Separation between second price auctions with personalized reserves and the revenue optimal auction

When buyer valuations are drawn IID from a known regular distribution, a second price auction with a symmetric reserve price is the revenue-optimal single-item auction. When this distribution is irregular, we provide the first separation result showing that a second price auction with reserves earns at most 0.778 times the revenue of Myerson’s optimal auction, even when the reserves can be asymmetric. Since the lower bound is 0.745 for i.i.d. buyers, our result is nearly tight.     

A tale of hydrogen abstraction,initially detected via X‐ray diffraction

Reaction of a bis‐tetrazinyl pyridine pincer ligand, btzp, with a vanadium(III) reagent gives not a simple adduct but dichlorido{3‐methyl‐6‐[6‐(6‐methyl‐1,2,4,5‐tetrazin‐3‐yl‐κN²)pyridin‐2‐yl‐κN]‐1,4‐dihydro‐1,2,4,5‐tetrazin‐1‐yl‐κN¹}oxidovanadium(IV) acetonitrile 2.5‐solvate, [V(C₁₁H₁₀N₉)Cl₂O]·2.5CH₃CN, a species which X‐ray diffraction reveals to have one H atom added to one of the two tetrazinyl rings. This H atom was first revealed by a short intermolecular N...Cl contact in the unit cell and subsequently established, from difference maps, to be associated with a hydrogen bond. One chloride ligand has also been replaced by an oxide ligand in this synthetic reaction. This formula for the complex, [V(Hbtzp)Cl₂O], leaves open the question of both ligand oxidation state and spin state. A computational study of all isomeric locations of the H atom shows the similarity of their energies, which is subject to perturbation by intermolecular hydrogen bonding found in X‐ray work on the solid state. These density functional calculations reveal that the isomer with the H atom located as found in the solid state contains a neutral radical Hbtzp ligand and tetravalent d¹ V center, but that these two unpaired electrons are more stable as an open‐shell singlet and hence antiferromagnetically coupled.     

Side chain engineering of naphthalene diimide–bithiophene‐based polymer acceptors in all‐polymer solar cells

Two novel polymeric acceptors based on naphthalene diimide (NDI) and 2.2′‐bithiophene, named as P(NDI2THD‐T2) and P(NDI2TOD‐T2), were designed and synthesized for all polymer solar cells application. The structural and electronic properties of the two acceptors were modulated through side‐chain engineering of the NDI units. The optoelectronic properties of the polymers and the morphologies of the blend films composed of the polymer acceptors and a donor polymer PTB7‐Th were systemically investigated. With thiophene groups introduced into the side chains of the NDI units, both polymers showed wider absorption from 350 nm to 900 nm, compared with the reference polymer acceptor of N2200. No redshift of absorption spectra from solutions to films indicated reduced aggregation of the polymers due to the steric hindrance effect of thiophene rings in the side chains. The photovoltaic performance were characterized for devices in a configuration of ITO/PEDOT:PSS/PTB7‐Th:acceptors/2,9‐bis(3‐(dimethylamino)propyl)anthra[2,1,9‐def:6,5,10‐def]diisoquinoline‐1,3,8,10(2H,9H)‐tetraone (PDIN)/Al. With the addition of diphenyl ether as an additive, the power conversion efficiencies (PCEs) of 2.73% and 4.75% for P(NDI2THD‐T2) and P(NDI2TOD‐T2) based devices were achieved, respectively. The latter showed improved J_sc, Fill Factor (FF), and PCE compared with N2200 based devices. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3679–3689     

Detecting itinerant single microwave photons

Single-photon detectors are fundamental tools of investigation in quantum optics and play a central role in measurement theory and quantum informatics. Photodetectors based on different technologies exist at optical frequencies and much effort is currently being spent on pushing their efficiencies to meet the demands coming from the quantum computing and quantum communication proposals. In the microwave regime, however, a single-photon detector has remained elusive, although several theoretical proposals have been put forth. In this article, we review these recent proposals, especially focusing on non-destructive detectors of propagating microwave photons. These detection schemes using superconducting artificial atoms can reach detection efficiencies of 90% with the existing technologies and are ripe for experimental investigations.     

