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31.
Effects of allelochemicals on plant respiration and oxygen isotope fractionation by the alternative oxidase 总被引:8,自引:1,他引:8
The goal of this investigation was to determine the effects of allelochemicals on plant respiration that thereby may be responsible for their role in growth inhibition. We have tested the effects of juglone, quercetin, cinnamic acid, and-pinene on respiration rates, and electron partitioning through the cytochrome and alternative respiratory pathways, by measuring on-line oxygen consumption and oxygen isotope fractionation in soybean cotyledon tissue. Cinnamic acid and-pinene decreased the oxygen consumption rate and increased the relative partitioning of electron transport to the alternative pathway. Possible biochemical mechanisms of these effects are discussed. 相似文献
32.
E. Rivera-Muñoz D. Lardizabal G. Alonso A. Aguilar M.H. Siadati R.R. Chianelli 《Catalysis Letters》2003,85(3-4):147-151
MCM-41- and silica gel-supported MoS2 catalysts were prepared. MCM-41 was synthesized and impregnated with precursor, then activated to obtain the active phase. The sol–gel method was used for providing the SiO2 support as well as for including the catalyst precursors in one single step of preparation. Such catalysts have applications particularly in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) processes. A comparison of the activities of the catalysts was made. The catalytic activity results showed the method of preparation used in this study was successful in producing very efficient catalysts for the HDS of dibenzothiophene (DBT).A higher selectivity for direct C–S bond cleavage was observed for the MoS2 catalyst supported on SiO2 by the sol–gel method. X-ray diffraction studies showed that the catalysts were poorly crystallized with a very weak intensity of the (002) line of 2H-MoS2. 相似文献
33.
Molecular dynamics (MD) simulations of-Al2O3, using a pairwise additive interaction potential of Pauling's type with four different radii for aluminum atoms, were analysed in order to determine the influence of the radius on the modification of coordination numbers of A1 relative to the ideal structure, at two different temperatures of 300 and 1500 K. It is found that the best choice is the radius of penta-coordinated aluminum, reproducing structural and vibrational properties of the compound in excellent agreement with experimentally observed properties. 相似文献
34.
J. A. Segura M. L. Herrera M. C. Añón 《Journal of the American Oil Chemists' Society》1995,72(3):375-378
Time-dependent flow properties of both commercial and pilot plant-made margarines were characterized under steady shear. Flow
curves were fitted to the kinetic expression τ = τ
i
+a e
−k1t
+b e
−k2t
. A first-order kinetic model did not describe the observed destruction process of the margarine structure in an adequate
manner. In the proposed model, two structures with different destruction rates are postulated. Each structure contributes
to a part of the shear stress necessary to deform the margarine sample. The parameters τ
i
a andb are temperature-dependent. Decreasing temperatures produce an exponential increase of τ
i
, a linear increase ofb and an increase ofa up to a point beyond which it remains constant. A physical interpretation of the model is proposed. The role of the aqueous
phase was also studied. Greater hardness was detected at higher water content. Parameter τ
i
increased, at any selected temperature, with increasing aqueous phase content of the sample. Parametera increased with decreasing temperatures and higher water content. On the other hand, parameterb was not affected by the amount of aqueous phase. This kinetic model could be employed to perform studies on the influence
of different parameters of margarine formulation on its rheologic behavior. 相似文献
35.
Emilio Soto Candela Mario Ortega Pérez Clemente Marín Romero David C. Pérez López Gustavo Salvador Herranz Manuel Contero Mariano Alcañiz Raya 《Multimedia Tools and Applications》2014,70(3):1837-1868
In this paper, a computer vision based interactive multi-touch tabletop system called HumanTop is introduced. HumanTop implements a stereo camera vision subsystem which allows not only an accurate fingertip tracking algorithm but also a precise touch-over-the-working surface detection method. Based on a pair of visible spectra cameras, a novel synchronization circuit makes the camera caption and the image projection independent from each other, providing the minimum basis for the development of computer vision analysis based on visible spectrum cameras without any interference coming from the projector. The assembly of both cameras and the synchronization circuit is not only capable of performing an ad-hoc version of a depth camera, but it also introduces the recognition and tracking of textured planar objects, even when contents are projected over them. On the other hand HumanTop supports the tracking of sheets of paper and ID-code markers. This set of features makes the HumanTop a comprehensive, intuitive and versatile augmented tabletop that provides multitouch interaction with projective augmented reality on any flat surface. As an example to exploit all the capabilities of HumanTop, an educational application has been developed using an augmented book as a launcher to different didactic contents. A pilot study in which 28 fifth graders participated is presented. Results about efficiency, usability/satisfaction and motivation are provided. These results suggest that HumanTop is an interesting platform for the development of educational contents. 相似文献
36.
