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排序方式: 共有163条查询结果,搜索用时 15 毫秒
1.
Hongyu Wang Yolande Berta Gary S. Fischman 《Journal of the American Ceramic Society》1992,75(5):1080-1084
The microstructure of silicon carbide whiskers synthesized by carbothermal reduction of silicon nitride has been studied using transmission electron microscopy. All of the whiskers examined are single crystals, and grow in the (111) crystallographic direction. Two different forms of stacking faults and microtwins were observed; in one the planar defects are normal to the whisker growth direction, and the other has the defect planes at an angle of about 70° to the growth axis, while both forms of the defects are on the [111] closed-packed planes. Without the addition of catalyst, droplets containing metallic impurities were not found at the tips of the whiskers synthesized by the present process. A core and outer regions were observed in the single-crystal whiskers, which may be evidence that the whiskers were formed by a two-stage mechanism. 相似文献
2.
C Folwaczny M Jochum N Noehl D Schnettler K Loeschke H Fricke 《Canadian Metallurgical Quarterly》1998,36(8):625-633
Isolated hearts from two strains of rats bred for sensitivity or resistance to amygdala kindling that also exhibit, in vivo, differential sensitivity to the cardiotoxicity of cocaine were studied. The goal was to determine if the differential cardiotoxic sensitivity was due, at least in part, to intrinsic strain-dependent differences in the heart. The Langendorff preparation was used (n=8 per strain). Hearts were perfused with increasing concentrations of cocaine (5 x 10(-6), 1 x 10(-5), 5 x 10(-5), 1 x 10(-4), and 5 x 10(-4) M) for 5 min with a 5 min washout between exposure to successive concentrations. Consistent with in vivo observations, hearts from genetically slow amygdala kindling rats (Slow) required lower cocaine doses to develop cardiac arrhythmias and arrest as compared to the hearts from genetically fast amygdala kindling rats (Fast). At 5 x 10(-5) M cocaine arrhythmias occurred in 38% (3/8) Slow and 0% Fast hearts. Five of 8 Slow hearts and none of 8 Fast hearts were arrested by 10(-4) M cocaine. Arrest in Fast hearts occurred only with 5 x 10(-4) M cocaine. Cocaine constricted coronary arteries (no significant difference between strains). On the other hand, coronary arteries of Slow but not Fast hearts dilated during cocaine washout after perfusion with all but the highest concentration of cocaine. We conclude that factors intrinsic to the heart and coronary artery influence the sensitivity or response of these structures to cocaine. 相似文献
3.
Noemi Eiro Sandra Cid Nuria Aguado María Fraile Nagore de Pablo Berta Fernndez Francisco Domínguez Luis O. Gonzlez Francisco J. Vizoso 《International journal of molecular sciences》2021,22(1)
Tumor-infiltrating immune cells phenotype is associated with tumor progression. However, little is known about the phenotype of the peripheral blood mononuclear cells (PBMC) from breast cancer patients. We investigated MMP1 and MMP11 expression in PBMC from breast cancer patients and we analyzed gene expression changes upon their interaction with cancer cells and cancer-associated fibroblasts (CAF). We measured the impact of PBMC on proinflammatory gene expression in breast cancer cells, normal fibroblast (NF), and CAF and the impact on proliferation and invasiveness capacity of breast cancer cells. Gene expression of MMP1 and MMP11 in PBMC from breast cancer patients (n = 54) and control (n = 28); expression of IL1A, IL6, IL17, IFNβ, and NFĸB in breast cancer cell lines (MCF-7 and MDA-MB-231); and, additionally, IL10 and MMP11 in CAF and NF were analyzed by qRT-PCR before and after co-culture. Our results show the existence of a subpopulation of breast cancer patients (25.9%) with very high levels of MMP11 gene expression in PBMC. Also, gene expression of MMP1 and MMP11 increases in PBMC after co-culture with breast cancer cell lines, NF or CAF. PBMC from healthy or breast cancer patients induce an increased proliferation rate on MCF-7 and an increased invasiveness capacity of MDA-MB-231. Finally, we show a differential expression profile of inflammatory genes in NF and CAF when co-cultured with control or breast cancer PBMC. We have observed that MMPs’ expression in PBMC is regulated by the microenvironment, while the expression of inflammatory genes in NF or CAF is differentially regulated by PBMC. These findings confirm the importance of the crosstalk between stromal cells and suggest that PBMC would play a role in promoting aggressive tumor behavior. 相似文献
4.
