First solar butterfly diagram from Schwabe's observations in 1825-1867

The original sunspot observations by Heinrich Samuel Schwabe of 1825-1867 were digitized and a first subset of spots was measured. In this initial project, we determined more than 14 000 sunspot positions and areas comprising about 11% of the total amount of spots available from that period. The resulting butterfly diagram has a typical appearance, but with evident north-south asymmetries.Comment: 3 pages, 1 figure, Proceedings of IAU symposium 273, Physics of Sun and star spots, Ventura, California 22-26 August 201

Thin-film piezoelectric-on-substrate resonators and narrowband filters

A new class of micromachined devices called thin-film piezoelectric-on-substrate (TPoS) resonators is introduced, and the performance of these devices in RF and sensor applications is studied. TPoS resonators benefit from high electromechanical coupling of piezoelectric transduction mechanism and superior acoustic properties of a substrate such as single crystal silicon. Therefore, the motional impedance of these resonators are significantly smaller compared to typical capacitively-transduced counterparts while they exhibit relatively high quality factor and power handling and can be operated in air. The combination of all these features suggests TPoS resonators as a viable alternative for current acoustic devices. In this thesis, design and fabrication methods to realize dispersed-frequency lateral-extensional TPoS resonators are discussed. TPoS devices are fabricated on both silicon-on-insulator and thin-film nanocrystalline diamond substrates. The performance of these resonators in simple and low-power oscillators is measured and compared. Furthermore, a unique coupling technique for implementation of high frequency filters is introduced in which dual resonance modes of a single resonant structure are coupled. The measured results of this work show that these filters are suitable candidates for single-chip implementation of multiple-frequency narrow-band filters with high out-of-band rejection in a small footprint.Ph.D.Committee Chair: Farrokh Ayazi; Committee Member: James D. Meindl; Committee Member: John D. Cressler; Committee Member: Nazanin Bassiri-Gharb; Committee Member: Oliver Bran

Retinal Differentiation of Human Induced Pluripotent Stem Cells in a Continuously Perfused Microfluidic Culture Device

In this thesis, effects of stable concentration of key growth factors on retinal differentiation of human induced pluripotent stem cells (hiPSCs) were investigated in a microfluidic culture device (MFCD). In vitro culture dishes such as flasks and well-plates lack microenvironmental controls required for maintaining stable culture conditions. Unlike cell culture dishes, microfluidic devices provide greater microenvironmental controls resulted from shorter characteristic length and use of laminar flow. It is hypothesised that using the MFCD, a flow rate can be found which keeps key growth factors in retinal differentiation culture in steady-state. Subsequently, steady-state concentration of growth factors would result in upregulation of retinal progenitor (Pax6, Lhx2, Six6 and VSX2/Chx10) and precursor markers (Crx and Nrl). Initially, degradation and consumption of growth factors (DKK-1, Noggin, IGF-1 and bFGF) used in retinal differentiation were studied to establish an order of importance. These findings along with dimensionless ratios, Péclet and Damköhler numbers, were utilised to establish a perfusion rate of 130 μL/h. At this flow rate growth factors DKK1 and Noggin were delivered to the cells in steady-state conditions. A second perfusion culture with the same media exchange rate as the static culture at flow rate of 5.2 μL/h was added to act as a second control. Perfusion cultures were performed for 5, 10, and 21 days (n=3). The MFCD with higher flow rate showed significantly higher expression of markers Crx (p<0.05) and Rhodopsin (compared to lower MFCD, p<0.05) on day 21. The MFCD with lower flow rate, showed significantly higher expression of Pax6 (p<0.05), Vsx2/Chx10 (p<0.01) and Crx (p<0.05) on day 5, Nrl (p<0.01) on day 10 and Six6 (p<0.05) on day 21. This was the first continuously perfused long-term (21 days) retinal differentiation of hiPSCs in a microfluidic device, and results illustrated the importance of steady-state conditions in stem cell bioprocessing

