Stiffness tomography by atomic force microscopy.

The atomic force microscope is a convenient tool to probe living samples at the nanometric scale. Among its numerous capabilities, the instrument can be operated as a nano-indenter to gather information about the mechanical properties of the sample. In this operating mode, the deformation of the cantilever is displayed as a function of the indentation depth of the tip into the sample. Fitting this curve with different theoretical models permits us to estimate the Young's modulus of the sample at the indentation spot. We describe what to our knowledge is a new technique to process these curves to distinguish structures of different stiffness buried into the bulk of the sample. The working principle of this new imaging technique has been verified by finite element models and successfully applied to living cells.

Investigation of High Performance Concrete Pavement, MLR-05-01, 2006

The Iowa DOT has been using blended cements in ternary mixes since 1999. Use of these supplementary cementitious materials gives concrete with higher strengths and much lower permeability. Use of these materials has been incorporated for use in High Performance Concrete (HPC) decks to achieve lower permeability and thus long term performance. Since we have been using these materials in paving, it would be informative to determine what concrete pavement properties are enhanced as related to high performance concrete. The air void system was excellent at a spacing factor of 0.0047 in (0.120 mm). AVA spacing factor results are much higher than the hardened air void analysis. Although only 3 samples were tested between the image analysis air content and the RapidAir457, there is pretty good agreement between those test methods. Air void analysis indicates that excessive vibration was not required to place the concrete. Vibration was well within the specification limits with an average of 6683 vpm’s with a standard deviation of 461. Overall ride of the project was very good. The average smoothness for the project was 2.1 in/mile (33.8 mm/km). The International Roughness Index (IRI) was 81 in/mi (1.29 m/km). The compressive strength was 6260 psi (43.2 MPa) at 28 days and 6830 (47.1 MPa) at 56 days. The modulus of rupture by third point loading (MOR-TPL) tested at 28 days was 660 psi (4.55 MPa). The AASHTO T277 rapid chloride permeability results at 28 days using the Virginia cure method correlate fairly well with the 56 and 90 day results with standard curing. The Virginia cure method 28 day results were 2475 coulombs and the standard cure 56 and 90 day test results were 2180 and 2118, respectively.

Evaluation of Long-Term Field Performance of Cold In-Place Recycled Roads: Field and Laboratory Testing, TR-502, 2007

Cold in-place recycling (CIR) has become an attractive method for rehabilitating asphalt roads that have good subgrade support and are suffering distress related to non-structural aging and cracking of the pavement layer. Although CIR is widely used, its use could be expanded if its performance were more predictable. Transportation officials have observed roads that were recycled under similar circumstances perform very differently for no clear reason. Moreover, a rational mix design has not yet been developed, design assumptions regarding the structural support of the CIR layer remain empirical and conservative, and there is no clear understanding of the cause-effect relationships between the choices made during the design/construction process and the resulting performance. The objective of this project is to investigate these relationships, especially concerning the age of the recycled pavement, cumulative traffic volume, support conditions, aged engineering properties of the CIR materials, and road performance. Twenty-four CIR asphalt roads constructed in Iowa from 1986 to 2004 were studied: 18 were selected from a sample of roads studied in a previous research project (HR-392), and 6 were selected from newer CIR projects constructed after 1999. This report describes the results of comprehensive field and laboratory testing for these CIR asphalt roads. The results indicate that the modulus of the CIR layer and the air voids of the CIR asphalt binder were the most important factors affecting CIR pavement performance for high-traffic roads. For low-traffic roads, the wet indirect tensile strength significantly affected pavement performance. The results of this research can help identify changes that should be made with regard to design, material selection, and construction in order to improve the performance and cost-effectiveness of future recycled roads.

