Search results for "Modeling"
showing 10 items of 4489 documents
Translocation dynamics of a short polymer driven by an oscillating force
2013
Under the terms of the Creative Commons Attribution 3.0 Unported License.
Self-Diffusion of Small Molecules into Rubbery Polymers: A Lattice Free-Volume Theory
2010
In the framework of the Free Volume Theory, a new equation was derived for the evaluation of self-diffusion coefficients of small molecules in polymers above the mixture glass transition temperature. The derivation of the equation turned out to be straightforward once the equivalence between the free-volume and the unoccupied volume given by Thermodynamic Lattice Theories is assumed. A parameter evaluation scheme is proposed, which is substantially simpler compared to the conventional Vrentas-Duda approach, even without losing generality. The key assumption is discussed and its consistency is verified from a numerical viewpoint. A comparison with experimental solvent self-diffusion coeffici…
Responses of soil carbon and nitrogen transformations to stump removal
2012
We studied in central Finland whether stump harvesting after clear felling of coniferous forest poses further short-term changes in soil carbon and nitrogen dynamics when compared to the traditional site preparation method, mounding. Exposed mineral soil patches in Norway spruce (Picea abies) dominated clear-cut stands were sampled 1â5 years after the treatments. The extent of the exposed mineral soil surface was significantly larger at the stump removal sites when compared to the mounding sites. No differences were found in soil pH, organic matter content or total concentration of soil C between the treatments or treatment years. Total concentration of soil N was consistently higher and …
Theory and Simulation of Multiphase Polymer Systems
2010
The theory of multiphase polymer systems has a venerable tradition. The 'classical' theory of polymer demixing, the Flory-Huggins theory, was developed already in the forties of the last century. It is still the starting point for most current approaches -- be they improved theories for polymer (im)miscibility that take into account the microscopic structure of blends more accurately, or sophisticated field theories that allow to study inhomogeneous multicomponent systems of polymers with arbitrary architectures in arbitrary geometries. In contrast, simulations of multiphase polymer systems are relatively young. They are still limited by the fact that one must simulate a large number of lar…
DESASS: A software tool for designing, simulating and optimising WWTPs
2008
This paper presents a very useful software tool to design, simulate and optimise wastewater treatment plants. The program is called DESASS (DEsign and Simulation of Activated Sludge Systems) and has been developed by CALAGUA research group. The mathematical model implemented is the Biological Nutrient Removal Model No.1 (BNRM1) which allows simulating the most important physical, chemical and biological processes taking place in treatment plants. DESASS calculates the performance under steady or transient state of whole treatment schemes including primary settlers, volatile fatty acid generation systems by primary sludge fermentation, activated sludge systems for biological organic matter a…
Analysis of gate freeze-off time in injection molding
2004
Gate solidification time is an important topic in injection molding technology, as it determines cycle time, which itself is an important issue in the economics of the production process. In this work, a study of the effect of both gate and cavity geometries on gate solidification time was conducted, using a commercial polymer, injection molded with constant holding pressure into a rectangular cavity. Three cavity lengths were used, and for each, two cavity thicknesses were adopted. Spe- cial dies containing different gates were assembled in the mold. Gate thickness was found to be the most important factor determining gate sealing time. However, the cavity geometry is also quite important.…
Distribution of volatile organic compounds in Sicilian groundwaters analysed by head space-solid phase micro extraction coupled with gas chromatograp…
2008
This work presents the results of an assessment of the existence and concentration of 13 volatile organic compounds (VOCs) in groundwaters from 14 hydrological basins in Sicily (25,710km (2)). On the basis of hydrological, hydrogeochemical and geological studies, 324 sampling points were selected. All groundwater sampled were collected twice, from October to December 2004 and from February to May 2005, and were analysed to determine the concentration and spatial distribution of the VOCs in the aquifers. The need to analyze a large number of samples in a short space of time so as to obtain quantitative analyses in trace concentration levels spurred us to create a new analytical method, both …
Cathepsin L in Normal and Pathological Bone Remodeling
2011
Abstract Cathepsin L is a ubiquitous lysosomal cysteine endopeptidase that is mainly involved in the metabolic turnover of intracellular proteins. However, it is now well established that this enzyme may also be implicated in the regulation of other important biological processes includ- ing bone resorption. Therefore, altered expression levels of Cathepsin L may result in disturbances of bone homeo- stasis and, eventually, in the onset of pathological condi- tions associated with altered bone turnover. These observations support the concept that Cathepsin L may be regarded as an additional target for the development of novel therapeutic options for the treatment of patients with bone disea…
Linking food webs to ecosystem processes: Piecewise linear models of soil microcosms
2008
Abstract A piecewise linear approach to link decomposer biomass and soil nitrogen dynamics is proposed. Dynamics of a detritus–fungus–nematode food chain were studied in a microcosm experiment and modelled to evaluate the role of fungal-feeding nematodes in N mineralization. The nematode dynamics switched from exponential growth to a resource-limited phase. At the same time the amount of ammonium nitrogen in soil started to increase, following an initial immobilization phase. Both nematode and ammonium dynamics could be described by two-phase linear equations. Two nitrogen models were compared. A model in which the nematode accounted for all mineralization could be fitted to the ammonium da…