Spectroscopie Raman de fibres électrofilées : développement de méthodes et application aux fibres individuelles

L’électrofilage est une technique de mise en œuvre efficace et versatile qui permet la production de fibres continues d’un diamètre typique de quelques centaines de nanomètres à partir de l’application d’un haut voltage sur une solution concentrée de polymères enchevêtrés. L’évaporation extrêmement rapide du solvant et les forces d’élongation impliquées dans la formation de ces fibres leur confèrent des propriétés hors du commun et très intéressantes pour plusieurs types d’applications, mais dont on commence seulement à effleurer la surface. À cause de leur petite taille, ces matériaux ont longtemps été étudiés uniquement sous forme d’amas de milliers de fibres avec les techniques conventionnelles telles que la spectroscopie infrarouge ou la diffraction des rayons X. Nos connaissances de leur comportement proviennent donc toujours de la convolution des propriétés de l’amas de fibres et des caractéristiques spécifiques de chacune des fibres qui le compose. Les études récentes à l’échelle de la fibre individuelle ont mis en lumière des comportements inhabituels, particulièrement l’augmentation exponentielle du module avec la réduction du diamètre. L’orientation et, de manière plus générale, la structure moléculaire des fibres sont susceptibles d’être à l'origine de ces propriétés, mais d’une manière encore incomprise. L’établissement de relations structure/propriétés claires et l’identification des paramètres qui les influencent représentent des défis d’importance capitale en vue de tirer profit des caractéristiques très particulières des fibres électrofilées. Pour ce faire, il est nécessaire de développer des méthodes plus accessibles et permettant des analyses structurales rapides et approfondies sur une grande quantité de fibres individuelles présentant une large gamme de diamètre. Dans cette thèse, la spectroscopie Raman confocale est utilisée pour l’étude des caractéristiques structurales, telles que l’orientation moléculaire, la cristallinité et le désenchevêtrement, de fibres électrofilées individuelles. En premier lieu, une nouvelle méthodologie de quantification de l’orientation moléculaire par spectroscopie Raman est développée théoriquement dans le but de réduire la complexité expérimentale de la mesure, d’étendre la gamme de matériaux pour lesquels ces analyses sont possibles et d’éliminer les risques d’erreurs par rapport à la méthode conventionnelle. La validité et la portée de cette nouvelle méthode, appelée MPD, est ensuite démontrée expérimentalement. Par la suite, une méthodologie efficace permettant l’étude de caractéristiques structurales à l’échelle de la fibre individuelle par spectroscopie Raman est présentée en utilisant le poly(éthylène téréphtalate) comme système modèle. Les limites de la technique sont exposées et des stratégies expérimentales pour les contourner sont mises de l’avant. Les résultats révèlent une grande variabilité de l'orientation et de la conformation d'une fibre à l'autre, alors que le taux de cristallinité demeure systématiquement faible, démontrant l'importance et la pertinence des études statistiques de fibres individuelles. La présence de chaînes montrant un degré d’enchevêtrement plus faible dans les fibres électrofilées que dans la masse est ensuite démontrée expérimentalement pour la première fois par spectroscopie infrarouge sur des amas de fibres de polystyrène. Les conditions d'électrofilage favorisant ce phénomène structural, qui est soupçonné d’influencer grandement les propriétés des fibres, sont identifiées. Finalement, l’ensemble des méthodologies développées sont appliquées sur des fibres individuelles de polystyrène pour l’étude approfondie de l’orientation et du désenchevêtrement sur une large gamme de diamètres et pour une grande quantité de fibres. Cette dernière étude permet l’établissement de la première relation structure/propriétés de ces matériaux, à l’échelle individuelle, en montrant clairement le lien entre l’orientation moléculaire, le désenchevêtrement et le module d'élasticité des fibres.