Matrix compositions based on Si2N2O, with Al2O3 and CaO additions, were used to hot press Nicalon SiC fibre-reinforced composites at 1600 °C. With both CaO and Al2O3 additions, eutectic melting formed an appreciable volume of liquid phase during hot pressing, which remained as a stable glassy phase in the cooled composites. This liquid phase fostered formation of 240 nm thick carbon-rich interphases between the fibres and the matrix. These interphases showed relatively low interfacial shear strength and resulted in composites which showed non-catastrophic, notch-independent fracture. Matrices using either Al2O3 or CaO did not form adequate liquid phase to form coarse interphases, and fracture was catastrophic in nature. Post-heat treatment of the composites at 1000 °C showed peripheral oxidation (removal of the carbon content of the interphase) indicating limited protection afforded when glassy phase was present in the matrix. Controlled cooling in the hot press did not cause the liquid regions to devitrify. 相似文献
5.
Berta Gorospe Jos J. G. Moura Carlos Gutierrez-Merino Alejandro K. Samhan-Arias 《International journal of molecular sciences》2022,23(23)
Caveolin-2 is a protein suitable for the study of interactions of caveolins with other proteins and lipids present in caveolar lipid rafts. Caveolin-2 has a lower tendency to associate with high molecular weight oligomers than caveolin-1, facilitating the study of its structural modulation upon association with other proteins or lipids. In this paper, we have successfully expressed and purified recombinant human caveolin-2 using E. coli. The structural changes of caveolin-2 upon interaction with a lipid bilayer of liposomes were characterized using bioinformatic prediction models, circular dichroism, differential scanning calorimetry, and fluorescence techniques. Our data support that caveolin-2 binds and alters cholesterol-rich domains in the membranes through a CARC domain, a type of cholesterol-interacting domain in its sequence. The far UV-CD spectra support that the purified protein keeps its folding properties but undergoes a change in its secondary structure in the presence of lipids that correlates with the acquisition of a more stable conformation, as shown by differential scanning calorimetry experiments. Fluorescence experiments using egg yolk lecithin large unilamellar vesicles loaded with 1,6-diphenylhexatriene confirmed that caveolin-2 adsorbs to the membrane but only penetrates the core of the phospholipid bilayer if vesicles are supplemented with 30% of cholesterol. Our study sheds light on the caveolin-2 interaction with lipids. In addition, we propose that purified recombinant caveolin-2 can provide a new tool to study protein–lipid interactions within caveolae. 相似文献
6.
