Non-oxide ceramic matrix composites for application in hot gas atmospheres – requirements and potential

In spite of the ambitious efforts to increase the portion of alternative and renewable resources the energy production based on fossil fuels will still represent the main part of energy in the next years. Caused by the increasing energy price and the stronger requirements in environmental protection the main focus of future generations of gas turbines will be emphasized on an increased efficiency with a simultaneous reduction of the emissions. From technical point of view these goals can be obtained only by higher hot gas temperatures. Ceramic matrix composites (CMC) offer a high potential for applications as structural parts in advanced gas turbines. During recent years, significant progress in material development of oxide and non-oxide CMC has been achieved, however, there are still considerable deficits especially in the long-term behavior of the materials in hot gas conditions. The present study is focused on the environmental stability of the materials. Caused by the high water vapor pressure in combination with high temperatures and gas velocities, corrosion processes at the surface and inside the materials were observed resulting in significant material degradation and mass loss. Hence, environmental barrier coatings (EBC) have been presented to be the solution to protect the surface of the ceramic materials. Systematic studies on the hot gas corrosion of non-oxide CMC have been performed with and without EBC. Based on a detailed understanding of the processes in the whole system, EBC and the ceramic base material during application in hot gas environments at elevated temperatures, general concepts for the development of environmental barrier coatings will be discussed

Investigating Small-Scale Air–Sea Exchange Processes via Thermography

The exchange of trace gases such as carbon dioxide or methane between the atmosphere and the ocean plays a key role for the climate system. However, the investigation of air–sea gas exchange rates lacks fast and accurate measurement techniques that can also be used in the field, e.g., onboard a ship on the ocean. A promising way to overcome this deficiency is to use heat as a proxy tracer for gas transfer. Heat transfer rates across the aqueous boundary layer of the air–water interface can be measured via thermography with unprecedented temporal and spatial resolution in the order of minutes and meters, respectively. Either passive or active measurement schemes can be applied. Passive approaches rely on temperature differences across the water surface, which are caused naturally by radiative and evaporative cooling of the water surface. Active measurement schemes force an artificial heat flux through the aqueous boundary layer by means of heating a patch at the water surface with an appropriate heat source, such as a CO2 laser. The choice of the excitation signal is crucial. It is beneficial to apply periodic heat flux densities with different excitation frequencies. In this way, the air–water interface can be probed for its response in terms of temperature amplitude and phase shift between excitation signal and temperature response. This concept from linear system theory is also well established in the field of non-destructive material testing, where it is known as lock-in thermography. This article gives a short introduction into air–sea gas exchange, before it presents an overview of different thermographic measurement techniques used in wind-wave facilities and at sea starting with early implementations. The article closes with a novel multifrequency excitation scheme for even faster measurements

Distribution, autecology, genetic characterization, and conservation of the Western Mediterranean endemic dragonfly Orthetrum nitidinerve (Selys, 1841): insights from Italy

Aquatic macroinvertebrates are a primary component of freshwater ecosystems and one of the most threatened by anthropogenic pressures. Among them, dragonflies are a charismatic group of growing scientific and social interest. However, little is known about the natural history of several species. One paradigmatic example is the declining Orthetrum nitidinerve, a Western Mediterranean endemic anisopteran. We reviewed published and new data on this species, addressing distribution, autecology, and conservation (with a focus on Italy), and provide its first genetic characterization and phylogenetic placement within the genus. In Italy, the species is known from 50 sites so far (only 17 breeding populations) located in Sardinia and Sicily (1841–2019, only 22 from 1990 onward). Records from continental Italy are due to misidentification. The flight period in Italy spans between May and September. Habitat consists of permanent freshwater (mostly helocrene sources, seepages, and small brooks), slow-flowing, shallow, with muddy bottom deposits at elevation from the sea level up to 1000 m asl. All the breeding populations are found in open and sunny landscapes, almost invariably in extensive pasturelands. The species has strongly declined in Sicily, whereas several large populations still occur in Sardinia. The major threats identified so far are agriculture and grazing intensification or abandonment and drought/source desiccation determined by water overexploitation and climate change. The first ever provided mitochondrial COI barcode and ITS nuclear sequences allowed a first tentative phylogenetic placement of the species as a sister group of the O. brunneum/O. lineostigma lineage

Effect of filler synergy and cast film extrusion parameters on extrudability and direction-dependent conductivity of PVDF/carbon nanotube/carbon black composites

In the present study, melt-mixed composites based of poly (vinylidene fluoride) (PVDF) and fillers with different aspect ratios (carbon nanotubes (CNTs), carbon black (CB)) and their mixtures in composites were investigated whereby compression-molded plates were compared with melt-extruded films. The processing-related orientation of CNTs with a high aspect ratio leads to direction-dependent electrical and mechanical properties, which can be reduced by using mixed filler systems with the low aspect ratio CB. An upscaling of melt mixing from small scale to laboratory scale was carried out. From extruded materials, films were prepared down to a thickness of 50 µm by cast film extrusion under variation of the processing parameters. By combining CB and CNTs in PVDF, especially the electrical conductivity through the film could be increased compared to PVDF/CNT composites due to additional contact points in the sample thickness. The alignment of the fillers in the two directions within the films was deduced from the differences in electrical and mechanical film properties, which showed higher values in the extrusion direction than perpendicular to it