Composition of sedimentary rocks from the Shapkina River valley, Bolshezemelskaya Tundra

A facies-genetic and stratigraphic subdivision of the Quaternary sequence in the Shapkina River valley has been accomplished. The riverbank shows outcrops of three glacial complexes with different mineralogical-petrographic compositions and structural characteristics, which can be correlated and stratificated. Datings of intermoraine horizons (alluvial, marine, lacustrine, and lacustrine-boggy sediments) have been based on palynological and paleomicrotheriological data. The Middle Neopleistocene section can be divided into two till horizons corresponding to two autonomous glaciations (Pechora and Vychegda). They are separated by a member of subaqueous Rodionov sediments. The Pechora till formed in the course of glacier motions from the northeast. Glacial horizons are mainly composed of the Vychegda till transported from the Northwest terrigenous provenance. Lithology of the Upper Neopleistocene Polyarnyi till testifies to its formation in the upper course of the river from material transported from the Northeast terrigenous-mineralogical provenance in the upper course of the river and from the Fennoscandian glaciation center in the lower course of the river. The paper presents the first lithological investigation and substantiation of genesis of various facies of Neopleistocene intermoraine marine sediments (sediments of the beach and fore-beach zones and shallow-water shelf).

1980 census of housing.

Tables.

1990 census of population and housing.

"Census '90"--Cover.

Submicron dispersions of hexosomes based on novel glycerate surfactants

Glycerate-based surfactants are a new class of swelling amphiphiles which swell to a finite degree with water. Among this class of surfactants, oleyl (cis-octadec-9-enyl) glycerate is very similar in structure to a well characterized mesophase-forming lipid, glyceryl monooleate (GMO). Despite the similar structural characteristics, a subtle change in connectivity of the ester bond substantially alters the binary surfactant-water phase behaviour. Whereas the phase behaviour of GMO is diverse and dominated by cubic phases, the phase behaviour of oleyl glycerate and a terpenoid analogue phytanyl (3,7,11,15-tetramethyl-hexadecane) glycerate is much simplified. Both exhibit an inverse hexagonal phase (H-II), which is stable to dilution with excess water, and an inverse micellar phase (L-II) at ambient temperatures. The inverse hexagonal phases formed by oleyl glycerate and phytanyl glycerate have been characterized using SAXS. Analogous to GMO cubosomes, the inverse hexagonal phase of phytanyl glycerate has been dispersed to form hexagonally facetted particles, termed hexosomes, whose structure has been verified using cryo-TEM.

Interfacial interactions and structure of polyurethane intercalated nanocomposite

Understanding the interfacial interactions between the nanofiller and polymer matrix is important to improve the design and manufacture of polymer nanocomposites. This paper reports a molecular dynamic Study on the interfacial interactions and structure of a clay-based polyurethane intercalated nanocomposite. The results show that the intercalation of surfactant (i.e. dioctadecyldlmethyl ammonium) and polyurethane (PU) into the nanoconfined gallery of clay leads to the multilayer structure for both surfactant and PU, and the absence of phase separation for PU chains. Such structural characteristics are attributed to the result of competitive interactions among the surfactant, PU and the clay surface, including van der Waals, electrostatic and hydrogen bonding.

Nephron number, hypertension, renal disease, and renal failure

Essential hypertension is one of the most common diseases in the Western world, affecting about 26.4% of the adult population, and it is increasing (1). Its causes are heterogeneous and include genetic and environmental factors (2), but several observations point to an important role of the kidney in its genesis (3). In addition to variations in tubular transport mechanisms that could, for example, affect salt handling, structural characteristics of the kidney might also contribute to hypertension. The burden of chronic kidney disease is also increasing worldwide, due to population growth, increasing longevity, and changing risk factors. Although single-cause models of disease are still widely promoted, multideterminant or multihit models that can accommodate multiple risk factors in an individual or in a population are probably more applicable (4,5). In such a framework, nephron endowment is one potential determinant of disease susceptibility. Some time ago, Brenner and colleagues (6,7) proposed that lower nephron numbers predispose both to essential hypertension and to renal disease. They also proposed that hypertension and progressive renal insufficiency might be initiated and accelerated by glomerular hypertrophy and intraglomerular hypertension that develops as nephron number is reduced (8). In this review, we summarize data from recent studies that shed more light on these hypotheses. The data supply a new twist to possible mechanisms of the Barker hypothesis, which proposes that intrauterine growth retardation predisposes to chronic disease in later life (9). The review describes how nephron number is estimated and its range and some determinants and morphologic correlates. It then considers possible causes of low nephron numbers. Finally, associations of hypertension and renal disease with reduced nephron numbers are considered, and some potential clinical implications are discussed.

