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31.
Omar Snchez Estrella Asp María C Martí Marlene Roeckel 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(11):1261-1267
Most of the kinetic studies on nitrification have been performed in diluted salts medium. In this work, the ammonia oxidation rate (AOR) was determined by respirometry at different ammonia (0.01 and 33.5 mg N‐NH3 L?1), nitrite (0–450 mg N‐NO2? L?1) and nitrate (0 and 275 mg N‐NO3? L?1) concentrations in a saline medium at 30 °C and pH 7.5. Sodium azide was used to uncouple the ammonia and nitrite oxidation, so as to measure independently the AOR. It was determined that ammonia causes substrate inhibition and that nitrite and nitrate exhibit product inhibition upon the AOR. The effects of ammonia, nitrite and nitrate were represented by the Andrews equation (maximal ammonia oxidation rate, rAOMAX, = 43.2 [mg N‐NH3 (g VSSAO h)?1]; half saturation constant, KSAO, = 0.11 mg N‐NH3 L?1; inhibition constant KIAO, = 7.65 mg N‐NH3 L?1), by the non‐competitive inhibition model (inhibition constant, KINI, = 176 mg N‐NO2? L?1) and by the partially competitive inhibition model (inhibition constant, KINA, = 3.3 mg N‐NO3? L?1; α factor = 0.24), respectively. The rAOMAX value is smaller, and the KSAO value larger, than the values reported in diluted salts medium; the KIAO value is comparable to those reported. Process simulations with the kinetic model in batch nitrifying reactors showed that the inhibitory effects of nitrite and nitrate are significant for initial ammonia concentrations larger than 100 mg N‐NH4+ L?1. Copyright © 2005 Society of Chemical Industry 相似文献
32.
In this article, a general synthesis method is proposed for the design of discontinuous feedback strategies leading to asymptotically stabilizing sliding regimes. The method is applicable to the class of nonlinear dynamical systems possessing constant equilibrium points. A family of nonlinear stabilizing sliding manifolds, parametrized by generic desired equilibrium point, is specified on the basis of the extended linearization approach. Some examples including simulations are presented for illustrative purposes.
Editor: S. Zak 相似文献
33.
Zirconium(IV) tungstoiodophosphate has been synthesized under a variety of conditions. The most chemically and thermally stable
sample is prepared by adding a mixture of aqueous solutions of 0·5 mol L−1 sodium tungstate, potassium iodate and 1 mol L−1 orthophosphoric acid to aqueous solution of 0·1 mol L−1 zirconium(IV) oxychloride. Its ion exchange capacity for Na+ and K+ was found to be 2·20 and 2·35 meq g−1 dry exchanger, respectively. The material has been characterized on the basis of chemical composition, pH titration, Fourier
transform infrared spectroscopy (FTIR) and thermogravimetric analysis. The effect on the exchange capacity of drying the exchanger
at different temperatures has been studied. The analytical importance of the material has been established by quantitative
separation of Pb2+ from other metal ions. 相似文献
34.
Jonathan P. Belnoue Giang D. Nguyen Alexander M. Korsunsky 《International Journal of Fracture》2007,144(1):53-60
This paper presents a new 1-D non-local damage-plasticity deformation model for ductile materials. It uses the thermodynamic
framework described in Houlsby and Puzrin (2000) and holds, nevertheless, some similarities with Lemaitre’s (1971) approach.
A 1D finite element (FE) model of a bar fixed at one end and loaded in tension at the other end is introduced. This simple
model demonstrates how the approach can be implemented within the finite element framework, and that it is capable of capturing
both the pre-peak hardening and post-peak softening (generally responsible for models instability) due to damage-induced stiffness
and strength reduction characteristic of ductile materials. It is also shown that the approach has further advantages of achieving
some degree of mesh independence, and of being able to capture deformation size effects. Finally, it is illustrated how the
model permits the calculation of essential work of rupture (EWR), i.e. the specific energy per unit cross-sectional area that
is needed to cause tensile failure of a specimen. 相似文献
35.
