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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
311

The equation of state of the Hydrogen-Helium mixture with application to the Sun / Equation d’état du mélange hydrogen-helium à basse densité et application au Soleil

Wendland, David 30 October 2015 (has links)
L’étude des propriétés d’équilibre d’un système Coulombien quantique à plusieurs composantes présente un intérêt théorique fondamental, au-delà de ses nombreuses applications. Le mélange hydrogène-hélium est omniprésent dans la nébuleuse interstellaire ou les planètes géantes, et c’est aussi le constituant majoritaire du Soleil, où les interactions entre électrons et noyaux sont purement électrostatiques en première approximation.Ce travail est dévolu à l’équation d’état de ce mélange vu comme un plasma quantique constitué de protons, de noyaux d’Hélium et d’électrons. Dans ce cadre, nous développons des méthodes numériques pour estimer des intégrales de chemin représentant des ingrédients essentiels. En outre, nous construisons une nouvelle version de la diagrammatique à la Mayer resommée bien adaptée à nos objectifs.Tout d’abord, nous améliorons le double développement basse température et basse densité, dit SLT, pour l’hydrogène pur, grâce à de meilleures estimations des termes à trois corps, les résultats étant par ailleurs comparés à la fameuse équation d’état OPAL. Les densités plus élevées sont atteintes de manière non-perturbative, en utilisant des fonctions de partition d’entités recombinées suffisamment précises. Ainsi l’ionisation par pression est décrite sur une base théorique robuste. Nous étudions également d’autres quantités d’équilibre, comme l’énergie interne et la vitesse du son. Dans la dernière partie, nous calculons l’équation d’état du mélange hydrogène-hélium en incluant les effets d’écran associés aux ions He+, ainsi que des corrections à la Debye déterminées de manière auto-cohérente. Nos résultats nous permettent de comprendre le contenu physique d’approches ad-hoc et de déterminer leurs régimes de validité. Nous obtenons aussi une description plus fiable du mélange, qui devrait être précise le long de l'adiabate du Soleil. / The study of the thermodynamic properties of a multi-component quantum Coulomb system is of fundamental theoretical interest and has, beyond that, a wide range of applications. The Hydrogen-Helium mixture can be found in the interstellar nebulae and giant planets, however the most prominent example is the Sun. Here the interaction between the electrons and the nuclei is almost purely electrostatic.In this work we study the equation of state of the Hydrogen-Helium mixture starting from first principles, meaning the fundamental Coulomb interaction of its constituting particles. In this context we develop numerical methods to study the few-particle clusters appearing in the theory by using the path integral language. To capture the effects of the long-range Coulomb interaction between the fundamental particles, we construct a new version of Mayer-diagrammatic, which is appropriate for our purposes. In a first step, we ameliorate the scaled-low-temperature (SLT) equation of state, valid in the limit of low density and low temperature, by taking three-body terms into account and we compare the predictions to the well-established OPAL equation of state. Higher densities are accessed by direct inversion of the density equations and by the use of cluster functions that include screening effects. These cluster functions put the influence of screening on the ionization, unto now treated ad-hoc, on a theoretically well-grounded basis. We also inspect other equilibrium quantities such as the speed of sound and the inner energy. In the last part we calculate the equation of state of the Hydrogen-Helium mixture including the charged He+ ions in the screening process. Our work gives insights in the physical content of previous phenomenological descriptions and helps to better determine their range of validity. The equation of state derived in this thesis is expected to be very precise as well as reliable for conditions found in the Sun.
312

Aspects géométriques et topologiques du crochet de Poisson des variétés symplectiques

