共查询到20条相似文献,搜索用时 520 毫秒
1.
Rui Yang Hongshen Liu Zhijie Ding Jinfeng Zheng John C. Mauro Seong H. Kim Qiuju Zheng 《Journal of the American Ceramic Society》2021,104(8):3973-3981
Glass for pharmaceutical packaging requires high chemical durability for the safe storage and distribution of newly developed medicines. In borosilicate pharmaceutical glasses which typically contain a mixture of different modifier ions (alkali or alkaline earth), the dependence of the chemical durability on alkaline earth oxide concentrations is not well understood. Here, we have designed a series of borosilicate glasses with systematic substitutions of CaO with MgO while keeping their total concentrations at 13 mol% and a fixed Na2O concentration of 12.7 mol%. We used these glasses to investigate the influence of R = [MgO]/([MgO] + [CaO]) on the resistance to aqueous corrosion at 80°C for 40 days. It was found that this type of borosilicate glass undergoes both leaching of modifier ions through an ion exchange process and etching of the glass network, leading to dissolution of the glass surface. Based on the concentration analysis of the Si and B species dissolved into the solution phase, the dissolved layer thickness was found to increase from ~100 to ~170 nm as R increases from 0 to 1. The depth profiling analysis of the glasses retrieved from the solution showed that the concentration of modifier ions (Na+, Ca2+, and Mg2+) at the interface between the solution and the corroded glass surface decreased to around 40%–60% of the corresponding bulk concentrations, regardless of R and the leaching of modifier cations resulted in a silica-rich layer in the surface. The leaching of Ca2+ and Mg2+ ions occurred within ~50 and <25 nm, respectively, from the glass surface and this thickness was not a strong function of R. The leaching of Na+ ions varied monotonically; the thickness of the Na+ depletion layer increased from ~100 nm at R = 0 to ~200 nm at R = 1. Vibrational spectroscopy analysis suggested that the partial depletion of the ions may have caused some degree of the network re-arrangement or re-polymerization in the corroded layer. Overall, these results suggested that for the borosilicate glass, replacing [CaO] with [MgO] deteriorates the chemical durability in aqueous solution. 相似文献
2.
Enio Campiglia Roberto Mancinelli Emanuele Radicetti Sara Marinari 《Nutrient Cycling in Agroecosystems》2011,89(3):399-412
There is not sufficient knowledge concerning the risks involved in NO3–N leaching in relation to the use of cover crops and mulches. A 2 year field experiment was carried out in a pepper (Capsicum annuum L.) crop transplanted into different soil management treatments which involved the addition of mulch of three different types
of winter cover crops (CC) [hairy vetch (Vicia villosa Roth.), subclover (Trifolium subterraneum L.), and a mixture of hairy vetch/oat (Avena sativa L.)], and an un-mulched plot. At the time of CC conversion into mulch, the hairy vetch/oat mixture accumulated the highest
aboveground biomass (5.30 t ha−1 of DM), while hairy vetch in pure stand accumulated the highest quantity of N (177 kg ha−1) and showed the lowest C/N ratio (12). The marketable pepper yield was higher in mulched than in conventional (on average
33.5, 28.9, 27.7 and 22.2 t ha−1 of FM for hairy vetch, subclover, hairy vetch/oat mixture, and conventional, respectively). Generally, the NO3–N content of the soil was minimum at CC sowing, slightly higher at pepper transplanting and maximum at pepper harvesting
(on average 15.2, 16.8, and 23.3 mg NO3-N kg−1 of dry soil, respectively). The cumulative leachate was higher during the CC period (from October to April) than the pepper
crop period (from April to September), on average 102.1 vs 66.1 mm over the years, respectively. The cumulative NO3–N leached greatly depended on the type of mulch and it was 102.3, 95.3, 94.7, and 48.2 kg ha−1 in hairy vetch, subclover, hairy vetch/oat mixture, and conventional, respectively. A positive linear correlation was found
between the N accumulated in the CC aboveground biomass and the NO3–N leached during pepper cultivation (R
2 = 0.87). This research shows that winter legume cover crops, especially hairy vetch in pure stand, converted into dead mulch
in spring could be used successfully for adding N to the soil and increasing the yield of the following pepper crop although
the risks of N losses via leaching could be increased compared to an un-mulched soil. Therefore when leguminous mulches are
used in the cultivation of a summer crop, appropriate management practices of the system, such as a better control of the
amount of irrigation water and the cultivation of a graminaceous or a cruciferous catch crop after the harvesting of the summer
crop, should be adopted in order to avoid an increase in NO3–N leaching. 相似文献
3.