First record of Ixodes ariadnae in Germany — Short communication

A long-legged tick was collected from a hibernating greater mouse-eared bat (Myotis myotis) in Baden-Württemberg, Germany. Based on morphological characteristics as well as on partial COI and 16S rDNA gene sequences the tick was identified as an engorged female of Ixodes ariadnae. The greater mouseeared bat is a new host record for this tick species. Taking into account the geographical position of the collection site and the known migration distance of the greater mouse-eared bat, the present data suggest the autochthonous occurrence of I. ariadnae in Germany. This is the first record of I. ariadnae in Germany, and in any country other than Hungary, where this species has been recently discovered

SU(3) Symmetry Breaking and Octet Baryon Polarizabilities

Static polarizabilities of the low--lying $1/2^+$ baryons are studied within the collective coordinate approach to the three flavor generalization of the Skyrme model; in particular, magnetic polarizabilities are considered. Predicted polarizabilities, which result from different treatments of the strange degrees of freedom in this model, are critically compared. Their deviations from the flavor symmetric formulations are discussed.Comment: 11 pages, LaTeX, 4 tables, no figures, final version to be published in Phys. Lett.

Combined Clinical, Epidemiological, and Genome-Based Analysis Identified a Nationwide Outbreak of Burkholderia cepacia Complex Infections Caused by Contaminated Mouthwash Solutions

Background: In September 2018, Burkholderia cepacia complex (BCC) infections in 3 patients associated with exposure to a mouthwash solution (MWS) were reported to the Robert Koch Institute (RKI). As the product was still on the market and the scale of the outbreak was unclear, a nation-wide investigation was initiated. Methods: We aimed to investigate BCC infections/colonizations associated with MWS. Hospitals, laboratories, and public health services were informed that BCC isolates should be sent to the RKI. These isolates were typed by pulsed-field gel electrophoresis (PFGE) and whole-genome sequencing (WGS) including development of an ad hoc core genome MLST (cgMLST) scheme. Results: In total, 36 patients from 6 hospitals met the case definition, the last patient in November 2018. Twenty-nine isolates from 26 of these patients were available for typing. WGS analysis revealed 2 distinct cgMLST clusters. Cluster 1 (Burkholderia arboris) contained isolates from patients and MWS obtained from 4 hospitals and isolates provided by the manufacturer. Patient and MWS isolates from another hospital were assigned to cluster 2 (B. cepacia). Conclusions: The combined clinical, epidemiological, and microbiological investigation, including whole-genome analysis, allowed for uncovering a supraregional BCC outbreak in health care settings. Strains of B. arboris and B. cepacia were identified as contaminating species of MWS bottles and subsequent colonization and putative infection of patients in several hospitals. Despite a recall of the product by the manufacturer in August 2018, the outbreak lasted until December 2018. Reporting of contaminated medical products and recalls should be optimized to protect patients.Peer Reviewe

High degree of mitochondrial gene heterogeneity in the bat tick species Ixodes vespertilionis, I. ariadnae and I. simplex from Eurasia

Background: Phylogeographical studies allow precise genetic comparison of specimens, which were collected over large geographical ranges and belong to the same or closely related animal species. These methods have also been used to compare ticks of veterinary-medical importance. However, relevant data are missing in the case of ixodid ticks of bats, despite (1) the vast geographical range of both Ixodes vespertilionis and Ixodes simplex, and (2) the considerable uncertainty in their taxonomy, which is currently unresolvable by morphological clues. Methods: In the present study 21 ticks were selected from collections or were freshly removed from bats or cave walls in six European and four Asian countries. The DNA was extracted and PCRs were performed to amplify part of the cytochrome oxidase I (COI), 16S and 12S rDNA genes, followed by sequencing for identification and molecular-phylogenetic comparison. Results: No morphological differences were observed between Ixodes vespertilionis specimens from Spain and from other parts of Europe, but corresponding genotypes had only 94.6 % COI sequence identity. An I. vespertilionis specimen collected in Vietnam was different both morphologically and genetically (i.e. with only 84.1 % COI sequence identity in comparison with I. vespertilionis from Europe). Two ticks (collected in Vietnam and in Japan) formed a monophyletic clade and shared morphological features with I. ariadnae, recently described and hitherto only reported in Europe. In addition, two Asiatic specimens of I. simplex were shown to differ markedly from European genotypes of the same species. Phylogenetic relationships of ticks showed similar clustering patterns with those of their associated bat host species. Conclusions: Although all three ixodid bat tick species evaluated in the present study appear to be widespread in Eurasia, they exhibit pronounced genetic differences. Data of this study also reflect that I. vespertilionis may represent a species complex