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11.
Jeannette Aumo Johanna Lilja Päivi Mäki-Arvela Tapio Salmi Mats Sundell Hanna Vainio Dmitry Yu. Murzin 《Catalysis Letters》2002,84(3-4):219-224
A polymer-supported Pd catalyst was investigated in hydrogenation of citral (3,7-dimethyl-2,6-octadienal), which is a stereoisomer with an isolated and a conjugated double bond as well as a carbonyl group. The catalyst was a fibrous polymer-supported catalyst modified with functional groups and immobilized metals. A comparison of the polymer-supported catalyst with conventional catalysts was made. 相似文献
12.
Atle Wibe Anna-Karin Borg-Karlson Monika Persson Torbjörn Norin Hanna Mustaparta 《Journal of chemical ecology》1998,24(2):273-287
The enantiomeric composition of seven monoterpene hydrocarbons in headspace volatiles of spruce sawdust and seedlings (Picea abies), pine seedlings (Pinus sylvestris), and branches of juniper (Juniperus communis) was determined by gas chromatographic separation on a -Cyclodextrin column. For the six monoterpenes, -pinene, camphene, -pinene, sabinene, limonene, and -phellandrene, both enantiomers were present, whereas for 3-carene only the (+)-configuration was found. The amount of each enantiomer varied considerably both in relation to total amount of all of them, and for the six pairs also in relation to the opposite enantiomer. One olfactory receptor neuron in the pine weevil (Hylobius abietis) showed a strong response to -pinene when stimulated with all four headspace materials via a GC equipped with a DB-WAX column. The same neuron was subsequently tested with repeated stimulations via the GC effluent containing the (+)- or (–)-enantiomer. A marked better response to (+)- than to (–)--pinene was elicited. Another olfactory receptor neuron that responded strongly to limonene when stimulated with the spruce volatiles was tested for enantiomers of limonene. This neuron responded more strongly to (–)- than to (+)-limonene, when stimulated alternately with each of the limonene enantiomers. Discrimination between enantiomers by plant olfactory receptor neurons suggests that the enantiomeric ratios of volatile compounds may be important in host location by the pine weevil. 相似文献
13.
Electrical conductivity of concrete containing silica fume 总被引:15,自引:0,他引:15
S. A. Abo El-Enein M. F. Kotkata G. B. Hanna M. Saad M. M. Abd El Razek 《Cement and Concrete Research》1995,25(8):1615-1620
The influence of silica fume on concrete properties represents an important technical research. In general, silica fume tends to improve both mechanical characteristics and durability of concrete. Thus the electrical properties of concrete containing silica fume can be studied to clarify its physical performance during hydration. The electrical conductivity of neat cement, mortar and concrete pastes was measured during setting and hardening. The ordinary Portland cement was partially replaced by different amounts of silica fume by weight. The changes in the electrical conductivity were reported during setting and hardening after gauging with water. The results of this study showed that the electrical conductivity can be used as an indication for the setting characteristics as well as the structural changes of the hardened pastes made with and without silica fume. 相似文献
14.
Sanna Järvelä Paul A. Kirschner Allyson Hadwin Hanna Järvenoja Jonna Malmberg Mariel Miller Jari Laru 《International Journal of Computer-Supported Collaborative Learning》2016,11(3):263-280
The field of computer supported collaborative learning (CSCL) is progressing instrumentally and theoretically. Nevertheless, few studies examine the effectiveness and efficiency of CSCL with respect to cognitive, motivational, emotional, and social issues, despite the fact that the role of regulatory processes is critical for the quality of students’ engagement in collaborative learning settings. We review the four earlier lines in developing support in CSCL and show how there has been a lack of work to support individuals in groups to engage in, sustain, and productively regulate their own and the group’s collaborative processes. Our aim is to discuss how our conceptual work in socially shared regulation of learning (SSRL) contributes to effective and efficient CSCL, what tools are presently available, and what the implications of research on these tools are for future tool development. 相似文献
15.
We propose a finite structural translation of possibly recursive π-calculus terms into Petri nets. This is achieved by using high-level nets together with an equivalence on markings in order to model entering into recursive calls, which do not need to be guarded. We view a computing system as consisting of a main program (π-calculus term) together with procedure declarations (recursive definitions of π-calculus identifiers). The control structure of these components is represented using disjoint high-level Petri nets, one for the main program and one for each of the procedure declarations. The program is executed once, while each procedure can be invoked several times (even concurrently), each such invocation being uniquely identified by structured tokens which correspond to the sequence of recursive calls along the execution path leading to that invocation. 相似文献
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17.
