排序方式： 共有48条查询结果，搜索用时 15 毫秒
31.
Polyphenols from the ethanol extracts of Sargassum tenerrimum (ST) with potent antiallergic effects were studied to optimize separation process through column chromatography. The adsorption
and desorption characteristics of three widely used adsorbents: macroporous resin, silica gel, and polyvinylpolypyrrolidone
(PVPP), were critically evaluated respectively and studied for the optimization of preparative separation of polyphenols.
Static operations on these adsorbents showed that macroporous resin had the best adsorption and desorption capability among
the three adsorbents. Dynamic adsorption and desorption with macroporous resin packed column were also conducted to optimize
the parameters such as: with the optimal values shown in brackets, the concentration of extract solution (4 times diluted),
pH value (6–7), adsorption speed (3 BV h−1, bed volumes/per hour), concentration of ethanol (80%), elution speed (3 BV h−1) and elution volume (7 BV). The chromatographic process so optimized gave a purity of 62.43% from the crude polyphenols,
providing a promising basis for large scale preparation of bioactive polyphenols upon further scaling up tests. 相似文献
32.
Polyphenols from the ethanol extracts of Sargassum tenerrimum （ST） with potent antiallergic effects were studied to optimize separation process through column chromatography. The adsorption and desorption characteristics of three widely used adsorbents： macroporous resin, silica gel, and polyvinylpolypyrrolidone （PVPP）, were critically evaluated respectively and studied for the optimization of preparative separation of polyphenols. Static operations on these adsorbents showed that macroporous resin had the best adsorption and desorption capability among the three adsorbents. Dynamic adsorption and desorption with macroporous resin packed column were also conducted to optimize the parameters such as： with the optimal values shown in brackets, the concen- tration of extract solution （4 times diluted）, pH value （6-7）, adsorption speed （3BVh-1, bed volumes/per hour）, concentration of ethanol （80%）, elution speed （3 BV ht） and elution volume （7 BV）. The chromatographic process so optimized gave a purity of 62.43% from the crude polyphenols, providing a promising basis for large scale preparation of bioactive polyphenols upon further scaling up tests. 相似文献
33.
In this paper, we study the validity of the generalized second law (GSL) in phantom dominated universe in the presence of a Reissner-Nordström (RN) black hole. Our study is independent of the origin of the phantom like behavior of the considered universe. We also discuss the GSL in the neighborhood of transition from quintessence to phantom regime. We show that for a constant equation of state parameter, the GSL may be satisfied provided that the temperature is proportional to de Sitter temperature. It is shown that in models with (only) a transition from quintessence to phantom regime the generalized second law does not hold in the transition epoch. Next we show that if the phantom energy has a chemical potential, then the GSL will hold if the mass of black hole is above from a critical value. 相似文献
34.
O. Jamil R. P. Fender C. R. Kaiser 《Monthly notices of the Royal Astronomical Society》2010,401(1):394-404
In the following paper, we present an internal shocks model, iShocks, for simulating a variety of relativistic jet scenarios; these scenarios can range from a single ejection event to an almost continuous jet, and are highly user configurable. Although the primary focus in the following paper is black hole X-ray binary jets, the model is scale and source independent and could be used for supermassive black holes in active galactic nuclei or other flows such as jets from neutron stars. Discrete packets of plasma (or 'shells') are used to simulate the jet volume. A two-shell collision gives rise to an internal shock, which acts as an electron re-energization mechanism. Using a pseudo-random distribution of the shell properties, the results show how for the first time it is possible to reproduce a flat/inverted spectrum (associated with compact radio jets) in a conical jet whilst taking the adiabatic energy losses into account. Previous models have shown that electron re-acceleration is essential in order to obtain a flat spectrum from an adiabatic conical jet: multiple internal shocks prove to be efficient in providing this re-energization. We also show how the high-frequency turnover/break in the spectrum is correlated with the jet power, ν b ∝ L ∼0.6 W , and the flat-spectrum synchrotron flux is correlated with the total jet power, F ν ∝ L ∼1.4 W . Both the correlations are in agreement with previous analytical predictions. 相似文献
35.
