Magnetoresistance (MR) was measured in a La1.48Nd0.4Sr0.12CuO4 single crystal in perpendicular magnetic fields H up to 9 T in the region of the structural transition from the low-temperature orthorhombic (LTO) to low-temperature tetragonal (LTT) phase. The hysteretic MR exhibits discrete jumps or avalanches only when the transition is approached from the LTT phase, and only during the first field sweep. The properties of the hysteresis are found to be independent of the field driving rate. The results are consistent with the presence of magnetostructural domains coupled with the charge degrees of freedom. 相似文献
Objective: The aims of this study were to formulate simvastatin (SV)-loaded self-microemulsifying drug delivery systems (SMEDDS), and explore the potential of these drug delivery systems to improve SV solubility, and also to identify the optimal place in the gastrointestinal (GI) tract for the release of SV using coupled in vitro/in silico approach.
Significance: In comparison to other published results, this study considered the extensive pre-systemic clearance of SV, which could significantly decrease its systemic and hepatic bioavailability if SV is delivered into the small intestine.
Methods: SV-loaded SMEDDS were formulated using various proportions of oils (PEG 300 oleic glycerides, propylene glycol monocaprylate, propylene glycol monolaurate), surfactant (PEG 400 caprylic/capric glycerides) and cosurfactant (polysorbate 80) and subjected to characterization, and physiologically-based pharmacokinetic (PBPK) modeling.
Results: According to the in vitro results, the selected SMEDDS consisted of 10.0% PEG 300 oleic glycerides, 67.5% PEG 400 caprylic/capric glycerides, and 22.5% polysorbate 80. The use of acid-resistant capsules filled with SV-loaded SMEDDS was found helpful in protecting the drug against early degradation in proximal parts of the GI tract, however, in silico simulations indicated that pH-controlled drug release system that dissolve in the distal parts of the intestine might further improve SV bioavailability (up to 7.20%).
Conclusion: The obtained results suggested that combined strategy for the improvement of SV bioavailability should comprise solubility enhancement and delayed drug release. The developed SV-specific PBPK model could potentially be used to assess the influence of formulation factors on drug absorption and disposition when developing SV oral dosage forms. 相似文献
Single cell analyses have gained increasing interest over bulk approaches because of considerable cell-to-cell variability within isogenic populations. Herein, flow cytometry remains golden standard due to its high-throughput efficiency and versatility, although it does not allow to investigate the interdependency of cellular events over time. Starting from our microfluidic platform that enables to trap and retain individual cells on a fixed location over time, here, we focused on unraveling kinetic responses of single Saccharomyces cerevisiae yeast cells upon treatment with the antifungal plant defensin HsAFP1. We monitored the time between production of reactive oxygen species (ROS) and membrane permeabilization (MP) in single yeast cells for different HsAFP1 doses using two fluorescent dyes with non-overlapping spectra. Within a time frame of 2 min, only <0.3% cells displayed time between the induction of ROS and MP. Reducing the time frame to 30 s did not result in increased numbers of cells with time between these events, pointing to ROS and MP induction as highly dynamic and correlated processes. In conclusion, using an in-house developed continuous microfluidic platform, we investigated the mode of action of HsAFP1 at single cell level, thereby uncovering the close interdependency between ROS induction and MP in yeast. 相似文献
Four new fullero-steroids were synthesized starting from γ-aminobutyric acid (GABA)-incorporated fulleropyrrolidine and corresponding sterols. The synthesis, characterization, preliminary study on in vitro antioxidant activity as well as the steady state photophysical properties are presented. All synthesized compounds showed antioxidant activity 2-3-fold higher than the parent fullerene. The most active compound appeared to be as potent as standard antioxidant BHT (2,6-di-tert-butyl-4-methylphenol). Also, all of them fluoresce 6-8-fold stronger than C60, thus representing potential irradiation assisted pro-oxidants. With significantly increased lipophilicity, it could be expected that attached steroidal subunit enables better penetration of C60 to living cell membranes, thus facilitating its antioxidant activity. Based on all obtained results, newly synthesized covalent fullero-steroidal conjugates represent good candidates for potential antioxidants as well as pro-oxidants. 相似文献
