Absence Of N2 Research Articles

메탄-산소 연소에서 침입공기의 위치 및 유량이 NO x 배출 특성에 미치는 영향에 관한 수치해석적 연구

In pure O₂ combustion, the absence of N₂ in the fuel theoretically eliminates the emission of NOx. However, when CH₄ combusts in the presence of O₂ in a reheating furnace, the influx of external air into the furnace introduces N₂, resulting in a significant emission of NOx. Therefore, in this study, we numerically investigated the effect of external-air intrusion on the production of NOx during CH4-O₂ combustion through computational fluid dynamics simulation. NOx emission characteristics were investigated in terms of the location and amount of external-air inflows. Results indicated that NOx emissions increased when external air flowed into the main combustion area where the temperature was high. Additionally, the flow rate of external air exhibited different effects on NOx emission characteristics depending on the inflow path of the air. When external air was introduced near the burner, the NOx emission concentration increased as the flow rate of the air decreased.

Electro-Catalytic Reduction of Nitrogen to Ammonia By Vanadium Oxide and Vanadium Oxynitride Thin Films: The Roles of Metal Oxophilicity, and Lattice Oxygen and Nitrogen Towards NRR

Electro-catalytic reduction of N2 to NH3 using Earth-abundant oxide and oxynitrides is an energy- and environmentally-friendly alternative to the Haber-Bosch process. The present contribution summarizes our recent progress on vanadium oxide (VO) and vanadium oxynitride (VON) thin films1,2 as electrochemical nitrogen reduction reaction (NRR) catalysts at neutral pH conditions. In the case of VO films, the N-free VIII/IV-oxide, created by O2 plasma oxidation of polycrystalline vanadium, exhibited N2 reduction at an onset potential of -0.16 V vs. Ag/AgCl. DFT calculations indicated that N2 scission from O-supported V-centers is energetically favorable by ~18 kcal/mole as compared to N-supported sites. Interestingly, in the case of VON catalysts, both electrochemistry and photoemission data revealed the involvement of both lattice N and dissolved N2 in the NRR process. Our results also show that NH3 production from VON lattice N occurs in the presence or absence of N2 and involves the formation of V≡N: intermediates or similar unsaturated VN surface states. This is in contrast to VO where N2 reduction occurred in the presence or absence of lattice N, and without N incorporation into a vanadium oxide lattice. Thus, both lattice N and N2 reduction mechanisms involve oxide-supported V surface sites ([V]O) in preference to N-supported sites ([V]N). DFT calculations revealed the formation of V≡N:, V-N=N-H, plus other plausible reaction intermediates that are energetically favored at [V]O rather than at [V]N surface sites. Acknowledgment: This work was supported by the National Science Foundation through grants DMR-2112864 (to JAK, TRC, and FD) and partial support by CHE-1953547 (to TRC). Additional NSF support for the UNT CASCaM HPC cluster via Grant CHE-1531468 is also gratefully acknowledged. Ganesan, A. Osonkie, P. Chukwunenye, T. Cundari, F. D'Souza, J. Kelber. Electrochemical Reduction of N2 to ammonia by vanadium oxide thin films at neutral pH, J. Electrochem. Soc., 2021, 168, 026504.Osonkie, A. Ganesan, P. Chukwunenye, F. Anwar, K. Balogun, M. Gharee, I. Rashed, T. R. Cundari, F. D’Souza, and J. A. Kelber, Electro-catalytic reduction of nitrogen to ammonia: The roles of lattice O and N in reduction at vanadium oxynitride surfaces, ACS Adv. Mater & Interface, 2021, in revision.

Electrocatalytic Reduction of Nitrogen to Ammonia: the Roles of Lattice O and N in Reduction at Vanadium Oxynitride Surfaces.

Vanadium oxynitride and other earth-abundant oxynitrides are of growing interest for the electrocatalytic reduction of nitrogen to NH3. A major unresolved issue, however, concerns the roles of lattice N and lattice O in this process. Electrochemistry and photoemission data reported here demonstrate that both lattice N and dissolved N2 are reduced to NH3 by cathodic polarization of vanadium oxynitride films at pH 7. These data also show that ammonia production from lattice N occurs in the presence or absence of N2 and involves the formation of V≡N: intermediates or similar unsaturated VN surface states on a thin vanadium oxide overlayer. In contrast, N2 reduction proceeds in the presence or absence of lattice N and without N incorporation into a vanadium oxide lattice. Thus, both lattice N and N2 reduction mechanisms involve oxide-supported V surface sites ([V]O) in preference to N-supported sites ([V]N). This result is supported by density functional theory-based calculations showing that the formation of V≡N:, V-N═N-H, and a few other plausible reaction intermediates is consistently energetically favored at [V]O rather than at [V]N surface sites. Similar effects are predicted for the oxynitrides of other oxophilic metals, such as Ti.