Hyperbolic type metrics and distortion of quasiconformal map pings

This Ph.D. thesis consists of four original papers. The papers cover several topics from geometric function theory, more specifically, hyperbolic type metrics, conformal invariants, and the distortion properties of quasiconformal mappings. The first paper deals mostly with the quasihyperbolic metric. The main result gives the optimal bilipschitz constant with respect to the quasihyperbolic metric for the M¨obius self-mappings of the unit ball. A quasiinvariance property, sharp in a local sense, of the quasihyperbolic metric under quasiconformal mappings is also proved. The second paper studies some distortion estimates for the class of quasiconformal self-mappings fixing the boundary values of the unit ball or convex domains. The distortion is measured by the hyperbolic metric or hyperbolic type metrics. The results provide explicit, asymptotically sharp inequalities when the maximal dilatation of quasiconformal mappings tends to 1. These explicit estimates involve special functions which have a crucial role in this study. In the third paper, we investigate the notion of the quasihyperbolic volume and find the growth estimates for the quasihyperbolic volume of balls in a domain in terms of the radius. It turns out that in the case of domains with Ahlfors regular boundaries, the rate of growth depends not merely on the radius but also on the metric structure of the boundary. The topic of the fourth paper is complete elliptic integrals and inequalities. We derive some functional inequalities and elementary estimates for these special functions. As applications, some functional inequalities and the growth of the exterior modulus of a rectangle are studied.

Comparison of the quantification of caffeine in human plasma by gas chromatography and ELISA

In the present study we evaluated the precision of the ELISA method to quantify caffeine in human plasma and compared the results with those obtained by gas chromatography. A total of 58 samples were analyzed by gas chromatography using a nitrogen-phosphorus detector and routine techniques. For the ELISA test, the samples were diluted to obtain a concentration corresponding to 50% of the absorbance of the standard curve. To determine whether the proximity between the I50 of the standard curve and that of the sample would bring about a more precise result, the samples were divided into three blocks according to the criterion of difference, in modulus, of the I50 of the standard curve and of the I50 of the sample. The samples were classified into three groups. The first was composed of 20 samples with I50 up to 1.5 ng/ml, the second consisted of 21 samples with I50 ranging from 1.51 to 3 ng/ml, and the third of 17 samples with I50 ranging from 3.01 to 13 ng/ml. The determination coefficient (R² = 0.999) showed that the data obtained by gas chromatography represented a reliable basis. The results obtained by ELISA were also reliable, with an estimated Pearson correlation coefficient of 0.82 between the two methods. This coefficient for the different groups (0.88, 0.79 and 0.49 for groups 1, 2 and 3, respectively) showed greater reliability for the test with dilutions closer to I50.

Effect of addition of different hydrocolloids on pasting, thermal, and rheological properties of cassava starch

Starches and gums are hydrocolloids frequently used in food systems to provide proper texture, moisture, and water mobility. Starch-gum interaction in food systems can change the starch granule swelling and its gelatinization and rheological properties. In this study, the effect of the addition of xanthan gum (XG), sodium carboxymethyl cellulose (SCMC), and carrageenan (CAR) at the concentrations of the 0.15, 0.25, 0.35 and 0.45% (w/v) on the pasting, thermal, and rheological properties of cassava starch was studied. The swelling power (SP) and the scanning electron microscopy (SEM) of the starch gels were also evaluated. The results obtained showed that xanthan gum (XG) had a strong interaction with the cassava starch penetrating between starch granules causing increase in pasting viscosities, SP, storage and loss (G', and G", respectively) modulus and reduction in the setback of the starch; sodium carboxymethyl cellulose (SCMC) greatly increased the pasting viscosities, the SP, and the storage and loss (G', and G", respectively) modulus of the starch-mixtures, mainly due to its greater capacity to hold water and not due to the interaction with cassava starch. Carrageenan (CAR) did not change any of the starch properties since there was no interaction between this gum and cassava starch at the concentrations used.

