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排序方式: 共有136条查询结果,搜索用时 15 毫秒
71.
Wei Cheng Hongwei Fang Haojie Lai Lei Huang Subhasish Dey 《Journal of Soils and Sediments》2018,18(10):3055-3069
Purpose
Biofilm growth changes the sediment properties and the characteristics of the bed, which further influences the interactions between the flow and the sediment bed, such as the turbulence characteristics of the flow and the erosion response of the sediment to hydrodynamic forces. In this study, the effects of biofilm on the turbulence characteristics of the flow and bio-sediment suspension are investigated.Materials and methods
Cohesive sediments were collected from the bottom of the Three Gorges Reservoir, which have a median size of less than 0.1 mm. Flume experiments were conducted for the erosion of the sediment bed with and without biofilm under the same flow rate. Acoustic Doppler Velocimetry (ADV) was used to measure the velocities along the depth, based on which the distribution of Reynolds shear stress, time-average velocity, turbulence intensities, turbulence kinetic energy flux and budgets, and bursting events of the flow were determined. Meanwhile, the biofilm effects on the physical characteristics of sediments, such as the diameter, density, and falling velocity, were summarized from previous studies. Then, the changes of the vertical distribution of suspended sediment concentration and the near-bed concentration were evaluated.Results and discussion
After biofilm growth, the time-averaged velocity increases by approximately 6.7% under the low flow rate condition with a flat bed, and by more than 20% under the high flow rate condition with a deformed bed. The vertical distribution of the turbulence intensity becomes more uniform under the high flow rate condition. However, the changes of the turbulence kinetic energy flux and budgets due to biofilm are hardly observed by the scattered measurement data, and more experiments need to be conducted in the future.Conclusions
Biofilm exerts an influence on the turbulence characteristics, mostly by affecting the deformation extent of the sediment bed. Meanwhile, the changes of the physical properties of sediments due to biofilm significantly influence the transport of suspended sediment.72.
Increased planting of hard mast oak species in the Lower Missouri River floodplain is critical as natural regeneration of
oak along the Upper Mississippi and Lower Missouri Rivers has been limited following major flood events in 1993 and 1995.
Traditional planting methods have limited success due to frequent flood events, competition from faster growing vegetation
and white-tailed deer herbivory. Results of early growth response of swamp white oak (Quercus bicolor Willd.) seedlings in relation to initial acorn mass and size, and early rapid shoot growth for seedlings produced by containerized
root production method (RPM™), are presented. Containerized RPM™ seedlings grown in the greenhouse under optimal conditions
demonstrate that seed size had no discernable impact on first-year root or shoot size. Seedling survival for the first two
years and acorn production for the first three years after outplanting are presented, comparing use of containerized RPM™
swamp white oak seedlings to nursery stock. Flood tolerant precocious RPM™ oak seedlings in the floodplain provide a source
of food for acorn-consuming wildlife ten to fifteen years sooner than oaks originating from natural regeneration, direct seeding
or traditional bare root planting. Compared to bare root nursery stock that produced no acorns, some RPM™ swamp white oak
seedlings averaged 4.3, 5.2, and 6.3 acorns/seedling in the first three years after fall outplanting.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
73.
The value of initial stem diameter near the root collar, shoot length and number of first-order lateral roots (FOLR) as morphological indicators of stock quality and field performance was examined for bareroot (1+0, undercut) red oak (Quercus rubra L.) underplanted in a shelterwood in central Ontario. These three attributes were measured on more than 400 seedlings prior to planting, and their relationship with height and basal diameter growth two years after planting was determined using correlation and regression analysis. Initial diameter, shoot length and number of FOLR were positively and significantly correlated with second-year height and diameter. These relationships were strongest for diameter, but this variable explained less than 25% of the total variation in growth. Of the three indicators, diameter was also the best predictor of several physical characteristics of root systems two years after planting. Initial diameter was significantly correlated with root volume, root area and lateral root, taproot and total root dry mass. Weaker relationships existed between initial shoot length and number of FOLR and second-year root system features. Stem diameter two years after planting was more strongly related to root volume, area and dry mass than was initial diameter, the probable result of adjustment in root-shoot balance of planting stock to the shelterwood environment. 相似文献
74.
A recombinant LipL 32 antigen-based dipstick ELISA was developed as a screening test for the detection of leptospiral antibodies in serum samples from dogs. The antibodies were detected by a change in the colour of the substrate solution when the recombinant antigen-coated dipsticks were dipped into it. The relative sensitivity, specificity and accuracy of the test, compared with the standard microscopic agglutination test, were 95.9 per cent, 93.8 per cent and 94.8 per cent, respectively. 相似文献
75.
76.
77.