Micro-Resonators: The Quest for Superior Performance

Microelectromechanical resonators are no longer solely a subject of research in university and government labs; they have found a variety of applications at industrial scale, where their market is predicted to grow steadily. Nevertheless, many barriers to enhance their performance and further spread their application remain to be overcome. In this Special Issue, we will focus our attention to some of the persistent challenges of micro-/nano-resonators such as nonlinearity, temperature stability, acceleration sensitivity, limits of quality factor, and failure modes that require a more in-depth understanding of the physics of vibration at small scale. The goal is to seek innovative solutions that take advantage of unique material properties and original designs to push the performance of micro-resonators beyond what is conventionally achievable. Contributions from academia discussing less-known characteristics of micro-resonators and from industry depicting the challenges of large-scale implementation of resonators are encouraged with the hopes of further stimulating the growth of this field, which is rich with fascinating physics and challenging problems

Soil stabilization with gypsum: A review

The demand for sustainable ground improvement methods is rising as urban development expands into areas with challenging soil conditions. Traditional approaches, mostly reliant on cement and lime, contribute significantly to anthropogenic greenhouse gas emissions. Researchers, therefore, are constantly searching for new environmentally friendly stabilization methods to improve the engineering properties of soils. One alternative material used for this purpose is gypsum in its hydrated and dehydrated (hemihydrate/anhydrate) states. Not only can natural gypsum be used for ground improvement but also industrial waste and by-products (e.g. used or waste plasterboard, phosphogypsum, flue gas desulfurization gypsum, titanium dioxide production gypsum by-product) can be recycled, and used. Successful application of these materials could lower the carbon footprint of the construction industries (by reducing the consumption of cement and lime) as well as other industries (by recycling their waste and by-products). However, using gypsum presents challenges due to its moderate water solubility, the formation of swelling clay minerals under certain conditions, and the tendency of dehydrated gypsum to swell upon exposure to water, to name a few. Furthermore, the mechanisms leading to the improved behavior of the gypsum-treated soils are complicated, which has resulted in some seemingly contradictory results reported in the literature. This study presents a systematic and extensive review of the observed behavior of gypsum-treated soils and the different mechanisms causing the observed behavior. The research gaps and the required future steps to address these gaps have been identified and reported. A summary of the effect of gypsum treatment on the mechanical and engineering properties of soils, including unconfined compressive strength (UCS), California Bearing Ratio (CBR), swell potential, Atterberg limits, optimum moisture content (OMC), maximum dry density (MDD), durability, and environmental effects has also been presented

A non-local model for the description of twinning in polycrystalline materials at moderate strains: application to a magnesium alloy

A polycrystalline plasticity model, which incorporates the contribution of deformation twinning, is proposed. For this purpose, each material point is treated as a composite material consisting of a parent constituent and multiple twin variants. In the constitutive equations, the twin volume fractions and their spatial gradients are treated as external state variables to account for the contribution of twin boundaries to free energy. The set of constitutive relations is implemented in a spectral solver, which allows solving the differential equations resulting from equilibrium and compatibility conditions. The proposed model is then used to investigate the behavior of a AZ31 magnesium alloy. For the investigated loading conditions, the mechanical behavior is controlled by the joint contribution of basal slip and tensile twinning. Also, according to the numerical results, the development of crystallographic texture, morphological texture and internal stresses is consistent with the experimental observations of the literature

Surface plasmon resonance assisted rapid laser joining of glass

Rapid and strong joining of clear glass to glass containing randomly distributed embedded spherical silver nanoparticles upon nanosecond pulsed laser irradiation (∼40 ns and repetition rate of 100 kHz) at 532 nm is demonstrated. The embedded silver nanoparticles were ∼30–40 nm in diameter, contained in a thin surface layer of ∼10 μm. A joint strength of 12.5 MPa was achieved for a laser fluence of only ∼0.13 J/cm2 and scanning speed of 10 mm/s. The bonding mechanism is discussed in terms of absorption of the laser energy by nanoparticles and the transfer of the accumulated localised heat to the surrounding glass leading to the local melting and formation of a strong bond. The presented technique is scalable and overcomes a number of serious challenges for a widespread adoption of laser-assisted rapid joining of glass substrates, enabling applications in the manufacture of microelectronic devices, sensors, micro-fluidic, and medical devices