Simple, high-performance type II β-BaB2O4 optical parametric oscillator

A visible /near-IR optical parametric oscillator (OPO) based on type II phase matching in β-BaB2O4 (BBO) is described. Pumped at 355 nm, this OPO covers 410-2500 nm completely with a single set of standard Nd:YAG cavity optics. The output efficiency is >25 %, the linewidth of the OPO is narrower than 1 -2 cm^-1 without the use of gratings or etalons, and the signal-beam divergence is <400 µrad. Three type I BBO doubling crystals are used to extend the tuning range from 208 to 415 nm. Doubling efficiencies as high as 40% are easily obtained. The reasons for the high doubling and overall system efficiency are discussed

From mean-motion resonances to scattered planets: Producing the Solar System, eccentric exoplanets and Late Heavy Bombardments

We show that interaction with a gas disk may produce young planetary systems with closely-spaced orbits, stabilized by mean-motion resonances between neighbors. On longer timescales, after the gas is gone, interaction with a remnant planetesimal disk tends to pull these configurations apart, eventually inducing dynamical instability. We show that this can lead to a variety of outcomes; some cases resemble the Solar System, while others end up with high-eccentricity orbits reminiscent of the observed exoplanets. A similar mechanism has been previously suggested as the cause of the lunar Late Heavy Bombardment. Thus, it may be that a large-scale dynamical instability, with more or less cataclysmic results, is an evolutionary step common to many planetary systems, including our own.Comment: 12 pages, 7 figures, submitted to Ap

Doctor of Philosophy

dissertationMolecular biorecognition is at the heart of all biological processes and has come to the center stage in designing new biologics. Coiled-coils result from molecular biorecognition of multiple protein α-helices. We have designed a series of coiled-coil motifs that self-assemble into supercoils, which in turn function as physical cross-linkers in the construction of hybrid biomaterials. This dissertation describes our endeavors following the hypothesis below: the selfassembly of coiled-coil forming peptides into coiled-coils can be used as a cross-linking mechanism in the construction of hybrid hydrogels and the development of a drug-free macromolecular therapeutic. In the first part, a macromonomer free radical copolymerization strategy was developed and HPMA graft copolymers containing coiled-coil motifs of different chain lengths were synthesized. Results indicated that the primary structure of these motifs greatly influenced gel formation. At least four heptads were needed to mediate effective gelation. The gelation process was highly dependent on the environmental temperature and copolymer concentration. In the second part, a drug-free macromolecular therapeutic was designed to take full advantage of the facts that CD20 is one of the most reliable biomarkers for B-cell non- Hodgkin's lymphoma (NHL), and cross-linking of CD20 antigens induces apoptosis of B cells. The drug-free therapeutic was composed of two components: Fab' fragment of 1F5 iv anti-CD20 antibody conjugated with one coiled-coil motif (CCE) and polyHPMA copolymer grafted with multiple copies of the complementary coiled-coil motif (CCK). In vitro studies showed the conjugates could colocalize on Raji cell surfaces and a clinically relevant magnitude of apoptosis was achieved. A systemic NHL murine model was used to evaluate in vivo efficacy. Significant delay of hind-limb paralysis onset was observed after treatment. In groups receiving multiple-dose treatment, the surviving mice were disease-free and no presence of Raji B cell in bone marrow could be detected after 100 days. In summary, the possibility of integrating molecular biorecognition of short nonnatural coiled-coil motifs into new smart biomaterials is presented. This specific biorecognition can be used with or without adjuvant pharmacology to mediate a biofunctional process in combating diseases

Stocktaking Global Warming:The outcomes of the 2023 Dubai Climate Summit (COP28)

This briefing reviews outcomes of the 28th United Nations Climate Change Conference of the Parties (COP28)held in Dubai, United Arab Emirates in late 2023. In particular, it considered the first Global Stocktake [GST] of actions taken by signatory nations to the 2015 Paris Agreement on Climate Change. The GST examined the potential impact of bottom-up national pledges on ‘greenhouse gas’ [GHG] mitigation required to limit global warming to 1.5°C above pre-industrial levels by the end of the 21st Century. The achievements at COP28 were mixed, and disappointed many from the climate-vulnerable states at high risk from extreme weather events and rising sea levels. There is a significant GHG emissions gap between that needed to “keep 1.5°C alive” and climate actions identified in the GST. Nonetheless, the Parties agreed to “transition away from fossil fuels in energy systems” in order to reach net zero GHG emissions (i.e., carbon neutrality) by 2050, and to triple renewable energy capacity and double energy efficiency by 2030. The present assessment sets out the background to what needs to be achieved at future annual COP summits, including the next GST at COP30 to beheld in the Brazilian city of Belém later in 2025

Stocktaking Global Warming:The outcomes of the 2023 Dubai Climate Summit (COP28)

This briefing reviews outcomes of the 28th United Nations Climate Change Conference of the Parties (COP28)held in Dubai, United Arab Emirates in late 2023. In particular, it considered the first Global Stocktake [GST] of actions taken by signatory nations to the 2015 Paris Agreement on Climate Change. The GST examined the potential impact of bottom-up national pledges on ‘greenhouse gas’ [GHG] mitigation required to limit global warming to 1.5°C above pre-industrial levels by the end of the 21st Century. The achievements at COP28 were mixed, and disappointed many from the climate-vulnerable states at high risk from extreme weather events and rising sea levels. There is a significant GHG emissions gap between that needed to “keep 1.5°C alive” and climate actions identified in the GST. Nonetheless, the Parties agreed to “transition away from fossil fuels in energy systems” in order to reach net zero GHG emissions (i.e., carbon neutrality) by 2050, and to triple renewable energy capacity and double energy efficiency by 2030. The present assessment sets out the background to what needs to be achieved at future annual COP summits, including the next GST at COP30 to beheld in the Brazilian city of Belém later in 2025