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Start Over Coverage 191-200

2. Comparison of cell centered and vertex centered formulation of finite volume method

Creator:
Dobeš, Jiří, Deconinck, Herman, and Fořt, Herman
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
finite volume method, transonic flow, linear reconstruction, limiter, parallel method, and implicit method
Language:
English
Description:
Finite volume methods for solving hyperbolic systems on unstructured meshes are known for a long time. There are two basic formulations of the method: cell centered and vertex centered. For the cell centered method, the (finite) volumes used to satisfy the integral form of the equation are the mesh elements itself. For the vertex centered approach, the finite volumes are elements of the mesh dual to the computational mesh. We present comparison of both formulations. The method is first evaluated on a scalar advection equation. Knowing the analytical solution of the problem, convergence studies are performed. More complex test cases involve the 3D transonic flow past an Олега M6 airfoil. Discussion includes influence of the reconstruction and limiters on the solution. The results of the parallel implementation for a Linux PC cluster both with explicit and implicit time integration method are presented. and Obsahuje seznam literatury
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

3. Effects of NaCl stress on the structure, pigment complex composition, and photosynthetic activity of mangrove Bruguiera parviflora chloroplasts

Creator:
Parida, A. K., Das, A. B., and Mittra, B.
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
electron transport, hydroponic plants, light-harvesting complexes, pigment-protein complexes, photosystems, polypeptides, salt stress, and thylakoids
Language:
Multiple languages
Description:
Exposure of two-month-old seedlings of Bruguiera parviflora to NaCl stress (0 to 400 mM) for 45 d under hydroponic culture caused notable disorganisation of the thylakoid structure of chloroplasts in NaCl-treated leaves as revealed from transmission electron microscopy. The absorption spectra of treated and control thylakoid samples were similar having a red peak at 680 nm and Soret peaks at 439 and 471 nm in the blue region of the spectrum. The spectra of treated samples differed from control samples by gradual decrease in absorbance of 100, 200, and 400 mM NaCl treated samples at 471 and 439 nm, which could be due to scattering of radiation in these samples. Thus, absorption characteristics of thylakoid membranes indicated no major alterations in the structural integrity of the photosynthetic membranes during salt stress in B. parviflora. Analysis of pigment protein complexes of thylakoids on non-denaturing gel showed that CP1 complex consisting of photosystem (PS) 1 reaction centre decreased marginally by 19% and the CP47 constituting the core antenna of PS2 declined significantly by 30% in 400 mM NaCl treated samples in respect to control. This decrease in structural core antenna might cause inefficient photon harvesting capacity. However, CP43 content did not alter. An increase in CP2/CP1 ratio from 3.2 in control to 4.0 in 400 mM NaCl treated samples indicated significant structural changes in the thylakoids of salt treated plants. Haem staining of thylakoids revealed significant losses in cytochrome (Cyt)f and Cyt b 6 contents by NaCl stress. However, Cyt b 559 content remained nearly constant in both control and NaCl treated samples. SDS-PAGE of thylakoid proteins showed that the intensity of many of Coomassie stained polypeptide bands ranging from 15-22 and 28-66 kDa regions decreased significantly in NaCl treated samples as compared to control. Electron transport activity of thylakoids, measured in terms of DCPIP photoreduction, was 22% lower in 400 mM NaCl treated plants than in the control ones. Hence, NaCl induces oxidative stress in chloroplasts causing structural alterations in thylakoids. These structural alterations might be responsible for declined efficiency of photosystems and reduced electron transport activity. and A. K. Parida, A. B. Das, B. Mittra.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

4. Qb site modification and the binding of photosystem 2 directed inhibitors during photoinhibition

Creator:
Giardi, M. T., Rigoni, F., and Barbato, R.
Format:
print
Type:
model:internalpart and TEXT
Language:
Multiple languages
Description:
Binding kinetics of some photosystem 2 (PS 2)-directed ínhibitors to isolated pea thylakoids during photoinUbition were studied. Changes in the herbicide binding activity were overshadowed by the redox statě of the plastoquinone (PQ) pool. After extraction of the PQ pool from the thylakoids, a correlation between the decline of herbicide binding activity and the electron transfer activity during strong irradiation was found in the presence of oxygen; in anaerobiosis this correlation was absent. The opposite was observed for the binding kinetics of the electron transfer acceptor 2,6-dichlorophenol indophenol, that was affected faster under anaerobic conditions. Following irradiation, a movement of damaged Dj-protein products from the appressed to the non-appressed regions of the membrane was observed. This observation was correlated to the fínding of an increased level of atrazine bound to the non-appressed regions of irradiated membranes.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