Payette, Jordan 07 1900 (has links)
Cette thèse étudie deux problèmes de nature géométrique et topologique associés au crochet de Poisson sur les variétés symplectiques. Le premier problème porte sur la notion de submersion symplectique que nous introduisons dans le présent texte et qui généralise la notion de symplectomorphisme. Il s'avère qu'une submersion symplectique est un morphisme de Poisson : il s'agit d'une application entre variétés symplectiques qui préserve le crochet de Poisson. Notre intérêt pour ces fonctions réside dans le fait que le théorème de non-tassement de Gromov porte sur l'aire minimale possible pour les images des submersions symplectiques (allant d'une boule symplectique vers le plan symplectique) obtenues comme compositions d'un plongement symplectique dans l'espace symplectique euclidien de dimension 2n et de la projection standard vers le plan de coordonnées conjuguées (p_1, q_1). Nous investiguons le problème inverse dit « de représentabilité » : nous obtenons des conditions nécessaires et suffisantes pour qu'une submersion symplectique comme ci-dessus se factorise comme précédemment à travers un plongement ou une immersion symplectique dans l'espace euclidien. Nous montrons par ailleurs qu'il existe une submersion symplectique qui ne se factorise pas de la sorte à travers une immersion et qu'il existe aussi une submersion symplectique qui se factorise de la sorte à travers une immersion, mais pas à travers un plongement. Le deuxième problème porte sur la conjecture du crochet de Poisson de Polterovich. Étant donné une variété symplectique (M, omega) et un recouvrement U de M, nous pouvons définir l'invariant pb(F) associé à une partition de l'unité F subordonnée à U, qui est une sorte de norme sur les crochets de Poisson entre les paires de fonctions de la partition. En dénotant e(U) l'énergie de disjonction de Hofer maximale d'un ouvert du recouvrement U, la conjecture demande s'il existe une constante positive C indépendante de U et de F telle que le produit de pb(F) et de e(U) soit supérieur à C. Cette conjecture a été établie récemment par Buhovski-Logunov-Tanny dans le cas des surfaces ; en nous inspirant de travaux antérieurs de Buhovski-Tanny, nous avons aussi démontré la conjecture pour les surfaces de genre plus grand que 1. Nous exposons notre approche dans le second chapitre de cette thèse. À l'aide des submersions symplectiques, nous généralisons nos méthodes afin d'attaquer la conjecture en dimensions supérieures ; nous obtenons ainsi une nouvelle preuve d'un théorème de Polterovich et de Buhovski-Tanny concernant l'invariant pb pour des recouvrements formés de petits ouverts. Afin de rendre cette thèse aussi accessible et auto-suffisante que possible, nous débutons par une introduction à la topologie symplectique. Des annexes recueillent les faits plus particuliers que nous utilisons tout au long de ce travail. / This thesis studies two problems of geometric and topological nature associated to the Poisson bracket on symplectic manifolds. The first problem concerns the notion of "symplectic submersion" that we introduce here and which generalizes the concept of symplectomorphism. A symplectic submersion turns out to be a Poisson morphism, namely a map between symplectic manifolds which preserves the Poisson bracket. Our interest in those maps stems from the fact that Gromov's nonsqueezing theorem is a statement about the minimal area possible for the images of the symplectic submersions (going from a symplectic ball to a symplectic plane) which are compositions of a symplectic embedding into the Euclidean symplectic space and of the standard projection onto the plane of conjugated variables (p_1, q_1). We investigate the inverse "representability" problem: we give necessary and sufficient conditions for a symplectic submersionas above to factorize in the previous way either through a symplectic embedding or through a symplectic immersion into Euclidean space. We show moreover that there exists a symplectic submersion which does not factorize in this way through an immersion, and also that there exists a symplectic submersion which does factorize in this way through an immersion, but not through an embedding. The second problem concerns Polterovich's Poisson bracket conjecture. Given a symplectic manifold (M, omega) and an open cover U of M, we can define the invariantpb(F) of a partition of unity F subordinated to U, which is a sort of norm on the pairwise Poisson brackets of the functions in F. Denoting e(U) the maximal Hofer displacement energy of a set in U, the conjecture asks whether there exists a positive constant C independent of U and F such that the product of pb(F) and e(U) is greater than C. This conjecture was proved recently by Buhovsky-Logunov-Tanny in the case of surfaces; based on earlier work of Buhovsky-Tanny , we also proved the conjecture for surfaces of genus one and above. We present our approach in the second chapter of this thesis. Using symplectic submersions, we generalize our methods in order to tackle the conjecture in higher dimensions; in particular, we obtain a new proof of a theorem of Polterovich and Buhovsky-Tanny about the pb invariant of covers made up of small open sets. In order to make this thesis as accessible and self-contained as possible, we first give an introduction to symplectic topology. The appendices also collect the more specialized facts we use throughout this work.
313

