Theoretical studies of the energetics and dynamics of chemical reactions     

Dunning TH  Harding LB  Wagner AF  Schatz GC  Bowman JM 《Science (New York, N.Y.)》1988,240(4851):453-459

Computational studies of basic chemical processes not only provide numbers for comparison with experiment or for use in modeling complex chemical phenomena such as combustion, but also provide insight into the fundamental factors that govern molecular structure and change which cannot be obtained from experiment alone. We summarize the results of three case studies, on HCO, OH + H(2), and O + C(2)H(2), which illustrate the range of problems that can be addressed by using modern theoretical techniques. In all cases, the potential energy surfaces were characterized by using ab initio electronic structure methods. Collisions between molecules leading to reaction or energy transer were described with quantum dynamical methods (HCO), classical trajectory techniques (HCO and OH + H(2)), and statistical methods (HCO, OH + H(2), and O + C(2)H(2)). We can anticipate dramatic increases in the scope of this work as new generations of computers are introduced and as new chemistry software is developed to exploit these computers.  相似文献   

Haematologic parameters in goats     

Eiselt N  Wagner H  Wehrend A 《Tier?rztliche Praxis. Ausgabe G, Grosstiere/Nutztiere》2011,39(1):49-55

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Respiratory function and pulmonary lesions in pigs infected with porcine reproductive and respiratory syndrome virus   总被引：1，自引：0，他引：1  

Judith Wagner  Annette Kneucker  Elisabeth Liebler-Tenorio  Vicky Fachinger  Melanie Glaser  Stefan Pesch  Michael P. Murtaugh  Petra Reinhold   《Veterinary journal (London, England : 1997)》2011,187(3):310-319

Pulmonary dysfunction was evaluated in pigs infected with porcine reproductive and respiratory syndrome virus (PRRSV, isolate VR-2332) and compared to clinical and pathological findings. Infected pigs developed fever, reduced appetite, respiratory distress and dullness at 9 days post-inoculation (dpi). Non-invasive pulmonary function tests using impulse oscillometry and rebreathing of test gases (He, CO) revealed peripheral airway obstruction, reduced lung compliance and reduced lung CO-transfer factor. PRRSV-induced pulmonary dysfunction was most marked at 9–18 dpi and was accompanied by a significantly increased respiratory rate and decreased tidal volume. Expiration was affected more than inspiration. On histopathological examination, multifocal areas of interstitial pneumonia (more severe and extensive at 10 dpi than 21 dpi) were identified as a possible structural basis for reduced lung compliance and gas exchange disturbances.  相似文献   

Salt‐resistant and salt‐sensitive wheat genotypes show similar biochemical reaction at protein level in the first phase of salt stress     

Muhammad Saqib  Christian Zrb  Sven Schubert 《植物养料与土壤学杂志》2006,169(4):542-548

Salinity has a two‐phase effect on plant growth, an osmotic effect due to salts in the outside solution and ion toxicity in a second phase due to salt build‐up in transpiring leaves. To elucidate salt‐resistance mechanisms in the first phase of salt stress, we studied the biochemical reaction of salt‐resistant and salt‐sensitive wheat (Triticum aestivum L.) genotypes at protein level after 10 d exposure to 125 mM–NaCl salinity (first phase of salt stress) and the variation of salt resistance among the genotypes after 30 d exposure to 125 mM–NaCl salinity (second phase of salt stress) in solution culture experiments in a growth chamber. The three genotypes differed significantly in absolute and relative shoot and root dry weights after 30 d exposure to NaCl salinity. SARC‐1 produced the maximum and 7‐Cerros the minimum shoot dry weights under salinity relative to control. A highly significant negative correlation (r² = –0.99) was observed between salt resistance (% shoot dry weight under salinity relative to control) and shoot Na⁺ concentration of the wheat genotypes studied. However, the salt‐resistant and salt‐sensitive genotypes showed a similar biochemical reaction at the level of proteins after 10 d exposure to 125 mM NaCl. In both genotypes, the expression of more than 50% proteins was changed, but the difference between the genotypes in various categories of protein change (up‐regulated, down‐regulated, disappeared, and new‐appeared) was only 1%–8%. It is concluded that the initial biochemical reaction to salinity at protein level in wheat is an unspecific response and not a specific adaptation to salinity.  相似文献   

Proton release by N2‐fixing plant roots: A possible contribution to phytoremediation of calcareous sodic soils     

Manzoor Qadir  Diedrich Steffens  Feng Yan  Sven Schubert 《植物养料与土壤学杂志》2003,166(1):14-22

