A single-threshold quantum-utilizing device in which the excited carriers thermally equilibrate among themselves, but not with the environment, can convert solar energy with an efficiency approaching that of an infinite-threshold device. Such a hot-carrier flat-plate device operated under typical terrestrial conditions (AM 1.5 illumination, 300 K) can convert solar energy with an efficiency of 66%, substantially exceeding the 33% maximum efficiency of a quantum device operating at thermal equilibrium, and the 52% maximum efficiency of an ideal thermal conversion device. This high efficiency is achieved in part through an unusual inversion, in which the chemical potential of the excited electronic band is below that of the ground band. This negative potential difference reduces radiation losses, permitting a low threshold energy, and a high Carnot efficiency resulting from a high carrier temperature.
A limit on the thermodynamic potential difference between the ground and excited states of any photochemical system is established by evaluating the potential difference at which the rate of photon absorption and emission are equal; the relationship between absorption and emission is given by a Planck-law relation, provided that there is thermal equilibrium between the sublevels of each electronic band. The actual potential developed may be evaluated if the quantum yield of luminescence is known. The maximum amount of power storage obtainable is evaluated by lowering the potential difference until the product of the potential difference and the fraction of the quanta retained is maximized. The history and applications of the Planck-law relation between absorption and emission spectra are discussed briefly, and applications of the potential difference calculation are mentioned.
BACKGROUNDPreimplantation genetic screening (PGS) has been used in an attempt to determine embryonic aneuploidy. Techniques that use new molecular methods to determine the karyotype of an embryo are expanding the scope of PGS.METHODSWe introduce a new method for PGS, termed ‘parental support’, which leverages microarray measurements from parental DNA to ‘clean’ single-cell microarray measurements on embryonic cells and explicitly computes confidence in each copy number call. The method distinguishes mitotic and meiotic copy errors and determines parental source of aneuploidy.RESULTSValidation with 459 single cells of known karyotype indicated that per-cell false-positive and false-negative rates are roughly equivalent to the ‘gold standard’ metaphase karyotype. The majority of the cells were run in parallel with a clinical commercial PGS service. Computed confidences were conservative and roughly concordant with accuracy. To examine ploidy in human embryos, the method was then applied to 26 disaggregated, cryopreserved, cleavage-stage embryos for a total of 134 single blastomeres. Only 23.1% of the embryos were euploid, though 46.2% of embryos were mosaic euploid. Mosaicism affected 57.7% of the embryos. Counts of mitotic and meiotic errors were roughly equivalent. Maternal meiotic trisomy predominated over paternal trisomy, and maternal meiotic trisomies were negatively predictive of mosaic euploid embryos.CONCLUSIONSWe have performed a major preclinical validation of a new method for PGS and found that the technology performs approximately as well as a metaphase karyotype. We also directly measured the mechanism of aneuploidy in cleavage-stage human embryos and found high rates and distinct patterns of mitotic and meiotic aneuploidy.
This study represents the first attempt to gain a detailed insight into the extent and type of chromosome errors seen at the blastocyst stage, using a comprehensive molecular cytogenetic method. Our data suggest that the blastocyst stage does not represent an absolute selective barrier, and that the majority of aneuploid embryos are lost at the time of implantation or shortly thereafter.
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