Measurement of forces between and within bilayers of neutral phospholipids

Phospholipids in water form lamellar phases made up of alternating layers of water and bimolecular lipid leaflets. Three complementary methods, osmotic, mechanical, and vapour pressures, were used to measure the work of removing water from lamellar phases composed of frozen dipalmitoylphosphatidylcholine ( DPPC ), melted DPPC, egg phosphatidylethanolamine or equimolar mixtures of DPPC and cholesterol ( DPPC/CHOL ), Concurrently the structural changes that resulted from this water removal were measured using X-ray diffraction. The work was divided into that which forces the bilayers together ( F ) and that which compresses the molecules together within the bilayers ( F )# A large repulsive force exists between bilayers composed of each of the lipids studied and this force increases exponentially as bilayer separation is decreased. F is affected by the nature of the head groups, conformation of the acyl chains and heterogeneity of these chains. In general all of the melted phosphatidylcholines ( melted DPPC, egg lecithin and DPPC/CHOL ) have large equilibrium separations in excess water resulting from large repulsive hydration forces between these bilayers. By comparison, egg PE has an increased attractive force, and frozen DPPC has a decreased hydration force; each results in smaller separations in water for these two lipids. The chemical potentials of the water between the bilayers for all these lipids lie on a continuum, indicating that interbilayer water cannot be characterized by two discrete states, usually referred to as "bound" or "non**bound". For all lipids studied a maximum of 25 % of the total work done on the system goes into deforming the bilayers. The method used here viii to separate repulsion from deformation, developed for us by v. A. Parsegian, provides a unique method for the measurement of lateral pressure of a bilayer and its modulus of deformability ( Y ). Lateral pressure is affected by the nature of the head group, conformation and heterogeneity of the acyl chains. For small changes in molecular surface area ( A ) near equilibrium, both melted and frozen DPPC have similar values for the deformability modulus. Thus in this regime it requires about the same force to change the angle of tilt of frozen chains as it does to compress the fluid bilayer. The introduction of cholesterol into bilayers of DPPC reduces dramatically the lateral pressure of the bilayers over a large range of molecular surface areas ( A ). The variation in the magnitude of bilayer repulsion with different phospholipids provides a basis for the mechanism of lipid segregation in mixed lipid systems and suggests that interacting heterogeneous membranes may influence or modulate the composition of the opposing membrane. The measurements of deformabilities of bilayers provides a direct comparison of them with the properties of monolayers.

The role of water in determining structure and function of macromolecules and macromolecular assemblies /

The interaction of biological molecules with water is an important determinant of structural properties both in molecular assemblies, and in conformation of individual macromolecules. By observing the effects of manipulating the activity of water (which can be accomplished by limiting its concentration or by adding additional solutes, "osmotic stress"), one can learn something about intrinsic physical properties of biological molecules as well as measure an energetic contribution of closely associated water molecules to overall equilibria in biological reactions. Here two such studies are reported. The first of these examines several species of lysolipid which, while present in relatively low concentrations in biomembranes, have been shown to affect many cellular processes involving membrane-protein or membrane-membrane interactions. Monolayer elastic constants were determined by combining X-ray diffraction and the osmotic stress technique. Spontaneous radii of curvature of lysophosphatidylcholines were determined to be positive and in the range +30A to +70A, while lysophosphatidylethanolamines proved to be essentially flat. Neither lysolipid significantly affected the bending modulus of the monolayer in which it was incorporated. The second study examines the role of water in theprocess of polymerization of actin into filaments. Water activity was manipulated by adding osmolytes and the effect on the equilibrium dissociation constant (measured as the criticalmonomer concentration) was determined. As water activity was decreased, the critical concentration was reduced for Ca-actin but not for Mg-actin, suggesting that 10-12 fewer water molecules are associated with Ca-actin in the polymerized state. Thisunexpectedly small amount of water is discussed in the context of the common structural motif of a nucleotide binding cleft.