There are some foods that contain mutagenic or carcinogenic agents, some of which occur naturally and others that may be formed during preparation or cooking. Several foods such as legumes, also contain natural antimutagens and/or anticarcinogens. Lupine is one such legume that contains high amounts of protein (40%) and oils (14%). About 90 species of lupine have been reported throughout Mexico. However, the use of this crop as a source of food has been limited by the presence of antinutritional agents such as phenolic compounds (PC), carbohydrates (CH) and quinolizidinic alkaloids (Qas). It has also been suggested that consuming these compounds can affect human health and may even reduce the risk of disease. The objective of this work was to determine the effect of PC, CH and Qas, isolated and quantified from Lupinus campestris on the mutagenicity of 1-nitropyrene (1-NP) as a model mutagen and we used the Salmonella typhimurium tester strain YG1024 by the Kado microsuspension method. The results indicate that L. campestris seeds have 11 mg (+)catechin equivalent g(-1) seed coat; 120.3 mg g(-1) seeds and 2.13 mg g(-1) seeds of PC, CH and Qas, respectively. 1-NP mutagenicity was inhibited by 86% for PC, 76% for CH and 75% for Qas at concentrations of 200, 512 and 13.6 microg/tube, respectively. 相似文献
36.
Yewang Su Baohua Ji Yonggang Huang Kehchih Hwang 《Journal of Materials Science》2007,42(21):8885-8893
Wet adhesion is widely adopted in biological adhesion systems in nature. Wet adhesion is studied in this paper with the focus
on the effect of different contact shapes (flat, concave, convex, and ring-like) on the adhesion force. The evolution of the
liquid bridge between a fiber tip and substrate during the detaching process shows two transition points. The first transition
from the radius-controlled to the contact-angle controlled process is critical to influence the strength and robustness of
adhesion. We show that a concave shape is more effective than a flat one, while a convex shape has no advantage. A ring-like
contact shape has advantages in a hydrophobic environment and on a rough surface. 相似文献
37.
Irine Banu Lucy 《Journal of Materials Science》2007,42(14):5875-5879
Capacitance and dielectric loss measurements were carried out using an Al/Cu–GeO2/Al sandwich structure for 0 to 10 vol% Cu films, 120–400 nm thick, deposited at 0.4–1.5 nm/s in the frequency and temperature
range 1–106 Hz and 90–573 K, respectively. The variation of capacitance and dielectric loss with frequency and temperature follows the
Goswami and Goswami model. Capacitance decreases slowly with increasing thickness and also varies with the change in deposition
rate of the cermet film. 相似文献
38.
V. Thomas Paul S. Saroja P. Hariharan A. Rajadurai M. Vijayalakshmi 《Journal of Materials Science》2007,42(14):5700-5713
This paper presents the results of a study on the microstructural and microchemical variations in a multipass Gas Tungsten
Arc weld (GTAW) of modified 9Cr-1Mo steel. The changes brought about in the steel due to the heating and cooling cycles during
welding and the subsequent effects due to reheating effects during multipass welding are described. Detailed analytical transmission
electron microscopy has been carried to study the type and composition of the primary and secondary phases in this steel.
The systematic changes in microstructural parameters such as Prior Austenite Grain Size, martensite lath size, number density,
size and microchemistry of carbides, have been understood based on the different transformations that the steel undergoes
during the heating and cooling process. Based on the observed microstructure, an attempt has been made to identify distinct
microstructural zones and possible thermal cycles experienced by different regions of the weldment. 相似文献
39.
Nina Georgieva Kostova Elka Kraleva Alla A. Spojakina Erika Godocikova Peter Balaz 《Journal of Materials Science》2007,42(10):3321-3325
The Al-MCM-41 has been used as support to prepare Mo-containing catalysts. The 12- molybdophosphoric heteropoly acid (HPMo)
is used as initial compound. The catalysts are synthesized by two different methods: incipient impregnation with aqueous solution
of the acid and mechanochemical synthesis. The samples were tested in the reaction of the thiophene hydrodesulfurization after
activation with mixture H2 + H2S. The effect of the preparation method of the catalysts on their physicochemical and catalytic properties has been studied.
A partial destruction of the loaded compound is observed in mechanochemically treated sample whereas the aggregates are formed
from the particles of different size in the impregnated sample. The specific surface area of the sample prepared by mechanical–chemical
treatment decreases 2–3 times, while the total pore volume is about four times lower. The HDS activity is higher on the impregnated
sample than on the mechanochemically treated one. 相似文献
40.
Prabhakar R. Bandaru 《Journal of Materials Science》2007,42(5):1809-1818
A review on the syntheses and electrical characterization of Y-shaped multi-walled carbon nanotube morphologies is presented.
Modified thermal CVD processes, using Ti precursors, are used to grow Y-junctions of different geometries and distribution
of catalyst particles. It has been established that novel electrical switching behavior is feasible, where any one of the
three branches of the Y-junction can be used for modulating the electrical current flow through the other two branches. Current
blocking behavior, leading to perfect rectification, is seen which could be related to the interplay of the carrier lifetime
and the transit time. The overall goal is to investigate the possibility of obtaining novel functionality at the nanoscale,
which can lead to new device paradigms. 相似文献