Segmentation and structuring of video documents for indexing applications / Segmentation et structuration de documents video pour l'indexation

Tapu, Ruxandra Georgina 07 December 2012 (has links)
Les progrès récents en matière de télécommunications, collaboré avec le développement des dispositifs d'acquisition d’images et de vidéos a conduit à une croissance spectaculaire de la quantité des données vidéo stockées, transmises et échangées sur l’Internet. Dans ce contexte, l'élaboration d'outils efficaces pour accéder aux éléments d’information présents dans le contenu vidéo est devenue un enjeu crucial. Dans le Chapitre 2 nous introduisons un nouvel algorithme pour la détection de changement de plans vidéo. La technique est basée sur la partition des graphes combinée avec une analyse multi-résolution et d'une opération de filtrage non-linéaire. La complexité globale de calcul est réduite par l’application d'une stratégie deux passes. Dans le Chapitre 3 le problème d’abstraction automatique est considéré. Dans notre cas, nous avons adopté un système de représentation image-clés qui extrait un nombre variable d'images de chaque plan vidéo détecté, en fonction de la variation du contenu visuel. Le Chapitre 4 traite la segmentation de haut niveau sémantique. En exploitant l'observation que les plans vidéo appartenant à la même scène ont les mêmes caractéristiques visuelles, nous introduisons un nouvel algorithme de regroupement avec contraintes temporelles, qui utilise le seuillage adaptatif et les plans vidéo neutralisés. Dans le Chapitre 5 nous abordons le thème de détection d’objets vidéo saillants. Dans ce contexte, nous avons introduit une nouvelle approche pour modéliser l'attention spatio-temporelle utilisant : la correspondance entre les points d'intérêt, les transformations géométriques et l’estimation des classes de mouvement / Recent advances in telecommunications, collaborated with the development of image and video processing and acquisition devices has lead to a spectacular growth of the amount of the visual content data stored, transmitted and exchanged over Internet. Within this context, elaborating efficient tools to access, browse and retrieve video content has become a crucial challenge. In Chapter 2 we introduce and validate a novel shot boundary detection algorithm able to identify abrupt and gradual transitions. The technique is based on an enhanced graph partition model, combined with a multi-resolution analysis and a non-linear filtering operation. The global computational complexity is reduced by implementing a two-pass approach strategy. In Chapter 3 the video abstraction problem is considered. In our case, we have developed a keyframe representation system that extracts a variable number of images from each detected shot, depending on the visual content variation. The Chapter 4 deals with the issue of high level semantic segmentation into scenes. Here, a novel scene/DVD chapter detection method is introduced and validated. Spatio-temporal coherent shots are clustered into the same scene based on a set of temporal constraints, adaptive thresholds and neutralized shots. Chapter 5 considers the issue of object detection and segmentation. Here we introduce a novel spatio-temporal visual saliency system based on: region contrast, interest points correspondence, geometric transforms, motion classes’ estimation and regions temporal consistency. The proposed technique is extended on 3D videos by representing the stereoscopic perception as a 2D video and its associated depth
314

Mixed-integer programming representation for symmetrical partition function form games

