Periodic polymer photonic bandgap structures for on-chip optical cavities

Integrated on-chip optical platforms enable high performance in applications of high-speed all-optical or electro-optical switching, wide-range multi-wavelength on-chip lasing for communication, and lab-on-chip optical sensing. Integrated optical resonators with high quality factor are a fundamental component in these applications. Periodic photonic structures (photonic crystals) exhibit a photonic band gap, which can be used to manipulate photons in a way similar to the control of electrons in semiconductor circuits. This makes it possible to create structures with radically improved optical properties. Compared to silicon, polymers offer a potentially inexpensive material platform with ease of fabrication at low temperatures and a wide range of material properties when doped with nanocrystals and other molecules. In this research work, several polymer periodic photonic structures are proposed and investigated to improve optical confinement and optical sensing. We developed a fast numerical method for calculating the quality factor of a photonic crystal slab (PhCS) cavity. The calculation is implemented via a 2D-FDTD method followed by a post-process for cavity surface energy radiation loss. Computational time is saved and good accuracy is demonstrated compared to other published methods. Also, we proposed a novel concept of slot-PhCS which enhanced the energy density 20 times compared to traditional PhCS. It combines both advantages of the slot waveguide and photonic crystal to localize the high energy density in the low index material. This property could increase the interaction between light and material embedded with nanoparticles like quantum dots for active device development. We also demonstrated a wide range bandgap based on a one dimensional waveguide distributed Bragg reflector with high coupling to optical waveguides enabling it to be easily integrated with other optical components on the chip. A flexible polymer (SU8) grating waveguide is proposed as a force sensor. The proposed sensor can monitor nN range forces through its spectral shift. Finally, quantum dot - doped SU8 polymer structures are demonstrated by optimizing spin coating and UV exposure. Clear patterns with high emission spectra proved the compatibility of the fabrication process for applications in optical amplification and lasing.

Hydrogeophysical characterization of anisotropy in the Biscayne Aquifer using geophysical methods

The anisotropy of the Biscayne Aquifer which serves as the source of potable water for Miami-Dade County was investigated by applying geophysical methods. Electrical resistivity imaging, self potential and ground penetration radar techniques were employed in both regional and site specific studies. In the regional study, electrical anisotropy and resistivity variation with depth were investigated with azimuthal square array measurements at 13 sites. The observed coefficient of electrical anisotropy ranged from 1.01 to 1.36. The general direction of measured anisotropy is uniform for most sites and trends W-E or SE-NW irrespective of depth. Measured electrical properties were used to estimate anisotropic component of the secondary porosity and hydraulic anisotropy which ranged from 1 to 11% and 1.18 to 2.83 respectively. 1-D sounding analysis was used to models the variation of formation resistivity with depth. Resistivities decreased from NW (close to the margins of the everglades) to SE on the shores of Biscayne Bay. Porosity calculated from Archie's law, ranged from 18 to 61% with higher values found along the ridge. Higher anisotropy, porosities and hydraulic conductivities were on the Atlantic Coastal Ridge and lower values at low lying areas west of the ridge. The cause of higher anisotropy and porosity is attributed to higher dissolution rates of the oolitic facies of the Miami Formation composing the ridge. The direction of minimum resistivity from this study is similar to the predevelopment groundwater flow direction indicated in published modeling studies. Detailed investigations were carried out to evaluate higher anisotropy at West Perrine Park located on the ridge and Snapper Creek Municipal well field where the anisotropy trend changes with depth. The higher anisotropy is attributed to the presence of solution cavities oriented in the E-SE direction on the ridge. Similarly, the change in hydraulic anisotropy at the well field might be related to solution cavities, the surface canal and groundwater extraction wells.^

Cardiac Neural Crest Cells Affect the Development of the Myocardium and Conduction System in the Mouse

Neural crest cells originate from the dorsal most region of the embryonic neural tube. These cells migrate into several embryonic locations and differentiate into a variety of cell types. Cardiac neural crest (CNC) cells are a set of neural crest progenitors that aid in the proper formation of the cardiac septum, which separates the pulmonary from the systemic circulation. We have used Splotch mice to investigate whether the murine CNC cells play a role during the development oft he myocardium and the conduction system. Splotch mice carry a mutation in the P AX3 transcription factor, and display a problem in CNC cell migration. A scanning-electron-microscopy analysis of Splotch mutant-embryonic-hearts reveals abnormalities in the interventricular septum. In addition, the right and left ventricular cavities appear dilated relative to a wild type heart. Hoechst nuclei staining of Splotch heart cryosections demonstrates a decreased number of cardiomyocytes and a corresponding thinner ventricular wall. The absence of Connexin 40 in the ventricles of Splotch mutants, suggests conduction system defects. These results support the evidence that CNC cell signaling plays a role in modulating the growth and development of murine cardiomyocytes and their differentiation into conductile cells.

