31. Effect of heat treatment on thermal conductivity of additively manufactured AISI H13 tool steelSamo Tome, Blaž Karpe, Irena Paulin, Matjaž Godec, 2024, published scientific conference contribution Abstract: AISI H13 is commonly used for tooling, where higher wear resistance, thermal fatigue resistance, or hot toughness is required. Such examples include forging dies, plastic molds, hot shear blades, high-pressure die casting, and extrusion dies. Thus, thermal conductivity is one of the most important factors for hot work tools. Typically, the work cycle of a hot work tool designed for forging consists of four main phases: the forging stroke, with which the die imparts its shape onto the part, a brief pause while the die is reset to its original position, a lubrication phase, and a post lubrication dwell phase. During the forging phase, a significant amount of heat is transferred to the die while it is in contact with the part. This heat must then be dispelled for the part to return to a working temperature. While somewhat different, other hot work processes mentioned above are similar in that the hot work tool gets heated to a high temperature due to the contact with the object of deformation. The process of additive manufacturing (AM) promises better, more efficient tool production with features like conforming cooling channels, which would reduce the thermal fatigue of tools, prolonging tool life. However, the powder bed fusion (PBF) method creates a columnar microstructure, which has a detrimental effect on the thermal conductivity of H13 tool steel. Our investigation focused on the beneficial effect of heat treatment, specifically annealing at different temperatures, on the thermal conductivity of AM-produced H13 parts.
Keywords: SLM, thermal conductivity, tool steel, heat treatment
Published in DiRROS: 28.02.2024; Views: 186; Downloads: 82
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32. Extreme environments simplify reassembly of communities of arbuscular mycorrhizal fungiNataša Šibanc, Dave R. Clark, Thorunn Helgason, Alex J. Dumbrell, Irena Maček, 2024, original scientific article Abstract: The ecological impacts of long-term (press) disturbance on mechanisms regulating the relative abundance (i.e., commonness or rarity) and temporal dynamics of species within a community remain largely unknown. This is particularly true for the functionally important arbuscular mycorrhizal (AM) fungi; obligate plant-root endosymbionts that colonize more than two-thirds of terrestrial plant species. Here, we use high-resolution amplicon sequencing to examine how AM fungal communities in a specific extreme ecosystem—mofettes or natural CO2 springs caused by geological CO2 exhalations—are affected by long-term stress. We found that in mofettes, specific and temporally stable communities form as a subset of the local metacommunity. These communities are less diverse and dominated by adapted, “stress tolerant” taxa. Those taxa are rare in control locations and more benign environments worldwide, but show a stable temporal pattern in the extreme sites, consistently dominating the communities in grassland mofettes. This pattern of lower diversity and high dominance of specific taxa has been confirmed as relatively stable over several sampling years and is independently observed across multiple geographic locations (mofettes in different countries). This study implies that the response of soil microbial community composition to long-term stress is relatively predictable, which can also reflect the community response to other anthropogenic stressors (e.g., heavy metal pollution or land use change). Moreover, as AM fungi are functionally differentiated, with different taxa providing different benefits to host plants, changes in community structure in response to long-term environmental change have the potential to impact terrestrial plant communities and their productivity
Keywords: arbuscular mycorrhiza, elevated CO2, long-term experiments, soil biodiversity, soil hypoxia, next-generation sequencing, NGS
Published in DiRROS: 28.02.2024; Views: 264; Downloads: 141
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33. Characterization of hFOB 1.19 cell line for studying Zn-based degradable metallic biomaterialsEva Jablonská, Lucie Mrázková, Jiří Kubásek, Dalibor Vojtěch, Irena Paulin, Tomáš Ruml, Jan Lipov, 2024, original scientific article Abstract: In vitro testing is the first important step in the development of new biomaterials. The human fetal osteoblast cell line hFOB 1.19 is a very promising cell model; however, there are vast discrepancies in cultivation protocols, especially in the cultivation temperature and the presence of the selection reagent, geneticin (G418). We intended to use hFOB 1.19 for the testing of Zn-based degradable metallic materials. However, the sensitivity of hFOB 1.19 to zinc ions has not yet been studied. Therefore, we compared the toxicity of zinc towards hFOB 1.19 under different conditions and compared it with that of the L929 mouse fibroblast cell line. We also tested the cytotoxicity of three types of Zn-based biomaterials in two types of media. The presence of G418 used as a selection reagent decreased the sensitivity of hFOB 1.19 to Zn2+. hFOB 1.19 cell line was more sensitive to Zn2+ at elevated (restrictive) temperatures. hFOB 1.19 cell line was less sensitive to Zn2+ than L929 cell line (both as ZnCl2 and extracts of alloys). Therefore, the appropriate cultivation conditions of hFOB 1.19 during biomaterial testing should be chosen with caution.