The effects of gramicidin on the structure of phospholipid assemblies /

Gramicidin is an antibiotic peptide that can be incorporated into the monolayers of cell membranes. Dimerization through hydrogen bonding between gramicidin monomers in opposing leaflets of the membrane results in the formation of an iontophoretic channel. Surrounding phospholipids, with various associated mechanical properties, have been shown to influence the gating properties of this channel. Conversely, gramicidin incorporation has been shown to affect the structure of spontaneously formed lipid assemblies. Using small-angle x-ray diffraction and model systems composed of phospholipids and gramicidin, the physical effects incurred by gramicidin incorporation were measured. The reverse hexagonal (H^) phase composed of dioleoylphosphatidylethanolamine (DOPE) monolayers decreased in lattice dimension with increasing incorporation of gramicidin. This indicated that gramicidin was adding negative curvature to the monolayers. In this system, gramicidin was measured to have an apparent intrinsic radius of curvature (Rop*™") of -7. 1 A. The addition of up to 4 mol% gramicidin in mixtures with DOPE did not result in the monolayers becoming stiffer, as indicated by unaltered bending moduli for each composition. Dioleoylphosphatidylcholine (DOPC) alone forms the lamellar (LJ phase when hydrated, but undergoes a transition into the H^ phase when mixed with gramicidin. The lattice repeat dimension decreases systematically with increased gramicidin content. Again, this indicated that gramicidin was adding negative curvature to the monolayers. At 12 mol% gramicidin in mixtures with DOPC, the apparent radius of intrinsic curvature of gramicidin (Rop*"^) was measured to be -7.4 A. This mixture formed monolayers that were very resistant to bending under osmotic pressure, with a measured bending modulus of 1 15 kT. The measurements made in this study demonstrate that peptides are able to modulate the spontaneous curvature and other mechanical properties of phospholipid assemblies.

Etude des propriétés physicochimiques des vecteurs nanoparticulaires

Cette thèse rapporte l’étude des propriétés physicochimiques des nanoparticles polymériques et leur impact sur l’interaction avec les cellules vivantes. Nous nous sommes tout spécialement attachés à étudier l’effet des propriétés adhésives et mécaniques des nanoparticules sur leur capacité de pénétration de la membrane cellulaire. Pour ce faire, nous avons tout d’abord utilisé des nanoparticules d’acide polylactique (PLA) fonctionnalisées en surface avec un ligand des sélectines E et P. Le greffage du ligand sur la particule s’est fait par une nouvelle méthode expérimentale garantissant la présence du ligand à la surface de la particule durant toute sa durée de vie. Cette méthode consiste à mélanger un polymère fonctionnalisé avec le ligand avec un autre polymère non fonctionnalisé. La présence du ligand à la surface des nanoparticules formées à partir de ce mélange de polymères a été confirmée par analyse ToF SIMS. Nous avons pu prouver que les particules possédant le ligand greffé à leur surface démontraient une capacité adhésive supérieure à leurs homologues non fonctionnalisés sur des cellules endothéliales HUVEC activées par différentes drogues. De plus, le captage des particules par les cellules HUVEC est modulé par le niveau d’expression des récepteurs selectine E et P et aussi par la quantité de ligand libre. Ces résultats montrent clairement que le greffage du ligand confère aux particules des propriétés adhésives accrues et spécifiques ce qui permet leur usage postérieure comme vecteur pharmaceutique capable de cibler un récepteur particulier à la surface d’une cellule. Nous avons aussi démontré que l’interaction entre les nanoparticules et la membrane cellulaire peut aussi être contrôlée aussi bien par les propriétés mécaniques de la cellule que de la nanoparticule. Dans une première étape, nous avons mesuré à l’aide de l’appareil de forces de surface l’élasticité de cellules macrophagiques déposées sur différents substrats. En contrôlant l’interaction entre la cellule et le substrat sur lequel elle repose nous avons montré qu’il était possible de modifier à ii volonté les propriétés mécaniques cellulaire. Une augmentation de l’élasticité cellulaire s’accompagne d’une augmentation systématique de l’internalisation de nanoparticules de PLA non fonctionnalisées. Ceci suggère un rôle prépondérant des propriétés mécaniques du cortex cellulaire dans le captage des nanoparticules de PLA. Dans une seconde étape, nous avons étudié l’effet des propriétés mécaniques des nanoparticules sur leur capacité de pénétration cellulaire. Pour ce faire, nous avons synthétisé des particules d’hydrogel dont l’élasticité était contrôlée par le degré d’agent réticulant inclus dans leur formulation. Le contrôle des propriétés mécaniques des nanoparticules a été confirmé par la mesure du module de Young des particules par microscopie de force atomique. L’impact des propriétés mécaniques de ces particules sur leur capacité de pénétration dans les cellules vivantes a été étudié sur des cellules macrophagiques de souris. Les résultats ont montré que la cinétique d’internalisation, la quantité de particules internalisées et le mécanisme d’internalisation dépendent tous du module de Young des nanoparticules. Aucune différence dans le trajet intracellulaire des particules n’a pu être observée malgré le fait que différentes voies d’internalisation aient été observées. Ce dernier résultat peut s’expliquer par le fait que les nanoparticules sont internalisées par plusieurs voie simultanément ce qui facilite leur accumulation dans les organelles digestives intracellulaires. Un modèle simple permettant d’expliquer ces résultats a été proposé et discuté.

