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61.
A classical and quantum mechanical generalized second law of thermodynamics in cosmology implies constraints on the effective equation of state of the universe in the form of energy conditions, obeyed by many known cosmological solutions, forbids certain cosmological singularities, and is compatible with entropy bounds. This second law is based on the conjecture that causal boundaries and not only event horizons have geometric entropies proportional to their area. In string cosmology the second law provides new information about nonsingular solutions. 相似文献
62.
Uwe Muller Christian Schubert Anton E. M. van de Ven 《General Relativity and Gravitation》1999,31(11):1759-1768
We derive an integral representation whichencodes all coefficients of the Riemann normalcoordinate expansion and also a closed formula for thosecoefficients. 相似文献
63.
J.-M. Colet C. Piérart F. Seghi I. Gabric R.N. Muller 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,134(2):199-205
The relative contributions of intravascular and intracellular compartments to the proton transverse relaxation of the isolated and excised rat liver were determined during the phagocytosis of superparamagnetic particles. The evolution of the proton transverse magnetization of the organ perfused with increasing doses of starch-coated magnetic microspheres was followed up using a Carr–Purcell–Meiboom–Gill sequence with various echo times. From the multiexponential fit of the echo train, the amplitudes and the relaxation ratesR2of the liver tissue were obtained. The results clearly indicate that shortly after contrast medium administration, an internalization takes place which can be followed by the rapid and biphasic evolution of the transverse relaxation rate of the water protons. A very fast decaying component looking like an initial loss of the magnetization is observed together with an increase of the relaxation rate of the remaining water tissue. This regime is strongly dependent on both the echo time and the iron concentration, a behavior characteristic of the agglomeration of magnetic particles. The examination of the liver tissues by electron microscopy shows that this clustering arises in cytoplasmic vacuoles. 相似文献
64.
Laurence Muhr Steve Pontvianne Katalin Selmeczi Cdric Paris Sandrine Boschi‐Muller Laetitia Canabady‐Rochelle 《Journal of separation science》2020,43(11):2031-2041
Some metal‐chelating peptides have antioxidant properties, with potential nutrition, health, and cosmetics applications. This study aimed to simulate their separation on immobilized metal ion affinity chromatography from their affinity constant for immobilized metal ion determined in surface plasmon resonance, both technics are based on peptide‐metal ion interactions. In our approach, first, the affinity constant of synthetic peptides was determined by surface plasmon resonance and used as input data to numerically simulate the chromatographic separation with a transport‐dispersive model based on Langmuir adsorption isotherm. Then, chromatographic separation was applied on the same peptides to determine their retention time and compare this experimental tR with the simulated tR obtained from simulation from surface plasmon resonance data. For the investigated peptides, the relative values of tR were comparable. Hence, our study demonstrated the pertinence of such numerical simulation correlating immobilized metal ion affinity chromatography and surface plasmon resonance. 相似文献
65.
Dr. Shi Jiang Dr. Wahiba Ramdani Dr. Eric Muller Dr. Changru Ma Dr. Marc Pera-Titus Dr. François Jerôme Prof. Karine De Oliveira Vigiera 《ChemSusChem》2020,13(7):1699-1704
The production of amine intermediates from biomass is capturing increasing attention. Herein, a simple and efficient preparation of l furan-derived amines was developed [e.g., 1-(furan-2-yl)-4-methylpentan-2-amine] with high yield (up to 95 %) from (E)-1-(furan-2-yl)-5-methylhex-1-en-3-one. The catalyst used was Ru/C, and it was recyclable up to the fourth cycle. To further realize cost-efficiency, a one-reactor tandem concept was attempted. To this aim direct reaction from furfural was investigated. A high yield (74 %) towards 1-(furan-2-yl)-4-methylpentan-2-amine could be achieved starting directly from furfural in the presence of methyl isobutyl ketone, NH3, H2, and Ru/C catalyst. 相似文献
66.
67.
Dr. I van Scodeller Prof. Karine De Oliveira Vigier Dr. Eric Muller Dr. Changru Ma Dr. Frédéric Guégan Dr. Raphael Wischert Dr. François Jérôme 《ChemSusChem》2021,14(1):313-323
The synthesis of relevant renewable aromatics from bio-based furfural derivatives and cheap alkenes is carried out by using a Diels-Alder/aromatization sequence. The prediction and the control of the ortho/meta selectivity in the Diels-Alder step is an important issue to pave the way to a wide range of renewable aromatics, but it remains a challenging task. A combined experimental-theoretical approach reveals that, as a general trend, ortho and meta cycloadducts are the kinetic and thermodynamic products, respectively. The nature of substituents, both on the dienes and dienophiles, significantly impacts the feasibility of the reaction, through a modulation on the nucleo- and electrophilicity of the reagents, as well as the ortho/meta ratio. We show that the ortho/meta selectivity at the reaction equilibrium stems from a subtle interplay between charge interactions, favoring the ortho products, and steric interactions, favoring the meta isomers. This work also points towards a path to optimize the aromatization step. 相似文献
68.
