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1.
A self-consistent model describing the influence of a pulsed discharge on H 2-air mixtures is developed. The model includes the processes of ionization, dissociation, and excitation of the gas molecules by electron impacts; a set of ion-molecular reactions determining the time evolution of the charged particle densities; the processes involving electronically excited atoms and molecules; and a set of reactions describing the ignition of hydrogen-oxygen mixtures. Results are presented from simulations of the oxidation dynamics of hydrogen molecules in a stoichiometric H 2-air mixture and the ignition of such a mixture under the action of a pulsed high-current discharge. The simulation results are compared with available experimental data and calculations performed by other authors. 相似文献
2.
Results are presented from experimental studies of the destruction of chlorofluorocarbon (CF 2Cl 2) molecules in a methane-oxygen (air) gas mixture whose combustion is initiated by a high-current slipping surface discharge. It is found that a three-component CH 4+O 2(air)+CF 2Cl 2 gas mixture (even with a considerable amount of the third component) demonstrates properties of explosive combustion involving chain reactions that are typical of two-component CH 4+O 2 mixtures. Experiments show the high degree of destruction (almost complete decomposition) of chlorofluorocarbons contained in the mixture during one combustion event. The combustion dynamics is studied. It is shown that the combustion initiated by a slipping surface discharge has a number of characteristic features that make it impossible to identify the combustion dynamics with the formation of a combustion or detonation wave. The features of the effects observed can be related to intense UV radiation produced by a pulsed high-current surface discharge. 相似文献
3.
Results are presented from experimental and theoretical studies of the sterilization of medical products by the plasmas of dc glow discharges in different gas media. The sterilization efficiency is obtained as a function of discharge parameters. The plasma composition in discharges in N 2 and O 2 is investigated under the operating conditions of a plasma sterilizer. It is shown that free surfaces of medical products are sterilized primarily by UV radiation from the discharge plasma, while an important role in sterilization of products with complicated shapes is played by such chemically active particles as oxygen atoms and electronically excited O 2 molecules. 相似文献
4.
The formation of electronically excited states during hydroperoxide metabolism is analysed in terms of recombination reactions involving secondary peroxyl radicals and scission of the O? O bond of peroxides by haemoproteins, mainly myoglobin. Both processes may be sequentially interrelated, for the cleavage of H 2O 2 by metmyoglobin leads to the formation of a strong oxidizing equivalent with the capability to promote peroxidation of polyunsaturated fatty acids. The decomposition of lipid hydroperoxides by ferryl-hydroxo complexes, as that formed during the oxidation of metmyoglobin by H 2O 2, is a source of peroxyl radicals, the recombination of which proceeds with elimination of a conjugated triplet carbonyl or singlet oxygen. 相似文献
5.
The current dynamics in a non-self-sustained glow discharge in atmospheric-pressure nitrogen (with a small admixture of oxygen) at cryogenic and room temperatures is studied experimentally and theoretically. For the first time, the theoretical model incorporates the processes of the decomposition of O 2 + ·N 2 and NO +·N 2 complex ions in collisions with vibrationally excited nitrogen molecules and the associative ionization reactions with the participation of excited nitrogen and oxygen atoms. The computation results agree quite satisfactorily with the experimental data on the current dynamics and the duration of the stable phase of a non-self-sustained discharge for various applied voltages. Even a small (0.01%) oxygen admixture is found to greatly affect the dynamics of the ion composition and the characteristic duration of the stable phase of a non-self-sustained discharge in atmospheric-pressure nitrogen. 相似文献
6.
Experiments with quasi-steady high-current discharges in crossed E × B fields in various gases (Ar, N 2, H 2, and SF 6) and gas mixtures (Ar/SF 6 and Ar/O 2) at pressures from 10 −3 to 5 Torr in discharge systems with different configurations of electric and magnetic fields revealed a specific type of
stable low-voltage discharge that does not transform into an arc. This type of discharge came to be known as a high-current
diffuse discharge and, later, a nonsputtering impulse magnetron discharge. This paper presents results from experimental studies
of the plasma parameters (the electron temperature, the plasma density, and the temperature of ions and atoms of the plasma-forming
gas) of a high-current low-pressure diffuse discharge in crossed E × B fields. 相似文献
7.
