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941.
Marco D. R. Gomes da Silva Higuinaldo J. Chaves das Neves 《Journal of separation science》1997,20(5):275-283
The aroma composition of three different Fragaria anannassa cul-tivars Selva, Chandler, and Osso Grande) is studied by purge-and-trap HRGC and the components identified by MRGC-MS and HRGC-FTIR. The chromatographic aroma profiles from four different maturation stages in each variety are compared and the similarities accessed by principal component analysis (PCA). The contents in n-hexanal and hex-2(Z)-enal are characteristic features of the green stage in the three varieties where the content differences in methyl, ethyl, and butyl acetates act as typifying variables among varieties. Ethyl acetate acts as an important differentiation variable for the Selva variety. In the mature stage, the three cultivars may be distinguished from each other through their relative contents of methyl and ethyl 2-methylbutyrate (Selva), methyl 2-methyl-butyrate, methyl butyrate (Chandler), methyl and ethyl butyrates, and methyl caproate (Osso Grande). 相似文献
942.
LilianM.M. Cesar ClaudioF. Tormena MauricioR. Marques GilV.J. Silva MariaA. Mendes Roberto Rittner MarioS. Palma 《Helvetica chimica acta》2005,88(4):796-801
A new, highly active tetrahydro‐β‐carboline toxin from the spider Parawixia bistriata, the most‐common species of social spider occurring in Brazil, was isolated. The new toxin was identified as 1,2,3,4‐tetrahydro‐6‐hydroxy‐β‐carboline (=N‐[3‐(2,3,4,9‐tetrahydro‐6‐hydroxy‐1H‐pyrido[3,4‐b]indol‐1‐yl)propyl]guanidine; 3 ). This type of alkaloid, not common among spider toxins, was found to be the most‐potent constituent of the spider's chemical weaponry to kill prey. When P. bistriata catch arthropods in their web, they apparently attack their prey in groups of many individuals injecting their venoms. In vivo toxicity assays with 3 demonstrated a potent lethal effect to honeybees, giving rise to clear neurotoxic effects (paralysis) before death. The compound's toxicity (LD50 value) was determined to be ca. 8 ng/g of honeybee. The investigation of the pharmacological properties and neurotoxic actions of 3 may be used in the future for the development of new drugs to be applied for pest control in agriculture. 相似文献
943.
Antonio Da Costa Christian Mathieu Yolande Barbaux Hilde Poelman Gisele Dalmai-Vennik Lucien Fiermans 《Surface science》1997,370(2-3):339-344
Constant force images of the V2O5(001) surface were recorded in ambient conditions with atomic force microscopy. All images exhibit the 11.5 Å × 3.5 Å. periodicity expected for a bulk terminated surface. However, images reveal differences from the ideal structure. The experimental results are interpreted in terms of preferential adsorption sites for water molecules. Because these sites are thought to influence the catalytic properties of the surface, their characterization is an important step towards understanding how the atomic-scale structure of a surface influences its properties. 相似文献
944.
Daniel P. Silva Tomáš Brányik Giuliano Dragone António A. Vicente José A. Teixeira João B. Almeida e Silva 《Chemical Papers》2008,62(1):34-41
This study deals with two innovative brewing processes, high gravity batch and complete continuous beer fermentation systems.
The results show a significant influence of the variables such as concentration and temperature on the yield factor of the
substrate into ethanol and consequently on the productivity of the high gravity batch process. The technological feasibility
of continuous production of beer based on yeast immobilization on cheap alternative carriers was also demonstrated. The influence
of process parameters on fermentation performance and quality of the obtained beers was studied by sensorial analysis. No
significant difference in the degree of acceptance between the obtained products and some traditional market brands was found.
Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May
2007. 相似文献
945.
The surface-enhanced Raman scatterihg (SERS) spectra of human gallstones is investigated. Complicated Raman bands were due to multiple components that include bilirubin, bilirubinate salts, cholesterol, fatty salts and proteins. The results suggest that besides bilirubin and cholesterol, fatty salts and proteins may play an important role in the formation of gallstone. The experimental data supply an useful information for the research of the formation mechanism of gallstones. 相似文献
946.
José Bento Borba da Silva Maria Bert?lia Oss Giacomelli Ivan Gonçalves de Souza Adilson José Curtius 《Microchemical Journal》1998,60(3):249-257
Performance of graphite platforms coated with Ir, Rh, and a mixture of both, as permanent modifiers for Ag, As, Bi, Cd, and Sb, was evaluated. The coating process is very simple: a solution containing Ir, Rh, or a mixture of both is pipetted on the platform inserted in a graphite tube, and this is submitted to a temperature program. High pyrolysis temperatures are allowed, especially for As and Bi, 1400°C, in the Ir + Rh-coated platform. The sensitivity remains about the same for all analytes with different coatings, except for As in the Ir-coated platform, for which a remarkable gain was obtained in comparison to the other coatings. The lifetimes of the treated tubes were in the range 50 to more than 1000 cycles, being especially long for Sb and Ag in the Rh-coated platform, more than 600 and 1000 cycles, respectively. The Rh coating could not be used for Bi and Cd. Analysis of a certified reference water and of acid oyster tissue digests showed the absence of interference and good precision. Advantages of the permanent coatings are the possibility of low blanks byin situcleaning of the modifier and shorter analysis time. 相似文献
947.
Jean-Pierre Aubin Giuseppe Da Prato 《NoDEA : Nonlinear Differential Equations and Applications》1995,2(4):511-525
This paper is devoted to stability properties of solutions to stochastic differential equations obtained by a stochastic Lyapunov method. 相似文献
948.
Yi‐Lei Chen Chang‐Heng Tan Jun‐Jie Tan Shi‐Jin Qu Heng‐Bin Wang Qiang Zhang Shan‐Hao Jiang Da‐Yuan Zhu 《Helvetica chimica acta》2007,90(12):2421-2426
Pyrocallianthasides A ( 1 ) and B ( 2 ), a new dimer and a new mono‐deglucosyl trimer of homoarbutin (=4‐hydroxy‐3‐methylphenyl β‐glucopyranoside), and callianthaside A ( 3 ), a new ursane‐type triterpene glycoside, together with three known phenolic glycosides and three known ursane‐type triterpenoids, were isolated from the whole plants of Pyrola calliantha. The structures of 1 – 3 were elucidated by chemical and spectroscopic methods. 相似文献
949.
The routine determination of mercury (Hg) by inductively coupled plasma mass spectrometry (ICP-MS) is affected by a pronounced memory effect in the sample introduction system. This results in long washout times for the analyte, which affects the accuracy and reliability of the analytical procedure. By using a combination of flow injection sample introduction and a sulfur-containing compound in the carrier solution, it was possible to decrease the memory effect of mercury to that for the internal standard (rhodium). The carrier solution contained 2-mercaptoethanol (2-ME) and the developed method was evaluated using three different fish tissue certified reference materials: CRM 464 (BCR, Brussels); DORM-1; and DORM-2 (NRC, Canada). The samples were mineralized using a combination of concentrated nitric acid and hydrogen peroxide and heating in a closed microwave oven. The developed flow injection ICP-MS procedure gave values for total mercury in all three CRM materials in agreement with the certified concentration range. Cold vapour atomic fluorescence spectrometry (CV-AFS) confirmed the results from the developed method. The developed flow injection method had a detection limit (defined as three times the standard deviation of the blank concentration) for mercury of 5.1 μg l−1. 相似文献
950.