Pepin, Justine 11 1900 (has links)
In contexts involving multiple agents (players), determining how they can cooperate through the formation of coalitions and how they can share surplus benefits coming from the collaboration is crucial. This can provide decision-aid to players and analysis tools for policy makers regulating economic markets. Such settings belong to the field of cooperative game theory. A critical element in this area has been the size of the representation of these games: for each possible partition of players, the value of each coalition on it must be provided. Symmetric partition function form games (SPFGs) belong to a class of cooperative games with two important characteristics. First, they account for externalities provoked by any group of players joining forces or splitting into subsets on the remaining coalitions of players. Second, they consider that players are indistinct, meaning that only the number of players in each coalition is relevant for the SPFG. Using mixed-integer programming, we present the first representation of SPFGs that is polynomial on the number of players in the game. We also characterize the family of SPFGs that we can represent. In particular, the representation is able to encode exactly all SPFGs with five players or less. Furthermore, we provide a compact representation approximating SPFGs when there are six players or more and the SPFG cannot be represented exactly. We also introduce a flexible framework that uses stability methods inspired from the literature to identify a stable social-welfare maximizing game outcome using our representation. We showcase the value of our compact (approximated) representation and approach to determine a stable partition and payoff allocation to a competitive market from the literature. / Dans tout contexte impliquant plusieurs agents (joueurs), il est impératif de déterminer comment les agents coopéreront par la formation de coalitions et comment ils partageront les bénéfices supplémentaires issus de la collaboration. Ceci peut fournir une aide à la décision aux joueurs, ou encore des outils d'analyse pour les responsables en charge de réguler les marchés économiques. De telles situations relèvent de la théorie des jeux coopérative. Un élément crucial de ce domaine est la taille de la représentation de ces jeux : pour chaque partition de joueurs possible, la valeur de chaque coalition qu'on y retrouve doit être donnée. Les jeux symétriques à fonction de partition (SPFG) appartiennent à une classe de jeux coopératifs possédant deux caractéristiques principales. Premièrement, ils sont sensibles aux externalités, provoquées par n'importe quel groupe de joueurs qui s'allient ou défont leurs alliances, qui sont ressenties par les autres coalitions de joueurs. Deuxièmement, ils considèrent que les joueurs sont indistincts, et donc que seul le nombre de joueurs dans chaque coalition est à retenir pour représenter un SPFG. Par l'utilisation d'outils de programmation mixte en nombres entiers, nous présentons la première représentation de SPFG qui est polynomiale en nombre de joueurs dans le jeu. De surcroît, nous caractérisons la famille des SPFG qu'il est possible de représenter, qui inclut notamment tous les SPFG de cinq joueurs ou moins. De plus, elle dispose d'une approximation compacte pour le cas où, dans un jeu à six joueurs ou plus, le SPFG ne peut pas être représenté de façon exacte. Également, nous introduisons un cadre flexible qui utilise des méthodes visant la stabilité inspirées par la littérature pour identifier, à l'aide de notre représentation, une issue stable qui maximise le bien-être social des joueurs. Nous démontrons la valeur de notre représentation (approximée) compacte et de notre approche pour sélectionner une partition stable et une allocation des profits dans une application de marché compétitif provenant de la littérature.
315

Heirs' property disputes on forestlands, partition actions, and the determinants of court verdicts

Tiwari, Mahesh Prasad 08 December 2023 (has links) (PDF)
Heirs' property is generated through the intergenerational transfer of a property to several co-owners when the original owner dies without a will. Such co-owners hold undivided fractional interest in the entire land but lack a clear title. Co-owners face several legal, financial, and technical constraints to manage the forestlands and often seek partition of the land. However, the legal environment and empirical assessment of partition actions on forestlands owned as heirs' property has not been examined. This thesis evaluates statutory laws relevant to forestland partition and the factors instrumental in adjudicating partition lawsuits. The findings reveal that partition lawsuits are primarily adjudicated using common law rather than statutory law. The magnitude of co-owners' fractional interest, the income withheld from forestlands, and the presence of absentee co-owners favor partition claimants. The study results have implications for heirs' property owners, legal entities and personnel, and policymakers.
316

Modelling and optimisation of oxidative desulphurization process for model sulphur compounds and heavy gas oil : determination of rate of reaction and partition coefficient via pilot plant experiment : modelling of oxidation and solvent extraction processes : heat integration of oxidation process : economic evaluation of the total process