Evaluation of argon-induced hydrogen production as a method to measure nitrogen fixation by cyanobacteria.

The production of dihydrogen (H2 ) is an enigmatic yet obligate component of biological dinitrogen (N2 ) fixation. This study investigates the effect on H2 production by N2 fixing cyanobacteria when they are exposed to either air or a gas mixture consisting of argon, oxygen, and carbon dioxide (Ar:O2 :CO2 ). In the absence of N2 , nitrogenase diverts the flow of electrons to the production of H2 , which becomes a measure of Total Nitrogenase Activity (TNA). This method of argon-induced hydrogen production (AIHP) is much less commonly used to infer rates of N2 fixation than the acetylene reduction (AR) assay. We provide here a full evaluation of the AIHP method and demonstrate its ability to achieve high-resolution measurements of TNA in a gas exchange flow-through system. Complete diel profiles of H2 production were obtained for N2 fixing cyanobacteria despite the absence of N2 that broadly reproduced the temporal patterns observed by the AR assay. Comparison of H2 production under air versus Ar:O2 :CO2 revealed the efficiency of electron usage during N2 fixation and place these findings in the broader context of cell metabolism. Ultimately, AIHP is demonstrated to be a viable alternative to the AR assay with several additional merits that provide an insight into cell physiology and promise for successful field application.

Geração de Filmes de Titânia meso-macroporosa por Modelagem de Esferas de Látex

RESUMO: Este artigo trata da síntese e formação de filmes de titânia meso-macroporosa por meio da modelagem de esferas de látex. A infiltração do molde por solução precursora de titânia resultou em filmes compactos que geraram uma rede de poros invertida decorrente da remoção do molde como foi observado por medidas de Microscopia Eletrônica de Varredura (MEV). O objetivo deste trabalho consiste em analisar a deposição de esferas de látex em substratos de vidro e eventual infiltração por solução precursora de titânia mesoporosa. O produto final foi filmes compactos com porosidade na escala micrométrica definida pelas esferas de látex. A síntese das esferas de látex realizou-se na ausência de N2 e a solução precursora de titânia foi obtida a partir do sistema ternário: HCl/P-123/1 Butanol. A caracterização dos filmes por MEV realizou-se após a remoção dos moldes de esferas de látex por calcinação em um forno tubular. A aparência dos filmes foi compacta para o filme de 30% V/Vo e houve uma rede de poros bem definida observada na caracterização por MEV associada à presença das esferas de látex que se auto-estruturaram pela técnica de Evaporação Controlada de Solvente (ECS). A caracterização da superfície por MEV mostrou que esferas de látex depositam em substratos vítreos e formaram uma rede de poros que poderia ser aplicada em dispositivos funcionais como: células solares, catalisadores e baterias. Há necessidade de diminuir a concentração da dispersão para formar filmes com monocamadas homogêneas que se tornem transparentes à luz visível.
 PALAVRAS-CHAVE: Nanotecnologia, óxido semicondutor, materiais auto-estruturados.

Dynamic Brain Responses Modulated by Precise Timing Prediction in an Opposing Process.

The brain function of prediction is fundamental for human beings to shape perceptions efficiently and successively. Through decades of effort, a valuable brain activation map has been obtained for prediction. However, much less is known about how the brain manages the prediction process over time using traditional neuropsychological paradigms. Here, we implemented an innovative paradigm for timing prediction to precisely study the temporal dynamics of neural oscillations. In the experiment recruiting 45 participants, expectation suppression was found for the overall electroencephalographic activity, consistent with previous hemodynamic studies. Notably, we found that N1 was positively associated with predictability while N2 showed a reversed relation to predictability. Furthermore, the matching prediction had a similar profile with no timing prediction, both showing an almost saturated N1 and an absence of N2. The results indicate that the N1 process showed a 'sharpening' effect for predictable inputs, while the N2 process showed a 'dampening' effect. Therefore, these two paradoxical neural effects of prediction, which have provoked wide confusion in accounting for expectation suppression, actually co-exist in the procedure of timing prediction but work in separate time windows. These findings strongly support a recently-proposed opposing process theory.

Visible-light-induced nitrogen photofixation ability of g-C3N4 nanosheets decorated with MgO nanoparticles

Visible-light-induced nitrogen photofixation ability of g-C3N4 nanosheets decorated with MgO nanoparticles

N2 Gas-Flushing Prevents Bacteria-Promoted Lipolysis and Proteolysis and Alleviates Auto-Oxidation in Bovine Raw Milk During Cold-Storage

Worldwide, tremendous amounts of food, including milk and dairy products, are lost or wasted. Although refrigeration permits longer storage of raw milk, low temperatures still do not prevent the action of other abiotic and biotic factors that promote biochemical, chemical, microbial, sensorial and nutritional changes in raw milk, which also affect milk-derived dairy products. Treatment by N2 gas flushing showed great potential in preserving the microbiological quality of raw milk during storage at low and milder temperatures. Here, we examined the impact of cold storage (at 6°C up to 7 days), on the ascorbic acid content, extent of auto-oxidation, and on levels of lipolysis and proteolysis along with bacterial growth, in three raw milk samples in the presence or absence of N2. When N2 gas was applied, lower levels of lipolysis and proteolysis were found to coincide with the detection of lower numbers of bacterial lipase and protease producers in raw milk. Furthermore, lower auto-oxidation was detected in N2-treated samples than in only cold stored controls. By demonstrating that key components of milk were better preserved during cold storage, the present study further highlights the advantages of the N2 flushing treatment in terms of preserving the quality and safety of raw milk and its derived dairy products.

Fluorescence Based Investigation of Temperature-Dependent Pb2+-Specific 8-17E DNAzyme Catalytic Sensor.

The 8-17E DNAzyme is a temperature-dependent DNA metalloenzyme catalyzing RNA trans esterification in the presence of Pb2+ metal ions. Labeling the stems of the substrate and DNAzyme with the Cy3 and Cy5 respectively, the considered DNAzyme was studied by the fluorescence spectroscopy. The temperature-dependent variability of the Pb2+-specific 8-17E DNAzyme catalytic sensor was investigated trough a number of successive temperature fluctuations from 4 to 25°C to obtain information. Investigating underlined biochemical system reveals that in this sensor, free single strands Enzyme (Cy5-E) and Substrate (Cy3-S) have higher fluorescence intensities than hybridized forms, suggesting that the fluorophores are in a contact quenched. Increasing the temperature has three effects: 1) Fluorescence intensities for the free fluorophores were reduced, 2) stability of the hybridized form was reduced and cleavage of substrate in presence of Pb2+was occurred, and 3) conformation of ES hybridized form was changed (before cleavage). As a result of conformation changes in ES, S was more affected than E in the ES. Pb2+ ion shows quenching effect on both fluorophores and in the absence of N2(g) purge the effect was more considerable. A main goal that we had in mind was to find if significantly lower concentrations of Pb2+ and ES, compared to previous reports, can generate any observable cleavage in substrate. Analysis of the cleavage reaction for 50nM ES indicates that S is cleaved at 25°C in presence of N2(g) and 0.5μM Pb2+, while in same condition no apparent change occurs in the 4 or 10°C. The rapid, sensitive and low cost strategy presented here can be applicable to study temperature-dependent behavior of other nucleic acid-based biosensors.

Poly-β-hydroxybutyrate Production by Methylosinus trichosporium OB3b at Different Gas-phase Conditions.

BackgroundThe utilization of methane for production of Poly-β-hydroxybutyrate (PHB) not only cuts the emissions of greenhouse gases but also greatly reduces PHB production cost.ObjectivesThe aim of this study was to determine the effects of gas-phase conditions on PHB production by Methylosinus trichosporium OB3b.Materials and MethodsBacterial cultivation and PHB production were conducted in a series of sealed serum bottles. Nitrogen-free mineral salts medium was used to induce PHB production in the presence or absence of N2 in the headspace.ResultsIn the absence of N2, the highest PHB content (i.e., 52.9% of the dry cell weight with a PHB concentration of 814.3 mg.L-1) was obtained at a ratio of CH4:O2=2:1. Further study at different O2 concentrations with a fixed CH4 partial pressure in absence of N2 showed that PHB accumulation by methanotroph could be tolerated high oxygen partial pressure and its respond to the variation of the oxygen concentration depends on the methane partial pressure. In presence of N2, with headspace gas replenished only when oxygen was almost depleted, the degradation of intracellular PHB has appeared. In the regimen of updating headspace gas at the point when the PHB content began to decrease, the highest PHB content (i.e., 55.5% of the dry cell weight with 901.8 mg.L-1 PHB concentration and 12.5 mg.L-1.h-1PHB productivity) was obtained at 0.2 atm O2 and PHB accumulation was depressed with an oxygen concentration greater than 0.3 atm.ConclusionsThe methanotroph responses differentially to the increase in the oxygen partial pressure with regard to PHB accumulation either in the presence or in the absence of N2.

Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters

Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters

Analysis of Styrene Polymerization Without Surfactant and N2 Gas in Cylindrical Flask.

The conditions of chemical synthesis can be crucial for polymerization of styrene in such a way that it can be produced latex beads at nanometric range (ϕ < 400nm). In this work, it will be analyzed how the absence of N2 and surfactant will result in colloidal particles with high affinity to agglomerate forming two kinds of nanostructured assemblies: colloidal crystals and nanowires. Four syntheses were realized and four parameters were changed: temperature, impeller speed, and initiator and styrene concentrations. The dispersion was filtered and coated on glass slides by evaporation induced self-assembly (EISA) process. Morphology and topography were observed at Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM) respectively. They show how the synthesis conditions play a vital a role on the formation of self assembly nanostructures that can be applied as templates for sensors and biomaterials devices.

Mechanism of N2 Reduction Catalyzed by Fe-Nitrogenase Involves Reductive Elimination of H2.

Of the three forms of nitrogenase (Mo-nitrogenase, V-nitrogenase, and Fe-nitrogenase), Fe-nitrogenase has the poorest ratio of N2 reduction relative to H2 evolution. Recent work on the Mo-nitrogenase has revealed that reductive elimination of two bridging Fe-H-Fe hydrides on the active site FeMo-cofactor to yield H2 is a key feature in the N2 reduction mechanism. The N2 reduction mechanism for the Fe-nitrogenase active site FeFe-cofactor was unknown. Here, we have purified both component proteins of the Fe-nitrogenase system, the electron-delivery Fe protein (AnfH) plus the catalytic FeFe protein (AnfDGK), and established its mechanism of N2 reduction. Inductively coupled plasma optical emission spectroscopy and mass spectrometry show that the FeFe protein component does not contain significant amounts of Mo or V, thus ruling out a requirement of these metals for N2 reduction. The fully functioning Fe-nitrogenase system was found to have specific activities for N2 reduction (1 atm) of 181 ± 5 nmol NH3 min-1 mg-1 FeFe protein, for proton reduction (in the absence of N2) of 1085 ± 41 nmol H2 min-1 mg-1 FeFe protein, and for acetylene reduction (0.3 atm) of 306 ± 3 nmol C2H4 min-1 mg-1 FeFe protein. Under turnover conditions, N2 reduction is inhibited by H2 and the enzyme catalyzes the formation of HD when presented with N2 and D2. These observations are explained by the accumulation of four reducing equivalents as two metal-bound hydrides and two protons at the FeFe-cofactor, with activation for N2 reduction occurring by reductive elimination of H2.

Prevention of intestinal ischemia-reperfusion injury in humanized mice

Prevention of intestinal ischemia-reperfusion injury in humanized mice

Formation pathway, structural characterization and optimum processing parameters of synthetic topaz – Al2SiO4(OH,F)2 – by CVD

Formation pathway, structural characterization and optimum processing parameters of synthetic topaz – Al2SiO4(OH,F)2 – by CVD

Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration for Differentiating N0 Versus N1 Lung Cancer

Endobronchial Ultrasound-Guided Transbronchial Needle Aspiration for Differentiating N0 Versus N1 Lung Cancer

Metabolic Pathways for Photobiological Hydrogen Production by Nitrogenase- and Hydrogenase-containing Unicellular Cyanobacteria Cyanothece

Current biotechnological interest in nitrogen-fixing cyanobacteria stems from their robust respiration and capacity to produce hydrogen. Here we quantify both dark- and light-induced H(2) effluxes by Cyanothece sp. Miami BG 043511 and establish their respective origins. Dark, anoxic H(2) production occurs via hydrogenase utilizing reductant from glycolytic catabolism of carbohydrates (autofermentation). Photo-H(2) is shown to occur via nitrogenase and requires illumination of PSI, whereas production of O(2) by co-illumination of PSII is inhibitory to nitrogenase above a threshold pO(2). Carbohydrate also serves as the major source of reductant for the PSI pathway mediated via nonphotochemical reduction of the plastoquinone pool by NADH dehydrogenases type-1 and type-2 (NDH-1 and NDH-2). Redirection of this reductant flux exclusively through the proton-coupled NDH-1 by inhibition of NDH-2 with flavone increases the photo-H(2) production rate by 2-fold (at the expense of the dark-H(2) rate), due to production of additional ATP (via the proton gradient). Comparison of photobiological hydrogen rates, yields, and energy conversion efficiencies reveals opportunities for improvement.

