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The paper presents a review of mathematical models used in economic analysis of environmental problems. This area of research combines macroeconomic models of growth, as dependent on capital, labour, resources etc., with environmental models describing such phenomena like natural resources exhaustion or pollution accumulation and degradation. In simpler cases the models can be treated analytically...
Feedforward neural networks are usually used for functions approximation [1]. This feature of such a class of networks is explained in the paper by Cybenko [2]. In literature we can find many different application of neural networks as universal approximators [3], [4]. It seems that one of the most interesting application (not trivial at all example) of neural networks is the reconstruction of attractors...
Thermal stabilizing effect of sugars on freeze-dried proteins is studied remarking the reaction between the stabilizing effect and the degree of crystallinity of sugars. It is found that thermal stabilizing effect is higher when sugar is amorphous than crystalline. This thermal stabilizing effect is closely related to hydrogen bond between sugar molecules and proteins. It is also found that except...
Investigation of the diffusion process taking place during removal of ethanol as a primary solvent from silica alcogel structure with near-critical carbon dioxide as a secondary solvent is presented. The investigation was conducted with two methods following this unsteady-state drying process. In the first method advantage was taken of the phenomenon of partial internal sample destruction during the...
It is demonstrated that different pore structures and morphologies in nanometer scales may be obtained using different strategies of drying of wet gels produced by the sol-gel method. The low temperature drying strategy (LTD), using supercritical carbon dioxide, gives similar nanopore structure as the high temperature supercritical drying (HTD) yet different morphology. Both methods lead to suppression...
Timber boards cut from a single stem of juvenile softwood are noted for their variable density. The effectiveness of presorting freshly sawn timber by green density is investigated to determine when the moisture uniformity of the kiln-dried boards can be improved. High-density timber is found to be primarily responsible for this moisture variation. By sorting timber into low and highdensity groups,...
The extensive experimental trials on the spray drying kinetics involving "in situ" analysis of the properties of continuous and dispersed phases from atomization to collection of dry product were performed. To accomplish this task a six meter long concurrent spray drying tower was designed, built and tested. Sophisticated experimental techniques (including laser techniques) to determine...
Direct heating of a material via flame jet impingement has several advantages over other means of heating. Flame impingement heating is used commonly in glass and metal processing. Flame heating can be extended to drying of various moist porous materials. However, in industrial heating/drying processes a uniform, clean, and stable impingement flame is desired. The radial jet reattachment combustion...
The difference of the mechanism to yield either dense or hollow particles may be caused rather at the stage prior to decomposition in the sequential steps because any structural change is not possible except for stress-induced strain and crack once a solid is formed. The stage of solidification and drying of the droplets plays an important role to determine the structure of the final particles in...
The economic basis of the optimisation of timber drying schedules for hardwood timber has been studied, in which costs due to leakage, humidification, venting, fan power, heat loses from the shell, drying, and heating of the wood and air have been considered. Heat losses and other energy-related losses are a small component of the costs compared with the added value of the timber, so the use of higher...
Two modifications of aluminium oxide [formulas] are analyzed in respect to their porous structure, single-particle drying kinetics and fluidized bed drying kinetics. The impact of structure is discussed phenomenologically and quantified in terms of hygroscopity and by means of appropriate normalization. Known fluidized bed models provide a successful link between single particle and fluid bed.
We present a mathematical model of the one dimensional, one-region hyperbolic plane moving boundary problem with Dirichlet boundary conditions. The model is adequate for the vacuum freeze drying at radiative heating and to vacuum freeze drying of disordered porous media e.g. biomaterials, pharmaceuticals, food etc. The model takes into account finite speed of thermal wave propagation allowing the...
This work presents thermodynamic criteria for optimization of work-assisted drying operations and compares these criteria with those conventional drying operations in sequential systems. For the work-assisted operations, which run jointly with thermal machines, such as heat pumps, total power input is minimized at constrains which describe dynamics of energy and mass exchange. Finite-rate models take...
A computational study was performed to predict the drying performance of a novel two-dimensional impinging stream dryer using superheated steam as the drying medium. The dryer is basically a flash dryer consisting of an opposing jet configuration. Assuming constant rate period drying kinetics, the drying behaviour of superheated steam-particle mixtures flowing in a turbulent two-phase flow is modelled...
In this work the effective diffusivity of Won clay was obtained by considering the mass transfer mechanisms ocurring in the pores and on the surface. The binary friction model was used to evaluate the effective gas diffusivity and the Maxwell-Stefan approach to mass transfer was applied to the surface diffusion. Different expressions for the effective diffusivity for porous solids were used considering...
Two network types are proposed for modelling a drying process in the vibrofluidized bed, namely multilayer perceptron network and radial basis function network. Network training procedures are based on experimental data obtained for silica gel, green peas, potatoes and cabbage. Capability of prediction of MLP and RBF networks are evaluated in a feed forward and recurrent structures.
During the drying process the flow rate of the drying air through a packed bed is a very important factor. In this paper the relation between the pressure difference and the flow rate is studied. Both theoretical and experimental approaches are discussed.
The convective heat and mass transfer coefficients for salt crystals dried in a vibrated fluid bed dryer were determined experimentally at various air velocities, frequecies of grid vibration, and static bed heights. The experimental data were correlated in terms of the Nusselt and Sherwood numbers as functions of the particle Reynolds number, bed geometry and vibration intensity. It is shown that...
In this paper the self-similarity of a multinomial measure is investigated and the impact of multifractal spectrum on queueing analysis results is discussed. The conclusion is that, in general, coarse grained multinomial measures are not exactly second-order self-similar but can be considered as asymptotic self-similar. In this article, such measures are used as client inter-arrival time processes...
In the paper, the computationally effective MATLAB based stability tests for discrete linear repetitive processes (DLRP) are presented. Despite the clear 2D character of repetitive processes, due to the finite pass length, asymptotic stability may be characterized in term of equivalent 1D state space model, and hence all well known standard stability tests for the discrete case may be adopted here...
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