Correlation of circular differential optical absorption with geometric chirality in plasmonic meta-atoms

We report a strong correlation between the calculated broadband circular differential optical absorption (CDOA) and the geometric chirality of plasmonic meta-atoms with two-dimensional chirality. We investigate this correlation using three common gold meta-atom geometries: L-shapes, triangles, and nanorod dimers, over a broad range of geometric parameters. We show that this correlation holds for both contiguous plasmonic meta-atoms and non-contiguous structures which support plasmonic coupling effects. A potential application for this correlation is the rapid optimization of plasmonic nanostructure for maximum broadband CDOA

Perspectives on development in Arid and Semi-Arid areas: Results of a ranking exercise

Decentralization and community participation are major themes in current development policy. This study investigates perspectives on development held by individuals in arid and semi-arid areas of northern Kenya and southern Ethiopia that are predominantly used for pastoral production. Using a ranking exercise, individuals were asked to identify the most helpful types of development interventions in their opinion in the past, and also indicate their priorities for future development interventions. Results suggest there is relative consensus around a few key development interventions. Interestingly, the highest ranked interventions for both the past and the future are not explicitly related to pastoral production. Across country differences are not very large, though across site differences are pronounced. In a similar fashion, individual characteristics seem to matter less than household level characteristics within sites

Chemical bath deposition of semiconductor thin films & nanostructures in novel microreactors

Chemical bath deposition (CBD) offers a simple and inexpensive route to deposit semiconductor nanostructures and thin fims, but lack of fundamental understanding and control of the underlying chemistry has limited its versatility. CBD is traditionally performed in a batch reactor, requiring only a substrate to be immersed in a supersaturated solution of aqueous precursors such as metal salts, complexing agents, and pH buffers. Highlights of CBD include low cost, operation at low temperature and atmospheric pressure, and scalability to large area substrates.In this dissertation, I explore CBD of semiconductor thin films and nanowire arrays in batch and continuous ow microreactors. Microreactors offer many advantages over traditional reactor designs including a reduction in mass transport limitations, precise temperature control and ease of production scale-up by \numbering up". Continuous ow micoreactors other the unique advantage of providing reaction conditions that are time-invariant but change smoothly as a function of distance down the reaction channel. Growth from a bath whose composition changes along the reactor length results in deposited materials whose properties vary as a function of position on the substrate, essentially creating a combinatorial library. These substrates can be rapidly characterized to identify relationships between growth conditions and material properties or growth mechanisms.I have used CBD in a continuous ow microreactor to deposit ZnO nanowire arrays and CdZnS films whose optoelectronic properties vary as a function of position. The spatially-dependent opto-electronic properties of these materials have been correlated to changes in the composition, structure or growth mechanisms of the materials and ultimately their growth conditions by rigorous spatial characterization. CBD in a continuous ow microreactor, coupled with spatial characterization, provides a new route to understanding the connection between CBD growth conditions and the resulting optoelectronic properties of the film.The high surface-to-volume ratio of a microreactor also lends itself to in situ characterization studies. I demonstrated the first in situ x-ray absorption fine-structure spectroscopy (XAFS) study of CBD. The high sensitivity and ability to characterize liquid, amorphous and crystalline materials simultaneously make in situ XAFS spectroscopy an ideal tool to study the CBD of inorganic nanomaterials.Ph.D., Chemical and Biological Engineering -- Drexel University, 201

Resonant Plasmonic–Biomolecular Chiral Interactions in the Far-Ultraviolet: Enantiomeric Discrimination of sub-10 nm Amino Acid Films

Resonant plasmonic–molecular chiral interactions are a promising route to enhanced biosensing. However, biomolecular optical activity primarily exists in the far-ultraviolet regime, posing significant challenges for spectral overlap with current nano-optical platforms. We demonstrate experimentally and computationally the enhanced chiral sensing of a resonant plasmonic–biomolecular system operating in the far-UV. We develop a full-wave model of biomolecular films on Al gammadion arrays using experimentally derived chirality parameters. Our calculations show that detectable enhancements in the chiroptical signals from small amounts of biomolecules are possible only when tight spectral overlap exists between the plasmonic and biomolecular chiral responses. We support this conclusion experimentally by using Al gammadion arrays to enantiomerically discriminate ultrathin (\u3c10 nm thick) films of tyrosine. Notably, the chiroptical signals of the bare films were within instrumental noise. Our results demonstrate the importance of using far-UV active metasurfaces for enhancing natural optical activity

Insuring against drought-related livestock mortality: Piloting index-based livestock insurance in northern Kenya

