Using electron beam lithography fine Au<SUB>60</SUB>Pd<SUB>40</SUB> wire samples have been made, which were then used to investigate size effects in disordered systems. The wires made had widths from 140nm to 36nm, and lengths from 125nm to 100μm. The thickness was varied from 10nm to 50nm. Using gas etching techniques it was possible to make these wires free-standing with lengths of over 100μm and thicknesses of 10nm. At first some of the important electrical and mechanical properties of the free-standing wires were investigated. The tensile strength was found to be much larger than that found in bulk gold, and a simple model was developed to predict at what voltage the wires would melt. At low temperatures localisation and interaction contributions to the resistance were seen both in wires on a substrate and when free-standing. Electric field heating of the wires on a substrate was used to find the electron-phonon scattering time, which was seen to be proportional to T<SUP>-2</SUP>. The resistance rise for the free-standing wires was less than for the same wires on a substrate. Magnetoresistance measurements revealed this to be due to an increased negative localisation term in the presence of strong spin orbit scattering. The inelastic lengths were consistent with strong magnetic scattering which was reduced on being made free-standing. Electric field heating of the free-standing wires revealed that the thermal conduction of the wire is dominated by the electron contribution. At 1K the phonons in the wires should be one dimensional, but no contribution to the heat conduction was observed from these phonons. Below 800mK conductance fluctuations were observed in the magnetoresistance of the short samples. Below 125 K the amplitude of the fluctuations saturated which is consistent with both the interaction and the inelastic lengths being longer than the wire.

No description available.

We report the design and assembly of three-dimensional (3D) multi-cellular liver models comprised of primary rat hepatocytes, liver sinusoidal endothelial cells (LSECs), and Kupffer cells (KCs). LSECs and KCs in the liver model were separated from hepatocytes by a nanoscale, detachable, optically transparent chitosan and hyaluronic acid (HA) polyelectrolyte multilayer (PEM) film. The properties of the PEM were tuned to mimic the Space of Disse found in liver. The thickness of the detachable PEM was 650 to 1000 nm under hydrated conditions. The Young's modulus of the PEM was approximately 42 kPa, well within the range of modulus values reported for bulk liver. The 3D liver models comprised of all three cell types and a detachable PEM exhibited stable urea production and increased albumin secretion over a 12 day culture period. Additionally, the 3D liver model maintained the phenotype of both LSECs and KCs over the 12 day culture period, verified by CD32b and CD163 staining, respectively. Additionally, CYP1A1 enzyme activity increased significantly in the 3D liver models. The number of hepatocytes in the 3D liver model increased by approximately 60% on day 16 of culture compared to day 4 indicating. Furthermore, only the 3D hepatic model maintained cellular compositions virtually identical to those found in vivo. DNA microarray measurements were conducted on the hepatocyte fractions of the 3D liver mimic to obtain insights into hepatic processes. Gene sets up-regulated in the 3D liver model were related to proliferation, migration, and deposition of extracellular matrix, all functions observed in regenerating hepatocytes. Taken together, these results suggest that inter-cellular signaling between the different cell types in the 3D liver model led to increased hepatic functions. To the best of our knowledge, this is the first study where three of the major hepatic cell types have been incorporated into a model that closely mimics the structure of the sinusoid. These studies demonstrate that the multi-cellular liver models are physiologically relevant. Such models are very promising to conduct detailed investigations into hepatic inter-cellular signaling. / Ph. D.

This thesis investigates the behavior of free-standing gabion walls in areas of mild seismicity. To investigate this behavior, three walls of varying internal cable patterns were constructed at a quarter-scale. These walls were tested with a mass shaker, and mode shapes, tone extractions, and damping ratios were calculated. A modal analysis was conducted using design spectra created from a suite of seven earthquakes from countries bordering Kenya. The corresponding lateral forces to these spectral displacements were found, and the restoring eccentricities from the soil restoring force were backed out through a summation of moments. All analysis was experimentally done due to the complexity of properly modeling the wall system for a secondary analytical comparison. This process was done under the assumption of linear behavior. Similarly, the criteria for failure involved the eccentricity of the restoring soil force exceeding the kern distance (assuming elastic behavior)—criteria that all three of the wall specimens met. However, further research into the nonlinear behavior of this wall type is suggested for future conclusions on free-standing gabion wall behavior.

