A folded π-system with supramolecularly oriented dipoles: single-component piezoelectric relaxor with NLO activity.

Organic molecules with an active dipole moment have a natural propensity to align in an antiparallel fashion in the solid state, resulting in zero macroscopic polarization. This primary limitation makes the material unresponsive to switching with electric fields, mechanical forces, and to intense laser light. A single-component organic material that bestows macroscopic dipole-driven electro-mechanical and optical functions, e.g., piezoelectric, ferroelectric and nonlinear optical (NLO) activity, is unprecedented due to the design challenges imparted by crystal symmetry and dipole orientations. Herein we report a crystalline organic material that self-assembles with a polar order (P 1), and is endowed with a high piezoelectric coefficient (d 33-47 pm V-1), as well as ferroelectric and Debye-type relaxor properties. In addition, it shows second harmonic generation (SHG) activity, which is more than five times that of the benchmark potassium dihydrogen phosphate. Piezoelectric force microscopy (PFM) images validated electro-mechanical deformations. Piezoresponse force spectroscopy (PFS) studies confirmed a signature butterfly-like amplitude and a phase loop. To the best of our knowledge, this is the first report of a folded supramolecular π-system that manifests unidirectionally oriented dipoles and exhibits piezoelectricity, ferroelectricity, and has excellent ability to generate second harmonic light. These findings can herald new design possibilities based on folded architectures to explore opto-, electro- and mechano-responsive multifaceted functions.

High-precision inversion of dynamic radiography using hydrodynamic features.

While radiography is routinely used to probe complex, evolving density fields in research areas ranging from materials science to shock physics to inertial confinement fusion and other national security applications, complications resulting from noise, scatter, complex beam dynamics, etc. prevent current methods of reconstructing density from being accurate enough to identify the underlying physics with sufficient confidence. In this work, we show that using only features that are robustly identifiable in radiographs and combining them with the underlying hydrodynamic equations of motion using a machine learning approach of a conditional generative adversarial network (cGAN) provides a new and effective approach to determine density fields from a dynamic sequence of radiographs. In particular, we demonstrate the ability of this method to outperform a traditional, direct radiograph to density reconstruction in the presence of scatter, even when relatively small amounts of scatter are present. Our experiments on synthetic data show that the approach can produce high quality, robust reconstructions. We also show that the distance (in feature space) between a testing radiograph and the training set can serve as a diagnostic of the accuracy of the reconstruction.

Posterior samples of the parameters of binary black holes from Advanced LIGO, Virgo's second observing run.

This paper presents a parameter estimation analysis of the seven binary black hole mergers-GW170104, GW170608, GW170729, GW170809, GW170814, GW170818, and GW170823-detected during the second observing run of the Advanced LIGO and Virgo observatories using the gravitational-wave open data. We describe the methodology for parameter estimation of compact binaries using gravitational-wave data, and we present the posterior distributions of the inferred astrophysical parameters. We release our samples of the posterior probability density function with tutorials on using and replicating our results presented in this paper.

Tidal Deformabilities and Radii of Neutron Stars from the Observation of GW170817.

We use gravitational-wave observations of the binary neutron star merger GW170817 to explore the tidal deformabilities and radii of neutron stars. We perform a Bayesian parameter estimation with the source location and distance informed by electromagnetic observations. We also assume that the two stars have the same equation of state; we demonstrate that, for stars with masses comparable to the component masses of GW170817, this is effectively implemented by assuming that the stars' dimensionless tidal deformabilities are determined by the binary's mass ratio q by Λ_{1}/Λ_{2}=q^{6}. We investigate different choices of prior on the component masses of the neutron stars. We find that the tidal deformability and 90% credible interval is Λ[over ˜]=222_{-138}^{+420} for a uniform component mass prior, Λ[over ˜]=245_{-151}^{+453} for a component mass prior informed by radio observations of Galactic double neutron stars, and Λ[over ˜]=233_{-144}^{+448} for a component mass prior informed by radio pulsars. We find a robust measurement of the common areal radius of the neutron stars across all mass priors of 8.9≤R[over ^]≤13.2 km, with a mean value of ⟨R[over ^]⟩=10.8 km. Our results are the first measurement of tidal deformability with a physical constraint on the star's equation of state and place the first lower bounds on the deformability and areal radii of neutron stars using gravitational waves.

Erratum: Tidal Deformabilities and Radii of Neutron Stars from the Observation of GW170817 [Phys. Rev. Lett. 121, 091102 (2018)].

This corrects the article DOI: 10.1103/PhysRevLett.121.091102.

Base triggered enhancement of first hyperpolarizability of a keto-enol tautomer.

This work describes the base triggered enhancement of first hyperpolarizability of a tautomeric organic molecule, namely, benzoylacetanilide (BA). We have used the hyper-Rayleigh scattering technique to measure the first hyperpolarizability (ß) of BA which exists in the pure keto form in water and as a keto-enol tautomer in ethanol. Its anion exists in equilibrium with the keto and enol forms at pH 11 in aqueous solution. The ß value of the anion form is 709 × 10(-30) esu, whereas that of the enol is 232 × 10(-30) esu and of the keto is 88 × 10(-30) esu. There is an enhancement of ß by ~8 times for the anion and ~3 times for the enol compared to the keto form. All these are achieved by altering the equilibrium between the three forms of BA by simple means. MP2 calculations reproduce the experimental trend, but the computed ß values are much lower than the measured values. DFT calculations with the standard B3LYP functional could not predict the right order in the ß values. The difference between experimental and calculated values is, perhaps, due to the fact that electron correlation effects are important in computing optical nonlinearities of large organic molecules and MP2 and B3LYP calculations done here for different forms of BA could not account for such effects adequately.