Climate related shocks are among the leading cause of production and efficiency losses in smallholder crop and livestock production in rural Africa. Consequently, the identification of tools to help manage the risks associated with climactic extremities is increasingly considered to be among the key pillars of any agenda to enhance agricultural growth and welfare in rural Africa. This paper describes the application of a promising innovation in insurance design – index-based insurance – that seeks to bring the benefits of formal insurance to help manage the weather-related risks faced by rural crop and livestock producers in low-income countries. In particular, we highlight the research and development agenda of a comprehensive effort to design commercially viable index based livestock insurance aimed at protecting the pastoral populations of northern Kenya from the considerable drought-related livestock mortality risk that they face. Detailing the conditions that make the pastoral economy in northern Kenya an ideal candidate for the provision of indexbased insurance products, the paper describes the contract design, defines its structure, offers analysis that indicates a high likelihood of commercial sustainability among the target market and describes the process of implementation leading up to the launch of a pilot in Marsabit District of northern Kenya in early 2010

Insuring against drought‐related livestock mortality: Piloting index based livestock insurance in northern Kenya

Climate related shocks are among the leading cause of production and efficiency losses in smallholder crop and livestock production in rural Africa. Consequently, the identification of tools to help manage the risks associated with climactic extremities is increasingly considered to be amongst the key pillars of any agenda to enhance agricultural growth and welfare in rural Africa. This paper describes the application of a promising innovation in insurance design – index‐based insurance – that seeks to bring the benefits of formal insurance to help manage the weather‐related risks faced by rural crop and livestock producers in low‐income countries. In particular, we highlight the research and development agenda of a comprehensive effort to design commercially viable index‐based livestock insurance aimed at protecting the pastoral populations of Northern Kenya from the considerable drought‐related livestock mortality risk that they face. Detailing the conditions that make the pastoral economy in Northern Kenya an ideal candidate for the provision of index‐based insurance products, the paper describes the contract design, defines its structure, offers analysis that indicates a high likelihood of commercial sustainability among the target market and describes the process of implementation leading up to the launch of a pilot in Marsabit district of Northern Kenya in early 2010

Role of Platelet-Activating Factor and Hypoxia in Persistent Pulmonary Hypertension of the Newborn — Studies with Perinatal Pulmonary Vascular Smooth Muscle Cells

Platelet-activating factor (PAF) plays an important physiological role of maintaining a high vasomotor tone in fetal pulmonary circulation. At birth, endogenous vasodilators such as nitric oxide and prostacyclin are released and facilitate pulmonary vasodilation via cAMP-dependent protein kinase (cAMP/PKA) and cGMP-dependent protein kinase (cGMP/PKG) pathways. Interaction between the cyclic nucleotides and PAF receptor (PAFR)-mediated responses in pulmonary arterial smooth muscle is not well understood. To further understand the interactions of PAF-PAFR pathway and the cyclic nucleotides in ovine fetal pulmonary arterial smooth muscle cells (FPASMC), effects of cAMP and cGMP on PAFR-mediated responses in pulmonary arterial smooth muscle cells (PASMC) were studied. Ovine FPASMC were incubated with 10μM cAMP or cGMP in normoxia (5% CO2 in air, pO2~100 Torr) or hypoxia (2% O2, 5% CO2, pO2~30-40 Torr). Proteins were prepared and subjected to Western blotting. Effect of cell permeable cAMP and cGMP on PAFR binding was also studied and effect of cAMP on cell proliferation was also studied by RNAi to PKA-Cα. cAMP and cGMP significantly decreased PAFR binding and protein expression in normoxia and hypoxia, more so in hypoxia, when PAFR expression was usually high. PKA-Cα siRNA demonstrated that inhibition of PAFR-mediated responses by the cyclic nucleotides occurred through PKA. These data suggest that the normally high levels of cyclic nucleotides in the normoxic newborn pulmonary circulation assist in the downregulation of postnatal PAFR-mediated responses and that under hypoxic conditions, increasing the levels of cyclic nucleotides will abrogate PAF-mediated vasoconstriction thereby ameliorating PAF-induced persistent pulmonary hypertension of the newborn

Role of geometric shape in chiral optics

The distinction of chiral and mirror symmetric objects is straightforward from a geometrical point of view. Since the biological as well as the optical activity of molecules strongly depend on their handedness, chirality has recently attracted high interest in the field of nano-optics. Various aspects of associated phenomena including the influences of internal and external degrees of freedom on the optical response have been discussed. Here, we propose a constructive method to evaluate the possibility of observing any chiral response from an optical scatterer. Based on solely the T-matrix of one enantiomer, planes of minimal chiral response are located and compared to geometric mirror planes. This provides insights into the relation of geometric and optical properties and enables identifying the potential of chiral scatterers for nano-optical experiments