Ana I.R.N.A. Barros Fernando M. Nunes Berta Gonçalves Richard N. Bennett Ana Paula Silva 《Food chemistry》2011
In this work the total vitamin C contents (ascorbic acid + dehydroascorbic acid) and antioxidant activity of raw and cooked chestnuts was evaluated. The vitamin C contents of raw chestnuts varied significantly between the different cultivars (cv) studied and it varied from 400 mg/kg dry weight (cv Lada) to 693 mg/kg dry weight (cv Martaínha). The different cultivars behave differently during the cooking process concerning the loss of vitamin C. A significant decrease in the vitamin C content of the chestnuts was observed, 25–54% for the boiling process and 2–77% for the roasting process. Boiled and roasted chestnuts can be good sources of vitamin C since it may represent 22.4%, 16.2%, 26.8% and 19.4%, respectively, of the recommended dietary intake for an adult man and woman. The cooking process significantly changed the antioxidant activity of the chestnuts. A difference was observed between the cultivars during the cooking processes, concerning the antioxidant activity. For the raw chestnuts the variation in vitamin C content of the chestnuts explains 99% of the antioxidant activity variation but for the roasted and boiled chestnuts this percentage significantly decreases to 51% and 88%, respectively. Although a high antioxidant activity is still present in the cooked chestnuts, the cause for this antioxidant activity is less dependent on the vitamin C content of the chestnuts, probably due to the conversion of ascorbic acid to dehydroascorbic acid. The increase in gallic acid during the cooking process, presumably transferred from the peels to the fruit, also contributes to the high antioxidant activity observed for the cooked chestnuts. 相似文献
7.
Paolo Casoli Andrea Vacca Gian L. Berta 《Simulation Modelling Practice and Theory》2010,18(2):125-138
This paper describes a numerical procedure for the prediction of the homogenizing performance of high pressure homogenizing valves used in diary plants. The method is based on a strict interaction between a complex CFD code and a simple homogenizing simulation code developed by the authors. This latter implements a mathematical model for the evaluation of droplets break-up, that needs an accurate evaluation of few significant fluid dynamic parameters in the whole fluid dynamic domain inside the valve. Due to the relevant pressure gradients within the flow and to the possibility of cavitation, particular attention has been paid in defining the fluid model, the mesh and the parameters required for CFD simulations. Notwithstanding the quite simple model of the homogenizing process, comparatively with the complexity of phenomena involved, the first results obtained are in general agreement with the experimental data available. These results point out the potential of the procedure proposed as a starting point for further implementation of more complex effects. 相似文献
8.
Carmen Coya Constanza Ruiz Ángel Luis Álvarez Susana Álvarez-García Eva M. García-Frutos Berta Gómez-Lor Alicia de Andrés 《Organic Electronics》2012,13(10):2138-2148
We present a series of differently substituted star-shaped hexaaryltriindoles with tunable light-emitting properties. The deep blue emission is unchanged by donor peripheral substituents while an increasing acceptor character produces a reduction of the optical gap, an increased Stokes shift and eventually leads to the appearance of a new electronic level and to the simultaneous deep blue (413 nm) and green (552 nm) emission in solution. Quenching by concentration increases with the acceptor character but is lower as the tendency of these compounds to aggregate is stronger. Solution processed thin films present optical and morphological qualities adequate for device fabrication and similar electronic structure compared to solutions with an emission range from 423 nm up to 657 nm (red), demonstrating the possibility of tuning the energy levels by chemical functionalization. We have fabricated and characterized single-layer solution processed organic light emitting diodes (OLED) to investigate the influence on transport and emission properties of the substituting species. We analyzed the I–V response using a single-carrier numerical model that includes injection barriers and non-uniform electric-field across the layer. As a result, we obtained the electric field dependence of the mobility for each device. Best results are obtained on the most electron rich derivative functionalized with six donor methoxy groups. This material shows the highest emission efficiency in solid state, due to aggregation-induced enhancement, and better transport properties with the highest mobility and a very low turn-on voltage of 2.8 V. The solution processed OLED devices produce stable deep blue (CIE coordinates (0.16, 0.16)) to white (CIE coordinates (0.33, 0.3)) emission with similar luminous efficiencies. 相似文献
9.
10.
The transit time of the coolant, and thus its velocity, has been measured using the temperature fluctuation at the outlet of a reactor core. An impulse response function estimation is introduced, which substitutes the widely used cross-correlation measurement technique. It is shown in theory and practice that the time delay estimation is improved when using the impulse response function instead of the cross-correlation function in parameter estimation. Extremely low velocities (down to 2 cm/sec) have been measured in a natural circulation regime in a research reactor. 相似文献