לוח שנה משולב

Basic thermodynamics informs us that concentrating solar radiation creates the potential for both higher solar power conversion efficiency, and achieving the ultra-high threshold temperatures and flux densities that are crucial for some novel solar utilization strategies. Three examples constituting distinct solar conversion paradigms will be explored in this presentation.
The first paradigm is ultra-efficient solar electricity generation stemming from the confluence of progress in multi-junction photovoltaic technologies and advanced solar concentrator design. The evolution from the initial optical and solid-state inventions to megawatt-scale commercial concentrator photovoltaic power plants will be reviewed. Several generations of new optics that approach the thermodynamic limit to concentration and optical tolerance, and have been tailored to the exigencies of the latest generations of concentrator solar cells, will be presented.
The second paradigm is the tantalizing prospect of using solar rectifying antennas for solar power conversion. Although direct sunlight is commonly viewed as incoherent – therefore ostensibly not suitable for antenna collection – all radiation exhibits spatial coherence on a sufficiently small scale. The theory and experimental confirmation of basic performance bounds based on the partial coherence of broadband solar radiation will be reviewed. The ramifications for using optical concentrators that can effectively replace orders of magnitude of antenna and rectifier elements will be discussed. In addition, a basic upper bound on the ability to rectify (AC to DC) the inordinately high-frequency broadband signals from solar antennae will be evaluated.
The third distinct solar paradigm is creating valued materials at the service of human technology, rather than using solar to generate heat, electricity or fuels (in collaboration with Reshef Tenne and his group at the WIS). It requires novel optical concentrators, and understanding the unique nature of solar reactor conditions (ultra-high temperatures with strong flux gradients and expansive ultra-hot annealing regions). Successful case studies subsume: cage-like nanostructures of Cs2O; high-yield syntheses for fullerene-like and nanotube MoS2, MoSe2, WS2, WSe2; nanowires and nanospheres of SiO2 generated for the first time from pure quartz; nanorods of pure Si; and SiC nanowires. Some of the MoS2 nanostructures achieve fundamentally minimum sizes predicted by molecular structural theory, as well as unique hybrid nanostructures.

The Eocene (56-34My ago) is one of the best analogs for a greenhouse climate, with high CO2 concentrations, generally high temperatures, and no polar ice caps. A major feature of the Eocene geochemical records suggests a reduced latitudinal gradient, in which most of the warming occurs in polar regions (possibly exceeding 30°C in the Antarctic margin), but less in the tropics. These results could have profound implications for understanding polar amplification of greenhouse warming, but they are not captured in climate models, pointing to important gaps in climate models and to major uncertainties in the geochemical data. We combine two temperature proxies - carbonate clumped isotopes in fossil bivalve shells and archaeal lipid TEX86 in the sediment associated with the bivalves - to constrain Eocene temperatures in Southern high latitudes. Clumped isotope paleothermometry is a thermodynamically controlled temperature proxy that is not dependent on the isotopic composition of seawater, and presents a novel opportunity to reduce uncertainties in Eocene sea surface temperature estimates. We use it to constrain the calibration of TEX86 in order to compare paleotemperatures in the Antarctic Peninsula (Seymour Island) to those in the South Pacific (Eastern Tasman Plateau), both at ~65°S paleo-latitude. The data indicates middle to late Eocene paleotemperatures of 10-17C in Seymour Island and ~7°C higher in the Eastern Tasman Plateau, suggesting a pronounced zonal heterogeneity in southern high latitude sea surface temperatures.