With a world‐wide occurrence on about 560 million hectares, sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect crop growth and yield. Amelioration of such soils needs a source of calcium (Ca²⁺) to replace excess Na⁺ from the cation exchange sites. In addition, adequate levels of Ca²⁺ in ameliorated soils play a vital role in improving the structural and functional integrity of plant cell walls and membranes. As a low‐cost and environmentally feasible strategy, phytoremediation of sodic soils — a plant‐based amelioration — has gained increasing interest among scientists and farmers in recent years. Enhanced CO₂ partial pressure (P_CO2) in the root zone is considered as the principal mechanism contributing to phytoremediation of sodic soils. Aqueous CO₂ produces protons (H⁺) and bicarbonate (HCO₃^‐). In a subsequent reaction, H⁺ reacts with native soil calcite (CaCO₃) to provide Ca²⁺ for Na⁺ Ca²⁺ exchange at the cation exchange sites. Another source of H⁺ may occur in such soils if cropped with N₂‐fixing plant species because plants capable of fixing N₂ release H⁺ in the root zone. In a lysimeter experiment on a calcareous sodic soil (pH_s = 7.4, electrical conductivity of soil saturated paste extract (EC_e) = 3.1 dS m^‐1, sodium adsorption ratio (SAR) = 28.4, exchangeable sodium percentage (ESP) = 27.6, CaCO₃ = 50 g kg^‐1), we investigated the phytoremediation ability of alfalfa (Medicago sativa L.). There were two cropped treatments: Alfalfa relying on N₂ fixation and alfalfa receiving NH₄NO₃ as mineral N source, respectively. Other treatments were non‐cropped, including a control (without an amendment or crop), and soil application of gypsum or sulfuric acid. After two months of cropping, all lysimeters were leached by maintaining a water content at 130% waterholding capacity of the soil after every 24±1 h. The treatment efficiency for Na⁺ removal in drainage water was in the order: sulfuric acid > gypsum = N₂‐fixing alfalfa > NH4NO3‐fed alfalfa > control. Both the alfalfa treatments produced statistically similar root and shoot biomass. We attribute better Na+ removal by the N₂‐fixing alfalfa treatment to an additional source of H⁺ in the rhizosphere, which helped to dissolve additional CaCO₃ and soil sodicity amelioration.  相似文献   

Persistence of Gunnison’s prairie dog colonies in Arizona, USA     

David M. Wagner  Lee C. Drickamer  Christopher J. Allender  Paul Keim 《Biological conservation》2006,130(3):331-339

Although the five species of prairie dogs (Cynomys spp.) are recognized as important components of grassland ecosystems in western North America, they have experienced major population declines due to poisoning, outbreaks of sylvatic plague, recreational shooting, and habitat conversion. From May 2000 to October 2001, we investigated 270 colonies of Gunnison’s prairie dog (Cynomys gunnisoni) in Arizona. Because these colonies were classified as active in previous surveys (1987, 1990-1994, 1998), we were able to examine their persistence. Most (70%) of the colonies became inactive between the initial and recent surveys, with colony extinctions spanning our study area. Colony persistence was positively associated with the persistence of the nearest neighboring colony but was not associated with major vegetation type, distance to nearest neighboring colony, or initial size of the colony. The amount of area occupied by individual colonies varied between surveys, sometimes dramatically. We found little evidence that the reduction in active colonies was due to poisoning, recreational shooting, or habitat conversion. Rather, direct and indirect evidence suggest plague is the primary factor negatively impacting Gunnison’s prairie dog populations in Arizona. Currently, there is no way to control or prevent plague outbreaks in Gunnison’s prairie dog populations. To mitigate the effects of localized plague outbreaks on the overall population of this species, we suggest that Gunnison’s prairie dog be reintroduced to public lands throughout its historical range.  相似文献   

Mixing of different mineral soil layers by endogeic earthworms affects carbon and nitrogen mineralization   总被引：1，自引：0，他引：1  

Sven Marhan  Stefan Scheu 《Biology and Fertility of Soils》2006,42(4):308-314

The effect of the endogeic earthworm species Octolasion tyrtaeum (Savigny) on decomposition of uniformly ¹⁴C-labelled lignin (lignocellulose) was studied in microcosms with upper mineral soil (Ah-horizon) from two forests on limestone, representing different stages of succession, a beech- and an ash-tree-dominated forest. Microcosms with and without lower mineral soil (Bw-horizon) were set-up; one O. tyrtaeum was added to half of them. It was hypothesised that endogeic earthworms stabilise lignin and the organic matter of the upper mineral soil by mixing with lower mineral soil of low C content. Cumulative C mineralization was increased by earthworms and by the addition of lower mineral soil. Effects of the lower mineral soil were more pronounced in the beech than in the ash forest. Cumulative mineralization of lignin was strongly increased by earthworms, but only in the beech soil (+24.6%). Earthworms predominantly colonized the upper mineral soil; mixing of the upper and lower mineral soils was low. The presence of lower mineral soil did not reduce the rates of decomposition of organic matter and lignin; however, the earthworm-mediated increase in mineralization was less pronounced in treatments with (+8.6%) than in those without (+14.1%) lower mineral soil. These results indicate that the mixing of organic matter with C-unsaturated lower mineral soil by endogeic earthworms reduced microbial decomposition of organic matter in earthworm casts.  相似文献   

