When an argument is the content: Rational number comprehension through conversions across registers

This article reframes previously identified misconceptions about repeating decimals by describing these misconceptions as limited understandings of how mathematics concepts are referenced. In particular, misconceptions about repeating decimals and their quotient of integer representations are recast as limited understandings of mathematics as a discipline that derives its content from representational systems and the denotations they provided. Under this framework, arguments (e.g., proofs) that convert repeating decimals to their quotient of integer representations provide content for “rational number,” which is represented in multiple ways, each offering distinct opportunities for mathematical activity. The notion of an argument as content is illustrated as arguments providing access to a concept. One Grade 8 student’s struggle with understanding rational number is used to illustrate this framework and its implications for teaching and learning.     

Enhancement of the molecular nitrogen dissociation and ionization levels by argon mixture in flue nitrogen plasma

In this work, the nitrogen molecular dissociation and ionization levels in Ar/N₂ flue plasma are evaluated as functions of plasma parameters such as Ar mixture quantity and N₂ flux in order to obtain the best condition for various applications such as thin film deposition and material surface modification. This plasma is operated at 10 kV and the nitrogen dissociation rate is determined by analyzing the optical emission of the nitrogen band. For different operating conditions, the dissociation rate [N] of N₂ molecules was enhanced, as the mixture quantity of Ar increased from 0.06 m³/h to 0.9 m³/h and the max of enhancement factor is 4.3. This factor becomes bigger when the N₂ flux becomes bigger. Moreover, the molecular nitrogen ionization density is calculated from the current intensity of the plasma. The ionization density was also enhanced, as the mixture quantity of Ar increased from 0.1 m³/h to 1.5 m³/h, under three different voltages. The max of enhancement factor of 1.96 is much smaller than the factor of the dissociation rate. These results are discussed in terms of the kinetics of the electrons, nitrogen ions, atoms and molecules.     

反相高效液相色谱法测定维格列汀

建立反相高效液相色谱法测定维格列汀的含量。采用Venusil MP C18色谱柱（250mm×4.6mm,5μm）,流动相为磷酸盐缓冲溶液(称取20mmol·L^-1磷酸二氢钾,用85%浓磷酸调至pH3.0)-乙腈（88:12,V/V）,检测波长为210nm,流速为1.0mL·min^-1,柱温为25℃。维格列汀在5—500μg·mL^-1范围内与峰面积呈良好的线性关系（r=0.9999）,维格列汀的平均回收率为102.0%,RSD为2.65%。方法准确、简便,适用于维格列汀的定量分析。     

Structures and stability of N9, N9 − and N9 + clusters

 Ab initio molecular orbital calculations for N₉, N⁻ ₉ and N⁺ ₉ isomers were carried out at the HF/ 6-31G*, B3PW91/6-31G*, B3LYP/6-31G* and MP2/ 6-31G* levels of theory. Stable equilibrium geometric structures were determined by harmonic vibrational frequency analyses at the HF/6-31G*, B3PW91/6-31G* and B3LYP/6-31G* levels of theory. The most stable free-radical N₉ cluster is structure 1 with C _{2 v} symmetry and that of anion N⁻ ₉ is structure 3 with C _s symmetry. Only one stable structure of the N⁺ ₉ cation with C _{2 v} symmetry was predicted. Their potential application as high-energy-density materials has been examined. Received: 15 June 1999 / Accepted: 11 October 1999 / Published online: 14 March 2000     

CVD synthesis of nitrogen doped carbon nanotubes using ferrocene/aniline mixtures

Nitrogen doped carbon nanotubes (N-CNTs) have been synthesized by the chemical vapour deposition (CVD) floating catalyst method using either 4-ferrocenylaniline or mixtures of varying concentrations of ferrocene/aniline together with toluene as added carbon source. The N-CNTs produced are less stable (thermal gravimetric analysis measurements), less graphitic and more disordered (transmission electron microscope measurements) than their undoped counterparts. The ratio of the Raman D- and G-band intensities increase with the nitrogen concentration used during the CNT growth. Furthermore, the transmission electron microscope (TEM) studies reveal that the CNTs are multi-walled (MW), and that the diameters of the N-MWCNTs can be controlled by systematically varying the concentrations of the nitrogen source. The TEM analysis also revealed that when ferrocenylaniline and ferrocene/aniline reactions are compared at similar Fe/N ratios, higher N doping levels are achieved (ca. 2-5×) when ferrocenylaniline is the catalyst.     

