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•The cooling rate dependence of the glass transition is measured in a cooling rate range of more than six decades.•The cooling rate dependence of the glass transition can be described ...by a Vogel–Fulcher–Tammann–Hesse equation.•The influence of the heat transfer conditions in a Flash DSC is discussed.
The thermal glass transition of polystyrene (PS) is measured in a range between 0.003K/s and 4000K/s using a conventional DSC 1 and a Flash DSC 1 from Mettler-Toledo. The dependency between the cooling rate and the glass transition temperature is in accordance with the Vogel–Fulcher–Tammann–Hesse (VFTH) equation, as it is usually used for description of the frequency–temperature relationship of the dynamic glass transition (or main relaxation process). Furthermore we discuss the influence of the thermal lag on the measurement and develop correction methods.
Background: Curcumin is a compound obtained from the rhizomes of Curcuma Longa. It has various pharmacological properties like anti-inflammatory, anti-oxidant, anti-hyperlipidemic, etc. However, it ...also has some limitations that restrict its use as a medicine. Material and method: In the present study, a eutectic mixture of curcumin and glycine (35% and 65%) was prepared to improve its dissolution rate and photostability, characterized by DSC, FTIR, and XRD studies. Result and discussion: After 40 minutes, the eutectic mixture dissolved 10-fold more than the parent drug. The photostability studies were conducted according to ICH Q1B guidelines; after the seventh day of accelerated photostability studies, curcumin-glycine eutectic mixtures showed 36% degradation, 34% less than pure curcumin. Conclusion: The present study revealed that the physicochemical properties of BCS class II drugs can be improved by forming an eutectic mixture.
Nanoporous TiO2 structures were successfully applied for the fabrication of DSC electrodes, providing high surface areas and large pore sizes at the same time. High photocurrent was induced in these ...DSCs by great adsorption of dye molecules and efficient electrolyte diffusion, caused by the generated hierarchical pore structures in the TiO2 layer.
A key problem of how to distinguish between biotic and abiotic carbonate minerals in nature and/or in the laboratory has confused researchers for some time. Although numerous studies have been ...performed to explore the formation mechanism and the unique characteristics of biotic minerals, the issue needs to be studied further. Here, biotic calcite precipitation was induced by the microorganism Bacillus cereus MRR2 (GenBank KY810857), while organogenic and inorganogenic calcite was investigated in parallel. The results indicate that carbonic anhydrase (CA, a common enzyme of bacteria) promoted carbon dioxide hydration to release HCO3− and CO32− in the process of calcite precipitation; the pH increased from 7.2 to 8.9 as a result of the combination effect of the released ammonia by B. cereus MRR2 and the HCO3− and CO32− ions originating from the CA reaction. Glutamic acid is the most abundant amino acid in the extracellular polymeric substances of the bacteria, and its free carboxyl ions with a large number of negative charges in the alkaline environment facilitated the adsorption of calcium ions. The biotic calcite has a series of unique characteristics different from the organogenic and inorganogenic calcites, such as particular morphologies, P element composition and a variety of organic functional groups. Intracellular amorphous nanospheres without any crystal structure are also recorded. Stable carbon isotope analyses show that the biotic calcite (−20.9‰) has more negative δ13C values than the organogenic calcite (−15.6‰) and inorganogenic calcite (−11.7‰), indicating that microbial activity strongly affected the carbon isotope composition of biotic calcite. More importantly, the crystallinity and activation energy of the biotic calcite are clearly higher than those of organogenic calcite, suggesting that the thermal stability of biotic calcite is much higher. Thus, this study provides important insights into understanding the mechanisms of microbial biomineralization and the processes of biotic calcite formation, especially the roles microbes played in mineral nucleation and growth, as well as the unique characteristics of the resulting minerals. This study may provide useful evidence for further recognizing biotic and abiotic calcite in the geological record.
The model of biotic, organogenic and inorganogenic calcite. Display omitted
•The pH increase is caused by the combination effect of ammonia and CA.•Biotic calcite has higher thermal stability than abiotic calcite.•Biotic calcite has more negative δ13C values than abiotic calcite.•Glutamic acid is the most abundant amino acid in EPS.•The intracellular amorphous nanospheres are found.