Khalfalla, Hamza Abdulmagid January 2009 (has links)
Heightened concerns for cleaner air and increasingly more stringent regulations on sulphur content in transportation fuels will make desulphurization more and more important. The sulphur problem is becoming more serious in general, particularly for diesel fuels as the regulated sulphur content is getting an order of magnitude lower, while the sulphur contents of crude oils are becoming higher. This thesis aimed to develop a desulphurisation process (based on oxidation followed by extraction) with high efficiency, selectivity and minimum energy consumption leading to minimum environmental impact via laboratory batch experiments, mathematical modelling and optimisation. Deep desulphurization of model sulphur compounds (di-n-butyl sulphide, dimethyl sulfoxide and dibenzothiophene) and heavy gas oils (HGO) derived from Libyan crude oil were conducted. A series of batch experiments were carried out using a small reactor operating at various temperatures (40-100 °C) with hydrogen peroxide (H2O2) as oxidant and formic acid (HCOOH) as catalyst. Kinetic models for the oxidation process are then developed based on 'total sulphur approach'. Extraction of unoxidised and oxidised gas oils was also investigated using methanol, dimethylformamide (DMF) and N-methyl pyrolidone (NMP) as solvents. For each solvent, the 'measures' such as: the partition coefficient (KP), effectiveness factor (Kf) and extractor factor (Ef) are used to select the best/effective solvent and to find the effective heavy gas oil/solvent ratios. A CSTR model is then developed for the process for evaluating viability of the large scale operation. It is noted that while the energy consumption and recovery issues could be ignored for batch experiments these could not be ignored for large scale operation. Large amount of heating is necessary even to carry out the reaction at 30-40 °C, the recovery of which is very important for maximising the profitability of operation and also to minimise environmental impact by reducing net CO2 release. Here the heat integration of the oxidation process is considered to recover most of the external energy input. However, this leads to putting a number of heat exchangers in the oxidation process requiring capital investment. Optimisation problem is formulated using gPROMS modelling tool to optimise some of the design and operating parameters (such as reaction temperature, residence time and splitter ratio) of integrated process while minimising an objective function which is a coupled function of capital and operating costs involving design and operating parameters. Two cases are studied: where (i) HGO and catalyst are fed as one feed stream and (ii) HGO and catalyst are treated as two feed streams. A liquid-liquid extraction model is then developed for the extraction of sulphur compounds from the oxidised heavy gas oil. With the experimentally determined KP multi stage liquid-liquid extraction process is modelled using gPROMS software and the process is simulated for three different solvents at different oil/solvent ratios to select the best solvent, and to obtain the best heavy gas oil to solvent ratio and number of extraction stages to reduce the sulphur content to less than 10 ppm. Finally, an integrated oxidation and extraction steps of ODS process is developed based on the batch experiments and modelling. The recovery of oxidant, catalyst and solvent are considered and preliminary economic analysis for the integrated ODS process is presented.
317

The Impact of SFAS No.35 Application on th Listed Firms' Stock Performance in Taiwan

