Wyniki wyszukiwania - Biblioteka Nauki

1

3D fracture mechanics investigation on surface fatigue crack propagation

100%

Shen H. , Guo W. , Lu G.

|

tom Vol. 14, no 4

1127-1138

EN

Surface fatigue crack propagation is the typical failure mode of engineering structures. In this study the experiment on surface fatigue crack propagation in 15 MnVN steel plate is carried out and the crack-shape and propagation life are obtained. With the concept of "equivalent thickness" brought into the latest 3D (three dimensional) fracture mechanics theory, one closure model applicable to 3D fatigue crack is put forward. By using the above 3D crack-closure model, the shape and propagation life of surface fatigue crack in 15 MnVN plates are predicted. The simulative results show that the 3D fracture mechanics based closure model for 3D fatigue crack is effective.

2

Increased nitrogen deposition alleviated the adverse effects of drought stress on Quercus variabilis and Quercus mongolica seedlings

88%

Xu N. , Guo W. , Liu J. , Du N. , Wang R.

|

tom 37

|

nr 06

EN

The plasticity response of Quercus variabilis and Quercus mongolica seedlings to combined nitrogen (N) deposition and drought stress was evaluated, and their performance in natural niche overlaps was predicted. Seedlings in a greenhouse were exposed to four N deposition levels (0, 4, 8, and 20 g N m-2 year-1) and two water levels (80 and 50 % field-water capacity). Plant traits associated with growth, biomass production, leaf physiology, and morphology were determined. Results showed that drought stress inhibited seedling performance, altered leaf morphology, and decreased fluorescence parameters in both species. By contrast increased N supply had beneficial effects on the nutritional status and activity of the PSII complex. The two species showed similar responses to drought stress. Contrary to the effects in Q. mongolica, N deposition promoted leaf N concentration, PSII activity, leaf chlorophyll contents, and final growth of Q. variabilis under well-watered conditions. Thus, Q. variabilis was more sensitive to N deposition than Q. mongolica. However, excessive N supply (20 g N m-2 year-1) did not exert any positive effects on the two species. Among the observed plasticity of the plant traits, plant growth was the most plastic, and leaf morphology was the least plastic. Therefore, drought stress played a primary role at the whole-plant level, but N supply significantly alleviated the adverse effects of drought stress on plant physiology. A critical N deposition load around 20 g N m-2 year-1 may exist for oak seedlings, which may more adversely affect Q. variabilis than Q. mongolica.

3

A Novel RNA Genetic Algorithm for the Parameter Estimation of the Ordinary Differential Equations with Multiple Solutions

75%

Si X. Y. , Fang G. H. , Yang F. , Guo W. , Wang T. , Si X. H.

|

tom R. 88, nr 9b

118-120

EN

In fluid mechanics, to obtain the multiple solutions in ordinary differential equations is always a concerned and difficult problem. In this paper, a novel RNA genetic algorithm (NRNA-GA) inspired by RNA molecular structure and operators is proposed to solve the parameter estimation problems of the multiple solutions in fluid mechanics. This algorithm has improved greatly in precision and the success rate. Multiple solutions can be found through changing accuracy and search coverage and multi-iterations of computer. At last, parameter estimation of the ordinary differential equations with multiple solutions is calculated. We found that the result has great accuracy and this method is practical.

PL

W artykule zaproponowano nowy algorytm genetyczny NRNA-GA inspirowany strukturą molekularną RNA przeznaczony do rozwiązywania równań z wieloma rozwiązaniami w mechanice cieczy.

4

The Response of Wetland Plant Communities to Disturbance : Alleviation through Symmetric Disturbance and Facilitation

75%

Xu F. , Li M. , Zhou D. , Liu X. , Wang R. , Guo W.

|

tom Vol. 64, nr 3

327--338

EN

The study pays attention to disturbances in early successional communities of wetland vegetation. We conducted artificial disturbances in a community of Suaeda salsa and Phragmites australis in the Yellow River Delta (China). Eight types of disturbances combining mowing treatments with species treatments were applied. Removal of the standing litters of P. australis or not was defined as mowing treatments, and removal of two species solo or both was defined as species treatments. We sampled 80 quadrats from the treatments plots at different intervals after the disturbance to investigate plant height, abundance, aboveground biomass, the distance between plants to reflect the effect of disturbance on composition, structure, productivity, and function of the plant communities. The strategies of seedling emergence and height growth differed as the canopy changed. Biomass contribution of different species, combined with disturbance intensity, was the main factors that affected the productivity. Homogeneity of disturbance was better for maintaining the functions of plant community in compared with the competitiveness (C), stress-tolerance (S) and ruderality (C-S-R) signatures with the control. Facilitations were reflected by the stagger arrangements in relative growth rates of the two species and in plant-plant interactions calculated by a modified function of competition. Adapting to symmetric disturbance and developing facilitative interactions are important requirements for early succession terrestrial vegetation to establish and stabilize in the seriously saline environments of wetlands.

