首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
A nowcasting system integrating observations and a numerical model was developed to better understand the spatial distributions and temporal variations in the dynamics of a small, subtropical lake occasionally influenced by severe rainstorms. The nowcasting system was used to monitor real-time meteorological conditions and thermal structures, to provide spatial information on the thermal and flow dynamics from model predictions, and to compare the predictions with the observations. The system was also able to determine whether the instruments collecting field data were performing correctly using telemetry operations. The nowcasting system was initially operated in the spring of 2009 in Yuan-Yang Lake, Taiwan. Rainstorm-induced mixing occurred due to Typhoon Morakot during August 7–9, 2009. The mixing was observed by the instruments, and the spatial distributions and temporal variations during the mixing were successfully predicted by the three-dimensional hydrodynamic lake model. A quantitative comparison of the energy balances among the heat, wind, and water inflow inputs to the lake implied that the typhoon-induced mixing was primarily caused by strong winds. The model predictions showed that the lake experienced mixing and flooding (large amounts of inflow/outflow discharges), resulting in homogenous temperatures and flows that moved to the outlet of the lake.  相似文献   

2.
We measured microcystins in blood from people at risk for swallowing water or inhaling spray while swimming, water skiing, jet skiing, or boating during an algal bloom. We monitored water samples from a small lake as a Microcystis aeruginosa bloom developed. We recruited 97 people planning recreational activities in that lake and seven others who volunteered to recreate in a nearby bloom-free lake. We conducted our field study within a week of finding a 10-μg/L microcystin concentration. We analyzed water, air, and human blood samples for water quality, potential human pathogens, algal taxonomy, and microcystin concentrations. We interviewed study participants for demographic and current health symptom information. Water samples were assayed for potential respiratory viruses (adenoviruses and enteroviruses), but none were detected. We did find low concentrations of Escherichia coli, indicating fecal contamination. We found low levels of microcystins (2 μg/L to 5 μg/L) in the water and (<0.1 ng/m3) in the aerosol samples. Blood levels of microcystins for all participants were below the limit of detection (0.147μg/L). Given this low exposure level, study participants reported no symptom increases following recreational exposure to microcystins. This is the first study to report that water-based recreational activities can expose people to very low concentrations of aerosol-borne microcystins; we recently conducted another field study to assess exposures to higher concentrations of these algal toxins.  相似文献   

3.
“金太龙”叶面肥对冬小麦产量及干热风抗性的影响   总被引：1，自引：0，他引：1  
为探究"金太龙"叶面肥对冬小麦产量及干热风抗性的调节作用,通过两因素随机区组试验,对不同水、肥喷施量下冬小麦产量及干热风抗逆指数进行了分析。结果表明,干热风胁迫下,冬小麦的产量、干热风抗性与叶面肥用量和喷施水量均密切相关。孕穗期喷施"金太龙"叶面肥的增产作用主要归因于穗粒数、千粒重增加,尤其是千粒重。喷施水量较低时,提高叶面肥用量不利于增加粒重,低叶面肥用量则可保证冬小麦高产和提高抗干热风的能力;喷施水量较高时,提高叶面肥用量有助于延长旗叶功能期,有利于增加粒重。综合来看,孕穗期"金太龙"叶面肥用量为3kg·hm~(-2)、喷施水量225kg·hm~(-2)时,冬小麦产量最高,对干热风的抗性最好。  相似文献   

4.
It has recently been proposed that water purification could be performed using aquatic plants, since they absorb nutrient salts. The behavior of a substance in a closed water area is affected by turbulent flows from wind-induced flow, which is a mechanical disturbance, and convective flow, which is a thermal disturbance. In a closed density stratified water area, wind-induced flow gives rise to the entrainment phenomenon at the density interface. This phenomenon, which is based on mixing between the upper and lower water layers, lowers the density interface and so affects the water quality. We experimentally investigated the effect of aquatic plants on the turbulent flow from a mechanical disturbance in the closed water area. Results indicated that the presence of floating and submerged plants had a significant effect on the scale of the turbulent entrainment, and that the entrainment velocity depended on the overall Richardson number to the power of –3/2.  相似文献   

