Molecular dynamics simulation of the structural and dynamic properties of dioctadecyldimethyl ammoniums in organoclays

The structural and dynamic properties of dioctadecyldimethylammoniums (DODDMA) intercalated into 2:1 layered clays are investigated using isothermal-isobaric (NPT) molecular dynamics (MD) simulation. The simulated results are in reasonably good agreement with the available experimental measurements, such as X-ray diffraction (XRD), atom force microscopy (AFM), Fourier transform infrared (FTIR), and nuclear magnetic resonance (NMR) spectroscopies. The nitrogen atoms are found to be located mainly within two layers close to the clay surface whereas methylene groups form a pseudoquadrilayer structure. The results of tilt angle and order parameter show that interior two-bond segments of alkyl chains prefer an arrangement parallel to the clay surface, whereas the segments toward end groups adopt a random orientation. In addition, the alkyl chains within the layer structure lie almost parallel to the clay surface whereas those out of the layer structure are essentially perpendicular to the surface. The trans conformations are predominant in all cases although extensive gauche conformations are observed, which is in agreement with previous simulations on n-butane. Moreover, an odd-even effect in conformation distributions is observed mainly along the chains close to the head and tail groups. The diffusion constants of both nitrogen atoms and methylene groups in these nanoconfined alkyl chains increase with the temperature and methelene position toward the tail groups.

A simulation model of cereal-legume intercropping systems for semi-arid regions I. Model development

Cereal-legume intercropping plays an important role in subsistence food production in developing countries, especially in situations of limited water resources. Crop simulation can be used to assess risk for intercrop productivity over time and space. In this study, a simple model for intercropping was developed for cereal and legume growth and yield, under semi-arid conditions. The model is based on radiation interception and use, and incorporates a water stress factor. Total dry matter and yield are functions of photosynthetically active radiation (PAR), the fraction of radiation intercepted and radiation use efficiency (RUE). One of two PAR sub-models was used to estimate PAR from solar radiation; either PAR is 50% of solar radiation or the ratio of PAR to solar radiation (PAR/SR) is a function of the clearness index (K-T). The fraction of radiation intercepted was calculated either based on Beer's Law with crop extinction coefficients (K) from field experiments or from previous reports. RUE was calculated as a function of available soil water to a depth of 900 mm (ASW). Either the soil water balance method or the decay curve approach was used to determine ASW. Thus, two alternatives for each of three factors, i.e., PAR/SR, K and ASW, were considered, giving eight possible models (2 methods x 3 factors). The model calibration and validation were carried out with maize-bean intercropping systems using data collected in a semi-arid region (Bloemfontein, Free State, South Africa) during seven growing seasons (1996/1997-2002/2003). The combination of PAR estimated from the clearness index, a crop extinction coefficient from the field experiment and the decay curve model gave the most reasonable and acceptable result. The intercrop model developed in this study is simple, so this modelling approach can be employed to develop other cereal-legume intercrop models for semi-arid regions. (c) 2004 Elsevier B.V. All rights reserved.

Optical communication based on the periodic nonlinear Fourier transform signal processing

In this work we introduce the periodic nonlinear Fourier transform (PNFT) and propose a proof-of-concept communication system based on it by using a simple waveform with known nonlinear spectrum (NS). We study the performance (addressing the bit-error-rate (BER), as a function of the propagation distance) of the transmission system based on the use of the PNFT processing method and show the benefits of the latter approach. By analysing our simulation results for the system with lumped amplification, we demonstrate the decent potential of the new processing method.

Fault diagnosis scheme for open-circuit faults in switched reluctance motor drives using fast Fourier transform algorithm with bus current detection

Reliability of power converters is of crucial importance in switched reluctance motor drives used for safety-critical applications. Open-circuit faults in power converters will cause the motor to run in unbalanced states, and if left untreated, they will lead to damage to the motor and power modules, and even cause a catastrophic failure of the whole drive system. This study is focused on using a single current sensor to detect open-circuit faults accurately. An asymmetrical half-bridge converter is considered in this study and the faults of single-phase open and two-phase open are analysed. Three different bus positions are defined. On the basis of a fast Fourier transform algorithm with Blackman window interpolation, the bus current spectrums before and after open-circuit faults are analysed in details. Their fault characteristics are extracted accurately by the normalisations of the phase fundamental frequency component and double phase fundamental frequency component, and the fault characteristics of the three bus detection schemes are also compared. The open-circuit faults can be located by finding the relationship between the bus current and rotor position. The effectiveness of the proposed diagnosis method is validated by the simulation results and experimental tests.

Méthodes moléculaires de détection d'animaux porteurs d'actinobacillus pleuropneumoniae : comparaison et validation d'épreuves PCR

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Développement de méthodes de synthèse pour les acides aminés indolizidin-9-ones substitués et utilisation des acides aminés azabicycloalcanes en tant que mimes peptidiques

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.

Étude des méthodes de saisie informatique relatives au forage de données appliquées à la prise de décision en urbanisme

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Les méthodes de construction des ponts couverts de bois du Québec ; un guide d'inspection et d'entretien

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Intégration de méthodes informatiques dans le processus de restitution en égyptologie

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Méthodes heuristiques pour un problème d'ordonnancement avec contraintes sur les ressources

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Expansion de requête dans la recherche d'information : comparaison des ressources et des méthodes

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Accélérer l'entraînement d'un modèle non-paramétrique de densité non normalisée par échantillonnage aléatoire

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Méthodes à noyaux appliquées à la gestion de portefeuille

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Développement d'un outil générique de simulation distribuée de marchés électroniques basés sur les enchères

Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

De la fusion du génie logiciel et d'une bibliothèque à source ouverte pour la modélisation/simulation de processus matériel et logiciel

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal.