Experimental and numerical investigation of strain-rate dependent mechanical properties of single living cells

The objective of this project is to investigate the strain-rate dependent mechanical behaviour of single living cells using both experimental and numerical techniques. The results revealed that living cells behave as porohyperlastic materials and that both solid and fluid phases within the cells play important roles in their mechanical responses. The research reported in this thesis provides a better understanding of the mechanisms underlying the cellular responses to external mechanical loadings and of the process of mechanical signal transduction in living cells. It would help us to enhance knowledge of and insight into the role of mechanical forces in supporting tissue regeneration or degeneration.

Studies on the failure of unreinforced masonry shear walls

This thesis aims at studying the structural behaviour of high bond strength masonry shear walls by developing a combined interface and surface contact model. The results are further verified by a cost-effective structural level model which was then extensively used for predicting all possible failure modes of high bond strength masonry shear walls. It is concluded that the increase in bond strength of masonry modifies the failure mode from diagonal cracking to base sliding and doesn't proportionally increase the in-plane shear capacity. This can be overcome by increasing pre-compression pressure which causes failure through blocks. A design equation is proposed and high bond strength masonry is recommended for taller buildings and/ or pre-stressed masonry applications.

General properties of electrochemical capacitors

The use of capacitors for electrical energy storage actually predates the invention of the battery. Alessandro Volta is attributed with the invention of the battery in 1800, where he first describes a battery as an assembly of plates of two different materials (such as copper and zinc) placed in an alternating stack and separated by paper soaked in brine or vinegar [1]. Accordingly, this device was referred to as Volta’s pile and formed the basis of subsequent revolutionary research and discoveries on the chemical origin of electricity. Before the advent of Volta’s pile, however, eighteenth century researchers relied on the use of Leyden jars as a source of electrical energy. Built in the mid-1700s at the University of Leyden in Holland, a Leyden jar is an early capacitor consisting of a glass jar coated inside and outside with a thin layer of silver foil [2, 3]. With the outer foil being grounded, the inner foil could be charged with an electrostatic generator, or a source of static electricity, and could produce a strong electrical discharge from a small and comparatively simple device.

Investigation of the effects of extracellular osmotic pressure on morphology and mechanical 1 properties of individual chondrocyte

It has been demonstrated that most cells of the body respond to osmotic pressure in a systematic manner. The disruption of the collagen network in the early stages of osteoarthritis causes an increase in water content of cartilage which leads to a reduction of pericellular osmolality in chondrocytes distributed within the extracellular environment. It is therefore arguable that an insight into the mechanical properties of chondrocytes under varying osmotic pressure would provide a better understanding of chondrocyte mechanotransduction and potentially contribute to knowledge on cartilage degeneration. In this present study, the chondrocyte cells were exposed to solutions with different osmolality. Changes in their dimensions and mechanical properties were measured over time. Atomic Force Microscopy (AFM) was used to apply load at various strain-rates and the force-time curves were logged. The thin-layer elastic model was used to extract the elastic stiffness of chondrocytes at different strain-rates and at different solution osmolality. In addition, the porohyperelastic (PHE) model was used to investigate the strain-rate dependent responses under the loading and osmotic pressure conditions. The results revealed that the hypo-osmotic external environment increased chondrocyte dimensions and reduced Young’s modulus of the cells at all strain-rates tested. In contrast, the hyper-osmotic external environment reduced dimensions and increased Young’s modulus. Moreover, by using the PHE model coupled with inverse FEA simulation, we established that the hydraulic permeability of chondrocytes increased with decreasing extracellular osmolality which is consistent with previous work in the literature. This could be due to a higher intracellular fluid volume fraction with lower osmolality.

Prediction of masonry compressive behaviour using a damage mechanics inspired modelling method