Conformational dynamics associated with ligand binding to vertebrate hexa-coordinate hemoglobins

Neuroglobin (Ngb) and cytoglobin (Cygb) are two new additions to the globin family, exhibiting heme iron hexa-coordination, a disulfide bond and large internal cavities. These proteins are implicated in cytoprotection under hypoxic-ischemic conditions, but the molecular basis of their cytoprotective function is unclear. Herein, a photothermal and spectroscopic study of the interactions of diatomic ligands with Ngb, Cygb, myoglobin and hemoglobin is presented. The impact of the disulfide bond in Ngb and Cygb and role of conserved residues in Ngb His64, Val68, Cys55, Cys120 and Tyr44 on conformational dynamics associated with ligand binding/dissociation were investigated. Transient absorption and photoacoustic calorimetry studies indicate that CO photo-dissociation from Ngb leads to a volume expansion (13.4±0.9 mL mol-1), whereas a smaller volume change was determined for Ngb with reduced Cys (ΔV=4.6±0.3 mL mol-1). Furthermore, Val68 side chain regulates ligand migration between the distal pocket and internal hydrophobic cavities since Val68Phe geminate quantum yield is ∼2.7 times larger than that of WT Ngb. His64Gln and Tyr44Phe mutations alter the thermodynamic parameters associated with CO photo-release indicating that electrostatic/hydrogen binding network that includes heme propionate groups, Lys 67, His64, and Tyr 44 in Ngb modulates the energetics of CO photo-dissociation. In Cygb, CO escape from the protein matrix is fast (< 40 ns) with a ΔH of 18±2 kcal mol-1 in Cygbred, whereas disulfide bridge formation promotes a biphasic ligand escape associated with an overall enthalpy change of 9±4 kcal mol-1. Therefore, the disulfide bond modulates conformational dynamics in Ngb and Cygb. I propose that in Cygb with reduced Cys the photo-dissociated ligand escapes through the hydrophobic tunnel as occurs in Ngb, whereas the CO preferentially migrates through the His64 gate in Cygbox. To characterize Cygb surface 1,8-ANS interactions with Cygb were investigated employing fluorescence spectroscopy, ITC and docking simulations. Two 1,8-ANS binding sites were identified. One binding site is located close to the extended N-terminus of Cygb and was also identified as a binding site for oleate. Furthermore, guanidinium hydrochloride-induced unfolding studies of Cygb reveal that the disulfide bond does not impact Cygb stability, whereas binding of cyanide slightly increases the protein stability.

Hydrogeophysical Characterization of Anisotropy in the Biscayne Aquifer Using Geophysical Methods

The anisotropy of the Biscayne Aquifer which serves as the source of potable water for Miami-Dade County was investigated by applying geophysical methods. Electrical resistivity imaging, self potential and ground penetration radar techniques were employed in both regional and site specific studies. In the regional study, electrical anisotropy and resistivity variation with depth were investigated with azimuthal square array measurements at 13 sites. The observed coefficient of electrical anisotropy ranged from 1.01 to 1.36. The general direction of measured anisotropy is uniform for most sites and trends W-E or SE-NW irrespective of depth. Measured electrical properties were used to estimate anisotropic component of the secondary porosity and hydraulic anisotropy which ranged from 1 to 11% and 1.18 to 2.83 respectively. 1-D sounding analysis was used to models the variation of formation resistivity with depth. Resistivities decreased from NW (close to the margins of the everglades) to SE on the shores of Biscayne Bay. Porosity calculated from Archie's law, ranged from 18 to 61% with higher values found along the ridge. Higher anisotropy, porosities and hydraulic conductivities were on the Atlantic Coastal Ridge and lower values at low lying areas west of the ridge. The cause of higher anisotropy and porosity is attributed to higher dissolution rates of the oolitic facies of the Miami Formation composing the ridge. The direction of minimum resistivity from this study is similar to the predevelopment groundwater flow direction indicated in published modeling studies. Detailed investigations were carried out to evaluate higher anisotropy at West Perrine Park located on the ridge and Snapper Creek Municipal well field where the anisotropy trend changes with depth. The higher anisotropy is attributed to the presence of solution cavities oriented in the E-SE direction on the ridge. Similarly, the change in hydraulic anisotropy at the well field might be related to solution cavities, the surface canal and groundwater extraction wells.