Surface functional properties of native, acid-treated, and reduced soy glycinin. 2. Emulsifying properties   总被引：8，自引：0，他引：8  

Wagner JR  Guéguen J 《Journal of agricultural and food chemistry》1999,47(6):2181-2187

Emulsifying properties of native and chemically modified soy glycinins were studied. The influence of ionic strength, protein sample composition and concentration, and assay conditions on the flocculation-creaming process and coalescence resistance was analyzed. Differences in these emulsifying properties were exhibited by native glycinins, which have a variable content of 4S, 11S, and 15S forms. Structure and functionality of native glycinin were modified by means of combined treatments: mild acidic treatments without heating or with heating at variable time and with or without disulfide bonds reduction. Modified glycinins presented different degrees of deamidation, surface hydrophobicity, and molecular mass. A slight enhancement of emulsifying stability at moderated deamidation degrees was observed. In different protein samples, a positive relationship between the flocculation-creaming rate constant and equilibrium oil volume fraction of emulsions with surface hydrophobicity was detected. A remarkable difference was observed between reduced and nonreduced samples, mainly with respect to behavior at low or high ionic strength.  相似文献   

Nitrate and ammonium nutrition of plants: Effects on acid/base balance and adaptation of root cell plasmalemma H+ ATPase     

Sven Schubert  Feng Yan 《植物养料与土壤学杂志》1997,160(2):275-281

The increase of rhizosphere pH in the course of nitrate nutrition results from H⁺ consumption in the external medium during uptake of NO₃^? in a H⁺ co-transport and from internal OH^? production during nitrate reduction. Synthesis of organic acids for NH₄⁺ assimilation as well as strong partial depolarization of membrane potential with NH₄⁺ uptake are the important reasons for rhizosphere acidification during ammonium nutrition. Despite differences in proton balance depending on N form, cytoplasmic pH changes are small due to physico-chemical buffering, biochemical pH regulation, H⁺ inclusion in vacuoles, and H⁺ release into the rhizosphere. Because of the large capacity for proton excretion the plasmalemma H⁺ ATPase of root cells plays an essential role during ammonium nutrition. An increase of the kinetic parameter V_max after ammonium nutrition relative to nitrate nutrition suggests that the capacity of H⁺ release may be adjusted to the particular requirements of ammonium nutrition. Moreover, H⁺ ATPase is adjusted not only quantitatively but also qualitatively. The increase of the kinetic parameter k_m as well as the capability of the plasmalemma vesicles in vitro to establish a steeper pH gradient favours the supposition that H⁺ ATPase isoforms are formed which allow H⁺ release into the rhizosphere under conditions of low pH or poor H⁺ buffering of the soil. In this respect species differences exist, e.g. between maize (efficient adaptation) and faba bean (poor adaptation).  相似文献   

Centimeter-scale variability in the chemistry of convective rains     

George H. Wagner  Kenneth F. Steele 《Water, air, and soil pollution》1994,72(1-4):9-18

A standard National Atmospheric Deposition Program (NADP) rain collection bucket was sectioned with 220 test tubes of 1.5 cm diameter. Eleven rains from thunderstorms were collected. Analyses were made for Ca, Na and K concentrations in the test tube liquids. The relative standard deviation (RSD), after correction for the analytical RSD, was 0 to 15% for Ca, 0 to 24% for Na, and 0 to 17% for K. Analytical RSD for Ca, Na and K determined from standards were, respectively, 5.4, 6.6 and 12%. Calculations indicate that the difference of 2 to 3 giant nuclei per test tube of calcite (Ca), sea salt (Na) and clay (K) would account for these different RSDs. Concentration ranges in the rains varied from 0.14 to 2.95 mg L^?1 for Ca, 0.024 to 0.23 mg L^?1 for Na, and 0.014 to 0.064 mg L^?1 for K. The area between the test tubes which was 40% of the total collector area provided a bottom sample which on average agreed within 1.3% of the average value of the test tubes.  相似文献