The food-borne pathogen Listeria (L.) monocytogenes is able to survive for months and even years in food production environments. Strains belonging to sequence type (ST)121 are particularly found to ...be abundant and to persist in food and food production environments. To elucidate genetic determinants characteristic for L. monocytogenes ST121, we sequenced the genomes of 14 ST121 strains and compared them with currently available L. monocytogenes ST121 genomes. In total, we analyzed 70 ST121 genomes deriving from 16 different countries, different years of isolation, and different origins-including food, animal and human ST121 isolates. All ST121 genomes show a high degree of conservation sharing at least 99.7% average nucleotide identity. The main differences between the strains were found in prophage content and prophage conservation. We also detected distinct highly conserved subtypes of prophages inserted at the same genomic locus. While some of the prophages showed more than 99.9% similarity between strains from different sources and years, other prophages showed a higher level of diversity. 81.4% of the strains harbored virtually identical plasmids. 97.1% of the ST121 strains contain a truncated internalin A (inlA) gene. Only one of the seven human ST121 isolates encodes a full-length inlA gene, illustrating the need of better understanding their survival and virulence mechanisms.
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Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Solid phase extraction (SPE) is often used for enrichment and clean-up prior to analysis of dissolved organic matter (DOM) by electrospray ionization (ESI) coupled to ultrahigh resolution Fourier ...transform ion cyclotron resonance mass spectrometry (FT-ICR MS). It is generally accepted that extraction by SPE is not quantitative with respect to carbon concentration. However, little information is available on the selectivity of different SPE sorbents and the resulting effect for the acquired DOM mass spectra. Freshwater samples were extracted by the widely used PPL, HLB and C18 sorbents and the molecular composition and size distribution of the DOM in the extracts and in the permeates was compared to the original sample. Dissolved organic carbon (DOC) recoveries ranged between 20% and 65% for the three tested SPE sorbents. Size-exclusion chromatography coupled to organic carbon detection (SEC-OCD) revealed that limited recovery by PPL and HLB was primarily due to incomplete elution of a fraction of apparent high molecular weight from the solid phase. In contrast, incomplete retention on the solid phase, mainly observed for the C18 cartridge, was attributed to a fraction of low molecular weight. The FT-ICR mass spectra of the original sample and the SPE extracts did not differ significantly in their molecular weight distribution, but they showed sorbent specific differences in the degree of oxygenation and saturation. We concluded that the selective enrichment of freshwater DOM by SPE is less critical for subsequent FT-ICR MS analysis, because those fractions that are not sufficiently recovered have comparatively small effects on the mass spectra. This was confirmed by the extraction of model compounds, showing that very polar and small molecules are poorly extracted, but also have a low response in ESI-MS. Of the three tested SPE cartridges the PPL material offered the best properties for DOM enrichment for subsequent FT-ICR MS analysis as it minimizes too strong and too weak DOM-sorbent interactions.
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So far, the human health impacts of nano- and microplastics are poorly understood. Thus, we investigated whether nanoplastics exposure induces inflammatory processes in primary human ...monocytes and monocyte-derived dendritic cells. We exposed these cells in vitro to nanoplastics of different shapes (irregular vs. spherical), sizes (50–310 nm and polydisperse mixtures) and polymer types (polystyrene; polymethyl methacrylate; polyvinyl chloride, PVC) using concentrations of 30–300 particles cell−1. Our results show that irregular PVC particles induce the strongest cytokine release of these nanoplastics. Irregular polystyrene triggered a significantly higher pro-inflammatory response compared to spherical nanoplastics. The contribution of chemicals leaching from the particles was minor. The effects were concentration-dependent but varied markedly between cell donors. We conclude that nanoplastics exposure can provoke human immune cells to secrete cytokines as key initiators of inflammation. This response is specific to certain polymers (PVC) and particle shapes (fragments). Accordingly, nanoplastics cannot be considered one homogenous entity when assessing their health implications and the use of spherical polystyrene nanoplastics may underestimate their inflammatory effects.
