Methods for evaluating particle coalescence and their implications in laser sintering

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordAn experimental study on the melt and coalescence of different Poly(aryl ether ketones) (PAEK) powders was carried out. The study consisted of evaluating individual particles and neck growth using a hot stage platform. Three different methods of assessing particles dimensions were evaluated, and the coalescence was compared for the grades on three different substrates: glass, glass coated silicone and amorphous PEKK films, the last substrate with the intent to relate with the laser sintering process. It was found that all individual particles shrink prior to melting, achieving up to 30% reduction in perimeter at temperatures just above melting. This shrinkage is followed by an increase in size, mostly driven by viscous flow. Shrinkage is expected to affect neck growth by delaying coalescence, as particles are pulled away whilst neck increases. This is a plausible explanation for why neck growth occurs at a lower rate than predicted by most coalescence models. The use of different substrates does not seem to affect particle coalescence or change in dimension. Viscosity and particle size influence overall particle behaviour and melt, whilst morphology and porosity do not have a great impact in particles coalescence.The authors would like to acknowledge the financial support of Arkema Innovations Chemistry for this study

Study of the virus vector genus Trichodorus (Diphtherophorina, Trichodoridae) from the Iberian Peninsula, an apparent centre of speciation

Trichodoridae are polyphagous root ectoparasites occurring worldwide. Their major pest status is as virus vector of Tobraviruses. Currently, the family has 102 species classified within 6 genera. The genus Trichodorus is the largest in number of species (56) and predominantly occurs in temperate regions. Traditional morphology-based taxonomy revealed for Europe, a very high species diversity within the Iberian Peninsula, comprising about one fifth of all Trichodoridae described. Characteristic for this fauna is the presence of a morpho-species group within Trichodorus, characterized in males by slightly ventrally curved spicules with a mid-blade constriction with bristles and females with relatively large vaginal sclerotized pieces, quadrangular to triangular in shape. Recent surveys for Trichodoridae in cultivated and natural environments in Southern Spain and compared with the fauna from Portugal revealed four new species of Trichodorus, three of them belonging to this morpho-species group. Molecular analyses based on nuclear ribosomal RNA genes (D2-D3 expansion segments of 28S and partial 18S gene) supported not only the new species but also the morpho-species group as a separate clade. The integrated approach of morphology based taxonomy with molecular and biogeographic data enhanced the accuracy of the observed biodiversity and strengthen the hypothesis of the Iberian Peninsula as a center of speciation.The Society of Nematologists (SON

Integrative taxonomic study of the virus vector family Trichodoridae from the Iberian Peninsula, an apparent centre of speciation

Trichodoridae are polyphagous root ectoparasites occurring worldwide. Their major pest status is as virus vector of Tobraviruses. Currently, the family has 102 species classified within 6 genera. 88% of the species belong to the didelphic genera (females with two well developed genital branches) with the genus Trichodorus being the largest in number of species (56). Trichodorus species predominantly occur in temperate regions. Surveys for trichodorids were carried out in cultivated and natural habitats in Spain and compared with the trichodorid fauna from Portugal. A comparative morphological study was carried out together with molecular analyses based on nuclear ribosomal RNA genes (D2-D3 expansion segments of 28S and partial 18S gene). Characteristic for the Iberian Peninsula is the high number of morphologically closely resembling species but clearly separated molecularly (cryptic species), characterized in males by slightly ventrally curved spicules with a mid-blade constriction with bristles and females with relatively large vaginal sclerotized pieces, quadrangular to triangular in shape. Molecular analyses demonstrated that D2-D3 expansion segments are suitable diagnostic markers for Trichodoridae. Comparative morphology and molecular analyses provide support for the Iberian Peninsula as an apparent centre of speciation. South Africa is another known centre of speciation of Trichodorus.Nematological Society of Southern Afric