5.
When floating vegetation grows on the water surface in a closed water body, the vegetation counteracts the magnitude of the wind acting on the water surface, and affects the fluid flow and the water quality variation in it. In this study, in order to investigate the counteraction effect of the luxuriant growth of floating vegetation on the fluid flow and water quality in the closed water body, we conducted hydraulic experiments on wind-induced flow with density stratification using a wind tunnel test tank and imitated vegetation. We used imitated vegetation made from polystyrene foam plates instead of using real floating vegetation. And we experimentally considered the effect of the vegetation using the concept of the wind-induced entrainment phenomenon. In particular, we focused the effect of the occupation rate and the swaying motion of vegetation. The results indicated that the swaying motion of imitated floating vegetation had an effect on the scale of entrainment. In addition the results had the same tendency as the previous study on the wind-induced entrainment phenomenon.  相似文献   

6.
This research studied thermal environment in paddy field which the main objective to evaluate it when the water was present in the field by means of observation and simulation. Heat exchange in soil and water, plant and atmosphere were calculated using a two-layer resistance model. The atmospheric boundary layers-thermal, humidity and wind velocity-were assumed horizontally uniform and were arranged in one-dimensional equations. The observed paddy field was located at Kyushu University Experimental Farm in Fukuoka, Japan. In the simulation, fix boundary conditions of wind velocity and humidity, and fluctuating boundary condition of temperature at 100 m height were used over the paddy field with the presence of 5 cm depth of water layer. The simulation was successful in estimating radiation, dissipation of heat fluxes, mechanism of atmospheric thermal changes and the temperature of leaf, air, and water. The results show that most of the available energy dissipates into latent heat, and less into sensible heat.  相似文献   

7.
气候条件对冬小麦千粒重的影响   总被引：14，自引：2，他引：14       下载免费PDF全文
通过多年多点多项多品种的小区试验、高产攻关与高产示范，研究了气候条件对冬小麦千粒童的影响。结果表明，从其开花到成熟期的诸因子中，天数是影响冬小麦千粒重高低的主导因子，其次是平均最低气温，平均最高气温的作用最小。冬小麦受干热风的危害较大，在后期浇水不当情况下会引起千粒重下降。干热风对千粒征的危害是多种因素综合影响的结果，而麦田土壤只要能满足小麦对水分的需要，干热风来临时能保持麦株体内的水份平衡，就可极大地削弱干热风的危害程度，使千粒重少下降，甚至不下降；麦田浇水的终止期在乳熟末期前2～3d，水分不足的麦田只要在终止期前浇水，且水量适宜，就有利于千粒重的提高。  相似文献   

8.
Using statistical experimental design, the effects of multi-stage hot drawing process on thermal shrinkage and crystallographic order of linear aliphatic-aromatic co-polyester fibres were statistically analyzed. Thermal shrinkage and fullwidth half-maximum (FWHM) of an X-ray scattering profile of the fibres have been quantitatively assessed, and the direction of increasing or decreasing the significant process parameters has been characterized. It has been found that the number of drawing stages, drawing temperature and relaxing stage ratio affect the shrinkage and crystallographic order together. Plate temperature and the interaction between drawing stages and drawing temperature or drawing ratio have an effect on thermal shrinkage; Spin finish application and relaxing temperature have an effect on crystallographic order. The data analysis has been characterized with regard to the relationship between the studied factors statistically analyzed and the scientific reasons suggested. Factorial statistical analysis simulates the combination of drawing process parameters and the selected as-spun environmentally friendly biodegradable fibre.  相似文献   