5

Effects of nitrogen addition on growth and photosynthetic characteristics of Acer truncatum seedlings

63%

Guo X. , Wang R. , Chang R. , Liang X. , Wang C. , Luo Y. , Yuan Y. , Guo W.

|

tom 72

EN

Increasing levels of atmospheric nitrogen deposition have greatly affected forest trees. Acer truncatum Bunge has a large distribution in northern China, Korea and Japan and plays an important ecological role in forest ecosystems. We investigated the responses of A. truncatum to a broad range of nitrogen addition regimes with a focus on seedling growth, biomass partitioning, leaf morphology, gas exchange physiology and chlorophyll fluorescence physiology. Moderate nitrogen addition promoted shoot height, stem diameter at ground height, total biomass, size of leaves and chlorophyll fluorescence and gas exchange performance, whereas extreme level of nitrogen addition did not result in such facilitation. Chlorophyll content, pattern of biomass partitioning, ratio of leaf length to width, leaf water content, and specific leaf area did not change among the addition regimes. The critical amount of nitrogen deposition should be defined in the context of a certain time period in a particular region for a certain species at a special developmental stage. The critical amount of N deposition that weakens total biomass facilitation in A. truncatum planted in mixed soil of yellow cinnamon soil and humic soil is approximately 10 g N m−2 y−1 during the first growing season.

6

Effect of Stubble Heights and Treatment Duration Time on the Performance of Water Dropwort Floating Treatment Wetlands (FTWS)

63%

Xin Z. , Li X. , Nielsen S. , Yan Z. , Zhou Y. , Tang Y. , Guo W. , Sun Y.

|

tom Vol. 19, nr 3

315-330

EN

Floating treatment wetlands (FTWs) with Water Dropwort (Oenanthe javanica) were established in winter to investigate their potential role in the purification of eutrophicated water, and to identify the effects of different stubble heights of the Water Dropwort on the performance of the FTWs. The results of the experiments demonstrated: The Water Dropwort FTWs were effective in buffering the pH of the experimental water. The Water Dropwort FTWs were efficient in purifying eutrophicated water, with removal rate for total nitrogen (TN), total phosphorus (TP), ammonium nitrogen ( NH N 4 + - ), and nitrate nitrogen ( NO N 3 - - ) at 91.3, 58.0, 94.6, and 95.5% in the 15-day experiment, respectively. No significant difference in the purification effect was found among different stubble heights of Water Dropwort FTWs. Significant differences between the zero control and the FTWs were found for the removal of TP in the first 11 days; and for the removal of NH N 4 + - in the first 4 days. No significant difference was found between the zero control and the FTWs for NO N 3 - - in the first 4 days, but significant difference was detected after day 4. The optimum treatment duration time for the FTWs with Water Dropwort will depend on the nutrients to be removed. These results will provide basis for further application of the FTWs at large scale, as well as for future studies on the mechanism of nutrient removal process.

PL

Badano proces oczyszczania wód z wykorzystaniem ruchomych mokradeł (FTW) obsadzonych Oenanthe javanica. Celem prowadzonych w zimie badań była ocena ich potencjalnej roli w oczyszczaniu wód zeutrofizowanych oraz określenie wpływu różnych wysokości ściernisk roślinnych na wydajność procesu. Wyniki eksperymentów wykazały, że systemy FTW skutecznie buforowały pH badanej wody. Za pomocą FTW ze zeutrofizowanej wody usunięto azot ogólny (TN), fosfor ogólny (TP), azot amonowy (NH N) 4 + - i azot azotanowy (NO N) 3 - - odpowiednio w ilościach: 91,3, 58,0, 94,6 i 95,5%, w czasie trwania 15-dniowego eksperymentu. Nie wykazano istotnych różnic w efekcie oczyszczania przy stosowaniu różnych wysokości ściernisk roślinnych. Stwierdzono wpływ czasu prowadzenia eksperymentu na usuwanie TP, którego usunięto najwięcej w pierwszych 11 dniach, a NH N 4 + - w ciągu pierwszych 4 dni trwania procesu. Nie stwierdzono istotnej różnicy między kontrolą i FTW dla NO N 3 - - w ciągu pierwszych kilku dni, ale znacząca różnica pojawiła się po 4 dniu. Optymalny czas trwania procesu z wykorzystaniem FTW zależy od składników odżywczych, które mają być usunięte. Opisane wyniki stanowią podstawę zarówno do rozwinięcia zastosowania FTW na dużą skalę, jak i dla przyszłych badań nad mechanizmem procesu usuwania składników odżywczych.