Evolution of PEKK crystallization measured in laser sintering

This is the final version. Available on open access from Frontiers Media via the DOI in this recordData availability statement: The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.The rising popularity of laser sintering (LS) technology has increased by the broadening of available materials for this process. Kepstan 6002 poly (ether ketone ketone) (PEKK) was recently launched as a high-performance polymer grade with a lower processing temperature and unique crystallization kinetics. This study aims to understand the progress of crystallization on samples manufactured throughout the laser sintering process. These results were compared with isothermal and dynamic differential scanning calorimetry (DSC) experiments with different cooling rates. Kepstan 6002 PEKK processed by high-temperature laser sintering (HT-LS) presents a kinetics of crystallization in the order of ∼10 times slower than its crystallized samples in the DSC. This result highlights the need for a part-based crystallization investigation rather than isothermal models to describe the crystallization in LS. The transmission electron microscopy (TEM) analysis reveals smaller spherulites in the samples subjected to prolonged cooling times and an almost amorphous structure for the PEKK samples exposed to almost no cooling. This experiment identified the surroundings of laser sintered particles as preferential sites for crystallization initiation, which grows as the particles penetrate the molten layers and spherulites are formed. The slower kinetics of crystallization of Kepstan 6002 PEKK grade improve the adhesion between layers in laser sintering and enable tailoring its properties according to the application. Understanding the relationship between intrinsic material characteristics and the resulting final properties is vital to optimizing the process and controlling the final performance of PEKK for different applications.University of ExeterArkema Chemistry Co

A route to improving elongation of high-temperature laser sintered PEKK

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordData availability: The dataset generated during the current study is not publicly available due to confidentiality reasons but can be made available on reasonable request with the approval of all authors.Laser sintering (LS) is one of the most popular additive manufacturing (AM) techniques as it produces parts of complex geometry with high dimensional accuracy and good mechanical strength. However, the nature of the LS process often leads to brittle behavior characterized by a low elongation at break if compared to conventional polymer processing techniques, e.g., injection molding (IM). For poly(ether ketone ketone) (PEKK), such elongation is currently below 3%. This study determines and then optimizes the relationship between cooling time and crystallization of PEKK during LS and the resulting elongation at break. The elongation at break of PEKK was successfully improved by using shorter cooling times. The combination of the slow crystallization kinetics of PEKK and a short cooling time of 1 h increased elongation at break to 14%; this is a striking result never achieved for PAEKs in LS before. A calibration curve was developed that can be used to correlate PEKK structure and mechanical properties to cooling conditions according to the application. This methodology can also be applied to select and optimize the mechanical properties of other LS polymers sharing similar kinetics of crystallization and processing temperatures. This work suggests a great potential for a wide range of “post-processing” heat treatments to be used in AM to tailor the ultimate mechanical properties.Arkema Innovations Chemistr

Genetic Structure of Xiphinema pachtaicum

The dagger nematodes Xiphinema pachtaicum and X. index are two of the most widespread and frequently occurring Xiphinema spp. co-infesting vineyards and other crops and natural habitats worldwide. Sexual reproduction is rare in these species. The primary objective of this study was to determine the genetic structure of X. pachtaicum and X. index populations using eight and seven populations, respectively, from different "wine of denomination of origin (D.O.) zones" in Spain and Sardinia (Italy), by studying mitochondria! (cytochrome oxidase c subunit 1 or COI) and nuclear (D2-D3 expansion segments of 28S rDNA) markers. Both Xiphinema spp. showed low intraspecific divergence among COI sequences, ranging from 0.2% (1 base substitution) to 2.3% (10 substitutions) in X. pachtaicum and from 0.2% (I base substitution) to 0.4% (2 substitutions) in X. index. Population genetic structure was strong for both species. Nevertheless, molecular differences among grapevine-growing areas were not significant, and intrapopulation diversity was very low. It is hypothesized that this genetic homogeneity in the nematode populations reflects their predominant parthenogenetic reproduction mode and low dispersal abilities. Our results also show that X. pachtaicum populations in Spain have possibly been established from two different populations of origin. Results also demonstrated that the two DNA regions studied are suitable diagnostic markers for X. index and X. pachtaicum

Coronal Density and Temperature Profiles Calculated by Forward Modeling EUV Emission Observed by SDO/AIA

We present a model for the intensity of optically thin extreme ultraviolet (EUV) emission for a plasma atmosphere. We apply our model to the solar corona as observed using the six optically thin EUV channels of the Solar Dynamics Observatory/Atmospheric Imaging Assembly instrument. The emissivity of the plasma is calculated from the density and temperature using CHIANTI tables and the intensity is then determined by integration along the line of sight. We consider several different profiles for the radial density and temperature profiles, each of which are constrained by the observational data alone with no further physical assumptions. We demonstrate the method first by applying it to a quiet region of the corona, and then use it as the background component of a model including coronal holes, allowing the plasma densities and temperatures inside and outside the hole to be estimated. We compare our results with differential emission measure inversions. More accurate estimates for the coronal density and temperature profiles have the potential to help constrain plasma properties such as the magnetic field strength when used in combination with methods such as seismology