Use of Amine Terminated Liquid Natural Rubber as a Plasticiser in Filled NR andNBR Compounds

Amine Terminated Liquid Natural Rubber (ATNR) was used as a plasticiser in filled NR and NBR compounds replacing oil/DOP. The scorch time and cure time were found to be lowered when ATNR was used as the plasticiser. ATNR was found to improve the mechanical properties like tensile strength, tear strength and modulus of the vulcanizates . The ageing resistance of the vulcanizates containing ATNR was superior compared to the vulcanizates containing oil/DOP.

Ultrasonic measurement of the elastic constants of selected nonlinear optical /semiorganic crystals with orthorhombic symmetry

Ultrasonic is a good tool to investigate the elastic properties of crystals. It enables one to determine all the elastic constants, Poisson’s ratios, volume compressibility and bulk modulus of crystals from velocity measurements. It also enables one to demonstrate the anisotropy of elastic properties by plotting sections of the surfaces of phase velocity, slowness, group velocity, Young’s modulus and linear compressibility along the a-b, b-c and a-c planes. They also help one to understand more about phonon amplification and help to interpret various phenomena associated with ultrasonic wave propagation, thermal conductivity, phonon transport etc. Study of nonlinear optical crystals is very important from an application point of view. Hundreds of new NLO materials are synthesized to meet the requirements for various applications. Inorganic, organic and organometallic or semiorganic classes of compounds have been studied for several reasons. Semiorganic compounds have some advantages over their inorganic and inorganic counterparts with regard to their mechanical properties. High damage resistance, high melting point, good transparency and non-hygroscopy are some of the basic requirements for a material to be suitable for device fabrication. New NLO materials are being synthesized and investigation of the mechanical and elastic properties of these crystals is very important to test the suitability of these materials for technological applications

Studies on the Production, Properties and Processability of Low Protein Latex

Latex protein allergy is a serious problem faced by users of natural rubber latex products. This is severe in health care workers, who are constantly using latex products like examination gloves, surgical gloves etc. Out of the total proteins only a small fraction is extractable and only these proteins cause allergic reactions in sensitized people. Enzymic deproteinisation of latex and leaching and chlorination of latex products are the common methods used to reduce the severity of the problem.Enzyme deproteinisation is a cubersome process involving high cost and process loss.Physical properties of such films are poor. Leaching is a lengthy process and in leached latex products presence of extractable proteins is observed on further storing. Chlorination causes yellowing of latex products and reduction in tensile properties.In this context a more simple process of removal of extractable proteins from latex itself was investigated. This thesis reports the application of poly propylene glycol (PPG) to displace extractable proteins from natural latex. PPG is added to 60 % centrifuged natural latex to the extent of 0.2 % m/rn, subssequently diluted to 30 % dry rubber content and again concentrated to obtain a low protein latex.Dilution of concentrated latex and subsequent concentration lead to a total reduction in non - rubber solids in the concentrate, especially proteins and reduction in the ionic concentration in the aqueous phase of the latex. It has been reported that proteins in natural rubber / latex affect its behaviour in the vulcanisation process. Ionic concentration in the aqueous phase of latex influence the stability, viscosity and flow behaviour of natural latex. Hence, a detailed technological evaluation was carried out on this low protein latex. In this study, low protein latex was compared with single centrifuged latex ( the raw material to almost every latex product), double centrifuged latex ( because dilution and second concentration of latex is accompanied by protein removal to some extent and reduction in the ionic concentration of the aqueous phase of latex.). Studies were conducted on Sulphur cure in conventional and EV systems under conditions of post ~ cure and prevulcanisation of latex. Studies were conducted on radiation cure in latex stage. Extractable protein content in vulcanised low protein latex films are observed to be very low. lt is observed that this low protein latex is some what slower curing than single centrifuged latex, but faster than double centrifuged latex. Modulus of low protein latex films were slightly low. In general physical properties of vulcanised low protein latex films are only siightly lower than single centrifuged latex. Ageing properties of the low protein latex films were satisfactory. Viscosity and flow behaviour of low protein latex is much better than double centrifuged latex and almost comparable to single centrifuged latex. On observing that the physical properties and flow behaviour of low protein latex was satisfactory, it was used for the preparation of examination gloves and the gloves were evaluated. It is observed that the properties are conforming to the Indian Standard Specifications. It is thus observed that PPG treatment of natural latex is a simple process of preparing low protein latex. Extractable protein content in these films are very low.The physical properties of the films are comparable to ordinary centrifuged latex and better than conventionally deprotenized latex films. This latex can be used for the production of examination gloves.

