X-Shooter observations of low-mass stars in the Eta Chamaeleontis association

The nearby Eta Chamaeleontis association is a collection of 4-10 Myr old stars with a disk fraction of 35-45%. In this study, the broad wavelength coverage of VLT/X-Shooter is used to measure the stellar and mass accretion properties of 15 low mass stars in the Eta Chamaeleontis association. For each star, the observed spectrum is fitted with a non-accreting stellar template and an accretion spectrum obtained from assuming a plane-parallel hydrogen slab. Five of the eight stars with an IR disk excess show excess UV emission, indicating ongoing accretion. The accretion rates measured here are similar to those obtained from previous measurements of excess UV emission, but tend to be higher than past measurements from H-alpha modeling. The mass accretion rates are consistent with those of other young star forming regions.Comment: Accepted for publication in Astronomy & Astrophysic

An Introduction To The Web-Based Formalism

This paper summarizes our rather lengthy paper, "Algebra of the Infrared: String Field Theoretic Structures in Massive ${\cal N}=(2,2)$ Field Theory In Two Dimensions," and is meant to be an informal, yet detailed, introduction and summary of that larger work.Comment: 50 pages, 40 figure

Anisotropic conjugated polymer chain conformation tailors the energy migration in nanofibers

Conjugated polymers are complex multi-chromophore systems, with emission properties strongly dependent on the electronic energy transfer through active sub-units. Although the packing of the conjugated chains in the solid state is known to be a key factor to tailor the electronic energy transfer and the resulting optical properties, most of the current solution-based processing methods do not allow for effectively controlling the molecular order, thus making the full unveiling of energy transfer mechanisms very complex. Here we report on conjugated polymer fibers with tailored internal molecular order, leading to a significant enhancement of the emission quantum yield. Steady state and femtosecond time-resolved polarized spectroscopies evidence that excitation is directed toward those chromophores oriented along the fiber axis, on a typical timescale of picoseconds. These aligned and more extended chromophores, resulting from the high stretching rate and electric field applied during the fiber spinning process, lead to improved emission properties. Conjugated polymer fibers are relevant to develop optoelectronic plastic devices with enhanced and anisotropic properties.Comment: 43 pages, 15 figures, 1 table in Journal of the American Chemical Society, (2016

Learning to Noise: Application-Agnostic Data Sharing with Local Differential Privacy

The collection and sharing of individuals' data has become commonplace in many industries. Local differential privacy (LDP) is a rigorous approach to preserving data privacy even from a database administrator, unlike the more standard central differential privacy. To achieve LDP, one traditionally adds noise directly to each data dimension, but for high-dimensional data the level of noise required for sufficient anonymization all but entirely destroys the data's utility. In this paper, we introduce a novel LDP mechanism that leverages representation learning to overcome the prohibitive noise requirements of direct methods. We demonstrate that, rather than simply estimating aggregate statistics of the privatized data as is the norm in LDP applications, our method enables the training of performant machine learning models. Unique applications of our approach include private novel-class classification and the augmentation of clean datasets with additional privatized features. Methods that rely on central differential privacy are not applicable to such tasks. Our approach achieves significant performance gains on these tasks relative to state-of-the-art LDP benchmarks that noise data directly

5D Black Rings and 4D Black Holes

It has recently been shown that the M theory lift of a IIA 4D BPS Calabi-Yau black hole is a 5D BPS black hole spinning at the center of a Taub-NUT-flux geometries, and a certain linear relation between 4D and 5D BPS partition functions was accordingly proposed. In the present work we fortify and enrich this proposal by showing that the M-theory lift of the general 4D multi-black hole geometry are 5D black rings in a Taub-NUT-flux geometry.Comment: 8 pages; version 2, with additional references and explanation

Correlated electron physics near a site-selective pressure-induced Mott transition in <i>α</i>-LiFe₅O₈

The Mott insulator-to-metal transition (IMT) driven by electron correlations has been among the main research topics in materials science over the past decades. The complex interplay between electronic and lattice degrees of freedom leads to various transition scenarios. Of particular interest may be the case of a transition involving the formation of complex phases comprising regions that differ significantly in their physical properties within the same material. Here, we present the results that advance the understanding of the IMT phenomenon, offering the documentation of a pure site-selective mechanism that is not complicated by any structural and spin transformation. Combining XRD, resistivity, Mössbauer and Raman spectroscopy measurements, we provide evidence for a pure pressure-induced Mott transition in α-LiFe5O8, characterized by site-selective delocalization of electrons, leading to the formation, above ~65 GPa, of a site-selective Mott phase consisting of metallic and insulating sublattices. We note that the electron delocalization in the partially disordered octahedral sublattice cannot be understood purely in terms of a Mott transition, the Anderson-Mott transition picture seems more adequate