Monitoring of NO2 in the ambient air with passive samplers before and after a road reconstruction event

Nitrogen dioxide (NO₂) concentrations were used to evaluate the air quality before and after the infrastructural change of an important traffic artery in Mortsel, Antwerp (Belgium). During the reconstruction works two pairs of traffic lanes were reduced to one in each direction. Two sampling campaigns were conducted: the first one before the works in 2003 and the second one in 2005, after the road works were finished. Sampling was performed on a weekly base with the use of passive diffusion tubes on the streets, and also indoors in nearby houses. The samples were analyzed by ion chromatography, from which data the NO₂ concentrations in air could be calculated. These results were compared with NO₂ values from the air monitoring station 42R801 of the Flemish Environment Agency in Borgerhout, Antwerp. On the base of different NO₂ concentrations, correlated well with the traffic density, sampling locations were classified into three groups as follows: 1) ‘heavily polluted’ (heavy traffic); 2) ‘moderately polluted’ (medium traffic); or 3) ‘less polluted’ (low traffic density). Sampling sites located further from the road works, enclosed to the group ‘less polluted’, showed the lowest NO₂ concentrations. The highest NO₂ level was found for the locations close to reconstruction works, which belonged to the group ‘heavily polluted’. The contribution of NO₂ was at the same level before and after the road works. During the first campaign it ranged from 30 ± 7 µg/m³ to 71 ± 11 µg/m³ and during the second sampling it was between 36 ± 17 µg/m³ and 73 ± 17 µg/m³. These modernization works had no impact on preventing the traffic-related pollutant as NO₂ and as a consequence no significant effect on the air quality in the studied region. It has been proven that the impact of traffic on the air quality is unmistakably high and simply reduction of the number of the traffic lanes, intended to discourage the traffic flow, had apparently no environmentally advantageous effect.     

Electrosynthesis of α-Amino Acids from NO and other NOx species over CoFe alloy-decorated Self-standing Carbon Fiber Membranes

The conversion of industrial exhaust gases of nitrogen oxides into high-value products is significantly meaningful for global environment and human health. And green synthesis of amino acids is vital for biomedical research and sustainable development of mankind. Herein, we demonstrate an innovative approach for converting nitric oxide (NO) to a series of α-amino acids (over 13 kinds) through electrosynthesis with α-keto acids over self-standing carbon fiber membrane with CoFe alloy. The essential leucine exhibits a high yield of 115.4 μmol h⁻¹ corresponding a Faradaic efficiency of 32.4 %, and gram yield of products can be obtained within 24 hours in lab as well as an ultra-long stability (>240 h) of the membrane catalyst, which could convert NO into NH₂OH rapidly attacking α-keto acid and subsequent hydrogenation to form amino acid. In addition, this method is also suitable for other nitrogen sources including gaseous NO₂ or liquidus NO₃⁻ and NO₂⁻. Therefore, this work not only presents promising prospects for converting nitrogen oxides from exhaust gas and nitrate-laden waste water into high-value products, but also has significant implications for synthetizing amino acids in biomedical and catalytic science.     

Molybdenum-catalyzed reduction of molecular dinitrogen into ammonia under ambient reaction conditions

Synthesis of transition metal–dinitrogen complexes and stoichiometric transformations of their coordinated dinitrogen into ammonia and hydrazine have so far been well investigated in order to achieve a novel nitrogen fixation under ambient conditions. As an extension of our study, the dimolybdenum–dinitrogen complex bearing PNP pincer ligands has been found to work as an effective catalyst for the formation of ammonia from dinitrogen, where 52 equiv of ammonia are produced based on the catalyst (26 equiv of ammonia are produced based on the molybdenum atom of the catalyst). This is the most effective catalytic reaction system for the formation of ammonia from molecular dinitrogen catalyzed by transition metal–dinitrogen complexes as catalysts under ambient reaction conditions. Herein, we describe recent results concerning the catalytic reaction, including the proposed reaction pathway.     

Preparation and spectroscopic characterization of visible light sensitized N doped TiO2 (rutile)

Nitrogen doped TiO₂ represents one of the most promising material for photocatalitic degradation of environmental pollutants with visible light. However, at present, a great deal of activity is devoted to the anatase polymorph while few data about rutile are available. In the present paper we report an experimental characterization of N doped polycrystalline rutile TiO₂ prepared via sol-gel synthesis. Nitrogen doping does not affect the valence band to conduction band separation but, generates intra band gap localized states which are responsible of the on set of visible light absorption. The intra band gap states correspond to a nitrogen containing defect similar but not coincident with that recently reported for N doped anatase.     

Influence of the Excited States of Atomic Nitrogen N(<Superscript>2</Superscript>D) and N(<Superscript>2</Superscript>P) on the Transport Properties of Nitrogen. Part I: Atomic Nitrogen Properties

In this paper, calculated values of the viscosity and thermal conductivity of atomic nitrogen, taking into account three species (the ground and two excited states), are presented. The calculations, which assume that the temperature dependent probability of occupation of the states is given by the Boltzmann factor, are performed for atmospheric-pressure in the temperature range from 1,000 to 20,000 K. Six collision integrals are used in calculating the transport coefficients and we have introduced new averaged collision integrals where the weight associated at each interacting species pair is the probable collision frequency. The influence of the collision integral values and energy transfer between two different species is studied. These results are compared which those of published theoretical studies.