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排序方式: 共有226条查询结果,搜索用时 15 毫秒
91.
Amélia S. F. Santos José A. M. Agnelli 《Polymer-Plastics Technology and Engineering》2013,52(3):254-259
This work was accomplished employing solid-state polymerization (SSP) under less severe vacuum intensity (30 mmHg) in static mode at different times and temperatures. The influence of these parameters on intrinsic viscosity measurements was performed using Response Surface Methodology. The effect of temperature on intrinsic viscosity gains showed to be less pronounced than expected due to SSP being surface diffusion-controlled. The SSP efficiency for temperature as high as 230°C and dwell times higher than approximately 330 min showed lower increment on intrinsic viscosity than at immediately lower temperatures, although above approximately 215°C. This effect is a consequence of higher conversion rates of side reactions with increasing temperatures, their cumulative effect with increasing dwell time, and lower increment of polycondensation convertion rate with temperature under less severe vacuum intensity. The process temperatures and intervals determined, which allow PET recycling into new injected bottles, were moderates. 相似文献
92.
93.
Biegelmeyer R Andrade JM Aboy AL Apel MA Dresch RR Marin R Raseira Mdo C Henriques AT 《Journal of food science》2011,76(7):C991-C996
Abstract: Strawberry guava (Psidium cattleianum Sabine) is a native fruit of Brazil widely consumed fresh and used in the food industry. In this context, the present study deals with the chemical characterization and the antioxidant activity of the red (Psidium cattleianum) and yellow (P. cattleianum var. lucidum Hort.) strawberry guava fruits, cultivars Irapuã and Ya‐Cy, respectively. Knowledge of chemical composition is fundamental to human nutrition, contributing to the quality of foods. Phenolic compounds in both fruits were analyzed by HPLC–DAD and the total flavonoid content was determined by the Folin–Ciocalteu assay. The antioxidant activity was evaluated by the total reactive antioxidant (TRAP) method. Psidium cattleianum presented a higher content of polyphenolic compounds than P. cattleianum var. lucidum (501.33 and 292.03 mg/100 g, respectively), with hyperoside being one of the major flavonoids identified for both cultivars. In addition to flavonoids, P. cattleianum presented an anthocyanin, identified as cyanidin. The antioxidant activity varied in a concentration‐dependent manner for both strawberry guava species. The volatile oils in fruits and fatty acids in seeds were quantified by GC‐EM. The analysis of the essential oil of yellow strawberry guava was compared with a previous study on the red cultivar, revealing β‐caryophyllene as the main component in both oils. The fatty acid composition was also quite similar and was especially characterized by the presence of unsaturated fatty acids (86.25% and 76%, respectively), among which linoleic acid as the most abundant. Practical Application: In this study, the chemical characterization and the antioxidant activity of the red (Psidium cattleianum) and yellow (P. cattleianum var. lucidum Hort.) strawberry guava fruits were investigated. This is important for potential application of strawberry guava as functional food. Moreover, it may be the experimental basis for further development and use in food industry. 相似文献
94.
Christine Hoelzl Siegfried Knasmüller Karl‐Heinz Wagner Leonilla Elbling Wolfgang Huber Nina Kager Franziska Ferk Veronika Ehrlich Armen Nersesyan Oliver Neubauer Aurélien Desmarchelier Maricel Marin‐Kuan Thierry Delatour Clotilde Verguet Claudine Bezençon Amélie Besson Dominik Grathwohl Tatjana Simic Michael Kundi Benoît Schilter Christophe Cavin 《Molecular nutrition & food research》2010,54(12):1722-1733
Scope: Coffee is among the most frequently consumed beverages. Its consumption is inversely associated to the incidence of diseases related to reactive oxygen species; the phenomenon may be due to its antioxidant properties. Our primary objective was to investigate the impact of consumption of a coffee containing high levels of chlorogenic acids on the oxidation of proteins, DNA and membrane lipids; additionally, other redox biomarkers were monitored in an intervention trial. Methods and results: The treatment group (n=36) consumed instant coffee co‐extracted from green and roasted beans, whereas the control consumed water (800 mL/P/day, 5 days). A global statistical analysis of four main biomarkers selected as primary outcomes showed that the overall changes are significant. 8‐Isoprostaglandin F2α in urine declined by 15.3%, 3‐nitrotyrosine was decreased by 16.1%, DNA migration due to oxidized purines and pyrimidines was (not significantly) reduced in lymphocytes by 12.5 and 14.1%. Other markers such as the total antioxidant capacity were moderately increased; e.g. LDL and malondialdehyde were shifted towards a non‐significant reduction. Conclusion: The oxidation of DNA, lipids and proteins associated with the incidence of various diseases and the protection against their oxidative damage may be indicative for beneficial health effects of coffee. 相似文献
95.