Nitrogen (N) leaching under grazed pastures can be very high directly under urine spots. The amount of N which is returned
by one excretion of urine or dung can locally exceed 1000 kg ha−1 a−1 which is far more than the uptake by surrounding plants during one grazing period. We therefore quantified the contribution
of N deriving from urine and dung to the total N leaching under urine and dung patches. Dung N and urine N was separately
sampled from a cow feed with 15N labelled grassilage, and were amended on lysimeters in October 2000 and October 2001. Lysimeters (350 mm diameter and 800 mm
length) were filled with sand, and an intact grass sod from a pasture, 4 lysimeter each were amended with the 15N labelled dung and urine; 4 lysimeters without an application of dung or urine served as control. During 11 months after
dung and urine amendment the amount of leachate was monitored and leachate was analysed for nitrate, ammonium and total N.
15N in these fractions was measured. Dung and urine applications of 1052 and 1030 kg N ha−1 in autumn increased N leaching. Leaching loss of nitrate and dissolved organic N deriving from dung was only 37 kg N ha−1 in both years, whereas under urine patches 447 kg nitrate-N ha−1, 108 kg N ha−1 ammonia-N and 53 kg ha−1 dissolved organic N leached on average of both experimental years. N not deriving from dung and urine exceeded the leached
N under the control by about 36 and 136 kg ha−1 on average of both years, suggesting the contribution of different priming processes. 相似文献
4.
Leaching losses of nitrate nitrogen and dissolved organic nitrogen from a yearly two crops system,wheat-maize,under monsoon situations 总被引:6,自引:0,他引:6
Manxiang Huang Tao Liang Zhu Ou-Yang Lingqing Wang Chaosheng Zhang Chenghu Zhou 《Nutrient Cycling in Agroecosystems》2011,91(1):77-89
A large amount of nitrogen (N) fertilizers applied to the winter wheat–summer maize double cropping systems in the North China
Plain (NCP) contributes largely to N leaching to the groundwater. A series of field experiments were carried out during October
2004 and September 2007 in a lysimeter field to reveal the temporal changes of N leaching losses below 2-m depth from this
land system as well as the effects of N fertilizer application rates on N leaching. Four N rates (0, 180, 260, and 360 kg N ha−1 as urea) were applied in the study area. Seasonal leachate volumes were 87 and 72 mm in the first and second maize season,
respectively, and 13 and 4 mm during the winter wheat and maize season in the third rotational year, respectively. The average
seasonal flow-weighted NO3-N concentrations in leachate for the four N fertilizer application rates ranged from 8.1 to 103.7 mg N l−1, and seasonal flow-weighted dissolved organic nitrogen (DON) concentrations in leachate varied from 0.8 to 6.0 mg N l−1. Total amounts of NO3-N leaching lost throughout the 3 years were in the range of 14.6 to 177.8 kg ha−1 for the four N application rates, corresponding to N leaching losses in the range of 4.0–7.6% of the fertilizers applied.
DON losses throughout the 3 years were 1.4, 2.1, 3.6, and 6.3 kg N ha−1 for the four corresponding fertilization rates. The application rate of 180 kg N ha−1 was recommended based on the balance between reducing N leaching and maintaining crop yields. The results indicated that
there is a potential risk of N leaching during the winter wheat season, and over-fertilization of chemical N can result in
substantial N leaching losses by high-intensity rainfalls in summer. 相似文献
5.