5. The differential effect of photoinhibition on the quantum yield of oxygen evolution and on the electron transport capacity studied with isolated spinach thylakoids

Creator:
Richter, M., Bóthin, B., and Wild, A.
Format:
print
Type:
model:internalpart and TEXT
Language:
Multiple languages
Description:
The light response changes of oxygen evolutíon in the isolated spinách (Spinacia oleracea L.) thylakoids associated with the photoinhibition, influenced by the temperature and radical protection, were determined. Photoinhibition was performed at 20 ®C with or without an addition of antioxidant mixture consisting of glutathione, ascorbate, superoxide dismutase and catalase, oř, altematívely, at 0 oC without the antioxidants. Beside the effects on decline of atrazine binding sites and variable room temperature fluorescence, the three variants of photoinhibition differed with respect to their effects on the yield of oxygen evolutíon. Quantum yield of oxygen evolutíon (<{>02) flecline preceded Úie decrease of electron transport capacity at the beginning, while similar low values were found at the end of the treatment. In the presence of antioxidants the electron transport capacity remained high, whereas marked decline of (|»o^ occurred with the equally treated thylakoids. Comparable deviating behaviour of (t»Oj and the electron transport capacity was not found following photoinhibition at 0 oC; both were affected to the same degree, regardless if ferricyanide or the Qg- independent electron acceptor siUcomolybdate were ušed. With isolated thylakoids the quotient FyF,„, which is often ušed as a measure for photochemical efficiency of open photosystem 2 reaction centres in whole plant studies, did not decline to the same extent as (|)Oj under the dififerent photoinhibitoiy conditions applied. The main conclusion is that in thylakoid photoinhibition the independent mechanisms are associated with the changes of both the and electron transport capacity, and that the (j>02-related mechanism is inhibited at 0 oC.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

6. Using Beerkan experiments to estimate hydraulic conductivity of a crusted loamy soil in a Mediterranean vineyard

Creator:
Alagna , Vincenzo, Bagarello , Vincenzo, Di Prima , Simone, Guaitoli , Fabio, Iovino, Massimo, Keesstra , Saskia, and Cerdà , Artemi
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
hydraulic conductivity, water infiltration measurements, soil surface crust, vineyard, and BEST procedure
Language:
Slovak
Description:
In bare soils of semi-arid areas, surface crusting is a rather common phenomenon due to the impact of raindrops. Water infiltration measurements under ponding conditions are becoming largely applied techniques for an approximate characterization of crusted soils. In this study, the impact of crusting on soil hydraulic conductivity was assessed in a Mediterranean vineyard (western Sicily, Italy) under conventional tillage. The BEST (Beerkan Estimation of Soil Transfer parameters) algorithm was applied to the infiltration data to obtain the hydraulic conductivity of crusted and uncrusted soils. Soil hydraulic conductivity was found to vary during the year and also spatially (i.e., rows vs. interrows) due to crusting, tillage and vegetation cover. A 55 mm rainfall event resulted in a decrease of the saturated soil hydraulic conductivity, Ks, by a factor of 1.6 in the inter-row areas, due to the formation of a crusted layer at the surface. The same rainfall event did not determine a Ks reduction in the row areas (i.e., Ks decreased by a non-significant factor of 1.05) because the vegetation cover intercepted the raindrops and therefore prevented alteration of the soil surface. The developed ring insertion methodology on crusted soil, implying pre-moistening through the periphery of the sampled surface, together with the very small insertion depth of the ring (0.01 m), prevented visible fractures. Consequently, Beerkan tests carried out along and between the vine-rows and data analysis by the BEST algorithm allowed to assess crusting-dependent reductions in hydraulic conductivity with extemporaneous measurements alone. The reliability of the tested technique was also confirmed by the results of the numerical simulation of the infiltration process in a crusted soil. Testing the Beerkan infiltration run in other crusted soils and establishing comparisons with other experimental methodologies appear advisable to increase confidence on the reliability of the method that seems suitable for simple characterization of crusted soils.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public