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Low-temperature fermentations (13 degrees C) are considered to improve wine aromatic profiles. However, because the risk of stuck and sluggish fermentations is high, these fermentations are not common. The aim of this paper was to analyze the effect of different preadaptation protocols in two commercial wine strains on the fermentation and some wine parameters. Preadaptation is understood to be the process between the rehydration of active dry yeast and the inoculation. In this study, it consisted of preparing a fermentation starter (addition of yeast grown at 25 degrees C) or inocula preadapted at low temperatures (as before, but grown at a fermentation temperature of 13 or 17 degrees C). These results were compared with those of rehydrated active dry yeast, and a commercial "cryotolerant" yeast was used as a reference. General fermentation kinetic parameters, yeast imposition, nitrogen consumption, and main wine products were analyzed. The results showed that the preadaptation of a yeast could improve the fermentation performance, although this improvement was strain-dependent. Low-temperature fermentations also had some general effects: reduction of acetic acid and fusel alcohol production and increased concentrations of glycerol. When the yeast performed better in fermentation because of preadaptation, nitrogen consumption was faster and the wine's "negative" attributes (acetic acid, fusel alcohols) were significantly reduced. Thus, in some strains, preadaptation could be an effective mechanism for improving low-temperature fermentation, which also significantly reduces detrimental wine attributes.  相似文献   
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Conical intersections play a crucial role in the chemistry of most polyatomic molecules, ranging from the simplest bimolecular reactions to the photostability of DNA. The real-time study of the associated electronic dynamics poses a major challenge to the latest techniques of ultrafast measurement. We show that high-harmonic spectroscopy reveals oscillations in the electronic character that occur in nitrogen dioxide when a photoexcited wave packet crosses a conical intersection. At longer delays, we observe the onset of statistical dissociation dynamics. The present results demonstrate that high-harmonic spectroscopy could become a powerful tool to highlight electronic dynamics occurring along nonadiabatic chemical reaction pathways.  相似文献   
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Evidence of hybridization in Haliotis has been mainly supported by hatchery experiences and collection of wild hybrid abalones among several species from natural populations worldwide. However, despite the importance to understand the role of the hybridization process through Haliotidae evolution, and also its impact on the abalone aquaculture, genetic studies in hybrid abalones have been poorly developed. Herein, cytogenetic approach allows studying the genetic conformation in hybrid organisms at the chromosome level. This paper reports a quantitative karyotype analysis in Haliotis rufescens, Haliotis discus hannai and their interspecific hybrid. Thus, to characterize chromosome pairs and establish cytogenetic comparisons, chromosome banding with distamycin‐A/4,6‐diamidino‐2‐phenylindole fluorochromes and morphologic measurements were performed. The results showed that the hybrids are successfully viable and their karyotypes evidenced a conservative chromosome number of 2n=36. The karyo‐idiogram showed a high correspondence in chromosome pair morphology among the hybrids and their parental species, except for a single heteromorphic pair that corresponds to the chromosome 16 from H. rufescens andH. d. hannai respectively. The implications of the abalone hybrid viability derived from its chromosome composition are discussed.  相似文献   
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Donors, scientists and farmers all benefit when research and development projects have high impact. However, potential benefits are sometimes not realized. Our objective in this study is to determine why resource-poor farmers in Togo (declined to) adopt recommended practices that were promoted through a multi-organizational project on soil fertility management. We examine the processes and outcomes related to the adoption process. The project was undertaken in three villages in the Central Region of Togo in West Africa. The development and research processes that took place during the implementation of the project were critically analyzed using a conceptual framework that may be useful for improving the impact of future participatory projects. At the macro level, opportunities for innovation were not deliberately explored with participating farmers and other village members; consequently “pre-analytical choices” made during the planning phase resulted in practices that resource-poor farmers were, for a variety of reasons, unable or unwilling to adopt. From the outset, donors and scientists focused on soil fertility management, but failed to take into account the wider economic context within which soil fertility management took place. This was a major obstacle to the subsequent adoption of recommended management strategies. Scientists and donor partners measured the success of the Project in terms of crop productivity, but