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排序方式: 共有141条查询结果,搜索用时 15 毫秒
61.
62.
Effects of pH control with phthalate buffers on hot-water extraction of hemicelluloses from spruce wood 总被引:1,自引:0,他引:1
Ground spruce wood was extracted with water at 170 °C at four different pH levels (3.8, 4.0, 4.2 and 4.4) achieved by using phthalate buffers. Static batch extractions were carried out in an accelerated solvent extractor (ASE-300). The extracted non-cellulosic carbohydrates, predominantly galactoglucomannans (GGMs), were characterised mainly by sugar unit analysis and molar mass determination. Compared to extraction with plain water, extractions with phthalate buffer solutions gave similar yields of non-cellulosic carbohydrates, but gave up to 70% less monosaccharides, and consequently higher molar masses of extracted GGMs. Moreover, at these pH levels, the hydrolysis of acetyl groups were decreased by 40% compared to extraction with plain water, thus maintaining the water solubility of GGMs. It is concluded that hot water extraction of hemicelluloses in high-molar-mass form (average Mw about 10 kDa) from wood in good yields (8% of wood) demands appropriate control of pH, to a level of about 4. 相似文献
63.
利用CART(classification and regression tree,分类和回归树)生态位模型,采用A2和B2气候情景,分析了气候变化对秦岭冷杉、祁连圆柏、楠木、麦吊云杉、马尾树、领春木和连香树分布范围及空间格局的影响。结果显示:气候变化下,这些植物目前适宜分布范围呈现缩小趋势;新适宜及总适宜分布范围,连香树、马尾树、楠木和祁连圆柏呈现减少趋势,秦岭冷杉在1991-2020年及2021-2050年时段呈现减少趋势,之后增加,其它植物呈现增加趋势。气候变化下,马尾树目前适宜分布的东南部一些区域将不再适宜,新适宜分布区将向西南、北部、西部和东北部一些区域扩展;秦岭冷杉目前适宜分布的东南部和东部一些区域将不再适宜,新适宜分布区将向西南部、西北部和西部一些区域扩展;其它植物目前适宜分布的东部、东南部、南部及东北部一些区域将不再适宜,新适宜分布区将向西部和西南部一些区域扩展。气候变化下,这些植物适宜分布范围与年均气温和降水量变化相关性并不一致,一些植物适宜分布范围与年均气温和降水量变化相关系数不显著。另外,一些植物适宜范围与年降水量和年均气温变化多元线性回归关系决定系数较小。结果说明,气候变化下,目前适宜范围缩小,新适宜范围主要向高海拔扩展,不同植物适宜分布范围与年均气温和年降水量变化的关系不同。 相似文献
64.
Reduced inhibition of enzymatic hydrolysis of steam-pretreated softwood 总被引:10,自引:0,他引:10
Softwood constitutes the main source of lignocellulosic material in Sweden which can be used for ethanol production from renewable resources. To make the biomass-to-ethanol process more economically feasible, it is preferable to include the sugar-rich prehydrolysate, i.e. the liquid obtained after the pretreatment step, in the enzymatic hydrolysis of the solid fraction. This study shows that the prehydrolysate inhibits cellulose conversion in the enzymatic hydrolysis step. When the prehydrolysate was included in the enzymatic hydrolysis, the cellulose conversion was reduced by up to 36%. However, this inhibition can be overcome by fermentation of the prehydrolysate prior to enzymatic hydrolysis. 相似文献
65.
66.
Bayesian calibration method used to elucidate carbon turnover in forest on drained organic soil 总被引:1,自引:1,他引:0
Leif Klemedtsson Per-Erik Jansson David Gustafsson Louise Karlberg Per Weslien Karin von Arnold Maria Ernfors Ola Langvall Anders Lindroth 《Biogeochemistry》2008,89(1):61-79
Depending on the balance between sink and source processes for C, drained organic forest soil ecosystems can be in balance
or act as net sinks or sources of CO2 to the atmosphere. In order to study the effect of groundwater level and soil temperature on C-flux, the CoupModel was calibrated
(climate data, groundwater levels, soil CO2 flux, net ecosystem fluxes of CO2-exchange, sensible heat flux and latent heat flux, forest production etc.) for a drained forest in Sweden. Bayesian calibration
techniques were used to elucidate how different parameters and variables were interlinked in C-circulation. The calibrated
model reproduced abiotic and biotic variables reasonably well except for root respiration, which was largely underestimated.