Rice is the staple food of about 50% of the world’s population. Rice yields in many parts of south Asia, however, are declining
due to conventional blanket and imbalanced use of fertilizers. Fertilizer application based on quantitative approaches such
as simulation modeling can assist in improving yields and nutrient use efficiency in rice. Field experiments were conducted
in 20 sites in Eastern India to assess the soil supply, requirement and internal efficiency of N, P, K and Zn in rice. The
data were used to calibrate the Quantitative Evaluation of the Fertility of Tropical Soils (QUEFTS) model for site-specific,
balanced fertilizer recommendations. The parameters of maximum accumulation (a) and dilution (d) of N (31, 87), P (192, 678),
K (33, 81) and Zn (32488, 153125) in plants were developed, which can be used as the standard parameters in the QUEFTS model
for rice. The relationships between chemical properties and nutrient supplying capacity of soil were also established. Grain
yield of rice showed good correlation with N (R
2 = 0.95**), P (R
2 = 0.71**), K (R
2 = 0.98**) and Zn uptake (R
2 = 0.57*). The NPK ratio to produce 1 Mg grain yield of rice was derived to be 6.5:1.0:6.8. Running the calibrated model with
observed field data from different locations in India with different amounts of N, P, K and Zn produced a good fit between
measured and calculated yields. The results suggested that the validated QUEFTS model could be used for calculating fertilizer
requirements and improved site-specific and balanced fertilizer management in rice. 相似文献
6.
Haq Nawaz Nadia Zafar Raheela Jabeen Adnan Amjad Mohibullah Shah Saba Munir 《European Journal of Lipid Science and Technology》2023,125(11):2300053
The repeated use of cooking oils and ghee for the deep frying of food materials may affect their nutritional quality. The present study evaluated the effect of repeated frying on the physicochemical characteristics and antiradical potential of canola oil and ghee. The oil and ghee were used for frying of fish and chicken for 2, 4, 6, 8, and 10 frying cycles followed by the analysis of physicochemical, oxidative stress, and antiradical parameters. Regression analysis of the data showed a frying cycle-dependent significant linear increase in saponification (R2 = 0.9507–0.9748), peroxide and acid values (R2 = 0.956–0.9915), and malondialdehyde (MDA) production (R2 = 0.9058–0.9557) of canola oil and ghee subjected to fish and chicken frying but exponential increase in saponification value (R2 = 0.9778) and MDA production (R2 = 0.7407) of canola oil and ghee used for fish frying. The increase in the number of frying cycles linearly decreased the iodine value (R2 = 0.9781–0.9924), and 1, 1-diphenyl-2-picrylhydrazyl, hydroxyl, and 2, 2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) radical scavenging potential (R2 = 0.9089–0.9979) of canola oil and ghee. Repeated frying in cooking oil and ghee increases oxidative stress and decreases their physicochemical and antioxidant qualities. Canola oil was comparatively more oxidative resistant than canola ghee. The regression equations derived from regression analysis will guide researchers to conduct similar types of univariate studies. 相似文献
7.
J. Henke U. Böttcher D. Neukam K. Sieling H. Kage 《Nutrient Cycling in Agroecosystems》2008,82(3):299-314
Winter oilseed rape (OSR) demands high levels of N fertilizer, often exceeding 200 kg N ha−1. Large amounts of residual soil mineral nitrogen (SMN) after harvest are regularly observed, and therefore N leaching during
the percolation period over winter is increased. In this study agronomic strategies (fertilization level, crop rotation, tillage
intensity) to control nitrate leaching after OSR were investigated by combining field measurements (soil mineral nitrogen,
soil water content, crop N uptake) of a 2-year trial and another 5-year field trial with simulation modeling. The crop-soil
model uses a daily time step and was built from existing and partly refined submodels for soil water dynamics, mineralization
processes, and N uptake. It was used to reproduce the complex processes of the N dynamics and to calculate N concentration
in the leachate and total volume of percolation water. Some parameters values were thereby newly identified based on the agreement
between measured data and model results. Although SMN in the 60–90 cm layer was overestimated, the model could reproduce the
measured data with an acceptable degree of accuracy. Overfertilization of OSR increased N leaching and therefore the precise
calculation of N fertilizer doses is a first step towards prevent N leaching. Compared to ploughing, minimum tillage decreased
N leaching when winter wheat was grown as the subsequent crop. Volunteer OSR and Phacelia tanacetifolia were grown as catch crops after OSR harvest. N leaching could be decreased especially when Phacelia was grown, but nitrate concentrations in the drainage water were higher and exceeded the European Union (EU) threshold for
drinking water when volunteer OSR was grown. The results of this study provide strong evidence that reduced tillage or growing
of noncruciferous catch crops decrease N leaching and may be used as an agricultural measure to prevent N pollution. 相似文献
8.