Isidoro Izquierdo Cubero Maria T. Plaza López-Espinosa Rafael Acuña Castillo 《Journal of chemical ecology》1991,17(8):1529-1541
The synthesis of the title compound13 has been carried out through the preparation of its precursor, (3R,4R,5S,6R)-3,4,5-trihydroxy-1,7-dioxaspiro[5.5]undecane (6), obtained fromd-fructose using Wittig's methodology, reduction, and spiroketalation. Compound6 was transformed into13 by a Barton deoxygenation at C-5 followed by a Corey dideoxygenation at C-3,4 of the appropriately protected derivatives.Enantiospecific synthesis of spiroacetals. Part II. For Part I, see Izquierdo and Plaza (1990). 相似文献
37.
The indigo method developed by Bader and Hoigné for aqueous ozone analysis was modified to allow for both gaseous and aqueous ozone determination. Gas or water samples were extracted with a gas-tight syringe containing a known volume of indigo reagent. The modified procedure provided a more consistent basis for gaseous and aqueous ozone determination allowing for more accurate ozone mass balance calculations. Direct gaseous ozone UV absorbance with molar absorptivity of 3,000 M?1cm?1 at 258 nm was used as primary standard to determine the molar absorptivity of the indigo reagent. The molar absorptivity of indigo reagent, assuming a 1:1 stoichiometric ratio for the reaction between indigo and ozone, was determined to be 23,150 ± 80 M?1cm?1, or approximately 16 percent higher than that of 20,000 M?1cm?1 suggested by Bader and Hoigné. An independently calibrated membrane-electrode ozone monitor showed good correlation with indigo method results using the molar absorptivity value determined in this study. The apparent molar absorptivity of aqueous ozone at the wavelength of 258 nm measured by the modified indigo method increased from 2,400 to 3,600 M?1cm?1 in the investigated ozone concentration range of 0.4 to 11.0 mg/L. This variation might have been caused by the inherent interference of unidentified ozone byproducts, which presence was supported with scanning spectra in the wavelength range of 200 to 300 nm. 相似文献
38.
The present work investigates the relationships between the microstructural state and fracture properties in commercial polypropylene‐based materials. In this case an isopolypropylene homopolymer and three ethylene propylene block copolymers (EPBC) with different ethylene content (EC) have been studied. A variety of morphologies were obtained by a combination of several processing methods (injection molding, injection molding‐annealing, and compression molding) and thickness. Fracture behavior of deeply double‐edged notched specimens was evaluated by scanning electron microscopy (SEM) and by the essential work of fracture (EWF) method, analyzing the influence of processing, thickness (t), EC, and orientation respect to melt flow direction (MD and TD). The testing direction and EC are the most relevant variables that affect the ability of the crack tip to deform plastically during the crack propagation, determining the final fracture behavior. The fracture parameters obtained with the EWF method, specific EWF, we, and plastic item, βwp, have proved to be very sensitive to the processing induced morphology, finding interesting relationships between such morphologies (characterized by crystallinity index, orientation level, and skin/core ratio) and the fracture parameters of the plaques. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2714–2724, 2006 相似文献
39.
This retrospective analysis was conducted between May 1997 and May 2000 at the Centro de Atención Nutricional Infantil de Antímano, CANIA, in Caracas, Venezuela to assess the efficacy of two treatments (ambulatory versus day-care) of mild and moderate malnourished children. Inclusion criteria were: children under 10 years old with mild and moderate malnourishment, who attended a minimum of 3 control visits during a period of 12 months. One hundred fourteen malnourished children were included: fifty seven in ambulatory treatment and fifty seven in day-care treatment paired per nutritional diagnosis, gender and age (thirty nine mild and eighteen moderate malnourished children). The nutritional recovery criterion was weight for height above tenth percentile. No relation was found between treatment approaches and nutritional recovery at 3 and 6 months of treatment. In the group of mild malnourished children, the percentage of recovered patients at 3 months of treatment, that kept their recovered condition at 6 months was 83% (15/18) in the ambulatory treatment and 82% (18/22) in the day-care treatment Age of children, associated disease, acute morbidity, dietetic risk and mother's education and age were not associated with nutritional recovery at 6 months of treatment (p > 0.05). The day-care approach resulted as effective as ambulatory in mild malnourished children. In moderate malnourished new studies will need to be conducted with greater number of patients. 相似文献
40.
Henri Berthiaux Antonio Guttierrez Lavin Julio Bueno De Las Heras Marisol Muñiz Alvarez 《加拿大化工杂志》2007,85(2):158-170
Despite of its general use in industry, particle sedimentation is still a not well understood unit operation. Hydrodynamics is complex in essence, mainly because the possible volumes are depending on the operating conditions, which in turn has consequences on the stability of the equipment in unsteady state conditions. 相似文献