201 research outputs found
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Nonlinear Maxwell behavior of sodium silicate glass in the surroundings of glass transition temperature
Presented are results from uniaxial cylinder upsetting tests of sodium silicate glass at different constant deformation rates each combined with relaxation experiments in the temperature range 480 to 580°C. Due to the complete stress relaxation to final load zero (vanished carrying capacity) also below glass transition temperature Tg, it follows Maxwell behavior in principle. But the rheological analyses of loading and unloading experiments together show that only nonlinear Maxwell model approaches can adequately describe the deformation behavior of the glass in the surroundings of Tg
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Mechanical properties of sheet glass at high pressure during indentation experiments
Viscous flow is responsible for permanent deformation of glasses above the transformation temperature (Tg). The results of macroscopic indentation experiments (maximum loading forces Fmax ≥ 2 N) with sharp indenters (Vickers or Berkovich pyramids) demonstrate this property by crack-free indents at T ≥ Tg. But it is also possible to make crack-free indents at room temperature (RT), well below Tg, if the load, the contact area and the deformation rate, respectively, are small enough, which is consistent with glass as a supercooled liquid but inconsistent with glass as a well-known ideally brittle material at RT The mechanisms of this permanent deformation of glasses by indentation near RT have not been understood completely up to now. For the analysis of the macroscopic indentation experiments with Vickers pyramids and spherical indenters, respectively, a viscoelastic deformation behaviour is assumed for the complete temperature range from RT to Tg. Therefore the rheological analysis of all experiments were performed with the help of a simple Maxwell model. The results of Vickers indentation experiments were compared with cylinder compression experiments and ball indentation experiments which were analysed by the same rheological principles
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Viscosity of glass below the transformation temperature
Glass is an ideally brittle material at room temperature. The results of hardness indentation tests demonstrate this property by crack formation at the corners of the indent. But it is possible to avoid the crack formation if the load, the contact area and the deformation rate, respectively, are small enough. The mechanisms of this permanent deformation of brittle glasses by indentation close to room temperature have not been understood completely up to now. Viscous flow is responsible for permanent deformation of glasses above the transformation temperature (Tg). The same mechanism of deformation during indentation experiments is assumed in this work hypothetically, taking into account the very high stresses (GPa range) in the local volume around the indenter tip. This hypothesis of deformation at room temperature will be verified by independent experiments that work like viscometers in principle (e.g. cylinder compression experiments, ball indentation experiments). All experiments were analysed with the help of simple rheological models. Additionally some ball indents were analysed by topographical investigations to get first hints of viscoelastic deformation behaviour below Tg of glass
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Load dependence of the hardness of silicate glasses - Not just due to indenter tip defects
The real contact area of Berkovich indenters with typical indenter tip defects is calculated as a function of the penetration depth in a general form and compared with literature results for Vickers indenters. The influence of the tip defects on the load dependence of hardness is treated for both types of indenters, taking into account possible purely elastic deformation at the beginning of contact. Using the example of recording microhardness measurements on glass made using a Berkovich indenter, it is shown that a linear dependence exists between load and depth of penetration in the millinewton load region which can be explained by a rounded indenter tip. However, the resulting corrections for the real contact area are not sufficient to compensate for the load dependence of the hardness in the entire load region. A method is proposed for showing definitely that the load dependence of the hardness is caused not just by indenter tip defects but also by material properties. This method is tested on extensive measurements of the authors, as well as on results of Frischat and the Oak Ridge group
TG-FTIR measurement of CO2-H2O co-adsorption for CO2 air capture sorbent screening
Capturing atmospheric CO2 using solid sorbents is gaining interest. As ambient air normally contains much more (up to 100 times) water than CO2, a selective sorbent is desirable as co-adsorption will most likely occur. In this study, a convenient method based on an TG-FTIR analysis system is developed and used to characterize sorbents for their water and CO2 adsorption capacity when exposed to ambient air. The method allows to determine quantitatively the co-adsorbed amounts of CO2 and water from small sample sizes (10 mg range) and is expected to be a useful instrument in sorbent screening and evaluatio