The kinetic model of toluene decomposition in nonequilibrium low-temperature plasma generated by a pulse-periodic discharge operating in a mixture of nitrogen and oxygen is developed. The results of numerical simulation of plasma-chemical conversion of toluene are presented; the main processes responsible for C 6H 5CH 3 decomposition are identified; the contribution of each process to total removal of toluene is determined; and the intermediate and final products of C 6H 5CH 3 decomposition are identified. It was shown that toluene in pure nitrogen is mostly decomposed in its reactions with metastable N 2(A 3?? u + ) and N 2(a?? 1?? u ? ) molecules. In the presence of oxygen, in the N 2 : O 2 gas mixture, the largest contribution to C 6H 5CH 3 removal is made by the hydroxyl radical OH which is generated in this mixture exclusively due to plasma-chemical reactions between toluene and oxygen decomposition products. Numerical simulation showed the existence of an optimum oxygen concentration in the mixture, at which toluene removal is maximum at a fixed energy deposition. 相似文献
8.
A rapid heating of nitrogen-oxygen mixtures excited by gas discharges is investigated numerically with allowance for the following main processes: the reactions of predissociation of highly excited electronic states of oxygen molecules (which are populated via electron impact or via the quenching of the excited states of N 2 molecules), the reactions of quenching of the excited atoms O( 1 D) by nitrogen molecules, the VT relaxation reactions, etc. The calculated results adequately describe available experimental data on the dynamics of air heating in gas-discharge plasmas. It is shown that, over a broad range of values of the reduced electric field E/N, gas heating is maintained by a fixed fraction of the discharge power that is expended on the excitation of the electronic degrees of freedom of molecules (for discharges in air, η E?28%). The lower the oxygen content of the mixture, the smaller the quantity η E. The question of a rapid heating of nitrogen with a small admixture of oxygen is discussed. 相似文献
9.
The mechanism for the formation of the inverse electron distribution function is proposed and realized experimentally in a nitrogen plasma of a hollow-cathode glow discharge. It is shown theoretically and experimentally that, for a broad range of the parameters of an N 2 discharge, it is possible to form a significant dip in the profile of the electron distribution function in the energy range ε=2–4 eV and, accordingly, to produce the inverse distribution with df(ε)/ d?>0. The formation of a dip is associated with both the vibrational excitation of N 2 molecules and the characteristic features of a hollow-cathode glow discharge. In such a discharge, the applied voltage drops preferentially across a narrow cathode sheath. In the main discharge region, the electric field E is weak ( E<0.1 V/cm at a pressure of about p~0.1 torr) and does not heat the discharge plasma. The gas is ionized and the ionization-produced electrons are heated by a beam of fast electrons (with an energy of about 400 eV) emitted from the cathode. A high-energy electron beam plays an important role in the formation of a dip in the profile of the electron distribution function in the energy range in which the cross section for the vibrational excitation of nitrogen molecules is maximum. A plasma with an inverted electron distribution function can be used to create a population inversion in which more impurity molecules and atoms will exist in electronically excited states. 相似文献
10.
Three tricyclic 1,2‐dioxetane derivatives, 1a, 2a and 3a were synthesized from their corresponding 1,4‐dioxin acenaphthylene compounds, 1, 2 and 3, by reaction with singlet‐oxygen ( 1O 2) in dichloromethane. Evidence for the formation of the dioxetanes 1a, 2a and 3a is provided by the chemiluminescence (CL) that corresponds to the emission from the electronically excited diesters 1b*, 2b* and 3b*, which are decomposed thermally from the dioxetanes 1a, 2a and 3a, respectively. The highly strained 1,2‐dioxetane ring decomposes from a twisted geometry by simultaneous cleavages of the O–O and C–C bonds, producing the electronically excited diester that emits CL. It was observed that the CL from compound 2a is red‐shifted relative to that of compounds 1a and 3a suggesting a higher degree of stabilization for the excited state by the electron‐donating methoxy group. Also, a study of the solvent effect on fluorescence shows a significant red‐shift in compound 2b, indicating a more polar excited state. The kinetics of the thermal decomposition of the 1,2‐dioxetanes clearly demonstrate that the CL characteristics of compound 2a are quite different from those of compounds, 1a and 3a. These results are consistent with the proposed intramolecular chemically initiated electron exchange luminescence (CIEEL) mechanism which is triggered by the electron‐donating group of compound 2a. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
11.