Masonry under compression is affected by the properties of its constituents and their interfaces. In spite of extensive investigations of the behaviour of masonry under compression, the information in the literature cannot be regarded as comprehensive due to ongoing inventions of new generation products – for example, polymer modified thin layer mortared masonry and drystack masonry. As comprehensive experimental studies are very expensive, an analytical model inspired by damage mechanics is developed and applied to the prediction of the compressive behaviour of masonry in this paper. The model incorporates a parabolic progressively softening stress-strain curve for the units and a progressively stiffening stress-strain curve until a threshold strain for the combined mortar and the unit-mortar interfaces is reached. The model simulates the mutual constraints imposed by each of these constituents through their respective tensile and compressive behaviour and volumetric changes. The advantage of the model is that it requires only the properties of the constituents and considers masonry as a continuum and computes the average properties of the composite masonry prisms/wallettes; it does not require discretisation of prism or wallette similar to the finite element methods. The capability of the model in capturing the phenomenological behaviour of masonry with appropriate elastic response, stiffness degradation and post peak softening is presented through numerical examples. The fitting of the experimental data to the model parameters is demonstrated through calibration of some selected test data on units and mortar from the literature; the calibrated model is shown to predict the responses of the experimentally determined masonry built using the corresponding units and mortar quite well. Through a series of sensitivity studies, the model is also shown to predict the masonry strength appropriately for changes to the properties of the units and mortar, the mortar joint thickness and the ratio of the height of unit to mortar joint thickness. The unit strength is shown to affect the masonry strength significantly. Although the mortar strength has only a marginal effect, reduction in mortar joint thickness is shown to have a profound effect on the masonry strength. The results obtained from the model are compared with the various provisions in the Australian Masonry Structures Standard AS3700 (2011) and Eurocode 6.

Underwater Sustainability of the ``Cassie'' State of Wetting

A rough hydrophobic surface when immersed in water can result in a ``Cassie'' state of wetting in which the water is in contact with both the solid surface and the entrapped air. The sustainability of the entrapped air on such surfaces is important for underwater applications such as reduction of flow resistance in microchannels and drag reduction of submerged bodies such as hydrofoils. We utilize an optical technique based oil total internal reflection of light at the water-air interface to quantify the spatial distribution of trapped air oil such a surface and its variation with immersion time. With this technique, we evaluate the sustainability of the Cassie state on hydrophobic surfaces with four different kinds of textures. The textures studied are regular arrays of pillars, ridges, and holes that were created in silicon by a wet etching technique, and also a texture of random craters that was obtained through electrodischarge machining of aluminum. These surfaces were rendered hydrophobic with a self-assembled layer Of fluorooctyl trichlorosilane. Depending on the texture, the size and shape of the trapped air pockets were found to vary. However, irrespective of the texture, both the size and the number of air pockets were found to decrease with time gradually and eventually disappear, suggesting that the sustainability of the ``Cassie'' state is finite for all the microstructures Studied. This is possibly due to diffusion of air from the trapped air pockets into the water. The time scale for disappearance of air pockets was found to depend on the kind of microstructure and the hydrostatic pressure at the water-air interface. For the surface with a regular array of pillars, the air pockets were found to be in the form of a thin layer perched on top of the pillars with a large lateral extent compared to the spacing between pillars. For other surfaces studied, the air pockets are smaller and are of the same order as the characteristic length scale of the texture. Measurements for the surface with holes indicate that the time for air-pocket disappearance reduces as the hydrostatic pressure is increased.

Locating the seat of the solar dynamo

The hypothesis that the solar dynamo operates in a thin layer at the bottom of the convection zone is addressed. Recent work on the question whether the magnetic flux can be made to emerge at sunspot latitudes is reviewed. It is concluded that this hypothesis can fit the observational facts only if there is turbulence with a length scale of a few hundred kilometers in and around the dynamo region.

Hot corrosion of γ-Y2Si2O7 in strongly basic Na2CO3 molten salt environment

γ-Y2Si2O7 is a promising candidate both for high temperature structural applications and as thermal barrier coatings due to its unique combination of properties, such as high melting point, good machinability, high thermal stability, low linear thermal expansion coefficient (3.9 × 10-6 K-1, 25-1400 °C) and low thermal conductivity (<3 W/m K above 300 °C). In this work, the hot corrosion behavior of γ-Y2Si2O7 in strongly basic Na2CO3 molten salt at 850-1000 °C for 20 h in flowing air was investigated. In the employed conditions, multi-layer corrosion scales with total thickness less than 90 μm were formed. At 850-900 °C, the outmost layer of the scale was composed of the reprecipitation of Y2O3, the bottom of a Si-rich Na2O·xSiO2 (x > 3.65) melt layer, and the middle of a NaYSiO4 layer. At 1000 °C, the corrosion products turned out to be a mixture of NaY9Si6O26 and Si-rich Na2O·xSiO2 (x > 3.65). In all cases, a thin layer of protective SiO2 formed under the Na2O·xSiO2 melt and protected the bulk material from further corrosion.

