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The self-made KOH together with NH4OH pulping of corn stover was investigated. The combined alkaline system could effectively remove lignin during pulping. There are three stages of lignin removal during delginification. Approximately 90% of lignin could be removed after temperature reached 150ºC for over 30 minutes. The p-hydroxyl phenol groups in lignin could be completely removed during the delignification reaction. The tendency of the increase of the crystalline degree of cellulose is observed with increase of reaction temperature. The kinetics of delignification is found to be the first order with respect to the remained lignin and the 0.4 order with respect to the remained hydroxide concentration. The activation energy of delignification is 23 kJ/mol. The solution obtained from precipitation of lignin is rich in nitrogen, phosphorous, potassium elements and organic matters. Various techniques including FT-IR, GPC, DSC, were applied to characterize the acid precipitated lignin. The result shows that the lignin with the polydispersity of 1.4 still maintains the p-coumaryl, coniferyl, and sinapyl units in its matrix.

Using the self-consistent density functional method, we investigate the structural and electronic properties of cubic [Hf.sub.3][N.sub.4] with [Th.sub.3][P.sub.4] structure at ambient and high pressures. The lattice parameters, cell volume, bulk modulus, and pressure derivative at ambient pressure are obtained, which are in excellent agreement with the available measurements. The change of bond lengths for two different types of Hf-N bond with pressure suggests that the tetrahedral Hf-N bond is slightly less compressible than the octahedral ones, which agree well with the [Zr.sub.3][N.sub.4] and [Zn.sub.3][N.sub.2] results. The band gap pressure coefficient for c-[Hf.sub.3][N.sub.4] are fitted, which are 8.5 x [10.sup.-2] eV/GPa and -7.0 x [10.sup.-5] eV/[(GPa).sup.2], respectively. Based on the density of states analysis, band structure suggests that the investigated material can be used as a semiconductor optical material. Mulliken population analysis shows that the charge density of the Hf atom is less sensitive to pressure variation than that of the N atom. At last, the defect formation enthalpies of the cubic [Hf.sub.3][N.sub.4] are calculated. PACS Nos.: 62.50.-p, 71.15.Mb, 73.20.At. L'utilisation de la methode de la fonctionnelle de densite auto-coherente nous permet d'etudier les proprietes structurelles et electroniques du [Hf.sub.3][N.sub.4] cubique avec la structure [Th.sub.3][P.sub.4] a pression ambiante et haute. Nous obtenons les parametres du reseau, le volume de la cellule, le module de compression volumique et la derivee de la pression, le tout a pression ambiante et ces resultats sont en excellent accord avec les mesures disponibles. La variation avec la pression de la longueur de lien entre deux liens Hf-N differents suggere que le lien Hf-N tetraedrique est legerement moins compressible que l'octaedrique, ce qui agree avec les resultats pour [Zr.sub.3][N.sub.4] et [Zr.sub.3][N.sub.2]. Les coefficients de pression de la bande interdite de c-[Hf.sub.3][N.sub.4] sont alors ajustes numeriquement: 8.5 x [10.sup.-2] eV/GPa et -7.0 x [10.sup.-5] eV/GPa respectivement. Sur la base de l'analyse de la densite d'etats, la structure de bande suggere que ce materiau peut etre utilise comme semi-conducteur optique. L'analyse des charges de Mulliken montre que la densite de charge de l'atome Hf est moins sensible aux variations de pression que celle de l'atome N. Finalement, nous calculons l'enthalpie de formation de defauts dans [Hf.sub.3][N.sub.4] cubique. [Traduit par la Redaction], 1. Introduction Nitrides of transition metals that are used as hard materials have attracted great interest because of their high elastic moduli, ultrahardness, high melting points, and superconductivity [1-5]. Novel [...]

A microstrip-fed semi-elliptical dipole antenna (MFSEDA) is proposed and designed for ultrawideband (UWB) communications. The antenna has large bandwidth covering the frequency band from 3.1 to 10.6 GHz, radiation patterns similar to those of a conventional dipole antenna, and small size with the dimension of only about one third of the wavelength instead of half wavelength for the lower frequency. With simple and proper modification of the radiation patches, a frequency-notched antenna based on the MFSEDA is also designed and good band-notched performance from 5.0 to 6.0 GHz can be obtained. Measured results show that these MFSEDAs are suitable for UWB applications due to their high performances. Index Terms--Band-notched antenna, planar elliptical antenna, ultrawideband (UWB) antenna.

To explore the characteristics of the evolution of water resources in the Yellow River Basin, information entropy, CEEMDAN, and Copula theories are used to study the temporal and spatial evolution of precipitation in the Yellow River Basin from 1960 to 2017. It is found that, ① In the past 50 years, the precipitation in the Yellow River Basin as a whole has shown a downward trend, but the precipitation in the source area is increasing slowly; ② After 2002, the Spatiotemporal information entropy of precipitation in the Yellow River Basin declined and complexity decreased. ③ CEEMDAN decomposition results show that the observation and research on precipitation in the Yellow River Basin should be mainly focused on the short cycle of 2~4 years, RES balance reflects the overall decline of precipitation sequence but gradually recovered in recent years; ④ Through the Gumbel-Copula function, it is found that the combined distribution of annual and flood season precipitation in the Yellow River Basin at different stages is mainly abundant and dry, and the probability of synchronization increases after the mutation. This paper studies the spatiotemporal characteristics of precipitation in the Yellow River Basin at different stages, which helps to further understand and grasp the characteristics of the water circulation in the Yellow River Basin, and then provide support for the ecological protection and high-quality development of the Yellow River Basin. [ABSTRACT FROM AUTHOR]

Using molecular dynamics simulations combined with the embedded atom method potential, we investigate the heating, cooling, and energetic reacting of core-shell structured Al-Cu nanoparticles. The thermodynamic properties and structure evolution during continuous heating and cooling processes are also investigated through the characterization of the total potential energy distribution, mean-square-distance and radial distribution function. Some behaviors related to nanometer scale Cu/Al functional particles are derived that two-way diffusion of Al and Cu atoms, glass phase formation for the fast cooling rate, and the crystal phase formation for the low cooling rate. Two-way atomic diffusion occurs first and causes the melting and alloying. In the final alloying structure, Cu and Al atoms mixed very well except for the outmost shell which has more Al atoms. For the investigation of the thermal stability and energetic reaction properties, our study show that a localized alloying reaction between the Al core and Cu shell is very slow when the initial temperature is lower than 600 K. But a two-stage reaction may occur when the initial temperature is 700 K. The reaction rate is determined by the solid-state diffusion of Al atoms in the Cu shell at the first stage, yet the reaction rate is much faster at the second stage, due to the alloying reaction between the liquid Al core and the Cu shell. At higher temperatures such as 800 K and 900 K, the alloying reaction occurs directly between the liquid Al core and the Cu shell. [ABSTRACT FROM AUTHOR]