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排序方式: 共有373条查询结果,搜索用时 15 毫秒
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Richard H. Perry Thomas J. Cahill III Jennifer L. Roizen Justin Du Bois Richard N. Zare 《Proceedings of the National Academy of Sciences of the United States of America》2012,109(45):18295-18299
We have applied an ambient ionization technique, desorption electrospray ionization MS, to identify transient reactive species of an archetypal C–H amination reaction catalyzed by a dirhodium tetracarboxylate complex. Using this analytical method, we have detected previously proposed short-lived reaction intermediates, including two nitrenoid complexes that differ in oxidation state. Our findings suggest that an Rh-nitrene oxidant can react with hydrocarbon substrates through a hydrogen atom abstraction pathway and raise the intriguing possibility that two catalytic C–H amination pathways may be operative in a typical bulk solution reaction. As highlighted by these results, desorption electrospray ionization MS should have broad applicability for the mechanistic study of catalytic processes. 相似文献
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Some limited models have been suggested to determine the conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNTs). However, earlier models (e.g., the Kovacs model) cannot properly consider the roles of the interphase regions or tunneling properties on the percolation threshold and subsequent conductivity of PCNTs. In this paper, the Kovacs model is further developed by assuming that the CNT, interphase, and tunneling regions are separate phases. Also, some simple equations are provided to calculate the percolation threshold as well as the volume fractions and resistances of the CNT, interphase, and tunneling regions in conductive networks. The experimental conductivity results for several samples are compared with the predictions of the developed model. In addition, the calculations of the developed model at different parameter levels are explained and justified. The conductivity calculations show good agreement with the experimental data. Moreover, the developed model reasonably explains the roles of the different parameters on the conductivity. For example, long, thin, and straight CNTs efficiently improve the conductivity because they form large networks in the nanocomposites. Additionally, a thick interphase enlarges the conductive networks, resulting in a desirable conductivity. The conductivity of PCNTs only depends on the tunneling resistance; this is the case because the poor resistance/significant conductivity of the CNT and interphase regions do not influence the conductivity. The developed equations can replace conventional approaches for predicting the conductivity of nanocomposites.Some limited models have been suggested to determine the conductivity of polymer carbon nanotube (CNT) nanocomposites (PCNTs). 相似文献
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Hamid Badrian Amin Davoudi Meysam Molazem Mohammad Hossein Zare 《Journal of Indian Prosthodontic Society》2015,15(3):263-267
Background:
Dentistry equipment are exposed to different types of pathogenic microorganisms. The aim of this study was to investigate the effect of spraying three different types of disinfectants on condensational silicones after 5 and 10 min.Materials and Methods:
Totally, 66 circular samples of condensational silicone impression materials of 1 cm diameter and 2 mm thickness were contaminated by Staphylococcus aureus, Pseudomonas aeruginosa, and Candida albicans fungus. Except for control samples, all of them were disinfected with sodium hypochlorite (NaOCl) 0.525%, Deconex and Epimax by spraying method. Afterward, they kept in plastic bags with humid rolled cotton for 5 and 10 min. In order to isolate microbiotas, the samples were immersed in 2% trypsin for 1 h and diluted with normal saline in a portion of 1, 1/2, and 1/4. The trypsin suspensions were transferred to culture plates for incubation and colony-forming unit assay. The data were analyzed by Mann–Whitney test and SPSS software version 16 at a significant level of 0.05.Results:
There was a meaningful difference between disinfection effects of Epimax-Deconex for all mentioned microorganisms after 5 min (P = 0.034), and between disinfection effects of NaOCl 0.525%-Epimax for S. aureus (P = 0.043) and P. aeruginosa (P = 0.046) after 5 min. Furthermore, there was a meaningful difference between disinfection effects of Epimax-Deconex (P = 0.034) and NaOCl 0.525%-Epimax (P = 0.034) for P. aeruginosa after 10 min.Conclusion:
Condensational silicone can be effectively disinfected by spraying tested three disinfecting agents. More specifically, Deconex showed the best results compared to the other agents.Key Words: Condensational silicone, disinfection, impression materials, spray 相似文献7.
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Purpose
The aim of this study was to assess the various doses of oral oxybutynin on cardiac autonomic modulation by measuring short-term heart rate variability (HRV) indexes during supine rest position.Methods
Eight male healthy subjects (20–23 years) participated in the double-blind crossover randomized study. The single dose of oxybutynin (2.5, 5 and 10 mg) or placebo was given to the volunteers in four sessions within 5-day intervals. Before and minutes of 30, 60, 90 and 120 after administration, lead II electrocardiogram (ECG) was recorded for 5 min. ECG extracted RR intervals data became the base of the calculation of time domain and frequency domain HRV parameters, which indicate cardiac autonomic activity. Statistical analysis was done by using the nonparametric Wilcoxon and Kruskal–Wallis tests.Results
The data analysis has revealed that MNN (P < 0.001), SDNN (P < 0.05), PNN50% (P < 0.01), RMSSD (P < 0.001), HFnu (P < 0.05) and LF/HF ratio (P < 0.05) values were significantly increased relative to baseline at various time points in all the groups except in placebo group. LFnu (P < 0.05) values were significantly increased relative to baseline at various time points in all the groups except in placebo group.Conclusions
Our findings have revealed that acute consumption of 2.5, 5 and 10 mg oxybutynin (an anticholinergic compound) in the juvenile healthy male subjects produces a cholinergic effect according to time and frequency domain of HRV indexes. 相似文献10.
A Novel Protocol to Differentiate Induced Pluripotent Stem Cells by Neuronal microRNAs to Provide a Suitable Cellular Model
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Mehrak Zare Masoud Soleimani Abolfazl Akbarzadeh Behnaz Bakhshandeh Seyed Hamid Aghaee‐Bakhtiari Nosratollah Zarghami 《Chemical biology & drug design》2015,86(2):232-238
Neurodegenerative diseases are one of the most challenging subjects in medicine. Investigation of their underlying genetic or epigenetic factors is hampered by lack of suitable models. Patient‐specific induced pluripotent stem cells (iPS cells) represent a valuable approach to provide a proper model for poorly understood mechanisms of neuronal diseases and the related drug screenings. miR‐124 and miR‐128 are the two brain‐enriched miRNAs with different time‐points of expression during neuronal development. Herein, we transduced human iPS cells with miR‐124 and miR‐128 harboring lentiviruses sequentially. The transduced plasmids contained GFP and puromycin antibiotic‐resistant genes for easier selection and identification. Morphological assessment and immunocytochemistry (overexpressions of beta‐tubulin and neuron‐specific enolase) confirmed that induced hiPS cells by miR‐124 and miR‐128 represent similar characteristics to those of mature neurons. In addition, the upregulation of neuron‐specific enolase, beta‐tubulin, Map2, GFAP, and BDNF was detected by quantitative real‐time PCR. In conclusion, it seems that our novel protocol remarks the combinatorial effect of miR‐124 and miR‐128 on neural differentiation in the absence of any extrinsic factor. Moreover, such cellular models could be used in personalized drug screening and applied for more effective therapies. 相似文献