseous plasma with water, contains reactive oxygen and nitrogen species, which enhance the growth of plants. In this study, C. sativa was grown in a short-term toxicity test in a medium which consisted of plasma activated water prepared by dielectric barrier discharge with liquid electrode and different concentrations of cadmium or lead. Application of PAW on heavy metal contaminated C. sativa resulted in increased growth under Pb contamination as was determined by ecotoxicology tests. Furthermore, the PAW influence on the bioaccumulation of these metals as well as the influence on the nutrient composition of plants was studied primarily by applying Laser-induced breakdown spectroscopy (LIBS). The LIBS elemental maps show that C. sativa accumulates heavy metals mainly in the roots. The results present a new proof-of-concept in which PAW could be used to improve the growth of plants in heavy metal contaminated environment, while LIBS can be implemented to study the phytoremediation efficiency.
•PAW effect on the growth of Cannabis sativa contaminated by heavy metals was studied.•PAW decreased the negative effect of Pb on C. sativa.•Elemental maps recorded by LIBS show bioaccumulation of Cd and Pb in roots of plants.•Cadmium bioaccumulation causes lower concentration of nutrient elements in plants.
The purpose of this study was to determine the toxicity of two different sources of cadmium, i.e. CdCl2 and Cd-based Quantum Dots (QDs), for freshwater model plant Lemna minor L. Cadmium telluride ...QDs were capped with two coating ligands: glutathione (GSH) or 3-mercaptopropionic acid (MPA). Growth rate inhibition and final biomass inhibition of L. minor after 168-h exposure were monitored as toxicity endpoints. Dose-response curves for Cd toxicity and EC50168h values were statistically evaluated for all sources of Cd to uncover possible differences among the toxicities of tested compounds. Total Cd content and its bioaccumulation factors (BAFs) in L. minor after the exposure period were also determined to distinguish Cd bioaccumulation patterns with respect to different test compounds. Laser-Induced Breakdown Spectroscopy (LIBS) with lateral resolution of 200µm was employed in order to obtain two-dimensional maps of Cd spatial distribution in L. minor fronds. Our results show that GSH- and MPA-capped Cd-based QDs have similar toxicity for L. minor, but are significantly less toxic than CdCl2. However, both sources of Cd lead to similar patterns of Cd bioaccumulation and distribution in L. minor fronds. Our results are in line with previous reports that the main mediators of Cd toxicity and bioaccumulation in aquatic plants are Cd2+ ions dissolved from Cd-based QDs.
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•Cd-based QDs were less toxic than CdCl2 at the same total Cd exposure concentrations.•Bioaccumulation of Cd from CdCl2 and Cd-based QDs in L. minor was similar.•LIBS could be used for rapid 2D spatial distribution mapping of Cd in plants.•TEM demonstrated no presence of QDs inside or on the surface of L. minor fronds.
Scanning electron microscopy (SEM) is a common method for the analysis of painting micro-samples. The high resolution of this technique offers precise surface analysis and can be coupled with an ...energy-dispersive spectrometer for the acquisition of the elemental composition. For light microscopy and SEM analysis, the painting micro-samples are commonly prepared as cross-sections, where the micro-sample positioned on the side is embedded in a resin. Therefore, the sequence of its layers is exposed after the cross-section is polished. In common cases outside of cultural heritage, a conductive layer is applied on the polished side, but in this field, the measurements are mostly done in low-vacuum SEM (LV-SEM). Although the charging effect is reduced in LV-SEM, it can still occur, and can hardly be prevented even with carbon tape or paint. This work presents two conductive cross-section preparation methods for non-conductive samples, which reduce charging effects without impairing the sample integrity.
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