Evolution of supra-glacial lakes across the Greenland Ice Sheet 总被引:1,自引:0,他引:1
A.V. Sundal A. Shepherd E. Hanna P. Huybrechts 《Remote sensing of environment》2009,113(10):2164-2171
We used 268 cloud-free Moderate-resolution Imaging Spectroradiometer (MODIS) images from 2003 and 2005-2007 to study the seasonal evolution of supra-glacial lakes in three different regions of the Greenland Ice Sheet. Lake area estimates were obtained by developing an automated classification method for their identification based on 250 m resolution MODIS surface reflectance observations. Widespread supra-glacial lake formation and drainage is observed across the ice sheet, with a 2-3 week delay in the evolution of total supra-glacial lake area in the northern areas compared to the south-west. The onset of lake growth varies by up to one month inter-annually, and lakes form and drain at progressively higher altitudes during the melt season. A positive correlation was found between the annual peak in total lake area and modelled annual runoff. High runoff and lake extent years are generally characterised by low accumulation and high melt season temperatures, and vice versa. Our results indicate that, in a future warmer climate [Meehl, G. A., Stocker, T. F., Collins W. D., Friedlingstein, P., Gaye, A. T., Gregory, J. M., Kitoh, A., Knutti, R., Murphy, J. M., Noda, A., Raper, S. C. B., Watterson, I. G., Weaver, A. J. & Zhao, Z. C. (2007). Global Climate Projections. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K. B. Averyt, M. Tignor & H. L. Miller (eds.), Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.], Greenland supra-glacial lakes can be expected to form at higher altitudes and over a longer time period than is presently the case, expanding the area and time period over which connections between the ice sheet surface and base may be established [Das, S., Joughin, M., Behn, M., Howat, I., King, M., Lizarralde, D., & Bhatia, M. (2008). Fracture propagation to the base of the Greenland Ice Sheet during supra-glacial lake drainage. Science, 5877, 778-781] with potential consequences for ice sheet discharge [Zwally, H.J., Abdalati, W., Herring, T., Larson, K., Saba, J. & Steffen, K. (2002). Surface melt-induced acceleration of Greenland Ice Sheet flow. Science, 297, 218-221.]. 相似文献
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20.
Hanna E. Frischkorn Martha Wanderley-Casado und Claus G. B. Frischkorn 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1982,174(2):117-121
Zusammenfassung Furfurol und Hydroxymethylfurfurol können leicht mit Hilfe der Umkehrphasen-Chromatographie in Alkoholika bestimmt werden. Eine Probenvorbereitung ist nicht notwendig. Die beiden Aldehyde werden UV-spektrometrisch erfaßt, die absolute Nachweisgrenze bei Routinearbeiten beträgt 4–7 mg/100 l reinen Alkohol (entsprechend 0,01–0,03 mg/l im Getränk) und kann für Spurenbestimmungen auf 0,002–0,001 mg/l durch Injektion von größeren Probenvolumen erniedrigt werden. Die Peakhöhen der beiden Furfuroie sind im Bereich von 0,25–3 mg/l Getränk linear von der Konzentration abhängig. Die Gesamtanalyse dauert etwa 12 min. Mit der beschriebenen Methode werden brasilianischer Zukkerrohrschnaps (Cachaça) Bowie eine Reihe in Deutschland käuflicher Alkoholika untersucht.
Rapid determination of furfural and hydroxymethylfurfural in alcoholic beverages by reverse-phase-chromatographyComparative investigations on the content of furfurals in Brazilian Cachaça and other alcoholic liquors
Summary Furfural and Hydroxymethylfurfural can easily be determined in alcoholic beverages by means of reverse phase chromatography. A special sample preparation is not necessary. The aldehydes are detected by UV-spectrometry, the absolute detection limit in routine work is 4–7 mg/100 liters of pure ethanol (corresponding to 0.016–0.03 mg/l beverage) and can be extended down to 0.002–0.001 mg/l when injecting higher volumes for trace analysis. In the range of 0.25–3 mg/l linear relationship is obtained between peak hight and concentration. The complete assay procedure takes about 12 min. A series of Brazilian Cachaça samples and German commercial liquors were investigated with the here described method.
Sumário Os autores apresentam um método de determinação de Furfural e Hidroxi-metilfurfural em cachaça e outras bebidas alcoolicas, Cromatografia em alta pressão com colunas de fase reversa (C8; 5 m; 250 × 4 mm; CH3CN/H2O 5/95 como eluente) permite a separação e determinaçã sem pre-tratamento das amostras em 10–12 minutos. A sensibilidade da determinação em UV (254 nm) è 4–7 mg/100 L álcool puro (0.01–0.03 mg/L na bebida respectivamente). Usando um volume maior de injecção, o limite se pode abaixar até 0.002–0.001 mg/L bebida. A altura dos picos é proporçional à concentração entre 0.25–3 mg/L bebida. As cachaças investigadas possuem geralmente um conteúdo de Furfural e de Hidroxi-metilfurfural menor do que suposto e determinato pelo método de anilina recomendado pelo governo (determinação não específica).相似文献