No description available.

Metoda koneÄnch prvk implementovan v programu COMSOL Multiphysics je vyu­vna k analze tzv. free-standing kmitoÄtovÄ selektivn­ch povrch ve 3D. Tyto modely jsou nslednÄ doplnÄny o periodick© okrajov© podm­nky. Dle jsou free-standing povrchy doplnÄny o vrstvy dielektrika a je zkoumn jejich vliv na modul Äinitele odrazu. V analytick© Ästi jsou vyhodnoceny vlivy poÄtu element diskretizaÄn­ m­ky na pesnost vsledku a d©lku vpoÄt. Vsledky jsou srovnvny vzhledem k vsledkm uvedenm v literatue [5]. V zvÄreÄn© Ästi prce je vysvÄtlen postup pi generovn­ m-file pro obd©ln­kov element a pouit­ globln­ho optimalizaÄn­ho algoritmu PSO, kter automaticky upravuje rozmÄry vodiv©ho motivu tak, aby bylo dosaeno prbÄhu modulu Äinitele odrazu podle poadovan©ho prbÄhu.

This thesis examines the luminescence properties of nanoscale silicon (Si) by using spectroscopic techniques. Since the development of new optical devices requires understanding light emission mechanism optical spectroscopy has become more important tool in the analysis of these structures. In this thesis, Si nanocrystals embedded in SiO2 matrix will be studied. Photoluminescence (PL) and Time-resolved photoluminescence spectroscopy (TRPL) have been used to detect the light emission in UV-Vis-NIR range. Experiments have been performed in the temperature range 10-300 K. PL is sensitive to impurities and defects that affect materials quality and device performance. In this context, the role of defects in limiting the luminescence of Si nanocrystals and the removal of these defects by hydrogen passivation has been investigated. v TRPL was employed to determine the time evolution of photoluminescence as function of temperature. The decay time of the PL spectra was determined by a stretched exponential function and perfectly fitted to an expression based on three excitonic levels. Carrier lifetimes associated with these three levels were determined and compared with literature. Additionally, temporal variation of PL from free-standing Si nanoparticles is studied under a strong laser illumination. The observed bleaching behavior (time dependent emission intensity), which is reversible, have discussed in terms of exciton trapping at the interface between nanocrystal and the surrounding oxide layer. The results of this thesis will provide new insight on the understanding of light emission mechanism of Si nanocrytals.

No description available.

The thesis examines the adhesive interaction between graphite layers and atomically thin MoS2 crystals. Vertical van der Waals(vdW) heterostructures are fabricated by stacking different two-dimensional (2D) materials on top of each other. Blister test is used to measure the adhesive interactions between 2D heterostructures and their transferred substrates and between the layers themselves. This adhesive interaction is important in maintaining the mechanical integrity of the device during mechanical loadings and its understanding will help pave the way to the design and fabrication of micromechanical device from 2D heterostructures. Furthermore, applying controlled strains can be used to alter the electrical and optical properties thereby improving efficiency and performance. At first, we grew MoS2 and graphene by CVD and stacked the layers on top of each other using a dry transfer method. The MoS2/graphene heterostructure was then transferred onto pre-etched cavities on a silicon wafer. The blister test was used for controllably introducing strain into the heterostructure. Atomic Force Microscopy was used for measuring the shape of the deformed blister and Raman and Photoluminescence(PL) measured the optical response. The strain mismatch between the biaxial strain and a PL-converted strain suggests crumpling of the graphene layer and a substantial softening of the mechanical response. Lastly, we created graphite holes with photolithography to measure the work of separation between an atomically smooth graphite surface and MoS2. We found this value to be at least 320mJ/m2 which is higher than the MoS2/SiOx areas that was previously studied. / 2023-07-02T00:00:00Z

No description available.