戴思嫻, Tai,Shih-Hsien Unknown Date (has links)
本研究的目的在於探討兩個問題:一、上市公司因應財務會計準則公報第三十五號公報的採用而宣告資產減損,市場的反應是正面的(positive)還是負面的(negative)?亦即,資產減損宣告對公司價值的影響為何?二、投資人對於資產減損宣告會過度反應(over-reaction)還是反應不足(under-reaction)?由於財務會計準則公報第三十五號公報的實施截至目前為止尚不足兩年,本研究對於本課題的研究著重在資產減損宣告和股價的關係突顯了這個課題的獨特性和重要性。本研究係採事件研究法以檢驗台灣上市公司採用財務會計準則公報第三十五號公報對於其股價的表現是否會造成影響。除了全數樣本的分析之外,亦將全數樣本依照減損公司的特性和減損資產的特性分成子樣本;或在事件研究法中傳統的市場模型當中加入利率因素或產業因素兩個控制變數並區分成對金融業和非金融業加以分析——目的在於探討這些分類或因素是不是造成資產減損宣告對股價反應的原因。實證結果發現:一、不論是採用哪一種子樣本的分類方式,市場對資產減損宣告的反應都是負向的;二、和利率因素相比,產業因素比較能解釋資產減損宣告前後的股價反應,且對於金融業或非金融業結論皆然;三、30天期的股價反應顯示,投資人對於資產減損宣告有過度反應的現象,因為在產業分類之下股價在12天至18天左右有迴轉(reversal)的現象。 / The purpose of this paper is to answer two questions: 1. Does the market react positively or negatively to asset write-down announcements? Or, what is the impact of asset impairment on the firm value? 2. Do investors over-react or under-react to asset write-down announcements? Given the recent enforcement of SFAS No.35 about asset write-down, this study supplements the importance of that pronouncement by demonstrating the relation between write-downs and security prices. This study employs the event study methodology to examine the impact of SFAS No.35 on the stock performance of those listed firms (i.e., whose stocks are listed on the Taiwan Stock Exchange) that apply the regulation. Partitions methods based on write-down asset and write-down firm characteristics are adopted. Moreover, two other control variables—industry factor or interest rate factor—are added to the traditional market model for the financial industry and non-financial industries to see if these factors can also explain the market reaction around write-down announcements. The result shows that the market reacts negatively to asset written-down announcement whatever the partition method is adopted. And the industry return is proved to be the better factor that can explain the market reaction than the interest rate factor. The near-term stock performance in the (-30, 30) period shows that investors tend to over-react to write-down announcements, for the stock price signals a reversal after the announcement date.
318

Un périphérique d'ordinateur à l'usage des musiciens : problèmes d'interprétation de la musique et d'édition de partitions

Jaeger, Denis 17 April 1974 (has links) (PDF)
.
319

基於音樂特徵以及文字資訊的音樂推薦 / Music recommendation based on music features and textual information

張筑鈞, Chang, Chu Chun Unknown Date (has links)
在WEB2.0的時代,網際網路中充斥著各式各樣的互動式平台。就音樂網站而言,使用者除了聽音樂外,更開始習慣於虛擬空間中交流及分享意見,並且在這些交流、分享的過程中留下他們的足跡,間接的提供許多帶有個人色彩的資訊。利用這些資訊,更貼近使用者的推薦系統因應而生。本研究中,將針對使用者過去存取過的音樂特徵以及使用者於系統中留下的文字評論特徵這兩個部份的資料,做音樂特徵的擷取、找尋具有價值的音樂特徵區間、建立使用者音樂特徵偏好,以及文字特徵的擷取、建立使用者文字特徵偏好。接著,採用協同式推薦方式,將具有相同興趣的使用者分於同一群,推薦給使用者與之同群的使用者的喜好物件,但這些推薦之物件為該使用者過去並沒有任何記錄於這些喜好物件上之物件。我們希望對於音樂推薦考慮的開始不只是音樂上之特徵,更包含了使用者交流、互動中留下的訊息。 / In the era of Web2.0, it is flooded with a variety of interactive platforms on the internet. In terms of music web site, in addition to listening to music, users got used to exchanging their comments and sharing their experiences through virtual platforms. And through the process of exchanging and sharing, they left their footprints. These footprints indirectly provide more information about users that contains personal characteristics. Moreover, from this information, we can construct a music recommendation system, which provides personalized service. In this research, we will focus on user’s access histories and comments of users to recommend music. Moreover, the user’s access histories are analyzed to derive the music features, then to find the valuable range of music features, and construct music profiles of user interests. On the other hand, the comments of users are analyzed to derive the textual features, then to calculate the importance of textual features, and finally to construct textual profiles of user interests. The music profile and the textual profile are behaviors for user grouping. The collaborative recommendation methods are proposed based on the favorite degrees of the users to the user groups they belong to.
320

Percutaneous delivery of thalidomide and its N-alkyl analogues for treatment of rheumatoid arthritis / Colleen Goosen