The transient response of a two-terminal solion to a step-current input

The transition time associated with the time-variation of the voltage across a two-terminal diaphragm-less solion in response to a step-current stimulus has been studied experimentally. A theoretical analysis has also been made by solving the diffusion problem under the appropriate initial and boundary conditions. The behaviour of the theoretically predicted transition times is in agreement with the observed behaviour. The systems under study have been shown to be different from those used hitherto in thin-layer chronopotentiometry.

The transient response of a two-terminal solion to a stepcrrent input

The transition time associated with the time-variation of the voltage across a two-terminal diaphragm-less solion in response to a step-current stimulus has been studied experimentally. A theoretical analysis has also been made by solving the diffusion problem under the appropriate initial and boundary conditions. The behaviour of the theoretically predicted transition times is in agreement with the observed behaviour. The systems under study have been shown to be different from those used hitherto in thin-layer chronopotentiometry.

Effect of Nanostructuring and Ex situ Amorphous Carbon Coverage on the Lithium Storage and Insertion Kinetics in Anatase Titania

Implications of nanostructuring and conductive carbon interface on lithium insertion/removal capacity and insertion kinetics innanoparticles of anatase polymorph of titania is discussed here.Sol-gel synthesized nanoparticles of titania (particle size similar to 6 nm) were hydrothermally coated ex situ with a thin layer of amorphous carbon (layer thickness: 2-5 nm) and calcined at a temperature much higher than the sol-gel synthesis temperature. The carbon-titania composite particles (resulting size similar to 10 nm) displayed immensely superior cyclability and rate capability (higher current rates similar to 4 g(-1)) compared to unmodified calcined anatase titania. The conductive carbon interface around titania nanocrystal enhances the electronic conductivity and inhibits crystallite growth during electrochemical insertion/removal thus preventing detrimental kinetic effects observed in case of unmodified anatase titania. The carbon coating of the nanoparticles also stabilized the titania crystallographic structure via reduction in the accessibility of lithium ions to the trapping sites. This resulted in a decrease in the irreversible capacity observed in the case of nanoparticles without any carbon coating.

Nucleotide-sequence of 5S RNA from mycobacterium-smegmatis

32P labelled 5S RNA isolated fromMycobacterium smegmatis was digested withT 1 and pancreatic ribonucleases separately and fingerprinted by two dimensional high voltage electrophoresis on thin-layer DEAE-cellulose plates. The radioactive spots were sequenced and their molar yields were determined. The chain length of the 5S RNA was found to be 120. It showed resemblances to both prokaryotic and eukaryotic 5S RNAs.

Metabolism of a monoterpene ketone, R-(+)-pulegone—a hepatotoxin in rat

R-(+)-Pulegone was administered orally to rats and the urinary metabolites were investigated. Six metabolites were isolated and purified using column and thin layer chromatographic techniques. Metabolites were identified by i.r., n.m.r. and mass spectral analyses.The neutral metabolites isolated from urine of rats treated with pulegone (I) were: pulegol (II), 2-hydroxy-2(1'-hydroxy-1'-methylethyl)-5-methylcyclohexanone (III), 3,6-dimethyl-7a-hydroxy-5,6,7,7a-tetrahydro-2(4H)-benzofuranone (V) and menthofuran (VII). Metabolites II and III were also excreted in conjugated form.Acidic metabolites isolated from urine of rats treated with pulegone (I) were: 5-methyl-2(1'-methyl-1'-carboxyethylidene)cyclohexanone (IV) and 5-methyl-5-hydroxy-2(1'hydroxy-'-carboxyethyl)cyclohexanone (VI).

Occurrence of 1-methyladenosine and absence of ribothymidine in transfer ribonucleic acid of Mycobacterium smegmatis

The minor base composition of Mycobacterium smegmatis tRNA has been studied. Thin-layer chromatographic patterns of a ribonuclease T2 digest of mycobacterial tRNA indicated the presence of appreciable amounts of 1-methyladenosine (which is commonly present only in eucaryotic tRNA), dihydrouridine, and 7-methylguanosine. Ribothymidine was absent. The S-adenosylmethionine-dependent tRNA methylases of M. smegmatis catalyzed the formation of 1-methyladenosine when Escherichia coli tRNA was used as acceptor. Similarly, E. coli extracts methylated the tRNA of M. smegmatis, forming ribothymidine.

Locating the seat of the solar dynamo

The hypothesis that the solar dynamo operates in a thin layer at the bottom of the convection zone is addressed. Recent work on the question whether the magnetic flux can be made to emerge at sunspot latitudes is reviewed. It is concluded that this hypothesis can fit the observational facts only if there is turbulence with a length scale of a few hundred kilometers in and around the dynamo region.