On the magnetic, mechanical and rheological properties of rubber–nickel nanocomposites

Rubber–nickel nanocomposites were synthesized by incorporating freshly prepared nanometric nickel particles in two different matrices namely natural rubber and neoprene rubber according to specific recipes for various loadings of nano nickel and the cure characteristics of these composites were evaluated. The maximum torque values register an increase with the increase in loading of nickel in both composites and this is attributed to the non-interacting nature of nickel nanoparticles with rubber matrices. The cure time of natural rubber composites decreases with increase in the content of nickel, and in neoprene rubber cure, time increases with increase in filler content. In natural rubber, the curing reaction seems to be activated by the presence of nickel particles. The magnetization studies of the composites reveal that the magnetic properties of nickel are retained in the composite samples. The elastic modulus of natural rubber and neoprene rubber are largely improved by the incorporation of nickel particles

Modification of Polypropylene/High Density Polyethylene Blend Using Nanokaolinite Clay and E-Glass Fibre: Preparation, Characterization and Micromechanical Modelling

Upgrading two widely used standard plastics, polypropylene (PP) and high density polyethylene (HDPE), and generating a variety of useful engineering materials based on these blends have been the main objective of this study. Upgradation was effected by using nanomodifiers and/or fibrous modifiers. PP and HDPE were selected for modification due to their attractive inherent properties and wide spectrum of use. Blending is the engineered method of producing new materials with tailor made properties. It has the advantages of both the materials. PP has high tensile and flexural strength and the HDPE acts as an impact modifier in the resultant blend. Hence an optimized blend of PP and HDPE was selected as the matrix material for upgradation. Nanokaolinite clay and E-glass fibre were chosen for modifying PP/HDPE blend. As the first stage of the work, the mechanical, thermal, morphological, rheological, dynamic mechanical and crystallization characteristics of the polymer nanocomposites prepared with PP/HDPE blend and different surface modified nanokaolinite clay were analyzed. As the second stage of the work, the effect of simultaneous inclusion of nanokaolinite clay (both N100A and N100) and short glass fibres are investigated. The presence of nanofiller has increased the properties of hybrid composites to a greater extent than micro composites. As the last stage, micromechanical modeling of both nano and hybrid A composite is carried out to analyze the behavior of the composite under load bearing conditions. These theoretical analyses indicate that the polymer-nanoclay interfacial characteristics partially converge to a state of perfect interfacial bonding (Takayanagi model) with an iso-stress (Reuss IROM) response. In the case of hybrid composites the experimental data follows the trend of Halpin-Tsai model. This implies that matrix and filler experience varying amount of strain and interfacial adhesion between filler and matrix and also between the two fillers which play a vital role in determining the modulus of the hybrid composites.A significant observation from this study is that the requirement of higher fibre loading for efficient reinforcement of polymers can be substantially reduced by the presence of nanofiller together with much lower fibre content in the composite. Hybrid composites with both nanokaolinite clay and micron sized E-glass fibre as reinforcements in PP/HDPE matrix will generate a novel class of high performance, cost effective engineering material.