T.K. Behera S.S. Dey A.D. Munshi Ambika B. Gaikwad Anand Pal Iqbal Singh 《Scientia Horticulturae》2009,120(1):130-133
Gynoecism has been used on a large scale in heterosis breeding of cucumber. Production of hybrid seeds in bitter gourd is highly expensive because it is done mainly through hand pollination. But utilization of a gynoecious line would be more economical and easier method. Since gynoecious parent has only female flowers, the open pollinated seeds it produces will be F1 hybrid. It will reduce the cost of male flower pinching and hand pollination. Two gynoecious lines, DBGY-201 and DBGY-202 were crossed with two monoecious cultivars, “Pusa Do Mausami” and “Pusa Vishesh” and their F2 populations were observed to determine the inheritance pattern of gynoecious sex form. Another experiment was conducted to determine magnitude of heterosis by utilizing nine inbred lines including one gynoecious line, DBGY-201 in diallel (without reciprocal) mating system. All the gynoecious hybrids showed significant heterosis in a desirable direction for traits like sex ratio (male:female), days to first picking, number of fruits per plant, yield per plant, and vine length. The segregation pattern in F2 suggested that gynoecious sex form in bitter gourd was governed by single recessive gene. The gynoecious hybrids DBGY-201 × “Pusa Vishesh” and DBGY-201 × “Pusa Do Mausami” were important for early harvest (~50 days after sowing) whereas DBGY-201 × “Priya” and DBGY-201 × “Arka Harit” were promising for higher yield. 相似文献
78.
Light is the most common limiting factor in forest plant communities,influencing species composition,stand structure,and stand productivity in closed canopy stands.Stand vertical light structure is relatively simple under a closed canopy because most light is captured by overstory trees.However,wind disturbance events create canopy openings from local to landscape scales that increase understory light intensity and vertical light structural complexity.We studied the effects of an EF-1 tornado on horizontal and vertical(i.e.three-dimensional)light structure within a Quercus stand to determine how light structure changed with increasing disturbance severity.We used a two-tiered method to collect photosynthetic photon flux density at 4.67 m and 1.37 m above the forest floor to construct three-dimensional light structure across a canopy disturbance severity gradient to see if light intensity varied with increasing tornado damage.Results indicate that increased canopy disturbance closer to the tornado track increased light penetration and light structure heterogeneity at lower forest strata.Increased light intensity correlated with increased sapling density that was more randomly distributed across the plot and had shifted light capture higher in the stand structure.Light penetration through the overstory was most strongly correlated with decreased stem density in the two most important tree species(based on relative dominance and relative density)in the stand,Quercus alba L.(r=-0.31)and Ostrya virginiana(Mill.)K.Koch(r=-0.27,p<.01),and indicated that understory light penetration was most affected by these two species.As managers are increasingly interested in patterning silvicultural entries on natural disturbances,they must understand residual stand and light structures that occur after natural disturbance events.By providing spatial light data that quantifies light structure post-disturbance,managers can use these results to improve planning required for long-term management.The study also provides comparisons with anthropogenic disturbances to the midstory that may offer useful comparisons to natural analogs for future silvicultural consideration. 相似文献
79.
S. Piumsombun M. A. Rab M. M. Dey N. Srichantuk 《Aquaculture Economics & Management (Blackwell Science)》2013,17(1-2):265-287
ABSTRACT The paper reviews freshwater and coastal aquaculture practices in Thailand, and compares the productivity, costs, and benefits across various types of cultivation and various intensities of production. The paper is based on data that were collected in surveys conducted during 1998–2001 by the Department of Fisheries (DOF), Thailand and the WorldFish Center. More than 22% of Thailand's fish supply comes from aquaculture, with coastal aquaculture accounting for more than 88% of this in terms of value. Intensive culture of shrimp is the dominant form of coastal aquaculture, occupying 69% of the area under production. However, in some regions, the average net profit/kg of intensive shrimp culture is negative, and semi-intensive farming, with relatively lower fixed investment and operating costs, delivers the highest rate of return on investment. On the coast, grouper and sea bass are the most important cage-cultivated species, achieving an economic rate of return as high as 92%. In the same environment, culture of mollusks, such as green mussels, oysters, and blood cockles, is widespread. It can also be economically sustainable, with relatively low capital and operating costs. Although the relative share of freshwater aquaculture production is declining, the level of output has been increasing rapidly. While the average production from monoculture of carnivorous species is higher than that from polyculture, the average capital investment and operating costs associated with the former are also higher. The expansion of freshwater polyculture and of mollusk culture in coastal areas would greatly assist poor fish farmers. 相似文献
80.
Nutrient budget for shrimp (Penaeus monodon) culture was performed in ten culture ponds (0.4–1.0 ha) in Orissa, India, at stocking density of 10.0–22.10/m2. The average initial body weight of shrimps was 0.02 g. The culture period was for 4 months. Feed was the main input of nitrogen (N), phosphorus (P) and organic carbon (OC). The FCR varied from 1.35 to 1.75. At harvest time, the average weight of shrimps varied from 28 to 32 g. Total N, P and OC applied to these ponds through all the inputs ranged from 106.64 to 292.63, 23.17 to 57.55 kg and 763.10 to 1,831.20 kg per crop, respectively. Feed alone accounted for 94.43–95.03 % total N, 91.92–95.36 % total P and 80.33–92.48 % total OC, respectively. The harvest of shrimp accounted for recovery of 25.45–36.88 (av. 30.12) %, 10.07–12.94 (av. 11.16) % and 15.80–20.81 (av. 18.01) % of added N, P and OC, respectively. N, P and OC accumulated in sediment were 49.11, 64.07 and 64.82 %, respectively, of total nutrient retention in the culture system. Unaccounted N, P and OC were 13.29, 21.83 and 18.14 %, respectively, of the total nutrient retention in the system. N, P and OC outputs in the discharged water during harvest were 7.48, 2.94 and 2.03 %, respectively. 相似文献