The incorporation of legume cover crops into annual grain rotations remains limited, despite extensive evidence that they
can reduce negative environmental impacts of agroecosystems while maintaining crop yields. Diversified grain rotations that
include a winter cereal have a unique niche for interseeding cover crops. To understand how management-driven soil fertility
differences and inter-seeding with grains influenced red clover (Trifolium pratense) N2 fixation, we estimated biological N2 fixation (BNF) in 2006 and 2007, using the 15N natural abundance method across 15 farm fields characterized based on the reliance on BNF derived N inputs as a fraction
of total N inputs. Plant treatments included winter grain with and without interseeded red clover, monoculture clover, monoculture
orchardgrass (Dactylis glomerata), and clover-orchardgrass mixtures. Fields with a history of legume-based management had larger labile soil nitrogen pools
and lower soil P levels. Orchardgrass biomass was positively correlated with the management-induced N fertility gradient,
but we did not detect any relationship between soil N availability and clover N2 fixation. Interseeding clover with a winter cereal did not alter winter grain yield, however, clover production was lower
during the establishment year when interseeded with taller winter grain varieties, most likely due to competition for light.
Interseeding clover increased the % N from fixation relative to the monoculture clover (72% vs. 63%, respectively) and the
average total N2 fixed at the end of the first growing season (57 vs. 47 kg N ha−1, respectively). Similar principles could be applied to develop more cash crop-cover crop complementary pairings that provide
both an annual grain harvest and legume cover crop benefits. 相似文献
9.
Long-term simulations of nitrate leaching from potato production systems in Prince Edward Island,Canada 总被引:1,自引:0,他引:1
LEACHN was employed to simulate nitrate leaching from a representative potato production system in Prince Edward Island (PEI),
Canada and enhance the understanding of impacts of potato (Solanum tuberosum L.) production on groundwater quality. The model’s performance on predicting drainage was examined against water table measurements
through coupled LEACHN and MODFLOW modeling. LEACHN was calibrated and verified to data from tile-drain leaching experiments
of potato grown in rotation with barley (Hordeum vulgare L.) and red clover (Trifolium pratense L.) during 1999–2008. Long-term simulations using the calibrated model were performed to evaluate the effects of climate
and N fertilization for the potato crop on nitrate leaching. The modeling suggests LEACHN can be an effective tool for predicting
nitrate leaching from similar cropping systems in PEI. Both measurements and simulations showed nitrate leaching primarily
occurred during the non-growing season when crop uptake diminishes, and nitrate from mineralization and residual fertilizer
coexists with excessive moisture from rainfall and snowmelt infiltration. Annual average nitrate leaching following potato,
barley and red clover phases was predicted to be 81, 54 and 35 kg N ha−1, respectively, and the corresponding leached concentrations were 15.7, 10.1 and 7.3 mg N l−1. Increased N input for potato alone increased nitrate leaching not only during potato phase but also during the rotation
crop phases. To reduce the risk of nitrate leaching, practices should be developed to minimize nitrate accumulation in soil
both during and outside of the growing season and in both the potato and the rotation crop phases. 相似文献
10.
C. L. van Beek C. van der Salm A. C. C. Plette H. van de Weerd 《Nutrient Cycling in Agroecosystems》2009,83(2):99-110
Agriculture is a main contributor of diffuse emissions of N and P to the environment. For N the main loss pathways are NH3-volatilization, leaching to ground and surface water and N2(O) emissions. Currently, imposing restraints on farm inputs are used as policy tool to decrease N and P leaching to ground
water and to surface water, and the same measure is suggested to combat emissions of N2O. The response, however, to these measures largely depends on the soil type. In this study nutrient flows of three dairy
farms in The Netherlands with comparable intensity on sand, peat and clay soils were monitored for at least 2 years. The first
aim was to provide quantitative data on current nutrient loss pathways. The second aim was to explore the responses in partitioning
of the nutrient loss pathways when farm inputs were altered. Mean denitrification rates ranged from 103 kg N ha−1 year−1 for the sandy soil to 170 kg N ha−1 year−1 for the peat soil and leaching to surface water was about 73 kg N ha−1 year−1 for the sandy soil, 15 kg N ha−1 year−1 for the clay soil and 38 kg N ha−1 year−1 for the peat soil. For P, leaching to surface water ranged from 2 kg P ha−1 year−1 for the sandy site to 5 kg P ha−1 year−1 for the peat site. The sandy soil was most responsive to changes in N surpluses on leaching to surface water, followed by
the peat soil and least responsive was the clay soil. For P, a similar sequence was found. This article demonstrates that
similar reductions of N and P inputs result in different responses in N and P loss pathways for different soil types. These
differences should be taken into account when evaluating measures to improve environmental performance of (dairy) farms. 相似文献
11.