Editorial: diet, inflammation and colorectal cancer
This Research Topic was designed to provide the reader with an overview of the impact of body weight and adiposity, as well as of specific food compounds on the inflammatory status in health and disease states, such as CRC. We collected original and review articles featuring the role of specific food compounds in the regulation of immune response and their potential therapeutic implications, the effect of polyunsaturated fatty acids (PUFA), oligosaccharides, polyphenols and body weight in the modulation of inflammation and long-term disease outcomes, highlighting the link between diet, inflammation, and CRC
High-throughput Soxhlet extraction method applied for analysis of leaf lignocellulose and non-structural substances
The traditional Soxhlet extraction method is commonly employed to extract soluble components from non-soluble components in a solid matrix, for example, non-structural substances in biomass samples that can be separated from structural lignocellulosic compounds in biomass samples. Conventional laboratory procedures for such extractions typically involve a low sample throughput, with each run being performed individually, resulting in time-consuming and labour-intensive processes, making them impractical for analysing large sample sets. In research fields such as Earth Observation in Forest Ecosystems, extensive fieldwork sampling is required across large study areas, resulting in a substantial number of leaf samples, each with limited mass. In this study, an innovative adaptation of the conventional National Renewable Energy Laboratory (NREL) Soxhlet method is developed to create a high-throughput mini-Soxhlet apparatus that enables the simultaneous extraction of up to nineteen samples, each with a mass of 0.3 g per sample. With this adaptation, we measured the lignocellulose and extractive in 343 leaf samples collected from four temperate forest tree species. This modified approach enhances versatility and can be applied to all solid-liquid extractions and various types of vegetation tissues, such as tree leaves, shrubs, crops, feedstock, and other non-woody samples.• The solid-liquid extraction method has been implemented in a heating block facilitating 19 small flasks to measure multiple samples simultaneously while requiring only a small sample mass.• The apparatus set-up was constructed using an alumina heating block mounted on a standard laboratory heating plate. Boiling flask tubes were placed in the heating block and equipped with condenser caps and filters on glass rods on which the solid samples were placed.• The adjustments made the method suitable for application to diverse vegetation tissues and non-woody sample types. It holds particular appeal for research areas that necessitate a high sample number
Range estimation system for powered wheelchairs
In this paper, we present a method to estimate a wheelchair’s power consumption and therefore its battery autonomy. The wheelchair powertrain is modeled to enable a virtual driving simulation. The use of a white box model enables an adaption to other systems and configurations. This model outputs the actual battery and motor currents within a simulation for a given route and speed profile. These currents affect the battery’s SoC, whose total charge depends on its temperature. To account changes of the available charge, a simplistic model of the battery’s temperature dependence is introduced, that has been acquired via discharge cycles within a climate chamber. Furthermore, an a priori simulation uses the model to estimate the SoC after the virtual completion of a route with a corresponding height and velocity profile. Finally, the paper compares the results of the simulation with real measurements using the recorded tracks and the generated virtual routes. Since the input for the a priori estimation relies on virtual routes, their quality is assessed as well
Disruption of the murine major vault protein (MVP/LRP) gene does not induce hypersensitivity to cytostatics
Vaults are ribonucleoprotein particles with a distinct structure and a
high degree of conservation between species. Although no function has been
assigned to the complex yet, there is some evidence for a role of vaults
in multidrug resistance. To confirm a direct relation between vaults and
multidrug resistance, and to investigate other possible functions of
vaults, we have generated a major vault protein (MVP/lung
resistance-related protein) knockout mouse model. The MVP(-/-) mice are
viable, healthy, and show no obvious abnormalities. We investigated the
sensitivity of MVP(-/-) embryonic stem cells and bone marrow cells derived
from the MVP-deficient mice to various cytostatic agents with different
mechanisms of action. Neither the MVP(-/-) embryonic stem cells nor the
MVP(-/-) bone marrow cells showed an increased sensitivity to any of the
drugs examined, as compared with wild-type cells. Furthermore, the
activities of the ABC-transporters P-glycoprotein, multidrug
resistance-associated protein and breast cancer resistance protein were
unaltered on MVP deletion in these cells. In addition, MVP wild-type and
deficient mice were treated with the anthracycline doxorubicin. Both
groups of mice responded similarly to the doxorubicin treatment. Our
results suggest that MVP/vaults are not directly involved in the
resistance to cytostatic agents
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