Stefan Aeby Geoffroy J. Aubry Nicolas Muller Frank Scheffold 《Advanced Optical Materials》2021,9(6):2001699
Photonic crystals display partial or full band gaps that become more pronounced with rising refractive index contrast. However, imperfections in the material cause light scattering and extinction of the interfering propagating waves. Positive as well as negative defect volumes may contribute to this kind of optical perturbation. In this study, 3D woodpile photonic crystals are fabricated and characterized with a pseudo-bandgap for near-infrared optical wavelengths. By direct laser writing, defects are introduced in the periodic structure at selected positions. It is shown that defect scattering can be modeled by considering the difference between the disordered and the regular structure. The findings pave the way toward better control and understanding of the role of defects in photonic materials that will be crucial for their usability in potential applications. 相似文献
69.
Chantelle Human Dalene de Beer Magdalena Muller Marieta van der Rijst Marique Aucamp Andreas Tredoux Andr de Villiers Elizabeth Joubert 《Molecules (Basel, Switzerland)》2021,26(17)
Green rooibos extract (GRE), shown to improve hyperglycemia and HDL/LDL blood cholesterol, has potential as a nutraceutical beverage ingredient. The main bioactive compound of the extract is aspalathin, a C-glucosyl dihydrochalcone. The study aimed to determine the effect of common iced tea ingredients (citric acid, ascorbic acid, and xylitol) on the stability of GRE, microencapsulated with inulin for production of a powdered beverage. The stability of the powder mixtures stored in semi-permeable (5 months) and impermeable (12 months) single-serve packaging at 30 °C and 40 °C/65% relative humidity was assessed. More pronounced clumping and darkening of the powders, in combination with higher first order reaction rate constants for dihydrochalcone degradation, indicated the negative effect of higher storage temperature and an increase in moisture content when stored in the semi-permeable packaging. These changes were further increased by the addition of crystalline ingredients, especially citric acid monohydrate. The sensory profile of the powders (reconstituted to beverage strength iced tea solutions) changed with storage from a predominant green-vegetal aroma to a fruity-sweet aroma, especially when stored at 40 °C/65% RH in the semi-permeable packaging. The change in the sensory profile of the powder mixtures could be attributed to a decrease in volatile compounds such as 2-hexenal, (Z)-2-heptenal, (E)-2-octenal, (E)-2-nonenal, (E,Z)-2,6-nonadienal and (E)-2-decenal associated with “green-like” aromas, rather than an increase in fruity and sweet aroma-impact compounds. Green rooibos extract powders would require storage at temperatures ≤ 30 °C and protection against moisture uptake to be chemically and physically shelf-stable and maintain their sensory profiles. 相似文献
70.
Sithandiwe E. Mazibuko-Mbeje Sinenhlanhla X. H. Mthembu Andani Tshiitamune Ndivhuwo Muvhulawa Fikile T. Mthiyane Khanyisani Ziqubu Christo J. F. Muller Phiwayinkosi V. Dludla 《Molecules (Basel, Switzerland)》2021,26(20)
Our group has progressively reported on the impact of bioactive compounds found in rooibos (Aspalathus linearis) and their capacity to modulate glucose homeostasis to improve metabolic function in experimental models of type 2 diabetes. In the current study, we investigated how the dietary flavone, orientin, modulates the essential genes involved in energy regulation to enhance substrate metabolism. We used a well-established hepatic insulin resistance model of exposing C3A liver cells to a high concentration of palmitate (0.75 mM) for 16 hrs. These insulin-resistant liver cells were treated with orientin (10 µM) for 3 h to assess the therapeutic effect of orientin. In addition to assessing the rate of metabolic activity, end point measurements assessed include the uptake or utilization of glucose and palmitate, as well as the expression of genes involved in insulin signaling and regulating cellular energy homeostasis. Our results showed that orientin effectively improved metabolic activity, mainly by maintaining substrate utilization which was marked by enhanced glucose and palmitate uptake by liver cells subjected to insulin resistance. Interestingly, these effects can be explained by the improvement in the expression of genes involved in glucose transport (Glut2), insulin signaling (Irs1 and Pi3k), and energy regulation (Ampk and Cpt1). These preliminary findings lay an important foundation for future research to determine the bioactive properties of orientin against dyslipidemia or insulin resistance in reliable and well-established models of type 2 diabetes. 相似文献