Nitrate (NO3−) leaching and water contamination is a major environmental issue around the globe. In grazed grassland, most of the nitrate
leaching occurs under the animal urine patch areas because of high nitrogen (N) loading rates. The aim of this study was to
determine NO3–-N leaching losses and pasture responses as affected by different animal urine-N loading rates and application of a nitrification
inhibitor, dicyandiamide (DCD). Undisturbed monolith lysimeters (50 cm diameter by 70 cm deep) of a free-draining stony soil
(Pallic orthic brown soil; Udic Haplustept loamy skeletal) with a mixture of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) were used for the study. Results showed that total NO3–-N leaching losses increased significantly (P < 0.01) from 22.8 to 59.7, 188.1 and 254.9 kg NO3−-N ha−1, when urine N was applied at 0 (Control), 300, 700 and 1,000 kg N ha−1, respectively, without DCD. The application of DCD to the corresponding treatments significantly (P < 0.01) reduced the total NO3−-N leaching losses to 12.4, 9.9, 75.3 and 139.0 kg N ha−1, respectively, resulting in an average reduction of 63%. Pasture yield increased linearly with increasing urine-N application
rates and the application of DCD resulted in an average 25% increase in pasture dry matter production. The average N offtake
was increased by 32% with the application of DCD, confirming the effectiveness of the inhibitor in improving the N cycle.
These results indicate that the DCD nitrification inhibitor technology has the potential to be a valuable nitrogen management
tool in different grazed pasture systems (e.g. sheep, beef cattle and dairy cattle) to mitigate NO3− leaching and improve sustainable production. 相似文献
12.
The use of farmgate balances and soil surface balances as estimator for nitrogen leaching to surface water 总被引:2,自引:0,他引:2
Farmgate balances (FGBs), defined as the difference between nutrient input and nutrient output at farm level, are currently used as a tool to monitor changes in nitrogen (N) and phosphorus (P) leaching to groundwater and surface water. We postulate that the estimator value of FGBs for N and P leaching to groundwater and surface water depends on (1) the distribution of N and P surpluses over fields within farms, and (2) the partitioning of the surplus over the various nutrient loss pathways. In this study, we assessed intra-farm variability of N and P surpluses and its possible consequences on N leaching to surface waters. Furthermore, we investigated the effect of policies to decrease N and P surpluses at farm level on N and P surpluses at field level. FGBs were derived for six dairy farms in a hydrologically rather isolated polder with grassland on peat soil for three years (1999, 2000 and 2001). Soil surface balances (SSBs), defined as the differences between nutrient input and nutrient output at field level, were derived for the accompanying 65 fields for the same years. On average, FGB surpluses decreased from 271 kg N ha–1 y–1 and 22 kg P ha–1 y–1 in 1999 to 213 kg N ha–1 y–1 and 13 kg P ha–1 y–1 in 2001. Variances in N and P surpluses between fields per farm were compared with variances between farms. For N, variances between fields per farm exceeded variances between farms for all years. A non-linear model was fitted on the measured N loading of the surface water. This model showed that N leaching to surface water was underestimated by 5–46% if the variability in N surpluses between fields per farm was not taken into account. We concluded that estimation of N leaching to surface water, based on data at farm level, can lead to underestimation of the N leaching due to the large variability in N surpluses between fields per farm. The extent of this bias by a given distribution of N surpluses within farms was largely controlled by the partitioning of the N surplus over the various nutrient loss pathways, notably denitrification. 相似文献
13.