9.
Batters, from three wheat cultivars, were mixed up to their maximal consistency (tpeak) at different mixing speeds (N) and flour/water ratios [Auger, F., Morel, M.H., Lefebvre, J., Dewilde, M., Redl, A., 2008. A parametric and microstructural study of the formation of gluten network in mixed flour–water batter. Journal of Cereal Science 48, 349–358]. Gluten and starch were extracted from those batters using a process which included two successive steps: dilution and sieving. In order to reveal the specific influence of the mixing step, a standardized gentle washing and sieving procedure was selected. Mixing the batters at tpeak guaranteed a high and stable gluten protein recovery (ca. 82%) irrespective of mixing conditions. SE-HPLC analysis of protein, from flours and batters sampled at tpeak, demonstrated that mixing led to the almost total breakdown of the unextractable glutenin polymers (ca. 80%), whereas their re-assembly occurred during gluten extraction. The extent of glutenin re-assembly in gluten was influenced by the batter mixing history and was mainly related to the number of mixing rotations (N.tpeak). Gluten protein contents were also found related to N.tpeak. We proposed that the leaching of starch from the batter during gluten extraction was controlled by the elasticity of the protein network, i.e. the gluten content in unextractable glutenin. An innovating scheme relating the glutenin re-assembly capacity to the irreversible thiol protein oxidation is proposed.  相似文献   

10.
Dispersion and separation of fiber bundles into individual fibers, requires exposing them to a shear stress field to overcome inter-fiber frictional forces. To this end, fiber-mixing tanks are usually used to enhance shear and agitation in water and help the dispersion process. The required time and necessary agitation to separate and disperse fibers depend on fibers’ characteristics. It is well known that excessive agitation will give rise to the formation of rope defects in the output because of the high-energy vortices and optimizing the break up time is important in wet-lay process. In this work, experimental and numerical studies were done to investigate the effects of fiber characteristics on their dispersion in water for wet-laid nonwoven. The effective forces were analyzed using a one-way modeling of fiber behaviors in a stirred mixing tank. Results show that when the fiber diameter is increased, the required time for breaking up of fiber bundles and clumps is increased. The effects of fiber types on fibers break up and dispersing time, were also investigated. In the experimental work, an on-line vision system was designed to observe the dispersion behavior of polyester fibers. The effects of fiber length and fineness on the created defects (i.e. logs and ropes) in dispersion process, as well as on the dispersion speed, were studied. The results confirm that defects are increased by rising fiber length and fineness. It is also shown that increasing fiber length and fineness, decreases the required time for fiber clumps to be opened and reach a maximum number of individual fibers. On the other hand, when fiber length and fineness is increased, the dispersion speed increases.  相似文献   

11.
When examining quantitatively the material properties of wheat flour dough, the need arises to model the mixing of the dough in terms of some constitutive relationship which simulates the changing rheology of the dough during the mixing. In formulating a mathematical model of the mixing one key issue is the extent to which the mixing of the dough displays, at least with respect to certain mixers, rate-independent characteristics. Evidence is presented to support the hypothesis that, at least to first order, the evolving rheology, resulting from the mixing of a wheat flour dough in a MixographTM, (but not necessarily in some other recording or commercial mixers), has a clear rate-independent character. When mixed on a variable speed 35 gm MixographTM, flour water dough of constant moisture content, prepared from seven flours of widely differing protein contents, showed statistically significant differences in the number of mixer revolutions required to reach peak dough development and in their resistance at peak dough development. For each of the flours, the number of revolutions was essentially constant at the five different speeds examined, whereas the resistance increased gradually (and steadily) as the mixer speed increased.  相似文献   

12.
A micro Z-arm mixer and a 2g-Mixograph were used to compare the effect of pin and Z-arm-type mixing actions on mixing properties of wheat flour dough. Although the two mixing curves obtained with pin- and Z-arm-type mixing action showed a very similar mixing trace, no significant correlation was found between the two mixers other than the number of revolutions required for optimal dough consistency (peak resistance). Mixing requirement was described by a rate-independent parameter, the number of revolutions to peak dough development and was found to be greater in a Z-arm mixer than in a pin mixer. Mixing requirement showed significant correlation with stability, which is therefore a dough strength parameter. The change in the polymeric structure of gluten proteins of dough as indicated by %UPP (unextractable polymeric protein percentage) was monitored and showed a smaller decrease with Z-arm mixing than with pin mixing. Therefore, pin-mixing action is more energetic than Z-arm mixing. At peak resistance, Z-arm mixing gives a larger quantity of polymeric protein content in the dough relative to pin mixing. The degree of dough development at maximum resistance in the different mixers was shown to be different. A new parameter, delta-UPPMZUPPMZ (the difference between %UPP of dough obtained with pin vs Z-arm mixing actions) was identified and proposed to have some relationship to the stability of the polymeric proteins in the dough.  相似文献   