This work proposes a manufacturing chain that combines the two key technologies Incremental Swivel Bending (ISB) and Quenching and Partitioning (Q-P). While incremental forming methods offer chances ...for production flexibility, strain hardening often exhausts material’s ductility. Heat treatment processes can potentially renew the material’s capability to deform. Q-P, in particular, not only erases the influence of cold forming but also delivers advanced high strength properties (AHSS). Q-P has already been proposed for the incorporation of hot forming methods; however, integration methods for cold forming techniques represent a key research gap. The combined effects of cold forming of a Q-P suitable material in its initial pearlitic structure and subsequent Q-P heat treatment are investigated in this paper. Profiles of various cross sections are manufactured from a low alloyed, carbon enriched (42SiCr) steel and bent to various geometries by the flexible ISB process. An analytic model to determine the strain distribution caused by ISB is developed and validated within the bent areas by considering strain maps, local material properties and curvature distributions. Furthermore, material properties resulting from different Q-P treatments on the previously bent sections are evaluated with respect to accelerated heating gradients from quenching to partitioning. Tensile test specimens, locally extracted from the bent arcs, confirm the elimination of any remaining strain hardening after the heat treatments. Moreover, due to considerably high ductility at high tensile strength levels, the evaluation of energy dissipated during tensile tests demonstrates the Q-P treated material’s high potential to absorb energy even at elevated strain rates. The suggested manufacturing chain, combining ISB and Q-P, enables high production flexibility and delivers advanced high strength properties for the production of lightweight components, suitable for energy absorption at high strain rates, e.g. crash structures in cars.
is an environmentally adapted saprophyte that can change into a human and animal bacterial pathogen with zoonotic potential through several regulatory systems. In this review, the focus is on the ...occurrence of
and
in different ecological niches, the detection methods, and their analytical limitations. It also highlights the occurrence of
genotypes in the environment (soil, water, and wildlife), reflects on the molecular determinants of
for the saprophytic lifestyle and the potential for antibiotic resistance. In particular, the strain-specific properties with which some genotypes circulate in wastewater, surface water, soil, wildlife, and agricultural environments are of particular interest for the continuously updating risk analysis.
Mechanisms of fatigue crack propagation in a Q&P-processed steel Hockauf, Kristin; Wagner, Martin Franz-Xaver; Mašek, Bohuslav ...
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
04/2019, Letnik:
754
Journal Article
Recenzirano
The fatigue crack propagation (FCP) behavior of a quenched and partitioned (Q&P), low-alloyed CSiCrMn steel containing 12% of retained austenite is investigated in ΔK-controlled tests at different ...R-ratios and compared with its quenched and tempered (QT) counterpart, containing 4% of retained austenite. Characteristic features of the crack wake and FCP surfaces are examined by scanning electron microscopy and related to the presence or absence of martensitic transformation. Comparing the FCP behavior of the Q&P condition with its QT counterpart, the fatigue threshold ΔKth is higher, and fatigue crack growth rates in the Paris-regime are lower, for Q&P. With an increase of ΔK, Paris-lines intersect and, at high ΔK, the fatigue crack growth resistance of the Q&P condition becomes inferior. Such FCG behavior is attributed to the amount and stability of retained austenite: at low ΔK, contributions of the martensitic transformation are negligible, and thus a higher fraction of retained austenite accounts for an increased FCG resistance. With increasing ΔK, an increasing percentage of retained austenite in the cyclic plastic zone at the crack tip is transformed, providing brittle pathways for fast crack propagation and thus lowering FCG resistance. Analysing the crack surface, cleavage-like intergranular crack propagation can be directly related to martensitic transformation: in the threshold region, FCP occurs predominantly in a transgranular mode and the percentage of cleavage planes increases as ΔK increases. This study is the first one that examines the FCP behavior in a Q&P-processed steel and one of very few which deal with the near-threshold FCP behavior in TRIP steels.