Jean M. Sogbedji Harold M. van Es Kofi L. Agbeko 《Nutrient Cycling in Agroecosystems》2006,74(2):99-113
Mathematical models may be applied to simulate nitrogen (N) dynamics under different types of soil and environmental conditions
to assess fertilizer N needs or to predict nitrate-N (NO3–N) potential impact on water quality. The research version of LEACHMN was evaluated using data from lysimeters and field
experiments conducted at the University of Lomé Research Farm in Togo, West Africa. The model was calibrated for the mineralization,
nitrification, denitrification and volatilization rate constants with measured values of NO3–N leaching losses and maize (Zea mays L.) N uptake collected from the lysimeter experiment. The model was then tested against measured data of soil profile NO3–N distribution and maize N uptake from the field experiment and drainage water collected from the lysimeter experiment. The
testing procedure involved two scenarios with increasing level of generalization for transformation rate constants (i) rate
constant values for each N treatment and (ii) rate constant values averaged over N treatments. LEACHMN effectively simulated
drainage water volume and rate (r2= 0.94 to 0.99). During the calibration efforts, the model satisfactorily simulated NO3–N leaching losses (r2= 0.98) and accurately simulated growing season cumulative maize N uptake. The variation of the calibrated rate constants
among N treatments was primarily linked to the model's incapacity to accurately simulate maize N uptake throughout the growing
period. When tested using calibrated rate constants for each treatment, the model was successful in simulating soil profile
NO3–N distribution (r2 = 0.52 to 0.94). Simulations of soil profile NO3–N distribution were not satisfactory (r2= 0.03 to 0.49) when rate constants were averaged over N treatments. Improvement of the plant N uptake routine of the model
is needed to increase the model’s performance. Using the LEACHMN model to predict N dynamics on the Ferralsols of southern
Togo appears feasible when appropriate calibrations are performed. 相似文献
14.
Marwa Cherif Nuno Rodrigues Ana C. A. Veloso José Alberto Pereira António M. Peres 《Journal of the American Oil Chemists' Society》2021,98(10):1021-1032
The effect of typical domestic microwave heating (0–15 min, at 800 W) on the thermal degradation of unflavored and flavored olive oils' minor bioactive compounds and related antioxidant activity was studied. Olive oils from cv. Arbequina were flavored with lemon verbena essential oil (0%, 0.2% and 0.4%, w/w) leading to a linear increase of total phenols (112–160 mg gallic acid kg−1 oil, R-Pearson = +0.9870), total carotenoids (2.19–2.56 mg lutein kg−1 oil, R-Pearson = +0.9611), and, to a less extent, of chlorophyll (2.32–3.19 mg pheophytin kg−1 oil, R-Pearson = +0.8238). However, no such linear trend was observed for the oxidative stability (6.5–7.8 h) or the radical scavenging activity (inhibition rates: 40%–43%). The contents of total phenols, total carotenoids, and chlorophyll decreased with the rise of the microwave heating time, following their thermal degradation, a second-order kinetic model (0.8784 ≤ R-Pearson ≤ 0.9926). The essential oil addition did not influence the estimated second-order rate reaction constants of total phenols (0.00070–0.00072 kg oil min−1 mg−1 gallic acid)and total carotenoids (0.14–0.17 kg oil min−1 mg−1 lutein), with a broader variation observed for chlorophyll (0.014–0.022 kg oil min−1 mg−1 pheophytin). Globally, total carotenoids degraded faster than total phenols and chlorophyll (half-life of 2.3–3.4, 8.8–12.8, and 14.5–30.8 min, respectively). Moreover, except for chlorophyll, the half-life of total phenols and carotenoids linearly decreased with the essential oil addition (R-Pearson: −0.9999 and −0.9421, respectively), showing that flavoring did not have a protective effect against degradation when subjected to a microwave heating. 相似文献
15.
The series of trichlorotitanium 2-(2-pyridinyliminomethyl)phenolates, [4,6-tBu2C6H2O-2-CHNC5R1-4N]TiCl3 (R1-4 = H (1); R1,3,4 = H, R2 = Me (2); R1,2,4 = H, R3 = Me (3); R2,4 = H, R1,3 = Me (4); R1,3 = H, R2 = CF3, R4 = Cl (5)), were synthesized and characterized by elemental analysis and 1H/13C NMR spectroscopy. The molecular structures of the representative complexes 2 and 4 were confirmed by single-crystal X-ray diffraction, and revealed distorted octahedral geometry at titanium. In the presence of MAO, all titanium pro-catalysts showed good activities for ethylene polymerization with good thermal stability at the optimum temperature of 50 °C. In comparison with the ethylene polymerization results, the activity observed for the co-polymerization of ethylene/1-hexene was far lower, but the polymers produced were of high molecular weight. For the co-polymerization of ethylene/1-octene, enhanced catalytic activity was observed, with 1-octene incorporation of up to 3.83 mol%. 相似文献
16.
