 Award ID(s):
 1955318
 Publication Date:
 NSFPAR ID:
 10280852
 Journal Name:
 Journal of Porphyrins and Phthalocyanines
 Page Range or eLocationID:
 A to J
 ISSN:
 10884246
 Sponsoring Org:
 National Science Foundation
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The design/synthesis and characterization of organic donor–acceptor (D–A) dyads can provide precious data allowing to improve the efficiency of classical photoinduced bimolecular interactions/processes. In this report, two novel triplet D–A dyads (4 and 5) were synthesized and fully characterized. While the optical absorption and emission profiles of these new systems exhibit similar spectral structures as that of the triplet donor/sensitizer quinoidal thioamide (QDN), the transient absorption (TA) spectra of these two dyads produced new features that can be associated with triplet transients and charge transfer species. However, the kinetics of the excitedstate processes/dynamics is significantly influenced by the geometrical arrangement(s) of donor/acceptor chromophores. Further analysis of the TA data suggests that the dyad with slipstack geometry (4) is less effective in undergoing both intra and interdyad triplet energy transfer than the dyad with cofacial geometry (5). Subsequently, triplet sensitization of 9,10diphenylanthracene (DPA) using both dyads led to upconverted photoluminescence via triplet–triplet annihilation of DPA triplet transients. But, it was found that a maximum upconversion quantum yield could be achieved at a low power density using the cofacial type dyad 5. Altogether, these results provide valuable guidance in the design of triplet donor–acceptor dyads, which could be used for lightharvesting/modulation applications.

The dynamics of an oceanic storm track—where energy and enstrophy transfer between the mean flow and eddies—are investigated using observations from an eddyrich region of the Antarctic Circumpolar Current downstream of the Shackleton Fracture Zone (SFZ) in Drake Passage. Four years of measurements by an array of current and pressurerecording inverted echo sounders deployed between November 2007 and November 2011 are used to diagnose eddy–mean flow interactions and provide insight into physical mechanisms for these transfers. Averaged within the upper to midwater column (400–1000m depth) and over the 4yrrecord mean field, eddy potential energy [Formula: see text] is highest in the western part of the storm track and maximum eddy kinetic energy [Formula: see text] occurs farther away from the SFZ, shifting the proportion of eddy energies from [Formula: see text] to about 1 along the storm track. There are enhanced mean 3D wave activity fluxes [Formula: see text] immediately downstream of SFZ with strong horizontal flux vectors emanating northeast from this region. Similar patterns across composites of Polar Front and Subantarctic Front meander intrusions suggest the dynamics are set more so by the presence of the SFZ than by the eddy’s sign. A case study showing the evolution ofmore »

Modification to the law of the wall represented by a dimensionless correction function [Formula: see text] is derived using atmospheric turbulence measurements collected at two sites in the Amazon in nearneutral stratification, where z is the distance from the forest floor and h is the mean canopy height. The sites are the Amazon Tall Tower Observatory for [Formula: see text] and the Green Ocean Amazon (GoAmazon) site for [Formula: see text]. A link between the vertical velocity spectrum [Formula: see text] ( k is the longitudinal wavenumber) and [Formula: see text] is then established using a cospectral budget (CSB) model interpreted by the movingequilibrium hypothesis. The key finding is that [Formula: see text] is determined by the ratio of two turbulent viscosities and is given as [Formula: see text], where [Formula: see text], [Formula: see text], [Formula: see text] is a scaledependent decorrelation time scale between velocity components, [Formula: see text] is predicted from the Rotta constant [Formula: see text], and the isotropization of production constant [Formula: see text] given by rapid distortion theory, [Formula: see text] is the von Kármán constant, [Formula: see text] is the friction velocity at the canopy top, and d is the zeroplane displacement. Becausemore »

Auxetic foams exhibit novel mechanical properties due to their unique microstructure for improved energyabsorption and cavity expansion applications that have fascinated the scientific community since their inception. Given the advancements in material processing and performance of polymer open cell auxetic foams, there is a strong desire to fully understand the nonlinear ratedependent deformation of these materials. The influence of nonlinear compressibility is introduced here along with relaxation effects to improve model predictions for different stretch rates and finite deformation regimes. The viscoelastic behavior of the material is analyzed by comparing fractional order and integer order calculus models. All results are statistically validated using maximum entropy methods to obtain Bayesian posterior densities for the hyperelastic, auxetic, and viscoelastic parameters. It is shown that fractional order viscoelasticity provides [Formula: see text]–[Formula: see text] improvement in prediction over integer order viscoelastic models when the model is calibrated at higher stretch rates where viscoelasticity is more significant.

AlScN is attractive as a latticematched epitaxial barrier layer for incorporation in GaN high electron mobility transistors due to its large dielectric constant and polarization. The transport properties of polarizationinduced twodimensional (2D) electron gas of densities of [Formula: see text]/cm 2 formed at the AlScN–GaN interface is studied by Halleffect measurements down to cryogenic temperatures. The 2D electron gas densities exhibit mobilities limited to ∼300 cm 2 /V s down to 10 K at AlScN/GaN heterojunctions. The insertion of a ∼2 nm AlN interlayer boosts the room temperature mobility by more than five times from ∼300 cm 2 /V s to [Formula: see text] cm 2 /V s, and the 10 K mobility by more than 20 times to ∼6980 cm 2 /V s at 10 K. These measurements provide guidelines to the limits of electron conductivities of these highly polar heterostructures.