Disclosure versus recognition: the value relevance of pensions

This paper compares how pension obligations impact the market value of United States corporations under two accounting regimes. Using a sample of firms that disclosed pension liabilities under Statement of Financial Accounting Standards (SFAS) No. 87 from 2001 to 2005 and recognized them under SFAS No. 158 from 2006 to 2014, I find that equity market participants take into account the net position of the pension fund only if it is recognized on the sponsor's balance sheet, thus mispricing the pension deficit/surplus under the disclosure regime. I also provide evidence suggesting that investors' perception of pension deficits/surpluses changed with the introduction of SFAS No. 158 in 2006

Effects of interaction on the diffusion of atomic matter waves in one-dimensional quasi-periodic potentials

We study the behaviour of an ultracold atomic gas of bosons in a bichromatic lattice, where the weaker lattice is used as a source of disorder. We numerically solve a discretized mean-field equation, which generalizes the one-dimensional Aubry-Andr\`e model for particles in a quasi-periodic potential by including the interaction between atoms. We compare the results for commensurate and incommensurate lattices. We investigate the role of the initial shape of the wavepacket as well as the interplay between two competing effects of the interaction, namely self-trapping and delocalization. Our calculations show that, if the condensate initially occupies a single lattice site, the dynamics of the interacting gas is dominated by self-trapping in a wide range of parameters, even for weak interaction. Conversely, if the diffusion starts from a Gaussian wavepacket, self-trapping is significantly suppressed and the destruction of localization by interaction is more easily observable

Localization in momentum space of ultracold atoms in incommensurate lattices

We characterize the disorder induced localization in momentum space for ultracold atoms in one-dimensional incommensurate lattices, according to the dual Aubry-Andr\'e model. For low disorder the system is localized in momentum space, and the momentum distribution exhibits time-periodic oscillations of the relative intensity of its components. The behavior of these oscillations is explained by means of a simple three-mode approximation. We predict their frequency and visibility by using typical parameters of feasible experiments. Above the transition the system diffuses in momentum space, and the oscillations vanish when averaged over different realizations, offering a clear signature of the transition

Properties of intrinsic point defects and dimers in hexagonal boron nitride

Hexagonal boron nitride (hBN) is a wide gap 2D layered material with good insulating properties. Intrinsic point defects in hBN play an important role in its applications as a dielectric in 2D electronic devices. However, the electronic properties of these defects are still poorly understood. We have calculated the structure and properties of a wide range of intrinsic point defects in the bulk of hBN using hybrid density functional theory (DFT). These include vacancies and interstitial states of B and N as well as di- and tri-vacancies. For each isolated defect, multiple charge states are calculated, and for each charge state multiple spin states are investigated. Positions of defect charge transition levels in the band gap of hBN are calculated. In particular, we predict that B vacancies are likely to be negatively charged in contact with graphene and other metals. Calculations of the interaction between vacancies predict that divacancies in both B and N sublattices are strongly binding. Moreover, the interaction of single B and N vacancies in adjacent layers induces the creation of -N--N- and -B--B- molecular bridges, which greatly distort the local structure, leading to local bond weakening. These results provide further insight into the properties of defects which can be responsible for degradation of hBN based devices

A microscopic mechanism of dielectric breakdown in SiO2 films: An insight from multi-scale modeling

Despite extensive experimental and theoretical studies, the atomistic mechanisms responsible for dielectric breakdown (BD) in amorphous (a)-SiO2 are still poorly understood. A number of qualitative physical models and mathematical formulations have been proposed over the years to explain experimentally observable statistical trends. However, these models do not provide clear insight into the physical origins of the BD process. Here we investigate the physical mechanisms responsible for dielectric breakdown in a-SiO2 using a multi-scale approach where the energetic parameters derived from a microscopic mechanism are used to predict the macroscopic degradation parameters of BD, i.e. time-dependent dielectric breakdown (TDDB) statistics, and its voltage dependence. Using this modeling framework, we demonstrate that trapping of two electrons at intrinsic structural precursors in a-SiO2 is responsible for a significant reduction of the activation energy for Si-O bond breaking. This results in a lower barrier for the formation of O vacancies and allows us to explain quantitatively the TDDB data reported in the literature for relatively thin (3-9nm) a-SiO2 oxide films

Changes in the contents of micro- and trace-elements in wine due to winemaking treatments

Forty-four mineral elements quantified by ICP-OES and ICP-MS were measured in wines, (a) after wine fining, at three pH levels with 10 different bentonites (1 g·l-1), (b) after addition of yeast hulls from 2 suppliers to wine (180 and 360 mg·1-1). Bentonite fining resulted in statistically significant increases of the large majority of elements, but in significant lower levels of Cu, K, Rb and Zn. The addition of yeast hulls caused a statistically significant depletion of the contents of Ce, Cu, Fe, La, Sb, U, V and Y.

Observation of subdiffusion of a disordered interacting system

We study the transport dynamics of matter-waves in the presence of disorder and nonlinearity. An atomic Bose-Einstein condensate that is localized in a quasiperiodic lattice in the absence of atom-atom interaction shows instead a slow expansion with a subdiffusive behavior when a controlled repulsive interaction is added. The measured features of the subdiffusion are compared to numerical simulations and a heuristic model. The observations confirm the nature of subdiffusion as interaction-assisted hopping between localized states and highlight a role of the spatial correlation of the disorder.Comment: 8 pages, to be published on Physical Review Letter

Three decades of nucleic acid aptamer technologies: Lessons learned, progress and opportunities on aptamer development

Aptamers are short single-stranded nucleic acid sequences capable of binding to target molecules in a way similar to antibodies. Due to various advantages such as prolonged shelf life, low batch to batch variation, low/no immunogenicity, freedom to incorporate chemical modification for enhanced stability and targeting capacity, aptamers quickly found their potential in diverse applications ranging from therapy, drug delivery, diagnosis, and functional genomics to bio-sensing. Aptamers are generated by a process called SELEX. However, the current overall success rate of SELEX is far from being satisfactory, and still presents a major obstacle for aptamer-based research and application. The need for an efficient selection strategy consisting of defined procedures to deal with a wide variety of targets is significantly important. In this work, by analyzing key aspects of SELEX including initial library design, target preparation, PCR optimization, and single strand DNA separation, we provide a comprehensive analysis of individual steps to facilitate researchers intending to develop personalized protocols to address many of the obstacles in SELEX. In addition, this review provides suggestions and opinions for future aptamer development procedures to address the concerns on key SELEX steps, and post-SELEX modifications