A new approach for equal‐channel angular pressing (ECAP) of thin AA5083 sheets using two different orientations is investigated to address the issues of sheet metal ECAP. The method includes the ...deformation of a stack of 6 individual sheets supported by bulk material pieces placed on both sides of the stack. An excess length of the support materials and their pre‐deformation during an early stage of processing allows a buckling‐free deformation of the thin sheets for one of the investigated orientations. Multiple ECAP passes (up to N = 4) at room temperature following route C and microstructural analyses by electron back‐scatter diffraction are performed. Two passes of ECAP already result in considerable grain refinement with equiaxed grains, pronounced substructures and in an increased tensile strength at room temperature. At elevated temperatures (250 °C) a comparatively large elongation to failure (>130%) is found for the fine‐grained sheets. Diffusion‐controlled deformation mechanisms likely contribute to the deformation behavior of the investigated material. Scanning electron microscopy of the tensile specimens after testing reveals the formation of elongated and large cavities. These results highlight the suitability of the modified experimental method to produce (ultra)fine‐grained thin aluminum sheets with distinctly increased strength and ductility.
Equal‐channel angular pressing (ECAP) of thin AA5083 sheets using two different stack orientations is investigated. Multiple ECAP passes (N = 4) at RT following stack orientation B and deformation route C lead to a fine‐grained microstructure with equiaxed grains. This results in high ductility during tensile testing at elevated temperatures accompanied by the formation of large cavities indicating the contribution of diffusion‐controlled deformation mechanisms.
Background
Currently, determining procedural endpoints and treatment efficacy of vascular interventions is largely qualitative and relies on subjective visual assessment of digital subtraction ...angiography (DSA) images leading to large interobserver variabilities and poor reproducibility. Quantitative metrics such as the residual blood velocity in embolized vessel branches could help establish objective and reproducible endpoints. Recently, velocity quantification techniques based on a contrast enhanced X‐ray sequence such as qDSA and 4D DSA have been proposed. These techniques must be robust, and, to avoid radiation dose concerns, they should be compatible with low dose per frame image acquisition.
Purpose
To develop and evaluate a technique for robust blood velocity quantification from low dose contrast enhanced X‐ray image sequences that leverages the oscillating signal created by pulsatile blood flow.
Methods
The proposed spatiotemporal frequency domain (STF) approach quantifies velocities from time attenuation maps (TAMs) representing the oscillating signal over time for all points along a vessel centerline. Due to the time it takes a contrast bolus to travel along the vessel centerline, the resulting TAM resembles a sheared sine wave. The shear angle is related to the velocity and can be determined in the spatiotemporal frequency domain after applying the 2D Fourier transform to the TAM. The approach was evaluated in a straight tube phantom using three different radiation dose levels and compared to ultrasound transit‐time‐based measurements. The STF velocity results were also compared to previously published approaches for the measurement of blood velocity from contrast enhanced X‐ray sequences including shifted least squared (SLS) and phase shift (PHS). Additionally, an in vivo porcine study (n = 8) was performed where increasing amounts of embolic particles were injected into a hepatic or splenic artery with intermittent velocity measurements after each injection to monitor the resulting reduction in velocity.
Results
At the lowest evaluated dose level (average air kerma rate 1.3 mGy/s at the interventional reference point), the Pearson correlation between ultrasound and STF velocity measurements was 99%$99\%$. This was significantly higher (p<0.0001$p < 0.0001$) than corresponding correlation results between ultrasound and the previously published SLS and PHS approaches (91$\hskip.001pt 91$ and 93%$93\%$, respectively). In the in vivo study, a reduction in velocity was observed in 85.7%$85.7\%$ of cases after injection of 1 mL, 96.4%$96.4\%$ after 3 mL, and 100.0%$100.0\%$ after 4 mL of embolic particles.
Conclusions
The results show good agreement of the spatiotemporal frequency domain approach with ultrasound even in low dose per frame image sequences. Additionally, the in vivo study demonstrates the ability to monitor the physiological changes due to embolization. This could provide quantitative metrics during vascular procedures to establish objective and reproducible endpoints.
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