Dynamics of ammonia volatilization from simulated urine patches and aqueous urea applied to pasture I. Field experiments 总被引:1,自引:1,他引:0
Ammonia (NH3) volatilization losses from simulated sheep urine patches in a perennial ryegrass (Lolium perenne L.)/white clover (Trifolium repens L.) pasture in New Zealand were measured in the field during the summer, autumn and winter periods. An enclosure technique was used with microplots (23 cm diameter) receiving either sheep urine or aqueous urea at rates equivalent to 500 kg N ha–1 and monitored continuously until measured losses decreased to 0.5% per day. Mean volatilization losses for urine treated plots were 22.2% of the applied N in summer, 24.6% in autumn and 12.2% in winter. Corresponding losses for the urea treated plots were 17.9%, 28.9% and 8.5%. Differences between these two N sources were not significant although the seasonal differences were significant (P 0.05). Changes in NH3 gas fluxes were found to be related to measured changes in soil pH and air temperature. Two repeated applications of urine or aqueous urea to the same microplot resulted in significantly greater subsequent volatilization losses averaging 29.6% from the second and 37.5% from the third application.Most of the applied N was accounted for as either soil mineral N (NH
4
+
+ NO
3
-
+ NO
2
-
) or NH3(g)
. Urea hydrolysis was rapid and obeyed the first order kinetics during the 24 hours following application. Calculated half-lives of urea in urine and aqueous urea were significantly different and were 3.0 and 4.7 h respectively during the summer and 4.7 and 12.0 h during the autumn.Implications of the results obtained to practical field situation together with the efficacy of the enclosure technique for measuring volatilization losses are discussed. 相似文献
17.
Linfeng Ding Manuel Thieme Sylvie Demouchy Clemens Kunisch Boris J. P. Kaus 《Journal of the American Ceramic Society》2018,101(9):3936-3946
During industrial glass production processes, the actual distribution of stress components in the glass during scribing remains, to date, poorly quantified, and thus continues to be challenging to model numerically. In this work, we experimentally quantified the effect of pressure and temperature on the viscosity of SCHOTT N‐BK7® glass, by performing in situ deformation experiments at temperatures between 550 and 595°C and confining pressures between 100 and 300 MPa. Experiments were performed at constant displacement rates to produce almost constant strain rates between 9.70 × 10?6 and 4.98 × 10?5 s?1. The resulting net axial stresses range from 81 to 802 MPa, and the finite strains range from 1.4% to 8.9%. The mechanical results show that the SCHOTT N‐BK7® glass is viscoelastic near the glass transition temperature at 300 MPa of confining pressure. To elucidate the data, we incorporated both 1‐element and 2‐element generalized Maxwell viscoelastic models in an inversion approach, for which we provide MATLAB scrips. Results show that the 2‐element Maxwell model fits the experimental data well. The stress decreases with increasing temperature at 300 MPa and the temperature dependence yields a similar activation energy (601 ± 10 kJ mol?1 or ?H/R = 7.2 × 104 K) to a previously reported value at 1‐atm (615 kJ mol?1 or ?H/R = 7.4 × 104 K). The SCHOTT N‐BK7® glass shows a limited linear increase in viscosity with increasing pressure of ~0.1 log10 (Pa·s)/100 MPa, which is in agreement with the most recent 2‐internal‐parameter relaxation model (based on experiments). 相似文献
18.
To improve the hydrolysis resistant ability of trisiloxane surfactants, ethoxylated single-tail and double-tail trisiloxane
surfactants of the general formulas Me3SiOSiMeR1OSiMe3 (R
1 = (CH2)3NHCH2CH(OH)CH2(OCH2CH2)
x
OCH3; x = 8.4, 12.9, 17.5, 22) and Me3SiOSiMeR2OSiMe3 (R
2 = (CH2)3NR3CH2CH(OH)CH2(OCH2CH2)
x
OCH3; R
3 = CH2(CH2)
y
CH3; x = 8.4, 12.9, 17.5, 22; y = 2, 6) were synthesized. Their structures were characterized by 1H NMR and 13C NMR. The surface activity and hydrolysis resistant properties of the trisiloxane surfactants prepared were also studied.