Keywords: zinc degradable materials, in vitro cytotoxicity testing, hFOB 1.19 osteoblasts
Published in DiRROS: 28.02.2024; Views: 188; Downloads: 73
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37. Subchronic exposure of rats to sublethal dose of microcystin-YR induces DNA damage in multiple organsMetka Filipič, Bojana Žegura, Bojan Sedmak, Irena Horvat-Žnidaršič, Aleksandra Milutinović Živin, Dušan Šuput, 2007, original scientific article Abstract: Background. Microcystins (MCs) are cyclic heptapeptides that are considered tobe liver specific toxins. They are potent tumour promoters and recent studies indicate that they are also genotoxic. In this study we measured DNA damage in lymphocytes, liver, kidney (cortex and medulla), lung, spleen and brain cells of male Fisher F344 rats that were exposed to sublethal dose (every second day 10 Ugžkg b.w.č i.p) of microeysrin-YR (MCYR) for one month. Methods. At the end of exposure the animals were sacrificed, the lymphocytes were isolated from blood taken from jugular vein, liver cells were obtained byperfusion with collagenase A and the cells from other organs were isolated by incubating small tissue pieces with eollagenase A. The DNA damage in isolated cells was measured with the single cells gel electrophoresis (SCGE) also called the comet assay. Results. A significant increase of the % tail DNAin MCYR-exposed animals compared to the nonexposed control ones was observed in brain (2.5 fold), liver (2.1 fold), kidney medulla (1.9 fold), kidney cortex (1.8 fold) and lung (1.7 fold) cells, while the DNA from lymphocytes and spleen cells was not affected. Conclusion. This study demonstrated that subehronic exposure to sublethal doses of MCs can induce systemicgenotoxicity in mammals, and it affects not only the liver but also other vital organs.
Keywords: DNA damage, comet assay, cyanobacteria, bacterial toxins, rats, inbred F344
Published in DiRROS: 20.02.2024; Views: 192; Downloads: 46
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38. Cysteine cathepsins, stefins and extracellular matrix degradation during invasion of transformed human breast cell linesIrena Zajc, Aleš Bervar, Tamara Lah Turnšek, 2006, original scientific article Abstract: Background. Human breast cellular model, comprising four cell lines originating from spontaneously immortalized human breast epithelial MCF10A cell line, its c-Ha-ras transfectant, MCF10AT, and two tumourigenic derivatives, cultured from two sequential mouse xenographs, MCF10AT-Ca1a and MCF10AT-Ca1d, were used to compare the relative protein concentration of cathepsins and stefins in single cells. Methods. The relative protein concentration of cathepsins and stefins in single cells was analysed by confocal microscopy, and compared to their protein expression in cell homogenates. Results. The most invasive, MCF10AT cell line contained several fold higher protein concentration of cathepsin B and increased levels of stefins, but similar levels of cathepsin L, compared with the parental MCF10A cells. This was associated with five fold higher endocytosis of Matrigel-DQ-collagen IV (DQC) and a simultaneous increase in signal overlap between DQC and cathepsin L as well as DQC and stefin B, but a decrease in that of DQC and cathepsin B overlap in the MCF10AT cells. Simultaneously, increased signal overlaps between both cathepsins and between cathepsins-stefins pairs, were observed in this cell line. Conclusions. These results suggest that the increased collagen endocytosis and degradation in theinvasive phenotype significantly affect also the subcellular localization of cysteine cathepsins and stefins. Based on these and the reports of other authors, we hypothesize that the intracellular degradation may also be assoeiated with cathepsin L, whereas cathepsin B in the ras transformed breastcells is involved in both, the intracellular and pericellular degradation of extracellular matrix during cell migration and invasion.
Keywords: breast neoplasms, tumor cells cultured, neoplasms invasiveness, cathepsins, extracellular matrix
Published in DiRROS: 15.02.2024; Views: 195; Downloads: 46
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39. Managing anemia with epoetin alfa in patients with rectal cancerVaneja Velenik, Irena Oblak, Veronika Kodre, 2005, original scientific article Abstract: Background. Anemia is one of the most challenging problems in clinical oncology due to its high prevalence among the patients with malignant diseases. The purposes of our study were: (1) to assess the potential of epoetin alfa therapy to prevent the decline in Hb concentrations that typically accompanies chemotherapy/radiotherapy (ChT/RT) of the patients with rectal cancer; (2) to test the hypothesis that the use of epoetin alfa significantly reduces the transfusion requirements in the patients with rectalcancer treated with ChT/RTafter surgery, and (3) to evaluate the safety profile of the administration of epoetin alfa in the clinical setting. Methods. Sixty patients who underwent surgery for rectal cancer were prospectively enrolled. Group A consisted of 39 patients with Hb concentrations <13 g/dl at the start of ChT/RT following surgery, and group B of 17 patients with Hb concentrations >13 g/dl at the start of ChT/RT following surgery, but whose Hb concentrations fell below 13 g/dl during the ChT/RT protocol. The starting dose of epoetin alfa in both proups was 10,000 IU subcutaneously (se) three times a week (tiw). The following major parameters were evaluated: (1) change in Hb concentrations relative to the baseline as measured at 4-week intervals, (2) allogenic blood transfusion requirements in relation to Hb concentrations, and (3) incidence and severity of adverse events and their potential relationship to epoetin alfa administration. (Abstract truncated at 2000 characters)
Published in DiRROS: 14.02.2024; Views: 178; Downloads: 47
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40. MHC class II molecules and tumour immunotherapyIrena Oven, 2005, review article Abstract: Tumour immunontherapy attempts to use the specificity and capability of the immune system to kill malignant cells with a minimum damage to normal tissue. Increasing knowledge of the identity of tumour antigens should help us design more effective therapeutic vaccines. Increasing evidence has demonstrated that MHC class II molecules and CD4+T cells play important roles in generating and maintaining antitumour immune responses in animal models. These data suggest that be necessary to involve both CD+ and CD+T cells for more effective antitumour therapy. Novel strategies have been developed for enhancing T cell responses against cancer by prolonging antigen prersentation of denritic cells to T cells, by the inclusion of MHC class II-restricted tumour antigens and by genetically modifying tumour cells to present antigen to T lymphocytes directly. Vaccines against cancers aim to induce tumour-specific effector T cells that can reduce tumour mass and induce development of tumour-specific T cell memory, that can control tumour relapse.
Published in DiRROS: 14.02.2024; Views: 187; Downloads: 40
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