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991.
Sarlis NV Skordas ES Lazaridou MS Varotsos PA 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2008,84(8):331-343
The behavior of seismicity in the area candidate to suffer a main shock is investigated after the observation of the Seismic Electric Signal activity until the impending main shock. This is based on the view that the occurrence of earthquakes is a critical phenomenon to which statistical dynamics may be applied. In the present work, analysing the time series of small earthquakes, the concept of natural time chi was used and the results revealed that the approach to criticality itself can be manifested by the probability density function (PDF) of kappa(1) calculated over an appropriate statistical ensemble. Here, kappa(1) is the variance kappa(1)(=-(2)) resulting from the power spectrum of a function defined as Phi(omega)= summation operator(k=1)(N) p(k) exp(iomegachi(k)), where p(k) is the normalized energy of the k-th small earthquake and omega the natural frequency. This PDF exhibits a maximum at kappa(1) asymptotically equal to 0.070 a few days before the main shock. Examples are presented, referring to the magnitude 6 approximately 7 class earthquakes that occurred in Greece. 相似文献
992.
993.
AbstractReactive oxygen species including free radicals are responsible for noxious changes in living organisms which can be associated with many diseases for e.g. cardiovascular, neurodegenerative, and inflammatory diseases or cancer. In the struggle against free radicals the organism is supported by antioxidants. As they are often provided by nature, they can be considered safe. 5-Caffeoylquinic acid is one of main chlorogenic acids found in vegetables and fruits. The main objective of the presented article was monitoring the changes of 5-caffeoylquinic acid during the reaction with colorful radicals. The experiments were conducted at different molar ratios of radicals to antioxidant using liquid chromatography–mass spectrometry. Irrespective of the applied molar ratios, the obtained results proved that the antioxidant takes part in the reaction for three days. Additionally, during the radical neutralization the formation of semiquinones and/or quinones, methoxy adduct of caffeoylquinic acid, and quinones adduct with methanol was observed. 相似文献
994.
995.
AbstractExperimental studies conducted on some species of Mediterranean red algae allowed to identify Sphaerococcus coronopifolius Stackhouse as a valid alternative to the Pacific alga Gloiopeltis furcata (Postels & Ruprecht) J. Agardh, for the extraction of a material usable as natural consolidant and adhesive in the field of restoration. Promising results have been observed by comparing the extracts obtained from these two algae after the same extraction procedure. Chemical analysis (FTIR) revealed that S. coronopifolius has qualities similar to G. furcata. Even more promising results for S. coronopifolius compared to G. furcata were observed after the analysis of pH and conductivity, and the adhesion tests carried out on both extracts. 相似文献
996.
Rubén A. Toscano Rachel Mata José Calderon Rosabel Segura 《Journal of chemical crystallography》1996,26(10):707-711
Chloroform/Methanol extraction of the bark ofCedrela salvadorensis (Meliaceae), followed by chromatography afforded the crystalline C28H34O7 terpene. The structure first proposed by spectroscopy is confirmed by this X-ray analysis as 7-acetyloxy-14,15:21,23-diepoxy-4,4,8-trimethyl-d-homo-24-nor-17-oxachola-1,20,22-triene-3,16,-dione. The title compound crystallized in the orthorhombic space groupP212121 with unit cell parametersa=10.243(2),b=13.356(3) andc=18.058(4) Å. The molecule is comprised of a six-membered tetracyclic skeleton, with a circular arc overall conformation. No intermolecular hydrogen bonding is indicated. 相似文献
997.
《Electroanalysis》2018,30(1):109-118
The differential pulse adsorptive cathodic stripping voltammetry (DP‐AdsCSV) employing the hanging mercury drop electrode (HMDE) was used towards the determination of two psychotropic drugs in environmental samples. Voltammetric and experimental conditions to Clonazepam (CLO) and diazepam (DIAZ) were optimized and the methods were in‐house validated. Accumulation potentials were −0.3 V to CLO and −0.6 V to DIAZ at 120 s of accumulation time. Pulse amplitude, pulse time and scan rate were 80 mV, 20 ms and 25 mV s−1 to CLO and 100 mV, 20 ms and 40 mV s−1 to DIAZ, respectively. Recovery tests were done in three different concentrations to evaluate methods’ accuracy and the results were from 88±6 to 120±13 %. In precision tests, standard deviations were lower than 15 % for both methods. Goods limits of quantification 0.65 and 0.27 μg L−1 to CLO and DIAZ respectively were achieved without pre‐concentration steps such as SPE, etc. Voltammetry employing HMDE was first used for the determination of CLO and DIAZ in natural water. Natural samples were spiked and recovery tests confirmed the applicability of the methods developed. Nine samples from Parana state, Brazil, were analyzed and CLO and DIAZ values were below the limits of detection in all samples. 相似文献
998.
Shohei Nakamukai Kentaro Takada Kazuo Furihata Yuji Ise Shigeru Okada Yasuhiro Morii Nobuhiro Yamawaki Tomohiro Takatani Osamu Arakawa Kirk R. Gustafson Shigeki Matsunaga 《Tetrahedron letters》2018,59(26):2532-2536
Stellatolide H (1) was isolated from a deep-sea sponge Discodermia sp. as the cytotoxic constituent. The planar structure of 1 was elucidated on the basis of the NMR spectroscopic and mass spectrometric data. The absolute configurations of the constituent amino acid residues were determined by the Marfey’s method. Stellatolide H (1) is a peptide lactone of the callipeltin class with its N-terminus blocked by 3-hydroxy-6,8-dimethyldeca-(4Z,6E)-dienoic acid (Hdda). 相似文献
999.
1000.
Divergent Total Syntheses of Enmein‐Type Natural Products: (−)‐Enmein, (−)‐Isodocarpin,and (−)‐Sculponin R 下载免费PDF全文
Saiyong Pan Sicong Chen Guangbin Dong 《Angewandte Chemie (International ed. in English)》2018,57(21):6333-6336
Divergent total syntheses of the enmein‐type natural products (?)‐enmein, (?)‐isodocarpin, and (?)‐sculponin R have been achieved in a concise fashion. Key features of the strategy include 1) an efficient early‐stage cage formation to control succeeding diastereoselectivity, 2) a one‐pot acylation/akylation/lactonization to construct the C‐ring and C8 quarternary center, 3) a reductive alkenylation approach to construct the enmain D/E rings and 4) a flexible route to allow divergent syntheses of three natural products. 相似文献