Goosen, Colleen January 1998 (has links)
Rheumatoid arthritis (RA) is a chronic inflammatory joint disease associated with high levels of tumour necrosis factor-alpha (TNF-a) in synovial fluid and synovial tissue (Saxne et al., 1989). Thalidomide is a proven inhibitor of the biological synthesis of TNF-a (Sampaio et al., 1991) and is believed to rely on this action for its suppression of the wasting of tissue which accompanies RA. Oral administration of thalidomide has proven to be effective in RA, but unacceptable side effects are easily provoked (Gutierrez-Rodriguez, 1984). Administration of thalidomide via the dermal route can down-regulate TNF-a production in and around the affected joint, and this without raising the systemic blood level to a problematical level. Based on thalidomide's physicochemical properties, it is unlikely that it can be delivered percutaneously at a dose required for RA. Therefore, we have embraced the idea of using N-alkyl analogues of thalidomide. The most important feature that an analogue of this compound might contribute is decreased crystallinity and increased lipophilicity. Ordinarily both these parameters should favour percutaneous delivery. The current study was primarily aimed at exploring the feasibility of percutaneous delivery of thalidomide and subsequently, three of its odd chain IV-alkyl analogues (methyl, propyl and pentyl) via physicochemical characterization and assessment of their innate abilities to diffuse through skin as an initial step towards developing a topical dosage form for the best compound. The biological activities, more specifically their potential to inhibit the production of TNF-a was determined for thalidomide and its N-alkyl analogues. In order to achieve the objectives, the study was undertaken by synthesizing and determining the physicochemical parameters of thalidomide and its N-alkyl analogues. A high level of crystallinity is expressed in the form of a high melting point and heat of fusion. This limits solubility itself, and thus also sets a limit on mass transfer across the skin. Generally, the greater a drug's innate tendency to dissolve, the more likely it is that the drug can be delivered at an appropriate rate across the skin (Ostrenga et al., 1971). Therefore, the melting points and heats of fusion were determined by differential scanning calorimetry. Aqueous solubility and the partition coefficient (relative solubility) are major determinants of a drug's dissolution, distribution and availability. N-octanollwater partition coefficients were determined at pH 6.4. Solubilities in water, a series of n-alcohols and mixed solvents were obtained, as well as the solubility parameters of the compounds in study. Secondly, in vitro permeation studies were performed from these solvents and vehicles using vertical Franz diffusion cells with human epidermal membranes. Thirdly, tumour necrosis factor-alpha (TNF-a) inhibition activities were assessed for thalidomide and its N-alkyl analogues. By adding a methyl group to the thalidomide structure, the melting point drops by over 100°C and, in this particular instance upon increasing the alkyl chain length to five -CH2- units the melting points decrease linearly. Heats of fusion decreased dramatically upon thalidomide's alkylation as well. Methylation of the thalidomide molecule enhanced the aqueous solubility 6-fold, but as the alkyl chain length is further extended from methyl to pentyl, the aqueous solubility decreased exponentially. The destabilization of the crystalline structure with increasing alkyl chain length led to an increase in lipophilicity and consequently an increase in solubility in nonpolar media. Log partition coefficients increased linearly with increasing alkyl chain length. Solubilities in a series of n-alcohols, methanol through dodecanol, were found to be in the order of pentyl > propyl > methyl > thalidomide. The N-alkyl analogues have more favourable physicochemical properties than thalidomide to be delivered percutaneously. The in vitro skin permeation data proved that the analogues can be delivered far easier than thalidomide itself. N-methyl thalidomide showed the highest steady-state flux through human skin from water, n-alcohols and combination vehicles. Thalidomide and its N-alkyl analogues were all active as TNF-a inhibitors. Finally, active as a TNF-a inhibitor, N-methyl thalidomide is the most promising candidate to be delivered percutaneously for treatment of rheumatoid arthritis, of those studied. / Thesis (PhD (Pharmaceutics))--PU for CHE, 1999.

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