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81.
The reversal of humic matter-induced inhibition of callus growth and metabolism by 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in Pinus laricio. Two forest humic fractions (relative molecular mass (Mr) > 3500), derived from soil under Fagus sylvatica (Fs) and Abies alba (Aa) plantation, were used. Pinus laricio callus was grown for a subculture period (4 weeks) on Basal Murashige and Skoog (MS) medium plus forest humic matters (Fs or Aa), at a concentration of 1 mg C/l, and then was transferred, for an additional four weeks, to a MS medium culture without humic matter, but with different hormones: indole-3-acetic acid (IAA, 2 mg/1) or 2,4-dichlorophenoxyacetic acid (2,4-D, 0.5 mg/1) and/or 6-benzylaminopurine (BAP, 0.25 mg/1). Growth of calluse, glucose, fructose, and sucrose contents, and activities of soluble and bound invertases, glucokinase, phosphoglucose isomerase, aldolase, and pyruvate kinase were monitored. The results show a negative effect of humic fractions on callus growth, due to decreased utilization of glucose and fructose, and decreased activities of glycolytic enzymes. The effects are reversible. Substitution of humic fractions with 2,4-D+BAP or 2,4-D is followed by an increase of glycolytic enzyme activities and, consequently, by the utilization of glucose and fructose that induces a restart of growth. In contrast, the inhibitory effects of humic fractions persist when they are substituted with BAP alone, indicating that only the auxin 2,4-D is capable of reversing the negative effects. A possible competitive action on the auxin-binding site between 2,4-D and the chemical structures in the forest humic fractions is suggested. 相似文献
82.
We prove the existence of a P-type (proportional-type) space-learning control, which, on the basis of a kinematic third order nonlinear model of an autonomous nonholonomic vehicle and by a proper choice of the proportional control gain, guarantees asymptotic tracking of planar curves whose uncertain curvature is L-periodic in the curvilinear abscissa. The behavior of a human driver, who repetitively learns the correct action from the past experience in the space, is mathematically reproduced. A stability analysis is presented while simulation results demonstrate the effectiveness of the presented approach. 相似文献
83.
Crosslinked copolymers of acrylamide (AA) and ethylacrylate and some ion exchangers derived from them containing either primary amine groups, obtained by the Hofmann degradation of the amide groups, or carboxylic groups, obtained by the alkaline hydrolysis of the ester groups, were studied. Divinylbenzene and N,N′‐methylenebisacrylamide were used as crosslinkers. The starting copolymers and the corresponding ion exchangers were characterized by IR spectroscopy, swelling behavior, and thermogravimetric analysis. The ion‐exchanger properties were correlated with the crosslinker nature and the chemical reactions performed on the AA copolymers. The average molecular weight between two crosslinks, determined from the swelling data in water, was compared with that calculated on the basis of the copolymerization stoichiometry only for the carboxylic cation exchangers. In this way, the preservation of the crosslink density after the hydrolysis was revealed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2701–2707, 2003 相似文献
84.
C. Tuve' R. Potenza M. Chiorboli M.G. Grimaldi F. La Rosa F. Raimondo M. Marinelli E. Milani A. Tucciarone G. Verona Rinati M. Donato G. Faggio G. Messina S. Santangelo G. Pucella 《Diamond and Related Materials》2006,15(11-12):1986
Polycrystalline (pCVD) and single crystal (scCVD) diamond films grown from Chemical Vapour Deposition (CVD), if sufficiently pure at Raman analysis, are very good materials for beam or flux monitors inside accelerators or nuclear reactors. This is because they are very hard to damage in high radiation fields and very resistant to high temperatures. Films of pCVD diamond are, however, not so good as spectroscopy detectors due to inhomogeneities induced by their growth in grains with the consequent presence of grain boundaries which worsen their energy resolution. The latter can be significantly improved by growing scCVD diamond films onto HPHT synthetic diamond substrates. We have shown that it is possible to measure the density of defects inside diamond specimens using as probes suitable penetrating nuclear radiations. With the preliminary results reported here we'll show that, bombarding CVD diamond films grown at Roma “Tor Vergata” with energetic protons and 4He, 6Li and 12C ions produced in the accelerators of Catania laboratories, the pulse height defects are higher than those in silicon detectors and likewise well described by a power law in the deposited energy. Furthermore, we'll show that pulse heights for the same particles seem to depend on the duration of the measurement, thus exhibiting a sort of depolarization of the insulator when exposed to the electric voltage which makes it a particle detector. 相似文献
85.