The values of the critical micelle concentration of all trisiloxane surfactants prepared were at levels of 10−5 and 10−4 mol/L. They can reduce the surface tension of water to less than 24 mN/m. The hydrolysis resistant properties of double-tail
trisiloxane surfactants are superior to those of single-tail trisiloxane surfactants. The double-tail trisiloxane surfactants
1B (x = 8.4; y = 2) and 2C (x = 12.9; y = 6) can be stable for 8 days in an acidic solution (pH 4.0) and 11 days in an alkaline environment (pH 10.0). 相似文献
19.
Cynthia A. Cambardella Thomas B. Moorman Jeremy W. Singer 《Nutrient Cycling in Agroecosystems》2010,87(3):383-393
Coupling winter small grain cover crops (CC) with manure (M) application may increase retention of manure nitrogen (N) in
corn (Zea mays L.), -soybean [Glycine max (L.) Merr], cropping systems. The objective of this research was to quantify soil N changes after application of liquid swine
M (Sus scrofa L.) at target N rates of 112, 224, and 336 kg N ha−1 with and without a CC. A winter rye (Secale cereale L.)-oat (Avena sativa L.) CC was established prior to fall M injection. Surface soil (0–20 cm) inorganic N concentrations were quantified every
week for up to 6 weeks after M application in 2005 and 2006. Soil profile (0–120 cm in 5, 20-cm depth increments) inorganic
N, total N, total organic carbon and bulk density were quantified for each depth increment in the fall before M application
and before the CC was killed the following spring. Surface soil inorganic N on the day of application averaged
318 \textmg \textN \textkg - 1\textsoil 318\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}}} in 2005 and
186 \textmg \textN \textkg - 1\textsoil 186\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}} } in 2006 and stabilized at
150 \textmg \textN \textkg - 1\textsoil 150\,{\text{mg}}\;{\text{N}}\;{\text{kg}}^{ - 1}{_{\text{soil}}} in both years by mid-November. Surface soil NO3-N concentrations in the M band were more than 30 times higher in the fall of 2005 than in 2006. The CC reduced surface soil
NO3-N concentrations after manure application by 32% and 67% in mid- November 2005 and 2006, respectively. Manure applied at
224 kg N ha−1 without a CC had significantly more soil profile inorganic-N (480 kg N ha−1) in the spring after M application than manured soils with a CC for the 112 (298 kg N ha−1) and 224 (281 kg N ha−1) N rates, and equivalent inorganic N to the 336 (433 kg N ha−1) N rate. These results quantify the potential for cover crops to enhance manure N retention and reduce N leaching potential
in farming systems utilizing manure. 相似文献
20.
Liliana N. Ceci Amalia A. Carelli 《Journal of the American Oil Chemists' Society》2010,87(10):1189-1197
The relation between oxidative stability and composition in 58 virgin olive oils from different cultivars and Argentinian
regions was studied over four harvest years. The oxidative stability of the oils was assessed using the OSI index (110 °C,
20 L/h air flow). A multiple linear regression model is proposed using OSI values as the dependent variable (multiple R = 0.933, p = 1 × 10−15), with positive contributions of the independent variables: fatty acid composition [oleic acid/(linoleic acid + linolenic
acid), 55.3%, p = 1 × 10−15], total polyphenols (24.1%, p = 1.8 × 10−9), carotenes (4.8%, p = 6.1 × 10−5), β-tocopherol (1.9%, 6.0 × 10−3) and other compounds (13.9%). Highly significant correlation was observed between oxidative stability indexes estimated by
the compositional model and those experimentally determined by Rancimat method (b = 0.981, R = 0.924). Chlorophylls and Δ-5-avenasterol contributions to the model were non-significant when variables related with fatty
acids and polyphenols were included. The results suggest that the fatty acid composition and the polyphenol content are the
main factors that affect the oxidative stability of olive oils. The proposed model allows the estimation of the oxidative
stability in olive oils independently of the cultivar. The model was obtained also taking into account samples that lie out
of the international legal limits in some compositional values due to natural variations. 相似文献