13.
This research investigated the effect of repeated laundering and dry-cleaning on the physical and thermophysiological comfort properties such as air permeability, water vapour resistance and thermal resistance of fabrics made of meta-aramid (Nomex®) fibre. Two different types of fabric were selected for the study and subjected to repeated laundering and dry-cleaning (1, 5 and 10 cycles), which is commercially used for the care and maintenance of these fabrics. The fabric thickness, areal density, thermal resistance and water vapour resistance values increased with the number of laundering cycles, whereas the air permeability decreased due to the fabric shrinkage and swelling. On the other hand, the thickness and air permeability of the dry-cleaned fabric samples increased with the number of cycles; while the water vapour resistance and thermal resistance decreased. The scanning electron microscopy images showed the structural changes as indicated by the longitudinal fibrillation in the fabrics subjected to laundering or dry-cleaning.  相似文献   

14.
In this research work, the thermo physiological properties of polyester/polyethylene nonwoven composite wraps of varying thicknesses impregnated with aerogel were studied and compared. The SEM images were also taken to compare the physical configuaration of the aerogel based fibrous composites. Specific thermal properties like thermal conductivity, thermal resistance, thermal diffusivity and thermal absorptivity were measured using alambeta instrument. The air permeability of the thermal wraps was measured in air permeability tester. The relative water vapor permeability and absolute water vapor permeability was measured in Permetest. These tests were conducted to understand thermal properties, air and water vapor permeability of flexible aerogel based composites with nanoporous structure. The results of the experiments were statistically analyzed and found to be within confidence intervals.  相似文献   

15.
The effects of different mixing parameters (vacuum mixing and mixing time) on oat (70% oat flour) and wheat noodle dough were investigated on the basis of textural properties and gluten formation. The results showed that at a vacuum degree of −0.06 MPa and mixing time of 10 min, oat and wheat dough sheets exhibited the highest resistance to extension and glutenin macropolymer (GMP) content, and had the most compact and uniform gluten network. Compared with wheat noodle dough, oat dough had lower resistance to extension, lower tightly bound water content, and higher GMP content. Microstructural examination showed that oat noodle dough had a more aggregated distribution of gluten protein compared with wheat noodle dough under the optimum mixing parameters. Furthermore, the poor binding ability of vital wheat gluten with water molecules caused the indexes of oat noodle dough to be more strongly affected by the changes in mixing parameters than wheat noodle dough.  相似文献   

16.
Water interactions in polycarbonate films have been studied using fluorescence and NIR Fourier transform spectroscopy. During water sorption process, the fluorescence emission spectra showed sensitive changes with the peak at 332 nm red shifted by 18 nm with water sorption. This red-shifted peak could be due to phenyl-2-phenoxybezoate, which is one of two major thermal degradation products in polycarbonate. In the spectra of phenyl-2-phenoxybenzoate in dimethyl formamide solution, a progressive red shift was also observed with the water addition. By using the NIR spectra, hydrogen-bonding interactions of the sorbed water with polycarbonate were investigated. It was found that water can be analyzed as free water S0 or single hydrogen bonded water, S1 while double hydrogen bonded water was negligible. During water immersion, most water species which are present as S0 species decrease slightly, with a small increase in S1 species. During desorption, S0 species decrease sharply, while S1 species is reduced gradually. Two examples of S1 structure in water-sorbed polycarbonate are proposed.  相似文献   