Occurrence patterns of alien freshwater turtles in a large urban pond ‘Archipelago’ (Rome,Italy): Suggesting hypotheses on root causes 下载免费PDF全文
Maria Paola Di Santo Leonardo Vignoli Giuseppe M. Carpaneto Corrado Battisti 《Lakes & Reservoirs: Research and Management》2017,22(1):56-64
The patterns of the occurrence and distribution of alien freshwater turtle species in an urban pond archipelago (Rome, Italy) were analysed, with the aim of exploring the role of a set of factors (type of ponds, landscape context, size area, distance from the nearest road) with a generalized linear model approach. A total of 311 ponds subdivided in three types (fountains, small basins, lakes) embedded in different landscape contexts (public parks, private parks, urban areas) at differing distances from the nearest road were sampled. Six non‐native freshwater turtle species in 31 sites were recorded (9.97%). Lakes exhibited the highest occurrence rates of alien freshwater turtles, compared to small basins and fountains. Freshwater turtle species in urbanized areas were only observed in parks (both public and private). In both the public and private parks, the lakes exhibited the highest percentage of occupied sites, with fountains being the lowest. A direct and significant relationship was observed between pond size and species richness. The distance from the nearest road did not appear to affect species richness. A first interpretation of the data from this study facilitated the postulation of two a posteriori hypotheses that should be tested, as follows: (i) the causal process of turtle release is random, and the rate of extinction (and recapture) is higher in smaller ponds, thus producing the observed pattern; and (ii) the turtle release is not random, and people actively select the ponds they consider more suitable for their pet animals. In this study, it appears the lakes were perceived by those who abandon their pets as the most ecologically suitable habitats among other pond types to accommodate the different species of turtles. Knowledge of people's attitudes in regard to releasing pet animals also might assist managers of public green spaces to develop strategies aimed to preserve local biodiversity, and to educate the public about the conservation issue represented by the alien species. 相似文献
86.
D. S. Rosa I. Chiovatto Neto M. R. Calil A. G. Pedroso C. P. Fonseca S. Neves 《应用聚合物科学杂志》2004,91(6):3909-3914
The thermal and mechanical properties of low‐density polyethylene (LDPE), poly(ε‐caprolactone) (PCL), and their blends were evaluated. Differential scanning calorimetry showed that increasing the PCL content of the blend did not change the LDPE melting temperature, but reduced the crystallinity by up to 16.8%. This behavior was related to interactions between the PCL chains and the crystalline phase of LDPE. Tensile strength and elongation at break values for the blends were lower than those for the pure polymers, which suggested an incompatibility between the polymers. The values for Young's modulus under tensile increased when PCL was added to LDPE. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3909–3914, 2004 相似文献
87.
Méndez RO Bueno K Campos N López D Wyatt CJ Ortega MI 《Archivos latinoamericanos de nutrición》2005,55(2):187-193
Developing countries diets are based on a variety of plant foods that often are the main suppliers of important amounts of iron (Fe) and zinc (Zn). The objectives of this study were 1) to measure the total and dialyzable amounts of Fe and Zn in foods from Northern Mexico (Sonora) and from Southern Mexico (Oaxaca) and 2) to evaluate the effect of meat content of diets on the dialyzable amount of Fe and Zn. Methods to calculate the total dialyzable amount of Fe and Zn, were those of the AOAC and of Shen et al. Total Fe in e northern Mexican foods went from 0.78 +/- 0.0 to 11.59 +/- to 0.03 mg/ 100g (dry weight, DW); in southern Mexican foods the same micronutrient amounts were 0.86 +/- 0.18 to 8.8 +/- 0.57 mg/100 g (BS). Total Zn values were 0.91 +/- 0.00 to 13.58 +/- 0.05 mg/100 g (DW) in Sonora, and 0.64 +/- 0.18 to 20.80 +/- 0.33 mg/100 g (DW) in Oaxaca. In northern Mexico, foods dialyzable Fe had values from 0.1 +/- 0.04% to 10.6 +/- 0.36% and for Zn from 4.0 +/- 0.21% to 55.32 +/- 0.14%. Meanwhile, the range of values of dialyzable Fe for foods from Oaxaca were from 0.22 +/- 0.06% to 9.40 +/- 0.14% for and from 2.41 +/- 0.26% to 54.27 +/- 1.49% for dialyzable Zn. The average value for dialyzable Fe was higher in the foods that contained meat or meat products (p= 0.001). 相似文献
88.