Effects of O2–CO2 polarization beating on femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy of O2

Femtosecond coherent anti-Stokes Raman scattering (fs-CARS) spectroscopy has recently emerged as a promising laser-based temperature-measurement technique in flames. In fs-CARS, the broad spectral bandwidths of the pump and Stokes lasers permit the coupling of each ro-vibrational Raman transition via a large number of pump-Stokes photon pairs, creating a strong Raman coherence. However, the broad-bandwidth fs pulses also excite other molecular transitions that are in resonance. The polarization beating between these closely spaced Raman transitions can affect the coherence dephasing rate of the target molecule, making it difficult to extract accurate medium temperature. In a previous study our group investigated N2/CO polarization beating in N2 fs-CARS; in the present work we study O2/CO2 polarization beating in O2 fs-CARS. O2 fs-CARS can be particularly important for thermometry in non-air-breathing combustion in the absence of N2. The effects of O2/CO2 polarization beating are investigated in the temperature range 300–900 K at atmospheric pressure and also at 300 K for pressures up to 10 bar. Unlike in the N2/CO system, it was observed in the O2/CO2 system that the presence of CO2 can significantly alter the time evolution of the Raman coherence and, hence, affect the measured temperature.

Metal−Metal Multiple Bonds in Early/Late Heterobimetallics Support Unusual Trigonal Monopyramidal Geometries at both Zr and Co

Reduction of Zr/Co heterobimetallic complexes ICo(MesNP(i)Pr(2))(3)ZrCl (1) and ICo((i)PrNP(i)Pr(2))(3)ZrCl (2) with excess Na/Hg under N(2), followed by subsequent benzene extraction to remove coordinated Na halide salts, leads to neutral two-electron reduced, dinitrogen-bound complexes (THF)Zr(MesNP(i)Pr(2))(3)Co-N(2) (4) and Zr((i)PrNP(i)Pr(2))(3)Co-N(2) (5). Upon halide loss, a THF solvent molecule coordinates to the axial site of the Zr center in 4, while this axial site remains unoccupied in 5. X-ray crystallography reveals short Co-Zr distances in 4 and 5, indicative of metal-metal multiple bonding, and an unprecedented trigonal monopyramidal geometry about the Zr center in 5. Reduction of 4 under an Ar atmosphere (in the absence of N(2)) results in another unusual structure type: an unoccupied axial Co coordination site and a trigonal monopyramidal Co center in (THF)Zr(MesNP(i)Pr(2))(3)Co (6). X-ray crystallography reveals that, in the absence of coordinated N(2), the Co-Zr bond can attain full triple bond character with a Co-Zr distance of 2.14 A, the shortest M-M distance in an early/late heterobimetallic complex reported to date. To further assess the electronic structure and bonding in 4, 5, and 6, calculations were performed on these molecules using DFT and the results of these theoretical investigations will be discussed.

CO Formation in the 254 nm Gas Phase Photolysis of Nitrosobenzene-Oxygen Mixtures at Room Temperature

Abstract Large CO yields were detected in the gas phase photolysis of nitrosobenzene at 254 nm in the presence of O2 and N2 by long-path IR absorption in a 200 L photoreactor made of quartz. CO yields were measured at 298 K for partial pressures of O2 between 1 μbar and 1 bar and total pressures from 10 μbar to 1 bar. Depending on reaction conditions, the CO yield varied between ≤ 1 % (at p N2 = 1 bar, p O2 ≤ 120 μbar) and ≈ 100 % (for pO2 = 20 μbar, p N2 = 0). The dependencies of the CO yield (i) from the O2 partial pressure in O2-N2-mixtures at a total pressure of 1 bar, (ii) from the O2 pressure in the absence of N2, and (iii) from the total pressure at constant O2 pressures show very different behaviour. They can be reproduced well by a mechanism involving vibrationally excited phenyl (C6H5*), phenylperoxy (C6H5O2*) and phenoxyl (C6H5O*) radicals where collisional relaxation of the excited radicals competes with O2 addition for C6H5* and with both unimolecular decomposition and reaction with O2 for C6H5O2* and/or C6H5O*. The measured CO yields allow to select reaction conditions where nearly exclusively either highly vibrationally excited C6H5, C6H5O2 and/or C6H5O radicals (for CO yields ≈ 1) or thermally distributed C6H5, C6H5O2 and/or C6H5O radicals (for CO yields ≤ 1 %) are formed.