A model of the chemical composition and pyrolysis kinetics of lignin

This study presents a novel approach for the chemical representation of lignin for modelling the reaction kinetics of lignin in lignocellulosic biomass. This methodology relies on the definition of dimeric pseudo-components containing phenolic functionalities, i.e., p-hydroxyphenyl, guaiacyl and syringyl groups, as measured in real biomass and native lignin through wet chemistry and spectroscopic techniques. The reactivities of the lignin pseudo-components are modelled through a series of lumped unidirectional reactions, whose product formation and reaction rate constants are optimised to replicate a comprehensive experimental dataset gathered from several works available in the literature. The new kinetic model contributes to the state-of-the-art by providing a more accurate depiction of the conversion rates, selectivity of char vs. volatiles, and aromatic composition in condensable products in line with the inherent reactivity of lignin functionalities and the empirical observations of lignin depolymerisation and thermal degradation at low (<1?K/s) and high heating rates (>50?K/s).     

Timelike surfaces in the de Sitter space $$\mathbb S_1^3(1)\subset {{\mathbb R}_{1}^{4}}$$ S 1 3 ( 1 ) ⊂ R 1 4

Annals of Global Analysis and Geometry - This paper studies timelike minimal surfaces in the De Sitter space $$\mathbb S^3_1(1) \subset \mathbb R^4_1$$ via a complex variable. Using complex...     

Behavior of spherical solid particles released in a laminar boundary layer along a flat plate

The behavior of a very small solid spherical particle initially at rest on the surface of a flat plate in a laminar boundary layer along the plate is investigated. The Stokes drag is the only force considered to be acting on the particle. The fluid Reynolds number Re _f is assumed to be large, and the particle Reynolds number Re is assumed to be small. The equations describing the motion of the particle are two simultaneous, second order, nonlinear, ordinary differential equations with one parameter. A complete digital computer solution and analytic limiting solutions for large and small values of a dimensionless time have been obtained. The numerical and the analytic solutions are in close agreement. The results presented are the velocity, trajectory, and time history of the particle and the force acting on the particle. These results show that the particle comes into equilibrium with the fluid very quickly with respect to the spatial coordinates, rising only several radii from the surface in its entire flight.Nomenclature a diameter of the particle - F force acting on the particle - F ₁ lift force - F _M Magnus force - i, j unit vectors parallel and perpendicular to the plate, respectively - Re = u a ^–1 Reynolds number for the particle based on the reference fluid velocity - Re _f = u x ₀ ^–1, Reynolds number for the fluid - Re _p |w _f –w | a ^–1, Reynolds number for the particle - t time - u component of particle velocity parallel to the plate - u _f component of fluid velocity parallel to the plate - u free-stream fluid velocity - U , dimensionless component of particle velocity parallel to the plate - U _f Re _f Re ^–1 u ^–1 U _f, dimensionless component of fluid velocity parallel to the plate - v component of particle velocity perpendicular to the plate - v _f component of fluid velocity perpendicular to the plate - V , dimensionless component of particle velocity perpendicular to the plate - V _f Re _f ^3/2 Re ^–2 u v _f, dimensionless component of fluid velocity perpendicular to the plate - w u i+v j, velocity of the particle - w _f u _f i+v _f j, velocity of the fluid - w dw/dt - x horizontal distance of the center of the particle from the leading edge of the plate - x ₀ initial horizontal distance of the center of the particle from the leading edge of the plate - X xx ₀ ^–1 , dimensionless horizontal distance of the center of the particle from the leading edge of the plate - y vertical distance of the center of the particle from the plate - Y ya ^–1, dimensionless vertical distance of the center of the particle from the plate - ^–1 - 0.332 - Re Re _f ^–3/2 - - - viscosity of the fluid - _f ^–1 , kinematic viscosity of the fluid - _f density of the fluid - _p density of the particle - , dimensionless time - angular velocity of the particle     

Structural,optical and morphological properties of Ga1−xMnxAs thin films deposited by magnetron sputtering for spintronic device applications

In this work, GaMnAs alloy materials were deposited on 7059 Corning glass and GaAs (1 0 0) substrates via RF magnetron sputtering technique. A concentration of Mn about 0.28 was obtained by Energy Dispersive X-ray spectroscopy. The substrate temperature was changed from 440 to 520 °C and layer thicknesses between 172 and 514 nm were obtained. Characterization by atomic force microscopy and X-ray diffraction were performed to determinate surface morphology and crystal structure, respectively. From transmittance spectral measurements we were able to determine optical constants: band gap energy (E_g), absorption coefficient (α), and refraction index (n). A correlation between morphological properties and substrate type was also studied. Diluted magnetic semiconductors like GaMnAs are considered among promising materials for the development of new spin-electronic devices.