Search results for " AGRICULTURE"
showing 10 items of 2212 documents
Kinetic Monte Carlo Simulations of Flow-Assisted Polymerization
2012
We performed kinetic Monte Carlo simulations on a model of a polymerization process in the presence of a periodic oscillatory flow to explore the role of mixing in polymerization reactors. Application of an oscillatory flow field helps overcome the diffusive limitations that develop during a polymerization process due to an increase in the molecular weights of polymer chains, thereby giving rise to high rates of polymerization. A systematic increase in the flow strength results in a "dynamic" coil-stretch transition, leading to an elongation of polymer chains. Reactive ends of stretched (polymer) chains react more frequently than the reactive ends of coiled chains, which are screened by oth…
Molecular modifications—Mechanical behaviour relationships for gamma irradiated LLDPE/PA6 blends
1994
Abstract The molecular modifications, due to γ radiation under vacuum, of linear low density polyethylene/polyamide 6 blends are presented and related to their mechanical behaviour. Solubility and melt viscosity tests indicate that in blends the polyethylene component undergoes mainly crosslinking phenomena, whereas the main effect on polyamide is chain branching. According to these molecular modifications, the most relevant effect is the increase of the tensile modulus for the polyethylene rich blends and the increase of the impact strength for the polyamide rich blends.
Structural induced modifications in blends of polyamide with gamma irradiated low density polyethylene
1992
Abstract Blends of gamma irradiated and unirradiated low density polyethylene and polyamide 6 were made in order to study possible modifications induced by this irradiation. Results indicate that blends with gamma irradiated polyethylene have structure and properties significantly different with respect to blends made with the unirradiated one. This difference has been ascribed to the formation of functionalized groups in the polyethylene chains, which interact with polyamide.
Cyclodextrins in Polymer Synthesis: Enantiodiscrimination in Free-Radical Polymerization of Cyclodextrin-Complexed Racemic N -Methacryloyl-D,L -pheny…
2003
The enantiodiscriminating polymerization of racemic cyclodextrin-complexed N-methacryloylphenylalanine methyl ester is investigated 1 H NMR spectra of the complexes with methylated β-cyclodextrin in D 2 O manifest splittings due to chiral recognition. The different stabilities of the diastereomeric complexes influence the kinetics of the homopolymerization, particularly at 0°C. An enrichment of the residual N-methacryloyl-L-phenylalanine methyl ester of 14% was achieved after 21 h of polymerization.
Polymeric scaffolds based on blends of poly-l-lactic acid (PLLA) with poly-d-l- lactic acid (PLA) prepared via thermally induced phase separation (TI…
2012
Porous scaffolds based on blends of high crystalline Poly-L-lactic acid (PLLA) with low crystalline poly-D-L-lactic acid (PLA) were prepared via Ther- mally Induced Phase Separation (TIPS), with the aim of exploring the possibility to control the degradation behaviour of the PLA-based scaffold, simultaneously pre- serving the morphological characteristics required for tissue engineering applica- tions. Porous foams with different PLLA/PLA weight ratios (from 95/5 to 60/40) were produced and characterised in terms of pore size, porosity, and thermal properties. The scaffolds present an open porosity, with average pore sizes ranging from 30 to 70 lm. Results showed that, when dealing with a P…
Reversing agriculture from intensive to sustainable improves soil quality in a semiarid South Italian soil
2010
Intensive agriculture (IA) is widespread in South Italy, although it requires frequent tillage, large amounts of fertilizers and irrigation water. We have assessed the efficacy of reversing IA to sustainable agriculture (SA) in recovering quality of a typical South Italy soil (Lithic Haploxeralf). This reversion, lasting from 2000 to 2007, replaced 75% of nutrients formerly supplied inorganically by farmyard manuring and reduced the tillage frequency. Several chemical and biochemical properties, functionally related to C and N mineralisation–immobilisation processes and to P and S nutrient cycles, were monitored annually from 2005 to 2007 in the spring. Reversing IA to SA decreased soil bul…
Synthesis of a rod-based porous coordination polymer from a nucleotide as a sequential chiral inductor
2021
We report the two-step synthesis of a novel chiral rod-based porous coordination polymer (PCP). The chemical approach consists of the use of a previously prepared bis(ethylenediamine) copper monomer [Cu(en)]2(NO3)2 [where en = ethylenediamine] reacting with the cytidine 5′-monophosphate (CMP) nucleotide. The bis(ethylenediamine) copper compound—stabilized by axial coordination of nitrate counter-anions—reacts in the presence of sodium salt of CMP to yield right-handed copper(II) chains of P helicity with formula [Cu2(en)2(CMP)2]·5H2O (1). The axial coordination of the CMP2- ligands through the N3 and O2 sites (free nitrogen and carbonyl groups) of the cytosine nucleobase and oxygen atoms of…
Impact of surface state on polyethylene glycol conformation confined inside a nanopore.
2021
Solid-state nanopores are a promising platform for characterizing proteins. In order to improve their lifetime and prevent fouling, Polyethylene Glycol (PEG) grafting is one of the most efficient and low-cost solutions. Different models to calculate the PEG thickness do not consider their interaction with the nanopore inner surface nor the effect of confinement. Here, we investigate by molecular dynamic simulation the PEG conformation inside a nanopore in the case of hydrophobic and hydrophilic nanopores. Our results reveal that the nanopore inner surface plays a role in the PEG organization and, thus, in the speed of the salt constituent. The resulting pair interaction between PEG and its …
Reduction of the frequency of herbaceous roots as an effect of soil compaction induced by heavy grazing in rangelands of SW Spain
2017
Rangelands in SW Spain constitute the most extensive ranching system on the Iberian Peninsula. During the last few decades, a significant increase in livestock numbers, along with a progressive substitution of cattle for sheep, have led to land degradation processes such as the reduction of grass cover and increased soil compaction in heavily grazed areas. Nevertheless, a better understanding of how soil compaction affects grass production is still needed. In this study, some of the effects of soil compaction due to heavy grazing are analysed, mainly the reduction of the frequency of herbaceous roots and its relationships with bulk density and soil penetration resistance. The study was carr…
Dispersion of titanate nanotubes for nanomedicine: comparison of PEI and PEG nanohybrids.
2014
In the present study, we report the dispersion of titanate nanotubes (TiONts) via polymer grafting (PolyEthylene Glycol, PEG) or polymer adsorption (polyethylene imine, PEI) where different TiONts/polymer ratios have been investigated. The TiONts/PEI and TiONts/PEG nanohybrids were characterized by scanning and transmission electron microscopy as well as by zeta potential measurements in order to determine both their dispersion state and stability in water (at different pH for zetametry). The nature of the chemical bonds at the surface of these nanohybrids was investigated by Fourier-transformed infrared (FTIR) spectroscopy while the grafting densities of PEG on the nanotubes were quantifie…