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采用二苯代苦味肼基自由基(DPPH)体系、羟基自由基体系、超氧阴离子自由基体系,对蕨菜醇提取物抗氧化特性进行研究,并同Vc、2,6-二叔丁基对甲酚(BHT)进行比较.结果表明:蕨菜醇提取物对这几种自由基均有不同程度清除作用,对DPPH自由基清除能力最强,当浓度为0.6mg/mL时,清除能力已超过BHT,当醇提物浓度为0.8mg/mL时,清除率已达83.6%,但一直小于Vc.醇提物浓度为15mg/mL时,对羟基自由基的清除率为82.4%,对超氧阴离子清除率为52.6%,在实验浓度范围内,抗氧化性小于Vc和BHT. 相似文献
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以总还原力、对DPPH自由基和超氧阴离子自由基清除作用、金属离子螯合能力为指标评价2%柳叶蜡梅叶挥发油体外抗氧化活性。结果表明:挥发油总还原力和对DPPH自由基、超氧阴离子自由基的清除作用的IC50值分别为182.58、89.66、53.42μL。挥发油总还原力和对DPPH自由基的清除能力低于1mg/mL维生素C,而对超氧阴离子自由基清除能力和金属离子的螯合能力明显高于1mg/mL维生素C和0.5mg/mLEDTA。柳叶蜡梅叶挥发油具有较好的体外抗氧化活性,值得进一步开发利用。 相似文献
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传统的DPPH自由基清除活性评价方法以半数清除浓度EC50为评价指标,但EC50随DPPH初始加入量增加而增加,随分析体积增加而减小,因此,不同条件EC50值不具有可比性。提出以DPPH与抗氧化剂相互反应的化学计量数比(R)作为评价DPPH清除活性的指标,该指标只与DPPH与抗氧化剂相互反应的化学计量关系有关,与DPPH初始加入量和分析体积等因素无关,解决了EC50可比性差的问题。提出了测定化学计量数比(R)的光度微量滴定法,建立了利用滴定过程吸光度差(ΔA)与抗氧化剂加入量之间的滴定方程计算R值、以R计算EC50的光度微量滴定模型,并利用芦丁对模型进行验证。结果:芦丁与DPPH反应R值在1.817~1.846之间,当DPPH加入量为1.12×10-7,2.24×10-7,4.48×10-7和6.72×10-7 mol时,分别计算得EC50值分别为1.196×10-3,2.392×10-3,4.819×10-3和7.292×10-3 mg·mL-1。在此基础上,基于文献报道的芦丁清除DPPH条件,利用得到的芦丁R值计算出相应EC50,结果与文献报道EC50值相当。方法可比性好,样品消耗量明显降低,简单、成本低,结果可靠,为自由基清除活性评价提出了一种新的思路。 相似文献
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Optical activity of benzil as an example of optically active matter in the crystalline state only, not in solution, is studied for the wavelengths ranging from 0.320 m to 0.585 m. Previously measured experimental data are approximated by the theoretical set of formulas, which were derived by the use of the three coupled oscillators model. The earlier published formula consisting of six terms differed from the experimental data particularly in the wavelength region (0.380-0.510) m. This formula is replaced by the twelve-term formula which was computed by our specially worked computer program for the interpretation of the experimental data of optical activity based on the Marquardt-Levenberg method of the sum of least squares minimization. The possibility of molecular contribution to the resulting optical activity of benzil is mentioned. The use of Kramers-Kronig transforms for the determination of the circular dichroism curve based on the optical rotatory dispersion result is shown. The theoretically computed circular dichroism is compared with the available experimental data. 相似文献
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Cortical neurons in vivo show fluctuations in their membrane potential of the order of several milli-volts. Using simple and biophysically realistic models of a single neuron we demonstrate that noise induced fluctuations can be used to adaptively optimize the sensitivity of the neuron's output to ensembles of subthreshold inputs of different average strengths. Optimal information transfer is achieved by changing the strength of the noise such that the neuron's average firing rate remains constant. Adaptation is fast, because only crude estimates of the output rate are required at any time. 相似文献
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The results of measurements of the diffusion neutron flux from the thunderstorm storm occurred in Moscow in the night from July 13 to 14, 2016 at a distance ~30 km from detectors are presented. An increase in the frequency of coincidences of four channels of two scintillation detectors by ~10% with respect to coincidences in the absence of thunderstorm is found. The neutron yield in a single lightning discharge is estimated as ~1010 n/s. 相似文献
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Debate continues over differences in the dose-response functions used to predict the annoyance at different sources of transportation noise. This debate reflects the lack of an accepted model of noise annoyance in residential communities. In this paper a model is proposed which is focussed on activity interference as a central component mediating the relationship between noise exposure and annoyance. This model represents a departure from earlier models in two important respects. First, single event noise levels (e.g., maximum levels, sound exposure level) constitute the noise exposure variables in place of long-term energy equivalent measures (e.g., 24-hour Leq or Ldn). Second, the relationships within the model are expressed as probabilistic rather than deterministic equations. The model has been tested by using acoustical and social survey data collected at 57 sites in the Toronto region exposed to aircraft, road traffic or train noise. Logit analysis was used to estimate two sets of equations. The first predicts the probability of activity interference as a function of event noise level. Four types of interference are included: indoor speech, outdoor speech, difficulty getting to sleep and awakening. The second set predicts the probability of annoyance as a function of the combination of activity interferences. From the first set of equations, it was possible to estimate a function for indoor speech interference only. In this case, the maximum event level was the strongest predictor. The lack of significant results for the other types of interference is explained by the limitations of the data. The same function predicts indoor speech interference for all three sources—road, rail and aircraft noise. The results for the second set of equations show strong relationships between activity interference and the probability of annoyance. Again, the parameters of the logit equations are similar for the three sources. A trial application of the model predicts a higher probability of annoyance for aircraft than for road traffic situations with the same 24-hour Leq. This result suggests that the model may account for previously reported source differences in annoyance. 相似文献
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Dzhimak S. S. Malyshko V. V. Goryachko A. I. Sokolov M. E. Basov А. А. Moiseev A. V. Shashkov D. I. Kopytov G. F. Baryshev M. G. Isaev V. A. 《Russian Physics Journal》2019,62(2):314-322
Russian Physics Journal - The absorption activity of silver nanoparticles (AgNPs) on the surface of fibers of natural and artificial origin is estimated. In addition, it is determined that the... 相似文献
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In high frequency financial data not only returns but also waiting times between trades are random variables. In this work, we analyze the spectra of the waiting-time processes for tick-by-tick trades. The numerical problem, strictly related with the real inversion of Laplace transforms, is analyzed by using Tikhonov's regularization method. We also analyze these spectra by a rough method using a comb of Dirac's delta functions. 相似文献
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We study the activity of financial markets, i.e., the number of transactions per unit of time. Using the diffusion entropy technique we show that the autocorrelation of the activity is caused by the presence of peaks whose time distances are distributed following an asymptotic power-law which ultimately recovers an exponential behavior. We discuss these results in comparison with ARCH models, stochastic volatility models and multi-agent models showing that ARCH and stochastic volatility models better describe the observed experimental evidences.Received: 15 March 2004, Published online: 8 June 2004PACS:
89.65.Gh Economics; econophysics, financial markets, business and management - 05.45.Tp Time series analysis - 05.40.-a Fluctuation phenomena, random processes, noise, and Brownian motion 相似文献
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