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1. Limits on the Rate of Conversion of Potential to Kinetic Energy in Quasigeostrophic Turbulence

   https://doi.org/10.3390/fluids7080276  

   Grooms, Ian (August 2022, Fluids)

   Flow configurations that maximize the instantaneous rate of conversion from potential to kinetic energy are sought using a combination of analytical and numerical methods. A hydrostatic model is briefly investigated, but the presence of unrealistic ageostrophic flow configurations renders the results unrealistic. In the quasigeostrophic (QG) model, flow configurations that locally optimize the conversion rate are found, but it remains unclear if these flow configurations produce the global maximum conversion rate. The difficulty is associated with the fact that in the QG model, the vertical velocity is a quadratic function of the QG streamfunction, which renders the conversion rate a cubic function of the QG streamfunction. For these locally maximal conversion rates, the rate of conversion depends on the horizontal length scale of the flow: for scales larger than the deformation radius, the maximal rates are small and decrease as the horizontal scale increases; for scales smaller than the deformation radius, the maximal conversion rate rises until it becomes comparable to the maximal rate at which potential energy can be extracted from the mean flow. 

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2. Back-conversion suppressed parametric frequency conversion for ultrawide bandwidth and ultrahigh efficiency devices

   https://doi.org/10.1117/12.2548361  

   Moses, Jeffrey; Flemens, Noah; Ding, Xiaoyue; Schunemann, Peter G.; Schepler, Kenneth L. (March 2020, SPIE LASE, 2020, San Francisco, California, United States)

   For as widely used a tool as nonlinear optical frequency conversion is for both science and industry, it remains widely limited in eciency and bandwidth (and ultimately also in cost) due to the fundamental problem of backconversion in the nonlinear evolution dynamics. This review paper covers new developments and capabilities in frequency conversion devices, including optical up- and down-converters and ampli ers, based on nonlinear evolution dynamics in which back-conversion is suppressed. One such approach is adiabatic frequency conversion, in which the dynamics of rapid adiabatic passage replace the regular cyclic conversion evolution in phase-matched sum- and dierence-frequency generation. This approach has enabled devices far surpassing the conventional eciency-bandwidth trade-o. For example, in chirped quasi-phase matched quadratic crystals, microjouleenergy single-cycle mid-infrared pulses were generated with arbitrary pulse shaping capability, presenting a source with unique features for nonlinear spectroscopy and strong- eld physics applications. We review new developments in the use of optical bers as a cubic nonlinear platform for the same concept, utilizing a tapered core diameter or a pressure gradient to allow up- and down-conversion with ultra-wide bandwidth and high eciency. We also review a newly introduced concept for high eciency optical parametric ampli cation, via a novel approach for suppressing back-conversion in optical parametric ampli cation by simultaneously phasematching the idler wave for second harmonic generation. Keywords: Adiabatic wave mixing, ecient optical parametric ampli cation, octave-spanning 

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3. Electrospun Cadmium Selenide Nanoparticles-Loaded Cellulose Acetate Fibers for Solar Thermal Application

   https://doi.org/10.3390/nano10071329  

   Angel, Nicole; Vijayaraghavan, S. N.; Yan, Feng; Kong, Lingyan (July 2020, Nanomaterials)

   null (Ed.)

   Solar thermal techniques provide a promising method for the direct conversion of solar energy to thermal energy for applications, such as water desalination. To effectively realize the optimal potential of solar thermal conversion, it is desirable to construct an assembly with localized heating. Specifically, photoactive semiconducting nanoparticles, when utilized as independent light absorbers, have successfully demonstrated the ability to increase solar vapor efficiency. Additionally, bio-based fibers have shown low thermal conductive photocorrosion. In this work, cellulose acetate (CA) fibers were loaded with cadmium selenide (CdSe) nanoparticles to be employed for solar thermal conversion and then subsequently evaluated for both their resulting morphology and conversion potential and efficiency. Electrospinning was employed to fabricate the CdSe-loaded CA fibers by adjusting the CA/CdSe ratio for increased solar conversion efficiency. The microstructural and chemical composition of the CdSe-loaded CA fibers were characterized. Additionally, the optical sunlight absorption performance was evaluated, and it was demonstrated that the CdSe nanoparticles-loaded CA fibers have the potential to significantly improve solar energy absorption. The photothermal conversion under 1 sun (100 mW/cm2) demonstrated that the CdSe nanoparticles could increase the temperature up to 43 °C. The CdSe-loaded CA fibers were shown as a feasible and promising hybrid material for achieving efficient solar thermal conversion. 

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4. Little evidence for homoeologous gene conversion and homoeologous exchange events in Gossypium allopolyploids

   https://doi.org/10.1002/ajb2.16386  

   Conover, Justin L; Grover, Corrinne E; Sharbrough, Joel; Sloan, Daniel B; Peterson, Daniel G; Wendel, Jonathan F (August 2024, American Journal of Botany)

   Abstract PremiseA complicating factor in analyzing allopolyploid genomes is the possibility of physical interactions between homoeologous chromosomes during meiosis, resulting in either crossover (homoeologous exchanges) or non‐crossover products (homoeologous gene conversion). Homoeologous gene conversion was first described in cotton by comparing SNP patterns in sequences from two diploid progenitors with those from the allopolyploid subgenomes. These analyses, however, did not explicitly consider other evolutionary scenarios that may give rise to similar SNP patterns as homoeologous gene conversion, creating uncertainties about the reality of the inferred gene conversion events. MethodsHere, we use an expanded phylogenetic sampling of high‐quality genome assemblies from seven allopolyploidGossypiumspecies (all derived from the same polyploidy event), four diploid species (two closely related to each subgenome), and a diploid outgroup to derive a robust method for identifying potential genomic regions of gene conversion and homoeologous exchange. ResultsWe found little evidence for homoeologous gene conversion in allopolyploid cottons, and that only two of the 40 best‐supported events were shared by more than one species. We did, however, reveal a single, shared homoeologous exchange event at one end of chromosome 1, which occurred shortly after allopolyploidization but prior to divergence of the descendant species. ConclusionsOverall, our analyses demonstrated that homoeologous gene conversion and homoeologous exchanges are uncommon inGossypium, affecting between zero and 24 genes per subgenome (0.0–0.065%) across the seven species. More generally, we highlighted the potential problems of using simple four‐taxon tests to investigate patterns of homoeologous gene conversion in established allopolyploids. 

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5. Phase-Matching Schemes for Back-Conversion Suppression in Nonlinear Wave Mixing: Towards Ultra-High Efficiency and Ultra-Broad Bandwidth

   https://doi.org/10.1109/PN50013.2020.9166946  

   Moses, Jeffrey (May 2020, 2020 Photonics North (PN))

   null (Ed.)

   By suppressing the conversion-back-conversion cycles typical of optical parametric processes through novel phase-matching schemes, octave-spanning frequency conversion and highly efficient parametric amplification can be achieved. Several recent developments will be reviewed. 

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