W-Cu graded packings were produced under gravity and vertical vibration, from a granular medium (GM) formed by tungsten and copper agglomerates with agglomerate size distributions, which do not overlap. These bimodal packings were processed by powder metallurgy techniques to manufacture W-Cu graded pseudo-alloys with a variety of textures of the order of one millimeter. We present and discuss the temporal evolution of the W-Cu GM bed through photographs of two case- studies with frequencies of 600 and 900 Hz. Pre-sintered W-Cu-graded materials corresponding to vibration treatments of different duration are characterised by a SEM, and the tungsten concentration profiles are estimated by area analysis. Using a LASER dilatometer, we measured the temporal registers for the height of the GM bed for a wide range of frequencies and accelerations. Depending on the excitation level of the vibrated GM bed, three types of segregation regime were identified, as follows: segregation due to convection rolls, geometrical segregation aided by surface convection, and geometrical segregation. Only at low enough excitation, through geometrical segregation, does the GM bed reach a graded packing. This occurs due to the diffusive nature of this process, where the smaller agglomerates change their configurations through hopping in a potential energy gradient.We want to thank for the financial support by the Alexander von Humboldt Foundation and by the Deutsche Forschungsgemeinschaft within the program gradient materials under the project Mu 959/5. JF is very grateful to Prof. Manuel Cáceres and Prof. Shu San Hsiau and for stimulating discussions. 相似文献
There are several problems which are holding back the use of fuel cells. The utilization of fuel cells depends on the start-up costs which are very high due to the use of expensive materials for their construction. In that respect, we describe a cost-effective alkaline fuel cell (AFC) that uses solid, polymer based, membrane instead of conventionaly used, highly concentrated, corrosive, liquid alkaline electrolyte. This approach to AFC is potentially the basis of a simple, low-cost system, that can solve one of the problems of the highly-efficient and environment-friendly AFC.The focus of this paper are low cost composite alkaline membranes, based on poly(vinyl alcohol) (PVA). The PVA matrix is made by solution cast method and gamma irradiation crosslinking. Three different types of membranes are obtained in this manner - plain PVA membrane, PVA membrane cross-linked using gamma irradiation (γ-PVA) and composite PVA membrane doped with Mo (PVA-Mo). These membranes are immersed in the alkaline solution and investigated as anion exchange membranes. The performance of the solid alkaline fuel cells (SAFCs) containing these PVA membranes has been studied under hydrogen and oxygen gas flow on the Pt/C catalyst. Both, γ-PVA and PVA-Mo membranes are modified to absorb larger amounts of alkaline solution than the PVA membrane, thus greatly improving the performance of the SAFC, in terms of output power. This is clearly indicated in the polarisation curves. The electrochemical impedance spectroscopy measurements during the SAFC operation were also performed to give better insight in the effect observed. Investigation presented in this paper clearly indicates that solid alkaline PVA membranes can be used for the construction of the SAFCs. 相似文献
This study investigated the application of hydroxypropylmethylcellulose (HPMC) (2%, 3%, 4%), sugar beet fibre (SBF) (3%, 5%, 7%) and water (210%, 220%, 230%) into maize‐based gluten‐free (GF) formulations and their effects on the GF batter rheology and bread quality. HPMC incorporation in higher amounts reduced the compliance values of GF batter samples and increased the values of dynamic moduli indicating an improvement in the GF batter elastic characteristic. The same course of action with a less pronounced influence on mentioned rheological parameters had SBF addition. GF bread quality evaluation in terms of specific loaf volume and crumb texture (hardness, cohesiveness and springiness) reveals that HPMC and SBF incorporation at higher levels enhanced these quality parameters. The inclusion of HPMC and SBF coupled with adequate water content can improve the nutritional value of GF bread without negative influence on bread quality. 相似文献
The anatomy and ultrastructure of the short glandular trichomes occurring on young expanding leaves of Nicotiana tabacum were investigated using light and transmission electron microscopy. The objective of the present research was to characterize the cellular changes that occur during morphogenesis of short glandular trichomes, from initiation to senescence. Ultrastructural analysis of their secretory cells revealed characteristics common to gland cells: numerous mitochondria in highly organized cytoplasm, large nuclei, and an elaborate network of endoplasmic reticulum. Initial changes in nuclear and plastidial organization were observed at a more advanced secretory stage, marking the onset of senescence. During trichome senescence, gradual reduction of the cytoplasm density occurred along with structural changes of the plastids and the tonoplast. As a result of inward blebbing of the cytoplasm into the vacuole, membrane bound vesicular structures appeared in the vacuolar space. At the late secretory stage, marked by an increase in vacuolation and extraplasmic space, degenerative changes included further fragmentation of the cytoplasm and deterioration of the tonoplast. Multimembrane myelin bodies observed in the vacuolar space were indicative of membrane digestion although plasma membrane did not appear massively degraded. 相似文献