Plant proteins are becoming of increasing interest, since they are a more sustainable protein source than milk protein. One plant protein of interest would be pea protein. In contrast to milk ...proteins there has been less research done on extracting native pea proteins. Currently, commercial pea proteins are only available highly denatured and aggregated. There are three commonly used extraction methods on laboratory scale: alkali extraction with isoelectric precipitation, salt extraction and micellar precipitation. Within this study, these three extraction methods next to one modified production process and a commercial pea protein isolate were compared with each other focusing on conformational alteration during the extraction process. Solubility and particle size in combination with charge at different pHs and ionic strength and denaturation temperature and enthalpy change at pH 7 in 0.1 M NaCl and 1 M NaCl have been taken as indicators of conformational alteration. Differences in structure between the obtained protein products were observed. Albumins were lost during precipitation in alkali extraction – isoelectric precipitation and micellar precipitation. Solubility was highest for pH 3 and pH 8. Micellar precipitated protein product formed micelles at low ionic strength and solubility of these could be increased by addition of salt. It has been found, that both steps during the extraction process, solubilisation and precipitation, had an influence on the conformational alteration of the protein. Solubilisation had in impact on the denaturation of the protein. Precipitation had an impact on the protein profile and irreversible or reversible aggregation.
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•Rehydration and precipitation step have an influence on the conformational alteration.•The main influence on the protein profile is determined by the precipitation step.•Denaturation and irreversible aggregation can occur during rehydration and precipitation.•Freeze-drying at pH 7 versus pH 4.5 has an influence on conformational alteration.
The aim of this article is to study a fuzzy-based decentralized adaptive control strategy for the nonstrict-feedback fractional-order nonlinear large-scale systems with unknown control directions. In ...each step of the recursive processes, the fuzzy logic systems are employed to identify unknown nonlinear functions. To handle the difficulties caused by unknown control directions, a Nussbaum function technique is adopted. Furthermore, by introducing the dynamic surface control technique into the adaptive backstepping recursive design algorithm, a fuzzy-based decentralized adaptive control strategy is formulated. Both the stability of the controlled system and the convergence of the tracking errors are proved by constructing the fractional-order Lyapunov functions. Finally, the validity and effectiveness of the designed decentralized control scheme are confirmed via two simulation examples.
The microstructural evolution and precipitation kinetics of an Al-4.8 wt% Cu alloy were investigated by transmission electron microscope (TEM) and differential scanning calorimetry (DSC) under ...different heating rates. The DSC results of quenched Al–Cu alloy obtained at different heating rates were used to calculate kinetics parameters of θ′ precipitation. The activation energy for the precipitate growth obtained by the Kissinger method and the analytical model were determined as 53.54 kJ/mol and 85 ± 5 kJ/mol, respectively. For aged Al–Cu alloys, the typical microstructure of θ′ precipitates and the phase relationship with the matrix were obtained. In addition, θ′ phase coarsening kinetics is in coincident with the classical Liftshitz-Slyozov-Wagner (LSW) theory, and the calculated activation energy suggests that coarsening kinetics of θ′ is controlled by diffusion of Cu in the matrix of the investigated Al–Cu alloy.
•The activation energies of θ′ phase was calculated as 53.54 and 80~90 kJ/mol by Kissinger and Analytical model, respectively.•The coarsening activation energy of the θ′ precipitate for aged Al–Cu alloys (230, 260, 290, and 320 °C) was 80.2 kJ/mol.•The combination of the Analytical model and LSW can effectively investigate the precipitation kinetics of Al–Cu alloys.
The influence of minor solute additions of Mg, Ag and Zn and their combinations on the precipitation kinetics and strengthening of an Al-Cu-Li alloy has been systematically investigated. Combining ...differential scanning calorimetry (DSC) and small-angle X-ray scattering (SAXS) provides information on how alloy chemistry changes the precipitation sequence, the precipitation kinetics in non – isothermal and in isothermal conditions, and the related strengthening. When adding Mg, the precipitation kinetics are strongly accelerated, which is shown to be related to the dominant formation of T1 precipitates. When adding Ag and Zn together with Mg, further enhancement of precipitation kinetics is observed, without change of the precipitation sequence, probably due to a more efficient nucleation of T1. The intrinsic strengthening potential of the T1 phase is shown to be unchanged by the addition of Ag and Zn, and the higher strength reached in the alloys containing these additions is shown to be due to a higher precipitate volume fraction.
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