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Abstract: Bubble nucleation and growth dynamics exert a primary control on the explosivity of volcanic eruptions. Numerous theoretical and experimental studies aim to capture the complex process of melt vesiculation, whereas textural studies use vesicle populations to reconstruct magma behaviour. However, post-fragmentation vesiculation in rhyolitic bombs can create final quenched bubble (vesicle) textures that are not representative of the nature of fragmenting magma within the conduit. To examine bubble growth in hydrous rhyolitic bombs, we have used heated stage microscopy to directly observe vesiculation of a Chaitén rhyolite melt (with an initial dissolved water content of ∼0.95 wt %) at atmospheric pressure and magmatic temperatures upon reheating. Thin wafers of obsidian were held from 5 min up to two days in the heated stage at temperatures between 575 °C and 875 °C. We found that bubble growth rates, measured through changes in bubble diameter, increased with both temperature and bubble size. The average growth rate at the highest temperature of 875 °C is ∼1.27 μm s−1, which is substantially faster than the lowest detected growth rate of ∼0.02 μm s−1 at 725 °C; below this temperature no growth was observed. Average growth rate Vr follows an exponential relationship with temperature, T and inferred melt viscosity η, where Vr = 5.57 10−7e0.016 and Vr = 3270.26e−1.117η. Several stages of evolving bubble morphology were directly observed, including initial relaxation of deformed bubbles into spheres, extensive growth of spheres, and, at higher temperatures, close packing and foam formation. Bubble deformation due to bubble-bubble interaction and coalescence was observed in most experiments. We use our simple, experimentally-determined relationship between melt viscosity and bubble growth rates to model post-fragmentation vesicle growth in a cooling 1 m-diameter rhyolitic bomb. The results, which indicate negligible vesicle growth within 2–3 cm of the bomb surface, correspond well with the observed dense margin thickness of a Chaitén bomb of comparable dimensions. The experiments described can be used to effectively reconstruct the post-fragmentation vesiculation history of bombs through simple analytical expressions which provide a useful tool for aiding in the interpretation of pumiceous endmember textures in hydrous rhyolitic bombs.

Open Access

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Abstract: The study of live cells using Fourier transform infrared spectroscopy (FTIR) and FTIR microspectroscopy (FT-IRMS) intrinsically yields more information about cell metabolism than comparable experiments using dried or chemically fixed samples. There are, however, a number of barriers to obtaining high-quality vibrational spectra of live cells, including correction for the significant contributions of water bands to the spectra, and the physical stresses placed upon cells by compression in short pathlength sample holders. In this study, we present a water correction method that is able to result in good-quality cell spectra from water layers of 10 and 12 μm and demonstrate that sufficient biological detail is retained to separate spectra of live cells based upon their exposure to different novel anti-cancer agents. The IR brilliance of a synchrotron radiation (SR) source overcomes the problem of the strong water absorption and provides cell spectra with good signal-to-noise ratio for further analysis. Supervised multivariate analysis (MVA) and investigation of average spectra have shown significant separation between control cells and cells treated with the DNA cross-linker PL63 on the basis of phosphate and DNA-related signatures. Meanwhile, the same control cells can be significantly distinguished from cells treated with the protein kinase inhibitor YA1 based on changes in the amide II region. Each of these separations can be linked directly to the known biochemical mode of action of each agent.

Open Access

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Abstract: Mycoplasma contamination represents a significant problem to the culture of mammalian cells used for research as it can cause disastrous effects on eukaryotic cells by altering cellular parameters leading to unreliable experimental results. Mycoplasma cells are very small bacteria therefore they cannot be detected by visual inspection using a visible light microscope and, thus, can remain unnoticed in the cell cultures for long periods. The detection techniques used nowadays to reveal mycoplasma contamination are time consuming and expensive with each having significant drawbacks. The ideal detection should be simple to perform with minimal preparation time, rapid, inexpensive, and sensitive. To our knowledge, for the first time, we employed Fourier transform infrared (FTIR) microspectroscopy to investigate whether we can differentiate between control cells and the same cells which have been infected with mycoplasmas during the culturing process. Chemometric methods such as HCA and PCA were used for the data analysis in order to detect spectral differences between control and intentionally infected cells, and spectral markers were revealed even at low contamination level. The preliminary results showed that FTIR has the potential to be used in the future as a reliable complementary detection technique for mycoplasma-infected cells.

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Abstract: Aortic valve is a part of the heart most frequently affected by pathological processes in humans what constitute a very serious health problem. Therefore, studies of morphology and molecular microstructure of the AV are needed. µSR- FTIR spectroscopy and microscopy represent unique tools to study chemical composition of the tissue and to identify spectroscopic markers characteristic for structural and functional features. Normal AV reveals a multi-layered structure and the compositional and structural changes within particular layers may trigger degenerative processes within the valve. Thus, deep insight into the structure of the valve to understand pathological processes occurring in AV is needed. In order to identify differences between three layers of human AV, tissue sections of macroscopically normal AV were studied using µSR- FTIR spectroscopy in combination with histological and histochemical stainings. Tissue sections deposited onto CaF2 substrates were mapped and representative set of IR spectra collected from fibrosa, spongiosa and ventricularis were analysed by Principal Component Analysis (PCA) in the spectral range between 1850–1000 cm−1 and 3050–2750 cm−1. PCA revealed a layered molecular structure of the valve and it was possible to identify IR bands associated to different tissue parts. Spongiosa layer was well differentiated from other two layers mainly based on IR bands characteristic for the distribution of glycosaminoglycans (GAGs) in the tissue – like 1170 cm−1 (υas(C-O-S)) and 1380 cm−1 (acetyl amino group). Additionally, it was distinguished from fibrosa and ventricularis based on 1085 cm−1 and 1240 cm−1 bands characteristic for GAGs and for carbohydrates- ν(C-O) and ν(C-O-C) respectively and nucleic acids -νsym(PO2−) and νasym(PO2−) respectively, which were less specific for this layer. The use of µSR- FTIR spectroscopy demonstrated co-localization of GAGs and lipids in spongiosa layer what may indicate their contribution in the very early phase of aortic valve calcific degeneration.

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Abstract: Over the last few years, both synchrotron-based FTIR (S-FTIR) and Raman microspectroscopies have helped to better understand the effects of drugs on cancer cells. However, cancer is a mixture of cells with different sensitivity/resistance to drugs. Furthermore, the effects of drugs on cells produce both chemical and morphological changes, the latter could affect the spectra of cells incubated with drugs. Here, we successfully cloned sensitive and resistant leukaemia cells to nilotinib, a drug used in the management of leukaemia. This allowed both the study of a more uniform population and the study of sensitive and resistant cells prior to the addition of the drug with both S-FTIR and Raman microspectroscopies. The incubation with nilotinib produced changes in the S-FTIR and Raman spectra of both sensitive and resistant clones to nilotinib. Principal component analysis was able to distinguish between cells incubated in the absence or presence of the drug, even in the case of resistant clones. The latter would confirm that the spectral differences between the so-called resistant clonal cells prior to and after adding a drug might reside on those more or less sensitive cells that have been able to remain alive when they were collected to be studied with S-FTIR or Raman microspectroscopies. The data presented here indicate that the methodology of cell cloning can be applied to different types of malignant cells. This should facilitate the identification of spectral biomarkers of sensitivity/resistance to drugs. The next step would be a better assessment of sensitivity/resistance of leukaemia cells from patients which could guide clinicians to better tailor treatments to each individual patient.