Maria Luz Fernandez A. Karin Conde Laura R. Ruiz Carlos Montano John Ebner Donald J. McNamara 《Lipids》1995,30(7):619-626
To test the effects of exchanging dietary complex and simple carbohydrate for fat calories on lipoprotein metabolism, guinea
pigs were fed two different fat/carbohydrate ratios: 2.5∶58% (w/w) or 25∶29% (w/w) with either sucrose or starch as the carbohydrate
source. Animals fed high-fat had higher plasma low-density lipoprotein (LDL) and hepatic cholesterol concentrations than animals
fed low-fat diets (P<0.01). The cholesteryl ester content per particle was higher, and the number of triacylglycerol (TAG) molecules was lower
in very low density lipoprotein (VLDL) and LDL from animals fed high-fat diets. Intake of high-fat/sucrose resulted in higher
plasma LDL concentrations than intake of high-fat/starch, and animals fed low-fat/starch had the highest plasma TAG concentrations
associated with VLDL particles containing more TAG molecules, as well as a TAG-enriched LDL. The activity of plasma lecithin
cholesteryl:acyl transferase (LCAT) was highest in animals fed high-fat/sucrose, and heart lipoprotein lipase (LPL) activity
was higher in animals fed high-fat diets. Hepatic apoprotein B/E (apo B/E) receptor number (Bmax) was increased 21% with low-fat diets (P<0.01). These results suggest that the hypercholesterolemia induced by high-fat and by sucrose intake are associated with
a higher plasma LCAT activity which results in a cholesteryl ester-enriched VLDL which, by the action of LPL, might be more
readily converted to LDL through the delipidation cascade leading to downregulation of hepatic apo B/E receptors. The hypertriglyceridemia
associated with low-fat intake may result from increased production of VLDL TAG, which would explain the increased TAG content
and the higher TAG/CE ratio of VLDL from animals fed the low-fat/starch diet. 相似文献
89.
Elisabetta Tornatore Pasquale Vetro Stefania Maria Buccellato 《Neural computing & applications》2014,24(2):309-315
We propose a stochastic disease model where vaccination is included and such that the immunity is permanent. The existence, uniqueness, and positivity of the solution and the stability of the disease-free equilibrium are studied. 相似文献
90.
In many studies on lipoxygenase catalysis, nonionic detergents are used to obtain an optically transparent solution of the
fatty acid substrate. In order to resolve some controversies that exist with regard to the interpretation of kinetic data
obtained with solutions containing nonionic detergents, a systematic investigation was undertaken into the effects of Lubrol,
Tween-20 and Triton X-100 (0–0.8 g/L) on the kinetics of linoleate (2.5–110 μM) dioxygenation, catalyzed by lipoxygenase-1
or lipoxygenase-2 from soybean, at pH 9 or 10, at 25°C. Under most conditions, it was found that the detergents slowed down
the reaction. However, at high linoleate concentrations, where substrate inhibition of lipoxygenase is significant, small
amounts of detergent increased the dioxygenation rate. In a quantitative analysis of the results, a kinetic model in which
the incorporation of linoleate in the detergent micelles is formulated as a simple reversible equilibrium, and in which both
lipoxygenase-1 and-2 interact with free linoleate, but not with linoleate incorporated in the micelles, appeared to be sufficient
to predict experimental results over a wide range of experimental conditions. According to this model, the changes in the
dioxygenation kinetics caused by the presence of nonionic detergents are similar (but not equal) to those caused by competitive
inhibitors. The conclusions that monomeric, nonmicellar linoleate is the preferred substrate for lipoxygenase and that the
observed inhibition and stimulation are solely due to changes in the effective linoleate concentration strongly corroborate
the earlier observations by Galpin and Allen [Biochim. Biophys. Acta 488 (1977), 392–401]. 相似文献