farmers’ choices were influenced by a complex mix of socio-economic, political and technical factors. We also illustrate the importance of selecting appropriate categories of farmers for a particular experiment. We conclude that for participatory research and development projects to be successful, it is not enough to develop technologies that “work” in a technical sense. In order to be scaled up and widely implemented, such technologies must also meet a variety of needs of resource-poor farmers and be acceptable from a socio-cultural point of view. Suzanne Nederlof holds a PhD in Communication and Innovation Studies from Wageningen University in the Netherlands. After finishing her MSc. degree in Development Sociology at the same university she worked at a research project in Burkina Faso and at the International Center for Soil Fertility and Agricultural Development (IFDC) in Togo. Subsequently, she was based at the FAO regional office for Africa in Ghana, assigned to the Convergence of Sciences Program. She conducted the fieldwork for this article during that period. She completed her PhD research on agricultural research with a scholarship from the Netherlands Organization for Scientific Research. She is currently employed as an advisor in rural innovation at the Royal Tropical Institute (KIT) in Amsterdam, The Netherlands. Constant Dangbégnon worked for several years (1990–1998) on Inter-University Cooperation (Benin, the Netherlands and Israel) in the area of indigenous knowledge and the soft side of natural resource management. This work constituted the basis of his PhD from Wageningen University in The Netherlands. He joined IFDC – Africa Division in Lomé (Togo) in June 1999 as a socio-economic extension specialist in the Input Accessibility Program (IAP).  相似文献   
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Two complementary experimental approaches were utilized to examine the extent to which free soil hydrogenases and H2-oxidizing bacteria contribute to the soil uptake of atmospheric H2. First, high affinity hydrogenase activity and H2-oxidizing bacteria were fractionated in non-axenic soil and axenic soil colonized with the high affinity H2-oxidizing bacterium Streptomyces sp. PCB7. Non-axenic soil was fractionated by buoyant density centrifugation. High affinity H2 oxidation activity measured in individual fractions was proportional to the copy number of hhyL gene, specifying the large subunit of putative high affinity [NiFe]-hydrogenases. 2.5% of the hydrogenase activity was recovered in bacteria-free soil extract. Similarly, sequential centrifugation and wet filtrations of strain PCB7-colonized soil dispersed in solubilization buffer caused a loss of the activity, at a ratio proportional to the number of living cells removed. No abiontic hydrogenase activity was detected in bacteria-free fractions. The second experimental approach was designed to verify whether or not the [NiFe]-hydrogenase of strain PCB7 retains high affinity H2 oxidation activity in soil, under the abiontic state. H2 oxidation rates of crude enzyme extract of strain PCB7 measured under aerobic and anaerobic conditions were indistinguishable, indicating that the high affinity hydrogenase of strain PCB7 is oxygen-tolerant. The hydrogenase activity of sterile soil spiked with as much as 0.14 mg(protein) g(soil-dw)−1 was equivalent to the H2-oxidation activity of only 106-107 CFU of strain PCB7 g(soil-dw)−1. Taken together, our results indicate that high affinity hydrogenase activity is proportional to the abundance of H2-oxidizing bacteria in soil and, that abiontic hydrogenases contribute only a few percent of the total high affinity H2 oxidation activity detected in soil.  相似文献   
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Measuring wood density by means of X-ray computer tomography   总被引:1,自引:0,他引:1  
  • ? Wood density is a characteristic of major interest. Usually, it is used as an indicator of wood quality; however, in the context of global change, it is increasingly used for biomass and carbon storage estimations. X-ray computer tomography is a method which enables quick estimates of wood density after applying a calibration procedure.
  • ? A review of the literature is presented in this article. Most of the previous studies have been performed in the 80’s or at the beginning of the 90’s.
  • ? In this study, the relationship between wood density and Hounsfield numbers was investigated using a recent medical scanner. A linear relationship was fitted using a calibration data set which consisted in tropical wood samples representing a large range of densities ranging between 133 and 1319 kg m?3, and then validated using an independent data set (mainly temperate tree species). The fitted relationships were very strong (R 2 > 0.999), whichever the tested scanner settings, with slight but significant effects of the current voltage and reconstruction filters. The RMSE values computed from the validation data set ranged between 5.4 and 7.7 kg m?3 for densities ranging between 364 and 821 kg m?3.
  • ? In conclusion, this method of calibration enables the use of a medical scanner to obtain maps of wood density, in a fast and non destructive way, and with a very good accuracy. Very interesting perspectives are opened regarding biomass distribution within trees.
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