Modelling sediment transport over partially non‐erodible bottoms

In‐depth‐averaged and cross‐section‐averaged morphodynamic models, based on explicit time integration, it may happen that the computed bed level becomes lower than the top level of a non‐erodible layer (e.g. concrete, bedrock or armoured layer). This is a standard pitfall, which has been addressed in different ways. In this paper, we present an original approach for avoiding computation of non‐physical bed levels, using an iterative procedure to correct the outward sediment fluxes. The procedure is shown to be computationally efficient while it achieves a high accuracy in terms of mass conservation. We compare our original approach with the existing Struiksma's method and with a reformulation of the problem in terms of mathematical optimization of a linear or nonlinear objective function under linear constraints. The new procedure has been incorporated into an existing finite volume morphodynamic model. It has been validated with several 1D benchmarks leading to configurations with sediment transport over non‐erodible bottom. The computation time has been verified not to increase by more than 15% compared with runs without non‐erodible bottom. Copyright © 2011 John Wiley & Sons, Ltd.     

Non‐intrusive reduced‐order modeling for multiphase porous media flows using Smolyak sparse grids

In this article, we describe a non‐intrusive reduction method for porous media multiphase flows using Smolyak sparse grids. This is the first attempt at applying such an non‐intrusive reduced‐order modelling (NIROM) based on Smolyak sparse grids to porous media multiphase flows. The advantage of this NIROM for porous media multiphase flows resides in that its non‐intrusiveness, which means it does not require modifications to the source code of full model. Another novelty is that it uses Smolyak sparse grids to construct a set of hypersurfaces representing the reduced‐porous media multiphase problem. This NIROM is implemented under the framework of an unstructured mesh control volume finite element multiphase model. Numerical examples show that the NIROM accuracy relative to the high‐fidelity model is maintained, whilst the computational cost is reduced by several orders of magnitude. Copyright © 2016 John Wiley & Sons, Ltd.     

Miscellaneous applications of ferrocene‐based peptides/amides

This article provides a critical review of the different applications of ferrocene‐based peptides/amides in biological as well as in non‐biological systems. Ferrocene‐based peptides/amides find many applications in different fields such as materials science, medicine, organic synthesis, bio‐organometallic and biological chemistry, asymmetric catalysis, nonlinear optics, in polymer science as redox active polymers and dendrimers, in molecular recognition as biosensors and in electrochemistry). Extensive research is being done on ferrocene‐based peptides/amides but we will highlight the various applications of ferrocene‐based peptides/amides for the period 2006–2010. The main factors that govern the potential biological and non‐biological applications are an electroactive core, a conjugated linker that can act as a chromophore and lower the oxidation potential of the ferrocene part, an amino acid or peptide derivative that can interact with other molecules via hydrogen bonding or any secondary bonding, and symmetric and asymmetric substitution on the ferrocene moiety. Copyright © 2011 John Wiley & Sons, Ltd.     

A new test on the conditional capital asset pricing model

Testing the validity of the conditional capital asset pricing model(CAPM) is a puzzle in the finance literatureLewellen and Nagel[14]find that the variation in betas and in the equity premium would have to be implausibly large to explain important asset-pricing anomaliesUnfortunately, they do not provide a rigorous test statisticBased on a simulation study, the method proposed in Lewellen and Nagel[14]tends to reject the null too frequently.We develop a new test procedure and derive its limiting distribution under the null hypothesis.Also, we provide a Bootstrap approach to the testing procedure to gain a good finite sample performanceBoth simulations and empirical studies show that our test is necessary for making correct inferences with the conditional CAPM.     

Blind separation of fluorescence spectra using sparse non‐negative matrix factorization on right hand factor

Sparse non‐negative matrix factorization on right side factor (SNMF/R) has better performance in feature extraction than non‐negative matrix factorization. In this work, SNMF/R was first used to separate the overlapped three‐dimensional fluorescence spectra of polycyclic aromatic hydrocarbons mixtures in pure water, lake water, and river water, respectively. It is found that the similarity coefficients between the acquired three‐dimensional spectra and the corresponding reference spectra with random initials are all above 0.80; the recognition rate of SNMF/R is higher than that of PARAFAC and non‐negative matrix factorization algorithms, especially in the case of lake water and river water samples. In addition, SNMF/R does not need any initialization scheme designing during spectra separation. These results demonstrate that SNMF/R is an appropriate algorithm to separate the overlapped fluorescence spectra of polycyclic aromatic hydrocarbons in aquatic environment accurately and effectively. Copyright © 2015 John Wiley & Sons, Ltd.