Results are presented from experimental studies of the glow dynamics of active nitrogen in the stage of its excitation by a current pulse and during the discharge afterglow. The mechanism is proposed for the generation of a light splash in a highly activated nitrogen after the end of its pulsed excitation. The key role in the generation of this splash is played by the D-V processes, by which the dissociation energy is transferred to the vibrational degrees of freedom in the course of recombination of nitrogen atoms, and the V-E processes, by which the vibrational energy of highly excited molecules N 2( X, v ≥ 25–27) is transferred to the emitting electronic states N 2( B, v) after the V-V delay. Results of simulations based on the mechanism proposed are also presented. 相似文献
12.
Reactive N is closely related to the global issues of climate change and regional pollutions. Nitrous oxide (N2O), the fourth important gas among greenhouse gases, is produced as an intermediate in nitrification and denitrification processes. As methane (CH4) is the end product in the anoxic decomposition of organic materials, mitigation options of N2O emission are different from those of CH4 emission. Nitrate is another reactive N bringing about the eutrification of aqueous environments and the hazard of drinking water. Mitigation of NO3 problem also relates closely to the N2O emission. Therefore, holistic approaches are necessary for solving the problems of Earth warming and environmental eutrification by reactive N at the same time. In this paper, the deforestation in the tropics, and the present situations of food supply and sustainable agriculture in Japan are re-evaluated in terms of N2O emission and NO3 discharge from the agricultural sector. The magnitude of N2O emission by deforestation in the tropics may fall within the similar order of magnitude by N fertilization. As more N is imported as foods and fodder than the amount of fertilized N in Japan, more attention should be paid to the phases of their consumption and waste treatment. Sole attention to the production stage is not enough for the total mitigation of various environmental problems by reactive N in relation to agriculture. Parameters holistically evaluating the impact of reactive N on the Earth and respective regions are urgently necessary. 相似文献
13.
Reactive N is closely related to the global issues of climate change and regional pollutions. Nitrous oxide (N 2O), the fourth important gas among greenhouse gases, is produced as an intermediate in nitrification and denitrification processes. As methane (CH 4) is the end product in the anoxic decomposition of organic materials, mitigation options of N 2O emission are different from those of CH 4 emission. Nitrate is another reactive N bringing about the eutrification of aqueous environments and the hazard of drinking water. Mitigation of NO 3 problem also relates closely to the N 2O emission. Therefore, holistic approaches are necessary for solving the problems of Earth warming and environmental eutrification by reactive N at the same time. In this paper, the deforestation in the tropics, and the present situations of food supply and sustainable agriculture in Japan are re-evaluated in terms of N 2O emission and NO3 discharge from the agricultural sector. The magnitude of N 2O emission by deforestation in the tropics may fall within the similar order of magnitude by N fertilization. As more N is imported as foods and fodder than the amount of fertilized N in Japan, more attention should be paid to the phases of their consumption and waste treatment. Sole attention to the production stage is not enough for the total mitigation of various environmental problems by reactive N in relation to agriculture. Parameters holistically evaluating the impact of reactive N on the Earth and respective regions are urgently necessary. 相似文献
14.