Mechanical disruption of seagrass in the digestive tract of the dugong

The cheek teeth in dugongs are considered to be largely non-functional whereas the oral horny pads are important both in mechanical disruption of the diet and in conveying seagrass through the mouth. Particle size distributions of digesta from 41 dead stranded dugongs were examined to investigate the relationship between degree of food breakdown, gut region and functional surface area of the mouthparts. The in vitro ease of fracture of major dietary seagrass species were compared. The rate of food breakdown through the gut appears to be more closely linked to fibre level of the diet than to size or age of the dugong and its mouthparts. Low fibre seagrass, for example Halophila ovalis, breaks down at a faster rate than high fibre seagrass, for example Zostera capricorni both in dugong guts and in vitro. Several structural characteristics of seagrass, including level and arrangement of fibre, and water content, make it particularly amenable to mechanical breakdown. The soft mouthparts of the dugong are highly modified so that the entire oral cavity functions to crush low fibre seagrasses. Thus, the dugong has developed an efficient method of food ingestion and mastication that is suited to processing large quantities of soft seagrass during short dive times. The potential cost to the dugong in having lost its hard dental surfaces is that it has become restricted to a low fibre diet.

Growth hormone as a cytokine

1. The growth hormone (GH) receptor was the first of the class 1 cytokine receptors to be cloned. It shares a number of structural characteristics with other family members and common signalling mechanisms based on common usage of the Janus kinase 2 (JAK2). 2. Growth hormone receptor activation is initiated by GH-induced homodimerization of receptor molecules. This has enabled the creation of specific hormone antagonists that block receptor dimerization. 3. The details of the transcription factors used by the activated receptor are being revealed as a result of promoter analyses and electrophoretic mobility gelshift analysis. 4. Growth hormone receptors are widespread and their discovery in certain tissues has led to the assignment of new physiological roles for GH, Some of these involve local or paracrine roles for GH, as befits its cytokine status. 5. Four examples of such novel roles are discussed, These are: (i) the brain GH axis; (ii) GH and the vitamin B-12 axis; (iii) GH in early pre-implantation development; and (iv) GH in development of the tooth. 6. We propose that the view that GH acts through the intermediacy of insulin-like growth factor-1 is simplistic; rather, GH acts to induce an array of growth factors and their receptors and the composition of this array varies with tissue type and, probably, stage of development.

Diastolic dysfunction is a manifestation of ventricular-vascular interaction in patients with type 2 diabetes mellitus

Vascular disease is accelerated in patients with Type 2 diabetes mellitus (T2DM). Since the systemic vasculature plays a pivotal role in myocardial loading, this study aimed to determine the effect of arterial characteristics on left ventricular (LV) morphology and function in patients with T2DM. Conventional echocardiography and tissue Doppler imaging were performed in 172 T2DM patients (95 men; aged 55±11y) with preserved ejection fraction (62±5%). Patients were stratified into groups based on LV geometric pattern (normal [n = 79], concentric remodeling [n = 33], concentric hypertrophy [n = 29], eccentric hypertrophy [n = 31]). Total arterial compliance (TAC) was recorded by simultaneous radial tonometry and aortic outflow pulsed wave Doppler. Arterial (brachial and carotid) structure and function were determined by standard ultrasound methods. There were no significant differences between the LV geometric groups in demographic or clinical parameters. The concentric hypertrophy group had significantly increased carotid artery diameter (6.0±0.7mm versus 6.5±0.7mm; p < 0.05) and stiffness (1912±1203 dynes/cm2mm versus 2976±2695 dynes/cm2mm×10−6; p < 0.05) compared to those with normal geometry. However, TAC did not differ between groups. LV diastolic function, as determined by the ratio of diastolic mitral inflow velocity to mitral annulus tissue velocity (E/E_), was significantly associated with carotid artery relative wall thickness and intima media thickness (p < 0.05). Moreover, E/E_ was independently predicted by carotid artery relative wall thickness (β = 22.9; p = 0.007). We conclude that structural characteristics of the carotid artery are associated with abnormal LV structure and function in patients with T2DM. The LV functional irregularities may be a downstream consequence of amplified pressure wave reflections effecting sub-optimal ventricular-vascular interaction.