The objective of the study was to examine the psychometric properties of a new self-report questionnaire, the Instability of Self-Esteem Scale (ISES), designed to be a complement to the Rosenberg Self-Esteem Scale (RSES), which measures global self-esteem. A total of 383 nonclinical adolescents participated in an assessment consisting of the ISES, the RSES, and two measures of psychopathology, the Center for Epidemiological Studies-Depression scale (CES-D), and the Borderline Personality Inventory (BPI). The ISES had satisfactory internal consistency and test-retest stability. The ISES and RSES were weakly correlated, this finding suggesting that they measure quite independent constructs. The different pattern of intercorrelations of the ISES and RSES with the CES-D and BPI provides support for the divergent validity of the ISES. (PsycINFO Database Record (c) 2010 APA, all rights reserved) 相似文献
96.
C Beaudu-Lange S Despeyroux P Marcaggi JA Coles T Amédée 《Canadian Metallurgical Quarterly》1998,10(5):1796-1809
Regulation of expression of functional voltage-gated ion channels for inward currents was studied in Schwann cells in organotypic cultures of dorsal root ganglia from E19 mouse embryos maintained in serum-free medium. Of the Schwann cells that did not contact axons, 46.5% expressed T-type Ca2+ conductances (ICaT). Two days or more after excision of the ganglia, and consequent disappearance of neurites, ICaT were detectable in only 10.9% of the cells, and the marker 04 disappeared. On Schwann cells deprived of neurons, T- (but not L-) type Ca2+ conductances were re-induced by weakly hydrolysable analogues of cAMP, and by forskolin (an activator of adenylyl cyclase) after long-term treatment (4 days). With CPT cAMP (0.1-2 mM), 8Br cAMP, db cAMP or forskolin (0.01 or 0.1 mM), the proportion of cells with ICaT was not significantly different from the proportion in the cultures with neurons. These agents also induced expression in some cells of tetrodotoxin-resistant Na+ currents, which were rarely induced by neurons, but 04 was not re-induced by cAMP analogue treatments that re-induced ICaT. Inward currents (Ba2+ or Na+) were partly restored (P < 0.05) on Schwann cells cultured for 6-7 days beneath a filter bearing cultured neurons. In contrast, addition of neuron-conditioned medium was ineffective. The results suggest that neurons activate, via diffusible and degradable factors, a subset of Schwann cell cAMP pathways leading to expression of IcaT, and activate additional non-cAMP pathways that lead to expression of 04. 相似文献
97.
Amélie Bazzoni Suhua Ma Qianqian Wang Xiadong Shen Marco Cantoni Karen L. Scrivener 《Journal of the American Ceramic Society》2014,97(11):3684-3693
Impure tricalcium silicate (C3S) in portland cement may contain various foreign ions. These ions can stabilize different polymorphs of C3S at room temperature and may affect its reactivity. In this paper, the effects of magnesium and zinc on the polymorph type, hydration kinetics, and the hydrate morphology of C3S were investigated. The pure C3S has the T1 structure while magnesium and zinc stabilize polymorphs M3 and T2/T3, respectively. The two elements have distinct effects on the hydration kinetics. Zinc increases the maximum heat released. Magnesium increases the hydration peak width. The C–S–H morphology is modified, leading to longer needles in the presence of zinc and thicker needles in the presence of magnesium. Zinc is incorporated into C–S–H, while magnesium is only incorporated slightly, if at all, but rather seems to inhibit nucleation. Implementing experimentally measured parameters for C–S–H nucleation and growth in the μic hydration model captured well the observed changes in hydration kinetics. This supports C–S–H nucleation and growth to be rate controlling in the hydration of C3S. 相似文献
98.
From an arbitrary temporal logic institution we show how to set up the corresponding institution of objects. The main properties
of the resulting institution are studied and used in establishing a categorial, denotational semantics of several basic constructs
of object specification, namely aggregation (parallel composition), interconnection, abstraction (interfacing) and monotonic
specialization. A duality is established between the category of theories and the category of objects, as a corollary of the
Galois correspondence between these concrete categories. The special case of linear temporal logic is analysed in detail in
order to show that categorial products do reflect interleaving and reducts may lead to internal non-determinism.
Received: 30 May 1996 / 4 November 1997 相似文献
99.
100.
In this paper transmitter antenna diversity for the downlink of a cellular system is proposed in conjunction with optimum anti-fading diversity. In spectrally efficienttransmitter antenna, frequency and time diversity schemes the information bit stream is divided into sub-streams and each sub-stream is transmitted over a different antenna, a different frequency, or a different time slot.The present work provides a fading resistant transmission scheme where a base station uses M1 antennas and M2 time slotsM=M1+M2. These transmissions are coordinated tomitigate the effects of multi-path Rayleigh fading and the mobilereceiver can recover the entire M-dimensional transmitted vector as longas the signal energy of at least one coordinate is large enough. TheSelective Transmitter Antenna Diversity (space diversity) scheme iscoordinated with new Orthonormal Complex Rotation Matrices(time diversity) to get the highest BER performance for low and medium signaltonoise ratio. Orthonormal Complex Rotation Matrices with variable and maximum peak toaverage amplitude ratio (PAR) are presented. The modulations considered in this workareQPSK, 8PSK and 16QAM. 相似文献