17.
The aim of the present study was to describe the physicochemical events occurring during batter mixing at different water contents (51.8, 54.4, and 56.7 g of water/100 g of dough) using near infrared (NIR) spectroscopy. An FT-NIR spectrometer over the 1000–2500 nm range with a fibre optic probe was used to record NIR spectra in-line. The analysis of both one-dimensional statistical method (principal components analysis) and two-dimensional statistical methods (generalised two-dimensional correlation spectroscopy) was conducted to evaluate the possibilities of NIR spectroscopy to monitor physical and physicochemical modifications observed during mixing of batter. The NIR results were in agreement with the physical and physicochemical analysis traditionally used to study bread dough mixing (consistency and glutenin depolymerisation). PCA on raw NIR spectra demonstrated that PC1 describes the same traces as the dough consistency curves. PCA on raw NIR spectra can be used to monitor the batter mixing and to identify the NIR mixing time close to the tpeak.PCA on spectra after second derivative demonstrated that PC1 and PC2 traces described different traces compared to the dough consistency curves. The loading spectra associated to PC1 and PC2 suggested that almost the same physicochemical and chemical mechanisms occur during the dough mixing at 51.8 or 54.4% water contents, but with kinetic and intensity differences. The 2D COS method allowed a sequence of chemical events occurring during mixing for the batters at 51.8 and 54.4% water contents to be tentatively proposed. The 2D COS did not give clear physicochemical differences between the three batters during mixing. The NIR results for the highly hydrated batter (56.7%) were difficult to analyse due to its high water content.  相似文献   

18.
The aim of the present study was to describe the physicochemical events occurring during batter mixing at different water contents (51.8, 54.4, and 56.7 g of water/100 g of dough) using near infrared (NIR) spectroscopy. An FT-NIR spectrometer over the 1000–2500 nm range with a fibre optic probe was used to record NIR spectra in-line. The analysis of both one-dimensional statistical method (principal components analysis) and two-dimensional statistical methods (generalised two-dimensional correlation spectroscopy) was conducted to evaluate the possibilities of NIR spectroscopy to monitor physical and physicochemical modifications observed during mixing of batter. The NIR results were in agreement with the physical and physicochemical analysis traditionally used to study bread dough mixing (consistency and glutenin depolymerisation). PCA on raw NIR spectra demonstrated that PC1 describes the same traces as the dough consistency curves. PCA on raw NIR spectra can be used to monitor the batter mixing and to identify the NIR mixing time close to the tpeak.PCA on spectra after second derivative demonstrated that PC1 and PC2 traces described different traces compared to the dough consistency curves. The loading spectra associated to PC1 and PC2 suggested that almost the same physicochemical and chemical mechanisms occur during the dough mixing at 51.8 or 54.4% water contents, but with kinetic and intensity differences. The 2D COS method allowed a sequence of chemical events occurring during mixing for the batters at 51.8 and 54.4% water contents to be tentatively proposed. The 2D COS did not give clear physicochemical differences between the three batters during mixing. The NIR results for the highly hydrated batter (56.7%) were difficult to analyse due to its high water content.  相似文献   

19.
  相似文献   

20.
The role of oxygen during mixing of bread dough was investigated using a unique air-tight mixer in which oxygen content of the atmosphere surrounding the dough was fixed at different levels ranging from 10 to 30%. Effects of the presence in bread dough composition of various O2 consumers, such as yeast, lipoxygenase (LOX), and additional glucose oxidase (GOX) and/or soybean or horse bean flour (containing LOX), were studied in order to characterize the competition phenomena for oxygen in the different conditions. O2 uptake by dough during mixing was followed and relaxation tests were performed on the resulting bread dough. Variation of O2 level of the gaseous atmosphere had no rheological impact on basic bread dough (with no additional oxidative system), even though this level was found to lead to an increase of O2 consumption by dough, especially at the beginning of mixing. The competition for O2 consumption among yeast, LOX and GOX was decreased by kneading under a 30% O2 atmosphere, enabling GOX to reveal its structuring effect. Finally, mixing bread dough containing GOX under O2-enriched atmosphere enabled keeping a standard dough relaxation index, even though dough water content was increased. This opens new perspectives for improving bread softness.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号