A feeding trial was conducted in a recirculating water system to investigate the effects of dietary protein levels on growth,
feed utilization, hepatosomatic index and liver lipid deposition of juvenile red snapper, Lutjanus argentimaculatus (average initial wet weight 8.0 ± 0.39 g and total length 3.14 ± 0.3 cm). In the experiment, six fishmeal-based diets were
formulated to contain various protein levels (20% to 45% in 5% increments), with dietary energy ranging from 2210.7kJ lOOg
to 2250.2kJlOOg dry matter. The protein to energy ratios of diets ranged from 8.58 mg protein kJ−1 to 20.03 mg protein kJ−1. Diets were fed for 90d to triplicate groups of fish stocked in 0.128m3 seawater tanks, 25 individuals each. The daily ration of 2% wet body weight was offered to the fish thrice a day. The fish
at the end of the study had more than ten-fold (77.0g) increase in weight compared to the initial (8.0g). Fish fed diets of
40% and 45% protein produced significantly (P<0.05) higher weight gain of 77.2g and 76.5g, and specific growth rate (SGR) of 2.65% and 2.62% than those of 67.0 g and 68.3g,
and 2.49% and 2.51% of the other diets. The broken-line regression of SGR against dietary protein level yielded an optimum
dietary protein requirement of 42.6% (Y=−1.6295 + 0.1114 X
2,P<0.05). Survival remained 100% among groups. Feed conversion ratio decreased from 0.45 for fish fed 20% dietary protein to
0.35 for fish fed 45% dietary protein. Nitrogen intake increased with an increase in dietary protein, which in turn resulted
in an increase in nitrogen gain of fish whole body. Fish fed 40% and 45% protein diets showed higher (P<0.05) nitrogen gain (0.27g and 0.26g) than those (0.23g and 025g) fed all other diets. Gross energy intake (GEI) in fish
fed 45% protein was lower (600.67kJ) than that (607.97 kJ) of 40% protein diet, though the differences were not statistically
significant (P>0.05); GEI ranging from 677.31 kJ to 663.20 kJ at remaining four diets (20% to 35% protein) did not appear to differ significantly
(P>0.05). The highest energy gain of 518.33 kJ was obtained with fish fed 40% protein, resulting in the highest energy retention
efficiency of 85.26%. The hepatosomatic index of fish fed diets of 20%, 25%, 30% and 35% protein were significantly (P<0.05) higher (2.09% to 2.57%) than those (1.44% and 1.41%) of fish fed diets containing 40% and 45% protein. Liver lipid
contents decreased from 8.72% to 7.0% in fish fed dietary protein of 20% to 45% in 5% increments. Results suggest that the
diet containing 40% to 42.6% protein with a P/E ratio of 17.6 mg protein kJ−1 is required for good growth of L. argentimaculatus weighing between 8.0 g and 85.2 g under the culture conditions of the present study. 相似文献
36.
对虾冷藏过程中肌肉蛋白特性的变化比较 总被引：1，自引：0，他引：1
从生物化学、物理学两方面,比较养殖对虾和海捕对虾在冷冻贮藏过程中肌动球蛋白的特性变化,探讨不同贮藏温度和时间对蛋白特性的影响,及特性指标之间的相关性。冷藏后ＡＭ溶解度下降,ＡＴＰａｓｅ活性下降,总ＳＨ和未遮盖ＳＨ数均减少,疏水性增大,而ＡＴＰ感度呈下降趋势。所有指标变化表明随着冻藏时间的延长,蛋白质变性加剧,变性程度为－１０℃＞－１８℃＞－３０℃。各项指标均显示养殖对虾蛋白质的耐冻性比海捕对虾弱。 相似文献
37.