Direct numerical simulation of turbulent flow and mass transfer around a rotating circular cylinder

Turbulent flow around a rotating circular cylinder has numerous applications including wall shear stress and mass-transfer measurement related to the corrosion studies. It is also of interest in the context of flow over convex surfaces where standard turbulence models perform poorly. The main purpose of this paper is to elucidate the basic turbulence mechanism around a rotating cylinder at low Reynolds numbers to provide a better understanding of flow fundamentals. Direct numerical simulation (DNS) has been performed in a reference frame rotating at constant angular velocity with the cylinder. The governing equations are discretized by using a finite-volume method. As for fully developed channel, pipe, and boundary layer flows, a laminar sublayer, buffer layer, and logarithmic outer region were observed. The level of mean velocity is lower in the buffer and outer regions but the logarithmic region still has a slope equal to the inverse of the von Karman constant. Instantaneous flow visualization revealed that the turbulence length scale typically decreases as the Reynolds number increases. Wavelet analysis provided some insight into the dependence of structural characteristics on wave number. The budget of the turbulent kinetic energy was computed and found to be similar to that in plane channel flow as well as in pipe and zero pressure gradient boundary layer flows. Coriolis effects show as an equivalent production for the azimuthal and radial velocity fluctuations leading to their ratio being lowered relative to similar nonrotating boundary layer flows.

ASPECTOS PSICODINÂMICOS E CAPACIDADE MATERNA DE MÃES DE CRIANÇAS ABRIGADAS

Este estudo teve como objetivos investigar aspectos da dinâmica intrapsíquica de mães de crianças institucionalizadas em abrigo por ordem judicial, e identificar recursos defensivos utilizados por essas mães. Para atingir estes objetivos, realizou-se uma investigação clínica com estudo de três casos de mães de crianças abrigadas. Foram utilizados dois instrumentos: a) Roteiro de Entrevista roteiro de temas a serem abordados em uma ou mais entrevistas não diretivas de cunho clínico, a fim de auxiliar na investigação da psicodinâmica destas mães. b) Procedimento de Desenho Estória com Tema técnica projetiva que associa o uso de desenhos com estórias, como forma de explorar livre e dinamicamente os conteúdos da personalidade. A técnica permite o estudo das características formais e estruturais da personalidade, pois tem a particularidade de facilitar a expressão de aspectos inconscientes relacionados a pontos de angústias presentes, focos conflituosos e perturbações emergentes. Estes procedimentos foram realizados nas dependências da instituição (abrigo) onde as crianças estavam hospedadas. Os principais resultados comuns aos três casos foram: Ambigüidade e os Impeditivos de Crescimento a primeira mãe entrevistada ao mesmo tempo ataca a mãe que a abandona (mãe biológica e a mãe adotiva), em busca de uma mãe idealizada. Essa ambigüidade a impede de crescer. Nota-se a mesma tentativa de idealização na segunda mãe estudada que demonstra dificuldade em aceitar a atual situação em que vive e não consegue perceber que a aproximação de sua mãe é por causa da doença que ela adquiriu e não por continência. A terceira e última mãe entrevistada demonstra conteúdos persecutórios diante do abrigamento dos filhos e dificuldade de sentir gratidão. Os mecanismos predominantes que aparecem nos três casos são os de: idealização e regressão a estágios primitivos. Nota-se ainda, depressão, dificuldade de elaboração da posição depressiva. Estas mães não conseguem vivenciar continuamente a realidade psíquica, que implicaria na elaboração da posição depressiva, pois não conseguem fazer, ainda que tentem, uma comparação entre os mundos interno e externo, o que as levariam à uma melhor compreensão das semelhanças e diferenças. De modo que, a figura dos pais (principalmente da mãe) fica cindida entre aterrorizante e idealizada, porém os mecanismos predominantes são suas fantasias que propiciam idealização; identificação projetiva maciça. A persecutoriedade e a culpa, ao mesmo tempo parecem indicar a depressão que pode ser tão forte que levam à intensificação destes sentimentos. Há a presença da inveja que também intensifica as angústias persecutórias, requerendo mecanismos de defesa que violentam as funções psíquicas.(AU)

