Photoluminescence of Seven-Coordinate Zirconium and Hafnium Complexes with 2,2′-Pyridylpyrrolide Ligands

Luminescent seven-coordinated zirconium and hafnium complexes bearing three mono-anionic 2,2′-pyridylpyrrolide ligands and one chloride were synthesized. Solid-state structures and the dynamic behaviors in solution were probed by X-ray crystallography and variable temperature ¹H NMR experiments, respectively. Absorption spectroscopy and time-dependent density functional theory (TD-DFT) calculations supported a hybrid of ligand-to-metal charge transfer (LMCT)/ligand-to-ligand charge transfer (LLCT) for the visible light absorption band. The complexes (^MePMP^Me)₃MCl (M=Zr, Hf, ^MePMP^Me=3,5-dimethyl-2-(2-pyridyl)pyrrolide) are emissive in solution at room temperature upon irradiation with visible light due to a combination of phosphorescence and fluorescence characterized by excited state lifetimes in the μs and low to sub-ns timescale, respectively. Electrochemical experiments revealed that the zirconium complex possesses a reversible redox event under highly reducing condition (−2.29 V vs. Fc^+/0).     

Approaches to Modeling Bed Drag in Pine Forest Litter for Wildland Fire Applications

Transport in Porous Media - Modeling flow in vegetative fuel beds is a key component in any detailed physics-based tool for simulating wildland fire dynamics. Current approaches for drag modeling,...     

A Study of Tate Homology via the Approximation Theory with Applications to the Depth Formula

Acta Mathematica Sinica, English Series - In this paper we are concerned with absolute, relative and Tate Tor modules. In the first part of the paper we generalize a result of Avramov and...     

Asymptotic models for a long,elastic cylinder

We study asymptotic expansions for the displacement field of a long elastic cylinder under various constitutive assumptions. We show that under simple hypotheses it is possible to derive from the equations of continuum mechanics two known beam equations and several different string models. Some of the string models correspond to those studied by S. Antman and R. Dickey. We also show that under our assumptions the problem of asymptotic expansion can be reduced to that of algebraic geometry.Research partially supported by NSF Grant DMR-8612369.     

Experimental investigation of creep-crack-tip deformation using moiré interferometry

High-temperature moiré interferometry was applied to obtain full-field creep-crack-tip displacements of a three-point bend Al 2024-T4 specimen uner constant temperature of 200°C up to 720 hr.C ^* was evaluated by the moiré data obtained at discrete time intervals. Test results indicate that under steady-state creep condition, the creepcrack-tipv-displacement rate agrees with the asymptotic solution based on theC ^* integral. However, no creeping behavior was observed for the crack-tipu-displacement field aftert=276 hr. This discrepancy may be due to the initial large creep-crack-tip blunting and cavitation damage which alter the creep-crack-tip singular field such that theC ^* integral is no longer applicable to characterize the steady-state creep-crack-tip field. Postmortem studies of the tested specimen also revealed transgranular fracture path with the ordered grain boundaries perpendicular to the crack line, which may relate to the existence of the substantial crack-tip blunting and noncreeping behavior of theu-displacement field, i.e., the size and shape of material grain boundaries play an important role in the crack-tip-creeping behavior of the material.Paper was preseted at the 1991 SEM Spring Conference on Experimental Mechanics held in Milwaukee, WI on June 9–13.     

An innovative extensional viscometer for low-viscosity and low-elasticity liquids

A spinline-type extensional viscometer is described in which an innovative method of tensile stress measurement is employed. A limited amount of liquid flows through a vertical capillary at a constant flow rate under the influence of a constant pressure head. The drainage time decreases when the liquid stream leaving the capillary is stretched by the application of vacuum. These drainage times are measured in a manner similar to that used for intrinsic viscosity measurements. The measured difference in drainage times, with and without stretching, is trivially related to the extensional stress at the capillary exit, and this provides a very simple method of accurately determining fluid stretching forces having a magnitude as low as 10^-4 N; stresses at other axial locations in the stretched liquid jet are obtained by means of a force balance in the usual manner. The validity of the proposed technique is demonstrated by obtaining the expected results for a Newtonian oil having a shear viscosity of 56.2 mPa-s. Also presented are preliminary data on polyethylene oxide-in-water solutions having an even lower shear viscosity.