Litter inputs are expected to have a strong impact on soil N 2O efflux. This study aimed to assess the effects of the litter decomposition process and nutrient efflux from litter to soil on soil N 2O efflux in a tropical rainforest. A paired study with a control (L) treatment and a litter-removed (NL) treatment was followed for 2 years, continuously monitoring the effects of these treatments on soil N 2O efflux, fresh litter input, decomposed litter carbon (LCI) and nitrogen (LNI), soil nitrate (NO 3 ?–N), ammonium (NH 4 +–N), dissolved organic carbon (DOC), and dissolved nitrogen (DN). Soil N 2O flux was 0.48 and 0.32 kg N 2O–N ha ?1 year ?1 for the L and NL treatments, respectively. Removing the litter caused a decrease in the annual soil N 2O emission by 33%. The flux values from the litter layer were higher in the rainy season as compared to the dry season (2.10 ± 0.28 vs. 1.44 ± 0.35 μg N m ?2 h ?1). The N 2O fluxes were significantly correlated with the soil NO 3 ?–N contents ( P < 0.05), indicating that the N 2O emission was derived mainly from denitrification as well as other NO 3 ? reduction processes. Suitable soil temperature and moisture sustained by rainfall were jointly attributed to the higher soil N 2O fluxes of both treatments in the rainy season. The N 2O fluxes from the L were mainly regulated by LCI, whereas those from the NL were dominated jointly by soil NO 3 ? content and temperature. The effects of LCI and LNI on the soil N 2O fluxes were the greatest in the 2 months after litter decomposition. Our results show that litter may affect not only the variability in the quantity of N 2O emitted, but also the mechanisms that govern N 2O production. However, further studies are still required to elucidate the impacting mechanisms of litter decomposition on N 2O emission from tropical forests. 相似文献
15.
The aqueous decomposition of the iridium coordinated nitrosothiols (RSNOs) trans-K[IrCl 4(CH 3CN)NOSPh] ( 1), and K 2[IrCl 5(NOECyS)] ( 2, ECyS = cysteine ethyl ester), was studied by MS analysis of the gaseous products, ESI-MS, NMR, and UV-Vis spectroscopy. Bent NO (NO −, nitroxyl anion), sulfenic acids and nitrite were observed as coordinated products in solution, while nitrous oxide (N 2O) and nitrogen were detected in the gas phase. The formation of coordinated NO − and N 2O, a nitroxyl dimerization product, allows us to propose the formation of free nitroxyl (HNO) as an intermediate. Complex 1 decomposes 300 times slower than free PhSNO does. In both cases ( 1 and 2) kinetic results show a first order decomposition behavior and a very negative Δ S≠, which strongly indicates an associative rate-determining step. A proposed decomposition mechanism, supported by the experimental data and DFT calculations, involves, as the first step, nucleophilic attack of H 2O on to the sulfur atom of the coordinated RSNO, producing an NO − complex and free sulfenic acid, followed by two competing reactions: a ligand exchange reaction of this NO − with the sulfenic acid or, to a minor extent, coordination of N 2O to produce an NO −/N 2O complex which finally renders free N 2 and coordinated NO 2−. Some of the produced NO − is likely to be released from the metal center producing nitroxyl by protonation and finally N 2O by dimerization and loss of H 2O. In conclusion, the decomposition of these coordinated RSNOs occurs through a different mechanism than for the decomposition of free RSNOs. It involves the formation of sulfenic acids and coordinated NO −, which is released from the complexes and protonated at the reaction pH producing nitroxyl (HNO), and ultimately N 2O. 相似文献
16.
Results are presented from experimental and theoretical studies of the optical characteristics and parameters of the plasma
of an atmospheric-pressure barrier discharge excited in a HgBr 2: N 2: He mixture, which was used as the working medium of a small-size (with a radiation area of 8 cm 2) exciplex gas-discharge radiation source. The mean radiation power of 87 mW was achieved at the radiation wavelength λ max = 502 nm. The electron energy distribution function, the transport characteristics, the specific energy lost in the processes
involving electrons, the electron temperature and density, and the rate constants of elastic and inelastic electron scattering
by the components of the working mixture were calculated as functions of the reduced field E/ N. The plasma of a discharge excited in a HgBr 2: N 2: He mixture can be used as the working medium of a small-size blue-green radiation source. Such a source can find application
in biotechnology, photonics, and medicine and can also be used to manufacture gas-discharge display panels. 相似文献
17.