Modelling foreign direct investment in China

This thesis consists of three empirical and one theoretical studies. While China has received an increasing amount of foreign direct investment (FDI) and become the second largest host country for FDI in recent years, the absence of comprehensive studies on FDI inflows into this country drives this research. In the first study, an econometric model is developed to analyse the economic, political, cultural and geographic determinants of both pledged and realised FDI in China. The results of this study suggest that China's relatively cheaper labour force, high degree of international integration with the outside world (represented by its exports and imports) and bilateral exchange rates are the important economic determinants of both pledged FDI and realised FDI in China. The second study analyses the regional distribution of both pledged and realised FDI within China. The econometric properties of the panel data set are examined using a standardised 't-bar' test. The empirical results indicate that provinces with higher level of international trade, lower wage rates, more R&D manpower, more preferential policies and closer ethnic links with overseas Chinese attract relatively more FDI. The third study constructs a dynamic equilibrium model to study the interactions among FDI, knowledge spillovers and long run economic growth in a developing country. The ideas of endogenous product cycles and trade-related international knowledge spillovers are modified and extended to FDI. The major conclusion is that, in the presence of FDI, economic growth is determined by the stock of human capital, the subjective discount rate and knowledge gap, while unskilled labour can not sustain growth. In the fourth study, the role of FDI in the growth process of the Chinese economy is investigated by using a panel of data for 27 provinces across China between 1986 and 1995. In addition to FDI, domestic R&D expenditure, international trade and human capital are added to the standard convergence regressions to control for different structural characteristics in each province. The empirical results support endogenous innovation growth theory in which regional per capita income can converge given technological diffusion, transfer and imitation.

Environmental scanning electron microscope imaging of vesicle systems

The structural characteristics of liposomes have been widely investigated and there is certainly a strong understanding of their morphological characteristics. Imaging of these systems, using techniques such as freeze-fracturing methods, transmission electron microscopy, and cryo-electron imaging, has allowed us to appreciate their bilayer structures and factors that influence this. However, there are a few methods that study these systems in their natural hydrated state; commonly, the liposomes are visualized after drying, staining and/or fixation of the vesicles. Environmental scanning electron microscopy (ESEM) offers the ability to image a liposome in its hydrated state without the need for prior sample preparation. We were the first to use ESEM to study the liposomes and niosomes, and have been able to dynamically follow the hydration of lipid films and changes in liposome suspensions as water condenses onto, or evaporates from, the sample in real-time. This provides an insight into the resistance of liposomes to coalescence during dehydration, thereby providing an alternative assay for liposome formulation and stability.

Assessment of cell viability in a three-dimensional enzymatically cross-linked collagen scaffold

Microbial transglutaminase (mTGase) is an enzyme that introduces a covalent bond between peptide bound glutamine and lysine residues. Proteins cross-linked in this manner are often more resistant to proteolytic degradation and show increased tensile strength. This study evaluates the effects of mTGase mediated cross-linking of collagen on the cellular morphology, behaviour and viability of murine 3T3 fibroblasts following their seeding into collagen scaffolds. Additionally, cell mediated scaffold contraction, porosity and level of cross-linking of the scaffold has been analysed using image analysis software, scanning electron microscopy (SEM), colorimetric assays, and Fourier transform infrared spectroscopy (FTIR). We demonstrate that the biocompatibility and cellular morphology, when comparing cultures of fibroblasts integrated in mTGase cross-linked collagen scaffolds with the native collagen counterparts, remained unaffected. It has been also elicited that the structural characteristics of collagen have been preserved while introducing enzymatically resistant covalent bonds.