(Phosphanyl)phosphaketenes as building blocks for novel phosphorus heterocycles.

Although BH3 simply coordinates the endocyclic P of (phospholidino)phosphaketene 1Dipp , the bulkier B(C6F5)3 gives rise to a zwitterionic diphosphirenium, which is a novel type of 2π-electron aromatic system as shown by the calculated NICS values. While the reaction of 1Dipp with Na[PCO(dioxane) x ] is unselective, the same reaction with the sterically bulky (phospholidino)phosphaketene 1Ar** [Ar** = 2,6-bis[di(4-tert-butylphenyl)methyl]-4-methylphenyl selectively affords a sodium bridged dimer containing a hitherto unknown λ3,λ5,λ3-triphosphete core. The latter formally results from "P-" addition to a 1,3-P/C-dipole. Similarly, adamantyl isonitrile adds to 1Dipp giving a 4-membered phosphacycle. In contrast to 1, the phosphaketene derived from the electrophilic diazaphospholidine-4,5-dione is unstable and reacts with a second molecule of Na[PCO(dioxane) x ] to afford a 1,3,4-oxadiphospholonide derivative

Discovery of a mRNA Mitochondrial Localization Element in Saccharomyces Cerevisiae by Nonhomologous Random Recombination and In Vivo Selection

In budding yeast, over 100 nuclear-encoded mRNAs are localized to the mitochondria. The determinants of mRNA localization to the mitochondria are not well understood, and protein factors involved in this process have not yet been identified. To reveal the sequence determinants for mitochondrial localization in a comprehensive and unbiased manner, we generated highly diversified libraries of 3’ UTR regions from a known mitochondrially localized mRNA by nonhomologous random recombination (NRR) and subjected the resulting sequences to an in vivo selection that links cell survival to mitochondrial mRNA localization. When applied to the yeast ATP2 mRNA, this approach rapidly identified a 50-nt consensus motif, designated Min2, as well as two Min2-homologous regions naturally present downstream of the ATP2 stop codon, which are sufficient when appended to the 3’ end of various reporter mRNAs to induce mitochondrial localization. Sitedirected mutagenesis of Min2 revealed primary and secondary structure elements that contribute to localization activity. In addition, the Min2 motif may facilitate the identification of proteins involved in this mode of establishing cellular asymmetry.Chemistry and Chemical Biolog

Non-Fermi liquids from holography

We report on a potentially new class of non-Fermi liquids in (2+1)-dimensions. They are identified via the response functions of composite fermionic operators in a class of strongly interacting quantum field theories at finite density, computed using the AdS/CFT correspondence. We find strong evidence of Fermi surfaces: gapless fermionic excitations at discrete shells in momentum space. The spectral weight exhibits novel phenomena, including particle-hole asymmetry, discrete scale invariance, and scaling behavior consistent with that of a critical Fermi surface postulated by Senthil.Comment: 10 pages, 16 figures. v2: added references, corrected figures, some minor changes. v3: figure 5 replace

Algorithmic Fairness from a Non-ideal Perspective

Inspired by recent breakthroughs in predictive modeling, practitioners in both industry and government have turned to machine learning with hopes of operationalizing predictions to drive automated decisions. Unfortunately, many social desiderata concerning consequential decisions, such as justice or fairness, have no natural formulation within a purely predictive framework. In efforts to mitigate these problems, researchers have proposed a variety of metrics for quantifying deviations from various statistical parities that we might expect to observe in a fair world and offered a variety of algorithms in attempts to satisfy subsets of these parities or to trade o the degree to which they are satised against utility. In this paper, we connect this approach to fair machine learning to the literature on ideal and non-ideal methodological approaches in political philosophy. The ideal approach requires positing the principles according to which a just world would operate. In the most straightforward application of ideal theory, one supports a proposed policy by arguing that it closes a discrepancy between the real and the perfectly just world. However, by failing to account for the mechanisms by which our non-ideal world arose, the responsibilities of various decision-makers, and the impacts of proposed policies, naive applications of ideal thinking can lead to misguided interventions. In this paper, we demonstrate a connection between the fair machine learning literature and the ideal approach in political philosophy, and argue that the increasingly apparent shortcomings of proposed fair machine learning algorithms reflect broader troubles faced by the ideal approach. We conclude with a critical discussion of the harms of misguided solutions, a reinterpretation of impossibility results, and directions for future researc