F-essence is a generalization of the usual Dirac model with the nonstandard kinetic term. In this paper, we introduce a new
model of spinor cosmology containing both Ricci scalar and the non minimally coupled spinor fields in its action. We have
investigated the cosmology with both isotropy and anisotropy, where the equations of motion of FRW and Bianchi type-I spacetimes
have been derived and solved numerically. Finally the quantization of these models through Wheeler-De Witt (WD) wave function
has been discussed. 相似文献
38.
Davi C. D. Melo Jamil A. A. Anache Cristiano das N. Almeida Jaqueline V. Coutinho Geraldo M. Ramos Filho Lívia M. P. Rosalem 《水文科学杂志》2020,65(8):1262-1280
ABSTRACT
In-situ
hydrological monitoring is essential for a proper decision-making process and modelling. Efforts have been made in Brazil to carry out field activities at the basin scale, but how complete and comprehensive are those studies? Where are they located? How long have they been carried out? What are the main findings? To answer these questions, an overview of experimental monitoring basins in Brazil is presented, listing their geographical locations, monitored variables, operational status, monitoring periods and main publications. We identified 60 monitored sites, spread across most Brazilian biomes, with an average monitoring period of 12 years. However, some publications from these monitoring studies are not fully accessible to the international community. Field hydrology activities in Brazil contribute to a better understanding of hydrological processes in humid and semi-arid regions and inform us about the impacts of land-use change on water quality and quantity. 相似文献39.
The devastating effect of soil erosion is one of the major sources of land degradation that affects human lives in many ways which occur mainly due to deforestation, poor agricultural practices, overgrazing,wildfire and urbanization. Soil erosion often leads to soil truncation, loss of fertility, slope instability, etc.which causes irreversible effects on the poorly renewable soil resource. In view of this, a study was conducted in Kelantan River basin to predict soil loss as influenced by long-term land use/land-cover(LULC) changes in the area. The study was conducted with the aim of predicting and assessing soil erosion as it is influenced by long-term LULC changes. The 13,100 km~2 watershed was delineated into four sub-catchments Galas, Pergau, Lebir and Nenggiri for precise result estimation and ease of execution. GIS-based Universal Soil Loss Equation(USLE) model was used to predict soil loss in this study. The model inputs used for the temporal and spatial calculation of soil erosion include rainfall erosivity factor,topographic factor, land cover and management factor as well as erodibility factor. The results showed that 67.54% of soil loss is located under low erosion potential(reversible soil loss) or 0-1 t ha~(-1) yr~(-1) soil loss in Galas, 59.17% in Pergau, 53.32% in Lebir and 56.76% in Nenggiri all under the 2013 LULC condition.Results from the correlation of soil erosion rates with LULC changes indicated that cleared land in all the four catchments and under all LULC conditions(1984-2013) appears to be the dominant with the highest erosion losses. Similarly, grassland and forest were also observed to regulate erosion rates in the area. This is because the vegetation cover provided by these LULC types protects the soil from direct impact of rain drops which invariably reduce soil loss to the barest minimum. Overall, it was concluded that the results have shown the significance of LULC in the control of erosion. Maps generated from the study may be useful to planners and land use managers to take appropriate decisions for soil conservation. 相似文献
40.
JIN Jianjun FRANCISCO Jamil Paolo SPOANN Vin BUDDHAWONGSA Piyaluk MA Hua 《资源与生态学报(英文版)》2016,7(2):115-121
The purpose of this study was to measure the effect of maximum price information and contextual factors on people’s bidding behaviors in a controlled Becker-DeGroot-Marschak (BDM) experimental auctions. 354 respondents from three Asian countries (China, Cambodia and the Philippines) participated in this study. In each country, both households with piped water connection and households without piped water connection were investigated. The sample in each country was then randomly assigned to two groups: one group was provided with a maximum price of a water filter and the other group was not provided with the maximum price information. The results show that the treatment group with maximum price information had a higher actual willingness-to-pay than the control group without maximum price information, but they were not significantly different. Our results also indicate that contextual and socioeconomic factors did play a role in participants’ bid results for the water filter. 相似文献