Bayesian calibration reduced the uncertainties in the model and highlighted the fact that calibrations should be performed
with a high number of parameters instead of specific parameter values. 相似文献
67.
Ewa Puchalska Barbara Czajkowska Magorzata Kiekiewicz 《Acta Physiologiae Plantarum》2008,30(2):225-232
Our investigations suggest that the usually observed avoidance by O. ununguis of current year’s twigs of P. glauca ‘Conica’ as a place for feeding and development may be connected with their morphological and anatomical structure as well
their biochemical composition. Needles of the current year’s twigs were covered with a thicker layer of wax and formed more
extensive epidermis cell walls, in comparison with needles of 1-year-old twigs. Young needles also showed lower concentration
of reducing sugars and soluble proteins, which might additionally reduce their nutritional suitability for mite development.
Differences were also found between the 1-year-old growth and current growth in contribution of essential oils and a range
of other compounds. Further analyses of the effect of these compounds on mite behavior may provide additional explanation
of the feeding preferences of the mite.
相似文献
Barbara CzajkowskaEmail: |
68.
Partly depolymerized hemicelluloses isolated from wood chips of spruce and aspen employing microwave treatment were resolved using size-exclusion chromatography (SEC) into oligo- and polysaccharide fractions containing components with a narrow range of sizes, as determined by MALDI mass spectroscopy. The degree of substitution with acetyl moieties (DS) was also calculated on the basis of the MALDI-MS spectra obtained prior to and following deacetylation. For spruce hemicelluloses, the low molecular mass fraction contained small arabino-4-O-methylglucuronoxylan oligosaccharides, with DP values ranging from 4 to approximately 20, separated primarily on the basis of their charge density. The fraction eluted last consisted of an O-acetyl-(galacto)glucomannan polysaccharide of peak-average DP value (DP(p)) 14. The degree of substitution with acetyl groups (DS) decreased with decreasing DP, a value DS of 0.39 being obtained for the fraction with DP(p) 12. For the aspen hemicelluloses, the SEC fractions eluted first contained an acidic O-acetyl-4-O-methylglucuronoxylan polysaccharide with DP ranging from 10 to approximately 28 and an average DS of approximately 0.75. The fractions eluted last consisted of oligosaccharide mixtures composed primarily of small neutral O-acetyl-xylooligosaccharides (DP(p) 6, DS 0.41), together with minor quantities of an O-acetyl-glucomannan. 相似文献
69.
Kazianis S Khanolkar VA Nairn RS Rains JD Trono D Garcia R Williams EL Walter RB 《Comparative biochemistry and physiology. Toxicology & pharmacology : CBP》2004,138(3):291-299
Xiphophorus fishes and their hybrids are used as models for the study of melanoma and other diseases. The cyclin-dependent kinase inhibitor gene family in humans is comprised of four members, including CDKN2A (P16), and dysregulation of this gene is implicated in numerous neoplasms including melanomas. We have investigated the status of the gene family in the southern platyfish X. maculatus. Xiphophorus harbors at least two such loci, which we now term CDKN2A/B and CDKN2D. Both loci map to Xiphophorus linkage group 5, a genomic area that has long been known to harbor the DIFF tumor suppressor locus. Within this report, we report on the complete cloning, genomic exon/intron boundary delineation, linkage mapping and expressional characteristics of Xiphophorus CDKN2D. We also compare and contrast this expression to that of the previously isolated CDKN2AB locus in normal and neoplastic tissues derived from non-hybrid and hybrid fishes. The hypothetical evolutionary relationships of gene family members and their involvement in melanoma is evaluated. In comparison to CDKN2A/B, the RNA expression of Xiphophorus CDKN2D differs in normal tissues and is not associated with melanotic/pathologic tissues, confirming functional divergence between obvious homologues. 相似文献
70.
The gene for β-hydroxyacyl ACP dehydratase, a de novo fatty acid biosynthetic enzyme, was cloned from Picea mariana (black spruce) and consists of five exons and four introns. The first intron of the β-hydroxyacyl ACP dehydratase mRNA is alternatively spliced. Retention of intron 1 in splice variants results in truncation of the β-hydroxyacyl ACP dehydratase ORF at a premature termination codon. In addition, splicing of intron 1 was found to be associated with cold temperature. mRNAs retaining intron 1 increase with seed imbibition at 22°C but not 4°C, whereas, splicing of intron 1 increases in winter weeks with temperatures below freezing. These results provide evidence that alternative splicing may also contribute to regulation of lipid biosynthesis in Picea mariana. 相似文献