Restored forested wetlands reduce N loads in surface discharge through plant uptake and denitrification. While removal of reactive N reduces impact on receiving waters, it is unclear whether enhanced denitrification also enhances emissions of the greenhouse gas N 2O, thus compromising the water-quality benefits of restoration. This study compares denitrification rates and N 2O:N 2 emission ratios from Sharkey clay soil in a mature bottomland forest to those from an adjacent cultivated site in the Lower Mississippi Alluvial Valley. Potential denitrification of forested soil was 2.4 times of cultivated soil. Using intact soil cores, denitrification rates of forested soil were 5.2, 6.6 and 2.0 times those of cultivated soil at 70, 85 and 100% water-filled pore space (WFPS), respectively. When NO 3 was added, N 2O emissions from forested soil were 2.2 times those of cultivated soil at 70% WFPS. At 85 and 100% WFPS, N 2O emissions were not significantly different despite much greater denitrification rates in the forested soil because N 2O:N 2 emission ratios declined more rapidly in forested soil as WFPS increased. These findings suggest that restoration of forested wetlands to reduce NO 3 in surface discharge will not contribute significantly to the atmospheric burden of N 2O. 相似文献
18.
Results are presented from experimental studies of decomposition of toluene (C 6H 5CH 3) in a polluted air flow by means of a steady-state atmospheric pressure glow discharge at different water vapor contents in the working gas. The experimental results on the degree of C 6H 5CH 3 removal are compared with the results of computer simulations conducted in the framework of the developed kinetic model of plasma chemical decomposition of toluene in the N 2: O 2: H 2O gas mixture. A substantial influence of the gas flow humidity on toluene decomposition in the atmospheric pressure glow discharge is demonstrated. The main mechanisms of the influence of humidity on C 6H 5CH 3 decomposition are determined. The existence of two stages in the process of toluene removal, which differ in their duration and the intensity of plasma chemical decomposition of C 6H 5CH 3 is established. Based on the results of computer simulations, the composition of the products of plasma chemical reactions at the output of the reactor is analyzed as a function of the specific energy deposition and gas flow humidity. The existence of a catalytic cycle in which hydroxyl radical OH acts a catalyst and which substantially accelerates the recombination of oxygen atoms and suppression of ozone generation when the plasma-forming gas contains water vapor is established. 相似文献
19.
Excitation of a microwave discharge at the end of a cylindrical electrode in nitrogen at a pressure of 1 Torr and incident
powers of 60–140 W was investigated experimentally by using K-008 and K-011 video cameras and analyzing oscillograms of discharge
emission. The times during which the discharge is established in the radial and axial directions are found to be on the order
of 10 −4 and 10 −2 s, respectively. The results obtained are analyzed using one-dimensional simulations of a discharge in nitrogen in a quasistatic
approximation. The kinetic scheme includes 50 processes involving electrons, ions, and excited molecules and atoms. The time
evolution of the concentrations of molecular nitrogen in the N 2( C
3II
u
) and N 2( B
3II
g
) states, responsible for the recorded discharge emission, is compared with the experimental data. 相似文献
20.
Soil faunal activity can be a major control of greenhouse gas (GHG) emissions from soil. Effects of single faunal species, genera or families have been investigated, but it is unknown how soil fauna diversity may influence emissions of both carbon dioxide (CO 2, end product of decomposition of organic matter) and nitrous oxide (N 2O, an intermediate product of N transformation processes, in particular denitrification). Here, we studied how CO 2 and N 2O emissions are affected by species and species mixtures of up to eight species of detritivorous/fungivorous soil fauna from four different taxonomic groups (earthworms, potworms, mites, springtails) using a microcosm set‐up. We found that higher species richness and increased functional dissimilarity of species mixtures led to increased faunal‐induced CO 2 emission (up to 10%), but decreased N 2O emission (up to 62%). Large ecosystem engineers such as earthworms were key drivers of both CO 2 and N 2O emissions. Interestingly, increased biodiversity of other soil fauna in the presence of earthworms decreased faunal‐induced N 2O emission despite enhanced C cycling. We conclude that higher soil fauna functional diversity enhanced the intensity of belowground processes, leading to more complete litter decomposition and increased CO 2 emission, but concurrently also resulting in more complete denitrification and reduced N 2O emission. Our results suggest that increased soil fauna species diversity has the potential to mitigate emissions of N 2O from soil ecosystems. Given the loss of soil biodiversity in managed soils, our findings call for adoption of management practices that enhance soil biodiversity and stimulate a functionally diverse faunal community to reduce N 2O emissions from managed soils. 相似文献
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